Forming threads - achieving a clean finish without chips
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While thread cutting holds a special place in our hearts, it’s far from being the sole method for thread creation. In reality, there are numerous ways to produce threads, each with their own distinct characteristics, benefits, and drawbacks. Your choice ultimately hinges on various factors like the type of material you’re working with, the machinery available in your workshop, and your individual experience and preferences. To make an educated decision, let’s explore some alternatives together! Today, we’re diving into a chip-free approach to thread generation—thread forming or thread rolling. Discover how it operates, when it’s the right choice, and what makes thread forming so remarkable in this blog post.
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### How Does Thread Forming Operate?
Thread forming differs significantly from thread cutting because it doesn’t involve removing material; instead, it displaces the material. This process is often termed “cold forming,†which happens when the shaping occurs below the material’s recrystallization temperature. As a result, there are no alterations on a molecular level within the crystal structure, leading to enhanced material strength. Unlike traditional cutting methods, cold forming preserves the integrity of the material while still achieving precise threading.
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### The Tools for Thread Forming
To execute thread forming, you’ll need a specialized tool—the thread forming tap, also known as a roll tap. When inserted into a pre-prepared core hole, the thread forming tap pushes the thread into the material. Since no chips are generated during this process, the tool doesn’t require flutes. However, narrow grooves might be beneficial for distributing coolant more effectively. A thread forming tap differs from a standard screw tap in that it lacks cutting edges. Instead, it features a pilot taper, with all thread teeth fully developed on this taper and gradually increasing in diameter. Moreover, the forming tap has a polygonal profile rather than being circular.
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### The Steps for Thread Forming
The procedure for thread forming resembles that of cutting threads. Initially, you must drill a core hole. Keep in mind that specific dimensions apply to core holes for thread forming. Chamfering the core hole with a countersink can enhance the process. After completing these preparatory steps, you can move forward with thread forming.
During thread forming, claw marks form at the thread tips—small voids that are characteristic of this manufacturing technique. These marks don’t impact the functionality of the thread.
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### The Core Hole Diameter for Thread Rolling
In thread rolling, the core diameter exceeds that of thread drilling but has stricter tolerances. This leaves less room for error regarding the core hole diameter. You can compute 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 narrow tolerances, you should only attempt the calculation if you’re confident in your abilities. Otherwise, consult a table to determine the correct core hole diameter for thread forming to prevent mistakes.
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### When Is Thread Forming Practical?
Thread forming is only feasible for thread production when dealing with highly cold-formable materials, including light metals, light metal 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. Materials outside this range are incompatible with thread forming.
Material properties also impose limits on pitch. In thread forming, the pitch can be a maximum of 3 to 4 mm. However, the achievable thread depth surpasses that of machining tools and is solely constrained by the tool’s length.
Thread forming generates considerable friction forces, causing heat buildup. Consequently, compared to other thread generation methods, proper lubrication and cooling become even more vital. If you cannot consistently provide sufficient lubrication, thread forming may not be the ideal method for your needs.
Additionally, thread rolling works best with stationary machine tools. This method isn’t well-suited for manual operations.
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### The Benefits of Thread Forming
Despite these limitations, thread forming offers several advantages. One standout benefit is the absence of chips during the process. This eliminates common issues related to chips, which frequently cause errors in thread generation. Thread rolling doesn’t necessitate separate tools for blind holes versus through holes. Furthermore, thread forming produces threads with exceptional strength and superior surface quality due to cold forming.
Thread forming avoids the problem of axial misalignment, which is a concern when cutting threads and can compromise the entire thread. Thread rolling supports higher cutting speeds and extends tool life. Thread forming tools are built for prolonged usage. However, it’s worth noting that unlike thread cutting tools, thread formers cannot be resharpened once they wear out.
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### Is Thread Forming Right for You?
If you’re working with a compatible material and wish to eliminate chips—perhaps because you’re creating threads in a blind hole—thread formers present a practical alternative. Nevertheless, you should be mindful of the challenges involved. Counteracting the high friction forces demands a generous supply of high-quality lubricant. Precision is critical 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 damage.
If thread forming intrigues you, feel free to visit the BAER online shop! As your screw tap manufacturer, we offer a broad selection of thread forming taps. For any queries, reach out to our customer service via the contact form.
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In conclusion, thread forming represents a fascinating and efficient alternative to traditional thread cutting methods. While it comes with certain constraints, its benefits make it a compelling choice for many applications. Whether you’re looking to streamline production or improve thread quality, thread forming could be the solution you’ve been searching for!