When manufacturing fasteners, the choice of material is crucial, but equally important is the process used to form the threads. So, what kinds of metals can be turned into threads using flat thread rolling dies? Flat thread rolling dies can process a wide range of ductile metals, including most grades of steel (low-carbon, medium-carbon, and some alloy steels), stainless steel, brass, copper, and various aluminum alloys. The key requirement is that the material must possess sufficient ductility and be capable of being cold-formed without fracturing. This makes thread rolling a versatile and highly efficient method for manufacturing fasteners from common engineering materials.

This article will explore the specific material properties required for thread rolling, the various metal types that are successfully processed, and how the choice of material impacts the thread rolling process itself.

Table of Contents:

• What is the Core Material Requirement for Thread Rolling?
• What Types of Steel Can Be Processed by Flat Thread Rolling Dies?
• Can Stainless Steel Be Thread Rolled?
• How Do Non-Ferrous Metals Perform in Thread Rolling?
• How Does Material Hardness Affect the Thread Rolling Process?
• What Materials Are Not Suitable for Flat Thread Rolling Dies?

What is the Core Material Requirement for Thread Rolling?

The core material requirement for thread rolling is sufficient ductility, which is the ability of a material to deform plastically under tensile stress without fracturing. Since thread rolling is a cold-forming process, it works by displacing metal rather than cutting it. The material must be soft and pliable enough to be compressed and forced into the thread’s shape by the dies without cracking or tearing. This property allows for a chipless process that enhances the final product’s strength.

The ductility of a material is often inversely related to its hardness. A material that is too hard will not deform properly and may cause excessive die wear or fracture the part. A material that is too soft may not hold the thread’s shape well. Therefore, the ideal material has a balance of good ductility and a controlled hardness level, which is why pre-rolling heat treatment is often used to prepare the material.

What Types of Steel Can Be Processed by Flat Thread Rolling Dies?

Flat thread rolling dies can process a variety of steel types, primarily low- to medium-carbon steels and many common alloy steels, all of which offer the necessary combination of ductility and strength. These steels are the most widely used for fasteners because they are cost-effective and respond well to the cold-forming process. The carbon content and alloying elements determine the steel’s suitability for rolling.

• Low-Carbon Steels (e.g., 1006, 1018): These are the most common and easiest to roll. Their high ductility makes them ideal for standard screws and bolts that do not require high strength.
• Medium-Carbon Steels (e.g., 1038, 1045): These steels are stronger than low-carbon steels. They are often used for fasteners that require heat treatment after rolling to achieve higher tensile strength. They can be rolled but require more force.
• Alloy Steels (e.g., 4140, 8620): These steels contain alloying elements like chromium and molybdenum to increase their strength and hardenability. They are used for high-performance bolts in critical applications. They can be thread-rolled but may require specialized dies and more powerful machinery due to their increased strength.

The key to rolling steel successfully lies in ensuring the material’s properties, particularly its ductility and hardness, are within the acceptable range for the specific die and machine setup.

Can Stainless Steel Be Thread Rolled?

Yes, stainless steel can be successfully thread rolled, but it requires specific considerations due to its high work-hardening rate and galling tendencies. While many grades of stainless steel have excellent ductility, they harden rapidly when cold-formed. This means that rolling can be more challenging and requires robust dies and powerful machines to handle the increased force. Additionally, stainless steel’s properties make it prone to galling (material adhesion) against die surfaces.

To address these challenges, manufacturers take several steps:

• Lubrication: High-performance lubricants are essential to prevent galling and reduce friction between the die and the workpiece.
• Die Material and Coating: Dies made from high-quality, wear-resistant tool steels or carbide with specialized coatings (like CrN or DLC) are used to combat the abrasive and adhesive nature of stainless steel.
• Machine and Tooling: More robust machines and tooling designed for higher loads are often necessary to effectively roll stainless steel.
• Material Grade: The specific grade of stainless steel matters. Austenitic grades like 302 and 304 are generally more ductile and easier to roll than martensitic grades like 410.

When performed correctly, thread rolling produces stainless steel fasteners with superior fatigue life and strength compared to cut threads, making it a valuable process for demanding applications.

How Do Non-Ferrous Metals Perform in Thread Rolling?

Non-ferrous metals like brass, copper, and aluminum alloys perform exceptionally well in thread rolling due to their inherent ductility and malleability, making them ideal for fasteners that do not require the strength of steel. These materials can be formed with lower pressures and are less prone to causing excessive die wear. However, their softness can also be a disadvantage in applications where threads need to withstand high forces.

• Brass and Copper: These materials have very high ductility, making them easy to thread roll. They are commonly used for electrical connectors, plumbing fittings, and decorative fasteners where corrosion resistance and conductivity are more important than high strength. The process produces excellent thread finishes and is highly efficient.
• Aluminum Alloys: Many aluminum alloys, especially those used for fasteners, are very ductile and can be easily thread rolled. The resulting threads are strong for the material’s weight. Aluminum fasteners are used in aerospace, electronics, and automotive industries where weight savings are a priority. Specific alloys (e.g., 2024, 7075) can be rolled but may require annealing to increase ductility before forming.

For non-ferrous materials, the primary challenge is not the material itself, but ensuring the threads are formed accurately and without damaging the part, as they are often softer than steel.

How Does Material Hardness Affect the Thread Rolling Process?

Material hardness directly affects the thread rolling process by influencing the amount of force required, the lifespan of the dies, and the quality of the final threads. A material that is too hard will not deform properly, leading to increased die wear and potential tool breakage. A material that is too soft may not retain the thread’s shape, resulting in poor-quality threads. The ideal hardness range for thread rolling typically falls between 60 to 100 on the Rockwell B scale (HRB) or a similar measure.

Manufacturers often perform pre-rolling heat treatment, such as spheroidize annealing, to achieve the optimal hardness and ductility for the material. This ensures the best possible outcome, balancing ease of rolling with the desired final product properties.

What Materials Are Not Suitable for Flat Thread Rolling Dies?

Materials that are generally not suitable for flat thread rolling dies are those with low ductility, high hardness, or an insufficient ability to be cold-formed without fracturing. These include brittle materials like cast iron, certain high-carbon tool steels, and hardened steel alloys. The process requires the material to be pliable enough to flow, a property that these materials lack, making them prone to cracking or sudden failure under rolling pressure.

• Cast Iron: Cast iron has a crystalline structure with graphite flakes that make it very brittle. It cannot be plastically deformed and would shatter under the rolling dies.
• High-Carbon Tool Steels: Once hardened, steels like D2 or H13 are too hard and lack the ductility required for rolling. They would cause severe damage to the dies or fracture the workpiece.
• Very Hardened Materials: Any material that has already undergone a full hardening heat treatment is typically unsuitable. The material must be in an annealed or “as-rolled” condition to be successfully formed.

For materials that are too hard or brittle, threading must be done by machining (cutting) or grinding, which are processes that remove material rather than displacing it.

Conclusion

Flat thread rolling dies are a cornerstone of modern manufacturing, providing the speed, precision, and strength required for high-volume fastener production. Their widespread use across critical industries, from automotive to electronics, underscores their importance as a superior cold-forming method that produces stronger, more durable threads with minimal waste. By understanding the unique benefits and applications of flat thread rolling, manufacturers can make informed decisions to optimize their production processes and ensure the highest quality of their fasteners.

At Xiluo Mold, our expertise in thread rolling dies is second to none. With over 24 years of experience, we specialize in designing and manufacturing high-precision flat and cylindrical thread rolling dies. As the only one-stop R&D and production screw mold factory in China, we meticulously control every step of the process. We use high-quality imported steel and stringent quality control. This ensures our tooling delivers the superior durability, accuracy, and performance required for your most demanding cold-forming operations.