Holding parts Choosing the right workholding
The benefits of 5-axis machines are greatest when workholding is chosen based on the size and shape of the workpiece instead of the limitations of the table interface. Now, some quick advice on choosing the right workholding for a new 5-axis machine. Find a balance between stability and access. The fixture may be large and provide rigid holding but may limit access to the workpiece—and vice versa. If a part is too small for your fixture, consider palletizing multiple parts. If a part is too big for your fixture, consider upgrades if you have a modular system, or add custom pieces, if possible. Know what parts are coming down the line. If the parts are prismatic, most often a vise will do just fine. If the part is round, you’ll need to hold onto an outer or inner diameter on the part. Whether the part will be raw material, a casting or partially finished is also an indicator what the workholding will have to accommodate. For example, a round raw bar from the mill may have an OD tolerance of ±.005 " , but if a part is cast, then the size may be ±.02 " —could be better, could be worse. If a part has already been machined, then the size is not a variable—it’s a known controlled value. Choose the right chuck and lay it out carefully. Depending on the material of the fixture plate, the part or fixture should not extend too far beyond the diameter of the chuck. With a steel plate that’s at least 20mm thick, you can generally go 40mm off diameter without losing stability. If it’s an aluminum plate 25mm or thicker, 20mm off the diameter should be about the limit. Thicker plates are an option, but material costs start getting a little higher than most customers want to bear. When it comes to multiple chucks, plate material and thickness are key. General guidelines for maintaining accuracy and rigidity: if the diameter is less than a 138mm chuck, spacing should max out at about 200mm; for bigger diameters, we recommend a maximum spacing of about 350mm.
6
Powered by FlippingBook