Mar. 10, 2025
Thread rolling frequently asked questions.
In cold forming, the thread rolls are pressed into the component, stressing the material beyond its yield point. This causes the component material to be deformed plastically, and thus, permanently. Unlike thread cutting, the grain structure of the material is displaced not removed.
As the material will be plastically deformed by pressure, it should have a minimum elongation of 5% and a maximum tensile strength of 246,000 PSI.
Materials that have less than 5%
Elongation or a significant hardness greater than 40 Hrc, such as cast iron, hard brass alloys and other hardened materials are not suitable candidates for the thread rolling process.
The only requirement for the rolling process is that either the component or the rolling head, or both, are rotating toward one another.
Thread rolling tools can be used on a wide variety of standard and special machine tools:
Threads are produced in seconds and in only one (1) pass, whereas CNC single point thread cutting requires numerous passes and a much longer cyle time. Long roll-life eliminates costly down time for tool changes.
In cold forming operations, extremely short cycle times are not just a welcome attribute, but rather a condition of the process. In plastic deforming, the material must be caused to flow, therefore, higher rolling speeds are better than low speeds.
Axial rolling:
Recommended rolling speeds are 90-270 SFM. Length of thread determines cycle time.
Radial rolling:
Recommended rolling speeds are 45-90 SFM. Since radial rolling is complete in one revolution of the roll, rolling time is extremely short (less than 1 second).
Tangential rolling:
Recommended rolling speeds are 60-240 SFM. The controlled feed rate required in this operation must enable the rolling operation to be completed within 15-30 revolutions of the component. Higher material strengths require lower rolling speeds.
Thread rolling requires no more power than what is normally provided on a standard machine tool.
Axial-method: Threads are progressively formed along the axis of the workpiece. Axial heads require only 60% of the torque necessary to cut threads.
Radial-method: A complete thread is formed in a single revolution of the rolls. Although this method requires more torque than axial, it does not exceed the machine capabilities.
Tangential-method: A thread is formed in 15-30 revolutions of the component. In this case, the drive power of the spindle is not a critical factor. The power to roll the profile comes from the drive of the cross slide (or turret).
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Conventional cutting fluids are normally suitable for rolling applications. For instance, emulsions having a 1:10 to 1:20 dilution are commonly used, sometimes with a high pressure additive. High pressure additives will reduce friction between rolls and components, thereby increasing the life of the thread rolls.
A thread rolling screw (TRS) is a type of threaded fastener that utilizes threads to reliably and securely fasten different materials. These types of screws create threads in the material by forcing the material outward. As a result, they are most popular in applications where you want to avoid loose chips that are typically created by thread-cutting screws.
Unlike traditional screws, thread rolling screws do not require a pre-tapped hole. As a member of the tapping screw family, these fasteners 'roll' or form their own threads by displacing the material instead of removing it. The name 'thread rolling screw' is typically reserved for self-tapping screws that have a coarse pitch and a standard machine screw thread form.
While a standard bolt and thread rolling screw can appear to be similar, there are distinct differences.
Pictured above is a standard M10 metric flange screw. This type of screw can be threaded into a tapped hole or a mating nut. With this type of screw, make sure to recognize how the lead thread is rounded and uniform.
The screws pictured above are both thread rolling screws and will create their own threads into the properly prepared light metal or steel. With thread rolling screws, it's important to recognize the triangular shape to the point. You should also notice the distinct tapering of the first two to three threads.
The unique tapered lead threads and different shapes are instrumental in helping start rolling threads in the mating material. Although several different point styles can be used with thread rolling screws, they must all meet performance specifications in the corresponding fastener standards such as:
Thread rolling screws are typically case-hardened. This attribute allows them to create threads into ductile metals that may be up to twice their diameter. The surface hardness of the screw must be harder than the material it's being threaded into. And thread rolling screws are not ideal for brittle materials, such as cast iron.
When using thread-forming fasteners, hole preparation is paramount. The hole size can vary based on the thickness and type of material. Because of this, it's vital to refer to foundational literature, such as the chart below:
You can view this table and other technical literature on the technical section of our website at www.bossard.com.
When creating a pilot hole, the displacement of the material at the entrance of the hole must be taken into consideration. One tip is to add a countersink to the hole, so the bulge isn't created upon thread forming. The creation of a bulge could result in the parts not seating flat against each other.
When deciding whether to use thread-rolling screws, it's important to evaluate the needs of your application. And the engineers at Bossard offer decades of experience providing expert guidance in all matters involving fasteners and thread rolling screws.
For more information on Thread Rolling Screws or any type of fasteners, check out www.bossard.com or contact us at .
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