Week 1:- Introduction to BiW and Fixtures Challenge

1. What is BIW & define its parts?

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BIW stands for Body in White, which refers to the stage in automobile manufacturing in which the car body’s components have been joined together, using one or a combination of different techniques: welding, riveting, clinching, bonding, laser brazing, etc.

BIW parts consist of Cover, Body, Floor and Encon. Cover is a closure which mainly consists of side/back door, hood and roof. Body consists of other components like A-pillar and outer body frame. Floor consists of driver/passenger cabin and Encon consists of engine components

BIW structure can be divided in following substructures:

•  Hood 
•  Fender
•  Roof
•  Back Door 

•  Hood 

It is the covering for engine in front engine vehicles, which protects the engine from sunlight and dust.

It functions are-

 Helps in aerodynamical flow.

 Protects the passenger and pedestrian.

 Reduces the air resistance.

•  Fender

Fender is the car body part that frames the wheel. Its purpose is to prevent sand, dirt, rocks and other road spray from being thrown into air by the rotating tire and close the engine component.

• Roof

Roof is the top most covering provided for the vehicle and for safety side it’s important for roll over kind of accidents, which the basic test performed for safety purpose. In order to give strength, it is provided with embosses on top of the roof

It consists of Front, Rear, Centre, Bow Roof I & II roof rails. Bow roof rails are provided for the support of the roof surface. The bow roofs are provided with mastic sealant as they are assembled with the surface as welding is not possible, whereas the ditch area, front and rear area is welded with the roof

Front and rear roof rails are cut a part as there will be mounting of A and C pillars. Centre roof rail has two layers(reinforcement) as to protect it from roll over crash. Bow roof 1 and bow roof 2 are provided for better protection of roof from crash. Front and rear bow roofs are provided with optimal angle of inclination to meet the production criteria (positive draft angle) and visibility criteria. Mounting of windshield and rear glass becomes easier

• Backdoor

Tailgate is the hinged door at the rear part of a vehicle and can be moved up or down. It lets us access the boot space or trunk.

Parts of Back door assemble –

 Inner Panel

 Outer Panel 

 Hinge Mounting Bracket

 Hinge Inner Reinforcement

 Latch Inner Reinforcement

 Wiper Motor Mounting Bracket

 Gas Stay mountings and reinforcement(Heaver back doors

2. What do you understand by BIW nomenclature?

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A nomenclature in BIW is basically naming every part of the body. These names can be said as subparts of the already categorized parts above. The nomenclature differs a little bit from region to region but the overall idea is to name individual automotive sheet metal components. Below images show the nomenclature of BIW: 

• The terms are standard but they differ in some countries.
• As automotive industries spread worldwide, the terms and standards will be different for similar components.
• For example, One component of BIW is known as inner wing pannel in the UK description another side the same component of BIW is known as the Motor compartment side panel in the US description.

Q3. What are fixture & its types? 

A fixture is a device that uses the 3-2-1 principle to hold the work piece to be processed in the appropriate place.
Because we'll be welding the components together, the fixture will need to be made up of several different sections to hold the automobile together. The fittings must be built in such a way that the work piece is held in the correct position to avoid distortion and achieve the intended geometry.

For the reasons stated above, the fixture must be constructed with the following considerations:

• It must securely grasp the work piece to prevent distortion during welding.
• Attention should be paid to the placement of items.
• Clamping should be light enough to avoid deforming the panel but stiff enough to keep it in place.
• Clamping elements must not obstruct the welding region.
• To endure vibrations caused by welding strains, the fixture must be robust and rigid.

General types of fixtures:

Pre-production fixture: It is generally designed as a prototype fixture for the initial batch production to study the feasibility and make any changes and improvements for the production fixtures. Thus this is a base fixture which helps us rectify any short comings which we might face at the pre production level. But as this has a longer cycle time, we don’t usually practice this and jump to production fixture keeping all the standards and parameters in mind to save time and money.

Production fixture: These fixtures are used for mass production purposes. These are where the car body will be assembled and will be made market ready thus it has a critical role. The materials used for this fixture should be tested along with the hardness and aesthetics. The production fixtures will require maintenance very often thus it must be easily accessible.

Checking fixture: It is used for checking or inspecting an assembly coming out of geo fixture. The only difference between geo fixtures and checking fixtures is that it is not used to perform any operation but is mounted with various inner and external gauges for inspecting dimensions and tolerance along with gaps and flushness on the assembly. This is also used to check the welding points if they are at proper location. 

Q4. What is the basic priciple of fixture design ?

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• The fixture is designed based on how the workpiece is fixed on the fixture. All the Degrees of Freedom of the workpiece are to be constraint.
• The 3-2-1 principle is used.

• The workpiece has twelve Degree of Freedom. six transitional DOF and 6 rotational DOF.
• Transistional: X, -X, Y, -Y, Z, -Z.
• Rotational: Clockwise around X axis (CROT-X); Anticlockwise around X axis (ACROT-X); Clockwise around Y axis (CROT-Y); Anticlockwise around Y axis (ACROT-Y); Clockwise around Z axis (CROT-Z);  Anticlockwise around Z axis (ACROT-Z).
• The rotational DOF have to be constraint.
• Using 3-2-1 priciple.
• First the workpiece is constraint by 3 pins on below surface. This lock the Y DOF,Clockwise around X axis (CROT-X); Anticlockwise around X axis (ACROT-X)  the Clockwise around Z axis (CROT-Z);  Anticlockwise around Z axis (ACROT-Z).

• Then another side perpendicular to the below surface is constraint by 2 pins. This locks -Z and +ZDOF and Clockwise around Y axis (CROT-Y); Anticlockwise around Y axis (ACROT-Y).
• Then any one side perpendicular to both the below and the other 2 side of the workpiece is constaraint by 1 pin. This locks X DOF.
• The part is now fully constraint and cannot move

Q5.  Elaborate types of BIW Stations? 

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The BIW assembly line is where different types of panels are joined together in each specified zone like Underbody zone, Hood zone Etc.

These zones are further subdivided into stations, where various processes like welding gluing and inspection are done to the part of that particular zone before they are being assembled together. For instance, in the roof zone, various reinforcement is to be added before they are married to the side zone.

The BIW assembly line can be classified as follows:

1. Tools
2. Grippers
3. Stands
4. Miscellaneous

A tool is a fixture which consists of number of different units together to hold a car panel or assembly. 

Re-spot Tool:

• A re-spot tool is a fixture where already welded panels are brought to be welded further.
• For example, on a certain panel we needed to have 50 weld but due to assembly line constrains we managed to achieve 30 on geo tool, then the remaining 20 will be achieved on the re-spot tool.
• Pin tolerance for the re-spot tool is -0.28mm.

B)Process grippers

• These grippers are used to carry out some specific processes like gluing, welding, riveting in addition to material handling.
• The gripper will go under gluing stand in case of gluing process & will goes under the pedestal weld stand in case of the welding process.

1. C) Pedestal stands

• Weld gun is mounted on the fixed stand which is mounted to the floor The gripper can carry the panel under the stand to do the operation.

Q6. What are the basic terminologies used in the BIW fixture? 

Basic terminologies used in the BIW fixture

• The following terminologies are used in BIW

2. A) NC/Mylars/Fingers

• Mylars are the component that holds the panel while These are placed from topside & from the bottom side also. The top side Mylars called Clamping Mylars & the bottom side Mylars called Resting Mylars. Every clamping Mylars have resting Mylars. It doesn't allow deformation of the part due to welding stresses.
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B) Principle locating point (PLP)

• These are the points that are used for the accurate location of the part to maintain the geometry of the part. There is lots of holes on the panel which are not accurate due to stamping operation. The PLP are defined in the drawing. The positional dimensions or relative dimensions are very precise in stamping & in fixtures also.
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C) Risers

• Risers are of different types like L-typer rises, Square tube riser Riser is the manufacturing part which gives height to the assemblies.

D) Blade

• Blades are plates mounted on the Other parts like cylinder, arms, etc are mounted on the blade.

E) Shims

• Shims are the small part that comes with the thickness of 0.1mm, 0.2mm, 0.5mm, etc. These will compensate for the stackup tolerance which reflects at the panel holding part called We give tolerance to all the parts of the fixture. Due to this tolerance, the Mylars will either lift up or goes down from their defined position.
• If the Mylars go down from the defined height it will make an impression or dent on the panel.
• If the Mylars lift up then there will be a distorsion due to welding stress. To adjust the Mylars At its defined position we use shims so the panel won't be deformed & also don't get any impression on it.

F) Rough locators

• The operator can place the part in the wrong orientation The rough locator will work as a guide while placing the part in the fixture & the part will be loaded in the desired orientation. It is a part of foolproofing.

G) Hardware

• Hardware is like the Hex head bolts, Allen Bolts, Hex nuts, Spring washers, Self-locking nuts

H) CMM

• CMM stands for coordinate measuring machine. It is a device that measures the geometry of physical objects by sensing discrete points on the surface of the object with a probe. It generates a report by comparing the data with the CAD file data.

I) Unit

• The fixture is the assembly of different types of units to form a part. There are different units like pin unit, base unit, clamping unit, etc.

J) Number plates

• The number plate is the aluminum embossed plate placed on each unit for easily recognizing the part unit.

K) Nameplate

• The data like manufacturing company name, fixture type, Fixture weight is embossed on the plate & joined to the fixture.

L) Clamp Arm

• The clamp arm is the part of the clamp unit which moves an Over clamp arm the Mylars are mounted.

M) Pivot

• It is an axis about which the clamp arm will rotate

N) Class A Surface/Skin surface

• The outer panels of the car like a hood, door, backdoor, fender, roof are visible to the customer.
• The outer panels should be aesthetically very good. No scratches or dent is acceptable over it.
• While designing the fixture to the skin surface the clamping material should be soft, so that it could not able to left any impression or dent over the skin. generally, nylon or PU material is used for clamping purposes.