Thread forming reduces costly machine downtimes
Chip-free process avoids jam and tool breakage
One of the key differences between this process and thread cutting is that it does not produce chips. Subsequently, there is no need to periodically back out the tap to clear away swarf, which, with a cutting tap, can jam and break the tap, resulting in costly machine downtime and component rework as the broken tap will need to be removed – often using an EDM drill.
Tests have shown the process of thread forming increases not only the yield strength of the thread, but also its surface finish, hardness and wear resistance. As a result, higher cutting speeds are recommended for forming taps than for the corresponding cutting taps in the same material.
To enable companies to take full advantage of thread forming, Dormer has a comprehensive program of forming taps. Manufactured from premium grade High Speed Cobalt (HSS-E), all are designed to support high performance thread production in a wide range of materials, and can be specified with an optional oil groove to ensure lubrication supply to the working edge.
The one important characteristic recommended for fluteless tapping is the use or addition of an extreme pressure additive within the lubricant used. Lubricants maintain the lubricity required in this type of machining application. A lack of lubrication during tapping will allow metal-to-metal contact with possible breakage.
For a thread cutting tap, the drilled hole is sized to the peak of the finished thread, with the tap removing the material between the pitch peaks to create the thread profile. No parent material is removed during thread forming, so the drilled hole size for an equivalent thread needs to be a slightly larger diameter. The raw material is then "pushed" by the tap to form the finished thread profile.
As the material flows to create the thread it becomes stronger and the surface finish generated is smoother, which means that the finished thread will offer an extended application life. Finally, it could also offer design engineers the opportunity to evaluate the use of smaller diameter fixings.
By Simon Winstanley, Dormer Tools.