7 MPa Planning
Step 5: (Optional)
Where . . .
If total estimated clamping time is not within the cycle time requirements you’ve targeted but is within device limitations, a larger power source is required — one with greater capacity. Select such a source and repeat the above calculations to ensure it will provide the clamping cycle times required. If the total estimated clamping time in the initial calculation is significantly less than the time allowed, your initial power source selection may have been too large. In such a case, select a smaller power source and repeat the above calculations to ensure it still provides the clamping cycle times desired. If a smaller power supply is not possible, a flow control may be used to limit the speed of device positioning. This will help devices perform correctly and not “bounce” or become damaged by excessive flow. Additional factors you should consider when selecting a power source include shop floor plan and/or machine layout and your own preference for the type of power source (shop air vs. electric). If desired, large electrical power sources may be used to supply several workholding systems, each operating independently at several machines. In this case, the timing and sequence of operations for each individual system must be calculated as shown above in order to arrive at a size for the power source. Step 10: Select valves and other control components to accomplish the sequence of operations you outlined in Step 2. See the valve section of this catalog for guidance. Step 11: Select appropriate safety control mechanisms. All VektorFlo ® electrical power modules have a hydraulic pressure switch as standard equipment to ensure consistent forces are maintained at all times. However, when a power source is used to power several separate individual systems, each system should also have its own pressure monitor.
Normally you need to calculate the forces required to overcome work piece weight and friction and to move the part into position against fixture stops if you are using positioning cylinders as your first hydraulic operation of your fixture.
First, determine the nature of the operation to be performed, the number of parts to be processed per cycle, and whether operations will be performed on more than one surface of each part. Also determine the time that should be allowed for part loading, unloading, and clamping the part. Consult your machine tool file to determine the available work space on the machine table, bed, or other surface, as applicable. Be sure that the space available will accommodate the part or quantity of parts to be processed according to your manufacturing work-flow. If not, revise your plan. In the initial phases of system planning, include adequate measures and devices to ensure the safety of workers and equipment. Step 2: Prepare an outline of the sequence of events that will take place during the manufacturing cycle. This will assist you in determining the types of special sequencing valves you might need, as well as any external control (such as a tie-in with machine controls) your application may require. Step 3: Calculate the cutting forces generated in the machining process and note the direction these forces tend to act on the work piece. If you are planning a retrofit of a manual clamping system, you may use the torques presently being used. However, it is recommended that cutter forces be calculated as a precaution in such a case to ensure that workholding devices are sized to provide an adequate margin of safety. The operation manuals of many machine tools contain tables that list machining forces or simple formulas for calculating these forces.
After you have determined the machine cutting forces, it is easy to calculate the clamping force required to hold the work piece on the fixture or machine table. Again, a simple formula is all you need to arrive at an answer for the materials you’ll be working. Give us a call if you need help.
Determine where clamps should contact the part to hold or support it securely and to avoid interference with machine operations. If clamps cannot be located so as to avoid interference with manufacturing operations, it will be necessary to use an external control device to move the clamps out of the way as the need arises during the manufacturing sequence. This will require that electrically actuated valves be used to control the offending devices separately.
Determine the type and number of workholding devices you need based on the total clamping force required and clamping positions you’ve selected; on the size, strength and shape of the part; and on the machine operation. Step 9: To help determine the capacity of the power source you’ll need, add the total oil displacement requirements for the devices you have selected. Then choose a power source with equal or greater capacity and determine if it will operate the system within your clamping time constraints by working out the following formulas: (Device Cap.) ÷ (L. P. Flow) = Position Time Where . . . “L.P.” flow is low pressure pump oil volume expressed in cubic centimeters/minute. “Device Cap.” is total device oil capacity expressed in cubic centimeters (cm 3 ). Position time is time to position expressed in decimal parts of a minute.
Plan your fixture(s) with positive fixed stops to resist the majority of cutting forces and to ensure correct location of the work piece using the primary part locating features.
© Vektek January 2019
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