Sticky pin mounting

Montering av tröga tappar

David Lilja

Faculty of health, science and technology

Degree project for master of science in engineering, mechanical engineering

30 credit points

Supervisor: Leo De Vin

Examiner: Jens Bergström

Date: 07-2016

Abstract

The study was conducted at Volvo Arvika were pins sometimes are sticky to mount

during assembly of wheel loaders. This causes problems regarding ergonomic,

quality, cost and productivity. Due to deviations in tolerances, defects and errors,

assemblers are forced to use equipment such as sledgehammers to mount the pins.

The purpose of this study is to achieve and assembly process which meets Volvo´s

criteria’s. By investigation the flows for frames at Volvo Arvika, defects and errors

were discovered and mapped in a fish bone diagram. The study was focused on a

specific joint, the E-joint for which and p-FMEA was performed. Measurement of

tolerances and surface roughness were performed together with determination of

the real frequency of problematic joints. Cooling and heating methods for pins and

joints were evaluated and a prototype for pre-heating was built in order to achieve a

temporary expansion to facilitate the mounting. The material effect for both heating

and cooling was also evaluated.

The results shows several defects and errors which occurs during processing but

most of them are connected to the production flow for frames and methods during

assembly. The real frequency of problematic E-joints was 33% where the smaller

L60 model was most problematic. Pre-heating was a success and room tempered

pins could be mounted whereas today they are cooled in freezers. No metallurgical

effects should occur during usage of the evaluated concepts within heating and

cooling methods.

Sammanfattning

Studien är utförd på Volvo i Arvika där tapparna ibland går trögt under montering

vid assemblering av hjullastare. Detta orsakar problem angående eregonomi,

kvalitet, kostnad och produktivtet. På grund av toleransavikelser, defekter och fel,

tvingas montörer att använda utrustning så som släggor för att montera tapparna.

Syftet med denna studie är att uppnå en monteringsprocess som möter Volvos krav.

Genom undersökningar av flödet för ramar på Volvo i Arvika upptäcktes defekter

och fel som kartlades i ett fiskbensdiagram. Studien var inriktad emot E-förbandet

för vilket också en p-FMEA utfördes. Mätningar av toleranser och ytjämnhetskrav

utfördes tillsammans med bestämning av den verkliga frekvensen av problematiska

förband. Kyl och värme-metoder utvärderades där en prototyp för förvärmning

konstruerades för att åstadkomma en expansion och underlätta monteringen.

Materialpåverkan för både kyl och värme-metoder utvärderas också.

Resultatet påvisar flertal defekter och fel som uppstår under bearbetning men de

flesta är knutna till produktionsflödet för ramar och metoder under montering. Den

verkliga frekvensen av trögmonterade tappar är 33% varvid den minsta modellen,

L60 är mest problematisk. Förvärmning var en succe där rumstempererade tappar

kunde monteras jämfört med nuläget där de kyls i frysar. Inga metallurgiska

förändringar borde uppstå under användning av de utvärderade koncepten för

förvärmning och kylning.

Acknowledgement

I would like to thank my supervisor at Karlstad University, Leo De Vin for support

and advice throughout the project. I would also like to thank all the people at

Volvo Arvika involved in this project for their support and help. Special thanks to

my supervisor Erik Sundbäck at Volvo in Arvika for his guidance and commitment

to this project.

David Lilja

Karlstad, June 2016

Contents

1. Introduction .....................................................................................................................1

1.1 Background ................................................................................................................1

1.2. Problem description ..................................................................................................1

1.3. Purpose .....................................................................................................................1

1.4 Goal ............................................................................................................................1

1.5 Delimitations ..............................................................................................................2

2. Method ............................................................................................................................3

2.1 Strategy of work .........................................................................................................3

2.1.1 Collecting data .....................................................................................................3

2.1.2 Cause and effect ..................................................................................................3

2.1.3 Analysis and development of solutions ...............................................................4

2.1.4 Gantt chart ..........................................................................................................4

2.1.5 Theory .................................................................................................................5

2.2. Data collection ..........................................................................................................5

2.2.1 Production of frames ...........................................................................................5

2.2.2 Painting of frames ...............................................................................................7

2.2.3 Storage of frames ................................................................................................9

2.2.4 Assembly lines .....................................................................................................9

2.2.5 Volvo´s standards ..............................................................................................14

2.2.6 Definition of a sticky pin and corresponding problems .....................................15

2.2.7 Equipment and freezers ....................................................................................15

2.2.8 Pins and packaging ............................................................................................17

2.2.9 Material .............................................................................................................19

2.2.10 Existing data ....................................................................................................20

2.3. Execution .................................................................................................................21

2.3.1 Defects ..............................................................................................................21

2.3.2 Frequency of problematic E-joints ....................................................................22

2.3.3 p-FMEA for E-joint .............................................................................................22

2.3.4 Measurements of pins and joints ......................................................................26

2.3.5 Corrosion analysis .............................................................................................30

2.3.6 Concepts of cooling and heating .......................................................................31

2.3.7 Evaluation of concepts ......................................................................................32

2.3.7 Prototype research ............................................................................................33

2.3.8 Prototype and Pre-heating ................................................................................33

2.3.9 Analysis of material effects ...............................................................................37

3. Results ............................................................................................................................42

3.1 Defects .....................................................................................................................42

3.2 Frequency of problematic E-joints ...........................................................................42

3.3 p-FMEA .....................................................................................................................44

3.4 Measurements of diameter and roughness .............................................................44

3.5 Corrosion analysis ....................................................................................................48

3.6 Pre-heating ...............................................................................................................48

3.7 Material affect by liquid nitrogen .............................................................................51

4. Discussion.......................................................................................................................53

4.1 Defects .....................................................................................................................53

4.2 Measurements and analysis .....................................................................................53

4.3 p-FMEA .....................................................................................................................54

4.4 Pre-heating ...............................................................................................................55

4.5 Material effects ........................................................................................................55

4.6 Project Work ............................................................................................................56

5. Conclusions & Recommendations .................................................................................57

Bibliography .......................................................................................................................58

Appendix A .........................................................................................................................60

Appendix B .........................................................................................................................62

Appendix C .........................................................................................................................64

Appendix D .........................................................................................................................67

Appendix E .........................................................................................................................68

Appendix F .........................................................................................................................70

Appendix G .........................................................................................................................81

Appendix H .........................................................................................................................82

Appendix I ..........................................................................................................................84

1

1. Introduction

1.1 Background Volvo construction equipment is today one of the leading suppliers of wheel

loaders, trucks, buses and movers. They are also active within drive system for

boats and industry-applications while offering complete solutions for financing and

service. This project will be performed at Volvo CE in Sweden, Arvika which is a

high technology factory with experience over 130 years within production. It is one

of Värmlands largest company with over 1000 employees and Volvo´s global core

factory for manufacturing of wheel loaders. They manufacture wheel loaders in

various models using a flow line of stations which assembly different parts of the

wheel loader.

1.2. Problem description The joint that creates the linkage for the wheel loaders lifting frame and steering

suffers from great strains during operation. Quality and life span are highly

prioritized by Volvo´s customers and as a result there are big demands on the

tolerances in the joint. As follows, this leads to an assembly process and

manufacturing process that requires high precision in order to achieve the correct

tolerances. The assembly process is heavily affected due to the narrow tolerance

which causes the pins mounted in joints to be sticky and hard to get in place. Right

assembly method and equipment is important in order to achieve the correct

tolerances but also to meet the criteria from an ergonomically and productivity

view. Currently Volvo has high focus on the problem with sticky pins and is

actively working to solve this problem. This project is a part in a bigger

investigation where several projects work in parallel. For this project, a big part is

to determine the underlying factor which influences the sticky mounting of pins

and also the real frequency of problematic joints. The second part of the project is

to choose to develop either a cooling method for the pins using liquid nitrogen or

develop a method to preheat the joints in order to facilitate the mounting of pins.

1.3. Purpose The purpose of this study is to achieve an assembly-process which meets Volvo´s

demands regarding safety, productivity and quality. It is also desirable that the

solutions can be implemented with a low investment cost at several stations.

1.4 Goal

Collect and compile data for current known defects that leads to sticky

mounted pins and locate the source where they arise from. As a

complement this study also has a goal to give possible solutions on 50% of

the found defects.

2

Determine frequency of problematic E-joints at Medium line, the joint

connecting the tilt cylinder with the front frame.

Develop a prototype for pre-heating the joints which meets Volvo´s criteria

regarding quality, safety, productivity and ergonomic. Also test the

prototype and analyze the results. Related to this also investigate material

effects regarding heating and cooling.

1.5 Delimitations The project will examine the inside of Arvika plant of the Medium and Large

manufacturing flow. The project is also limited to a closer examination of the E-

joint that the tilt-cylinder and the front frame constitutes for own analysis regarding

tolerances of pins, holes and frequency of sticky pins. The projects also have a

time limit where it shall be conducted during the spring of 2016 from week 4 to

week 23. Due to the time limit, introduction of the developed pre-heats method to

the assembly line is not possible.

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2. Method

2.1 Strategy of work Following text will describe the strategy for this project regarding how information

are obtained and documented. Also how the obtained information is processed in

order to obtain solutions regarding the different errors.

2.1.1 Collecting data

Methods for data collections can vary depending on the task that is being

performed. For this project it was decided that the most suitable methods would be

observations, interviews and existing data [1].

Observation is an objective method to gather information about different situations

or processes in their real state. This would also give a detailed background of the

problem and the difficulties that follows with the problem. Direct observations

would be done where the observer would be present during the processes and

gather data with notes and photos.

Interview is a great tool in order to gather fundamental data regarding the problem

and how different people see and experience the problem. Half structured

interviews was used where specific questions and areas of discussion was prepared.

At the same time new and open questions would be asked depending on the

answers and discussion. This would give the essential background for each area

with prepared questions and a more in depth knowledge as follow up questions and

own initiatives of the interviewed person was possible.

Existing data is always useful in order to get information about how the problem

has been developing. How past problem has been dealt with and statistic on

different problem for different processes. With the help of existing data one could

establish a base where further analysis could be oriented around.

2.1.2 Cause and effect In order to map the different defects and errors that would cause a pin to be sticky,

fishbone diagram would be used. A fishbone diagram is a graphic tool which

illustrates the main problem and part problems in categories and breaks it down.

There are four steps in the process for solving problems using fishbone diagram,

which is illustrated by Figure 1 [1].

Figure 1: Four steps for solving problems with a fishbone diagram.

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The last step, rank essential causes, was to be made using a failure mode and effect

analysis. FMEA is a tool used to analyze the connections between different errors

and their following consequences. In the analysis there are three main questions

which form the basis [1].

What errors may occur?

What is the impact of the errors?

What are the reasons for the errors?

These questions were to be investigated and briefly described in text. With known

errors and their corresponding impacts and reasons, FMEA could be conducted.

Existing FMEA are available which will be used as a basis to develop new ones for

specific areas. The errors would be evaluated according to three different factors to

form a RPN (Risk Priority Number) value. The three factors are Po, probability of

occurrence, S, severity of defect and Pd, probability of detection. The RPN value

would be used in order to prioritize were solutions or changes in the flow of

production were most needed.

2.1.3 Analysis and development of solutions

With known categories and part causes that leads to sticky pin there will be short

analysis regarding where the defects arises in the flow and also proposals on

solutions, how to prevent or fix them. There will also be an evaluation of general

solution regarding cooling or pre-heating of pins respectively joints which will be

an all-around solution. These solutions will however be like a bandage on a wound,

they will not fix the root of the problem itself, rather temporarily grant the ability to

mount the pins with ease. Evaluation between concepts of Volvo´s interest will be

done in order to choose a concept to investigate further. The evaluation will be

performed using a matrix chart [2].

2.1.4 Gantt chart

The plan for the thesis study can be seen in the Gantt chart, Figure 2.

Figure 2: Initial Gantt chart for the study.

5

2.1.5 Theory

Since this study is focused on data collection and analysis, no section of theory will

exists. Instead theory will be explained in continuous text.

2.2. Data collection In order to understand the problem and locate all defects and where they arise from,

a review of all processes involved in the value stream inside in Arvika plant for

defects on affected components for joints was done. The following text will

describe the different flows for production of frames and the following processes

such as painting and storage before it is taken to the assembly lines. The assembly

line where the pins are mounted will also be described. The different models,

frames and external components which constitute the different joints together with

equipment and method will be described. A simplified picture of the overall flow

can be seen in Figure 3.The flow inside Arvika plant for frames were divided into

four sections as illustrated in Figure 3. Each section will be described for a better

understanding on where and how different defects and errors arise. The blue

section is the production of frames and the red section is the painting process. The

triangles represent storages of the frames where the orange ones represent indoor or

room temperate storages and the blue ones represent outdoor storage with

temperatures of surrounding environment. The green section represents the

assembly lines where frames and external components are assembled as a unit to

form the wheel loader.

Figure 3: The flow for a frame at Arvika plant.

2.2.1 Production of frames

Arvika produces wheel loaders of different size and designs which can be divided

into three categories depending on what assembly lines they are assembled at. At

Medium line the models produces can be seen in the bullet list below. H and F

indicate the emission standard for the different market regions. H standards are sold

6

in Europe and USA while F standards are sold in South America, Asia, Australia

and Africa.

L60 H/F

L70 H/F

L90 H/F

L110 H/F

L120 H/F

The larger models of wheel loaders are assembled at large line and can be seen in

the following bullet list.

L150 H

L180 H

L220 H

L250 H

Frames are produced according to two different methods, standard and cast

method. In the start both flows have subcomponents for the front frame and rear

frame. These subcomponents are first stapled and welded individually. What makes

the methods different is when the holes of frames are being processed. For the

standard method the holes are processed in the last step after blasting but for the

CAST method they are processed in the start as subcomponents before being

stapled into a frame. The CAST (common architecture shared technology) method

is a standardized module approach for manufacturing. This method is however only

applied to the smaller rear frames, L60H, L70H and L90H. All other frames are

produced according to the standard method, which will be the described method for

this study. The production of frames can be divided into six sections which are

illustrated in Figure 4.

Figure 4: The flow for production of a frame.

Subcomponents stapling/welding is the first station where parts of the rear or front

frame are tack welded together. This could for instance be the side of a rear frame

being stapled in a fixture to be sent towards Stapling where the other component

7

which constitutes the rear frame comes together. This is done manually by an

operator with MIG welds.

Stapling is done by fixture of the prior components which constitutes a frame. A

fixture is applied according to standards so products are identical. The components

are then tack welded manually with an MIG weld by an operator.

Robotic weld is the station where the whole frames are welded together. The

robotic weld operates after a RPS coordinate system. The RPS system is a general

fixture system where certain points of the frame are fixture as a reference

throughout several processes. The process takes approximate 180 min and

temperatures of approximate 70 ᵒC are reached at the bearing surfaces.

Manual weld are done by operators, using MIG welds to weld small components

like ears to the frames which can’t be done in the robotic weld. Fixtures are used

here as well and the process takes approximate 180 min. Temperatures of

approximate 70 ᵒC for the bearing surfaces reached during the manual weld.

Blasting of frames is done in order to clean the frames from dirt and scrap by

propelling a stream of particles to the surfaces under a high pressure.

Processing is the last step in the production of frames. Holes in the frames which

later constitute the joints are processed with a rotating mandrel. The mandrel

processes both holes which later constitute a joint from one way to ensure linearity

and parallelism. The holes are first processed with two rough cuts and thereafter a

finer cut. After being processed the holes are measured using a dial indicator. The

last step is to burr the holes to avoid sharp and raised edges, this is done manually

by the operator.

2.2.2 Painting of frames

After the production of frames they are moved to the painting area where they are

put into storage 2 according to Figure 3. The storage time varies between one to

three days depending on shifts of the workers and weekends. The frame will

undergo the painting process which can be divided into five sections. The process

is illustrated in Figure 5 where each section with respectively subsection is shown.

8

Figure 5: The flow for the painting process.

Before the painting itself the frames undergo a pre-treatment. The whole process is

done within a contained area where fluids are sprayed upon the frame with help of

pumps. After each rinse the fluids are allowed to flow away for about 60 to 90

seconds.

The first step is to wash the frames with a mixture of water, Bonderite C-AD

2000(degreasing) and Bonderite M-FE 3990-1 which acts as an accelerator to

create a layer of iron phosphate. This layer will ease the application of paint and

also act as a protection against corrosion. This process has a fluid temperature of 70

ᵒC.

The following two steps are to wash the frame with water. The first rinse is done in

order to wash away dirt and particles that are attached to the frame. The second

rinse is done with more pure water in order to completely wash the frame clean.

Both processes have water temperatures of about 20-25 ᵒC.

The frames are then treated with a mixture of water and Bonderite S-FN 7400 with

a temperature of 70 ᵒC. This is a corrosion protection that forms a thin layer,

protecting the steel surface from direct contact with the surrounding atmosphere.

The last step is to dry the frame manually by the use of an air-pressure pump. The

drying is however prioritized at surfaces which are going to be covered with

plastics, not the holes of the frame.

Mask is performed on surfaces that should not be painted. The two areas which are

masked are the holes of the joints and the surfaces that will have screws and bolt

9

applied. This is done in order to avoid paint in both joints and holes as is it would

complicate assembly.

Painting of frames is done manually with spray equipment in two different zones.

In the first zone a primer layer is applied to the whole frame. In the second zone the

top-coat is applied which will cover the frame with a thicker layer of paint.

The drying process starts with frames being kept in a flash-off zone. They stand

inside the flash- off zone for six minutes with a temperature of 30 ᵒC. This is done

in order steam away the solvent in the paint to prevent blisters which otherwise

would arise due to the high temperature in the drying areas. The drying process

consists of six areas where the frames are transported through. The temperature

during the drying process is 80 ᵒC and the whole process takes 72 min.

Cooling is the last step, frames are placed in a cooling area where air from the

outside are pumped in order to cool it down. Since the frames are very hot from the

drying process this is done in order for the operator to remove the mask of surfaces

and holes without any risk of getting burned. When all masking is removed, frames

are transported to storage 4.

2.2.3 Storage of frames

Five significant storages exists from production to assembly line. The storages are

numbered 1-5 for simplicity in Figure 3 and will be referred likewise in following

text. The five storages can be seen in Appendix A. Storage 1 is the first storage

which is located after the robotic weld. The storage is inside the factory where

room temperature is kept, next to the manual welds. Storage 2 is the storage after

the manual welds which are located outside at the quay. This storage is directly

exposed to the environment and the outside temperatures. Storage 3 is the storage

between processing and painting process which are located inside the factory next

to the painting area. Storage 4 and storage 5 are located in tents outside the factory.

Storage 4 has no heating and keeps a temperature equivalent to the outside

temperature. Storage 5 on the other hand is heated in order for frames to have a

room temperature when they are moved to the assembly lines. The frames are

occasionally cleaned manually with rags in storage 5 when the weather is bad.

Transportation of frames from and to storages are performed by a fork lift driver,

the frames are placed on a rack which are lifted by the truck.

2.2.4 Assembly lines

Volvo construction equipment in Arvika has three different assembly lines where

there are several stations working on different parts of the wheel loader. The three

lines are Medium line, Large line and Heavy line. The three lines both have

similarities and differences regarding the tact time, models produced with different

techniques of the assembly and the equipment used. The three assembly lines have

different stations along the line where certain assembly processes occur within a

10

given timer interval, which is the tact time. At the end of the tact time the part of

the wheel loader is moved to the next station with different supportive tools for

each assembly-line. The three assembly lines have different amount of stations and

the assembly order are also different comparing the three assembly lines. Each

assembly line produces different models of wheel loaders and each station within

the different assembly lines have a specific amount of assemblers. The assemblers

operate according to a standard instruction file which describes each task of the

process and the time it should take to perform the task. The gear that the

assemblers shall use to build the wheel loader and the equipment they should use

with corresponding guide are also described for each task. In order to compile all

defects and errors regarding sticky pin mounting, it is of importance to know the

different methods and problems for each pin mounting station. The following text

will describe the flow for Medium and Large line with focus on the pin mounting,

with corresponding method and equipment used.

Both Medium and Large line works with three main components, the rear frame,

loading unit and front frame, which can be seen in Figure 6-8.

Figure 6: A rear frame.

Figure 7: A loading unit.

11

Figure 8: A front frame.

External products such as piston cylinders are also mounted, where each end has

pin mounted through it, locking it between or to the main components. The piston

cylinder can be seen in Figure 9.

Figure 9: A piston cylinder which constitutes a part of the E, F, C and P-joint.

Both Medium and Large line has different models, varying in size and slightly in

design and construction. The general parts that are being mounted are practically

the same but there is a difference in tact time and when different parts are brought

into the assembly. The tact time for Medium line is approximate 30 minutes while

for Large line it is approximate 60 minutes. When the tact time is due, the frames

are moved one step to the next station with different supportive tools.

The joints that have pin mounted to them are the same for Medium and large line,

but occur at different stages in the flow. The different joints that are mounted with

pins in the assembly lines are the E-joint, F-joint, O-joint, P-joint, C-joint, 1-joint.

2-joint, 3-joint, 4-joint, 5-joint and 6-joint.

The mentioned joints can be seen in Figure 10-12. The E-joint consist of the tilt

cylinder which is mounted to the front frame, the joint can be seen in Figure 10.

The tilt cylinder is marked with yellow, the front frame with grey and pin with red

12

color. The F-joint consist of the tilt cylinder and the GHF-linkage, the joint can be

seen in Figure 10. The tilt cylinder is marked in yellow, the GHF-linkage in grey

and the pin in purple color. The O-joint consist of the front frame and the loading

unit, the joint can be seen in Figure 10. The front frame is marked in grey, the

loading unit in turquoise and pin in orange color. The P-joint and C-joint can also

be seen in Figure 10. The P-joint consists of the lift cylinder (green) and the front

frame (grey) with corresponding blue pin. The C-joint consist of the lift cylinder

(green) and the loading unit (turquoise) with corresponding pin in a light grey

color.

Figure 10 : Front frame and loading unit with corresponding joints explained with colors and designation.

The 1-joint and 2-joint can be seen in Figure 11, which are the two joints that connect the

front frame with the rear frame. The upper joint is the 2-joint and the lower is the 1-joint.

13

Figure 11: Joints connecting the front frame and rear frame.

The 3-joint, 4 –joint, 5-joint and 6-joint can be seen in Figure 12. The steering

cylinders are marked in purple and the pins are marked in blue for the 4-joint and

5-joint while the pins for the 5-joint and 6-joint are marked in green.

Figure 12: Joints connecting rear frame, steering cylinders and front frame.

Throughout the assembly lines several things are assembled. Hydraulic, electrical

units and more are brought together but the following text will focus on the pin

mounting. The technique used for mounting pins is pretty similar from one joint to

14

another. All pins mounted in joints should be cooled in freezers to achieve a

shrinkage effect. Before pins are being mounted the assemblers should, according

to Volvo standards, clean the surfaces of the joints and apply lubrication.

The joints shown in Figure 10 have pins mounted horizontally in the joints. The

components are aligned with supportive tools for respectively assembly line and a

crane which lifts the piston cylinder or loading unit in place. The crane is

controlled manually by the assembler which also steers it into place with his hands.

There is however no fixtures used and the alignments between components are

dependent on the assembler. The pins are taken out of the freezers by hand and

steered likewise at Medium line into the joint. At large line the assemblers have

access to cranes and straps which they lift the pins with. The mounting itself is

done with manual power of assembler, pushing the pin in place.

The 1 and 2-joint shown in Figure 11 and Figure 12 have pins mounted vertically

in the joints. The 3 and 4-joints are mounted similar to the joints in Figure 9.

Cranes lift the piston cylinders in position and pins are taken out of the freezer by

hand at Medium line or with cranes and straps at Large line. The pins are steered

by hand and mounted using manual power of the assembler.

The 1 and 2-joints between front frame and rear frame which are mounted at the

marriage station have different methods comparing Medium and Large line. The

marriage station is the first station for Large line where rear and front frame come

together. The front frame are lifted with cranes and aligned with the rear frame and

the pins are mounted with sledgehammers. The freezer temperature for the

marriage station at Large line are lower than the rest and keeps a temperature close

to -35 ᵒC.

For Medium line the front frame are similar to large line lifted with cranes and

aligned with the rear frame. The pins are taken out of the freezers by hand and have

a steering pin applied to them. They are thereafter steered into the hole and locked

with a fixture. A press is thereafter used to push the pins in place. A press had not

been used in the past but ever since the frames produced using the CAST-method

were implemented a press were needed. Two different presses are used to mount

pins in the 1-joint and 2-joint, the press used to mount the 2-joint are illustrated in

Appendix B.

Other joints than the described exists but are not mounted at the assembly lines and

are therefore not included in this study.

2.2.5 Volvo´s standards

According to Volvo there are seven conditions that need to be fulfilled in order to

mount a pin.

Pin and joint dimensions must be within the set tolerances.

15

Both pin and the joint it will be mounted in should be clean and the joint should

be lubricated.

The assembler should have the right conditions regarding equipment and other

supplements.

Goods that are clean means that there should be no hue deviate on the painted

surface.

There should be no water that can cause corrosion.

Lubricants protecting against corrosion should not be considered as dirt.

Surface roughness of processed joints should be within tolerance.

2.2.6 Definition of a sticky pin and corresponding problems

After observing mounting of pins at the assembly lines and doing several

interviews with the employees of Volvo in Arvika together with questioning the

assemblers one could conclude that defining a sticky pin is a diffuse issue.

Depending on what station involving the mounting of pin there was different

answers and definition on what a sticky pin really is. Some of the employees

considered a pin being sticky depending on the amount of hits using a

sledgehammer or a regular hammer. Several also thought a pin where sticky if

there was a need to use any sort of equipment to get it in place. Another opinion

was that a pin was sticky if it pinched during the mounting. To get a definition of a

sticky pin that was measurable it was decided for this report that a sticky pin is a

pin that requires the use of equipment, sledgehammers or similar.

During observation of pin mounting one could see the direct problems that sticky

pins can cause. The need to use a sledgehammer in order to get the pin can be a

heavy and troublesome process. Many hits can be required which negatively affects

the ergonomic and environment for the assembler. If the assembler is unable to

mount the pin in its right place it could potentially lead a stop in the flow and need

for extra assistance. This would negatively affect the productivity of the flow,

especially if the frame is needed to be moved out from the flow for reprocessing,

creating a gap in the flow. The quality of wheel loaders can also be affected since

information regarding pin and joint when a sticky pin is mounted can’t be

evaluated. If a great amount of force is required to mount the pin it could

potentially damage the pin or the hole, affecting the lifetime of the joint negatively.

2.2.7 Equipment and freezers

Mounting of pins requires several tools, both for the mounting itself and for

preparation. Overall assembly instruction with instructions and standards for pin

mounting exists. According to standards the assembler should have access to rags

which are used to clean the hole, where after lubrication shall be applied. The

lubrication is Gleitmo 805 which is a lubricating paste which should be available at

all stations involving pin mounting. The pins should be cooled to a temperature of -

25 ᵒC which corresponds to a cooling time of eight hours inside the freezer

16

according to assembly instructions [3]. Sledgehammers and crowbars together with

the press used for mounting sticky pins can be seen together with the burring tool

in Appendix B.

Volvo in Arvika currently has two types of freezers where they keep the pins. The

regular freezers which are used at almost every station involving pin mounting.

have temperatures varying between -13 to -21 ᵒC. This type of freezers can be seen

in Figure 13, where there are several wooden pallets filled with pins inside each of

them. Other types of freezers exist but in small amounts and they keep a

temperature of -35 ᵒC. These are located at the marriage station at large line, one

containing the pins and the other contains bearing rings and link layers, this type of

freezer can be seen in Figure 14. Each freezer contains three types of pins with

three corresponding buffers, making it a total of 6 pallets.

Figure 13: Industry freezers used at assembly lines which keeps a temperature of approximate - 20 ᵒC.

Figure 14: Ordinary freezer used at the marriage station at Large line which keeps a temperature of approximate -35ᵒC.

Measurements of the processed holes to ensure whether they are within tolerances

are done with standardized dial indicators and a measuring device called Marposs.

Measurements are conducted immediately after the holes are processed, manually

by the operator of the processing machine. The measurements are done for two

directions in the hole, perpendicular to each other. The dial indicators are used to

measure holes processed according to the standard method and the Marposs tool

are used for frames produced according to the CAST method. The measuring tools

can be seen in Appendix B.

17

The plugs used during the painting process come in standardized kits for each

model. The plugs can be seen in Figure 15. The purpose of the plugs is to prevent

the paint from getting inside the holes and they are designed on this basis. The

diameter is barely larger than the hole and no significant protection for the edges

are provided. There is however an ongoing project to replace the current plugs with

new plugs which has a bigger diameter. The masking used to cover surfaces can be

seen in Figure 16.

Figure 15: Plug used during the painting process.

Figure 16: Mask used to protect surfaces from paint.

2.2.8 Pins and packaging

Pins vary in size and design depending on what model it belongs to and also in

what joint it should be mounted to. Currently Volvo has 3 different suppliers of

pins, Supplier 1 which is an English company, Supplier 2 which is a Chinese

company and Supplier 3 which is a Swedish company.

There is a difference in packaging of pins which can be illustrated by comparing

Figure 17-19. Figure 18 shows the packaging of pins from Supplier 2, which

travels a long way by ship. The pins are packaged in a wooden pallet where each

pin is wrapped in plastic, inside a plastic bag. The pins are also slightly smeared

with a corrosive protective agent. Figure 17 shows the packaging of the English

company, Supplier 1. As seen in Figure 17 the packaging consists of a pallet with

cardboard paper separating the pins from each other and from the bottom of the

pallet. Since these are shipped from England the possibility of corrosion is

considered low so there is no lubrication or grease of any kind applied to them.

18

Figure 19 shows the packaging of pins delivered from Supplier 3, which only

consists of the wooden pallet. When the wooden pallet arrives at the cargo section,

lid of each individual wooden pallet is removed and then preserved inside the

factory on racks. When the assembler has used up all the pins of the lower level of

the freezer a fork lift driver will remove the bottom pallet and insert a new one

from the buffer. Then the fork lift driver will refill the buffer by moving a new

pallet of pins from the racks into the buffer. The lead time they are stored inside the

cargo section varies. The lead times they stay at the racks before being moved to

the freezers are approximately 1 day.

Figure 17: Packaging of pins delivered from Supplier 1.

Figure 18: packaging of pins delivered from Supplier 2.

19

Figure 19: Packaging of pins delivered from Supplier 3.

2.2.9 Material The material which the pin are made of is the steel grade SS 2234-04, which is a

chromium based steel. SS 2234-04 is tempering steel which has high demands on

both strength and toughness [4]. The composition of the steel can be seen in Table

1 [4], [5].

Table 1: Chemical composition of SS 2234-04

C % Cr % Mo % Mn % Fe%

0,30-0,37 0,90-1,20 0,15-0,30 0,50-0,80 NA

The pins are manufactured of bars which are heat treated in order to achieve correct

hardness and toughness. The pins are first austenitized at 850-900 ᵒC in ovens and

quenched in 60 ᵒC oil. The pins are then tempered for one hour in an oven at a

temperature of 550-600 ᵒC and cooled slowly in room temperature. The pins are

thereafter induction hardened at a surface depth of 2-4 mm by heating them to 850-

900 ᵒC and quench in 25 ᵒC water. The whole pin is then tempered in an oven at

160-200 ᵒC for one hour and cooled slowly in room temperature [6].

The casting breasts which the E-joint are a part of are made of the steel grade

VSC480/20IS+N and are only normalized at 900-980 ᵒC. The composition can be

seen in Table 2 [7].

20

Table 2: Chemical composition of VSC480/20IS+N

C % Si % Mn % P % S% Ni Fe

0,17-0,23 0,6 1.00-1.60 0.020 0.020 0.80 NA

2.2.10 Existing data

Existing data on frequency of problematic joints existed which can be seen in

Appendix C. There was also a measurement conducted on the tolerances between

pins delivered from Supplier 1 and Supplier 2 which can be seen in Appendix C.

Documents regarding lowest temperature pin should be cooled to in order to avoid

problems were also existed. Failure mode and effect analysis had been conducted

for the 2-joint at Medium line regarding pin mounting. The FMEA can be seen in

Appendix C.

Frequency of problematic joints

To establish frequency of problematic joints for all stations and lines would require

several people and cooperation between the assembler and observer. Because of

this the problem was decided to be oriented around one type of joints. It was also of

interest to choose a joint that would have a history of a high frequency of problems

during mounting to investigate further. Therefore an analysis of existing loggings

was conducted in order to see which joint had a high frequency of problem and

together with supervisors of the project choose one to examine further.

The existing logging together with the experience of employees at Volvo pointed

towards three problematic joint. The loggings where conducted between 2015-04-

29 and 2016-01-07 with a total of 131 loggings, the loggings can be seen in

Appendix C. From the loggings one could see that there are three joints that stand

out regarding high frequency of problematic pin mountings. The three joints with

corresponding models are marked in light orange where a clear trend of elevated

loggings can be seen. The logging indicates that 2- joint between the front frame

and sub frame has the highest frequency of sticky pins. Also from experience

Volvo has been having big issues with it. Volvo has however already and active

project to resolve the problems for this joint. Because of this it was decided that

this project would be specified on one of the second most problematic joint, the E-

joint which is shown in Figure 20. Further analysis will therefore be conducted

with focus on the E-joint with corresponding pins.

21

Figure 20: The E-joint which connects tilt cylinder with the front frame.

Measurements of pins and joints

Earlier measurements of pins had been done in Volvo that showed variation in

tolerances. The measurement was conducted on pins belonging to the 1-joint

between front and rear frame. The measurements can be seen in Appendix C. The

result indicates that pins delivered from Supplier 2 have a tendency to be closer

towards the lower tolerance limit, or even below it. The pins delivered from

Supplier 1 had a tendency to stay within the tolerances and be towards the upper

limit. Due to this it was of interest to measure pins which belongs to the E-joint and

the joint itself.

Cooling criteria’s of pins

Document with recommendation regarding maximum cooling temperature of pins

existed, stating that a minimum cooling temperature of pins should be -30 ᵒC.

Otherwise could possible retained austenite transform into brittle martensite. This

could develop micro cracks which would turn into fatigue cracks. The cooling of

the surface could also give rise to shrink tension stresses which could result in

surface cracksI. Since Volvo is interested to cool the pins more than -30 ᵒC, an

investigation on material effect will be conducted.

2.3. Execution 2.3.1 Defects

In order to map and verify the defects which lead to sticky pin mounting, a review

of the mentioned process which frames undergo (Figure 3) were performed. Even

though this study would be specified towards the E-joint, the general defects which

affect all joints at Medium and Large line would be investigated. During

observation, several defects could be found. Fishbone diagram was created where

the defects and errors were divided into categories. The categories which defects

and errors were divided into were Contaminations, Packaging, Technique,

Environment, Measurements, Material, Processing and Frame construction.

I Interview with Marcus Nävehed, Quality engineer, 16/2-2016.

22

2.3.2 Frequency of problematic E-joints

The investigation of frequency of problematic E-joints was conducted on a time

interval of 5 weeks. During this time mounting of pins into E-joints was observed

and the total number of hits with either a hammer or crowbar was recorded. This

was done for all models in order to verify the perceived thoughts of the smaller

models being more problematic. The data collection was performed by observing

pin mountings during several occasions and recording for each model the total

number of hits when pins were problematic. The numbers of hits were divided into

four intervals, 1-3, 4-6, 7-9 and 10+.

2.3.3 p-FMEA for E-joint

An extensive process FMEA (p-FMEA) was done on the E-joint which are

delivered in a processed state. The existing FMEA covered general defects but a

specific p-FMEA on the E-joint had never been conducted. The p-FMEA was

performed in order to improve the existing process and to understand how people,

material, equipment and method could cause problems. With a p-FMEA one can

expose the defects and errors which occur during the processes and optimize for

best performance, with respect to pin mounting in this case [8].

The following text will describe the cycle of processes which a casting breast

undergo from delivery to the processing stage with corresponding defects and

errors.

The holes of the E-joint are attached to a casting breast which comes delivered

from two manufactures. For the smaller models, L60, L70 and L90 the holes are

not processed within Arvika plant. This is because the processing machine at

Arvika plant is not able to process them. The holes of the frame which are designed

to let the mandrel reach different joints are too small because the construction

department are concerned that larger holes could affect the frames strength.

When are delivered casting breasts they come in pallets, two casting breasts for

each pallet. Inside the pallet they are wrapped in a yellow plastic bag and they also

have corrosive protective agents coated in the holes. The packaging can be seen in

Figure 21.

Figure 21: Packaging of delivered casting breasts.

23

The casting breasts are lifted with the shown tool in Figure 21, which are attached

to the holes of the casting breast. The breasts are unwrapped and further sent

towards stapling.

At the first station of stapling the casting breasts are stapled with rear plates, the

two components can be seen in Figure 22.

Figure 22: Casting breasts and rear plates that are stapled.

The casting breast and rear plate are first fixture according to standards, the fixtures

can be seen in Figure 23. One of the fixtures is placed inside the holes while the

other fixture is placed on the sides of the casting breast. The casting breasts are

lifted to this position using a lifting tool enveloped in rubber where the contact

between hole and tool occur. The operator mentioned however that the amount of

corrosive protective agent in the holes could be excessive in some cases which later

could affect the welding if it would spread across to the areas which were to be

welded.

Figure 23: Fixture applied to rear plate and casting breast.

After stapling these components together they are moved towards the next stapling

station where the casting breast with rear plate is to be stapled to the front frame.

First it has a fixture mounted on it according to Figure 24. The fixture together with

the casting breast are lifted with a crane and placed in correct position in

correlation to the frame. Sticks of the fixture are thereafter mounted in the holes of

24

the right picture of Figure 24, locking it in all directions and rotations. The casting

breast is then tack welded to the frame.

Figure 24: Fixture used for stapling casting breast to front frame.

The frame together with the casting breast is then sent towards the robotic weld

where frame and casting breast are fully welded together. A concern were that the

high temperatures during the welding could affect the holes, but a temperature

reading discovered that only temperatures of approximate 65 ᵒC were reached in

the holes for the E-joint.

The frames together with the casting breast are stored in storage 1 between 8-24

hours before being moved to the manual welds. In the manual welds smaller

components are welded to the front frame but no significant temperatures could be

measured which could alter the shape of holes. The frames are then moved to

storage 2, the quay, where they are stored 1-3 days.

The frames are move by truck from the quay further to the blasting process. During

the blasting process, holes constituting the E-joint are protected with a nylon mask.

This is to ensure the quality since the holes already are processed. The nylon

masking can be seen in Figure 25. During the observation the holes for the E-joint

were slightly affected by the blasting process, creating a small burr. After blasting,

frames are moved to an insignificant buffer consisting of three frames, next to the

processing machine.

25

Figure 25: Nylon masking which protects the E-joint during the blasting process.

The following processing of holes has the same routing for all models. Frames are

lifted in designated ears and placed for fixture. The holes for the E-joint are fixture

with a steering pin according to Figure 26. The steering pin is typically smaller

than regular pins which are mounted later in the assembly lines but can be

troublesome to mount as well. The operator said that in case of a sticky steering pin

the holes are burred with the tool shown in Appendix B, a hammer can be used as

well to get it in place. The burring are however not an action specified in the task

list and if it is done depends on the operator. The frame is also fixture in another

point which is shown in Figure 27, locking it in all directions and rotations.

Figure 26: Fixture consisting of a steering pin.

26

Figure 27: Fixture of frame, locking it in rotational direction.

Operations of processing, milling and threading are performed in the processing

machine. When the operations are done, holes are measured using dial indicators

and thereafter burred. Since E-joints not are processed, measuring and burring is

not a part of the operators instructions file and is not performed.

The risk that will be evaluated in the p-FMEA from the observations can be seen in

the bullet list below.

No burring of E-joints

Insufficient protection during blasting

Several fixtures applied in holes

Ovaility of holes from supplier

Parallelism of holes from supplier

Tolerance performance from supplier

2.3.4 Measurements of pins and joints

Assembly processes between pin and joint have different fits depending on

tolerances which can be divided into clearance fit, transition fit and interference fit.

The joints at Volvo should have a clearance fit which should allow the assemblers

to push in the joint by manual power. The tolerances mostly used between joint and

pin are the H/h which is a clearance fit. For the 60 model the pins has j tolerance

which belongs to the transition fit zone. The tolerance limits are also dependent on

the nominal diameter (DN). Tolerances with upper tolerance limit (UTL) and lower

tolerance limit (LTL) for pins for each model can be seen in Table 2. Tolerances

for E-joints for each model can be seen in Table 3 [5]. An overview of tolerances

can be seen in Figure 28.

27

Table 3: Tolerances and nominal diameter of pins for each model

Model DN[mm] Tolerance UTL[μm] LTL[μm]

L60 80 j6 12 -7

L70/L90 90 h6 0 -22

L110/L120 100 h6 0 -22

Table 4: Tolerances and nominal diameter of E-joints for each model

Model DN[mm] Tolerance UTL[μm] LTL[μm]

L60 80 H8 46 0

L70/L90 90 H8 54 0

L110/L120 100 H8 54 0

Figure 28: Tolerances illustrated for pin (blue) and joint (red) for different fits [9].

Pins belonging to the E-joint and E-joints were measured in order to determine how

good tolerances are kept and also what values they are controlled against. A

cooling model based on equation 1 was created in excel to verify that the wanted

shrinkage was achieved in the freezers [10]. The coefficient of thermal expansion,

α, was set to 12.2E6 according to [11].

TDD **0 (1)

The measurement of pins was done at two occasions, one when they were in a

cooled state and another in room temperature. The instrument used to measure the

pins was a digital measuring bracket together with fitting pieces which is illustrated

in Figure 29.

28

Figure 29: Equipment used for measurements, measuring bracket and fitting pieces.

The three different pins from Table 2 were measured in two directions and at three

different levels as illustrated in Figure 30. The pins were measured in this way to

not only obtain diameter and ovality, but also the change in diameter and ovality.

Figure 30: Directions and levels of measurements explained.

The first measurement was when the pins were cooled. The pins were taken

directly out of the same freezer which the assemblers take their pins for mounting.

The measuring bracket where calibrated with fitting pieces for each pin-model and

five pins with corresponding diameter were measured between each calibration.

The pins that were chosen to be measured had unfortunately defects, frozen

particles on the surface. The pins with the least amount of defects were chosen but

there was however significant scrap from packaging and surrounding environment.

Initially it was planned to measure the temperature of each pin before measuring

but due to insufficient equipment it was instead approximated to the temperature of

the freezer. The temperature of the freezer was -19 ᵒC at the time. The pins where

then measured continuously and then stored for three days until measuring them

again in room temperature, which was approximated to 18 ᵒC.

29

The same method for measuring pins in room temperature as described above was

used. Small indications of corrosion could be seen on the pins after storing them.

The pins were cleaned with a towel briefly to remove scrap and moisture and

measurements were conducted.

Measurements were also conducted on joints belonging to the L60H, L70H and

L90H to see how tolerances are kept for the delivered casting breasts. The joints

were measured using the Marposs tool in two levels and two directions for each

hole. This can be illustrated by considering Figure 31, where the numbers 1 and 2

illustrate the levels, being approximate 5 mm from the edge. Lod indicates vertical

direction and Våg indicates horizontally. In Figure 31 this is reversed but the

coordinate system was based upon the machine directory when the casting breast

had been welded upon the front frame. A total of 13 casting breast were measured

where six belongs to the 60H model, four belongs to the 70H model and three to

the 90H model.

Figure 31: Levels and directions for measuring illustrated on the holes of a single casting breast.

To determine whether joints are affected from the processing stage to the state

where they are mounted, a surface roughness test was performed. The roughness

test was conducted using a roughness measuring device which calculates the

average surface roughness, Ra. A rough surface is often associated with a higher

coefficient of friction which would make pins stickier to mount. Ra is the arithmetic

mean deviation of surface heights from the mean line of the profile and can be

calculated through equation 2. L is the total length of the measurement, y is the

height of the surface from the mean line for a specified distance x [13].

𝑅𝑎 = 1

𝐿 ∫ |𝑦(𝑥)| 𝑑𝑥

𝐿

0 (2)

The measuring device can be seen in Figure 32. The test were performed on the

L60,L70, L90 and the L110/120 front frames. For each model there would be two

frames measured with three corresponding joints for each frames. The measured

joints were the E-joint, the O-joint and the P-joint. One measurement of eight

frames would be conducted at the processing area and eight would be done in

30

storage 5, the storage before the assembly lines. For each joint there would be three

measurements in order to get an average value. The joints at Volvo have a

requirement of a Ra-value of 3.2 µm or less so this measurement was performed to

control that it is kept and whether surfaces of joints are affected from processing to

the last storage before the assembly lines.

Figure 32: Measuring device for the average surface roughness.

2.3.5 Corrosion analysis

Corrosion is a big problem for Volvo today where many of the joints that comes to

the assembly line for mounting of pins suffers from corrosion on the inside of

them. The otherwise fine surface will be rougher and lead to difficulties when

mounting pins. Corrosion has not always been a problem where they before used to

lubricate the holes of frames with grease in order to withstand the corrosion that

builds up during the storage process. This would however lead to other problems

where dust, gravel and other contamination would get stuck in the grease during

transportation and storage processes. Contaminations are a problem without grease,

but when using grease and not protecting the joint, a higher degree of

contamination will occur. This standard was however removed due to the lack of

cleaning during assembly and instead, joints are now affected by corrosionII.

In order to locate the source of the corrosion there were discussions with

employees on where joints show signs of corrosion. Several joints show indications

of corrosion after the washing process followed by the drying process. Questions

whether wrong conditions during either the washing process or the following

drying process was raised. In order to see whether the applied detergent in the

washing process affects corrosion, a test was conducted on four steel plates. Two of

II Interview with Per-Anders Olsson, Production technician, 12/2-2016.

31

the steel plates, plate M and plate N, went through the washing process and the

other two, plate L and plate P, had nothing applied to them. The plates would then

be stored first in the colder tent for a total of 6 days followed by storage of 4 days

in the warmer tent. The plates that went through the washing process were slightly

wet afterwards and placed likewise so in the storages. During the time in the

storages there would be intervals where photos were taken in order to follow

corrosion indication and development.

During observation from both the panting area and the storage 4-5 area, one could

see a clear difference between joints regarding corrosive affected surfaces. All the

joints except the E-joint frequently had surfaces affected by corrosion. This was

thought to be because the other joints are part of the subcomponents which are

welded together. The subcomponents have tolerances which allow them to be

slightly curved in their shape, resulting in a gap in the middle of joint. During both

processing and the washing process, a mixture of cutting fluid and the fluids from

pre-treatment would be stored inside the frame. Going through the drying process

the fluids would condense and the inside of joints would be filled with moistureIII

.

Since frames are moved directly to storage 4 without any further drying, wet joints

are stored in exposed environment which promote corrosion. The E-joints which

does not include this gap in the joint, shows no sign of corrosion after the drying

process or in the storage areas.

Based on the test, interviews and observation, the source of corrosion were to be

determined.

2.3.6 Concepts of cooling and heating

Volvo Arvika currently stands between a choice to achieve their goals regarding an

assembly process which does not require external equipment such as

sledgehammers or crowbars. This study, as mentioned, worked in parallel with

several projects which were considering several concepts within cooling and

heating. The concepts described will be evaluated in section 2.3.7 together with

employees at Arvika plant in order to choose a concept to investigate further.

Existing freezer

The industry freezers used at Volvo Arvika are brought into this evaluation to

compare it to the considered concepts. The Freezers will be considered as

implemented in the concept matrix. The concepts of use are as described in section

2.2.8 and 2.2.9.

Ordinary freezers

Ordinary freezers described in section 2.2.8 could be a possible solution as they

keep a lower temperature which would result in a larger shrinkage of the pins. The

III Interview with Freddy Rogne, Technical support, 20/4-2016.

32

freezers are mobile but are however deep and requires the assembler to reach down

for every pin.

Nitrogen cooled freezer

Nitrogen cooled freezers is a concept that is under consideration of Volvo.

Currently a company has delivered a prototype freezer which uses liquid nitrogen

that expands into gas inside the vessel and cools the products. Successful test has

been conducted on the bronze bushings in the loading unit. The steel bushings were

however unsuccessfully mounted which are thought to be due to the heat treatment

which includes carbonitriding.

Liquid nitrogen

Tests with liquid nitrogen had also been performed on the bushing for the loading

unit. A vessel containing liquid nitrogen had been designed where bushings were

submerged directly into liquid nitrogen and allowed to cool down. These tests were

only applied to the bronze bushing which could be mounted with ease in the

loading unit. One can however see significant risks with this solution as liquid

nitrogen could come in direct contact with the assembler.

Induction heating

Induction heating is widely used in industrial applications where heat is generated

by eddy currents. Volvo in Arvika currently uses induction to heat up the bearings

to facilitate the mounting of them at heavy lines. Induction is a possible solution for

heating the joints in a fast and controlled way.

Pre-heating

Pre-heating is an option recently discussed within Volvo at Arvika. A prototype

had been developed at Volvo in Braås for pre-heating joints before mounting pins

into them. Pre -heating by conductive heat transfer could have a variety of designs

with different heat sources.

2.3.7 Evaluation of concepts

The matrix diagrams which were used to evaluate the different concepts discussed

in section 2.3.6 were rated in several aspects. Areas such as ergonomic, cost,

maintenance and safety would be evaluated with pin mounting as focus. The

evaluation was done together with engineers at VolvoIV

. The purpose of this was

to present the different concepts and illustrate their strengths and weaknesses for

different areas. Some of the concepts could be better suited for areas with a long

tact time and with a few staffs working next to it while others are better for mass

production with several people and a short tact time.

The criteria’s was weighted in a scale from 1-5. For each criteria, points were given

in a scale from 1-5 for each concepts. Based on the on the matrix diagram which

IV Meeting with Marcus Nävehed and Erik Sundbäck, Production engineer, 7/3-2016.

33

can be seen in Appendix D, and that heating joints was something that never been

tried at Arvika plant, pre-heating was the concept that were chosen to investigate

further in this study. It was also the chosen concept due to its simplicity and small

production cost which made it suitable as a prototype.

2.3.8 Prototype research

A visit to Volvo in Braås was made which is a Volvo factory that produces

articulated haulers. This was in connection to the pre-heating prototype that was

going to be developed. Braås had recently developed a prototype to pre-heat the

joint which the front frames and rear frame constitutes. Braås had the same kind of

problems as Volvo Arvika when it came to mounting of pins and a visit was in

order to get knowledge about the current state. The prototype that they had been

developed can be seen in Figure 33. The prototype was a simple construction made

out of a cover with a soldering iron inside it. The soldering iron would have its

soldering tip removed and instead a pin was placed inside it to extend the range of

heating inside the cover. The operator at place said that the prototype was

successful and that improvements regarding an easier mounting process had been

obtained. There was however no logged data regarding temperature and expansion.

The maximum temperature that had been obtained with this prototype was 330 ᵒC,

which was far more then needed for the relevant application.

Figure 33: Prototype for pre-heating in Braås.

2.3.9 Prototype and Pre-heating

For this study, a similar prototype was to be built for pre-heating the E-joint.

Because rather than testing out different equipment and spend time on developing

concepts, Volvo wanted to know the reliability of pre-heating the joints and where

problems could arise. One of the main concerns regarding pre-heating the joints

was that it could require lots of energy due to the surrounding goods. This could

potentially lead to shrinkage instead of an expansion of the joint. This is due to the

surrounding material not expanding while the surface of the joint is warmed

significantly more. The small part which is heated around the surface will expand

34

but since the surrounding material are relatively cold and not expanding in the

same rate, the material at the surface will be forced to expand outwards.

To develop a prototype for the E-joint, a soldering iron was ordered. The soldering

iron was a LV-33R model and it´s dimensions can be seen in Appendix E. With

known dimensions of the soldering iron, both cover and extension pin was created

using Catia V.5, the dimensions can be seen in Appendix E. Aluminum was chosen

as material for cover and extension pin due to its conductive properties and also for

its low density. Tolerance dimensions were not used here due to high coefficient of

thermal expansion of aluminum so the equipment would not get stuck after pre-

heating [12]. An easy assemble and disassemble were also preferable. In addition

there was also features added to the prototype, it had a locking plate to prevent the

soldering iron from falling out and also a lifting tool.

With a finished prototype test were conducted on the E-joint for both loose casting

breasts and a finished front frame at assembly line.

The first tests were conducted on two loose casting breasts. The purpose was to

demonstrate the expansion in correlation to the goods temperature. Also check how

the heat spread throughout the body and whether heating is available option. The

joint of casting breasts were measured in diameter, first in room temperature and

after being heated. This would be done when temperatures close to 60 ᵒC were

obtained. A limit of 60C ᵒ was chosen due to safety laws and to not affect the paint.

A temperature this low would mean that no unwanted metallurgical transformation

occurs either. The time it would take to pre-heat the holes to the set temperature

was also of interest as it should be lower than the current tact time for Medium line.

This would simplify the implementation of the pre-heat method if it would be

brought into the assembly line.

The diameter was measured using a Marposs instrument, the instrument can be

seen in Appendix B. The holes for the two casting breast were measured in two

directions and in two levels according to Figure 31. During pre-heating,

measurements of temperature were conducted every two minutes. These

measurements were done using a laser for the first casting breast at designated

points. The points that were measured continuously during heating can be seen in

Figure 34. The points closest to the inner surface had a distance of approximate 5

mm while those further away were 20 mm from the inner surface. The last point,

number five, had a distance of 50 mm with a 45 degrees angle from the inner

surface.

35

Figure 34: Points marked for temperature measurements during pre-heating.

When the goods had reached the set temperature, there were tests conducted where

pins were mounted into the joint. Four pins would be mounted into the pre-heated

joints, two for each casting breast. For each casting breast there would be a pin in

room temperature and one in a cooled state mounted. The four pins had been

measured in respectively temperatures. The temperature of pins in room

temperature was measured to 19 ᵒC while the cooled ones had a freezer temperature

of -22 ᵒC. The measured pins dimensions can be seen in Table 4. Pin´s with id

number 1 and 2 were mounted in the first casting breast while 3 and 4 were

mounted in the second.

Table 5: Dimensions for pins mounted in test 1

Diameter [mm]

Level 1

Level 2

Level 3

No.

Temp

0⁰

90⁰

0⁰

90⁰

0⁰

90⁰

1

19

79.994

79.993

79.987

79.987

79.987

79.991

2

-22

79.962

79.959

79.956

79.951

79.952

79.955

3

19

79.998

79.997

79.993

79.992

79.993

79.995

4 -22 79.966 79.957 79.951 79.950 79.95 79.954

The equipment were mounted according to Figure 35, were the soldering iron was

closest to the right hole. The left hole should in theory obtain slightly lower

temperatures and was therefore chosen to be measured to obtain the set temperature

for both holes.

36

Figure 35: Mounted prototype in casting breast, pre-heating the joint.

The first casting breast was pre-heated when the equipment had a temperature

equivalent of the room temperature. After obtained the set temperature, one room

tempered and one cooled pin were mounted. The mounting was documented by

videos and notes.

The second casting breast had the exact same methods applied, only this time the

equipment was pre-heated from the last test. The equipment had a temperature of

approximate 85 ᵒC. This was intended in order to see how it would affect the

warmup time of the surrounding material. When the prototype was first built, a

simple test was done to see how fast the equipment itself warmed up. What could

be seen during the test was that it had a significant slow curve in the start and then

rapidly increased. Pre-heated equipment was thought to lower the warmup time

radically in order to sync with the tact time at assembly line.

For the second breast there was a change in equipment to measure the temperature.

Instead of the laser there was now a conductive thermometer used, which were

thought to give a more appropriate reading of the temperatures. After being pre-

heated to designated temperature with temperatures measured in intervals, one

room tempered and one cooled pin were mounted.

After testing on single casting breast and confirming that nothing drastically goes

wrong, a test on the assembly line were conducted. The purpose of this test was to

see how the prototype works in the real applications. Even though the goods

wouldn’t reach temperatures that would affect the paint of the wheel loaders, the

prototype itself gets significantly warmer. The test would check whether the paint

or any other surface or components such as wiring harness or hoses are affected.

Also surfaces close to the heated areas such as the rear plate of the casting breast

would be controlled in order to avoid burn risks for the assembler. A piston

cylinder was also included in the mounting to complete the joint, in order to see

how the pre-heating affects the problem with linearity between components.

37

The test was done in similar ways of the prior ones, five points were marked where

temperatures of the goods would be measured according to Figure 36. The holes

were measured using dial indicators. The intended Marposs tool was not used

because measurements were unreliable due to incorrect calibration. The holes were

measured in the exact same way for the prior test, in two directions and two levels,

see Figure 31. The equipment was pre- heated for 12 minutes where a temperature

of approximate 105 ᵒC was reached on the cover. The equipment was mounted into

the holes and temperatures were measured continuously in two minute intervals

while pre-heating. When a temperature of approximate 55 ᵒC had been obtained,

the prototype was removed and tilt cylinder was placed in the joint. A cooled pin

was then mounted which had been measured to and dimensions according to Table

2 with a temperature of -14 ᵒC. The holes were not cleaned or lubricated and a paint

edge could be observed which were not removed. This was intended in order to

have a joint with unfavorable mounting condition.

Figure 36: Points marked for temperature measurement.

Table 6: Dimensions of the cooled pin mounted in the test

Diameter [mm]

Level 1

Level 2

Level 3

0⁰

90⁰

0⁰

90⁰

0⁰

90⁰

79.972 79.971 79.976 79.975 79.974 79.978

2.3.10 Analysis of material effects

A part of this study was to investigate whether cooling and heating could cause any

metallurgical changes and subsequent problems. Volvo Arvika has problem with

their steel bushings when cooled rapidly by methods such as liquid nitrogen and

were worried similar problems would arise for pins. A theory was that the steel

bushings contained significant amount of retained austenite from their heat

treatment. When cooled rapidly the retained austenite could have transformed into

martensite, causing an expansion of the material, leading to an unsuccessful

mounting.

38

The effect of pre-heating was not investigated but should have no affect any part of

the joint or pin due to its relatively low temperature.

Material tests for pins were done to determine whether retained austenite existed in

pins and if it would transform into martensite when cooled with liquid nitrogen.

This investigation would be done from both a theoretical aspect and material tests.

Theoretical investigation

The pins are first heated to 850-900 C, which would correspond to a fully austenitic

structure for the given carbon amount (0.30-0.37%) according to the phase diagram

shown in Figure 37 [13].

Figure 37: Part of the Iron-carbon phase diagram [13].

To see what structures that are obtained when quenched, the hardenability of the

steel was investigated which can be seen in Figure 38 [14].

39

Figure 38: Hardenability of steel grade 2234 [14].

According to the graph, an 80 mm pin will obtain a hard martensitic surface while

the softer core could consist of binate or martensite depending on the cooling rate.

From the CCT-diagrams shown in Figure 39 this can be shown by considering two

different cooling rates as shown with red lines. The surface would obtain a

martensitic structure with the faster cooling rate while the core would obtain a

binate structure after quenching [14].

Figure 39: Continuous cooling temperature (CCT) diagram for the steel grade 2234 [14].

The amount of retained austenite in carbon steel after quenching can be described

by the graph illustrated in Figure 40. This indicates for the given steel grade with a

carbon content of 0.30-0.37% that retained austenite can exists in small amounts,

approximate 1% after quenching [15].

40

Figure 40: Relationship between the martensite content, retained austenite content, start temperature for martensitic transformation and carbon content [15].

After the first tempering at temperatures of 550-600 C˚ the material would undergo

a transformation. Martensitic lath boundaries are replaced with ferritic grains and

coarse spheroidized cementite carbides (Fe3C) in the grain boundaries. This will

enhance the toughness while lowering the hardness. Retained austenite will also

decompose into a ferritic structure for the given tempering temperature [14], [16].

By induction, the pin obtains an austenitic structure again for a surface depth of

approximate 4mm. By the following water spray quench, a martensitic structure is

obtained for that region with small amounts of retained austenite as before. By

tempering between 160-200 ᵒC, the core region will be unaffected which already

had transformed from the prior tempering. The induction hardened region will

however change, the martensite will coarsen and ε-carbides will precipitate. There

will however be no decomposition of retained austenite into ferrite and cementite

as it requires tempering temperatures above 200 ᵒC [16].

Based on theory one would except that the region below the induction hardened

surface to the core would have no retained austenite. In the induction hardened

region there could however be small amounts of retained austenite.

Material tests

In order to investigate both the sur