Week 4:- Pin Unit Design Challenge
Objective : To design 2 different types of fix pin unit and retractable pin unit.
Introduction :
Pin unit is a unit designed to locate a car panel using pins.
It is necessary to have 2 pin units to locate a car panel. And here one pin must arrest 4 way (4 translational) and other must arrest 2 way and other must arrest 2 way (i.e. 2 rotational) of a car panel.
Fundamentals of pin unit design :
- Pin should engage 3-4 mm from car part entry surface.
- All pin should be accomodated 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 should be used for 2 way arresting of car part only if the hole is slot.
- Diamond pins should be used for 2 way arresting of car part if the hole is round.
- Diamond pins should be used for 4 way arresting of car part if the hole is slotted.
- The axis of car panel hole and axis of pin should be the same.
- The pin tolerance for a geo pin will be of closer tolerance i.e. -0.15mm and for respot pin is -0.28mm.
Image explains point no. 1
Image explains point no. 4,5,6
Pin unit are of 2 types :
1. Fixed pin unit
2. Retractable pin unit
1. Fixed Pin unit :
A fixed pin unit usually consists of
1. Pin
2. Pin retainer
3. Shim / spacer
4. Block
5. Blade or Adaptor plate
6. Riser
Image : Fixed pin unit and its parts
1. Pin :
A part which locates the car panel. A pin can either be a make part or a standard part also.
Pin should have 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.
The mounting surface of the pin retainer to the blocks should be a machined surface.
All machined planes should be perpendicular to the axis of the pin shaft.
A pin must have a fastening provision like tapped hole from the bottom or V-groove from the side.
A pin must be hardened (Heat treatment) and black oxide finished in general.
Image : Pin
2. Pin retainer :
A pin retainer is a part which holds the pin in position, the pin retainer can be a make part or a stand part also.
Pin retainer should have a hole with a fit, on to which the pin will be fixed.
The pin mounting surface of the pin retainer should be a fine machined surface.
The pin mounting surface of the pin retainer should have a step to lock the rotation of the pin.
The mounting 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) and atleast with one screw hole to maintain the tolerance.
Image : Pin retainer
3. Block or L-block :
These parts are mainly used to accomodate the shimming directions as per fundamental in general. Also in some cases used for other design feasibility.
Image : L-Block
4. Shims / spacers :
Shims and spacers are some standard parts in general, which are used for adjustments of locators (NC Blocks and Pin retainers) for obtaining the desired values for the precise working of a unit with respect to car part. In general to adjust the design to manufacturing deviation.
Shims are the small parts which comes with the thickness of 0.1mm, 0.2mm, 0.5mm, 1mm etc. upto 5mm thickness.
Image : Shims pack
5. Blade :
Blade is part like a plate, which connects the parts of a unit to a riser. In general the blade can be either a make part or a standard part.
Image : Blade
6. Riser :
Riser is a part on which all the parts of a unit are mounted, and is mounted on the base plate of a tool. In general a riser can either be make part or standard part.
Image : Riser
7. Dowel holes and machined parts :
All make parts which are to be assembled with tolerance should be designed with 2 dowel holes and atleast of 1-6 threaded / free hole (depends on size). And to be fine machined for the mounting surface with 3 to 5 mm step machining.
Length of the screw = 1.5x(std hole size) + distance between surface of the part to the surface of the next part = (1.5x8)+25 = 37 = 40mm Allen screw cap.
2. Retractable pin unit :
A retractable pin unit is a unit designed to locate the car panel using pins, but the entire package parts will be mounted on the retractable pneumatic cylinder.
Image : Retractable pin units
Retractable pneumatic cylinder consists of 2 types : single rod mechanism cylinder and double rod mechanism cylinder.
Image : Single rod mechanism cylinder
Image : Double rod mechanism cylinder
The fixed pin units and retractable pin units are designed using the above parts as shown in the images below.
Conclusion : Therefore, as per the objective 2 fixed pin units and 2 retractable pin units are designed to perform the necessary operation on BIW sheetmetal parts.