TALAT Lecture 4106

Quality Assurance and Process Control

9 pages, 8 figures

Basic Level

prepared by Lothar Budde, Universität-Gesamthochschule Paderborn

Objectives: − to descibe the basic methods of quality assurance and process control for mechanical

fastening methods Prerequisites: − General mechanical engineering background − TALAT lectures 4101 - 4105 Date of Issue: 1994 EAA - European Aluminium Association

TALAT 4106 2

4106 Quality Assurance and Process Control

Table of Contents

4106 Quality Assurance and Process Control..................................................2

4106.01 Process Analysis .......................................................................................... 3

Comparison of Quality Assurance of Different Joining Technologies ....................3

Direct Process Control as a Supplement to Statistical Process Control...................3

Path of a Mechanical Fastening Process ..................................................................4

4106.02 Controlling Process Parameters .............................................................. 5

Characteristic Deformation Diagram of a Blind Rivet ............................................5

Controlling the Limiting Values for Mechanical Fastenings...................................6

Characteristic Force-Motion Studies for Clinching with Local Incision .................6

Cross-Section of a Clinch Joint with Characteristic Values for Joint Geometry.....7

Example of a Process Analysis for Clinch Joints with Local Incision ....................8

4106.03 Literature/References .............................................................................. 9

4106.04 List of Figures.............................................................................................. 9

TALAT 4106 3

4106.01 Process Analysis

• Comparison of quality assurance of different joining technologies • Direct process control as a supplement to statistical process control • Path of a mechanical fastening process

Comparison of Quality Assurance of Different Joining Technologies The predictability of mechanical fastenings in the production technology depends largely on the reproducibility of the joint, which, in turn, is correlated to the tolerance of the production process. Contrary to the combined adhesive and spot welded fastening, clinched and self-piercing riveted joints - as typical examples of mechanical joining methods - can, to a certain extent, be tested using non-destructive testing methods (Figure 4106.01.01).

4106.01.01

Source: Budde

Comparison of Quality Assurance of Different Joining Technologies

Joining Technology

CharacteristicsAdhesiveJoining

Spot Welding Clinching Riveting

Process ControlPossible Onlyin Partial Steps

Joint cannotbe Tested Non-Destructively

Quality Assurance Process ControlOnly ConditionallyPossible

Joint cannotbe Tested Non-Destructively

Process ControlOnly ConditionallyPossible

Joint can beTested Non-DestructivelyConditionally

Process ControlOnly ConditionallyPossible

Joint can beTested Non-DestructivelyConditionally

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Direct Process Control as a Supplement to Statistical Process Control It has often been pointed out here that the quality assurance of mechanical fastenings for aluminium constructions is of paramount importance. With automation it is possible to eliminate the influence of random and chronologically limited personal errors on the quality of the fastening. Supplementary to the destructive and non-destructive testing of samples, the process control and regulation of the mechanical fastening process offers a promising additional quality assurance method.

The direct process regulation and control based on the relevant data extracted during the actual joining process - i.e. in addition to the statistical process control - plays an important role in the mechanical fastening process (Figure 4106.01.02).

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Direct Process Control as a Supplement to Statistical Process Control

Source: Budde

4106.01.02Training in Aluminium Application Technologies

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Riveting Process

ProcessControl

StatisticalProcessControl

e.g. Rivet Element Formation (Random Sample)

e.g. Force Path

Rivet Element

Jointing Parts Riveted Joint

Post-ProcessIn-Process

Path of a Mechanical Fastening Process The force-motion analysis builds the basis of the direct process control and regulation of mechanical fastening (see Figure 4106.01.03). Based on process analysis, it is possible to follow the mechanical joining process qualitatively and, at the same time, to determine the quantitative correlation existing between the relevant chronological changes in the joining process and the quality of the joint produced, whereby the term quality is defined as the joint strength at varying loads.

The operational path of the mechanical fastening process illustrates that the process control and regulation is based on the determination of the actual current geometrical formation and on the assumption that each joint geometrical form (evaluated on the basis of the geometric joint characteristics) has an individual defined quality.

Path of a Mechanical Fastening Process 4106.01.03

Source : Budde

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Path

Forc

e

Joining Process Analysis

Process Steps of Joining

Form of Joining Element

Mech. Behaviour of Joint

Not ObservedVariables of State

CharacteristicJoint ValuesControllable

Input Variables

UncontrollableInput Variables

ObservedVariable of State

CharacteristicProcess Index

hNdN

Path

Forc

e

TALAT 4106 5

4106.02 Controlling Process Parameters

• Characteristic deformation diagram of a blind rivet • Controlling the limiting values for mechanical fastenings • Characteristic force-motion studies for clinching with local incision • Cross-section of a clinch joint with characteristic values for joint

geometry • Example of a process analysis for clinch joints with local incision

Characteristic Deformation Diagram of a Blind Rivet Blind riveting (mechanical fastening with auxiliary parts) and clinching (mechanical fastening without auxiliary parts) are processes for which process control and regulations have been applied (Figure 4106.02.01). The process steps during blind riveting can be divided into a in-slippage phase (in which the stem is pulled) and a clamping phase (in which the fastening parts are subject to a pre-stress). The clamping force and consequently the quality of the riveted joint can be predetermined by analysing the deformation diagram for blind riveting.

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Breaking Force for Rivet Mandrel

Form

ing

Forc

e [k

N]

Forming Path [mm]Characteristic Deformation Diagram of a Blind Rivet 4106.02.01

Source: Budde

1

3

0

2

0 2 4 8 10

Clamping Phase

Inslippage Phase

TALAT 4106 6

Controlling the Limiting Values for Mechanical Fastenings At the end of the process analysis of the mechanical joining process, one has to decide whether the quality requirements can be reliably fulfilled or whether a direct process control has to be carried out continuously. During a process control, the characteristic joint values are determined and constantly evaluated. On the basis of the process analysis, it is possible to develop appropriate control strategies like, for example, a control of the limiting values (Figure 4106.02.02).

Controlling the Limiting Values for Mechanical Fastenings 4106.02.02

Source: Budde

Evaluation :Joint in Good Condition!

Evaluation :Joint With Flaws!

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Force

Path

Force

Path

Characteristic Force-Motion Studies for Clinching with Local Incision Just as in the case of self-piercing riveting, it is possible to use force-motion diagrams to study the individual phases of the joining process during clinching (Figure 4106.02.03). Experiments have shown that the joint force determined point-wise (locally) or interactively can be treated as a universal control parameter. The chronological change of the joining force offers very significant information about the process and the forming of the joint.

TALAT 4106 7

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Source: Budde

12

3

Characteristic Force-Motion Studies for Clinchingwith Local Incision 4106.02.03

Compressionand Further Incision

Clinchingand Cutting

CuttingDie(SM)

PressPunch(DS)

SM

DS

F

S

F

S

7 8 9

Angle of CrankJo

inin

g Fo

rce

F

Punc

h Fo

rce

F

Single-Step Clinching (CL)with Hydraulic C Press

Multi-Step CLwith an Eccentric PressDependent on Path

Punch Path Ss

Cross-Section of a Clinch Joint with Characteristic Values for Joint Geometry Two types of characteristic values exist for the joint geometry, depending on whether these values can be measured with or without destroying the joint element. It has been found that for clinch joints, a linear correlation exists over a large range among the joining process dependent values of web thickness, web breadth and the joint strength. Consequently, the web thickness and/or breadth are used to optimise the joint and for non-destructive testing of the same (see also Figure 4106.02.04).

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Source: Budde

Cross-Section of a Clinched Joint withCharacteristic Values for Joint Geometry 4106.02.04

Joining Force F

ET

STB

mm

4

5

6

0

B

ET

ST

Web

Thi

ckne

ss S

T / P

enet

ratio

n D

epth

ET

mm3

0

1

2

Web

Wid

th B

TALAT 4106 8

Example of a Process Analysis for Clinch Joints with Local Incision Through the control of the joining force, it is possible to control every clinching or punch riveting process quasi on-line. Thus it is possible, for example, to clearly recognise different damages of the die during the single-step clinch process by studying the force-time curve (Figure 4106.02.05).

0 0,05 0,1 0,15 0,2 0,25 0,35sec

Time

0

4

8

12

16

20

kN

28

Join

ing

Forc

e

Expected Curve

Damage to Anvil

Single-Step Clinching (with Local Incision)of Shaped Sheet Parts

Damage to Spring Lamella

4106.02.05

Source: Bober, Liebig

Training in Aluminium Application Technologies

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This makes it possible to evaluate the quality of mechanical joints in aluminium shaped sheet and profile products using non-destructive methods. Although the process control during riveting and clinching makes it possible to guarantee the joint quality control of the mechanical fastening process, it is still necessary to collect comprehensive data if one wants to be able to influence the design of the aluminium construction within the framework of a more global quality assurance.

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4106.03 Literature/References 1. Budde, L. Untersuchungen zur Kombination quasi-formschlüssiger und

stoffschlüssiger Verbindungsverfahren. Dissertation Uni-GH-Paderborn, 1989 2. Schmid, G. Methoden der Qualitätssicherung beim Durchsetzfügen. Bänder Bleche

Rohre 32 (1991) 61-64 3. Budde, L. Qualitätssicherung beim Nieten - Möglichkeiten und Grenzen. Bänder

Bleche Rohre 32 (1991) 64-74 4. Liebig, H.P. und Mutschler, J. Qualitätssicherung beim Stanznieten

prozeßbegleitend überwachen. Bänder Bleche Rohre 34 (1993) 5, 52-54 5. Warnicke, H.-J. und Schweizer, M. Bleche sicher verbinden - Automatische

Nietprozeßüberwachung. Wissenschaft und Technik. Springer Verlag (1993) 1, 50-52

6. Lappe, W. und Budde, L.Qualitätsbewußt - Möglichkeiten der

Prozeßüberwachung beim Stanznieten von Blechen und Profilen. Maschinenmarkt 99 (1993) 48, 60-64

7. Liebig, H.P., Bober, J. und Göpfert, D. Qualitätssicherung durch

rechnerunterstützte Überwachung des betrieblichen Druckfügeprozesses. Blech Rohre Profile 39 (1992) 6, 466-471

4106.04 List of Figures Figure No. Figure Title (Overhead) 4106.01.01

Comparison of Quality Assurance of Different Joining Technologies

4106.01.02 Direct Process Control as a Supplement to Statistical Process Control 4106.01.03 Path of a Mechanical Fastening Process 4106.02.01

Characteristic Deformation Diagram of a Blind Rivet

4106.02.02 Controlling the Limiting Values for Mechanical Fastenings 4106.02.03 Characteristic Force-Motion Studies for Clinching with Local Incision 4106.02.04 Cross-Section of a Clinched Joint with Characteristic Values for Joint Geometry4106.02.05 Example of Process Analysis for Clinch Joints with Local Incision