Thread roller, which is also called thread rolling machine, is designed for creating external threads on screws, bolts, studs, and so on. The unique threads are generated by cold-form forming operation, which displaces and flows the metal materials into the shape. Thread roller regulates the force to rotate and applies it on the workpieces. The target metal pieces in thread rolling machines are also referred to as blanks. During thread rolling, hardened steel dies that are attached to the machines penetrate and press onto the rotating metal parts, reshaping the surface into thread form. The thread form refers to the threads profile that rolled onto the blank.
Thread rollers come in various types such as vertical die, horizontal die, planetary die type. High rolling speed and high precision make the rolling machine ideal thread forming machines for mass production. For example, planetary die thread rollers can produce tens of thousands of parts with threads per hour. There is no chip created from the operation, and also requires no pauses for cleaning, which saves time and reduces the risks of operation failure compared to some other machining process.
For starters, cylindrical workpieces or blanks can be fed into a thread roller manually or automatically. The hardened steel dies can be basically divided into two types: cylindrical dies or flat dies. The cylindrical dies rotate while the flat type dies reciprocate. As the dies forming the threads, the displaced metal material flows outward. Planetary thread rollers and rotary thread rollers are two main categories of thread rolling machines. The planetary thread rolling machines hold the blank stationary in the machine, manufacturing planetary roller screws which are utilized in precise applications. The normal rotary thread rollers roll around the workpieces, in contrast.
The cold-forming process can be utilized at room temperature, except for the case that the metal material is harder than RC45, which is more suitable for hot rolling to prolong the die life. The term RC refers to Rockwell scale, which represents how resistant the metal material is. Many alloys with blades have the hardness scales from RC45 to RC60. Thread rolling process is similar to centerless grinding, both of which are available for in-feed and thru-feed. Thru-feed refers to the feeding process where parts pass through the machine itself; in-feed, on the other hand, means the workpieces should be manually loaded into the thread rollers. In-feed is more commonly applied for products with complex or abnormal shapes.
Similar to other die casting or cutting applications, softer metal materials are easier to perform thread rolling. To ensure the overall success in operation, and lengthen the dies and machine life, you should be aware of the feature of the materials to not only reduce failures but ensure the product’s quality. Materials that are relatively softer allows rapider thread rolling, however, it results in poorer finish on the surface. For example, sulfur and lead allow high rolling rate but might have lower quality of the finish. Materials that are harder to deal with, such as stainless steel, are harder to roll but have ideal finishes. Another point that you should be aware of is that machining with steel, aluminum, sulfur, bismuth might create flakes. The balance of the quality of finish, the rolling speed, the life of the tool and the material formability all should be considered when selecting the materials for thread rolling.
Compared with cutting threads within other machines, thread rolling machines are more cost-efficient due to the less need for maintenance and longer tool life. They do not produce chips, reducing the pause time and errors in the process. Thread rolling is also greatly rapider than tapping or general threading. The features make the machines ideal for high volume production.
On the other hand, thread rolling machines that are specialized in high precision rolling are greatly suitable for small, sophisticated parts and applications in aerospace industry and other high technology applications require tight tolerance and high accuracy including motorsports. Screws manufactured by thread rollers have impressive advantages of resisting shear, tension and fatigue. The dimensional accuracy and cold formed properties including high density of material molecules, and the feature that no materials are removed during the thread rolling, all eliminate the disadvantage of some other high precision threading or cutting process.
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