Forming threads - achieving a clean finish without chips

While thread cutting remains close to our hearts, it’s not the sole method for creating threads. There are multiple ways to produce threads, each with distinct characteristics, pros, and cons. Your choice will depend on several factors like the material you’re working with, the machinery available in your workshop, and your personal experience and preferences. Let’s explore beyond the familiar! Today, we’re diving into a chipless approach to thread creation: thread forming or thread rolling. Discover how it works, when to use it, and what makes thread forming so remarkable in this article. ### How Does Thread Forming Work? Thread forming generates threads without removing any material, unlike thread cutting, which involves cutting away material. Instead of cutting, thread forming displaces the material. This process is commonly known as cold forming. Cold forming happens below the recrystallization temperature of the material, meaning there’s no change at the molecular level within the crystal lattice. This results in enhanced material strength. ### The Tool for Thread Forming Thread forming requires a specialized tool: the thread forming tap, also called a roll tap. When inserted into a prepped core hole, the thread forming tap pushes the thread into the material. Unlike regular taps, thread forming taps don’t have flutes since no chips are produced during the process that need to be removed. Narrow grooves might help distribute coolant more effectively. While a standard tap has cutting edges, a thread forming tap has a pilot taper. All the thread teeth are fully developed on the taper, gradually increasing in diameter. Moreover, the forming tap has a polygonal profile instead of being round. ### The Process of Thread Forming The steps for thread forming resemble those for cutting threads. First, you need to create a core hole. Be mindful of the specific dimensions required for core holes in thread forming. You can further chamfer the core hole using a countersink. After completing this step, you can move forward with thread forming. During thread forming, claw marks appear at the thread tips, which are small voids characteristic of this manufacturing process. These marks don’t impact the functionality of the thread. ### The Core Hole Diameter for Thread Rolling In thread rolling, the core diameter is larger than in thread cutting, but the tolerances are tighter. This means you have less room for error when it comes to the core hole’s diameter. You can calculate the appropriate dimensions for thread rolling using this formula: \[ Dk = D – (0.5 \times P) + 0.05 \] Where: - \( Dk \) = Core hole diameter - \( D \) = Thread major diameter - \( P \) = Pitch Due to the tight tolerances, you should only perform the calculation yourself if you’re confident in your abilities. Otherwise, it’s better to consult a table for the correct core hole diameter to prevent mistakes. ### When Is Thread Forming Practical? Thread forming is only practical for thread production when working with highly cold formable materials, including light metals and their alloys, nickel and cobalt alloys, titanium and its 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 suitable for 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 significantly greater than with machining tools and is only restricted by the tool’s length. Thread forming generates substantial friction forces, causing heat buildup. Consequently, lubrication and cooling are even more critical compared to other thread-generating methods. If you can’t consistently provide enough high-quality lubricant, thread forming isn’t a feasible option for you. Furthermore, thread rolling works best when performed on a stationary machine tool. This method is less ideal for manual work. ### The Advantages of Thread Forming Despite these constraints, thread forming offers several benefits. A major advantage is that no chips are generated during thread rolling. This eliminates chip-related issues, which are among the most common errors in thread generation. With thread rolling, you don’t need different tools for blind holes versus through holes. Additionally, thread forming produces threads with exceptional strength and superior surface quality due to cold forming. Thread forming avoids the problem of axial misalignment that can occur with cutting threads, which could potentially ruin the entire thread. Thread rolling enables higher cutting speeds and longer tool life. Tools for thread forming are designed for prolonged use. However, unlike thread cutting tools, thread formers cannot be resharpened once they wear out. ### Is Thread Forming Suitable for You? If you’re working with a compatible material and prefer to avoid chips, perhaps because you need to create threads in a blind hole, then thread formers are a viable alternative. Nevertheless, you should be aware that thread forming presents its own set of challenges. To counteract the high friction forces, you require a substantial amount of high-quality lubricant. Precision is also crucial when creating the core hole for thread forming due to the tight tolerances. It’s easy to make the hole either too large or too small, which can lead to an improperly formed thread or tool breakage. Are you intrigued by thread forming? Visit the BAER online shop! As your screw tap manufacturer, we offer a wide range of thread forming taps. For any questions, feel free to reach out to our customer service via the contact form.

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