Week 4:- Pin Unit Design Challenge

Design 2 different types of Fix pin unit & Retractable pin unit.

• pin unit is a unit designed to locate the car panel using a pin.
• Pin unit consists of the riser, blade, block, shims or spacer, pin retainer & pin.
• pin unit is the 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 & here one pin must arrest 4 ways (4 translational) & the other must arrest 2 ways (i.e. 2 rotational) of a car panel.
* The axis of the car panel hole & the axis of the pin should be the same (in general)
* The pin tolerance for a geo pin will be of closer tolerance i.e. -0.15mm & for the re-spot pin is -0.28mm

1)Pin should engage 3 to 5 mm from the car panel entry surface.
2) All pins should be accommodated with 2 way adjustable shims irrespective of the direction of arresting.
3)Round pins should be used in case of 4 way arresting of the car part if the hole is round.
4) Round pins can be used for 2 way arresting of car parts only if the hole is slot.
5)Diamond pins should be used in case of 2 way arresting of car part if a hole is round
6)Diamond pins should be used in case of 4 way arresting of car parts if the hole is slotted.

It can be divided into the following 2 types

1) Fixed pin unit- In this type of unit, the pin is fixed by means of a pin retainer & riser.
2) Retractable pin unit- In this type of unit, there is the provision of moving of pin in the up-down direction.

-Following are the requirements that need to be taken into account while designing the parts

1 PIN- Pin is the part that locates the car panel. It can be a make part of standard part.

a) Pin should be grinding surface on the shaft with fits on to which the pin retainer will be fitted.
b) The mounting surface of the pin should be a finely machined surface.
c) The pin should have a step machine surface to lock the rotation, which matches with the pin retainer.
d) All machined planes should be perpendicular to the axis of the pin shaft.
e) Pin must have a provision like a tapped hole from the bottom or a v-groove from the side.
f) A pin must be hardened (Heat treatment) & black oxide finished in general.
- Typically, locating pins are used for controlled, fine tolerance positioning of a workpiece. For example, a pallet that is moved along one axis, where the drive
mechanism is not accurate and stable enough to place it in a position sufficiently accurate to execute a particular process, the use of locating pins may be the
best solution.

The Diamond Shape is a critical feature that helps with machining inaccuracies and smoother locating operation. When two round head pins are installed onto
one plate, the distance between two mounting holes must be extremely precise and even then, the work piece will not be placed on the base as easily as it
would with the use of a diamond shape pin.

2 Pin Retainer- A pin retainer is a part that hold the pin in position, the pin retainer can either be a make part of a standard
part.

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

3 Block/L Block-

These parts are mainly used to accommodate the shimming directions as per fundamental in general. Also in some cases used
for other design feasibility.

4 Shims/Spacers-

Shims & Spacers are some standard parts in general, which are used for adjustments of locators(NC Blocks & pin retainers) for
desired values for the precise working of a unit with respect to car part. In general to adjust the design to manufacturing
deviation.

5 Blade- Blade is part like a plate, which connects the parts on a unit to a riser. In general, the blade can be either a make part or
a standard part.

6 Riser- It is a part on which all the parts of a unit are mounted & is mounted on the base plate of a tool.

7 Dowel holes & machined surface- All make parts that are to be assembled should be designed with 2 dowel holes & at least 1 to 6 threaded/ free
hole(depends on size) 7 to be finely machined for the mounting surface with 3 to 5 mm step machining.
Designed fixed pin units.

FINAL LOOK PART