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

Objective:

1. To design 3 Different types of Swivel Clamp Unit with Different Riser, Blade, and Clamp Arm for the given Car Panel and to maintain the stroke as 100mm.

2. To design a Pin-Clamp Unit for the given car panel.

Priciple of Locating Fixture:

3-2-1 Principle:

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).

A workpiece free in space can move in an infinite number of directions.For analysis,this motion can be broken down into twelve directional movements or "degres of freedom". All twelve degrees of freedom must be restricted to ensure proper referencing of workpiece.

The best and most effective method of part location is reffered to as the 3-2-1 method.

6 Translational degeers of freedom : +x,-x,+y,-y,+z,-z.

6 rotational degrees of freedom:

1. C-ROT around X - axis
2. AC-ROT around X - axis
3. C-ROT around Y - axis
4. AC-ROT around Y - axis
5. C-ROT around Z - axis
6. AC-ROT around Z - axis

If we fix the clamps as per the 12 degrees of freedom listed above,then we can arrest the panel in a fixed position.

6- degrees of fredom are restricted by 2- pin units.

6- degrees of freedom are restricted by 3-clamp units and rest units.

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 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:

1. Clamp Cylinder:

Cylinder designation:

In this unit we used Clevis cylinder for clamping designated as CKG_1B_63_100Y

Nomenclature of cylinder as belows:

CKG1: Series of cylinder

B: Clevis width as 19.5 mm.

63: Bore size

100: Stroke of cylinder

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

2. 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. It has two plates of 8 mm thickness welded & helps in rotating of clamp arm about pivoting point of blade.

• The distance between cylinder rod hole & pivoting hole should be 50 mm as shown in figure. This is necessary because cylinder stroke 100 mm must be achieved when it is at 90° open position & clamp arm mounting hole must be in line with cylinder rod axis as shown in below figure
• Sharpe edges must be removed. Chamfer or fillet always provided for aesthetic & safety purpose.

Below figure shows 100 mm stroke achieved & clamp arm end in line with cylinder rod. See Y & Z values.

3. 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. It has flat surface or sometimes its profile follow contour of car panel. As described in below figures.

• Clamp & rest mylar have two dowel holes of dia.6 & one M8 tapping hole. Also clamp mylar have same mounting hole pattern as like clamp arm. Also minimum centre distance between holes should be 15 mm. & reference dimension should be 8 or 10 mm. as described in below figure.

• Minimum distance between clamp mylar mounting face & car panel should be more than 5 mm

4. 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.

5. 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.

6. 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.

7. 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 three bushes are used of same internal (12 mm) & external diameter (18 mm) but different length.

8. Shims :

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.

There are images of 3 different Swivel Clamp Units:

P001_Z03_ST010_04_00_SWIVEL_CLAMP_UNIT

Image with opening position:

P001_Z03_ST010_05_00_SWIVEL_CLAMP_UNIT

Image with opening postion:

P001_Z03_ST010_06_00_SWIVEL_CLAMP_UNIT:

Image with opening position:

P001_Z03_ST010_07_00_PIN_CLAMP_UNIT:

PIN:

RETAINER:

L_BLOCK:

BLADE:

Image with opening position:

Final Design Of Fixture:

Structuring a design tree:

Structuring a design tree implies process where all the assemblies & parts are named in specific manner. Different customers have different set of standard like how to structure a design tree. So they will be give standard template based on that design tree structured, which helps us to identify specific part of assembly.

It specifies the Project number, station number, unit number; part number of each component so that it is easy to identify the parts.

It is an important process which helps us to identify a specific part or assembly as to which project, tool or unit, it belongs to. This helps us to avoid error during design study, manufacturing, assembly, inspection etc.

If parts or assemblies are not named properly or the design tree is not structured properly, it will create confusion to understand & create major possibilities of making an error. Naming of a fixture, a unit or a part gives the information as to which project or zone or assembly they do belong.

It can help us to identify quantity of items of same type or different types that are being used in assembly for e.g. bolt. It actually tells you how many bolts are particularly required in that assembly or unit.

Factors should consider while designing ClAMP UNIT

• Should use standard part as possible i.e.NAAMS standard.
• There should be adequate space between cylinder and other parts like riser,car panel.Because cylinder moves or swing while opening and closing.
• Pin clamp unit is use where two panel or component are located and clamp for welding.
• clamp make in such a way that it it clamp two car panel at once.
• every clamp mylar/NC blocks should have rest mylar or unit.
• clamp unit has shims in only one direction .
• ALL parts should snap and butt properly to eachother .
• Make sure that parts of clamp unit are 10 -12 mm away from the car panel.
• Design tree should structured in way that make part on the top and followed standard part.
• The position of clevies joint pin will be in one line.
• Avoid any clash , It will not rise issue at assembly.
• product should designed in such a way that it will easy to make ,assemble and quality check.
• we should preferably use quick acting clamps.The clamping method must not damage our work piece.
• clamp should open in such a way that clamp arm moves away from the operator.
• There must be adequate clearence for loading and unloading .so that the process becomes fast and easy.The variation in size must be accepted.
• Avoid sharp edges and corner ,they can harm operator and cause to the serious injury .provide chamfer or fillet to the corner.