Week 1:- Introduction to BiW and Fixtures Challenge

Q1- What is BIW and define its parts?

It is a stage in automobile design or automobile manufacturing where all the sheet metal component are assembled by means of welding, revieting, bolting etc. is called Body in white (B.I.W), moving parts such as Door, Hood, Trunk Lid, Front Fender, and the components (chassis, motor) and trim (windshields, seats, upholstery, electronics, etc.) are added in a later stage.

There are two types of BIW

1-Frame mounted on body structure.

2-Monocoqe body structure.

1) Frame mounted on body structure.

• It is also called as body on frame contruction.
• In this type body is mounted on the rigid frame
• Powertrains and suspension are mounted on the chasis.
• Used in utility vehicle, truck and buses.

2) Monocoqe body structure.

• It is also called as Chassis in built in body.
• It is not mounted on the top of anything therefore lower center of gravity hence better stability.

NOTE

• BIW accounts 50% weight of vehicle and we can consider this area to reduce the overall weight of the vehicle by using lighter materials and better structure.
• We mostly use steel in BIW industry becuse of easiness in fabrication, but in recent years fuel prices are increasing and in order to reduce the fuel consumption rate ,it becomes need to reduce weight of vehicle.

Materials commonly used in BIW industry

Steel

• We manfacture parts generally by stamping operations.
• Reinforcements are required to provide extra strength in critical structure.
• Parts made up of this material is having uniform thickness.
• Heavier in weight and more number of components.

Aluminium

• We manufacture parts generally by casting operations.
• Here as per our requirement we can increase the thickness of our part as casting gives you the room to vary the thickness as per our wish.
• Part made up of that material are lighter in weight and assembly required less number of component

CFRP (Carbon fiber reinforced plastics)

• It has low investment costs
• This material offer you to give increased design flexibility.
• Life of the component made up of this material is high
• We use non traditional machining for the manufacture of this component.

BIW NOMENCLATURE

We name the components of the car based on the U.K and U.S description.

BIW parts consists of

1) Under body system.

It consists of Frame/rail and cross member

• Frame/rail is the main structure and it is used for transferring the load of the engine and suspension.
• It is used for absorbing energy during frontal crash.
• It also support front and rear bumper.

Cross member

It is used to support transmission, Front and rear seats.

2) Body side system.

It consists of Pillars, roof rail and rocker

Pillars

• Pillars are responsible for protecting against roof crush and also they support the roof.
• they also required for the assembly of the door.
• A piller must satisfy the front visibility criteria.

Roof rail and Rocker

• They are much needed to complete the framing.
• They provide stiffness to the floor and the roof.

3) Front end system.

It consists of Shot gun and radiator support

Shot gun

• It transfer shock loads from the shock towers to the body.
• It absorbs part of crash energy.
• It supports battery and other parts.

Radiator support

• Support radiator.

4) Dash and cowl system.

Dash panel

It support accelerator, brake and clutch pedals.

Cowl system

It supports windshield and wiper motor.

It provide stiffness to the body.

5) Roof system.

Roof outer panel

It is a panel used to protect us from harsh environment conditions.

Roof inner panel

It is used to provide stiffness to the outer panel

6) Closure system.

It consists of Hood and trunk lid.

Hood

It is a component which is used to access the engine compartment.

Trunk lid

It is a component used to access the rear compartment of the vehicle.

What is Fixtures and it's type

Fixture is a device which is used to hold, locate and support the component.

It is used 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 3-2-1 principle.

Here Fixture does not guide the tool.

3-2-1 Principle

Basically 3-2-1 principle is used to lock all 12 degree of freedom ( 6 translational (+ , -) and 6 rotational (cw, ccw)).

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 12 degrees of freedom.

Types of fixtures

1. Turning fixtures.
2. Milling fixtures.
3. Broaching fixtures.
4. Grinding fixtures.
5. Boring fixtures.
6. Indexing fixtures.
7. Tapping fixtures.
8. Duplex fixtures.
9. Welding fixtures.
10. Assembly fixtures.

NOTE: Fixtures are named based on the type of machining operation for which they are designed and employed.

1-Turning fixtures

It is easy-to-hold regular workpieces on lathes in standard job holding devices like chucks and collets, between the centre and on mandrels or faceplates. But irregularly shaped components offer a lot of difficulties in holding them correctly.

Simple odd shaped jobs can be held in chuck also, say by proper adjustment of jaws in a four-jaw chuck or by using shaped soft jaws. However, workpieces having complicated shaped have to be necessarily held in position with the help of turning fixtures. These fixtures are normally mounted on the nose of the machine spindle or on a faceplate and the workpieces held them.

• Whenever necessary, the fixture must be provided with a counterweight so that to balance the unbalance fixture.
• These fixtures should be rigid enough
• They should have with minimum overhang.
• They should be designed to grip the workpieces very firmly
• They should not carry any dangerous projections for the machine operator or tool or both
• They should be able to provide proper support to thin and weak sections of the workpieces during the operation.

2-Milling fixtures

These fixtures are used on milling for carrying out different milling operations on the workpiece. The fixture is properly located on the table of the machine and secured in position by means of bolts and nuts.

The table is shifted and set in the proper position, in relation to the cutter. The workpieces are located no the base of the fixture and clamped before starting the operation.

Since the cutting forces involved are quite high, and also intermittent, the clamping elements. Proper locating of the fixture on the machine table is usually achieved with the help of two tenons provided under the fixture base. These tenons enter a T-slot of the table to provide the required location. The fixture base can then be secured to the table by means of T-bolts and nuts.

3-Broaching Fixtures

These fixtures are used on different types of broaching machines to locate, hold, and support the workpieces during the operations, such as keyway broaching operations, such as keyway broaching, hole broaching, etc. The use of a clamping plate as a fixture for internal pull-type hole broaching.

4-Grinding Fixture

Several different forms of fixtures are used in grinding machines to locate, hold, and support the workpieces during the operations. These fixtures may be the standard work-holding devices, such as chucks, mandrels, chuck with shaped jaws, magnetic chucks, etc.

For example; a vertical surface grinder with a rotary table will normally have a rotary fixture secured to its table. Similarly, a plain or string fixture may be provided on a surface grinder with the reciprocating table. A drill grinding attachment is a glaring example of a standard fixture used for grinding of drill geometry.

Whatever be the types of fixture designed for grinding operation, it should have provisions for supply and exit of coolant, mounting of wheel dressers and should be properly balanced, if it is a rotating fixture.

Boring Fixture

The operation can be performed in one of the following two ways:

• By keeping the boring bar (tool) stationary and feeding the touting workpiece on to the bar.
• By keeping the workpiece stationary and feeding the rotating boring bar into the work.

Accordingly, therefore, the boring fixture is made in two common designs.

One of these incorporates the principle of a drilling jig, and in this, the boring bar (tool) is guided through a pilot bush. such fixture is also often referred to as boring jigs. the other design facilitates holding of the workpiece incorrect position, relative to the boring bar.

Although this fixture incorporates almost all the common principles of jig and fixture design, their construction need not be as sturdy as that of the milling fixtures, because they never have to bear as heavy cutting loads as involved in milling fixtures, because they never have to bear as heavy cutting loads as involved in milling operations.

Indexing Fixture

Several components need machining on the different surface such that their machined surface surfaces or forms are evenly spaced.

Such components are required to be indexed equally as many as the number of surfaces to be machined. Obviously, the holding devices (jigs or fixtures) used are made to carry a suitable indexing mechanism. A fixture carrying such a device is known as an indexing fixture.

Tapping Fixture

Tapping fixture is specially designed to position and firmly secure identical workpieces for cutting internal threads in drilled holes in them. Odd shaped and unbalanced components will always need the use of such fixtures, especially when the tapping operation is to be carried out repeatedly on a mass scale on such components.

Duplex Fixtures

It is the name given to the fixture which holds two similar components simultaneously and facilitates simultaneously machining of these components at two separate stations. While one workpiece is machined at one station.

Both the operations according to the requirement may be similar or different. Once machining at both the stations is over, the fixture is indexed through 180 degrees so that the first component is shifted to the second station for the second operation and the finished component to the first station.

The finished component is then uploaded here, replaced by a fresh component and the first operation performed on it. The cycle goes on repeating, which enables mass production of components at a fairly high speed.

Welding Fixtures

Welding fixtures are carefully designed to hold and support the various components to be welded in proper locations and prevent distortions in welded structures. For this, the locating element need to be careful, clamping has to be light but firm, placement of clamping elements has to be clear of the welding area. The fixture has to be quite stable and rigid to withstand the welding stresses.

In many cases, a preferably and commonly used practice is to first tack weld the structure by holding it in welding jig and then transfer it to a holding fixture for full welding. This helps in reducing the chances of distortion considerably and the fixture is subjected to lesser stresses.

Assembly Fixture

The function of these fixtures is to hold different components together in their proper relative position at the time of assembling them. For example, two or more steel plates can be held together in relative positions and riveted.

These fixtures, which are used for holding the components for performing mechanical operations, are known as mechanical assembly fixtures. Against this, there are other types of fixtures which the components are held for joining, such as the welding fixtures are also assembly fixtures, but for hot joining.

Difference Between Jigs and Fixtures

Following are the fundamental difference between a fixture and jig:

1. A fixture holds and position the work but does not guide the tool, whereas a jig holds, locates and as well as guide the tool.
2. The fixtures are heavier in construction and are bolted rigidly on the machine table, whereas the jigs are made lighter for quicker handling and clamping with the table is often unnecessary.
3. The fixtures are employed for holding work in milling, grinding, planing or turning operations, whereas the jigs are used for holding the work and guiding the tool, particularly in drilling reaming or tapping operations.

Advantages of using jigs and fixtures in mass production work.

The following are the advantages of jigs and fixtures in mass production work.

1. Eliminates the making out, measuring, and other setting methods before machining.
2. It increases the machining accuracy because the workpiece is automatically located and the tool is guided without making any manual adjustment.
3. It enables the production of identical parts which are interchangeable. This facilitates the assembly operation.
4. It increases the production capacity by enabling a number of workpieces to be machined in the single set up, and in some cases, a number of tools may be made to operate simultaneously. The handling time is also greatly reduced due to the quick setting and locating of the work. The speed, feed and depth of cut for machining can be increased due to high clamping rigidity of jigs and fixtures.
5. It reduces the operator’s labour and consequent fatigue as the handling operations are minimised and simplified.
6. It enables a semi-skilled operator to perform the operations as the setting operation of the tool and the work is mechanised. This saves labour costs.
7. It reduces the expenditure on the quality control of the finish products.
8. It reduces the overall cost of machining by fully or partly automating the processes.

Applications of fixtures are:

• Drilling.
• Reaming.
• Tapping.

Basic Principle of fixture design

LOCATING POINTS: Locating the work is a prime necessity and requires suitable facilities. The correct setup ensures smooth insertion of a workpiece in the proper position and removing a workpiece from a jig without operational hassles or time consumption. The workpiece position needs to be precise with the guiding tool in the jig or setup pieces in the fixture.

FOOLPROOF: A foolproof design of jigs and fixtures does not permit a tool or workpiece to be placed in any other way other than the intended one.

REDUCTION OF IDLE TIME: Jigs and Fixtures must be designed in such a way that ensures smooth loading, clamping, machining, and unloading of a workpiece.

WEIGHT OF JIGS AND FIXTURES: A jig and fixture must be compact, easy to handle, and low cost regarding the number of materials used without giving up stiffness and rigidity.

MATERIALS FOR JIGS AND FIXTURES: Jigs and Fixtures are usually created with hardened materials to resist wear & tear and avoid frequent damage—for example, Mild steel, Cast iron, Die steel, High-speed steel, Caesium.

CLAMPING DEVICE: A suitable clamp is rated for its strength. It should be able to hold a workpiece firmly in its position while bearing the strain of the cutting tool simultaneously, without springing.

Broad rules of Jigs & Fixtures Design

• Compare the production cost of work between the existing tools and the tool to be made and see if the manufacturing price is not more than the expected gain.
• Determine location points and outline clamping arrangement.
• Make sure the clamping and binding pieces are as quick to act & efficient as possible.
• Make the jig and fixture foolproof.
• Make sure the locating points are adjustable.
• Do avoid intricate clamping arrangements.
• Round all corners.
• Make sure the operator has handles to make handling tasks easier.
• Provide ample amount of clearance.
• Provide holes for chips to escape.
• Systematically locate clamps to resist the pressure of the cutting tool while machining.
• To avoid springing action, place all clamps in proximity opposite to the bearing point of the workpiece.
• Test the jigs before putting them in a shop.

The 3-2-1 principle

Locating a part to be machined involves mainly three steps: Supporting, Positioning, and Clamping.

Two main intentions when placing a job on a jig/fixture are:

• Precisely positioning the part at the desired coordinates.
• Curbing all six degrees of movement so that the part cannot budge.

An extensively used method for obtaining these objectives is the 3-2-1 principle or six degrees of freedom for part location.

The 3-2-1 method is a work-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 perpendicular to the 1st plane, and at last, one pin on the plane is mutually perpendicular to the 1st and 2nd planes. The aim is to constrain the movement of the workpiece along all three axes.

Design objectives of Jigs and Fixtures

Before sitting down to design jigs/fixtures, the designer must consider the following points:

• The tool must be foolproof to prevent any mishandling or accidental usage by the operator.
• Easy to operate for increasing efficiency.
• Easy to manufacture using the lowest costs.
• Its ability to weather the tool life instead of appropriate materials.
• Must be consistent at producing high-quality parts.
• Must be safe and secure to use.

The designer must know the basics of the process and the tools associated with it for which the jig/fixture is designed. Overall objectives to look out for a while developing such tools are:

• Cycle time.
• Type of Jig/Fixture.
• Part Assembly sequence or Machining locations.
• Joining or machining process.
• Clamping method and clamping sequence.
• Required output accuracy.
• Type of equipment to be used with the jig.
• Method of ejecting finished output and transferring it to the next. Platform, whether the manual or automatic mode.
• The type of material, recommended weight, number of spots involving welding.