Week 4:- Pin Unit Design Challenge

PIN UNIT DESIGN -

OBJECTIVE - 1) Design two different types of fixed pin unit with different pins , pin retainers , blocks , blades , risers .

2) Design two different types of retractable pin unit with different pins , pin retainers , blocks , blades , risers .

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 .

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 .

Below are the parts included in the pin unit -

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 .

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 -

• It is like a plate which connect parts of unit to riser .
• It can be a standard part or make part .

6 . Riser -

• It is a part on which all parts are mounted , this riser is mounted on base plate of tool .
• In general riser is mostly a standard part , but it can be a make part also .

7 . Dowel holes / machined surface -

• All make parts which are assembled together should have 2 dowel holes and atleast 1-6 threaded or free hole .
• It should be fine machined for mountinfg surface with 3-5 mm step machining .

DESIGN METHODOLOGY -

Input - This is the surface body for which we have to prepare the BIW fixture . the thickness of the part is 1mm .

As we can see from above image , we have placed the locating pins in the two circular holes . one pin is circular which will arrest the 4 translational motion of the workpiece and other pin is diamond pin which will arrest 2 rotational motion of the workpiece .

1) Fixed pin unit -

• We have designed two fixed pin units . these units consist of pin,pin retainer , block , blade , riser , shimpacks .
• As we know all the parts should have atleat two dowel hole and one screw hole , this will ensure in good assembly of parts .
• we have given shimming in two directions .

• From the images below we can see see how the fixed pin units are locating the surface body of the workpiece .

2) Retractable pin unit -

• We have designed two retractable pin units . one is for single rod cylinder and other is for dual rod cylinder.
• These units consist of pin , pin retainer , block , blade , riser , cylinder , shimpack .

• From the below images we can see the open and close position of the rods in the retractable pin units .
• In retractable pin unit 1 , the circular pin is directly mounted on the rod of the cylinder , and by the actuating motion of the cylinder the rod will retract up and down .
• In retractable pin unit 2 , the diamond pin along with the pin retainer , block and blade is mounted to the two rods of cylinder . by the actuating motion of the cylinder the rod will move up and down .

• As we see from below images , both the retractable pin units are in open position .
• In this open position these units will locate the workpiece .

• As we can see from below images , both the retractable pin units are in closed positions .
• They will not locate the workpiece in this position .

CONCLUSION -

So we have designed two types of pin fixed pin units and retractable pin units that will locate the workpiece properly .