Week 4:- Pin Unit Design Challenge

Pin unit is a unit designed to locate the car panel using 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) & 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 same (in general).

General Points to be considered while designing the pin are as follows.

• The pin tolerance for a geo pin will be of closer tolerance i.e. -0.15mm & for re-spot pin is -0.28mm
• Pin should engage 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 in case of 4 way arresting of car part if the hole is round.
• Round pins can be used for 2 ways arresting of car part only if the hole is slot.
• Diamond pins should be used in case of 2 way arresting of car part if hole is round.
• Diamond pins should be used in case of 4 way arresting of car part if hole is slotted.

There are 2 types of pin units

1) Fixed pin unit: In this type of unit the pin is fixed by means of pin retainer & riser.

2) Retractable pin unit-In this type of unit there is the provision of moving of pin in up-down direction.

The Part of Fixed Pin Units are as follows

1. Locating Pin: - Pins are used to locking the rotational movement of the panel. Generally there two types of Pins, one is Round Pin and another one is a Diamond pin. We use two and three-directional shimming for pins as per the angle of the pin w.r.t. the carline. In some cases, we use a collared pin, when the pin is supposed to support the panel as well. For this kind of pin, we provide 3 ways shimming irrespective of pin angle to the carline. 
2. Pin Retainer: Pin Retainer holds the pin and rotational motion of the pins. Pin Retainers can be standard or manufactured one.
3. Shims: - Shim is a set of thin plates (2 mm, 1mm, 0.5 mm, 0.25mm) that are used to adjust the gap or used for a better fit. Shimming can be of thickness 5mm, 8mm, or 10mm. in case no proper fitting between mylar and Panel due to manufacturing errors then this error can be removed using shims. Shims are placed in the carline position so that gap can be adjusted in the required direction like X, Y, or Z.
4. L Block: - A plate shaped as L is called an L block. This part is used as a connection between mylar and Blade. Generally, L blocks are used to provide shimming. It is not necessary that L blocks are only used for shimming, its uses changes as per the requirements, at some places, it is used just to connect one part to another. Similar to the L block one more block is used which is in the shape of T. So this block is called a T Block.
5. Risers: - The part which is mounted on the base plate and holds a clamp or pin cylinder on it, is called Riser. Riser can be Standard Part or manufactured part; it varies from project to project. A riser can be a Single part or welded part. Standard risers also have various shapes and sizes.

Design Methodology of a Pin Unit

We will start by selecting the New Product and we will name this product by using the Zone Number, Station Number which will make identifying  BIW welding Fixture Easier.
This is usually called as TOOL which will contains all the different types of units such as Pin Unit, Rest Unit, Clamp Unit, Slide Unit, Dump Unit Etc.  which are used in the fixture.

We start by inserting the panel details onto the one more product & renaming it as Component. Inside this new component car panel for which fixture needs to be designed is inserted
Next we start by inserting one more product and renaming it to as a Pin Unit.

Usually Base unit is taken as 01 unit. Pin Unit is taken as 02 Unit and so on.
While designing, We must take care all the holes are in the nominal position. Avoid decimal position points

After Pin unit product is inserted we start inserting the parts inside the Pin Product. We start by designing the pin at the panel hole which will be locked.

Pin
Start with designing of the round pin. We need to take care pin should engage 3 to 5mm before the car panel entry surface. We can also use the standard  Pin Available like NAAMS STANDARD pins etc. This depends on the customer standards.

       


Collared pin is better than the non-collared as it will have adequate resting area.Step Machine surface is provided to lock the pin rotation.The pin should be grinding surface on a shaft with fits on to which the pin retainer will be fitted.The mounting surface of the pin should be a finely machined surface.

The pin should have a step machine 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 a 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: - A pin retainer is a part which holds the pin in position, the pin retainer can either be a make part of a standard part.

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 machined surface.

The pin mounting surface of the pin retainer should have a step to lock the rotation of the pin.

The pin mounting surface of the pin retainer to the blocks should be a machined surface.

The pin retainer will be fixed to a block or an L block to the riser with 2 dowel holes (pins) & at least one screw hole to maintain the tolerance.

            
NAAMS Standard Pin AP033M                 NAAMS Standard Pin APR065M

Shim Packs : -
Shim is generally used to adjust the design to manufacturing deviation.In general, shim is a thin and often tapered or wedged piece of material used to fill small gaps or spaces between objects.

Shims are typically used to support, adjust for better fit, or provide a level surface.Shims may also be used as spacers to fill gaps between parts subject to wear.

Shims are the small parts that come with thicknesses of 0.1mm,0.2mm,0.5mm,1.0mm, etc.which will be combined to form a Shim Pack.These will compensate the stack up a tolerance which reflects at the pins.
       

L Block: -
L Blocks are used to provide bidirectional shimming to the Pin Unit. This is used as a connection between Pin Retainer and Riser.
Sometime we use block shaped T for this purpose. Also called T block.

       

Blade: -
Blade is the part which connects riser to L block.


Riser: -
Riser is a part (make or standard) all the parts are mounted and Riser is connected to the Base Plate using Dowel and Bolts.
If it’s a Retractable Unit Cylinders are mounted on the riser.

Using the same principle we designed the Diamond Fixed unit for the other PLP point on the Panel.

Diamond Pin Unit:-
Diamond pin is used for 2 ways arresting of the lock panel.

The parts of this unit are similar to the one previously designed Fixed Pin Unit.


Retractable Pin Unit :-
In the Retractable Pin Unit  pins are mounted on the Pnuematic Cylinders which enables to move the pin up & down.There are two types of Pin Cylinders 

1.Single Rod Pin Cylinder Unit (Inline Retractable Pin Unit)
2.Double Rod Pin Cylinder Unit( Offset  Retractable Pin Unit)

Single Rod Pin Cylinder Unit (Inline Retractable Pin Unit)

Single Rod Pin Cylinder Unit  consist one Pin cylinder which operates the pin in one direction. In this unit Pin is directly mounted on the cylinder and it is must to have pin and cylinder in line with the hole or slot of the panel. Pin cylinder is controlled in two directions with the help of shimming. Below picture is an example of inline retractable pin cylinder. 

Pin cylinders have various stroke sizes like 30mm, 40mm, 60mm Cylinder. Uses of cylinder depends upon the area and available while building the fixture

Double Rod Pin Cylinder Unit( Offset  Retractable Pin Unit)

Offset Retractable Pin unit consist one Pin cylinder which operates the pin in one direction. In this unit Pin is mounted on the Pin retainer and then pin is controlled in two directions with the help of shimming . In this unit cylinder can be mounted away from the pin. 

These Pin cylinders have various stroke sizes like 30mm,40mm,60mm. Cylinder. Uses of cylinder depends upon the area and available while building the fixture. 

Whether we should go for inline cylinder or offset cylinder, depends upon the requirement and space available in the tool