Selecting Workholding
Selecting the way you want to fixture a part is most critical to the required end result you wish to achieve. In turn, the fixturing process should be viewed as being as equally important as the selecting of the actual machine and tooling.
Initial review of the Raw Material and Finish Part can point you in the right direction.
Dimensional integrity is the next step in the process. You see what datum points there are to work with and what critical dimensions have to be maintained. Surface finish requirements may also determine where and how to grip the part. Checking wall thickness can determine the proper clamp pressures and grip areas to avoid distortion. It is one thing to hold a part and another not to distort a part. There is nothing better than having the actual part available in your hands.
Next, Production Requirements will impact the selection of the machine and tooling just as it will impact the workholding.
Where production is low, a very primitive yet applicable method will do the job. On the other end of the spectrum, high volume production may require multiple part fixturing (along with hydraulic clamping) with very little effort for operator loading/unloading. Thus, maintaining the least amount of idle time.
Machining Requirements will also affect the way a part is held.
Certain part restrictions may not permit you to hold the part in the most efficient manner. Heavy depths of cuts and high feeds will necessitate rigid gripping. This may cause havoc in the machining and holding of the part. As we have all experienced, part configurations and dimensions do not always comply to our manufacturing needs. Of course this is the great manufacturing challenge.
When the Production and Manufacturing requirements are determined, you can now move forward to establish a Working Envelope.
Considerations for tooling clearances, sufficient room and minimal overhang allowances plus easy-operator-access are all critical components in the workholding design.
The decision can now be made regarding either the Manual Clamping or Hydraulic Clamping holding method.
Hydraulic Clamping is usually a must for high volume production and will normally keep the load/unload time at a minimum reduction of process time. If Manual Clamping allows you to meet production requirements, it is obviously less expensive (than Hydraulic Clamping), easier to maintain, …yet prone to human error.
The more parts you can place on a fixture, the better for production.
This may be true, but should be applied with caution. Placing too many parts on one fixture may cause other problems. Ample room has to be allowed for chip removal, load/unload, and, most importantly, there must be room to provide sufficient clamping and locating of the part itself. Ergonomically, you will want the fixture to provide ease of load/unload. And to make the process safe, it must be simplified and user-friendly for your operator.
Because there are many variances in workholding specifications and requirements, it is recommended that you communicate with the machine operator, tooling and programming engineer, and safety engineer to review the fixture design. This will insure that all aspects of the machining process are reviewed.
For over 45 years, we at Royal Machine and Tool Corporation have shared our workholding experiences and welcome the opportunity to discuss your fixturing requirements. We also encourage you to visit our website for informative ideas at www.royalworkholding.com.