Challenge

Week 5:- Rest Unit & Clamp Unit Design Challenge

SSomashekar B16 Nov 2023

DESIGN OF REST UNIT AND CLAMP UNIT

Q.1)

DESIGN OF REST UNIT

Rest Unit

Rest Unit is a support unit, which is used to rest the panels / plates on it, to perform the desired operations.

The Rest Unit has a Resting area which is a size specific custom built to rest the panels / plates at the dedicated points.

Because of the simplicity the rest unit is combined with other unit to reduce the cost of the overall project.

It can be combined with clamp unit to clamp as well as to rest the car panel. It can be combined with locating unit to locate as well as to rest the car panel. Also locating, clamping & Test unit can be combined together in one unit to reduce cost.

Ø Major parts of Rest Unit

The major parts of rest unit are as follows,

1. NC block/mylars.

2. Risers.

3. Blades.

4. shims.

NC BLOCK / MYLARS

MYLAR is one kind of block that touches the panel and holds or clamps the panel.

Mylars are always designed in CAR LINE. Mylar is also called NC (Numerically Controlled) Block. Mylars are mounted on any block or plate with Shimming, so that height of mylar can be adjusted accordingly at the assembly level.

For ‘A’ class surfaces Nylon mylars are used. So that surface can be saved from scratches.

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.

The Riser is shown in the above diagram by oval circle in green color.

BLADES

The plate which connects Riser to the Clamp cylinder is named as 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.

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.

There are three types of shimming. These are one-way, two-way, and three-way shimming.

Number of shimming depends upon the NC cut angle and PIN angle with the car line.

v If NC cut is less than 15 deg. then mylar will have one-way shimming.

v If NC cut is more than 15 deg. in one direction then mylar will have a 2-way direction shimming

v If NC has more than 15 deg. angle in two directions then mylar will have 3-way directional shimming.

Designed Rest unit

REST UNIT-1

REST UNIT-2

ASSEMBLED VIEW OF REST UNIT-1 AND REST UNIT-2

Q.2)

DESIGN OF CLAMP UNIT

A Clamp Unit is used to lock the panel position in transitional direction. It supports the panel with fixed Mylar and lock its movement with mobile Mylar, when panels come onto the tool then clamp is in open condition once panel sits down then clamp closes and joining process is done.

Once the joining process gets completed, then the cylinder arm opens. Complexity of the unit depends upon the gun reachability and panel area. Given below picture is just an example of a simple clamp unit.

The Functional requirement of Clamp unit should satisfy the below condition : -

Ø 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,

Ø 6 Translational Degrees of Freedom

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

Ø 6 Rotational Degrees of Freedom

1.) Clockwise around X axis (CROT-X)

2.) Anticlockwise around X axis (ACROT-X)

3.) Clockwise around Y axis (CROT-Y)

4.) Anticlockwise around Y axis (ACROT-Y)

5.) Clockwise around Z axis (CROT-2)

6.) 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.

MAJOR PARTS OF A CLAMP UNIT

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

2.) Clamp Arm.

3.) Shims.

4.) Blade.

5.) Riser.

CLAMP ARM

The Clamp Arm is a part of the Power Cylinder (Pneumatic operated), which is used to clamp the panel / surface part on which operations are performed.

The Clamp arm supports the extension arm, which has the Mylar Block, acting as the Upper Clamping device to hold the panel.

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.