Week 4:- Pin Unit Design Challenge

Aim:

To design two different types of Fixed Pin Unit and Retractable Pin Unit with different Pins, Riser, Blade, and Block design using Catia V5

OBJECTIVE:

To design 2 different types of fixed pin units with different pins, risers, Blades &Blocks, and 2 Different types of retractable pins units with different pins, risers, blades, cylinders & blocks

Pin Unit design:

Pin unit is a unit used to locate the car panel using pins(Cylindrical, Diamond etc). It consists of parts like riser, blade, block, shims or spacer, pin retainer and pin. The 3-2-1 principle is

used to completly arrest the Degree of freedom(DOF) of the panel. The pin unit is used to restrict the 6 degrees of freedom of the part and keep the panel in position while the welding.

Fundametal requirement of pin unit design:

• Generally two pins are required to locate a car panel. The first pin arrests 4 way(4 translational DOF) and second one arrests 2 way(rotational) DOF of a car panel.
• The axis of the car panel hole and the axis of the pin should be same.
• The pin tolerance for a geo pin is of tight tolerance of -0.15mm
• The pin tolerance for the re-spot pin is maintained at tolerance of -0.28mm.

Clearances for pin unit design:

• Pin should engage 3 to 5 mm from car panel entry surface.
• All the pin unit parts must be atleast 10mm away from the panel.
• All pins should be accomodated with 2 way adjustable shims irrespective of direction of arresting.
• Round pins should be used in case of 4 way arresting of car part if the hole is round.
• Round pins can be used for 2 way arresting of car part only if the hole is slot.
• Diamond pins should be used in case of 2 way arresting of car part if hole is round
• Diamond pins should be used in case of 4 way arresting of car part if hole is slotted.

Types of pin unit

Fixed pin unit:

In this type of unit the pin is fixed by means of pin retainer and riser. It can be adjusted only with the help of shims. The height of the pin unit cannot be changed.

Design requirements for the pin

• Pin should be grinding surface on shaft with fits on to which the pin retainer will be fitted.
• The mounting surface of the pin should be a fine machined surface.
• The pin should have a step machine surface to lock the rotation, which matches with the pin retainer.
• All machined planes should be perpendicular to the axis of the pin shaft.
• Pin must have a provision like tapped hole from the bottom or a v-groove from the side.
• A pin must be hardened by doing suitable Heat treatment and finished with black oxide coating to reduce wear.

Pin Retainer:

A pin retainer is a part which hold the pin in position, the pin retainer can either be a make part or a standard part

Design requirements

• Pin retainer should have a hole with a flat face, on to which the pin will be fixed.
• The pin mounting surface of the pin retainer should be a machined surface with close tolerance.
• The pin mounting surface of the pin retainer should have a step to prevent the undesirable movement of the pin.
• 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.

Block/L Block:

These parts are mainly used to provide the shimming in the required directions and can be made in the required shape to make the design feasible.

Shims/Spacers:

Shims or Spacers is used for adjustments of locators(NC Blocks & pin retainers) for desired values for the precise working of a unit with respect to car part. It is used to ajust the fixture if there is any deviation in the design intent during the manufacturing. Mostly the standard shims are used.

Blade:

Blade is plate like part, which connects the parts on the pin unit to the riser. The blade can be either a make part or a standard part based on the design feasibility.

Riser :

It is a part on which all the parts of a unit are mounted. The riser is mounted on the base plate of a tool. The riser can be custom made or standard one can be used.