If you're looking to create a thread, you'll need to decide on the best method for the job. While tapping is a common and effective approach, it's not the only option. Other methods such as milling, turning, or forming threads are also available. In this post, we’ll explore the process of thread forming in detail. Understanding the differences between each method will help you make an informed choice based on your specific application.
Thread forming, also known as rolling, is a chipless method of thread production. Unlike traditional cutting, where material is removed, forming displaces the material to shape the thread. This process is often referred to as cold forming because it occurs below the recrystallization temperature of the material. As a result, the fibers within the material remain intact, leading to stronger and more durable threads.
One of the key features of a thread forming tap is that it doesn’t have cutting edges. Instead, it has a polygonal shape with a forming cone at the tip. These taps don’t require flutes since no chips are produced during the process. Some models include oil grooves to ensure proper lubrication. The thread teeth are fully formed from the start, gradually increasing in diameter as the tap moves through the material.
When examining the thread itself, you may notice small hollows or "claws" at the tips. However, the main difference lies in how the material is affected. Thread forming compresses the material rather than cutting it, preserving the continuity of the fiber structure. This results in improved mechanical properties and higher tensile strength.
Another advantage of thread forming is that it allows for deeper threads compared to traditional machining methods. The depth is limited only by the length of the tool, provided there’s sufficient lubrication. Additionally, thread forming can be performed at higher rotational speeds, which increases productivity. However, due to the high friction involved, it's essential to use high-quality cooling lubricants to prevent overheating and ensure smooth operation.
The applications of thread forming are primarily limited to materials that are highly formable at room temperature. These include light metals, nickel and cobalt alloys, titanium, non-ferrous metals, and certain types of steel up to 1200 N/mm². For other materials, alternative threading methods may be more appropriate.
Pitch is another factor that affects the suitability of thread forming. Very fine pitches are difficult to achieve with this method, and the maximum pitch typically ranges from 3 to 4 mm depending on the material. If you need a larger pitch, thread forming may not be the best option.
When using a thread forming tap, it's important to pay attention to the core hole diameter. It must be calculated correctly to ensure proper fit and function. The formula for determining the core hole size is: Dk = D – (0.5 x P) + 0.05, where Dk is the core hole diameter, D is the nominal diameter of the thread, and P is the pitch. You can also refer to standard tables for accurate values.
Friction is a significant consideration when forming threads. High friction forces can lead to increased heat generation, so the right lubricant is crucial. Oil grooves or internal lubricant supply systems can help maintain consistent lubrication throughout the process. Proper lubrication not only improves performance but also extends the life of the tool.
In terms of benefits, thread forming offers several advantages. It produces high-quality threads with excellent surface finish, eliminates the risk of chip-related issues, and provides greater pull-out strength. It is also ideal for deep threads and can last longer than traditional taps.
However, there are some limitations. The method is not suitable for all materials, and tight tolerances must be maintained. Additionally, thread forming taps cannot be used as hand tools and require specialized equipment. This makes them less accessible for certain applications.
If you’re interested in thread forming taps and the appropriate cutting oils, you can find them in the online shop of tap manufacturer BAER. Explore our range and feel free to reach out if you have any questions or need assistance. Our friendly customer service team is always here to help.
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