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 locating 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.
• Its 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.
• Pins help to locate the part of an assembly very accurately for welding operation.

The basic parts of the pin unit are:-

• Pin
• Pin Retainer
• Shims
• Blade
• Riser

PIN:-

• Pins are used for accuretely locating the part to welded in an assembly.
• The holes in the part of assembly are inserted on these pins.
• The pins constrain the degreee of freedom of the part of the fixture.
• The diameter of the pins has tighter tolerence as compared to the diameter of the hole in part.
• The pin can be either rounded 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 dlock has two-way shims.

Shims:-

Shims are small parts of the thickness of 0.1,02,0.3 mm.The shims are used to compensate for difference due to the stack-up tolerence of the assembly,which eventually results in the improper holding of the panel if the mylar holds it loosely.

Block:-

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

Blades:-

• Blades are plates that are attached to the raiser.
• The cylinderand other additional arms are mounted on a blade.

Riser:-

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

Fundamental:-

3-2-1 principle:-

Our ultimate intention for using pin unit IS to fix the work piece so that it does not deviate from the position while the operation is being performed on it For this reason we use 3-2-1 principle.

Every component we know has 6 degrees of freedom they are listed below:

1. Translational motion along x-axis,
2. Translational motion along y-axis.
3. Translational motion along z-axis.
4. Rotational motion along x-axis.
5. Rotational motion along y-axis.
6. Rotational motion along y-axis.

Degrees of freedom can be simply understood as the direction in which any component cam move .These 6-degrees becomes 12 if we consider translation along negative and rotation in anti-clockwise direction too. That means, every component can move in all the direction when it is free But processes like welding, stamping or others and in fact every ether cannot be carried out on such free to move body for obvious reasons. Thus the body must be constrained in all the major direction in order for workman to work upon it. This constrain on motion is achieved by 3-2-1 principle.

In 3-2-1 principle we make use of locating pin sin the given order to fix if on a fixture

1. 1.3 pins are located on the bottom side of the component. These pins constrain the translation motion of the body in Z direction and rotational motion along x-axis and y-axis. Thus 3 degrees are restricted. But the body still can rotate along z-axis and translate in x axis and y-axis.
2. 2.2 pins are located on the back side of the -Component. These pins constrain the translation motion along x-axis and rotational motion along Z-axis Thus we have constrained 5 degrees in total. But translation along Y axis is still possible.
3. 1 pin located on the adjacent side of the 2 pins we can constrain the last degree that is translation along Y axis.

Thus we can constrain all the degrees of freedom of a body using 3-2-1 principle which used 6 pins for the same. The video explains the 3-2-1 principle

Fundamentals of pin unit design:-

• Its is nesessary to have two pins to locate the car panel.One pin will restrict 4 degrees of freedom and other pin will restrict two degrees of freedom.
• The pin should engage 3-5mm from the car part entery surface.
• All pins should have two ways of shimming to compasate the tolerances.
• The round pin should be used in case of a 2 way arresting of the car part if the hole is round.
• The diamond pin should be used in case of 4 way arresting of the car part if the hole is slot.
• The diamond pin should be used in case of a 2way 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 pins are designed as per the diameter of the hole and it is made sure that the axis of the hole must be coincident.The pins designed may be round or diamond-shaped.The pin should engage 3mm to 5mm from the car part entery.

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

• Pin retainer should have a hole with a fit, on to which the pin will be fixed.
• The pin mounting surface of the pin retainer should be a machined surface.
• The pin mounting surface of the pin retainer should have a step to lock the rotation of the pin
• The pin mounting surface of the pin retainer to the blocks should be a machined surface.
• The pin retainer will be fixed to a block or a L block to the riser with 2 dowel holes (pins) & at least with one screw hole to maintain the tolerance.

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

6. 5mm 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 to the base of the fixture.

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

Below are the images of different pin units:-

• Fixed pin unit with round pin:-

• Fixed pin unit with Diamond pin:-

• Retractable Pin units:-

1] single rod retractable pin:-

2]Double Rod Retractable Pin Unit:-

Conclusion:-

Hence,As per the objective,the 2 different types of fixed pin units and with different pins,oin retainer,bladesand risers and 2 different types of retracteble pin units and with different pins,pin retainer,blades,risers and cylinders are designed and rednered using CATIA V5 successfully.