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Thread rolling is a process of pressing screw or bolt threads into stock instead of cutting it. It uses a hardened steel tool bit to impress the shape of the thread into the surface of the stock. This method is less expensive than threading, produces stronger products, and generates no heat or swarf.
Thread rolling is a method of manufacturing fasteners that involves pressing screw or bolt threads into the stock instead of cutting it. This process uses a hardened steel tool bit formed into the shape of its thread. The raw, unformed stock is rotated at a controlled rate as the tool tip is pressed against it under high pressure, causing the shape of the screw thread to be impressed into the surface of the stock. The tip of the tool is constantly held under pressure and advanced towards the blank until the full depth threads are formed. Roll forming is a less expensive manufacturing process than threading and produces stronger and safer end products.
Bolts and screws are among the most commonly used fasteners, with huge quantities produced worldwide each year. These fasteners are usually mass-produced from raw metal stock, which is pre-formed before threads are introduced. There are two basic methods used to form threads, namely thread trimming and thread rolling. Thread cutting uses a cutting die that is fed along the length of the rotating stock physically cutting the metal surface to form threads. While effective, this method is time consuming and generates heat that could weaken the fastener.
The second method, thread rolling, is a superior process in many ways. In this process, a hardened tool tip is used to press the threads into the surface of the stock. The tip of the tool is formed into the shape of the threads and is forced, under great pressure, against the stock, which rotates at a controlled speed. The increased pressure causes the tip of the tool to gradually imprint its shape on the softer metal. As threads begin to form, the tip of the tool is advanced towards the stock while maintaining pressure against it. This causes the impressed strands to deepen to their full depth.
The thread rolling process offers many advantages over threading. The required machinery is simpler, the process requires fewer steps with a consequent increase in productivity and the tool tips have a longer life, with a good overall advantage in terms of costs and performance. The threading process also generates high temperatures which tend to weaken the blank. Roll burnishing is a cold working process and produces inherently stronger end products. Additionally, burnishing does not generate chips or swarf, which produces a cleaner environment and reduces the danger of injury from freshly cut sharp threads.
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