BIW FIXTURES-DESIGN OF SWIVEL CLAMP UNITS & PIN CLAMP UNIT

Aim: To design 3 Different types of Swivel Clamp Unit with Different Riser, Blade and Clamp Arm for the given Car Panel and to design a Pin-Clamp Unit for the given Car Panel.

Software Used:CATIA-V5

Car Panel:

Introduction:

This project is to design 3-Swivel clamp units and 1-Pin-clamp unit to fix it in fixed position.This project is done with respect to 3-2-1 principle,considering clamp force to be imposed on panel according to Tunkers.

3-2-1 Principle (achieved by Clamps): In order to completely restrict or specify the position in space of a three-dimensional object (such as the cube that’s shown), we refer to six coordinates with total 12 degrees of freedom known as Locating process,whereas 3-2-1 principle of that kind. Any free body has a total of twelve degrees of freedom as below.if we can arrest these 12 degrees of freedom,the component will be fixed in a desired position.The degrees of freedom are as follows:

• 6 translational degrees of freedom: +X, -X, +Y, -Y, +Z, -Z .
• 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-Z)
6. Anticlockwise around Z axis (ACROT-Z)

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

• 6-degrees of freedom are restricted by 2-pin units.
• 6-degrees of freedom are restricted by 3-clamp units and Rest units.

Clamping: The process of holding the position of the workpiece in the jig or fixture is called clamping. The primary devices used for holding a workpiece are clamps/Clamp unit.

Clamp Unit: Clamps hold the car part firmly and prevent the part from distortion while carrying welding operation. A single clamping unit consists of the following parts:

1. Finger: Finger is a movable part which is used to hold the Car part from top against the Back-up and they are usually mounted on the clamp arm.
2. L-Block: L - Shaped blocks (single or in combination) used to mount the finger to clamp arm, besides allowing adjustment for locator pin in two directions.
3. Shim and spacer: They allow the finger to be moved to the correct XYZ locating and / or allow the customer to make adjustments to improve the quality of their product.
4. Blade: Part onto which the aforesaid elements are attached to.
5. Blade spacer: It allows the finger to be moved to the correct location along one direction.
6. Riser: L- shaped tall block with regularly patterned holes to attach the above mentioned parts in modular way Blade space.

Clamping Force: Clamping force is the force required to hold a part against the locators. Clamping prevents the part from shifting or being pulled from the jig or fixture during the machining operation. The type and amount of clamping force needed to hold a part is usually determined by the tool forces working on the part and how the part is positioned in the tool. Sometimes the operation being performed is a factor. Clamping pressure, as a general rule, should only be enough to hold the part against the locators. The locators should resist the bulk of the thrust. If a part must be clamped with a great deal of pressure, the tool should be redesigned so that the tool thrust is directed at the locators and the tool body. Clamps must never be expected to hold all of the tool thrust.

General procedure for selecting clamp:

Clamp force depending upon outreach:

Clamp weight & length:

Types of Clamps: Various methods of clamping are common to both jigs and fixtures. The type of clamp the tool designer chooses is determined by the shape and size of the part, the type of jig or fixture being used, and the work to be done. The tool designer should choose the clamp that is the simplest, easiest to use, and most efficient.

1. Strap clamps: Strap clamps are the simplest clamps used for jigs and fixtures Their basic operation is the same as that of a lever. Strap clamps can be grouped into three classes, each representing a form of lever.
2. Screw Clamps: Screw clamps are widely used for jigs and fixtures. They offer the tool designer almost unlimited application potential, lower costs, and, in many cases, less complex designs. The only disadvantage in using screw clamps is their relatively slow operating speeds. The basic screw clamp uses the torque developed by a screw thread to hold a part in place—either by direct pressure or by its action on another clamp.
3. Swing Clamps: Swing clamps combine the screw clamp with a swinging arm that pivots on its mounting stud. The holding power with this clamp is generated by the screw. The rapid action needed is achieved by the swinging arm.
4. Hook Clamps: Hook clamps are similar to swing clamps but they are much smaller (Figure 4–17). They are useful in tight places or where several small clamps rather than one large clamp must be used. A variation of the hook clamp is shown in Figure 4–18. The modified hook clamp is made to be operated from the opposite side of the tool. It is useful in tight places or where a safety hazard may be present if the tool is operated from the front side.
5. Cam-action clamps: Cam-action clamps, when properly selected and used, provide a fast, efficient, and simple way to hold work (Figure 4–20). Because of their construction and basic operating principles, the use of cam-action clamps is limited in some types of tools.
6. Wedge Clamps: Wedge clamps apply the basic principle of the inclined plane to hold work in a manner similar to a cam. These clamps are normally found in two general forms, flat wedges and conical wedges.
7. Toggle-Action Clamps: Toggle-action clamps, shown in Figure 4–29, are made with four basic clamping actions: hold down, squeeze, pull, and straight-line. Toggle clamps are fast-acting. Because of how they are made, they have the natural ability to move completely free of the work, thus allowing for faster part changes. Another advantage is their high ratio of holding force to application force.
8. Power Clamps: Power-activated clamps are an alternative to manually operated clamping devices. Power clamping systems normally operate under hydraulic power or pneumatic power, or with an air-to-hydraulic booster. The system used is determined by the type of power supply available. The air-to-hydraulic system is preferred because it can operate from the regular shop line pressure and no pumps or high-pressure valves are needed. The advantages of power clamps are better control of clamping pressures, less wear on moving parts of the clamp, and faster operating cycles.

Purpose of Clamp unit: The purpose of clamping tools is to securely hold the workpiece in position without obstructing the production process. High clamping forces combined with compact dimensions are therefore the most important requirements for a clamping tool

Design of Swivel Clamp unit:

1. Study the PLP (Principle Location Points) data along with the nearby spot data.
2. Depending on the angle of cross section. Mylars will be having shimming either in one direction or in 2 directions. General Thumb rule if the section is inclined more than 15deg or clamping surface is 3D profile then 2 direction shimming are provided.
3. Take an overview of the working height if you’re having manual welding. For robotic welding also it’s important to see the working height in consideration of the robotic gun, turn table height if manual loading is done.
4. Put the proper gun at the spot location. If process engineer has gun shape stick to X, C or Y type of gun. Do the proper gun study and place the gun as per the GEO or re-spot decision and operator approach. Once basic gun is placed considering the throat depth and throat gap start building the clamp and rest block at the PLP.
5. Panel section creation: Take a section at PLP either in clamp opening direction or normal direction .Sections should be normal to base. Panel section through X, Y or Z direction passing through PLP. Section will help in finalizing the shape of clamp and rest block. Most importantly used for finalization of gun shape.
6. Finalization of a base plate plane – consider following things before deciding the base plate. Height of maximum and minimum weld spot from the floor. No gun arm should touch the base plate. Operator ergonomic while accessing all the spots.
7. Construction of Rest and Clamp Block: If standard Mylar has to be used (Few companies make standard height and length of steel blank with few holes and dowels for clamping) then select the proper blank size as per the requirement; consider 5 mm above the panel.
8. Select the clamping cylinder as per the pivot point distance from the PLP.Once clamp and rest block is build, start construction of mounting plate or fabrication structure as per the company standard to make the connection with the base plate. shimming is 5mm solid +5mm shim pack, In few companies 3mm shims are used. Make connection plate between rise and Mylar. Material can be C45, Teflon, Aluminium or S-Grun as per the customer requirement. Generally S-Grun mylars are made of more thickness.

PLP Location & Clamp plan:

PLP (Principle Locating Points): Principle locating points are the points which are used for the accurate location of the panels sub-assemblies to maintain the geometry of the assembly. There are lots of holes on the panel which are not accurate due to stamping operations. So the PLP are defined in the drawings. The PLP holes must be very much precise.

Clamp Plan: Clamp plan provides the information of location of pins, Rest units, clamp unit, Dumps etc. It is the important input from customer. The clamp plan/position should not be changed without the knowledge of customers. It gives the detail of the exact position of the clamping units by mentioning a co-ordinates in the particular position.

Clevis clamp Cylinders:

Clevis Cylinder has been designed to operate as an actuator with a clevis clamp at the end to position the final control elements in accordance with the controller signal. Clevis cylinder are mechanical devices which use the power of compressed gas to produce a force in a reciprocating linear motion. Like hydraulic cylinders.

Parts of Clevis Clamp Unit:

1)Clamp cylinder
In clevis clamp unit, swivel type cylinder is used.Pneumatic cylinder (sometimes known as air cylinder) are mechanicl devices which use the power of compressed gas to produce a force in a reciprocating linear motion.Like hydraulic cylinder, something forces a piston to move in the desired direction. The piston is a disc or cylinder, and the piston rod transfers the force it develops to the object to be moved. Engineers sometimes prefer to use pneumatics because they are quieter, cleaner, and do not require large amounts of space for uid storage.Because the operating uid is a gas, leakage from a pneumatic cylinder will not drip out and contaminate the surroundings, making pneumatics more desirable where cleanliness is a requirement.Once actuated, compressed air enters into the tube at one end of the piston and imparts force on the piston. Consequently, the piston becomes displaced.
2)Finger
A nger is a NC block, which is mounted on clamp arm of the cylinder, and press the car panel towords the rest, so it holds the car panel.
3)Clamp Arm
A clamp arm is make part, it's made as per the position of clamp cylinder, stopper and shim. clamp arm made from hard material.
4)Stopper
The function of stopper is to restrict clamp going beyond the limt. stopper is mounted betwwn clam arm and rest or blade. stopeer has two part, when this two part meets they restrict motion.
5)Blade
Blade is make part, designed according to position of riser, clamp cylinder, clamp arm, rest mylar and stopper.
6)Riser
Riser is standard part, which provide height to the Pin unit, clamp unit as per requirments. Riser should have adequate strength so it can sustain under load of car panel, clamping cylinder, blades.

Power Clamp cylinders Used:

CKG_1B_63_100Y.1

Design of Swivel clamp Units and Pin-Unit:

Clamping Plan:

Design Tree of the Product(P001_Z03_ST001_00_00)

P-Panel_Z-Zone_ST_Station_Product_Part

Design of Swivel Clamp Units:

CLAMP_UNIT_1 CLAMP_UNIT_2 CLAMP_UNIT_3

Design of Pin-Clamp Unit:

Panel after clamping:

Conclusion: Hence as per objective, the 3 different types of swivel clamp units & 1 Pin-clamp unit has been designed. Also the Materials Used, Purpose of clamp unit, (3-2-1 principle) achieved by clamping, PLP points (Principle locating points) & Clamp plans are briefly explained in detail.

References:

1.Fixture Design Amit Chaturvedi1, Narendra Kumar2 M.Tech. Scholar, ME Department1, Assistant professor, Mechanical Engineering Department Faculty of Engineering & Technology, Rama University, Kanpur, Uttar Pradesh, India.

2.Fundamentals of Tool Design Sixth Edition by Chief Technical Reviewer and Managing Editor Dr. John G. Nee, CMfgE Professor Emeritus Engineering and Technology Department Central Michigan University Contributors William Dufraine, President The duMont Company,John W. Evans, President Acme Industrial Company,Mark Hill, Professor CAD Drafting – Tool Design Ferris State University.

3.A Review on Design of Fixtures Shailesh S.Pachbhai1, Laukik P.Raut2 1Research Scholar, Department of Mechanical Engineering, G.H.Raisoni college of Engineering, Nagpur 440016 2Assistant Professor, Department of Mechanical Engineering, G.H.Raisoni college of Engineering, Nagpur 440016 .

4.Recommended applications of pneumatic clamps -Basic Vario series ,Christian Kleinschmidt TÜNKERS Maschinenbau GmbH Am Rosenkothen 4 –12 40880 Ratingen