An alternative to grinding internal threads in components—called “internal whirling”—is now available from Leistritz Corp. (Allendale, NJ; www.leistritzcorp.com/machine_tools.cfm). According to the company, the process can be performed in a variety of materials, even hardened steel (65 Rc) with CBN tooling. During the operation, the spindle operates at 2,000 rpm or less and the tool oscillates in and out of the workpiece thereby assuring the quality of the thread form and surface finish. The process often is performed dry.
A machine that Leistritz has developed to perform internal whirling is called the Innovation 200. It is a vertical machine with the chuck on top and the whirling head, which is fixed, below: the chuck brings the part to the tool. Because it is advantageous to hard turn a bore prior to whirling (this improves the quality of the thread), the Innovation 200 includes turning, milling and probing capabilities. During the operation, the tool rotates at approximately 600 sfpm and oscillates axially, dependant on the thread parameters and tooling circle data (for example, higher lead threads require large amounts of oscillation). The C axis is slowly rotated in the same direction as the tool. Typically a thread is performed in a single pass.
Automotive applications are said to be in such areas as steering system and brake manufacture.