With modern tools and the right control software, inside threads can now be produced both with and without chips. Experts differentiate between conventional tapping, coldforming tapping (thread forming) and thread milling. Find out what’s best…and when.
During tapping, threads are cut into predrilled holes with screw taps manually or by machine. This procedure can be used for practically all areas of application and materials. Cold-forming taps are used for the chipless, machine creation of standard threads. In contrast to tapping, the thread is not created by cutting out material, but by cold forming. The material is pressed into the required profile without interrupting the fiber orientation of the inside thread. With the development of computer controlled machine tools, thread milling was introduced as an additional procedure. The thread is milled into the hole through the specific superimposing of the circular and feed motion of the milling tool with its pivoting.
The "classic" method: tapping
In the tapping process, the material is taken off step-by-step in a continuous cut. Tapping comes up against its limits with materials with a hardness of more than 60 HRC and deep threads for which problems arise with dimensional accuracy through to tool breakage because of poor chip removal.
Chipless: cold-forming tapping
Cold-forming tapping is used for materials with a strength of less than 1200 N/ mm2 and a stretch at break of more than 8 percent. In the chipless process, the thread is created by a step-by-step reforming process and, thanks to coldforming, achieves higher static and dynamic strength in combination with a very good surface quality. Disadvantages of cold-form tapping are the high torques compared to conventional tapping and the need for highquality lubricants.
Productive and precise: thread milling
Thread milling is suitable for almost all materials and offers the greatest flexibility and productivity of all the procedures. The thread flanks are machined cleanly and there is no axial miscut. For hard-to-machine materials, thread milling is the best method – and not just because if the tool breaks it can be removed easily. There are restrictions relating to the thread depth, which can generally be no more than three times the thread diameter. But whatever method is used, one thing is certain: with the thread cycles in ShopTurn and ShopMill, programming is quick and easy.