Week 4:- Pin Unit Design Challenge

 DESIGN OF FIXED PIN UNIT AND RETRACTABLE PIN UNIT

DESIGN OF FIXED PIN UNIT

 

Fixed pin Units: -

Fixed pins are used to hold the panels firmly in a fixture assembly, to prevent the car panels from dislocation and mis-alignment on the resting members of the fixture.

Fixed pins assures that the panels are fixed while performing operation on it, without any motion in form of horizontal / vertical sliding from its original position.

A pin unit in which pin’s position is fix, is called Fixed Pin Unit. 

Pin unit is used to lock the rotational position of panel.  Round Pin is used to control panel in two directions while Diamond Pin is used to control panel in one direction.

Application of fixed pin unit

The fixed pin unit is the part of the 3-2-1 principle. It restricts 6 degrees of freedom of the car panel.

<!-- [if !supportLists]-->Ø <!--[endif]-->Principle of Location

In order to study the complete location of a workpiece within a fixture, let us consider a workpiece in air as shown in below figure. The workpiece is assumed to have true and flat faces. In state of freedom, it may move in either of the two opposed directions along three mutually perpendicular axes – XX, YY and ZZ.

These six movements are called the “movements of translation”. Also, the workpiece rotate in either of two opposed directions around each axis, clockwise and anti-clockwise. These movements are called “rotational movements”.

For any body there are total 12 Degrees of Freedom, as shown in above diagram,

<!-- [if !supportLists]-->Ø <!--[endif]-->6 Translational Degrees of Freedom

+X, -X, +Y, -Y, +Z, -Z

<!-- [if !supportLists]-->Ø <!--[endif]-->6 Rotational Degrees of Freedom

<!-- [if !supportLists]-->1.)  <!--[endif]-->Clockwise around X axis (CROT-X)

<!-- [if !supportLists]-->2.)  <!--[endif]-->Anticlockwise around X axis (ACROT-X)

<!-- [if !supportLists]-->3.)  <!--[endif]-->Clockwise around Y axis (CROT-Y)

<!-- [if !supportLists]-->4.)  <!--[endif]-->Anticlockwise around Y axis (ACROT-Y)

<!-- [if !supportLists]-->5.)  <!--[endif]-->Clockwise around Z axis (CROT-2)

<!-- [if !supportLists]-->6.)  <!--[endif]-->Anticlockwise around Z axis (ACROT-2)

We must fix all the 12 Degrees of Freedom in order to locate the workpieces in the fixture.

It is necessary to have 2 pins to locate car panel. one pin must arrest 4 way (4 translational motion) & other must arrest 2 way (2 rotational motion) of a car panel.

• DIFFERENT PARTS OF A FIXED UNIT

The Different parts of a Fixed Unit are shown below: -

1.) Pin.

2.) Pin retainer.

3.) Shims.

4.) Blade.

5.) Riser.

 

PIN

Pin is used to locate the panel in fixture assembly.

Typically, the locating pins are used to locate a body part in a position sufficiently accurate to execute a typical process / operation.

The body part is constrained by a set of appropriately locating pin, which restricts the motion of the panel from its original position.

Few different types of pins are shown below,

<!-- [if !supportLists]-->Ø <!--[endif]-->Bullet-nose dowels have a long, tapered nose. They are similar to bullet-nose pins, explained below, but have a smaller locating shoulder. They are almost always used with a bushing.

<!-- [if !supportLists]-->Ø <!--[endif]-->Cone locator pins can compensate for a moderate amount of misalignment. They are similar to round or diamond locating pins, but have cone-shaped tips.

 

<!-- [if !supportLists]-->Ø <!--[endif]-->Diamond locating pins have four flat, diamond-shaped edges on the head. They are often used with a round pin to provide multi-axis alignment.

PIN RETAINER

 

A pin retainer is a part which holds the pin firmly. The pin retainer can either be custom made or of standard make to suit the pin.

Pin retainer prevents pin from shifting to its position, thus making the panel to restrict from motion.

SHIMS

Shims are used in fixture construction for filling gaps and to compensate for manufacturing tolerances.

They are mainly used for adjusting the clamping points on tools or fixtures e.g. in the automotive or aerospace industry. A clamping point is used to fix one or more components.

The usually rectangular shape and one to three slotted holes allow you to replace the shims at the clamping points without having to turn the screws completely out of the fixture. Loosening the screws is sufficient here to remove sheets or to attach others.

BLADE

 

Blade are the supportive plate attached to the riser of the fixture.

 

 

The Blade supports the components like – L-block, Mylars, Mounting for Pneumatic Cylinders and other tooling attachment as per the requirement.

 

 

 

 

RISER 

Risers are the vertical members of the fixture assembly, which holds the respective tools to perform the operation on the panels.

 

 

 

DESIGN METHODOLOGY OF A FIXED PIN UNIT

 

<!-- [if !supportLists]-->1.) <!--[endif]-->FIXED PIN

<!-- [if !supportLists]-->Ø <!--[endif]-->Its necessary to have two pins to locate the car panel. One pin will restrict 4 degrees of freedom and other pin will restrict two degrees of freedom.

<!-- [if !supportLists]-->Ø <!--[endif]-->The pin should engage 3-5mm from the car part entry surface of the pin hole.

<!-- [if !supportLists]-->Ø <!--[endif]-->All pins should have two ways of shimming to compensate the tolerances.

<!-- [if !supportLists]-->Ø <!--[endif]-->The round pin should be used in case of a 2-way arresting of the car part if the hole entry in the part is round.

<!-- [if !supportLists]-->Ø <!--[endif]-->The diamond pin should be used in case of 4-way arresting of the car part if the hole entry in the part is slot.

<!-- [if !supportLists]-->Ø <!--[endif]-->The diamond pin should be used in case of a 2-way arresting of the car part if the hole entry in the part is round.

 

The two different types of Pin used in the designing of the PIN UNIT is shown in the below diagrams.

• PIN RETAINER

The pin retainer is the part in the fixed pin unit, which accommodates the pin by providing the seat to rest, when the pin entries the entry hole of the part.

The PIN RETAINER is usually a L-shaped block, with a step-down on one of its side, to make the PIN rest on it.

In the PIN, a side cut is made on the extended area of the PIN, which has a smaller thickness (<5>

The cut made on the extended area aligns with the step-down part of the retainer, where the PIN is restricted to rotate on its own axis.

The restricted motion, arrests the PIN from rotation and stabilizes the car part from dislocation.

• 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.

 

 

 

• BLADE 

The plate which connects Riser to the Clamp cylinder is named Blade. This plate plays an important role in building the unit. The plate can be of any shape. But we need to keep in mind that the plate should be as compact as possible.

• RISER 

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.

<!-- [if !supportLists]-->Ø <!--[endif]-->The Two types of Fixed pin Units Designed and modelled are shown in below images 

<!-- [if !supportLists]-->1.) <!--[endif]-->Round Fixed Pin unit design.

<!-- [if !supportLists]-->2.) <!--[endif]-->Square / Diamond shaped Fixed Pin unit design.

ROUND FIXED PIN UNIT DESIGN

SQUARE / DIAMOND SHAPED FIXED PIN UNIT DESIGN

DESIGN METHODOLOGY OF A RETRACTABLE PIN UNIT

<!-- [if !supportLists]-->1.) <!--[endif]-->RETRACTABLE PIN UNIT

<!-- [if !supportLists]-->Ø <!--[endif]-->It’s necessary to have two pins to locate the car panel. One pin will restrict 4 degrees of freedom and other pin will restrict two degrees of freedom.

<!-- [if !supportLists]-->Ø <!--[endif]-->The pin should engage 3-5mm from the car part entry surface of the pin hole.

<!-- [if !supportLists]-->Ø <!--[endif]-->All pins should have two ways of shimming to compensate the tolerances.

<!-- [if !supportLists]-->Ø <!--[endif]-->The  pin should be used in case of a 2-way arresting of the car part if the hole entry in the part is round.

<!-- [if !supportLists]-->Ø <!--[endif]-->The  pin should be used in case of 4-way arresting of the car part if the hole entry in the part is slot.

 

<!-- [if !supportLists]-->Ø <!--[endif]-->The  pin should be used in case of a 2-way arresting of the car part if the hole entry in the part is round.

The Two types of Retractable pin Units Designed and modelled are shown in below images,

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

 

Working of the Retractable cylinder

Double-acting pneumatic cylinders allow for complete control of the piston's movement. The below figure shows how the piston and piston rod move when compressed air enters the cap-end and rod-end ports.

• Positive position (A): The rod is extended from the body.
• Negative position (B): The rod is retracted into the body.

Compressed air enters the cap-end port and pushes the piston forward, extending the piston rod. Air exits the rod-end exhaust port.

To retract the piston rod, compressed air enters the rod-end port, forcing air out of the cap-end exhaust port and forcing the piston to retract.

 

 

<!-- [if !supportLists]-->Ø <!--[endif]-->The Two types of Retractable pin Units Designed and modelled are shown in below images

 

<!-- [if !supportLists]-->1.) <!--[endif]-->Retractable Round Pin unit design.

 

<!-- [if !supportLists]-->2.) <!--[endif]-->Retractable Square / Diamond shaped Pin unit design.

 

RETRACTABLE ROUND PIN UNIT DESIGN

 

 

 

RETRACTABLE SQUARE / DIAMOND SHAPED PIN UNIT DESIGN

 

 

 

FIXTURE UNIT ASSEMBLY

 

Fixed Unit Assembly

 

 

 

Retractable Unit Assembly

ASSEMBLY FILE NAMES (to view in CATIA): - 

1.) FIXED PIN UNIT ASSEMBLY - P001_Z00_ST00_FIXED PIN UNITS ASSY_FPU00

2.) RETRACTABLE PIN UNIT ASSEMBLY - P002_Z00_ST00_RETRACTABLE PIN UNITS ASSY_RPU00