Week 4:- Pin Unit Design Challenge

Pin Unit Design

OBJECTIVE:

To design the pin units for the given component in both fixed and retractable types and to understand the designing procedures, fundamentals and standards for a pin unit of the BIW fixture design using CATIA V5.

INTRODUCTION:

• Pin unit is a unit designed to locate car panels using pins.
• It consists of riser, blade, block, pin retainer, pin, shims or spacers and cylinders(incase of retractable pin unit).
• Pin unit is a part of the 3-2-1 locating principle of fixture design.
• It restricts 6 degrees of freedom of the part.

Fundamentals of pin unit design:

It is necessary to have 2 pins to locate a car panel where one pin must arrest 4 way(translational) movement and the another one must arrest 2 way(rotational) movement of a car panel.

The axis of the car panel hole and the axis of the pin should be same in general.

The pin tolerance for a geo pin will be of closer tolerence of -0.15mm & for the re-spot pin is -0.28mm.

• Pin should engage at 3 to 5 mm from car panel entry surface.
• All pins should be accommodated with 2-way adjustable shims irrespective of direction of arresting.
• Round pins should be used incase of 4way arresting of car part if the hole is round.
• Round pins can be used for 2 way arresting of car parts only if the hole is slotted.
• Diamond pins should be used for 2 way arrresting of car part if the hole is round.
• Diamond pins should be used incase of 4 way arresting of car parts if the hole is slotted.

Various parts of the pin unit:

Pin:

• Pin is the part which locates the car panel. It can be a make part or standard part.
• It should be grinding surface on shaft with fits onto which the the pin retainer will be fitted.
• The mounting surface of the pin should be fine machined surface.
• The pin should have a step machined 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 (Heat treatment) & black oxide finished in general

Pin retainer:

• The pin retainer is a part which holds the pin in position, it can either be a make part or standard part.
• Pin retainer should have a hole with a fit, onto 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 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) & atleast with 1 screw hole to maintain the tolerance.

Block:

• Block is used to provide a 2 directional adjustment of pins with the help of shims.
• L-Blocks are most commonly used in general

Shims/Spacers:

• Shims/Spacers are standard parts which are used for adjustments of locators (NC Blocks & Pin retainers) to get precise location of a pin with respect to car part.
• It helps to compensate for deviation in manufacturing processes.

Blade/Riser Block:

• Blade is a plate, which is used to mount assembly of pin, pin retainer & block on a riser.
• The blade can be either a designed part or a standard part.

Riser:

• It is a part on which all the parts are mounted and it is mounted on the base plate of the fixture.

Dowel holes & machined surface:

• All make parts which are to be assembled should be designed with 2 dowel holes & atleast 1 to 6 threaded/free hole (depends on size). It is to be fine machined for the mounting surface with 3 to 5mm step machining.

1. Design of two different types of Fixed Pin Units with Round and Diamond pins

2. Design of two different types of Retractable Pin Units with single and double rod mechanism:

Single rod Retractable pin unit Double rod Retractable pin unit