Project 1- Design of fixtures for car panel

DESIGN OF FIXTURES FOR CAR PANEL

1) INTRODUCTION

The fixture is a device used for holding and positioning the panel, locating and setting the tool but no guidance will be given to the tool. The fixtures are the units that are used to constrain the car panel in the manufacturing process. The fixture design consists of the data of the car panel, location of the fixture, robot arm data, weld spot and spot gun data. There are different types of fixtures that are used in the industries for constraining the car panel. The 12 DOF are acting on the panel when it is in space. There are 6 translations and 6 rotations in X, Y and Z coordinates. To restrict the motion of the panel, all the 12 DOF needs to be arrested.

The different types of fixture units that are utilized to stop the motion of the panel in all the DOF are:

1. Fixed pin unit
2. Retractable pin unit
3. Power Clamp unit
4. Swivel Clamp unit
5. Rest Unit
6. Base unit
7. Rough Locators

The principle that is used for constraining all the DOF is the 3-2-1 principle. This is used for locating the cartesian coordinate system of components. The 3,2,1 are the number of pins provided in three mutually perpendicular planes for arresting the required number of degrees of freedom of the panel.

3 pins – 5 DOF – (4 Rotation + 1 Translation)

2 pins – 3 DOF – (2 Rotation + 1 Translation)

1 pin – 1 DOF – (1 Translation)

2) OBJECTIVE

The objective of the project is to design the fixture for the given car panel that restricts the motion of the panel in all the DOF. Designing the fixed pin unit, retractable unit, power clamp unit, swivel clamp unit and base unit in the CATIA V5 following all the design considerations.

3) DESIGN METHODOLOGY

The fixture units for the given car panel are modelled in the CATIA V5. The feature tree is named “P01_Z01_ST010_00_00” in which

P01 – Project 1

Z01 – Zone 1

S010 – Station 10

00 – Unit number

00 – Part number

For every unit, the unit number and part number change but the project, zone and station remain the same.

1) FIXED PIN UNIT

A fixed pin unit is a unit designed to locate the car panel using pins.

The parts of the fixed pin are:

• Pin
• Pin retainer
• Shim / spacer
• Block
• Blade or Adapter plate
• Riser.
• The centre of the hole is taken and the pin outline is modelled as per the standards.

A typical Pin unit

Fixed Pin units designed for the Fixture

Pin units with the workpiece

• The blocks are modelled in such a manner that the pin can be adjusted in longitudinal and translational directions.
• A 5 mm space is provided between the block and retainers as the shims or spacer blocks are present.
• The dowel holes are present in all the parts of the pin units which are to be assembled with tolerance should be designed with 2 dowels and at least 1 to 6 treated / free holes (depends on size). And to be finely machined for the mounting surface with 3 to 5 mm step machining.
• The blade is a plate that connects the riser to the block, usually, the blades are standard parts if needed can be designed.
• The riser is a part on which all the parts of a unit are mounted and is mounted on the base plate of a tool. In general, the riser can either be made part of a standard part.

2) RETRACTABLE UNIT

A retractable pin unit is a unit designed to locate the car panel using pins. It is mostly used where the removal of the panel is complicated.

The parts of the retractable pin are:

1. Pin
2. Pneumatic cylinder
3. Shim / spacer
4. Block
5. Riser.

Retractable Pin units designed for the Fixture

• The blocks are modelled in such a manner that the pin can be adjusted in longitudinal and translational directions.
• A 5 mm space is provided between the block and retainers as the shims or spacer blocks are present.
• The dowel holes are present in all the parts of the pin units which are to be assembled with tolerance should be designed with 2 dowels and at least 1 to 6 treated / free holes (depends on size). And to be finely machined for the mounting surface with 3 to 5 mm step machining.
• The riser is a part on which all the parts of a unit are mounted and is mounted on the base plate of a tool. In general, the riser can either be made part of a standard part.

3) POWER CLAMP/PIN CLAMP UNIT

A Power Clamp unit is a unit designed to clamp/hold the car panel with NC blocks/ Mylars/ Rest by using a pneumatic clamp cylinder.

The parts of the clamp unit are:

A typical Power clamp unit

• Rest block /Mylar
• L - block
• Shim / spacer
• Blade or Adapter plate
• Riser.
• Clamp Arm
• Pneumatic cylinder
• The standard pneumatic cylinders are downloaded from Tunker's website.
• The L- blocks / Mylars / Rest blocks are modelled in such a manner that there won’t be any movement of the car panel in the transverse direction. The clamp unit restricts the transverse direction translation and rotation.
• The clamp arm is a bought-out part, to which all the movable parts are fixed. In general, a clamp arm is a part of a clamp cylinder. Clamp arms are different for the different bore of cylinders. Clamp arms are available in different hole patches. Clamp arms are available as Middle arm – A10, Right arm – A11, Left arm – A12.
• A 5 mm space is provided between the clamp arm and mylars as the shims or spacer blocks are present.
• The dowel holes are present in all the parts of the pin units which are to be assembled with tolerance should be designed with 2 dowels and at least 1 to 6 treated / free holes (depends on size). And to be finely machined for the mounting surface with 3 to 5 mm step machining.
• A clamp cylinder is a pneumatic device that works with pressurised air. The clamping cylinder is used to open and close the parts fixed to the clamp arm fixed to the clamp body. Clamp cylinders are in general 40,50,63 and 80 bore capacity. Opens up to 135° for horizontal clamp mounting. Opens up to 105° for vertical clamp mounting.
• The riser is a part on which all the parts of a unit are mounted and is mounted on the base plate of a tool. In general, the riser can either be made part of a standard part.

Power pin clamp units designed for the Fixture (yellow represents open position)

Power pin Clamp unit with the workpiece

4) SWIVEL CLAMP/ PIN CLAMP UNIT

A Swivel Clamp unit is a unit designed to clamp/hold the car panel with NC blocks/ Mylars/ Rest by using a swivel cylinder.

A typical Power clamp unit

The parts of the clamp unit are:

• Rest block /Mylar
• L - block
• Shim / spacer
• Blade or Adapter plate
• Riser.
• Clamp Arm
• Swivel cylinder
• The swivel cylinder (CKG-1B-63-100Y) is imported as the name suggest the stroke of the cylinder in the y-direction is 100 mm.
• The L- blocks / Mylars / Rest blocks are modelled in such a manner that there won’t be any movement of the car panel in the transverse direction. The clamp unit restricts the transverse direction translation and rotation.
• The clamp arm is consisting of pivots connected to the blade and swivel cylinder. The open condition of the clamp arm must be below the stroke length of the cylinder and exactly in line with the swivel cylinder in a vertical direction.
• A 5 mm space is provided between the clamp arm and mylars as the shims or spacer blocks are present.
• The dowel holes are present in all the parts of the pin units which are to be assembled with tolerance should be designed with 2 dowels and at least 1 to 6 treated / free holes (depends on size). And to be finely machined for the mounting surface with 3 to 5 mm step machining.
• The blade is modelled in the way that; it gives support to the bottom rest blocks and also connects the cylinder. A stopper is present in the blade which helps to stop the clamp arm at a certain distance in the closed condition.
• The riser is a part on which all the parts of a unit are mounted and is mounted on the base plate of a tool. In general, the riser can either be made part of a standard part.

Different types of Swivel pin clamp units designed for the Fixture ( yellow represents open position)

Swivel pin Clamp units with the workpiece at different locations

5) REST UNIT

The rest unit is used to support/rest the car panel using NC blocks/ Mylars

A typical Rest unit

Rest unit designed for the Fixture

Rest units supporting the workpiece

6) BASE UNIT

A Base unit is a unit designed to mount all the other units(Clamp, pin, rest units) of the tool, also other parts necessary for a tool like a pneumatic valve box, trunking cable path will be mounted onto the base unit.

A typical Base unit

• A Base unit should cover all the units with its outer periphery including openings.
• A base plate is preferred to be designed to BCS coordinates.
• A base plate should be drilled with datum holes/measuring holes in line with a pitch of 1000 mm in general.
• The number of datum holes is dependent on the size of the base plate.
• Datum holes must be drilled in nominal values of coordinates and terms of 50 and 100.
• Datum holes should be drilled with a diameter 100 mm away from other units.
• Datum holes should be covered with a cover plate.
• There must be a minimum space for the trunking channels.
• The weld gun position and the weldment have to be checked. A minimum of 5 mm gap must be present between the gun and the units.

Base unit designed for the Fixture

Base unit with Fixture units mounted on it

7) ROUGH LOCATORS

• Rough locators are used where manual loading of panels are to be implemented on the fixture.
• These are used to guide the panels in the correct position and orientation.
• These also help for proper Poka-Yoke, which means to avoid errors
• Materials used for rough locators are mild steel or similar metal.

Rough Locator designed for the fixture

Rough Locators with the workpiece

Fixture Assembly without Rough locators

Fixture Assembly with Rough locators

8) 3D-FINISH

3D finish is the process where the design is finished and to be ready for final simulation and 2D detailing.

Points to consider:

• Hole concentricity and sizes have to be checked for the rest blocks, mylars, blades and riser. All the holes must be concentric.
• If any surface of a part comes in contact with the other surface of the part, the surface has to be machined. To indicate the machined surface light brown colour is indicated in the design.
• All the units must be nominally designed. The pin is anyhow fixed so the pin is considered as the reference point and all the unit surfaces must be nominal with the pin unit.
• Pneumatic cylinder pipes, wires from different units has to be done in pneumatic lay-outing.
• There should be adequate gaps between the units and the weld gun.
• All the hardware required for the units has to be checked. It helps in documenting the project.
• Holes must be coloured as per the requirements. The dowel holes must be sky blue colour, open holes must be dark blue colour and threaded holes must be yellow colour.
• The parts and assemblies must be properly named as per the company standards.
• 

Different views of the Assembly

CONCLUSION

The fixture is designed for the car panel with all the design considerations. The positioning and locating of the car panel are done.