If you're looking to create a thread, the first decision you'll face is choosing the right method. While tapping is a common and effective technique, it's not the only option available. You can also mill, roll, turn, or form threads. In this blog post, we’ll take a closer look at the last method—thread forming. Understanding the differences between each threading process will help you make an informed choice based on your specific needs.
Thread forming is a chipless method of thread production. Unlike traditional cutting methods that remove material, thread forming works by displacing it. This means no chips are generated, and the material remains intact. The process is often called cold forming because it takes place below the recrystallization temperature of the material, which helps improve the thread’s pull-out strength.
Compared to thread cutting, thread forming taps have a different design. They don’t have cutting edges and instead feature a polygonal shape. Since no chips are produced, they typically don't require flutes. Some models include oil grooves for better lubricant distribution. Instead of a chamfer, a forming cone is used to begin the thread, and the teeth gradually increase in diameter as the thread is formed.
One key difference between forming and cutting is what happens inside the material. Thread forming compresses the fibers rather than cutting them, maintaining their continuity. This results in stronger, more durable threads. Additionally, the maximum thread depth achievable with forming is generally greater than with machining, provided proper lubrication is used.
Another advantage of thread forming is that it allows for higher circumferential speeds compared to traditional cutting methods. However, due to the high friction involved, it's essential to use high-quality cooling lubricants effectively. Torque levels during forming are also higher than with cutting, depending on factors like diameter, material, pitch, and coating.
Thread forming is best suited for materials that are highly formable at cold temperatures. These include light metals, nickel and cobalt alloys, titanium, non-ferrous metals, and certain types of steel. It's important to note that very fine pitches may not be achievable through forming, with typical limits around 3–4 mm. If you need a larger pitch, other methods might be more suitable.
When using a thread forming tap, the core hole diameter must be calculated correctly. It’s usually larger than in traditional tapping but with tighter tolerances. The formula for calculating the core hole diameter is Dk = D – (0.5 x P) + 0.05, where D is the nominal diameter and P is the pitch. Alternatively, you can refer to standard tables for accurate values.
Due to the high friction forces involved, proper lubrication is crucial. Oil grooves or internal lubricant systems can help ensure even distribution. Also, the tight tolerances required for the borehole demand careful attention to detail.
In terms of advantages, thread forming eliminates chips, produces strong threads, and offers excellent surface quality. It's also ideal for deep threads and has a longer tool life compared to conventional taps. However, there are some limitations: it's only suitable for specific materials, requires precise lubrication, and can generate significant heat. Additionally, thread forming taps aren't typically used as hand tools and require specialized equipment.
If you're interested in thread forming taps or compatible cutting oils, you can find them in the online shop of tap manufacturer BAER. Explore our selection today, and feel free to reach out if you have any questions or need assistance. Our customer service team is always happy to help!
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