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

                                                                 WEEK 6 : CLAMP UNIT AND PIN UNIT DESIGN

Objective: To design 3 swivel type clamp units and one pin-clamp unit with different clamp arm, blade, riser while maintaining the stroke of the cylinder as 100mm.

Fundamentals: 

3-2-1 Principle: Our ultimate intention for using a pin unit is to fix the workpiece so that it doesn't move or deviate from the position while 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:

•  Translational motion along the x-axis.
• Translational motion along the y-axis.
• Translational motion along the z-axis.
• Rotational motion about x-axis.
• Rotational motion about y-axis.
• Rotational motion about z-axis.

                                              

                                 

Clamp unit:

Clamp unit is the unit designed to clamp/hold the car panel with NC blocks/mylar/ rest by using a pneumatic clamp cylinder and below are different parts of a clamp unit in general. Usually clamp open position is 90deg. Fingers are attached to the clamp mylar.In clamp unit shim to one side is more than enough because it will restrict translational motion in upward and downward direction only. There is another type of clamp unit known as swivel type.

Factors to be considered while designing a clamp unit:

• There should be adequate space between the cylinder and another part like riser, car panel because cylinder moves or swings while opening and closing.
• Pin clamp unit is used where two panels or components are located for welding.
• Clamping is made in such a way that it clamps two car panels at once.
• All parts should snap and butt properly to each other.
• Make sure that parts of the clamping unit are 10 to 12mm away from the car panel so that they do not damage the car panel.
• Avoid any clash. It will not arise at the time of assembly.

Clamp plan:

• The customer provides the clamp plan which consists of the position of the clamp , pins , rest and dump etc.
• It has the exact coordinates of these components and in addition it also has the hole’s dimension and tolerances.
• As this is critical input data, it must not be modified.
• In case the spot for welding and the clamp position is nearby and it may create problems later and there is need to change the position of the clamp, the same must be done so with the permission of the customer as it will be easy for the customer to make changes from his side also

Swivel clamps: The primary components of swivel clamps include clamp arm, blade , cylinder, angle riser, locator block and finger. Swivel clamps shall typically be designed with the center of the clamp cylinder, the center of the locator, and the center of the clamp arm on a common line. However it is acceptable to offset the clamp point from the clamp cylinder to allow for improved access for welding and part load and unload.

The clamp arm shall be welded construction including 20mm thick arm with integral pivot to accommodate a 19.5mm wide swivel. The female portion of the swivel shall always be part of the arm. The male portion of the swivel shall always be part of the blade.

Clamp cylinder:

Nomenclature of cylinder as below:

• CKG1: Series of cylinders.
• B: Clevis width as 19.5mm
• 63: Bore size
• 100: Stroke of cylinder
• Y: End bracket ie double knuckle joint(M6 without tap).

Clamp arm: It is a part to which clamp mylar is mounted and also clamp cylinder is attached to the end of arm with the use of clevis pin. It has two plates 8mm thickness welded and helps in rotating the clamp arm about the pivoting point of balde.

NC block/Mylar:

• NC blocks or popularly also known as mylar are the ones which hold the panel.
• It prevents the panel from deforming while welding.
• They always come in pairs.
• Top mylars is known as clamping mylar and bottom mylar is known as resting mylar

Few points to remember about mylar:

• Generally mylar clamping block clamp cross section( the area which is in contact with the car panel) is considered as 20mm*20mm
• Most of the OEMs/Tier 1 prefer mylar to have 5mm allowance material for machining. Most of the mylar are CNC machined if it is clamping 3D profile.
• Depending on the angle of the cross section, Mylar will be shimming either in one direction or in 2 directions. General thumb rule is if the section is inclined more than 15 deg or clamping surface is 3D profile the directional shimming is provided. The reason being simple mathematics. Equation of inclined line/ plane will have 2 parameters to control and we control with shimming in 2 directions. Less than 15deg does not mean that there are not 2 parameters. These are there but they are neglected if the angle is less than 15 deg.

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 and female.

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

Bush:

Bush is friction type bearing. It is lubricated with grease, oil.It permits relative motion between two mating parts. It is also made of hard material. It is press fitted and after worn out it is replaced with new one instead of replacing other part which save cost.Mostly phosphor bronze or gunmetal material used for making bush.In this unit three bushes are used of same internal(12mm) and external diameter(18mm) but different length.

Pin:

• It locates the car panel.It can either be a make part or a standard part.
• A pin should have a grinding surface on the shaft with fits onto which the pin retainer is fixed.
• The mounting surface of the pin should be a fine machined surface.
• It should have a step machine surface to lock rotation which matches with the pin retainer.
• The mounting surface of the pin retainer to the block should be a machined surface.
• All machined planes should be perpendicular to the axis of the shaft.
• Pin must have a fastening provision like a tapped hole from the bottom or a V groove from the side.
• A pin must be hardened ( heat treatment) (55 to 60 HRC) and black oxide finish in general.
• Material- hardened material like C45, 16MNCR5, EN31 etc.
• Surface finish- black oxide, zinc coating, chrome plating.

SHIM:

• Shims are washers or thin strips of material used to align parts, make them fit or reduce wear.
• Shims are designed to fit in between blocks and fixtures to provide support or reach a dimension required in the assembly.
• Typically designed in a U shape matter so that they can fit between mounting screws . This shape helps to make them easy to install and remove or replace.
• Designers will use shims individually or as packs of 5, 6 or 7 pieces. Thickness ranges from 0.25mm to 2mm.
• Many assemblies require a tolerance to be hit in relation to a length or height; shims allow designers to hit these tolerances. They can be stacked between NAAMS NC blocks, L blocks, or pin retainers.

RISER:

• Riser is a structure generally used to mount the toggle clamp and rest, clamp mylar and location pin and to give height to the assembly.
• It is not necessary to have one riser where all the parts of clamp or rest or location units are mounted.
• Risers can either be a standard part or make part.

CLAMP-PIN UNIT:

CLAMP UNIT TYPE-1:

CLAMP UNIT TYPE 2:

CLAMP UNIT TYPE 3

CONCLUSION: Hence we have designed three different types of clamp units and one Clamp-pin unit.