Threading is the process of creating a screw thread. There are many method f generating threads, including thread turning and milling, tapping, thread rolling and forming.
Thread turning, as compared to thread forming and rolling, is used when full thread depth is required, when the quantity is small, when the blank is not very accurate, when threading up to a shoulder is required, when threading a tapered thread, or when the material is brittle.
Tapping is an easy, well known and highly efficient threading process. This method offers productive and economical threading, especially for smaller threads, through reduced machine downtime, higher cutting speeds, and long tool life.
Forming taps and cutting taps come in different designs. The material, coating, and geometry of the tap are very important features to be considered for each tap style. A tap design for a specific area that works well for one material/application may not be working effectively for another material/application.
Tapping covers the most common thread profiles and is suitable for all kind of machine tools, both rotating and non-rotating components.
Thread milling produces threads with the circular ramping movement of a rotating tool. The lateral movement of the tool in one revolution creates the thread pitch.
Although not as widely used as thread turning; thread milling achieves high productivity in certain applications.
In addition to thread turning, often called thread rolling, we understand the non-cutting production of threads by cold forming, in which the profile is rolled into the surface of the corresponding blank. According to DIN 8580, thread rolling is part of forming, more accurate pressure forming, and rolling.
The forming is based on the generation of compressive stresses by tools imaging the workpiece.
There are different types of thread rolling, which are differentiated according to the type of tools used:
Flat jaw rollers: The blank is processed between two profiled flat jaws, which are moved linearly to each other.
Segment rollers: The blank is machined between a segment-shaped profile surface and a roller, which rotates in the tread surface.
Grooving and continuous axial thrusting: The blank is machined between two profiled rolls.
The thread rolling is much faster and cheaper in large quantities than other methods for producing threads, namely the thread cutting. Further advantages of thread rolling are:
The grain boundaries are not interrupted unlike cutting
Cold forming achieves surface hardening
Press-polished thread flanks
Higher wear resistance
Reduced notch sensitivity
No chips, therefore less material requirement
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