What is Thread Rolling? (Explained with Images)

Thread rolling

What is Thread Rolling?
Thread rolling is a cold working technique of making external threads on the cylindrical workpiece.

In Thread Rolling, the threads are made by pressing the thread rolling dies against the workpiece.

By using thread rolling, the operation can be performed very fast and hence a large number of components can be made in less time.

Also the thread cutting operation can be performed by semi skilled workers, so this operation is economical too.

The thread cut by this method has good dimensional accuracy and surface finish.

Thread rolling is a chipless operation, so there is no wastage of material by this method.

By performing thread rolling operation, the fatigue strength as well as tensile strength of the workpiece increases.

But, it also has a limitation that it is used only for ductile metals as the threads are cold formed.

This method of metal threading is suitable for diameters upto 20mm.

Types of thread rolling machines

There are basically 4 types of thread rolling machines.

  1. Fixed and reciprocating flat die machine
  2. Cylindrical two die machine
  3. Cylindrical three die machine
  4. Rotary planetary die machine

Let’s discuss each of these thread rolls one by one.

#1) Flat die machine

Flat die machine

The flat thread rolling die machine is a machine in which the bottom die is held stationary and the other die reciprocates above it.

The workpiece is placed on one end of the stationary die and the upper die (reciprocating die) is rolled over the workpiece.

Because of the sharp cutting edges of the dies and the pressure exerted on the blank, the threads are generated on it.

The blank (or workpiece) coming out from the other end will have the finished threads.

#2) Cylindrical two die machine

Cylindrical two die machine

The cylindrical two die machine is shown in the above image. You can see that the workpiece is supported between the two dies (which is quite similar to that of centerless grinding).

#3) Cylindrical three die machine

Cylindrical three die machine

In the case of a three die machine, the workpiece is supported by three rolling dies.

The dies move radially outward and the threads are made on the workpiece due to the extreme pressure of three rolling dies.

This method of thread rolling is mostly done on turret lathe and screw machines to cut threads on ductile metals.

#4) Rotary planetary die machine

Rotary planetary die machine

Rotary die machine is a thread rolling machine that possesses one or more outer dies which remain fixed and the inner dies rotate (see above image).

By this process, a large number of jobs can be manufactured in less time.

Because of this, rotary die machines have more productivity, but it has a limitation that it is used only for small workpieces.

External links:
Thread rolling: Image by Tosaka, CC BY 3.0, via Wikimedia Commons

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