Forming threads - achieving a clean finish without chips

While thread cutting holds a special place in our hearts, it’s not the sole method for producing threads. There are multiple ways to create threads, each with distinct characteristics, pros, and cons. Your choice will depend on factors like the material you're working with, the machinery available in your workshop, and your personal expertise and preferences. To help you decide, let’s explore a chip-free method of thread creation: thread forming or thread rolling. In this blog post, we’ll delve into how it works, when it’s ideal to use, and why thread forming stands out. ### How Does Thread Forming Work? Thread forming is a process that doesn’t involve removing material, unlike thread cutting, which cuts away pieces. Instead, thread forming displaces the material. This is commonly known as cold forming, where the shaping happens below the material's recrystallization temperature, ensuring no molecular changes occur in the crystal lattice. This results in stronger material properties. ### The Tool for Thread Forming To perform thread forming, you'll need a specialized tool: the thread forming tap, also called a roll tap. When inserted into a prepped core hole, this tool pushes the thread into the material. Unlike thread cutting taps, thread forming taps don't have flutes since no chips are produced that would need removal. Narrow grooves might be useful for distributing coolant effectively. While a regular tap has cutting edges, a roll tap features a pilot taper. All thread teeth are fully developed on this taper, gradually increasing in diameter. Additionally, the forming tap has a polygonal shape rather than being round. ### The Process of Thread Forming The steps for thread forming are somewhat similar to those for cutting threads. Initially, you need to create a core hole. Be mindful, as core holes for thread forming follow specific dimensions. You can further chamfer the core hole using a countersink. Once completed, you can move forward with thread forming. During thread forming, claw marks form at the thread tips—small voids that characterize this manufacturing process. These marks don’t impact the thread’s functionality. ### The Core Hole Diameter for Thread Rolling In thread rolling, the core diameter is larger than in thread drilling, yet the tolerances are tighter. This leaves little room for error when determining the core hole's diameter. You can calculate the right dimensions for thread rolling using this formula: Dk = D – (0.5 x P) + 0.05 Where: - Dk = Core hole diameter - D = Thread major diameter - P = Pitch Due to the tight tolerances, it’s advisable to only calculate this yourself if you’re confident in your abilities. Otherwise, it’s better to refer to a table for the correct core hole diameter to avoid mistakes. ### When Is Thread Forming Practical? Thread forming is only suitable for thread production when working with materials that are highly cold formable. This includes light metals, light metal alloys, nickel and cobalt alloys, titanium and titanium alloys, non-ferrous metals, steels up to approximately 1200 N/mm², and corrosion-resistant, acid-resistant, and/or heat-resistant steels up to 1200 N/mm². Other materials aren’t compatible with thread forming. Material properties also impose limits on pitch. The maximum pitch in thread forming can be 3 to 4 mm. However, the achievable thread depth is much greater than with machining tools and is solely limited by the tool’s length. Thread forming generates significant friction forces, causing heat buildup. Consequently, lubrication and cooling become even more crucial compared to other thread-generating methods. If you can’t ensure a consistent supply of high-quality lubricant, thread forming isn’t the best option for you. Additionally, thread rolling works best when using a stationary machine tool. This method is less practical for manual work. ### The Advantages of Thread Forming Despite these limitations, thread forming offers several benefits. One major advantage is the absence of chips during thread rolling. This eliminates chip-related problems, which are a common source of errors in thread generation. With thread rolling, you don’t need different tools for blind holes versus through holes. Moreover, thread forming produces threads with exceptional strength and superior surface quality due to cold forming. Thread forming prevents axial misalignment, which is a concern with cutting threads and could potentially damage the entire thread. Thread rolling allows for higher cutting speeds and longer tool life. Tools for thread forming are designed for extended use. However, it’s worth noting that unlike thread cutting tools, thread formers can’t be resharpened if they wear out. ### Is Thread Forming Right for You? If you’re working with a compatible material and want to avoid chips, perhaps because you need to create threads in a blind hole, then thread formers are a great alternative. However, you should be aware that thread forming comes with its own set of challenges. To counteract high friction forces, you need a substantial amount of high-quality lubricant. Precision is crucial when creating the core hole for thread forming due to the tight tolerances. It’s easy to make the hole too large or too small, which can lead to improperly formed threads or tool breakage. If thread forming intrigues you, feel free to visit the BAER online shop! As your screw tap manufacturer, we offer a wide range of thread forming taps. You can reach out to our customer service via the contact form with any questions. Whether you’re a seasoned professional or just starting out, thread forming opens up exciting possibilities in thread production.

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