Week 4:- Pin Unit Design Challenge

INTRODUCTION -

Fundamentals of pin unit design:

It is necessary to locate car panel with two pins . one pin to restrict 4 way motion (4 translational ) and one pin to restrict 2 way motion (2 rotational ) .

• Pin should engage 3-5 mm from car panel entry surface .
• All pins should be accomodated with 2 way adjustable shims irrespective of direction of aresting .
• Round pin should be used in arresting 4 way in car panel if the hole is round .
• Round pin should be used in arresting 2 way in car panel if the hole is slot .
• Diamond pin should be used in arresting 4 way in car panel if the hole is slot .
• Diamond pin should be used in arresting 2 way in car panel if the hole is round .
• The axis of the car panel hole and the axis of the pin should be same (in general ) .
• The pin tolerance for geo pin will be -0.15 mm and for respot pin will be -0.28 mm

MATERIALS USED:

In general, the materials used for pins, pin retainers, shims, shim block, blades & risers are:

1. Pin: C45, EN31, SAE 8620 Steel,
2. Pin retainer : Steel / ASTM A-36, SS type 303 or 304,
3. Shims/spacer: S.A.E. 1010 CRS FULL HARD, COLD ROLLED STRIP STEEL S.A.E. 1010 FULL HARD, S.A.E. 1020 HRS, etc.
4. Shim block : STEEL ASTM A-36, NM Stainless, STEEL ASTM A-36, SS type 303 or 304,
5. Blade : STEEL ASTM A-36,
6. Riser : STEEL ASTM A-36.

SURFACE FINISH:

In general, the hardness of the materials for pins, pin retainers, shims, shim block, blades & risers are:

1. Pin: Chrome plating, Zinc coating, Pins with TiN codes shall have 1 to 2 microns of nitride added to
2. Pin retainer: BLACK OXIDE FINISH, No black oxide finish for "SS TYPE" components (SURFACES TO BE FLAT, PARALLEL &

PERPENDICULAR TO O WITHIN 0.015 T.I.R).

1. Shims/spacer: BLACK OXIDE FINISH (SURFACES TO BE FLAT AND PARALLEL TO WITHIN 0.015 mm T.I.R).
2. Riser: SURFACES TO BE FLAT, PARALLEL & PERPENDICULAR TO WITHIN 0.015 T.I.R.

PIN TOLERANCE:

The pin tolerance for a geo pin will be of closer tolerance i.e -0.15mm & for respot, the pin is -0.28mm.

PURPOSE OF PIN UNIT:

• As by the 3-2-1 locating principle, the introduction of two pins helps to arrest the 6 degrees of freedom (4 axial & 2 radial movements) whereas the other 6 degrees of freedom are arrested by introducing a minimum of three supports.
• Typically, the locating pins are used to locate a body part in a position sufficiently accurate to execute a welding process.
• The body part is constrained by a set of appropriately locating pin so total constraint by locating pin should be fully constrained at all times to prevent any movement.

There are two types of pin units -

1)Fixed pin unit -

Fixed pin unit is a unit designed to locate the car panel using pins .

2)Retractable pin unit -

A retractable pin unit is designed to locate the car panel using pins , but the entire pin package is mounted in the retractable cylinder . the cylinder will move the unit up and down .

FORMULA & CALCULATION:

Formula to calculate the length of the screw,

Length of the screw = [1.5 X (std. hole size)] + {distance between the surface of the part to the first surface of the other part

Length calculation for the length of the screw.

• To fix the pin retainer & the shim block using standard screws we need to find the length of the screw using the above-mentioned formula.
• The highlighted surfaces shown in the figure are the {distance between the surface of the part to the first surface of the other part}
• Since the given tap holes are M8 & the distance is 25mm as shown in the figure then,
• Length of the screw = [1.5 X (std. hole size)] + {distance between the surface of the part to the first surface of the other part} Length of the screw = [1.5 X 8] + 25 = 37 = 40mm Allen cap screw
• Then the standard size of the screw should be 40mm for connecting the pin retainer & the shim blocks for this example.

1 . Pin

• It locates the car panel . it can either be a make part or a standard part .
• A pin should have a grinding surface on shaft with fits onto which the pin retainer is fixed .
• The mounting surface of pin should be fine machined surface .
• It should have step machine surface to lock rotation which matches with pin retainer .
• The mounting surface of pin retainer to the block should be machined surface .
• All machined planes should be perpendicular to the axis of shaft .
• Pin must have fastening provision like tapped hole from bottom or a V groove from side .
• A pin must be hardened ( heat treatment ) (55 to 60 HRC) and black oxide finished in general .
• Material - Hardened material like C45 , 16MNCR5 , 20MNCR5 , EN31 etc .
• Surface finish - black oxide , Zinc coating , Chrome plating .

Typically, locating pins are used for controlled, fine tolerance positioning of a, 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 When two round headpins are installed onto one plate, the distance between two mounting holes must be extremely precise and even then, the workpiece will not be placed on the base as easily as it would with the use of a diamond shape pin.

There are several styles of Pin Head They serve different purposes and can be utilized in a variety of applications.

2 . Pin retainer

• It is a part which holds the pin in position , it can either be a make or a standard part .
• It should have a hole with a fit onto which pin is fixed .
• The pin mounting surface should be fine machined .
• It should have a step to lock rotation of pin .
• The mounting surface of pin retainer to block should be machined surface .
• The pin retainer will be fixed to block or a L block to riser with 2 dowel holes (pins) and atleast one screw hole to maintain tolerance .

3 . Blocks/ L blocks

• These parts are used to accomodate the shimming direction as per fundamental in general, also in some cases used for other design feasibility

4 . Shims/ spacer

• It is a standard part in general , which are used for adjustment of locator ( NC block and Pin retainer ) for obtaining the desired value for precise working of unit wrt car part .

5. Blade

• A blade is part like a plate, which connects the parts on a unit to an 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 which are to be assembled should be designed with 2 dowel holes & at least of 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.

INPUT:

1. Design 2 Different types of Fixed Pin Unit with Different Pins, Riser, Blade, and Block.

2. Design 2 Different types of Retractable Pin Unit with Different Pins, Riser, Blade, Cylinder, and Block.

THE YELLOW COLOUR PARTS SHOWS THE RETRACTABLE POSITION

FIXED PIN UNIT

RETRACTABLE PIN UNIT WITH SINGLE ROD AND MULTI ROD

THE LINKED RAR FELS IS THE CADPART FILE AND THE MAIN CADPART IS NAMED AS(S001_Z01_ST010_00_00(PROJECT))