Week 4:- Pin Unit Design Challenge

CONCEPT OF FIXED PIN UNIT AND RETRACTABLE PIN UNIT

OBJECTIVE:

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

SOFTWARE USED:

CATIA V5

DESIGN PROCEDURE:

FORMULA & CALCULATION:

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

To fix the pin retainer & shim block using a standard screw we need to find the length of the screw using above mentioned formula.

The highlighted surfaces shows in fig are the {distance between surface of the part to first surface of the other part}

Since, the given tap hole is M8 & the distance is 25mm.

Length of the screw=[1.5×8]+25 = 37 = 40mm

Then the standard size of the screw should be 40mm for connecting the pin retainer & the shim blocks for this example.

MATERIAL USED:

In general, the material used for pins, pin retainer, 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 etc.
4. Shim block: STEEL ASTM A-36, NM stainless, STEEL ASTM A-36, SS type 3030 or 304 etc.
5. Blade: STEEL ASTM A-36 etc.
6. Riser: STEEL ASTM A-36 etc.

HARDNESS:

In general the hardness of material for pins, pin retainer ,shims, shims block. Blades & risers are:

55-60 HRC to a depth of 0.5-0.7mm after grinding.

PIN TOLERANCE:

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

PURPOSE OF PIN UNIT:

• As by 3-2-1 locating principle, the introduction of two pins helps to arrest the 6 degrees of freedom (4 axial & 2 radial movements) whereas other 6 degrees of freedom arrested by introducing minimum three supports.
• 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 approximately locating so total constraint by locating pin should be fully constraint at all times to prevent any movement.

FUNDAMENTALS OF PIN UNIT DESIGN:

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

1. Pin should engage 3mm to 5mm from car part entry surface.
2. All pin should be accommodated with 2 way adjustable shims irrespective of direction of arresting.
3. Round pin should be used for 4 ways arresting of car panel only if the hole is round.
4. Round pin should be used for 2 ways arresting of car panel only if the hole is slot.
5. Diamond pin should be used in case of 2 ways arresting of car panel only 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.

Fig. shows the 1^st point in the fundamentals of pin unit design.

Fig. shows the 3^rd point in the fundamentals of pin unit design

FIG. shows the 4^th, 5^th,6^th points in the fundamentals of pin unit design

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 unit in general.
• Pin retainer is used to hold pin firmly.

Fig. 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.

Fig.shows fixed pin unit without car panel.

As per the objective 2 different types of fixed pin units.

(P001_Z01_STD10_01_00) &(P001_Z01_STD10_02_00) with different pins, pin retainers, blade, & risers designed and those fixed pin units CAD model used in this projects are

PICTURES OF FIXED PIN UNIT-1

(P001_Z01_STD10_01_00):

DIFFERENT PARTS OF THE FIXED PIN UNIT:

The different parts of the fixed pin units are as follows,

1. Pin
2. Pin retainer
3. Shims
4. L-block
5. Blade
6. Riser
7. 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 approximately locating pin so total constrained at all times to prevent any movement.
• There are dozens of styles of locating pin that can be utilized in a design. Commonly used pin as shown in below figs.

Locating pins which are used in projects.

1. Pin retainer:

• A pin retainer is a part which holds the pin in position, the pin retainer can eiether be a make part or a standard part also.
• Pin retainer is used to hold the locating pins firmly.

Consideration while designing & manufacturing of pin retainers:

• 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 fined machined surface.
• The pin mounting surface of the pin retainer should have the step to lock the rotation of the pin.
• The pin mounting surface of the pin retainer to the blocks should be machined surface.
• The pin retainer will be fixed to a block or a L-block to the riser with two dowel holes & at least with one screw hole to maintain the tolerance.

• Pin retainers which used in the project.

  1. Shims:
  • In general, a 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 in order 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 which comes with the thickness of 0.1mm, 0.2mm, 0.5mm,1.0mm etc.
  • These will compensate the stack up tolerance which reflects at the mylars.
  • We give tolerances to all parts of the fixture, due to this tolerance the mylars will eiether lift up moves down from its defined position.
  • To adjust the mylars for getting the defined positin we use shims.
  • Shims will be added above the mylar for adjusting according to tolerance.

1. L-Block/ block:

• These parts are mainly used to accommodate the shimming directions as per fundamental in general.
• Also in some cases used for other design feasibility.

Fig. types of L-blocks used in this project

1. RISER:

• Riser is a manufacturing part used to raise/ height the assemblies of fixture.
• One end of the riser will be attached to the base unit while the other end of riser will be attached to the blade.
• It is the part on which all the parts of unit are mounted on the base plate of a tool.
• In general, the riser can eiether be a make part or a standard part.
• Riser can be of two types. They are,

1. L type risers.
2. Square tube risers.

L TYPE RISERS: L type risers are of welded type. Where the stiffner will be added at the centre for support, as shown in the below fig the wedge shaped structure is known as stiffner which is used as a support to withstand load.

SQUARE TUBE RISERS: Square tube risers are of frame type.

1. BLADE:

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

Types of 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 fined machined for the mounting surface with 3 to 5mm step machining.

CONCLUSION:

As per the objective to design 2 different types of fixed pin unit with different pins, risers, blade & block( P001_Z01_STD10_01_00) & (P001_Z01_STD10_02_00) and two different types of Retractable pin unit with different pins, risers, blade, cylinder & block (P001_Z01_STD20_01_00) &(P001_Z01_STD20_02_00) are designed and rendered by using CATIA V5 successfully.