Forming threads - achieving a clean finish without chips
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While thread cutting is something we hold dear, it’s not the sole way to generate threads. There are numerous methods available, each with their own distinct characteristics, pros, and cons. Your choice will depend on several factors, including the material you’re working with, the machinery at your disposal, and your personal expertise and preferences. To make an informed decision, let’s explore beyond the obvious! Today, we’re diving into a chipless approach to thread creation—thread forming or thread rolling. Discover how it operates, when it’s best applied, and what makes thread forming so remarkable in this blog post.
How Does Thread Forming Work?
Thread forming creates threads without removing any material, unlike thread cutting where material is cut away. Instead, thread forming displaces the material rather than severing it. This process is commonly referred to as cold forming. Cold forming happens below the recrystallization temperature of the material, meaning there are no changes at a molecular level in 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 known as a roll tap. When inserted into a prepared core hole, the thread forming tap presses the thread into the material. Unlike traditional taps, the thread forming tap doesn’t need flutes since no chips are produced during this process that would need to be removed. Narrow grooves might be useful for better coolant distribution. A thread forming tap differs from a standard tap in that it has a pilot taper. All thread teeth are fully developed on the taper, increasing in diameter. Additionally, 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 must drill a core hole. Be mindful, as specific dimensions apply to core holes for thread forming. You can further chamfer the core hole with a countersink. Once this is completed, you can move forward with thread forming.
During thread forming, claw marks form at the thread tips—small voids that define 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 margin for error when it comes to the core hole diameter. You can calculate the appropriate 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 narrow tolerances, you should 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 for thread forming to avoid mistakes.
When Is Thread Forming Practical?
The thread forming method is only suitable for thread production when working with materials that are highly cold formable. This includes light metals and light metal alloys, nickel and cobalt alloys, titanium and titanium alloys, non-ferrous metals, steels up to around 1200 N/mm², and corrosion-resistant, acid-resistant, and/or heat-resistant steels up to 1200 N/mm². Other materials are not compatible with thread forming.
Material properties also impose limits on pitch. The pitch in thread forming can be a maximum of 3 to 4 mm. However, the achievable thread depth is far greater than with machining tools and is only constrained by the tool's length.
Thread forming generates significant friction forces, causing heat buildup. Thus, compared to other methods of thread generation, lubrication and cooling become even more crucial. If you cannot guarantee a consistent supply of lubricant in sufficient quantity, thread forming isn’t a suitable method for you.
Furthermore, thread rolling works best with stationary machine tools. This method of thread generation is less ideal for manual work.
The Advantages of Thread Forming
Despite these limitations, thread forming offers several advantages. One of the primary benefits is that no chips are generated during thread rolling. This eliminates chip-related issues, which are one of the most common causes of 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 excellent surface quality thanks to cold forming.
Thread forming prevents the problem of axial misalignment that can occur with cutting threads, which could potentially ruin 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 important to note that unlike thread cutting tools, thread formers cannot be resharpened if 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. However, you should be aware that thread forming has its 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 too large or too small, which can lead to an improperly formed thread or tool breakage.
Intrigued by thread forming? 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 through the contact form with any questions.
For those who want to learn more, check out the video below demonstrating the thread forming process in action. Understanding thread forming can open new possibilities in your manufacturing processes, especially when working with specific materials and applications.
[Embed a video here showing the thread forming process]
Stay tuned for more insights into manufacturing techniques and tools. If you found this information helpful, consider sharing it with others who might benefit from understanding thread forming. And remember, whether you’re a seasoned professional or just starting out, there’s always more to discover in the world of engineering and manufacturing!