Introduction to BIW and Fixtures Challenge

What is BIW & define its parts?

Body in white (BIW) refers to the stage in automobile manufacturing in which a car body’s components have been joined together, using one or a combination of different techniques: welding (spot, MIG/MAG), riveting, clinching, bonding, laser brazing, etc.

Body in White, or BIW, is a stage in the production of automobiles in which all sheet metal components such as the roof, body side, underbody, backdoor, cross members, and other details are welded together. The resulting body is dipped in a primer solution, which has a greyish color and thus gives the body its name. The car's shape is determined by the BIW, which is obtained after welding and before painting.

BIW is mainly categorized as follows:

1. Body side
2. Underbody
3. Closures
4. Roof
5. Fender
6. Reinforcements

BODY SIDE consists of:

Body side outer

Body side inner

It generally refers to both sides of the car that are left and right sides. It mounts various BIW components like A-pillar, B-pillar, C-pillar, Panel side sill, etc.

UNDERBODY consists of:

Front end under frame: This is the compartment where the engine and other components of the automobile like battery, radiator, etc mount.

Main floor: This is the compartment where the interior parts like seats; infotainment panels etc will be mounted.

Rear end under frame: This compartment shapes the rear end of the car. This is what provides space for mounting rear closure parts and boot space.

CLOSURE components consist of:

Front door: Two front doors on each side.

Rear door: Two rear doors on each side.

Hood: To cover the engine compartment.

Trunk lid: To cover the interior and boot space.

ROOF consists of:

Roof inner

Roof outer

FENDER: The component seats between the side body and front end under the frame.

The below image shows precisely what a BIW of monocoque consists of

What do you understand by BIW nomenclature?

A nomenclature in BIW is 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. The 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 the inner wing panel in the UK description another side of the same component of BIW is known as the Motor compartment side panel in the US description.

3. What is a fixture & its types?

The fixture is a holding device that holds the workpiece to be processed. In general, fixtures are designed using the 3-2-1 principle. Further, the fixture should firmly hold the workpiece without causing vibrations, distortions, and stresses in the workpiece, and also fixture should not disturb or interfere with the processing of the workpiece.

Types of fixture:

Production fixture

These fixtures are used for mass production. Since these fixtures are used for mass production, they should be simple, rigid, and hard. These fixtures should be periodically maintained at regular intervals to avoid errors and repairs. The design of the fixture should be in such a way that it should be easy to load and unload the workpiece within seconds to increase the productivity of the processing/assembly.

Pre-production operation fixture

These fixtures are newly designed fixtures for the new products or parts. These may be complex, manual, and heavy based on the application. These can be referred to as prototype fixtures. Once the preproduction operation fixture functions properly, then modifications are made to improve and to make it simple and reliable. These fixtures are used in special cases or during the initial or trial stages of processing/production

Checking fixture

These fixtures are used for checking and inspection purposes. No processing is done in these fixtures. These fixtures consist of gauges for checking the dimensions and tolerances and their accuracies. In some checking fixtures, fixtures are fixed and CMM devices check the geometrical accuracies.

4 What is the basic principle of fixture design?

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 constrained.

The 3-2-1 principle is used.

The workpiece has twelve Degrees of Freedom. six transitional DOF and 6 rotational DOF.

Transitional: X, -X, Y, -Y, Z, -Z.

Rotational: Clockwise around the X axis (CROT-X); Anticlockwise around the X axis (ACROT-X); Clockwise around the Y axis (CROT-Y); Anticlockwise around the Y axis (ACROT-Y); Clockwise around the Z axis (CROT-Z); Anticlockwise around Z axis (ACROT-Z).

The rotational DOF has to be constrained.

Using the 3-2-1 principle.

First, the workpiece is constrained by 3 pins on the below surface. This lock the Y DOF, Clockwise around the X axis (CROT-X); Anticlockwise around the X axis (ACROT-X) the Clockwise around Z axis (CROT-Z); Anticlockwise around the Z axis (ACROT-Z).

Then another side perpendicular to the below surface is constrained by 2 pins. This locks -Z and +ZDOF Clockwise around the Y axis (CROT-Y); Anticlockwise around the Y axis (ACROT-Y).

Then any one side perpendicular to both the below and the other 2 sides of the workpiece is constrained by 1 pin. This locks X DOF.

The part is now fully constraint and cannot move

The 3 points are used as 3 points to define a plane. Four points cannot be used due to the irregularity of the surface in the real world.

5. Elaborate on types of BIW Stations?

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

These zones are further subdivided into stations, where various processes like welding gluing, and inspection is done to the part of that particular zone before they are assembled. 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:

Tools

Grippers

Stands

Miscellaneous

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

Geo Tool:

A geo tool is a fixture in which the geometry of the panel which is welded together is defined accurately.

In the geo fixture, two panels will be loaded and welded together.

The pin tolerance for the geo fixture is about -0.15mm.

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 welds but due to assembly line constraints we managed to achieve 30 on the geo tool, then the remaining 20 will be achieved on the re-spot tool.

The pin tolerance for the re-spot tool is -0.28mm.

Marriage or hemming tool:

A marriage or hemming tool is a fixture in which the inner panel and outer panel are joined together.

Hemming is not done for every part but only for those parts where we want to join two panels without other joining processes as it may affect the aesthetics of the car.

Hemming can be found on the Hood, Back door, etc.

Checking stations:

It is used to check the automotive part or assembly to ensure all the coordinated, relative dimensions and positions are as per tolerance. It can be classified as follows:

Gauge type checking fixture is where the workpiece is held and various gauges are introduced to ensure the dimensions and repeatability.

Fixed type checking fixture is where the workpiece is fixed using clamps and pins and the Coordinate Measuring Machine is used to measure the coordinates of different points of the panel and compare it with the nominal value and give its report to rectify any errors.

Automated checking fixture is where the automated setting is being done through sensors, PLCs, switches, etc, to give a signal in case of any irregularities which can be rectified. As it is expensive, it is not widely used.

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.

Different grippers are used in BIW as follows,

1. A) Material handling gripper

As the name suggests These grippers are used for material

These grippers can pick up assembly from one station & will drop the assembly at another

Process grippers

These grippers are used to carry out some specific processes like gluing, welding, and riveting in addition to material handling.

The gripper will go under gluing stand in the case of gluing process & will go under the pedestal weld stand in the case of the welding process.

C)Combo Gripper

Combo grippers are the ones that can carry out multiple tasks like it can do material handling & also it can carry out specific processes like gluing, and welding as well.

Weld gun + Gripper

1. D) Dual Gripper

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

1. A) Pedestal stands

The 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.

1. B) Gluing & sealer stand

Gluing gun or sealer gun is fixed to a welded or a standard stand which is grouted to the floor

1. C) Docking Stand

The robots have some limitations such as the payload capacity of the robot & also due to the lack of

When we select the robot for multitasking it can't do both the task simultaneously due to

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

Hence the robot can drop a gripper or gun & pick the next operation equipment to complete the task from the docking

1. D) Date stamp stand

Every manufactured product has some data to be stamped or to be embossed on it like serial no, batch no, and Date for some future reference, or data collection.

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

4) Miscellaneous stand

1. A) Curing

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

1. 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 They are also used to store the inventory while the machine is undergoing some maintenance.

1. C) Take out trolleys

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

1. D) Conveyor

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

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

1. A) NC/Mylars/Fingers

Mylars are the component that holds the panel while These are placed from the top side & the bottom side also. The top side of Mylars is called Clamping Mylars & the bottom side of Mylars is called Resting Mylars. Every clamping Mylars have resting Mylars. It doesn't allow deformation of the part due to welding stresses.

1. 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 are lots of holes on the panel which are not accurate due to the stamping operation. The PLP is defined in the drawing. The positional dimensions or relative dimensions are very precise in stamping & fixtures also.

1. C) Risers

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

1. D) Blade

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

1. E) Shims

Shims are small part that comes with a thickness of 0.1mm, 0.2mm, 0.5mm, etc. These will compensate for the stack-up tolerance which reflects in the panel holding part called We give tolerance to all the parts of the fixture. Due to this tolerance, the Mylars will either lift 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 then there will be distortion 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.

1. 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.

1. G) Hardware

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

1. 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.

1. 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.

1. J) Number plates

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

1. K) Nameplate

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

1. L) Clamp Arm

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

1. M) Pivot

It is an axis about which the clamp arm will rotate

1. N) Class A Surface/Skin surface

The outer panels of the car like the hood, door, backdoor, fender, and 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 for 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.

O)Reed switches & sensors

These are the electric components used in automated The reed switch is an electrical switch operated by an applied magnetic field. The detects whether the panel is loaded or not is done by sensors.