Week 4:- Pin Unit Design Challenge

DESIGN OF FIX PIN AND RETRACTABLE PIN UNIT

AIM:

To design a different types of fixed pin unit and retractable pin unit with different pin, riser, blade, cylinder and block

INTRODUCTION:

FIXED PIN

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.

The fix pin and the retractable pin units are hole constraining fixtures for car panels.

The parts of fixed pin are:

1. Pin
2. Pin retainer
3. Shim / spacer
4. Block
5. Blade or Adapter plate
6. Riser.

Pins

• Pins are used for accurately locating the part to welded in an assembly.
• The holes in the part of the assembly are inserted on these pins.
• The pins constrain the degrees of freedom of the part of the fixture.
• The diameter of the pins has tighter tolerances as compared to the diameter of the hole in the part.
• The Pin can be either round or diamond-shaped. Generally, diamond-shaped pins are used to avoid over constraint.

Pin Retainer

Pin retainer is used to hold the locating pins. The pin retainer block has two-way shims.

Shims

Shims are small parts of the thickness of 0.1,0.2,0.3 mm. The shims are used to compensate for the difference due to the stack-up tolerance of the assembly, which eventually results in the improper holding of the panel if the Mylar holds it loosely.

Block

Blocks are used to connect the pin retainer with the blade, riser, and cylinders in case of a retractable pin unit. The shims are also attached to the blocks for multiple shimming directions.

Blade

• Blades are plates that are attached to the raiser.
• The cylinders and other additional arms are mounted on a Blade.

Raiser

• A raiser is a part that is used to raise the height of the fixture.
• The raiser is fixed to the base of the fixture and the blade is mounted on the raiser.

RETRACTABLE PIN UNIT:

• Retractable pin unit is opposite to fixed unit which can be moved up and down up to a certain distance.
• It is used for unloading complex panels after welding.

FUNDAMENTALS OF PIN UNIT DESIGN

3-2-1 principle:-

Our ultimate intention for using pin unit IS to fix the work piece so that it does not deviate from the position while the operation is being performed on it For this reason we use 3-2-1 principle.

Every component we know has 6 degrees of freedom they are listed below:

1. Translational motion along x-axis,
2. Translational motion along y-axis.
3. Translational motion along z-axis.
4. Rotational motion along x-axis.
5. Rotational motion along y-axis.
6. Rotational motion along y-axis.

• It is necessary to have two Pins to locate the car panel. One pin will restrict 4 degrees of freedom and the other pin will restrict two degrees of freedom.
• The pin should engage 3-5 mm from the car part entry surface.
• All pins should have two ways adjustable shims.
• The round pin should be used in case of a 4 way arresting of the car part if the hole is round.
• The round pin should be used in case of a 2 way arresting of the car part if the hole is Slot.
• The diamond pin should be used in case of a 4 way arresting of the car part if the hole is Slot.
• The diamond pin should be used in case of a 2 way arresting of the car part if the hole is round.

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

• Pin : C45, EN31, SAE 8620 Steel, etc.
• Pin retainer : Steel / ASTM A-36, SS type 303 or 304, etc.
• 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.
• Shim block : STEEL ASTM A-36, NM Stainless, STEEL ASTM A-36, SS type 303 or 304, etc.
• Blade : STEEL ASTM A-36, etc.
• 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.

PIN TOLERANCE

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

Procedure:

• The car panel for which the fixture is to be designed is imported into the project.

• The Holes and slots are located and the pins are designed as per the diameter of the hole and it is made sure that the axis of the pin and the axis of the hole must be coincident. The pins designed may be Round or diamond-shaped.

• Pin retainers are designed to accommodate the pin and also the shims.

• The blocks are used to provide shimming in multiple directions. They are designed in such a way that shims are mounted for two way adjustments.

• The risers are designed such that all the above parts are mounted on it. The risers are mounted to the base of the fixture.

• The parts that are to be assembled are provided with two dowel holes and a threaded hole.

1. Fixed Pin unit with Round pin and Diamond pin:

The same proceudre is used for the case of Retractable pin units.

The above image shows the Double rod retractable pin and the yellow parts show the retracted position.

Retractable cylinders used:

1. SZKD 63.5 BR3 LINEAR CYLINDER

With dual guide, Flat housing of high-strength aluminium material and mounting areas on three sides, Driven by oval-shaped oblong cylinder Ø 63 mm for thrust and tensile forces of 1400 N, Simultaneously driven guide rods, double-supported in bronze/ graphite bushings, Integrated sensors

2. SZK_30_8_T12(make_TUNKERS):

Pnumatic cylinder in aluminium block design with precision guide of the piston rod,secured against rotating.compact housing made from high strength aluminium with mounting options on several sides.Drive mechanism with circular-section cylinder for thrust forces and extraction forces of approx.350/250N. Total stroke 40mm.Integrated inductive sensing system(T12).

Final Assembly Model:

• Fixed Pint unit:

• Retractable pin unit:

CONCLUSION:

Hence as per the objective the 2 different types of fixed pin unit with different pins, rin retainers , blocks ,blade, amd riser & 2 different types of retratable pin unit with different pins, blocks,blade, and risers are designed and rendered using CATIA V5 R20.