Week 5:- Rest Unit & Clamp Unit Design Challenge
1..
OBJECTIVE;
1. TO UNDERSTAND AND DESIGN TWO DIFFERENT TYPES OF REST UNIT FOR THE GIVEN THE CAR PANNEL
2. TO UNDERSTAND AND DESIGN THREE DIFFERENT TYPES OF POWER CLAMP UNIT AND ,RISER,BLADE,SHAMES, ETC.
Rest Unit:
• Rest unit is unit designed to support car panel using Mylar/ NC block/ rest component is rested only, no upper clamp or force applied there. It is the simplest unit to design because it has fewer parts to design & the purpose is only resting of the car panel. Because of the simplicity the rest unit is combined with other unit to reduce the cost of the overall project.
• It can be combined with clamp unit to clamp as well as to rest the car panel. It can be combined with locating unit to locate as well as to rest the car panel. Also locating, clamping & Test unit can be combined together in one unit to reduce cost
• There is no cylinder attached to it. It has rest Mylar, blade and riser & below is different parts of rest unit. Rest unit is also divided into simple support unit, multiple support units & retractable support unit.
Clamp Unit:
• A clamp unit is a unit designed to clamp/hold the car panel with NC blocks/Mylars/rest by using a pneumatic cylinder Clamp arm, finger, Rest/backup, L-block shims, riser, pneumatic cylinders are the typical parts of clamp unit.
• Clamping force should be considered while designing clamp unit. 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 direction and downward direction only There is another type of clamp unit known as swivel type There is pivot pin around which clamp arm rotate
Purpose of Rest Unit &Clamp Unit:
The purpose of clamping tools is to securely hold the workpiece in position without obstructing the production process. It prevents the distortion during welding process and other processes.
High clamping forces combined with compact dimensions are therfore the most important requirements for a clamping tool For this reason, clamps are also equipped with mechanical transmission gear units.
Design Methodology:
• 3-2-1 Principle achieved by clamping and resting The 3-2-1 principle is the fundamental principle of all fixture design. While designing a fixture a major part of time is spent in locating the workpiece in the fixture. The best & the most effective method of part location is referred to as the 3-2-1 method Fixtures work on the 3-2-1 principle
• 3 locators or supports are placed under the workpiece which establishes the part plane. Three locators are generally positioned at the primary locating surface. This restricts 2 axial movements downward & upward and 4 radial movements. As a result the 3 locators arrest six degrees of freedom
• Thus by using 3-2-1 principle, introducing a minimum of 3 clamping & resting blocks
will restrict 6 DOF( 2 axial translational about z-axis & 4 rotational about the x&y axes respectively)
• Remaining 6 DOF are restricted by introducing Pin unit of minimum 2 nos.
Clamping- The process of holding the workpiece in the jig/fixture is called clamping. The primary devices used for holding the workpieces are clamps/clamp unit.
• Resting - The car panel will rest on the rest unit. It resists the clamping force of the finger . exerted by the clamp cylinder and thus clamps the car panel.
Forces acting in the clamp and rest unit:
while designing a clamp unit 2 forces are considered that act in clamp unit
1. Clamping force
2. Holding force
1.Clamping force:
it signifies the force applied to the workpiece by the drive mechanism via the clamp arm during gripping or clamping operations
2. Holding force:
Holding force, on the other hand denotes the maximum force after locking the knee-lever (over centre position, that can be applied by the workpiece on the gripper/clamp arm without destroying the mechanism. Therefore, particular attention must be paid to the maximum holding force when, for example during the production process (welding bonding), there is a possibility of distortion of the component or if the clamp arm is used as a fixed stop it the holding force specified in the technical details is exceeded this will inevitably result in the destruction of the mechanism, the clamp arm or the bearing position
Finding the outreach of clamp arm By measuring the distance between pivot center of cylinder and the centre of clamping of clamping mylars one can get the outreach of clamp arm
The respective outreach of the clamp arm taken from the clamp unit used in this project are as follow
1. POO1_203 ST010_03_00_CLAMP UNIT-outreach of clamp arm is 164mm.
2. POOI 203 ST010_04_00_CLAMP UNIT-outreach of clamp arm is 120mm.
3. POO1 703 STO10_05_00_CLAMP UNIT outreach of clamp arm is 174mm.
By relating the sheet thickness and the outreach as shown above, now the selection of power clamp is done as per our requirements. The bore capacity of clamp cylinders are found and the power clamp cylinder is selected. Average Clamping force (Fs) = 1200N (for size of 50 bore dia and mean length of clamp arm)
Two different types of Rest Units
THREE DIFFERENT TYPES OF POWER CLAMP UNIT
1. Finger/clamp mylar: It is a NC block mounted on the clamp arm of the cylinder. It is used for clamping / holding the car panelit presses the car panel towards the rest. It presses the car panel towards the rest.
2. Backup/Rest Mylar: It is a NC block fixed to the unit to support the car panel It helps in resisting the clamping force of cylinder onto the panel, thus clamping is achieved
Riser:
Riser is a part on which all the parts of a unit are mounted, and is mounted on the base plate of a tool. In general the riser can either be make part or a standard part.
Blade:
Blade is part like a plate, which connects the parts of a unit to a riser. In general the blade can be either a make part or a standard part.
Clamp arm:
• Clamp arm is a part of the clamp cylinder and it is a bought out part which is available in some standards. All the moveable parts in teh clamp unit are fixed to the clamp arm.
Clamp arm is different for different bore size of cylinder, it is available in different hole pitch
Clamp cylinder:
• Clamp cylinder is a pneumatic device which works with the flow of pressurised air. Clamp cylinder is a brought out part and some manufacturers are destaco, tuenkers, etc.,
• The clamp cylinder is used to open and close the moving part in the clamp unit It is generally available in 40, 50, 63 and 80 bore capacity. Clamp cylinder opens upto 135 degree for horizontal clamp mounting and it opens upto 105 degree for vertical clamping.
