Brief introduction to BIW

1. What is BIW & define its parts?

Answer- BIW stands for Body in White. BIW is an assemblage of all welded sheet metal panels as before going for priming and painting. BIW refer to the welded sheet metal structure to which other component will be married i.e. engine, chassis, exterior and interior trim.

Body in white or BIW refers to the stage in automotive design or automobile manufacturing in which car body sheet metal ( including door, hoods and deck lids) has been assembled or designed but before the components ( chassis, motor) and trim ( windshields, seats, upholstery, electronics, etc.) have been added. All activities in the production of a vehicle body or shell before it goes to the paint shop are done in a weld shop and the end product of a Weld shop is referred to as BIW.

This image shows welded BIW structure before priming or painting

Below image shows basic body building structure of BIW.

BIW structure can be divided in following substructures:

1. Underbody structure
2. Front end structure
3. Body side structure
4. Closure
5. Roof

1) An Underbody Structure consists of following major panels:

• 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- Riser connects Front floor to Rear Floor by providing a level difference
• 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

2) Front end structure consists of following major panels:

• 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.

3) BODY SIDE structure consists of following major 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.

4) Closures consists of following major panels:

• All Doors
• Hood/Bonnet -Hood is a hinged panel providing access to the engine compartment.

5) Roof structure consists of following major panels:

• Roof
• Headers- Header is the structural member above the windshield at the juncture with the forward edge of the roof panel.
• Bows- Those are used to support the roof.

Below image show BIW parts.

Below image show reinforcement component used as additional in BIW for strengthening

1. What do you understand by BIW Nomenclature?

Answer- Nomenclature is basically choosing names for thing. BIW have no. of parts in it. All parts have different names.

As automotive industry is spread worldwide. Every nation has its own language. So the same part in BIW have different name in its region.

For example, One component of BIW is called suspension tower in UK & same component called shock tower in U.S. Below fig show BIW nomenclature.

Below fig. shows UK Vs U.S. Nomenclature.

Below fig. shows U.S. nomenclature on car.

1. What is fixture & its type?

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

In general a welding fixtures (tool) consist of number of units together to hold car panel together. Welding fixtures are normally designed to hold and support the various component 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 welding area and the fixture has to be quite stable and rigid to withstand the welding stresses.

BIW fixture type:

1. Production Fixture – As name suggest this fixture is used for mass production. It is fixture on which car body get assemble & go to end customer. These types of fixture require high constancy through its operation to maintain geometry of parts. So material used for these types of fixture should be well tested as well as hardness level aesthetic. The quality in terms of dimension, tolerance should be met. These fixture need to maintain after certain period of time. The assembly & disassembly should be easy as low as possible. So maintenance person can easily access with saving time.

1. Pre-production Fixture- 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 preproduction operation fixture there will be more involvement of manual operations, engineer, and quality person. It has larger cycle time than production fixture. But won’t 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.
2. Checking Fixture- As name suggest this fixture is used for checking assembly which came out from geo fixture. 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 of that particular. The geometry of welded part also checked in this fixture to ensure part maintains the required dimension & geometry.

Below fig. shows sample of checking fixture.

1. What is basic principle of fixture design?

Answer: For a fixture designer major portion of design time is spent deciding how to locate the work piece in fixture. For any free body there are total twelve degrees of freedom as below.

6 translation degrees of freedom: +X, -X, +Y, -Y, +Z, -Z

And 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)

You must fix all the 12 degrees of in order to locate work piece in fixture. The main motive of fixture is to hold work piece so that it cannot move or distort when operation is being done. It must hold work piece rigidly & stable. Below fig illustrate degrees of freedom of any body

LOCATING PRINCIPLE

3-2-1 locating principle: Holding fixtures used in assembly operations often follow a 3-2-1 locating scheme to position parts. Under this scheme, three locators position a part in a primary plane or direction (e.g., high/low). Two locators then position the part in a secondary direction (e.g., in/out), leaving one locator for the tertiary direction (e.g., fore/aft). This approach fixes the part in 3-dimensional space and satisfies the six degrees of freedom constraint. Below fig. show 3-2-1 locating principle.

1. Elaborate types of BIW station?

Answer- In BIW assembly line is in where different types of panel are joined together in each specified zones. Each panel categories will have individual zone. As under body zone, door zone, hood zone etc. These zones are further divided into stations. There are following types of station in BIW. A Station is the place where an operation is done by couple of tools. For example, a station can contain one Geo set weld fixture (weld tool), robots, end effectors, etc. to perform a single operation in the assembly line. So there will be proper flow of inventory. Below fig. shows station category.

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

1. Tool station-

a) Geo station- Geo tool is a fixture in which geometry of the panels which are welded together are defined accurately. The pin tolerance for geo pin will be of closure tolerance i.e.-0.15 in general. For example, consider panel hole size 20mm, the pin diameter should be 19.85mm.

All parts must be located with two locating pin. Tolerance level in all terms should be very less with geo fixture. Pin should be undersize & pin tolerance for geo pin will be closer. Below fig. show geo station.

b) Re-spot station- Re-spot tool or station is fixture in which the remaining weld spot which are not achieved in geo tool are welded for the pre welded panel from the geo tool. The pin tolerance for re-spot pin will be of tolerance with -0.28 in general.

Suppose in assemble we need 50 weld stack. On one station we cannot complete all these operation because it will take more time & other station relative to assembly in idle condition

In this type of case we carefully choose some weld tack points which will define geometry of the part and also assembly will not get deformed after opening clamp or in transportation due to welding stresses. The remaining weld spot are completed in re-spot fixture.

c) Hemming/ marriage station- A marriage or a hemming tool is fixture in which the inner panel assembly and outer panel assembly are joined together. These are done by welding or hemming in case of closure panels. Below fig. shows re-spot & marriage station.

d) Framer station- Framer fixture is next station after marriage station. In framer fixture roof is attached to output of the marriage fixture and it form like frame hence it is called as framer tool.

e) Checking station- A checking station tool is fixture which is used to check the automotive parts or assemblies, ensuring all the co-ordinate, relative dimension and position as per the tolerances.

A checking station can be a gauge type, fixed type & automated checking fixture. A checking gauge is tool where work piece is hold & various measuring gauges are introduced to ensure the dimensions and repeatability.

A fixed type checking fixture is used where work piece is fixed with clamps & pin & CMM machine is used which measures the coordinates of different points of the panel or assembly. Compares it with the nominal values and give report. Below fig. shows checking fixture

1. Gripper station- A gripper is device or a fixture which holds the car panel & is fixed to the manipulating end of robot or an end effector. Also known as EOAT ( End of arm tooling)

a) Material handling grippers- Material handling grippers is designed for handling the car panel from one station to other. Below fig. shows material handling gripper.

b) Process Grippers- Process grippers are designed for handling the car panel one station to other & in addition to that it under goes process like pedestal welding, pedestal riveting, gluing, sealing etc.

c) Combo gripper- Combo gripper is designed for handling car panel from one station to other also with combination of weld gun at another side of gripper for welding. It is multiple tasking types.

Weld gun + Gripper

d) Dual gripper- Dual gripper is designed for handling car panel from one tool (station) to other, with two sided gripper. It can hold two panel simultaneously one RH & one LH side.

Gripper+ Gripper

1. Stand station- Below fig. show stand types

a) Pedestal stand- Weld gun is mounted to the floor permanently. The gripper can carry the panel under the stand to do some operation. Below fig shows pedestal stand

b) Gluing & sealer stand- Gluing or sealer gun is attached to standard stand which is grouted to floor permanently fixing is required. So stand should not move due to vibration or other factors

c) Docking stand-When robots are selected of multitasking like material handling & welding, which cannot carry both due to some limitations (payload capacity of robot or space constraint. It is also called as parking stand for gripper.

• In this case we add docking stand to put some equipment which is not use for current operation but will be required for next operation.
• Hence robot can drop or a gripper or gun & pick next operation equipment to complete the task from docking stand.

d) Date stamp stand- Every manufactured product have some data to stamped or to be embossed on it like serial no, batch no, date etc. For some future reference or for data collection.

The required data is stamped or embossed by using the stamping device mounted on stand.

1. Miscellaneous station-

a) Curing- After gluing it needs some time to cool down, so we put 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 easy way. They are also used to store the inventory while the machine is undergoing for some maintenance. Below fig shows buffer storage.

c) Take out trolley- It is used to take out some panels for inspection to rectify the process is going in right or not between the cycles. Below fig shows take out trolley.

d) Conveyor- Conveyor is material handling. They are used to transfer panel from one station to another station. It can be of two types gravity & powered.

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

Answer: The basic terminologies used in BIW are

1. NC/MYLARS/FINGERS- These are parts are used to hold panel. They are globally called as mylar. Top side mylar is called as clamping mylar & bottom side is called resting mylar. Every clamping mylar should have resting mylar. It is jaw type. It prevent panel from deforming while welding.
2. Principle locating point (PLP) – These are point which are used for the accurate location of part to maintain the geometry of assembly. means principle locating points are those where we use pin for locating panel. These are defined in drawing. The positional dimensions or relative dimensions are very precise in stamping & in fixture also.
3. Risers- Risers can be of L-type, welded or square tube or frame type. These are basically manufactured parts are used to give height to assembly.
4. Blades- Blades are plates attached to riser. Other part likes cylinder, arms etc are mounted on the blade.
5. Shims- In fixture we are providing tolerance to each part mostly manufactured. Those tolerance tend to stack up & reflect together. In order to avoid that we use shims so we can easily adjust after assembly so whatever stack up there we will rectify it through shims. Shims come in thickness of 0.1, 0.2, 0.5 etc.
6. Rough locators- Rough locators are those used majorly for manual fixture. There is chance that operator can place part in wrong orientation mistakenly. The rough locator will work as a guide while placing the part in the fixture & part will be loaded in desired orientation.
7. Hardwares- Hardwares are like the hex head bolts, allen bolt, hex nuts, spring washers, self locking nuts etc.
8. 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 object with probe. It generates report by comparing the data with the CAD file data.
9. Units- The fixture is assembly of different types of units to form a fixture. There are different unit like pin unit, base unit, clamping unit etc
10. Number plates- Number plate is the aluminum embossed plate placed on each unit to recognize the unit.
11. Co-ordinate plate- When we discuss about fixture on every fixture we have tooling hole which is called master hole through all fixture checked on CMM mastering that particular hole. Cover that hole so that it won’t get other impurities & hole does not get any wear, tear & distortion.
12. Name plate- The plate on which basic information described like company name, fixture name, fixture weight, panel name are embossed & joined to fixture.
13. Clamp arm- Clamp arm is part of clamp unit which moves about axis. Over clamp are mylars are mounted
14. Pivot- It is axis about which clamp arm will rotates.
15. Class ‘A’ surface/ skin surface- The outer panels of car like hood, door, backdoor, fender, roof etc are visible to customer. The outer panels should be aesthetically very good. No any scratches or dent mark is acceptable over it. While designing fixture to the skin surface the clamping material should be soft, so that it could not able to left any impression or dent over skin. Generally nylon or PU material is used for clamping purpose.
16. Reed switches & sensor- These are the electric components used in automated fixtures. The sensor & reed switches are used only in that situation where fixture is fully automatic or semiautomatic that run through PLC, control panel etc. Sensor are used to detect part present or not, clamp is close or open whereas reed switches confirms position of piston i.e. it is at top or down. Below fig shows unit used in BIW.