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.