Week 6:- Clamp Unit & Pin-Clamp Unit Design Challenge

1. Design 3 Different types of Swivel Clamp Unit with Different Riser, Blade and Clamp Arm for the given Car Panel.

2. Design a Pin-Clamp unit for the given Car Panel.

Aim/Introduction/ Objective:

In this challenge we have to Design 3 Different types of Swivel Clamp Unit with Different Riser, Blade and Clamp Arm for the given Car Panel & Design a Pin-Clamp Unit for the given Car Panel with the optimum use of material & space constraint also considering panel thickness as 1 mm for this unit.

Report & theory:

3-2-1 principle achievement:
3-2-1 principle is basis of any fixture design. Holding fixtures used in assembly operations often follow a 3-2-1 locating scheme to position parts. Under this scheme, three locators position a part in a primary plane or direction (e.g., high/low).
(3) minimum: Three locator blocks to establish part plane. Three locators or supports are placed under the work piece. Three locators are usually positioned at primary locating surfaces. This restrict two translation motion i.e. upward & downward & four rotational motion ( i.e. clockwise or anticlockwise). Together tree locators with clamp restrict six degrees of freedom. Below figure shows how (3) minimum in 3-2-1 locating scheme achieved by clamping & resting.
(2) Round locating pin in a round hole that defines location in four directions (4 ways) perpendicular to the plane previously established. This restricts four axial movements

With the four Swivel clamp unit restrict four rotational motion & two translation motion as shown in below figure. With the use of pin unit we restrict four translation motion. Together we restrict 10 degrees of freedom.

Clamp unit: Clamp unit is unit designed to clamp / hold the car panel with NC blocks/ mylar/ rest by using a pneumatic clamp cylinder & below are different parts of a clamp unit in general.

Usually clamp open position is 90°. Fingers are attached to clamp mylar.

In clamp unit shim to one side is more enough because it will restrict translation motion in upward & downward direction only. There is another type of clamp unit knows as swivel type. There is pivot pin around which clamp arm rotate.

Factors should be considered while designing a clamp unit:
• There should be adequate space between the cylinder & another part like riser, car panel because cylinder moves or swing while opening & closing

• Pin clamp unit used where two panel or component are located for welding.

• Clamping make in such way that it clamps two car panels at once

• All parts should snap & butt properly to each other.

• Make sure that parts of the clamping unit are 10 to 12 mm away from car panel so they do not damage car panel

• Avoid any clash. It will not arises issue at assembly.

Below are general parts of swivel clamp unit.

a) Clamp Cylinder: Cylinder designation: In this unit we used Clevis cylinder for clamping designated as CKG_1A_63_100Z 

CKG1: Series of cylinder

A: Clevis width as 16.5 mm.

63: Bore size

100: Stroke of cylinder

Z: End bracket i.e. double knuckle joint (M6 without tap)

b) Clamp arm: It is part to which clamp mylar mounted & also clamp cylinder is attached to the end of arm with the use of clevis pin. 

BROWN COLOR PART IS BUSH

c) Mylar/ NC blocks/ Fingers: These are parts are used to hold panel. They are globally called as Mylar. Top side Mylar is called as clamping Mylar & bottom side is called resting Mylar. Every clamping Mylar should have resting Mylar. It is jaw type. It prevent panel from deforming while welding. It is hardened to increase its wear strength. Following consideration should be taken into account while designing Mylar.
• The clamp & rest Mylar has the same size. It has standard size of 20mm x20mm. 

d) Stopper:
The function of stopper is to restrict motion of clamp arm. It avoids clamp arm to rotate beyond limit. It has two parts male & female.

e) Blade: Blade is part to which all other units are attached for e.g. mylar, stopper, clamp cylinder, riser. Blade is designed according to position of all other parts.

f) Riser: Risers can be of L-type, welded or square tube or frame type.

These are basically manufactured parts are used to give height to assembly.

It is machined at mounted ends only to save cost.

g) Bush: Bush is friction type bearing. It is lubricated with grease, oil.

It permits relative motion between two mating parts. It is made of hard material also its ID & OD are precisely machined or grinded. It press fitted & after worn out it is replaced with new one instead of replacing other part which save cost. Mostly phosphor bronze or gun metal material used for making bush.

In this unit FOUR bushes are used of same internal (12 mm) & external diameter (16 mm) but different length.

h) Shims/spacer: In fixture, we are providing tolerance to each part mostly manufactured. Those tolerances tend to stack up & reflect together. In order to avoid that we use shims so we can easily adjust after assembly so whatever stack up there we will rectify it through shims. Shims come in thickness of 0.1, 0.2, 0.5 etc.
We provide shim to accommodate clamp as well as rest mylar in two direction. Clamp & rest mylar can be adjusted in one direction only i.e. up or down. Also two way shim provided for locating pin to accommodate adjustment.

h) Hardware: These are standard parts. Parts are assembled together with help of washer and bolt. for better assembly should use two dowels and four bolts for riser and blade.

where for bolting one part should have tapping hole and on other part simple hole (1 to 2 mm larger from bolt size.)
Length of the bolt is decided by width of part + (1.5*D) For ex. where L=Length of Bolt D=diameter of bolt to be used Let's, take M13 Bolt L= 25 + (1.5 * 8) L=25+12 L=37 mm. But length of 37mm bolt is not available so we have to select 40mm Bolt. (Additional 2 to 3 for washers).

j) Dowel pins: These are standard part. There are various types of dowel pin like split, parallel, taper, clevis, and spring, grooved. Dowel pins are used to locate part precisely & to restrict movements. For mylar dia. 6 or 8 dowel pins should be used. For blade, shimming block dia.8 dowel pin should be used & for riser base dia. 10 or 12 pins are used.

k) Washer: Standard steel grade A plain normal series washer used.

PIN UNIT WITH CLAMP UNIT

To achieve 3-2-1 principle, all the child parts are placed in proper location using locating pins attached to the clamp unit.

all the locating pins are provided with two way shim adjustments.