Thread Rolling VS Thread Cutting. Why Manufacturers Prefer Rolled Thread?

What Is Thread Rolling?

Thread rolling is a cold forming or cold metal forming process that creates threads using precision thread rolling dies that are the mirror image of the thread being produced. This process is different from other processes like metal cutting, grinding, and chasing because it does not remove any metal to create the desired profile. Instead, these hardened steel thread rolls move and mold ductile metals quickly and very precisely into desired thread form.

When a thread is rolled, it means the thread was formed by cold forming the steel by pressing the part between either two flat plates or round dies that have the thread pitch machined onto their face. As the part "rolls" through the dies, the pressure applied by the plates creates the thread without cutting or removing material.

What Is Thread Cutting?

A cut thread (also called a machined thread) is made by machining away the material in order to create the thread form. Cut threads, as the name implies, are made by cutting away material.

Thread Rolling VS Thread Cutting

Are the threads cut or rolled? We are often asked this question in regards to how the threads were manufactured on a particular size bolt or screw that we stock. The main reason we are asked this question is because “rolled” threads are perceived to be superior to “cut” threads on externally threaded fasteners.

Strength, accuracy, economy, and fine surface finish are some of the advantages of thread rolling. In contrast to cutting or grinding threads, the rolling process allows for higher rates of production, lower material costs, and no chips or loss of metal.

Fatigue resistance is realized in several ways. Threads are produced with burnished roots and flanks, free from surface imperfections that might prove to be starting points for fatigue failure. Surface layers of the thread, particularly those in the roots, are stressed in compression. These compressive stresses must be overcome before the tensile stresses that cause fatigue failure can be built up. Fatigue strength is reported to be improved by 50 –75 percent. Test on bolts first heat treated to a hardness of 35-40 Rockwell C and subsequently rolled show increased fatigue strength.

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