Week 4:- Pin Unit Design Challenge

OBJECTIVE:

To design 2 different types of fixed pin unit with different pins, riser, blade & block and 2 different types of retractable pin unit with different pins, riser, blade, cylinder & block.

INTRODUCTION :

• Pin unit is a unit designed to locate car panels using pins.
• Components that consist of the unit are :

1. PIN
2. PIN RETAINER
3. SHIMS
4. BLOCKS
5. BLADE
6. RISER
7. CYLINDERS

• Pin unit is a part of the 3-2-1 locating principle of fixture design.
• It restricts 6 degrees of freedom of the part.

SOFTWARE USED:

CATIA V5

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} 

• To fix the pin retainer & the shim block using a 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 is M8 & the distance is 25mm as shownin 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.

MATERIALS USED:

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

1. Pin : C45, EN31, SAE 8620 Steel, etc. 
2. Pin retainer : Steel / ASTM A-36, SS type 303 or 304, etc.
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, etc.
5. Blade : STEEL ASTM A-36, etc.
6. Riser :  STEEL ASTM A-36, etc.

HARDNESS:

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

•  55 - 60 HRC / 58 - 62 HRC to a depth of 0.5 - 0.7 mm after grinding.

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

PIN TOLERANCE:

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

PURPOSE OF PIN UNIT:

• As by 3-2-1 locating principle, the intoduction of two pins helps to arrest the 6 degrees of freedom (4 axial & 2 radial movements) whereas other 6 degrees of freedom are arrested by introducting minimum 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 anymovement.

           Figure 3. 3-2-1 Principle concept (Arresting 6 DOF by introducing 2 pins)

FUNDAMENTALS OF PIN UNIT DESIGN:  

It is necessary to have two pins to locate a car panel. And here one pin must arrest 4 way (i.e 4 translation) & other must have arrest 2 way (i.e 2 rotational) of a car panel.

1. Pin should engage 3 to 5mm from car part entry surface.
2. All pin should be accomodated with 2 way adjustable shims irrespective of direction of arresting.
3. Round pin should be used in case of 4 way arresting of carpanel if the hole is round.
4. Round pin can be used for 2 way arresting of car panel only if the hole is slot.
5. Diamond pin should be used in case of 2 way arresting of car panel  if the hole is round.
6. Diamond pin should be used in case of 4 way arresting of car part if the hole is slotted.
7.  The axis of the car panel hole & the axis of the pin should be same in general.

TYPES OF PIN UNITS:

The types of pin units are: Fixed pin unit & Retractable pin unit.

FIXED PIN UNIT:

• Fixed pin unit is a unit designed to locate the car panel using pins.
• Pin, pin retainer, shims, blocks, blade, riser are the part of fixed pin units in general .
• pin retainer is used to hold the pin firmly. 

          Figure 7. Shows the Principle Locating Point (PLP) in fixed pin unit.

  Principle locating points is a hole in which we locate the panels. PLP holes must be very much precise. 

                                           Figure 8. Fixed pin unit with panel.

                            Figure 9. Fixed pin unit with panel (Side view).

                            Figure 10. Fixed pin unit without panel.

As per the objective the 2 different types of fixed pin units (P00_ST01_Z10_01_00) & (P00_ST01_Z10_02_00) with different  Pins, Pin retainer, Blades & risers are designed and those fixed pin units CAD model used in this projects are shown below in the form of picture.

PICTURES OF FIXED PIN UNIT - 1 (P00_ST01_Z10_01_00):

  Figure 12. Before & after rendering of fixed pin unit - 1 (P00_ST01_Z10_01_00).

RETRACTABLE PIN UNIT:

• A retractable pin unit is a unit designed to locate the car panel using pins, but the entire pin package parts will be mounted on the retractable pneumatic cylinder.
• Pin, shims, L Block, pneumatic retractable cylinder, riser are the parts of retractable pin unit. 

TYPICAL PARTS OF PIN UNIT: The different parts of the fixed pin units are as follows,

1. Pin. 
2. Pin retainer.
3. Shims.
4. L-block/shim block.
5. Blade.
6. Riser.

a. Pin:

• It is used for the location purpose of the panel.
• 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 anymovement.
• There are dozens of styles of locating pins that can be utilized in a design. 
• A pin can either be a make part or a standard part also. Below I have shown the commonly used pins.

  One of the most common pins is a stepped pin with either small or large head.

  

                                  Figure 24. Types of locating pin

    Figure 25. NAAMS standard locating pin (6 way small head) - Make: MISUMI 

Consideration while designing & manufacturing of pins:

• Pin should have grinding surface on shaft with fits on to which the pin retainers will be fitted.
• The mounting surface of the pin should be a fine machined surface.
• A 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 machined surface.
• All machined planes should be perpendicular to the axis of pin shat.
• Pin must have a fastening provision like tapped hole from the bottom or a v- grove from the side.
• A pin must be hardend ( 55 - 60 HRC) & black oxide finish in general.

        Figure 35. NAAMS standard riser.

         Figure 36. CAD model of different types of make riser used in this project.

f. Blade:

• Blade is a part like a plate,which connects the parts of a unit to a riser. In general, the blade can either be make part or a standard part.
• Blade are the plates which are attached to raiser.
• Blade is also attached or mounted with cylinders,arms etc.,

  Figure 37. CAD model of different types of make blade/adapter used in this project.

Dowel holes & machined surfaces in pin unit:

All make parts which are to be assembled with tolerance should be designed with 2 dowel holes & at least of 1 to 6 threaded or free hole (depends on size). And to be fine machined for the mounting surface with 3 to 5mm step machining (SURFACES TO BE FLAT, PARALLEL &
PERPENDICULAR TO O WITHIN 0.015 T.I.R).

BOUGHT OUTS:

Bought outs used in this projects to design a pin unit are,

1. Cylinders.
2. Fasteners.                 

 Figure 38. Pneumatic cylinder - Std: SZK_30_8_T12 (Make : Tunkers)