In today's injection mold industry, designs of multi-segmented Extruder Screws are more complexed than ever, and so are the demands on how these screws are to be manufactured. Ideally removing the maximum amount of material in the shortest possible time, while still leaving a high quality surface finish thus eliminating not only a costly but, very time consuming grinding operation.

Now those previously unattainable goals have all come together into one advanced machine from Leistritz, the PWM multipurpose machining center line. This CNC controlled multipurpose machine combines Whirling, Milling and Turning all on a single space saving vertical bed design.

Ralph Wehmann, National Sales Manager of machine tool sales at Leistritz Corporation, describes the advantages of this multipurpose machine: "Whirling is the fastest machining method for producing extruder screws, and if you compare whirling with milling, there is a big improvement in surface finish due to the smooth tangential cutting action you get by whirling." By improving profile finish, there is an elimination or at least a reduction in the need to grind or hand polish. Since these operations are normally very time consuming, the cost savings can be tremendous.

Whirling however, is not capable of cutting all profiles such as, screws with a very high helix angle or profiles with square flanks. Screws with these characteristics are better off milled. So which method is better for producing extruder screws? The answer is simple says Wehmann, "The Leistritz PWM multipurpose machine, it was developed with extruder screws in mind combining the speed and metal removal of whirling along with the versatility of milling, in effect what you have is a multiple machine in one."

Wehmann also states that the PWM Machining System allows the manufacturer to do nearly all the manufacturing operations to the screw in just one chucking. In addition to Whirling and Endmilling, Sidemilling operations can also be performed on splines, found on many of today's feedscrews.

Engineers at Leistritz have developed an efficient system in order to change cutting heads, it can go from Whirling to Milling in a matter of minutes. Traditionally feedscrews required multiple setups to perform many operations, usually on a variety of machines, but with the Leistritz system can this now be completed in just a single setup, with one PWM machine. Another important benefit resulting from machining all operations in one chucking and reducing part handling, is that the accuracy of any part becomes much greater.

The economics of the Leistritz PWM multipurpose machine are such that, no longer does a manufacturer need to have three separate whirling, milling and turning machines. They can get the same performance of all three machines in one, along with a reduction of manpower and shop floor space savings. But the real advantages come from the time savings generated by the speed of whirling and having the ability to quickly go from a whirling mode to milling or turning operation. Tests show that 2 to 3 times faster production rates can be expected from just a single Leistritz PWM Whirling, Milling, and Turning Machine.