The basic mechanism involves hardened steel dies reshaping the material surface of a cylindrical blank under high pressure into a thread form. Other threading processes remove material to produce the thread form, whereas thread rolling reshapes the material. The cylindrical work piece (or blank) is fed into the machine and the dies squeeze the blank while rotating it to produce the threads. Every thread form, shape, and size has a unique set of dies which are typically ground from heat treated tool steel. The dies have the reverse form of the finished thread. Properly formed threads require that the dies are exactly lined up and track properly in order to avoid internal defects, such as overlaps, cracks, folds, seams, and craters.
Thread rolling is primarily a cold forming process done at room temperature, but for blanks made from harder materials hot rolling is possible. Threads formed in this manner are preferred for high strength and critical applications like those found in the aerospace industry. Threads that are rolled, especially on heat treated parts, have higher tension, shear, and fatigue strength. No material is removed during the rolling process, eliminating one of the inherent weaknesses of cut or ground threads.
The cold formed properties include a higher density of material grains, or molecules, especially where they have been compacted along the lower flank of each thread pitch and in the root of the thread. A smooth finish is another advantage that roll threaded components have over other threaded components. The burnishing action of the dies means that the finish after rolling is extremely good, which improves assembly between external and internal threads and reduces wear between mating components.
Blanks are precision ground to a tolerance of 0.0005” to achieve the required dimensions and thread form. Redcliffe Precision Ltd rolls a wide range of thread sizes from 3mm to 2 1/8”, with a pitch from 0.5mm up to 4.5mm. RPL rolls a range of materials including, aluminium, steel, titanium. Five thread rolling machines are flexibly operated with the capacity to roll up to 60 tonnes.
Thread rolling produces a superior quality thread whilst retaining a higher degree of accuracy and greatly reduced production times when compared with other thread manufacturing methods.
Thread rolling accreditations include
- ABP 2-2333
- JES215 & JES286
Typical thread rolled components