Week 1:- Introduction to BiW and Fixtures Challenge

Question 1. What is BIW & define its parts?

Answer 1. BIW refers to the welded sheet metal components which form the vehicles structure to which the other components will be married or assembled. (Components like engine, chasis, exterior & interior trims).

Body in white (BIW) refers to the stage in automobile design or automobile manufacturing in which the car body's frame and Sheet metal components including doors, hood, roof and deck lids/ back door has been joined together, that is before painting and before the motor, chassis sub-assemblies, or trim (glass, door locks/handles, seats, upholstery, electronics, etc.) have been integrated into the structure. Assembly involves different techniques such as welding (spot, MIG/MAG), riveting, clinching, bonding and laser brazing.

BIW name derives, for "body in white" is the appearance of a car body after it is dipped into a white bath of primer (undercoat paint)— despite the primer's actual gray color. The process called Cathodic Electro Depostion "CED". The process is done to resist the rusting of the sheet metal.

• BIW is the steel structural shell composed of generally steel panels welded together. BIW structure supports the overall other subsystems in the vehicle.
• BIW encloses, protects the passengers & cargos. The BIW design needs to be stiff to support the mass & securely keep them all integrated.
• The structure is made from Steel or Aluminium panels (0.7 - 2.0 mm thickness). The pannels are stamped into shape and then spot is welded together.
• BiW constitutes about 27% of a car’s curb weight and remains the key determinant of how the car will perform.
• An important aspect of designing vehicle BIW with lightweight materials is ensuring crashworthiness and occupant safety. The present chapter has provided insight into how structural components can be designed with aluminum by ensuring similar levels of stiffness and plastic strength as in a comparable steel component, while simultaneously achieving significant weight reduction.
• Improvement of fuel economy also necessitates the use of lightweight materials in BiW, as it constitutes a significant share of car’s weight.
• BiW is expected to possess a number of significant properties. It must have high tensile -strnegth as well as high stiffness-bending, torsional, static, and dynamic. It must also provide good quality safety both to the car body and to its occupants against crashes of all kinds—front, rear, side, or even rollover.
• It should also be able to protect occupants from noise, vibration, and/or harshness (NVH) by absorbing or reducing these conditions.
• It should be easy to weld and form, as well as be highly paintable and easy to design. It should provide a good surface finish that is smooth, and should also be corrosion resistant.

Body Side Panels

• A-pillar- A-Pillar is the front most support to Roof.
• B-pillar- B-Pillar is the second support to the roof and situated on the locking side of the Front door.
• C/D pillars- C-Pillar is the Rear most support to roof in case of a two row seats car, OR third support to the roof. D-pillar is the forth support to the roof and usually on the rear side of quarter panel.
• Ring panel - Ring panel is a structure panel connecting the rear portion of the body to front, and constitutes a big part in side structure.
• Quarter panels- Quarter panel is rear most panel of a body side structure.
• Drip rails/Gutters- Drip rails/Gutters is an exposed channel applied to the roof over the side windows to direct water away from the windows and to cover structural welding.

Bodyside Outer-

• The outside panels provide the shape of the car body whereas the inner panels reinforce the shell of the body. The various curved shapes are given to outer panels to provide the strength to panels. It includes 'A,B,C and D'-Pillars, quarter panel,sill area,etc.

Bodyside Inner-

• The inner panel provides mounting locations for various trim panels and connecting assemblies. These two panels are welded together to pillars and rails so as to form the skeleton of the car body.

Underbody

Front End Under Frame (Engine compartment)-

It is an engine compartment area where all possible mounts for engine and other components get fixed.

• PLENUM Panel - Plenum is a chamber located between the throttle body and the runners of the intake manifold, used to distribute the intake charge evenly and enhance engine breathing.
• FRT wheel house/ Fender - FRT Wheel house or Fender is an encasement around the FRT wheel.
• Wing panel - Wing panel are the outer most side panel in the front.
• Cowl - Cowl is the portion of the body bounded by the front fenders, the base of the windshield, and the rear edge of the hood
• Upper tie bar- Upper tie bar is the upper panel in front connecting the two sides (RH/LH) of Front structure.
• Lower tie bar- Lower tie bar is the lower panel in front connecting the two sides (RH/LH) of Front structure.

Main Floor-

It is an area where transmission, instrumental panel or dashboard, seats and other components will fixed.

• Dash panel - Dash panel provides a partition between engine and the driver/passenger cabin inside car
• FRT Floor - provides a base for seats mounting and provides partition between transmission /propeller shaft/ground and the cabin.
• Riser connects Front floor to Rear Floor by providing a level difference

Rear End Under frame (Rear compartment)-

It is an area where spare wheel or stepheny will be placed as well as other components and will have boot space.

• Rear Floor- Rear Floor is the floor on the Rear of the car and provides a partition from ground also provide base for Rear seat mounting.
• Rear wheel house

Closures

Front & Rear Door(Inner & Outer panel)-

These are side closures of cars to protect the passengers.

Hood-

Inner & Outer Panel-

It covers the engine compartment.

Decklid/Backdoor/Tailgate-

It covers the boot space or rear compartment of the car.

Roof-

Inner & Outer Panel-

It covers the top of the car to protect from different weather conditions.

Fender-

It covers the top of the front wheels .

Re-inforcements-

BIW reinforcements mount are evaluated through CAE studies for various crash scenarios such as high-speed frontal crashes, side impact, pole impact and rollover. The CAE studies, performed using generic vehicle models, quantify the potential weight-savings in a vehicle by either replacing the existing reinforcements using a lighter system or by incorporating additional reinforcements in the BIW by down-gauging the existing BIW. The use of BIW reinforcements can achieve significant weight reduction in a vehicle, while also ensuring no compromise in crash performance.

Material Used for BIW- Generally BIW components are made of steel and aluminium, because lower weight of the vehice is concerned by manufactures for this, low density materials are considered.

Amid the raging debate on the suitability of aluminum as a replacement for steel in BiW, a major transformation has occurred in the form of the entire BiW being made up of carbon-fiber-reinforced plastics (CFRPs) in BMW’s i3 model.

BiW can be made into two structures: the more common monocoque structure where all body members are carrying load with chassis in-built with BiW and are integrated with each other, and the body-on-frame structure where the frame is the main load-carrying member.

Monocoque Chassis

Monocoque being french for 'single shell' or a 'single hull'. ... A monocoque is a shell around the car made by using both chassis as the frame in a single construction. This is the most commonly used chassis right now due to the number of advantages of has over the other two chassis.

Body-on-Frame/Ladder frame Chassis

Body-on-frame is a motor vehicle construction method, where a separate body or coach is mounted on a strong and relatively rigid vehicle frame or chassis that carries the powertrain (the engine and drivetrain) and to which the wheels and their suspension, brakes, and steering are mounted. While this was the original method of building automobiles, body-on-frame construction is now used mainly for heavy trucks, pickups, and predominantly large SUVs.

Question 1. What do you understand by BIW nomenclature?

Answer 1. Basically nomenclature is devising or choosing names for things. As we know that BIW has many number of parts in it and all of them have different names.

Automotive industry is spread worldwide and every nation has its own language. So, the every individual part of BIW have different name in different place or region. There are some BIW nomenclature from US and UK mentioned below-

Question 3. What is fixture & its types?

Answer 3. A Fixture is device which holds the work piece to be processed (Welded), by using 3-2-1 principle.

A fixture is a work-holding or support device used in the manufacturing industry. Fixtures are used to securely locate (position in a specific location or orientation) and support the work, ensuring that all parts produced using the fixture will maintain conformity and interchangeability.

In general a welding fixtures (tool) consist of number of units together to hold car panel, and is mounted on a base unit.

Welding fixtures are normally designed to hold and support the various components (work piece) to be welded. It is necessary to support them in proper location which is capable of preventing distortions in work pieces during welding. For this the locating elements need to be placed carefully, clamping has to be light but firm, placement of clamping elements has to be clear of the welding area and the fixture has to be quite stable and rigid to withstand the stresses generated during welding process.

Types of Fixtures- The general types of BIW fixtures are:-

1. Production Fixture – As the name suggests, this fixture is used for mass production. It is a type of a fixture on which car body get assembled. These types of fixture require high consistency through it's operation to maintain geometry of parts. So, material used for these types of fixture should be well tested as well as hardness level. The quality, in terms of dimension, tolerance should be met. These fixture needs to maintain after certain period of time. The assembly & disassembly should be easy as possible. So maintenance person can easily access with saving time.

BIW Welding fixtures

BIW Orientation Fixtures

2. Pre-production Fixture(PPO)- It is generally defined as prototype fixture. It is designed to study feasibility of initial batch production to check which things are need to be improving before starting production. This fixture is base of production fixture in benchmark and criteria & helps us to rectify error. In pre-production fixture there will be more involvement of manual operations, engineer, and quality person. It has larger cycle time than production fixture,but designers will not practice by designing preproduction fixture because it takes lots of time & cost. We have to maintain cost of car as low as possible so we directly go to production fixture by considering standards, checklist to maintain error free production.

3. Checking Fixture- As name suggest this fixture is used for checking assembly. Checking fixture are same as geo fixture except there are no operation done like welding, gluing or hemming. Instead of that we use different in built gauges or external gauges to check various dimension, gap, relative dimension, tolerance. These data is compared with data provided by designer or design team. The geometry of welded part also checked in this fixture to ensure the part maintains the required dimension & geometry.

Question 4. What is the basic principle of fixture design?

Answer 4. The principle of fixture design- The major portion of design time is spent deciding how to locate the workpiece in the fixture. We know that any free body has a total of twelve degrees of freedom.

Those are:- 6 translational degrees of freedom +X, -X, +Y, -Y, +Z, -Z

6 rotational degrees of freedom-

• 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)

To make sure the proper fixing of the part we need to restrict all 12 degrees of freedom of the workpiece.

PRIMARY LOCATOR-

First, the three locators or supports are placed under the workpiece. It will be positioned on the primary locating surface also known as a datum. It will restrict 5 degrees of freedom.

SECONDARY LOCATOR-

The next two locators are normally placed on the secondary surface, restricting an additional 3 degrees of freedom.

TERTIARY LOCATOR-

This locator is positioned at the end of the part. It restricts 1 degree of freedom

• All these 6 locators will restrict a total of 9 degrees of freedom. The remaining 3 degrees of freedom ( 1, 4 & 5 ) will be restricted by the clamps.
• To minimize the time consumption in assembly and disassembly, Have to use minimum numbers of pins to arrest a maximum number of degrees of freedom.
• The jig and fixture are tools used for holding the workpiece in a correct location for mass production. Various types of fixtures (like drilling fixtures, milling fixtures, and welding fixtures) are used in industry. The 3-2-1 method is the fundamental principle for all types of fixture design.

Question 5. Elaborate types of BIW Stations?

Answer 5. BIW Station is the part of BIW assembly line. The BIW assembly line is divided into zones and these zones are divided into stations.

The BIW stations are further divided into following-

1. Tool stations
2. Gripper stations
3. Stand stations
4. Miscellaneous stations

Tool Stations

1) Geo Fixtures-

• A Geo tool is a fixture in which the geometry of the panels which are welded together is defined accurately. The pin tolerence for a geo pin will be closer tolerence, i.e. -0.15 in general. For example- Consider panel hole size 20 mm, the pin diameter should be 19.85 mm.
• In Geo fixture spots/ MIG welding done in such sequence that after taking out from the fixture it achieve the desired accuracy and doesn’t get disturb during transportation from Geo fixture to re-spot fixture. Geo fixture control the sub assembly accuracy in all the 3 axis.

2) Re-spot Fixtures-

• A re-spot fixture/tool is a fixture in which the remaining weld spots which are not achieved in geo tool are welded for the pre welded panel from the geo tool.
• The Pin tolerence for a re-spot pin will be of tolerence with -0.28 in general.
• For example- Conside panel hole size 20 mm, the pin diameter should be 19.72 mm.

3) Marriage/Hemming Fixture-

• A marriage or a hemming tool is a fixture in which the inner panel assembly and outer panel aseembly are joined together.
• These are done by welding or hemming (in case of closure panels).

4) Checking Fixture

• These are used to check the assembly of parts, Tolerance, Dimensions &
• It can be of gauge type, Fixed type of automated checking.
• A checking gauge is a tool where the workpiece is held & different measuring gauges are introduced to ensure dimensions & repeatability.
• A fixed type checking fixture is used where the workpiece is fixed with clamps & pins & CMM is used which measures the coordinates of the different points of the panel or Then is compares with the CAD data & gives a report.

Grippers Stations

A gripper is a device that enables the holding of an object to be manipulated. The easier way to describe a gripper is to think of the human hand. Just like a hand, a gripper enables the holding, tightening, handling, and releasing of an object. A gripper is just one component of an automated system. A gripper can be attached to a robot or it can be part of a fixed automation system. Also known as EOAT (End Of Arm Tooling).

Different grippers are used in BIW as follows-

A) Material handling gripper

• Material handling gripper are designed for handling the car panel from one tool(station) to other tool(station).

B)Process grippers

• Process gripper are designed for handling the car panel from one tool(station) to other tool(station). In addition these grippers are also used to carry out some specific processes like gluing, pedestal welding, pedestal riveting, sealing, etc.

C)Combo Gripper

• Combo grippers are the ones which can carry out multiple tasks like it can do material handling and also with combination of weld gun at another side of the gripper for welding.
• Gripper+Weld Gun

D) Dual Gripper

• Dual grippers can also handle material and these are two-sided, in case when we want one LH & one RH part, these grippers are used. It can handle the material from one station to another station.
• Gripper + Gripper

Stands Stations

Stands are used to hold the part when not in use or also it is used to mount some parts or bodies on it.

Different stands are used in BIW-

A) Pedestal stands

• Weld gun is mounted on the fixed stand which is mounted to the floor permanently, where the process gripper carries the car panel to weld the spot with the fixed weld gun.

B) Gluing & sealer stand

• Gluing gun or sealer gun is fixed to a welded or a standard stand which is mounted to the floor.

C) Docking stand

• The robots have some limitations such as the payload capacity of the robot.
• When we select the robot for multitasking it can't do both the task simultaneously.
• In this kind of case, we add a docking stand to put some equipment that is not in use for the current operation but will be required for next operation.
• So, the robot can drop a gripper or gun & pick the next operation equipment to complete the task from the docking.

D) Date stamp stand

• Every manufactured product has some data to stamped or to be embossed on it like serial no, batch no, Date for some future reference, or for data collection.
• The required data is stamped or embossed by using the stamping device mounted on it.

Miscellaneous stand

A) Curing

• After gluing it needs some time to cool down, so we put the assembly on some belts & it will take the panel to another station & meanwhile gluing will cool down.

B) Buffer stand

• After some operation, we can put the no. of assemblies in this stand which is buffer stock & it can be transported to another station in easily. They are also used to store the inventory while the machine is undergoing some maintenance.

C) Take out trolleys

• It used to take out some panels for inspection to rectify the process is going in the right or not, between the cycle.

D) Conveyor

• The conveyor is the rotating moving path that transports the parts to the next station which are kept over it.

Question 5. What are the basic terminologies used in the BIW fixture?

Answer 5. The following terminologies are used in BIW are-

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.

B) Principle locating point (PLP)

• These are used to accurately locate the workpiece on the fixture to process the workpiece.

C) Blade

• Blades are the plates which are attached to the risers.

D) Risers

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

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. 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 exact orientation.

G) Hardware

• Hardware are 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) Units

• The fixture is the assembly of different types of units. There are different units like pin unit, base unit, clamping unit, etc. which makes a complete assembly.

J) Number plates

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

K) Co-ordinate Plates

• Every fixture has a tooling hole through which all fixture checked. Co-ordinate plates are used to cover the hole.

L) Nameplate

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

M) Clamp Arm

• The clamp arm is the part of the clamp unit which moves with the (Mylars mounted on it to hold the assembly).

N) Pivot

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

O) Class A Surface/Skin surface

• The outer panels of the car like a hood, door, backdoor, fender, roof are visible to the customer. Those outer panels should be aesthetically very good. No scratches or dent is acceptable over it.

• While designing the fixture for the skin surface the clamping material should be soft, so that it could not be able to left any impression or dent over the skin. Generally, nylon or PU material is used for clamping purposes.

P)Reed switches & sensors

• These are the electric components, the reed switch and sensors are only used in automated fixture. They detects that panel is loaded or not on the fixture assembly.