Introduction to BIW and Fixtures

1. What is BIW and define its parts?

Ans. Body in White (BIW) is an automotive manufacturing process in which a Vehicle's or a car body's frame is welded or joined together after dipping each BIW part into the white bath(undercoat). This stage comes between, after the primary electrochemical dipping process and before the painting of the chassis and moving on to the assemblies and sub-assemblies of engines, glasses, seats, etc.

There are two types of BIW structures;

1. Monocoque body structure( Inbuilt Chassis)

2. Frame-mounted body structure. ( Separate chassis)

source: Wikipedia

There are various parts that make BIW body

1. Front-end parts

there are subparts in the front-end parts 

- Dash assembly

- Dash panel

- cowl, etc.

2. Floor plan

there are subparts in the floor plan parts

- Front floor panel

- Tunnel, etc.

3. Rear-end

there are subparts in the rear-end parts

- Tailgate

- Rear floor

- Rear compartment, etc.

4. Roof

there are subparts in the roof parts

- roof panel

- roof bows

- Adapter parts, etc.

5. Upper body

there are subparts in the upper body parts

- A,B,C,D pillars

- Roof rails, etc.

2. What do you understand by BIW nomenclature?

 BIW nomenclature Is nothing but names given to each and every part that is joined or present in the BIW structure. So, let us see some of the parts that are present in the BIW structure.

(image is taken from Pinterest)

 there are also sub-components that are present in every single part like Risers, Dash panel, Dashboard, Back panel, etc.

3. What is fixture & their types?

A device that is used to hold, locate and support the component in the manufacturing industry is called a fixture. Fixtures ensure to provide the stability to the part when any process is being done on that part. That process can be welding, riveting, grinding, drilling, etc. In BIW fixture design Fixture works on the 3-2-1 principle.

 There are three types of BIW fixture processes that are used in companies.

- Pre Production Fixture

These kinds of fixtures are made commonly for the prototype stage, where they check the productivity and feasibility of the fixture. these fixtures require a lot of studies and detailing because it is at the preproduction stage. if 

a new standard or a process is needed, they first modify the preproduction fixture and upgrade to the production fixture at the assembly line.

- Production Fixture

These kinds of fixtures are used in the main production line or mass production departments in a company. for example, the assembly line is where all the sheet metal BIW parts are joined or welded together so a production fixture is used to check the geometries and fast production in less time.

- Checking Fixture

These types of fixtures are used to inspect the produced BIW sheet metal. to check the tolerances, Geometries, dimensions, etc. For fixing the Parts they actually use gauges to inspect and get a great accuracy while checking.

There are sub-units that make a fixture.

-Clamp units.

clamps hold the car part firmly and prevent the part from distortion while carrying out the spot welding operation. some of the clamps are,

L- Block, Shim, and Spacer, Blade spacer, Riser, etc.

- Pin units

the locating pins are used to locate a body part in a position sufficiently accurate to execute a welding process. Usually, two locating pins are enough to properly locate the body part on one plane. one of the pins is round, and another one is diamond-shaped. This configuration will allow the easier loading of body parts.

- Rest units

These units are used to rest the panel

- Standard parts

these parts are used and also available in the market for purchases. with the help of standard parts, the designing of other fixtures is easy. some of the standard parts are

suction cups, cylinders, etc.

4. What is the basic principle of fixture design?

The basic principle used in fixture design is 3- 2- 1 principles. It is also known as a six-pin or six-point location principle. In this, the three adjacent locating surfaces of the blank (workpiece) are resting against 3, 2, and 1 pin respectively, which prevent 9 degrees of freedom.

The 3-2-1 principle is a Component holding principle where three pins are located on the 1st principle plane, i.e. either XY, YZ, ZX. And two pins are located on the 2nd plane which is perpendicular to the 1st plane, and at last one pin on the plane which is mutually perpendicular to the 1st and 2nd planes.By using this method Componet can be arrested in all six degrees of freedom.

in order to follow this principle, one has to completely arrest all DOF of a given part.

 

Translational & rotational position along the X-axis

Translational & rotational position along the Y-axis

Translational & rotational position along the Z-axis

These six coordinates are known as the six degrees of freedom of a three-dimensional object. The translational and rotational positions can vary in either direction with respect to each of the three axes.

To completely prevent movement, all six degrees of freedom must be restricted.

So, to arrest each DOF Fixtures are used to contain the part for working.

5. Elaborate types of BIW Stations?

In the process of joining in assembly line , panels are moved from one section to another sections.Those sections are called Station. 

BIW stations are classified into these parts.

1. Geo tool station

In this station geometry of two parts are fixed. it can be either using welding or riveting . In this station precision and geomatry of the finished product is defined by Locating pins have closer tolerence of 0/-0.15.

2. Re-spot station

Once product comes out of the Geo Station and there are left out spots where spot welding or riveting is to be done. then it is moved to another station , that station is called Re-spot station.

In this station pins hve tolrence upto  0/-0.28.

3. Pedestal Station

In this station , Pedestal gun is mounted on a tool and panel is manipulated manually or by robot to weld the panels.

Pedestal station is generally a Re spot station.Re spot station and Pedestal station, both perform same kind of operation. but to decide whether to go for pedestal or a re-spot station some parameters needs to consider like cycle time, floor space, no. of welds, clamp plan, or size of the panel.

4. Loading Station

This station is used for loading of panel and  same station is used to change the orientation of the if it is required in the upcomin station.

Sometime this station is used when Robots are unable to transfer panel from one station to another.

5. Buffer station

This station is used to make the balance between the process.

Some stations carry out procees in lesser time as compared to their respective stations.In that case panels can be stored in one sation so that assembly line process remains smooth.

6. Sealer station

In this station Sealant application is carried out.This process can be carried out manually or by using robots. Sealer is used in between two panels so that panels do not flatter due to friction.

7. Marriage station

In this Station inner and outer panels are joined. In this station to avoid the imprssion on the outer panel(A class surface), copper strips are used in betweenn the weld tip and A-class surface.

8. Curing Station

In this Station product recieved after sealing application, is kept idle at ambient temperature, which allows sealent to get dry with better bonding between the panel.

In these stations, some Fixtures are used such as

- Grippers.

grippers are work holding devices that are used manually or by robots, these are used to lift Car body parts while assembly, welding and so on.

there are so many types of grippers.

- Material handling gripper

these are used to carry sheet metals

- Process gripper

these are used in geo station where welding takes place.

- Combo gripper

These are used in loading station where it transfers parts from one station to another.

- Dual gripper

these grippers are used to carry the part from both sides.

- Stands

stands are used to hold the tools of machining applicences like weld gun, Sealer gun, etc.

There are some types of stands,

- pedestal stands

it carries weld guns or welding tools.

- Sealing stand

it carries sealant tools.

- Docking stand

used for material handling purposes.

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

Some of the basic terminoligies in BIW fixtures are,

1. MYLAR

MYLAR is one kind of block that touches the panel and holds or clamps the panel. Mylars are always designed in CAR LINE. Mylar is also called NC(Numerically Controlled)Block. Mylars are mounted on any block or plate with Shimming, So that height of mylar can be adjusted accordingly at the assembly level. For ‘A’ class surfaces Nylon mylars are used. So that surface can be saved from scratches.

 

2. Pins 

Pins are used to locking the rotational movement of the panel. Generally there two types of Pins, one is Round Pin and another one is a Diamond pin. mostly they use two and three-directional shimming for pins as per the angle of the pin in the carline. In some cases,  a collared pin, when the pin is supposed to support the panel as well. For this kind of pin, they provide 3 way shimming irrespective of pin angle to the carline. 

 

3. Blade

The plate which connects Riser to the Clamp cylinder is named Blade. This plate plays an important role in building the unit. The plate can be of any shape.

4. L Blocks

A plate shaped as L is called an L block. This part is used as a connection between mylar and Blade. Generally, L blocks are used to provide shimming. It is not necessary that L blocks are only used for shimming, its uses changes as per the requirements, At some places, it is used just to connect one part to another. 

 

5.Riser

The part which is mounted on the base plate and holds a clamp or pin cylinder on it, is called Riser. Riser can be Standard Part or manufactured part, it varies from project to project. A riser can be a Single part or welded part. Standard risers also have various shapes and sizes.

6. Weldment

Weldment is the assembly of two or more parts that are joined by welding. To make a weldment it is the thumb rule to have a 5 mm overlay on each other plates so that space can be provided for welding. A weldment can be of any size and any number of plates.

7. Sensors

These are mostly used in checking stations. to check hole dimensions.

8. CMM 

A Coordinate Measuring Machine (CMM) is a measuring device to inspect the physical geometry of an object by sensing discrete points on the surface of the object or a part using a sensing probe. When the probe touches a surface, the transducer records the input and sends it as an electric impulse to the computer.