Chapter 1: What is Thread Rolling?
Thread rolling is an integral cold forming process, used to produce a variety of threads, knurls and helical gears. The process involves deforming a metal blank by rolling it through a die. This process forms external threads along the surface of the metal blank. Internal threads can be formed using the same principle. In contrast to other widely applied threading operations such as thread cutting, thread rolling is not a subtractive process. That means it doesn’t remove metal from the stock. Rolled threaded fasteners offer advantages such as stronger threads, precise final dimensions, good surface finish, and a lower coefficient of friction.
Circular thread rolling die gives more control to the rolling process, with power to all rolls and controlled penetration rates. This allows harder and more difficult materials to be threaded.
UKO carbide circle thread rolling die are made of the highest quality materials. Manufactured to exacting standards, we can offer standard and customized thread rolling dies for in-feed and through-feed applications. Thread forms are precision ground and dies are produced to fit most types of circular screw nail thread rolling machine.
Chapter 2: The Differences Between In-feed and Thru-feed
In-feed thread rolling dies
In the in-feed process, the profile grooves of the rolls have the pitch of the thread to be produced. The rolls, driven at the same speed, move in the same direction. During rolling, the work piece moves due to friction with no axial shifting. As the thread produced by this means is an exact copy of the rolling dies, threads of this kind have a very high pitch accuracy. The maximum length of the thread is limited by the width of the dies (30-200 mm).
In-feed rolling uses a timed machine cycle. This is used for general rolling of parts up to the maximum width of the face of the dies, less die chamfers. In-feed rolling dies, also known as plunge rolling, are suitable for threading with a shoulder or a headed workpiece.
Features:
- Helix angle ground into the dies.
- Work piece and dies are kept parallel on the machine.
- Work piece rotates between the dies, but has little or no axial movement.
Thru-feed thread rolling dies
Thru-feed rolling is used for rolling threads that exceed the maximum face width of the dies, as well as for continuous rolling of long threaded bars. Here, the rolling dies have grooves with no pitch; the groove cross-section is that of the standard flank profile. The thread pitch is produced by skewing the die axes by the pitch angle of the thread. This means the workpiece is given an axial thrust and moves one pitch length in the axial direction for every full revolution. As the axial thrust kicks in immediately when the workpiece enters the assembly, larger threads are not formed to full depth in one pass.
Features:
- Typically uses annular ring type die, with the thread form ground on the die in straight rings with no helix.
- Helix angle produced by tilting the spindles on the machine to the same helix as the work piece.
- Workpiece rides between the dies on a support blade.
- Multiple start threads (within range of machine) can be rolled by increasing helix angle tilt on the machine.
- Speed-up dies are used for high-speed rolling.
Conclusion：Through the above explanation, we summarize the three points of the thread rolling dies to make a clear comparison.
| Types | Helix angle of die | Axial movement | Workpiece |
| In-feed | Yes | No | Shorter than die |
| Thru-feed | No | Yes | Longer than die |
Chapter 3: Factors to Consider in Thread Rolling
Material Requirements: A known disadvantage of thread rolling is its incompatibility with hard materials. The materials to be rolled must have a hardness not greater than HRC 40. Materials that can be rolled are low-carbon steels, mild steels, stainless steels, copper alloys, and often, aluminum. Moreover, the material must have the right degree of ductility. The recommended range is 12 to 20% elongation factor.
Chamfer Angle: Chamfer is the tapered conical surface at the start of a thread. Before rolling, the edge at one end of the stock must be machined to have a chamfer. A correct chamfer angle must be set to properly shape the thread at the end. The recommended chamfer angle is 30° for most cases.
Feeding: There are three basic techniques for feeding the stock into the dies: radial in-feed, tangential feed, and through feed. In radial in-feed, the dies move radially towards the axis of the stock. For tangential feed, the pitch of the stock approaches the rollers from its side making square, tangential contact. Lastly, through feed involves a cylindrical die that mates against the stock causing it to move axially.
Thread Rolling Speeds: Thread rolling speeds depend on the mechanical and power limitations of the machine, the thread diameter, and the material and hardness of the metal stock. Rolling speeds can range from 30 to 100 m/min. Low rolling speeds are required for hard materials while high speeds are for soft and ductile materials.
Coolant and Lubricant: Coolants or cutting fluids are extensively used in thread cutting, but these are also necessary for thread rolling. Deforming the metal also generates heat which can compromise both the dies and stock. Moreover, coolants can act also as lubricants to reduce the friction between the dies and stock.
Choose the most suitable thread rolling tool for your work piece, or we can suggest you for the case as long as we have your work piece for the study in ahead!
