Week 6:- Clamp Unit & Pin-Clamp Unit Design Challenge
Week 6:- Clamp Unit & Pin-Clamp Unit Design Challenge
OBJECTIVE: To design 3 types of Swivel Clamp units and 1 Pin-Clamp unit with different Riser, Blade, and Clamp arms while maintaining the stroke of the cylinder as 100mm.
INPUT
FUNDAMENTALS:
3-2-1 principle: Our ultimate intention for using a pin unit is to fix the workpiece so that it does not deviate from the position while the operation is being performed. For this reason, we use the 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 along the x-axis.
- Rotational motion along the y-axis.
- Rotational motion along the y-axis.
FIG. DEGREE OF FREEDOM
Degrees of freedom can be simply understood as the direction in which any component can move. These 6 degrees become 12 if we consider translation along negative and rotation in an anti-clockwise direction too. That means every component can move in all directions when it is free. But processes like welding, stamping, or others and every other cannot be carried out on such free-to-move the body for obvious reasons. Thus the body must be constrained in all the major directions for the workman to work upon it. This constraint on motion is achieved by the 3-2-1 principle.
In the 3-2-1 principle, we make use of locating pins in the given order to fix it on a fixture:
3 pins are located on the bottom side of the component. These pins constrain the translational motion of the body in the z-direction and rotational motion along the x-axis and y-axis. Thus 3 degrees are restricted. But the body still can rotate along the z-axis and translate into the x-axis and y-axis.
2 pins are located on the back side of the component. These pins constrain the translational motion along the x-axis and rotational motion along the z-axis. Thus we have denied 5 degrees in total. But translation along the y-axis is still possible.
1 pin located on the adjacent side of the 2 pins we can constrain the last degree that is translation along the y-axis.
FIG. LOCATING PINS
Thus we can constrain all the degrees of freedom of a body using the 3-2-1 principle which used 6 pins for the same.
When we use clamps we restrict the following motions:
Translational motion along the z-axis.
Rotational motion along the x-axis.
Rotational motion along the y-axis.
sign two Rest units and three Power Clamp units with different Risers, Blade, and Clamp arms.
Clamp unit: A clamp unit is a 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 the clamp mylar. In a clamp unit shimming to one side is more than enough because it will restrict translation motion in upward & downward directions only. There is another type of clamp unit known as the swivel type. There is a pivot pin around which the clamp arm rotates.
Factors should be considered while designing a clamp unit:
There should be adequate space between the cylinder & other parts like the riser, or car panel because the cylinder moves or swing while opening & closing
A pin clamp unit is used where two panels or components are located for welding.
Clamping make in such a 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 the car panel so they do not damage the car panel
Avoid any clash. It will not arise an issue at assembly.
CLAMP PLAN:
The customer provides the clamp plan which consists of the position of the clamp, pins, rests and dump, etc.
It has the exact coordination of these components and in addition, it also has the hole’s dimensions and tolerances.
As this is critical input data, it must not be modified.
In case the spot for weld and the clamp position is nearby and it may create a problem later and there is a 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 the clevis clamp include the 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 unloading.
The clamp arm shall be welded construction including a 20.0mm thick arm with an integral pivot to accommodate a 19.50mm wide Swivel. The female portion of the clevis shall always be part of the arm. The male portion of the Swivel shall always be part of the blade.
Clamp Cylinder:
Cylinder designation: In this unit, we used a Clevis cylinder for clamping designated as CKG_1B_63_100YNomenclature of the cylinder as below:
CKG1: Series of cylinder
B: Clevis width is 19.5 mm.
63: Bore size
100: Stroke of cylinder
Y: End bracket i.e. double knuckle joint (M6 without tap)
FIG: Clevis cylinder
Clamp arm: It is the part to which the clamp mylar is mounted & also clamp cylinder is attached to the end of the arm with the use of a clevis pin. It has two plates of 8 mm thickness welded & helps in rotating of clamp arm about pivoting point of the blade.
The below figure shows the 100 mm stroke achieved & clamp arm end in line with the cylinder rod. See Y & Z values.
NC block/Mylar:
NC blocks or popularly also known as Mylar is the ones that hold the panel.
It prevents the panel from deforming while welding.
They always come in pairs.
Top Mylar 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 in the contact panel) is considered as 20mmx20mm.
Most of the OEMs/Tier 1 prefer Mylar to have a 5mm allowance material for machining. Most Mylar is CNC machined if it is clamping 3D profile.
Depending on the angle of the cross-section, Mylar will be having shimming either in one direction or in 2 directions. The general Thumb rule is if the section is inclined more than 15 deg or the clamping surface is a 3D profile then 2-direction shimming is provided. The reason is simple mathematics. The equation of inclined line/ plane will be having 2 parameters to control and we control with shimming in 2 directions. Less than 15 deg does not mean that there are not 2 parameters. These are there but they are neglected if the angle is less than 15 deg.
FIG: CLAMP &REST MYLAR
FIG: CLAMP &REST MYLAR
1mm is the component thickness. so the distance between the clamp and rest mylar is 1mm.
Stopper:
The function of the stopper is to restrict the motion of the clamp arm. It avoids the clamp of the arm to rotate beyond the limit. It has two parts male & female.
Blade: The blade is the part to which all other units are attached e.g. mylar, stopper, clamp cylinder, riser. The blade is designed according to the position of all other parts.
FIG: BLADE
Bush: Bush is a friction-type bearing. It is lubricated with grease, and oil. It permits relative motion between two mating parts. It is made of hard material also its ID & OD are precisely machined or ground. It presses fitted & after worn out it is replaced with new one instead of replacing another part which saves cost. Mostly phosphor bronze or gunmetal material is used for making bush. In this unit, three bushes are used of the same internal (12 mm) & external diameter (18 mm) but different lengths.
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 finely machined.
It should have a step machine surface to lock rotation which matches with pin retainer.
The mounting surface of the pin retainer to the block should be machined.
All machined planes should be perpendicular to the axis of the shaft.
The 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 finished in general.
Material - Hardened materials like C45, 16MNCR5, 20MNCR5, EN31, etc.
Surface finish - black oxide, Zinc coating, Chrome plating.
Typically, locating pins are used for controlled, fine tolerance positioning of, For example, a pallet that is moved along one axis, where the drive mechanism is not accurate and stable enough to place it in a position sufficiently accurate to execute a particular process, the use of locating pins may be the best solution.
The Diamond Shape is a critical feature that helps with machining inaccuracies and smoother locating When two round headpins are installed onto one plate, the distance between two mounting holes must be extremely precise and even then, the workpiece will not be placed on the base as easily as it would with the use of a diamond shape pin.
There are several styles of Pin Head They serve different purposes and can be utilized in a variety of applications.
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. Thicknesses range from 0.25mm to 2mm.
Many assemblies require tolerance to be hit about a length or height; shims allow designers to hit these tolerances. They can be stacked between NAAMS NC blocks, L blocks, or pin retainers.
FIG: SHIMS
Riser:
The riser is a structure generally used to mount the toggle clamp and rest, clamp Mylar and location pin, and give height to the assembly.
It is not necessary to have one riser where all the parts of the clamp or rest or location units are mounted.
Risers can either be a standard part or take part.
Hardware: These are standard parts. Parts are assembled with the help of a washer and bolt. for better assembly should use two dowels and four bolts for the riser and blade. Where for bolting one part should have a tapping hole and on the other part a simple hole (1 to 2 mm larger than bolt size.)
The length of the bolt is decided by the width of part + (1.5*D)
For ex. where
L=Length of Bolt
D=diameter of the bolt to be used
Let’s, take M8 Bolt
L= 25 + (1.5 * 8)
L=25+12
L=37 mm.
Dowel pins: These are standard parts. There are various types of dowel pins like split, parallel, taper, clevis, and spring, grooved. Dowel pins are used to locate parts precisely & to restrict movements. For mylar, dia. 6 or 8 dowel pins should be used. For the blade, shimming block dia.8 dowel pin should be used & for the riser base dia. 10 or 12 pins are used.
Washer: Standard steel grade A plain normal series washer used.
FIG: S001_Z01_ST010_01_00_CLAMP_UNIT
S001_Z01_ST010_02_00_CLAMP_UNIT
S001_Z01_ST010_03_00_CLAMP_UNIT
S001_Z01_ST010_04_00_PIN_CLAMP_UNIT
FIG: COMPONENT WITH CLAMP UNITS AND BASE UNIT
FIG: CLAMP UNITS
FIG: COMPONENT WITH CLAMP UNITS
CONCLUSION:
Hence as per the objective, the 3 different types of SWIVEL clamp units by validating & pin clamp units are designed in Catia v5 software.