Week 4:- Pin Unit Design Challenge

PIN UNIT DESIGN CHALLENGE

AIM

To design the fixed pin unit and the retracting pin unit for locating a BIW panel in a Fixture.

INTRODUCTION

FIXED PIN UNIT

• Fixed pin units are used in a fixture to locate the car panel during any operation.

RETRACTABLE PIN UNIT

• Retractable pin unit is opposite to fixed unit which can be moved up and down up to a certain distance.
• It is used for unloading complex panels after welding.

The purpose of the pin unit.

• The fixed pin unit is used to arrest the 6 degrees of freedom of the assembly of a fixture. The other six degrees of freedom are arrested by the three rest units.
• Pins help to locate the part of an assembly very accurately for the welding operation.

The basic parts of the Pin unit are

• Pin
• Pin Retainer
• Shims
• Blade
• Riser

Pins

• Pins are used for accurately locating the part to welded in an assembly.
• The holes in the part of the assembly are inserted on these pins.
• The pins constrain the degrees of freedom of the part of the fixture.
• The diameter of the pins has tighter tolerances as compared to the diameter of the hole in the part.
• The Pin can be either round or diamond-shaped. Generally, diamond-shaped pins are used to avoid over constraint.

Pin Retainer

Pin retainer is used to hold the locating pins. The pin retainer block has two-way shims.

Shims

Shims are small parts of the thickness of 0.1,0.2,0.3 mm. The shims are used to compensate for the difference due to the stack-up tolerance of the assembly, which eventually results in the improper holding of the panel if the Mylar holds it loosely.

Block

Blocks are used to connect the pin retainer with the blade, riser, and cylinders in case of a retractable pin unit. The shims are also attached to the blocks for multiple shimming directions.

Blade

• Blades are plates that are attached to the raiser.
• The cylinders and other additional arms are mounted on a Blade.

Raiser

• A raiser is a part that is used to raise the height of the fixture.
• The raiser is fixed to the base of the fixture and the blade is mounted on the raiser.

FUNDAMENTALS OF PIN UNIT DESIGN

• It is necessary to have two Pins to locate the car panel. One pin will restrict 4 degrees of freedom and the other pin will restrict two degrees of freedom.
• The pin should engage 3-5 mm from the car part entry surface.
• All pins should have two ways adjustable shims.
• The round pin should be used in case of a 4 way arresting of the car part if the hole is round.
• The round pin should be used in case of a 2 way arresting of the car part if the hole is Slot.
• The diamond pin should be used in case of a 4 way arresting of the car part if the hole is Slot.
• The diamond pin should be used in case of a 2 way arresting of the car part if the hole is round.

DESIGN METHODOLOGY

1.The designing process is started by giving a project title and proper structuring of the Specification tree.

2.The car panel for which the fixture is to be designed is imported into the project.

3.The Holes and slots are located and the pins are designed as per the diameter of the hole and it is made sure that the axis of the pin and the axis of the hole must be coincident. The pins designed may be Round or diamond-shaped.

4. Pin retainers are designed to accommodate the pin and also the shims.

5. The blocks are used to provide shimming in multiple directions. They are designed in such a way that shims are mounted for two way adjustments.

6. 5 mm shims are designed for the adjustment of the pin in multiple directions

7. The risers are designed such that all the above parts are mounted on it. The risers are mounted to the base of the fixture.

8. The parts that are to be assembled are provided with two dowel holes and a threaded hole.

Below are the images of different pin units.

Fixed Pin unit with Round pin.

Fixed pin Unit With Diamond Pin.

Fixed Pin Units Assembly

The above image shows the single rod retractable pin and the yellow pin shows the retracted position.

The above image shows the Double rod retractable pin and the yellow parts show the retracted position.

Retracted Pin Units Assembly

CONCLUSION

Hence, the fixed pin unit and the retractable pin units are designed for the given car panel as per the requirements.