Efficient five-axis workholding solutions locate and stabilize the workpieces without obstructing access to the top and sides of the part, and they also allow a clamped workpiece to be flipped into new orientations for subsequent machining operations without unclamping from the workholding. There is a natural limit of how close you can get to the table. The options are to make the tools
workpiece is stationary and the tool and spindle move completely around the workpiece? With the trunnion-style machine, the part must rotate and move at the same time to allow for full simultaneous machining. You need to be cognizant of clearance problems with the machine’s spindle housing and the machine’s table, especially at full tilt when the table is perpendicular.
With gantry-style machines,
we’re usually working with aerospace structural workpieces or molds for the automotive industry that are very large. We spread out the workholding system, based on the footprint of the machine. If we just take a standard vise and elevate it off the table, then the vise generates an offset for the center of the round workpiece. Although most modern five-axis machines can handle dynamic offsets, you create a clearance problem with either the front end or spindle end of the vise, resulting in a huge mass of material that is not really helping in any way but can cause interference or crashes with the spindle and housing. That’s where you see a lot of self- centering vises where both jaws move uniformly to minimize the amount of dynamic offset. Hydraulic or Shrink-Fit? In addition to workholding, the choice of tool holder has an impact on the process. Shrink- fit tool holders are deliberately undersized to accommodate the fact that heat is used to expand the inner diameter (ID) enough for the tool to fit, then cooled to collapse around the shank. In a scenario where a collet chuck’s nose or body diameter may risk collision with a table, these less bulky holders tend to offer good access to part features, particularly in long-reach applications. There are a variety of different shrink-fit profile shapes and extensions that provide even more options. Shrink-fit holders also boast excellent concentricity and accuracy thanks to even gripping across the entire circumference of the tool shank. That said, gripping power is dependent on tolerance of the cutting tool shank and outside
Efficient 5-axis workholding locates and stabilizes the workpieces without obstructing access to the top and sides of the part, and it also allows a clamped workpiece to be flipped into new orientations for subsequent machining operations without unclamping from the workholding.
excessively long or elevate the workpiece off the table. Since the general rule of thumb is that it’s better to use a short tool to minimize chatter and maximize tool life and accuracy, shops lean toward elevating the workpiece to allow the spindle access.
Taking Advantage of Workholding
Bulky workholding has traditionally introduced the chance for collision while limiting setup flexibility as well, but approaches have been developed to make it an asset in multi-axis machining.
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