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

Introduction-

Design 3 Different types of Swivel Clamp Unit and 1 pin clamp unit to fix in fixed postion. This project is done with respect to 3-2-1 principle consider clmap force to be imposed on panel according to tunkers.

3-2-1 Principle-

3-2-1 principle is used to restrict the degrees of freedom (DOF) of the object as we are studying Biw fixtures so in this project we are going to restrict the 12 DOF of the Biw panels so that we can fix the panel by using different clamps and Pin units which will help to join the two panels.

 

12 DOF- 12 degrees of freedom of an object in the space are as follows

Positive and negative translation along X-Y-Z axis- 6 DOF

Clockwise and anticlockwise rotation along X-Y-Z axis- 6 DOF

To restrict these degrees of freedom the basic criteria that we follows is

We placed the 3 locator unit on the largest face of the object which will restrict total 5 DOF but in our case we use 3 clamp units that will restrict 6 DOF

We use 2 locator units or if we have provision for pins then we can use pin units on the second largest face of the object to restrict the remaining  4 DOF, in our case we use 1 circular pin unit which will restrict 4 DOF

By the use of 1 locator unit we can restrict remaining degrees of freedom, in our case we use Diamond pin unit which help to restrict 2 DOF.

Basic terminologies used in the BIW fixture?

 

• NC/MYLARS/FINGERS: MYLAR is type of block that touches the panel and holds or clamps the panel. Mylars are always intended in car line. Mylar is also called NC (Numerically Controlled) Block.
• PIN: Pins are used to locking the rotational movement of the panel. Generally there two types of Pins, one is Round Pin and another one is a Diamond pin. We use two and three-directional shimming for pins as per the angle of the pin w.r.t. the carline.
• BLADE: The plate which connects Riser to the Clamp cylinder is named Blade. This plate plays an important role in building the unit.
• L BLOCK:A plate shaped as L is called an L block. This part is used as a connection between mylar and Blade. Generally, L blocks are used to provide shimming.
• PIN BOCK:Pin Block is also called Pin Retainer. This block holds the pin and restricts the rotational motion of the pin. Pin Block can be either manufactured one or Standard. 
• RISER: The part which is mounted on the base plate and holds a clamp or pin cylinder on it, is called Riser. Riser can be Standard Part or manufactured part, it varies from project to project.
• WELDMENT: Weldment is the assembly of two or more parts that are joined by welding. To make a weldment it is the thumb rule to have a 5 mm overlay on each other plates so that space can be provided for welding. 
• Principal Locating Points (PLP): PLP are the points at which the car panels are to be located onto the fixture. The welding fixture is designed with locator units to aid the operator to load the car panels onto the fixture at the right location and orientation.
• SHIMS:A shim is a thin and often tapered or wedged piece of material, used to fill small gaps or spaces between objects. Shims are typically used in order to support, adjust for better fit, or provide a level surface. Shims may also be used as spacers to fill gaps between parts subject to wear.
• ROUGH LOCATORS:Rough locators are used to help locate workpieces in the automation process. Locating refers to the desired location where you want the workpiece to be when it is getting worked on either by a person, team, or robot.It is a device to establish and maintain position of a part in a jig or fixture.
• PIVOT:The central point, pin, or shaft on which a mechanism turns or oscillates.
• CLAMP ARM: It is a part of clamp unit which moves over a particular axis.
• NUMBER PLATE: It is a plate attached to each unit with a unique number on it to recognise the unit.
• REED SWITCHES & SENSORS: A reed switch is an electromagnetic switch used to control the flow of electricity in a circuit. They are made from two or more ferrous reeds encased within a small glass tube-like envelope, which become magnetizedand move together or separate when a magnetic field is moved towards the switch. And the Device used to check whether the panel is loaded or not is done by sensors.
• CLASS-A SURFACE:Class-A ('Strak') is a term used in specifically in automotive design.It describes the final production surface data for the aesthetic parts of the car.

Design consideration for Fixture Design

1. We need to make sure that for the given panels each panel have 3 clamps that can be swivel clamps or normal clamps but each panel need to have 3 mylars which are going to clamp the panel.

2. Also we need to provide 2 pin units in the holes available in each panel need to provide one circular and one diamond pin unit (we don’t provide both as a circular pin unit in a single panel to avoid over constrain the panel instead of that we use one circular pin unit and one diamond pin unit so it will also provide ease to the operator to place the panel because he can adjust the panel during placement. One circular pin can restrict 4 dof but one diamond pin unit can restrict only 2 dof which help the operator for adjustment of the panels.)

                        

3. We also need to add shims to for each mylar and pin unit  for proper positioning the units ( we provide shims for clamp unit only along the Z axis and for pin unit we provide the shims along the X and Y direction the basic criteria for a shim placement is for which direction we are restricting the movement only along that direction we use the shims)

 

4. We also need to maintain the nominal distance and symmetric distance between the objects so that it will be ease for manufacturing of the object and also help during the programming of the robots which are going to perform the necessary operation on the panels.  

Images Of the Swivel Clamp Units