Chassis Initial Design (Part 2)

Student Name: JaberAlhaykiStudent ID: 20900143

ContentsChassis7Types of chassis71-Twin tube / Ladder chassis72-MonocoqueChassis83-Space Frame Chassis10Operating conditions of the chassis11Vertical bending11Longitudinal torsion11Lateral bending12Horizontal Lozenging12Product Design Specification (PDS)131-Car type132-Time133-Cost and material availability134-Process145-Environment146-Factor of safety (Thumb Rule)15Roll centre18Static mode18Cornering19Braking20Bumping21Material Selection22Material families22Ashby diagrams22Metals24Composites24Comparing materials24AISI 1020 steel24Stainless steel 30425Carbon fiber26The proper material27Design29Skills required30Oxyacetylene Welding (OA)31Brazing32Procedure32Arc welding33Procedure33Soldering34Procedure34TIG welding35Procedure35MIG welding36Procedure36General safety precautions37Personal safety tools:37Working area:37Generally:37Method of manufacturing42Tolerances43Material processing - Fabricating - Reforming43Causes of corrosion and preventing methods45Heat treatment46Chassis selection (Selection matrix)47Ergonomics48Components50Centre of Gravity CoG51Parts position52CoG calculation - Initial53CoG calculation / Forces Modified57CoG Calculation - Final58Forces59Static mode59Acceleration condition59Braking condition60Cornering condition61Clarification62Manufacturing steps Welding Pictures63Engineering drawings68Bibliography70

Table of figuresFigure 1 Ladder chassis7Figure 2Monocouque chassis8Figure 3 Space frame chassis9Figure 4Vertical bending10Figure 5Longitudinal torsion10Figure 6Lateral bending11Figure 7Horizontal Lozenging11Figure 8Roll center - Static mode17Figure 9 Roll center - Cornering18Figure 10 Roll center - Braking19Figure 11 Roll center -Bumping20Figure 12 Material families21Figure 13Strength vs. toughness22Figure 14Strength vs. cost22Figure 15Strength vs. density22Figure 16 Carbon Fiber tubes properties26Figure 17 Chassis Design28Figure 18 Welding29Figure 1930Figure 2031Figure 2132Figure 2233Figure 2333Figure 2434Figure 2535Figure 2636Figure 27 Fabricating37Figure 28Manual tube bender38Figure 29 Machining38Figure 30 Flap disc39Figure31 Cutting disc39Figure 32 Coating40Figure 33 Drilling40Figure 34 Fitting41Figure 35 Chassis design42Figure 36 Examples of fish mouth on square and rectangular tubes43Figure 37Straight simple cut (left) and angle cut (right)43Figure 38An example of an engine mount44Figure 39An example of a gearbox mount44Figure 40 Drive's position while driving48Figure 41 Initial sketch49Figure 42 Top view that shows the parts position49Figure 43 Position of the components and initial dimensions51Figure 44 Finding RR52Figure 45 Finding RF and CoG on X axis53Figure 46 Finding CoG height54Figure 47 Load percentage in the front and rear55Figure 48 Sketch of the components after changes56Figure 49 Position of the parts after re-allocation56Figure 50 Static mode58Figure 51 Reaction forces when accelerating58Figure 52 Reaction forces while braking59Figure 53 Reaction forces while cornering60Figure 54 The final design (Isometric)66Figure 55 Front view (Looking from the side)67Figure 56 Side view (Looking from the rear end67Figure 57 Top view (Left side is the front end)68Figure 58 Isometric view of the chassis68

Chassis

One of the major structures of any automobile is chassis which holds almost the entire car parts like, engine, wheels, axle components, steering, and brakes. The car body is flexibly shaped according to the chassis structure at the time of manufacturing. Composite plastics or sheet metal are usually used to make an automobile chassis as they offer the needed strength to support vehicular parts and the loads applied upon it. Automotive chassis advantages are to keep a vehicle stiff, rigid and bending-less. It also guarantees low levels of harshness, vibration, and noise throughout the vehicle.One of the main parts of chassis is the frame which the remaining parts of the chassis are bolted. High rigidity and strength are extremely requires for the frame to endure vibration, stresses, twists and shocks which are applied on the vehicle while driving on the road. It is supported on the wheel and tire assemblies. In order to provide short turning radius to front wheels, the frame is made narrowly in the front and it gets wider through the rear side to offer more space in the body.Types of chassis

1- Twin tube / Ladder chassis

Due to the use of heavy gauge material in this type, it is very durable and easy to manufacture. On the other hand, it is quite heavy and its torsional stiffness is very low comparing to other types. It is also simple as it offers good accessibility of mechanical parts and disposed to damage by accidents. This type uses sub-frames which makes it easier to fix mountings for each mechanical part. However, locating the suspension, engine, gearbox, differential and seat mountings, is initial to design this type of chassis. This will allow addressing the best chassis tubes position. But because torsional stiffness is not changing much by changing tubes position in this type, the previous point is not critical. Moreover, the frame of this type has to provide high loads and round tubes are not appropriate for such loads as the load capacity of this type is poor in bending. As the torsional stiffness also depends on the tube section, the torsional capacity of this type is low. See figure1

Figure 1 Ladder chassis

2- MonocoqueChassisThis type of chassis is made using a large stamping machine to form the different pieces of the chassis which in the end outlines the overall car shape. The base of the frame is the largest piece in this type which other pieces are welded to it to form one piece structure. This type is fit for mass production as its cost is low. Robot arms are used to spot weld or laser weld the pieces together in a systemized line of production that takes few minutes to be done. Other parts like doors and bonnet are added after that. This type uses much of metal which makes it safer in case of accidents. The figure below is an example of monocoque chassis. See figure2.

Figure 2Monocouque chassis

Advantages Space efficient Low cost Safe Good for mass productionDisadvantages Heavy weight Needs high amount of metal Low rigidity Cannot be manufactured in a small workshop3- Space Frame ChassisThis type of chassis is made by using circular or square section tubes. Although circular tubes offer high strength, some use square tubes for the ease of connecting to the frame sections. These tubes are linked (welded) together in various directions that form a complicated figure in order to resist loads from different directions. This type is suitable for sports cars as its strength is high and can handle loads from any direction. The figure below shows one of the space frame designs. See figure 3.

Figure 3 Space frame chassisAdvantages High efficiency High strength Can handle loads from any direction LightDisadvantages Costly Complicated design Cabin is not easily accessible

Operating conditions of the chassisIn order to design a vehicle chassis, we should understand the type of circumstances that the chassis would experience on the road. There are initially four main states of loading that the chassis would face which include Vertical bending Longitudinal torsion Lateral bending Horizontal lozengingVertical bendingSince the wheel axles is supporting the chassis frame at its ends and the weight of the driver, seats, and baggage are focused around the middle of the wheelbase, that leads the side members to be exposed to a vertical bending which makes them drop to the central area. The figure below is a simple example that indicates this state.

Figure 4Vertical bendingLongitudinal torsionAs the opposite rear and front wheels hit a bump at the same time, the ends of the chassis are twisting in the other directions. That means the cross members and the side ones are experiencing longitudinal torsion which caused the chassis to be twisted. The figure below is an example which clarifies the state.

Figure 5Longitudinal torsion

Lateral bendingThere are some states that expose that chassis to lateral / side force. When the car is turning on a corner is one state as it is exposed to centrifugal force, side wind is another state, the arc of the road, and the impact of an accident, all the previous states cause lateral bending of the chassis. The grip of the tires reacts with the lateral forces. To sum up, side members of the chassis are exposed to bending moment so the frame tends to bend with the force direction.

Figure 6Lateral bendingHorizontal LozengingAs the vehicle is driven, it is always exposed to road difficulties, such as, holes, bumps,etc. These could result in a deformation called lozenging. For instance, when the car hits a bump there are two types of forces applied, the horizontal force in the opposite direction of driving and a vertical force due to the hit of the bump. As the two wheels act against each other due to road obstacles, this causes the chassis to twist like the figure below shows (called paral-lelogram shape).

Figure 7Horizontal Lozenging

Product Design Specification (PDS)1- Car typeThe car that will be manufactured is a single seated rear wheel racing car as many people are attracted by them, which makes it easier to be sold. Bahrain International Circuit (BIC) is another reason of building this car as it would be driven and tested in front of audience and fans. In my opinion, this car would be a great motivation for the coming generations and future engineering students to start their own designs. However, the chassis has to be manufactured with a less number of members as possible as it is required to be light as possible for better performance. But at the same time, it should be rigid in both torsion and bending to ensure that the car can handle the forces experienced when cornering or hitting a bump for example. Moreover, that will be achieved by applying so many triangulations in the design so it could handle forces from any direction. The car will be manufactured to be used in a racing track where there are no bumps as it is assumed, but bumps will be considered for the worst case scenario.2- TimeAt this time, we are in the week 6 and at the end of this week (14th October 2014) the first submission is due which is the initial design and report (PDS). In the next week, we will start doing a design research with more details specified and it will be due on 9th November 2014. After the design research is done, the chassis and its components will be fully analyzed as the deadline for this will be 12th December 2014. Finally, by the date of 15th January 2015, the chassis should be manufactured, assembled, and finished as planned.3- Cost and material availabilityThe cost of the whole project is 3000 BD as decided by Bahrain Polytechnic. It is important to design this project within this budget; otherwise there would be a possibility of aborting the project or looking for a sponsor. However, there are some materials that are available at the workshop, but other materials could be ordered if needed and considering the limited budget is important in this stage. Moreover, there are properties that are required in the material that should be chosen for the chassis design (Race car) and the first thing to achieve that is to investigate different materials and compare between their properties to pull the suitable material that fits the design and the budget.

4- ProcessIn order to manufacture the chassis and make sure it is done carefully there are steps to be followed. These steps will also ensure the manufacturing is done within the allowed tolerances. However, the first step is to cut the tubes by the needed sizes and quantity. The next step is to weld the bottom layer and make the triangulations. After that comes the top layer following the same sequence as the bottom layer. Finally, link the top and bottom layers together and make the required triangulation between them. Note that it is necessary to use welding fixtures or jigs while welding the layers to prevent any movement that could possibly cause unbalanced design. Also, the manufacturing of the chassis needs some skills like cutting and welding. Welding is an important skill as we have to consider the types of welding available in the workshop, which are Tig, Mig, and gas welding. The team should have some practical classes for cutting and welding with the specific types available to get the confidence and skill required to get all the work done as perfect as possible.

5- EnvironmentAn important fact that should be considered is weather, as the weather beside the loads and forces applied has its effects on the material that would be chosen. As the car will be manufactured and used in Bahrain, it will be exposed to high temperatures and humid environment as Bahrain is a land and surrounded by water. As a result of humidity and hot weather, the chassis will be exposed to experience rust, wear out of material, and finally failure of the chassis as a worst case scenario. Therefore, the chassis will be coated to avoid any effects by the environment and to increase the life span of the chassis.

6- Factor of safety (Thumb Rule)Factor of safety can be basically defined as The structural capacity of a system beyond the expected or the actual loads. However, the factor of safety could be initially estimated using the following equation

The above equation could be reached by estimating the factor of safety for each component of the above as the equation shows. FS material

FS material = 1.1As the material properties could be taken from the internet and handbooks so far, the FS material was chosen to be 1.1 FS stress

FS stress = 1.3As there are some unknown forces on the chassis because it was not analyzed yet, the FS stress was chosen to be 1.3

FS geometry

As the team of students that will manufacture the chassis are not highly skilled, the manufacturing tolerance is average. Therefore, the FS geometry was decided to be 1.0FS geometry = 1.0 FS failure analysis

The car is exposed to accidents and therefore the FS failure analysis was 1.3FS failure analysis = 1.3 FS reliability

The chassis must be very highly reliable therefore this FS value will be at the max.FS reliability = 1.6After the previous FS factors are collected, now the factor of safety could be calculated as followingFoS = 1.1 x 1.3 x 1.0 x 1.3 x 1.6= 2.97

Roll centreStatic mode

Figure 8Roll center - Static mode

The figure above shows the front of the racing car which was drawn using SolidWorks software in order to estimate the roll center of our design. It shows the vehicle in the static mode as the distance from the ground to the chassis is 0.015 meter. The camber angle is 90.31 degrees and the roll centre is represented by the blue point as shown above.

Cornering

Figure 9 Roll center - Cornering

The figure above shows how the suspension and chassis look like when cornering to the left at 3 degrees. It is clear that the car is turning left as the weight transferred to the right and the reason of choosing 3 degrees is that the racing car has to have a hard spring which will be chosen later on. The roll centre position is good as it did not move much from its original position. The camber angle is acceptable as well as it is almost 90 degrees for the right wheel and almost 91 degrees for the inner wheel which is the left one.

Braking

Figure 10 Roll center - Braking

In this state, the chassis was lowered by 0.02m as shown in blue above and again that is because the spring of the racing car will be hard. The camber has changed slightly to 91.66 degrees which is acceptable and the roll center did not move to the right or left as there is no rolling in this state.

Bumping

Figure 11 Roll center -Bumping

This is how the suspension looks like when a wheel hits a bump. As the figure above shows, when the wheel on the right hits a 0.02m height bump the camber angle will be 91.66 degrees. However, this case is not highly considered as the racing car to be manufactured is expected to be driven on a clear track and will barely experience such case as assumed.

*This part is extracted from assignment 1 / Mechanical project 3

Material SelectionThe purpose of this part is to choose the suitable material for the chassis by comparing different materials properties and compromise between them. A research was done for several materials properties that could be used to build the chassis. However, there are some criteria that should be considered while researching, such as, strength, cost, density, weld ability, and availability. Finally, one material will be selected and justified according to the criteria of our chassis.Material familiesThere are four main families of materials that come under the materials tree as shown below. The four families are metals, ceramics, polymers, and composites. Some of the families will not be considered for our design.

Figure 12 Material familiesAshby diagramsThere are three diagrams below that were used to compare materials families. The diagrams chosen were all contain strength against different criteria as following:

Figure 13Strength vs. toughness

Figure 14Strength vs. cost

Figure 15Strength vs. density

MetalsMetals are the most common material used in building chassis because of their good machinability, fabrication and weld ability compared to other materials like ceramics and composites. As the first diagram above shows, metals are relatively tough but at the same time they have high density comparing to other materials. The diagram also shows that the price range of metals goes from average to high price and that would affect the budget in case of it is high.CompositesAccording to Ashby diagram above, composites have high strength to weight ration and toughness comparing to other materials. In other words, composites have high strength, toughness, and light weight comparing to metals. However, composites are more costly comparing to some other types of metals. Also, composites have a very good ability to resist corrosion and that makes them one of the best choices for the chassis.

Comparing materialsThree different materials were chosen to be compared and compromised in order to pick up the most suitable type that fits for our chassis and budget. The first one is AISI 1020 steel, the second one is stainless steel 304, and finally carbon fiber. Advantages and disadvantages are mentioned for each material.AISI 1020 steelThis type of steel consists of 17-23% of carbon, plus other elements as shown in the table below. This type of steel is very good for cold work and heat treatment. Moreover, AISI 1020 has a good weld ability which would help in the manufacturing process.

Advantages It has a good welding ability comparing to stainless steel or other types of steel. Low cost compared to carbon fiber and stainless steel. Good ductility and strengthDisadvantages It has relatively high density Low corrosion resistance

AISI 1020 steel elements is shown in the table below

The physical and mechanical properties of AISI 1020 are shown in the table below

Stainless steel 304Chromium and nickel are the main elements of stainless steel, which has unique characteristics. Corrosion is resisted by chromium as it provides an oxide cover that resists corrosion. That does not mean stainless steel has a 100% corrosion resistance as it could be exposed to some kinds of corrosion, therefore, it should be taken care of from time to time. Advantages High corrosion resistance High ductility comparing to AISI 1020Disadvantages More costly than AISI 1020 Poor weld ability, machinability, and difficult to be fabricated comparing to AISI 1020

Elements of stainless steel 304 is shown in the table below

Physical and mechanical properties of stainless steel 304

Carbon fiberThe main elements of carbon fiber are carbon and epoxy. This material is commonly used in the F1 industry as it has a combination of strength and light weight at the same time. However, the manufacturing of fiber tubes could be done in two ways, one is called Pultruded and the other way roll-wrapped.The Pultruded carbon fiber is made by aligning fibers in one axis, which results in making the tubes of fiber tough in one direction. On the other hand, roll-wrapped carbon fiber tubes are made by aligning the fibers in different directions which makes it withstand axial and lateral forces. This type of tubes has high cost.

Carbon fiber tubes properties

Figure 16 Carbon Fiber tubes properties

Advantages It has high strength Light weight Corrosion resistance Ease of shaping into a desired formDisadvantages High cost Difficult to manufacture Brittle in case of sudden impact The strength of carbon fiber depends on the fiber direction, so different directions of layers are needed to accomplish the desired propertiesThe proper materialAfter comparing and compromising between the three materials above, one material was chosen, which is AISI 1020 steel. First of all, the chassis main requirements are to have high strength in order to handle the maximum weight applied to it. Moreover, the chassis should be stiff in torsion so it handles the torsional forces due to road obstacles and cornering situations for example. Another thing is density as the material that would be chosen should be as light as possible for higher acceleration and enhanced handling. However, by comparing AISI 1020 with stainless steel 304 in terms of strength, 304 has higher yield strength but 1020 has acceptable 205 MPi in yield. AISI 1020 is more dense than carbon fiber which means it is heavier, but carbon fiber is more expensive than 1020 and needs high skills to be manufactured. Also, 1020 is the best of the three materials that are compared in terms of machinability and weld-ability, which should be considered as the groups that will make the project do not have enough experience or not highly skilled. Another advantage for 1020 steel over the two other materials compared is the availability of the 1020 steel in the workshop, plus the lower cost as the budget and time of the project are limited. Finally, the disadvantage of the low corrosion resistance of AISI 1020 could be resolved by applying a special coat (paint) on the chassis as a protective action and this also could give it a better look.

Design

Figure 17 Chassis Design

Several designs of the chassis were tried using solidworks software. The figure above shows the final design chosen. It consists of square and rectangular tubes made of steel (AISI 1020). The design also has triangulations to help distributing the forces across the chassis. There will bearound 20 brackets attached to the chassis for the wishbones and dampers. Some of them are attached in the rear of the chassis to the engine room, and the rest attached to the front end.

Skills requiredIn order to make the chassis, there are some necessary skills required to do the work. Most of the group members definitely had various work experiences through the work-placements, part time jobs in workshops, or even worked on their own vehicles. That ultimately gave them some practical experiences in different areas. Following are a list of the skills required to achieve the manufacturing of the chassis.

Figure 18 WeldingWelding is basically a process of joining two pieces together, normally metals. There are different types of joining metals together, such as, riveting, nut and bolt, and soldering. It's not possible to use riveting to hold the chassis as it's not strong for that purpose, but it could be used to hold sheets of aluminium on the chassis. Nut and bolt isn't strong enough for linking chassis parts as well, and if so, there would be a chance of looseness which would cause unbalancing in the chassis that is unacceptable. Moreover, shear force will be affecting the chassis if nut and bolt are used. Soldering is perfect, but not for a chassis welding. It's used for wires and electrical stuff, so it's neglected. Welding is the perfect method for our purpose which is joining the chassis parts together as it holds all the pieces and form them like one strong piece. There are different types of weldeing that are mentioned below.Oxyacetylene Welding (OA)One type of welding is the oxy-acetylene welding (OA). OA is very handy and it can be used for almost any metal, but needs practice and experience. The flame of OA burns at 6000 F and its hot enough to melt most metals. It is the only gas flame that can do that. The touching edges of two metals are melted together; this is the simple idea of OA welding. This process could be done using filler rod, or even without it.

Figure 19Procedure

Choose a suitable tip for the welding and fix it Make sure the main cylinders are opened (Acetylene & oxygen cylinders) Open the acetylene valve until you barely smell the gas Give a spark to the tip Set the flame by carefully controlling the two valves (Acetylene & oxygen valves) Set the working pieces together and tack weld both ends Take a proper position to weld Start welding from one side until a welding pool is created Ensure that the flame is at an angle of approximately 45 degrees Drive the pool carefully through the end Close the valves and allow the work to cool down

(StanfordUniversity, 2012)

BrazingBrazing is the process of joining two metals using a filler material. It is very similar to OA welding and soldering, as it has almost the same idea of using a filling material. The temperature applied in brazing must be less than the melting point of the working objects but not the filling material.

Figure 20Procedure Make sure the working parts are clean The working pieces must be close to each other (Proper clearance) The welding parts must be fixed safely while brazing The flux must be used to decrease oxidations The base metals must be heated first Apply the filler to the joint Make sure the filler metal goes through the other side of the joint to fill the whole joint Allow the brazing to cool down Finally, make sure to clean the joints(Achrnews, 2008)

Arc weldingArc welding is another type of welding, where a welding power source is necessary in order to produce an electric arc between an electrode and the base material. DC or AC could be used, as well as, consumable or non-consumable electrodes. The temperature in this type of welding reaches up to 4000 Co. (ESAB, 2000)

Figure 21Procedure Prepare the working metals by filing, grinding, or using a steel brush Set the proper amperage according to the thickness of the metal and electrode size (Use the standard chart) Find a comfortable position to weld Use one hand to hold the electrode holder and use the other hand as a support Start an arc by contacting the base metal and remove it slowly Drive the electrode in the direction of travel at an angle of 15 degrees Keep a proper arc length all the way through Allow the work to cool down and remove the slag using a chipping hammer

SolderingSoldering is the process of linking two pieces together using a soft filling material. It is usually used to join tiny parts of electronic devices, such as, printed circuit boards (PCB), wires, resistors, and many other uses. This type will be used to weld the electronic parts of our racing car if needed.

Figure 22

Figure 23Procedure Prepare the working place Ensure there is enough ventilation. If a group is working in a small room, put a fan to drive away fumes and vapours. Keep the working place clean at all time Set up the working piece Securely hold the working piece while soldering or use a vice to work more freely Before soldering, make sure the places of working are clean and free of dust, liquids, or any other material that affects the work Clean the soldering iron tip Hold both, the soldering iron and the solder the same way of holding a pen against each other at an angle of approximately 45 degrees Put the soldering iron near the work piece and touch the joint you want to solder by the tip for a few seconds to heat it up The solder should be melted on the parts to be jointed Take away the solder before the iron Wait for the joint to cool down, then see the final result of your work

TIG weldingA tungsten electrode is used to heat up the metal and a gas (usually Argon) for the protection of the weld pool from air affection. It uses non-consumable tungsten and creates high quality clean welds. (Miller, 2012)

Figure 24Procedure Make sure you wear the full safety set for this type of welding Hold the torch at an angle of 70-80 degrees angle Move it above the work about Dont let the tungsten touches the work Control the heat using the foot pedal Put the filler metal horizontally at a 15 degrees angle from the base metal Heat up the working piece and gently put the filler with the other hand

MIG weldingMIG welding is the abbreviation of Metal Inert Gas Welding. It uses a heat which is created by a short circuit welding gun wire and the working metal. It is used to weld carbon steel, aluminum, copper, and many other metals. (Noahw, 2007)

Figure 25Procedure Prepare the working piece and ensure it is clean, plus, the welding tools must be cleaned Full safety set must be worn Inspect the tension of the wire and set the speed rate of feeding Take a comfortable position and make sure you can move freely Put the tip about 6-8 mm above the surface of the welding metal Move it through the working metalThis is the type that will be used to weld the chassis pieces together as it is available in the workshop. Moreover, it is suitable for our material and the group of students who are working on this project are familiar with this type as practices was held on this particular type of welding previously. Below is a list of reasons for choosing this type of welding.

General safety precautionsPersonal safety tools: Always wear helmet or face shield for the head and face protection Always wear goggles to protect the eyes Always wear protective gloves for the hands Always wear overhaul, or lab coat for the protection of the body

Figure 26Working area: Ensure that all equipments are working properly Ensure there are no flammables, greasy, or oily materials in the working areaGenerally: Always wear the proper safety covers Never use any equipment that you are not trained to work on Never touch a cylinder with a flame or electrode Make sure you know where the nearest fire extinguisher is before starting to weld Make sure there is enough ventilation Check the valves, pipes, cylinders, and ensure they are free of leakageFind a correct and comfortable position while welding

Figure 27 FabricatingFabricating defines the make-up of metals commonly through cutting or bending. The cutting process could be done by sawing, shearing, chopping, or even torching. A manual (hacksaw) or controlled saw can be used for sawing. The manual one is controlled by the worker and the piece is fixed, unlike the controlled one (electrical) which is fixed and the working piece is moved to be cut as required. However, shearing is done by a big sharp blade which is applied on the piece to be cut. It will not be used in this case of the chassis as it's not purposed for tubes, but for sheets of metal mostly. It could be used though in case of cutting aluminium sheets for the chassis body. Chop saw is used for chopping and it's basically a circular blade. It consists of a spring-loaded pivot arm that the circular blade is mounted on. It is used by just aligning the blade with the cutting line of the object and apply the circular blade on it by the arm. It's important to clamp the object being cut properly. The chop saw will be mainly used for cutting the tubes of the chassis, as it's available in the workshop. The bending process could be done by hammering, press brakes, or tube bender. Hammering and press brakes could be used to bend flats which isn't efficient for the tubes of the chassis. What will be used for bending the tubes is a device called a manual tube bender (see the figure below), which is the best device available in building 30 (The workshop). It has a scale to determine the angle of bending which makes it valuable.

Figure 28Manual tube bender

Figure 29 MachiningMachining is the process that is involved in using machines to get a job done. Various machining processes would be used through the manufacturing of the chassis, such as, drilling, facing, and grinding. Drilling could be done by a free hand drill or a bench drill. They are both available in the workshop and could be used for drilling the brackets and mounts in case of chassis manufacturing. However, grinding is an improvement process of a surface finish that is used to smoothen hard surfaces or improving the tolerance of a surface by removing the tiny bits of material from the edge. There are two main types of grinding discs that are changed according to the required purpose. One type is called "Flap disc" which is used for facing or removing coating from a material. The other type is the "Cutting disc" which is basically used for cutting metals. Filing and using sand paper could do the same purpose of facing and removing excessive materials but they are manual. Plus, they are less effective than grinder and so they will be less used over the grinder.

Figure 30 Flap disc

Figure31 Cutting disc

Figure 32 CoatingCoating is the process of applying a layer on a surface of material as a protective process for the material, normally from corrosion. This can be done by painting using a brush or even spraying. There are more details that will be mentioned in this report (Corrosion and protection methods part below).

Figure 33 DrillingThe cutting process that is used to expand or cut a hole that has a circular cross section by a drill bit, is called drilling. The drill bit is a cutting tool that is rotary, which has the shape of spiral helix. Before starting to drill, always make sure that the piece that will be cut is fixed tightly to prevent movement while drilling. Pressing the drill bit that rotates from hundreds to thousands rpm on a material is the simple procedure of drilling.

Figure 34 FittingManufactured components are commonly involve mating with each others. The mating of two mechanical parts is called "Fitting". For example, after manufacturing the chassis the engine will be fitted. If the engine mounts are not welded in place according to the engine there will be a problem in fitting it, and so the measurements must be taken precisely and confirmed for perfect fitting. Another instance is the wishbones attaching, where they fitted in the brackets that are welded to the chassis using nut and bolt. However, there are different fitting methods such as riveting but is not used in the chassis.

However, that doesn't mean the team members are experts in all of these skills. They have the main principles and basics of doing such works as listed above. This means there is a need to improve these skills as no one of the team has done any of them recently. That will be achieved by training and practicing until they get the practical sense and be confidence while they're doing the job, or using a certain tool or machine. Without practicing and getting these skills the manufacturing of the chassis will not be achieved as required, but since they get through enough practical work preparations the goal of manufacturing the chassis will be achieved.

Method of manufacturingAlthough a chassis seems to be complicated at the first sight, it would be simple if it's break down into phases. Anyhow, while researching it was found that many people would prefer to cut all the chassis steel at a time and then link them together. After further research, it was recommended to cut each part as needed. This will give the option or the chance of trying the piece in its place and figure out if it fits well in place or not, and if not, it could be filed or grinded for the best fit. There is an exception here for the opposite tubes such as (M1 and M2) in the figure below, which could be cut parallel to each other (together) to ensure equality (The figure below is just an example and is not the real design).

Figure 35 Chassis designTolerancesTolerances define as the allowable limitations of change in dimensions and angles while building the chassis. The tolerance differs from each part to another as it gets smaller when dealing with smaller stuff and moving parts. For example, the tolerance of manufacturing the chassis is bigger than manufacturing the suspension and steering systems. Suspension and steering systems have much moving parts that should be fit properly with a small tolerance to prevent flapping and moving around, which would affect steering and handling. Tolerances to be followed are:Chassis building ==> 1 mm / 1 meterMoving parts ==> 0.1 mm(John Donald)Material processing - Fabricating - ReformingThe material of the chassis will basically be the circular tubes, square section tubes and rectangular tubes of 1020 steel, and sometimes sheets from the same type of steel. There are several processing methods of the material which includes fabricating and reforming in the case of the chassis. This will be basically cutting tubes and rectangular tubes in a precise or within a tolerance length. The thing is it will not always be a basic straight cut. There will be a need to cut the end of some tubes like an arc (fish mouth) as the figure below shows (Figure 36 Examples of fish mouth on square and rectangular tubes).

Figure 36 Examples of fish mouth on square and rectangular tubesThe purpose of forming a fish mouth to a tube is to attach it to another tube perfectly. Moreover, there will be angle cuts for each type of tubes, see the figure below.

Figure 37Straight simple cut (left) and angle cut (right)There is also a need to manufacture some brackets and mounts that are attached to the chassis. There will be ten brackets for the front wishbones and the damper, and another ten for the rear side. They will be manufactured using a sheet piece of metal bent equally from two sides at 90 degrees to form a U shape, but with a flat base. This could be also done by cutting two small sheets of metal as required and weld them directly to the chassis parallel to each other. The same manner could be followed to manufacture the engine and gearbox mounts.

Figure 38An example of an engine mount

Figure 39An example of a gearbox mountCauses of corrosion and preventing methodsThe deterioration of a material and its properties is caused by a chemical interaction with their surroundings, which is called corrosion. Corrosion could occur on metals mainly due to contact with water and humidity. It could cause rusty surfaces and mechanical properties loss of the material. However, the chassis could be exposed to these conditions (By rain, humid weather) and they could affect the chassis structure and lead to structure failure with time. Therefore, the chassis should be protected against corrosion and other situations, such as cracking or object impact. There are different methods that could be used to coat the chassis. One way is galvanizing which is basically applying a zinc layer onto the chassis. This is also called hot-dip galvanizing. This could be done by putting the chassis in a zinc bath at a temperature about 460oC. The pure zinc (Zn) counters with oxygen to structure zinc oxide (ZnO) and then counters with carbon dioxide (CO2) to structure zinc carbonate (ZnCO3). The process of hot dip galvanizing will cost more than other coating methods and dangerous too. Besides, it will need facilities and materials that are not available at the Polytechnic. Another way is powder coat the chassis and then put it in a curing oven. This is done using a powder coating gun. However, this is dangerous as it consists of hazardous fumes and flammables. The best possible way to protect the chassis from the above impacts is to treat it with an anti-rust primer and then coat it. There are different ways of painting the chassis. It could be handy painted using a brush, sprayed by a spray gun, or even by a spray-can. It is vital to cover the face and body parts while doing this job as a safety precaution. Heat treatmentIs it necessary? If were going to apply it, how? What type of heat treatment could we apply?Heat treatment is the process of applying a controlled heat and cool to a material to modify its properties, without changing the form. In addition to that, it is commonly used for softening and hardening purposes. There are different types of heat treatments, such as, annealing, normalizing, hardening, and tempering. All of these types have the same principle in common. But what identifies each type is the temperature of heating the material, the way it's cooled, and how fast it's cooled (time of cooling).However, heat treatment will be necessary after finishing the chassis. That will improve our design properties. The actual purpose of heat treating the chassis is relieving residual stresses from the joints. In order to apply heat treatment to the chassis, a furnace will be needed for such a big chassis. Unfortunately, this facility is not available at the Polytechnic which means it's not possible to treat the chassis in a furnace in this case. So, engineers have always to think of alternatives. The only possible way of heat treating the chassis is by normalizing. An important first step is the chassis should be clamped tightly on a flat surface to ensure it doesn't move or bend. This can be done by using the oxyacetylene cylinder which is available in building 34 (Mechanical Engineering Workshop). The flame shouldn't be sharp but big as the heat needed is not extreme for this purpose. In addition, a sharp flame could go through the tube of the chassis. The flame should be held from a reasonable distance and applied all over the chassis. It's recommended to heat treat part of the chassis, then go to a further part, and then come back to another further part to distribute heat fairly through the chassis. Even better way to do this is by bringing three or more torches and apply them all over the chassis at the same time. This will of course require more than one person to get the job done but will absolutely be more effective.

Chassis selection (Selection matrix)

Table1. Material selection criteriaCriteria Ladder Frame ChassisMonocoque ChassisSpace Frame Chassis

Strength 123

Safety 132

Cost231

Weight 213

Space Required 132

Ease of Manufacturing213

Ease of Designing 213

Total Marks111417

Table1 shows how the chassis type was chosen. It is called decision matrix and it is used to categorize, analyze and rate a system or a component referring to its specifications. The chassis that will be manufactured is required to have high strength, cost as less as possible as the budget is limited, light as it is a racing car, easy to manufacture and design as the time and materials are limited. Therefore, three different types of chassis were assessed as the table above shows and the highest mark goes to the space frame chassis as it will be chosen. To make it easier, the three types were ranked from 3 to 1. For instance in terms of weight, 3 goes to the lightest weight of the three, 2 for the second lightest and 1 for the heaviest. Another example is cost, where 3 goes for the cheapest, 2 for the second cheapest, and 1 for the highest cost. This order is applied for the other criteria in the table as well.Moreover, the selection of the chassis was based on some criteria as for example the design has to be as simple as possible and this is because the group of students is doing this project for the first time. Another important thing is rigidity in both bending and torsion so it can handle the cornering and bumping forces, specially it is a racing car and will be exposed to sharp corners at high speeds. However, as the chassis has to be designed in a way that can handle torsional and bending forces, it has to be light as possible for a better performance and handling. Nevertheless, accessibility is another important thing that is considered just in case there is any component like the engine or any other part needs to be replaced or repaired. As mentioned earlier, time is limited and therefore productivity time of our design should be low so we dont run out of time. Not to forget that the tools and material are limited in the workshop considering that the design should be done by the tools available, for instance, monocoque cannot be manufactured in our workshop as it needs a large stamping machine which is not available in our workshop. Plus, monocoque is heavy compared to ladder and space frame chassis and this is not recommended for our design. However, the final decision has been made to choose the space frame chassis it is stiff in torsion and bending as it has triangulations to distribute the forces and can handle forces from any direction. Although, ladder frame chassis is much lighter than monocoquein terms of weight, but it is not much lighter than space frame where weight could be improved by changing the material and modifying the chassis by putting less members as possible without affecting strength.ErgonomicsErgonomics is a scientific discipline that is related to basically designing a product that can be used by human considering safety, comfort, and ease of use. There are many things that should be considered while manufacturing our racing car. The car seat should be designed to provide a comfortable safe position of sitting for the driver, where everything is reachable and within his sight of seeing. When we say everything, that means the steering wheel, pedals, gear stick, and all the other controlling systems (Buttons or levers) that would be used by the driver. Not to forget that all indicators, gauges, and the road should be within the driver sight, so he would be aware of what is going on while driving (Fuel level, oil and engine temperature, speed, etc). Another thing that should be considered is the thigh and arm angles as straight hands or legs would cause tension and affect the blood circulation especially for long drives. Moreover, if the legs or arms are straight it would be harder to accelerate or control the steering. Finally, the driver should have a clear view of the road and the gauges at the same time, therefore the height of the dashboard should be considered. Below is a table of approximate dimensions of body parts taken for one of the students which would help in initially determine the dimensions of the seats and setting the inside components as reachable as possible and within the sight line for the driver while he drives comfortably.

Table2. Body parts dimensions

Figure 40 below shows how the driver will set in the car while driving as the dimensions in the table above were applied to the figure below to help in setting the most comfortable seating position and ensure the safety of the driver. The dimensions above are taken from a real body.

Figure 40 Drive's position while driving

Components

Figure 41 Initial sketchThe figure above is an initial sketch (side view) of our design which shows where the different components positions will be. To clarify, the engine and the transmission positions are in the rear side of the car. Moreover, in the front side of the car will be the radiator, battery, fuel tank, and then comes the driver. The fuel tank is a huge concern as it is related to the safety of the passengers. Therefore, it was not put in the rear side as the heat of engine flows around. That does not mean that it is safe to put it in the front as it would explode in case of accident, but the material and the position of the fuel tank could be modified to make it as safe as possible. Below is a top view that shows where the components will be placed in position and these positions could be changed slightly if required, such as, battery position as a safety precaution to be moved away from the fuel tank unless it could be fully isolated.

Figure 42 Top view that shows the parts position

Centre of Gravity CoG

Table3. The weight of the partsPartWeight in Kg

Chassis60

Engine & Transmission200

Driver90

Fuel tank30

Radiator 15

Battery15

Total410

The table above shows the parts of the racing car and the loads of them (Loads in KG). After estimating the figures in the table above, the position of each part was initially set using sketches to assist in identifying the CoG and CoG height.

Parts position

Figure 43 Position of the components and initial dimensions

In order to calculate the CoG of the car on the X axis, some figures should be known. These figures are the length of each component on the X axis, weights, and the position of each part (see figure 43 above). The first step taken before finding CoG is to find RR as the reference point chosen was RF. The second step is to find RF by taking off RR from the total weight. Note that to find RR and RF the basics of beam reaction were used. After that, CoG can be found as all the unknowns have been found and we just have to put the figure in the equation as shown in the next pages.

CoG calculation - Initial

Figure 44 Finding RR

Figure 45 Finding RF and CoG on X axis

Figure 46 Finding CoG height

Figure 47 Load percentage in the front and rear

CoG calculation / Forces Modified

Figure 48 Sketch of the components after changesThe sketch above shows the components position with changes done for a better weight distribution. In the previous design the weight in the front was 28% of the total weight and 72% in the rear. This distribution was improved by moving the front wheel 0.3m to the rear direction and the driver was moved a bit to the front and away from the engine (See the diagram below with the changes highlighted). Note that the calculations were done using Microsoft Excel to make it easier and saving time by applying the equations and just inserting the figures that are known (Dimensions and loads).

Figure 49 Position of the parts after re-allocation

CoG Calculation - Final

After re-allocating the components as mentioned above the percentage of total weight in the front was changed from 28% to 43%, and the rear from 72% to 57% which is a huge improvement in terms of weight distribution. This is will affect the handling and performance positively (comparing the initial calculations to the new ones). To summarize the changes, by moving the front wheel to the front by 0.3m the wheel base has become 2.1m while it was 2.4m. Then, the driver was moved a small bit away from the engine to support the weight in the front in order get as close to 50/50 weight as possible.

ForcesStatic mode

Figure 50 Static modeThe figure above shows a car in the parking condition, as the CG where the tatal weight of the car acts downward. RF and RR which are the wheels reactions to CG are acting upward which means adding RF to RR will give us the total weight of the car (CG).Acceleration condition

Figure 51 Reaction forces when acceleratingThe figure above shows the reaction forces when accelerating. This causes weight to transfer backward which makes the rear end of the car to tilt downward and the front end nose up a little. The friction force pushes the car forward and this is because its larger than (ma).

Braking condition

Figure 52 Reaction forces while brakingThe figure above shows the car condition while braking, which is like a mirror to the acceleration condition where the weight transfer to the front and (ma) pushes the car to the same direction. The friction here tries to stop the car where it acts and pulls the vehicle backward. Friction comes from the four wheels and since it is higher than (ma) the vehicle will eventually stop. The rear suspension experiences less weight as most of the weight is transferred to the front which makes the front end tilted downward unlike the rear end as shown above.

Cornering condition

Figure 53 Reaction forces while corneringThe figure above shows the reaction forces of the car when cornering. As seen above, the car is turning to the left and (ma) or weight is transferred to the opposite direction. As (ma) is acting on pushing the vehicle to the opposite direction of turning, friction forces work on pulling back the car to the direction of cornering which keeps the vehicle on track. If the friction force is ignored the car will basically slide away to the opposite direction of cornering. For example, when it rains friction force reduces because of the wet ground and the car could slide easily.

ClarificationCoG = Center of gravityRR = Reaction force on the rear wheelRF = Reaction force on the front wheelLR = Load on the rear sideLF = Load on the front sideWB = Wheel base (Distance from center of front wheel to the center of the rear wheel from side)TW = Track widthF = Friction forceL1 = Distance from the centre of the front wheel to CGL2 = Distance from the centre of the rear wheel to CGW = Weight (Total mass)ma = Mass x accelerationFL = Friction force on the left wheelsFR = Friction force on the right wheels

Manufacturing steps Welding Pictures

Firstly, the bottom layer will be welded

Then, the three tubes in the middle will be welded as shown above.

After that, the triangle in the rear end will be welded.

However, the tube along the chassis which is along the chassis will be welded.

Next, the triangulations in the bottom layer will be welded as shown above.

Now the bottom layer is done. Therefore, the top layer will be welded separately.

After the top and bottom layers are manufactured, now the vertical tubes that links the chassis layers together will be welded.

At this stage, the two layers are linked together by the vertical tubes. As shown above, the triangulations will be welded.

Finally, the two tubes across the chassis will be welded as shown above.

Figure 54 The final design (Isometric)

Engineering drawings

Figure 55 Front view (Looking from the side)

Figure 56 Side view (Looking from the rear end

Figure 57 Top view (Left side is the front end)

Figure 58 Isometric view of the chassis

BibliographyAchrnews. (2008). achrnews. Retrieved 2012, from achrnews.com: http://www.achrnews.com/articles/the-brazing-process-six-basic-stepsESAB. (2000). BASICWELDING FILLER METALTECHNOLOGY. Retrieved 2012, from esabna.com: http://www.esabna.com/EUWeb/AWTC/Lesson2_4.htmMiller. (2012). Retrieved 2012, from http://www.millerwelds.com/resources/tech_tips/TIG_tips/how_to_weld.htmlNoahw. (2007). Retrieved from http://www.instructables.com/id/How-to-Weld---MIG-Welding/StanfordUniversity. (2012). Stanford University. Retrieved 2012, from stanforduniversity: http://www.stanford.edu/group/prl/documents/html/OAweld.htmwikipedia. (2012). Retrieved from http://en.wikipedia.org/wiki/Hyperbaric_welding

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