Detailed explanation of seven thread processing methods that cannot be missed
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Threading is a method of processing various internal and external threads with threading tools.
1. Thread cutting
Thread processing generally refers to the use of forming or grinding tools to process threads on a workpiece. Methods involved include turning, milling, tapping, thread grinding, grinding, and cyclone cutting. During turning, milling, and grinding threads, the machine tool's transmission chain ensures that the turning tool, milling cutter, or grinding wheel moves one lead accurately and evenly along the workpiece's axial direction.
In tapping or threading, the tool (tap or die) and the workpiece make a relative rotational motion. The thread groove formed first guides the tool (or workpiece) to move axially.
2. Thread turning
When it comes to turning threads on a lathe, there are two common methods: the forming turning tool or the thread comb. For single-piece or small-batch production, the forming turning tool is preferred due to its simple tool structure. On the other hand, turning threads with the thread comb tool is ideal for medium and large batch production, with high production efficiency. However, the tool structure is complex. When it comes to turning fine-threaded workpieces with short threads, the pitch accuracy of trapezoidal threads is generally limited to levels 8 to 9 using ordinary lathes. To achieve higher productivity and accuracy, specialized thread lathes are recommended.
3. Thread milling
The pitch accuracy of thread milling can generally reach levels 8 to 9, and the surface roughness is R5 to 0.63 microns. This method is suitable for batch production of threaded workpieces with general precision or rough machining before grinding.
4. Thread grinding
This text provides information about the use of precision thread grinders for processing threaded stainless steel turning parts. The grinding wheels used in this process can be classified into two types based on their cross-sectional shape - single-line grinding wheels and multi-line grinding wheels.
Single-line grinding wheel grinding can achieve a pitch accuracy of 5 to 6 levels and a surface roughness of R1.25 to 0.08 microns. This method is suitable for grinding precision screws, thread gauges, worms, small batches of threaded workpieces, and relief grinding of precision hobs. The grinding wheel dressing process is also relatively easy.
Multi-line grinding wheel grinding is further divided into two types - longitudinal grinding and plunge grinding. In longitudinal grinding, the width of the grinding wheel is smaller than the length of the thread to be ground, and the grinding wheel can be moved longitudinally once or several times to grind the thread to the final size. In plunge grinding, the width of the grinding wheel is greater than the length of the thread to be ground, and the grinding wheel cuts into the surface of the workpiece radially. This method is suitable for relieving large batches of taps and grinding certain fastening threads. The productivity is high, but the accuracy is slightly lower, and the grinding wheel dressing is more complicated.
Precision thread grinders are ideal for processing threaded workpieces with high accuracy and surface quality
5. Thread grinding
Grinding tools for nut-type or screw-type threads are typically made of soft materials like cast iron. The sections of the threads on the workpiece that have pitch errors are ground in both forward and reverse rotation to enhance pitch accuracy. Generally, hardened internal threads are ground to eliminate deformation and improve accuracy.
6. Tapping and thread threading
Tapping is to use a certain torque to screw a tap into a pre-drilled bottom hole on the workpiece to process an internal thread.
Threading involves cutting external threads on a bar or pipe workpiece using a die. The accuracy of the tapping or threading process depends on the accuracy of the die or tap. While there are several methods for processing internal and external threads, small-diameter internal threads can only be processed with taps. You can perform tapping and threading manually or use lathes, drill presses, tapping machines, and threading machines.
7. Thread rolling
- The advantages of thread rolling are:
Rolling is a thread forming process that has several advantages over traditional cutting methods such as turning, milling, and grinding. The surface roughness of the rolled threads is significantly smaller, and the strength and hardness of the thread surface is improved due to cold work hardening. Additionally, the process has a high material utilization rate, and its productivity is twice as high as cutting processing, which makes it easy to automate.
Moreover, the rolling die has a long life, but there are some limitations to the process. For example, the hardness of the workpiece material must not exceed HRC40, and the blank must have high dimensional accuracy. The accuracy and hardness requirements of the rolling mold are also high, making it challenging to manufacture the mold. Finally, rolling threads with asymmetric tooth shapes is not suitable - According to different rolling dies, thread rolling can be divided into two types: thread rolling and thread rolling.
- Thread rolling is a process that involves the use of two plates with threaded tooth profiles. These plates are arranged in a staggered manner, with a 1/2 pitch difference between them. The fixed plate remains stationary, while the movable plate moves back and forth in a straight line parallel to the static plate.
When a workpiece is fed between the two plates, the movable plate rubs against it and advances forward. This causes the surface of the workpiece to undergo plastic deformation, resulting in the formation of threads. - There are three types of thread rolling: radial thread rolling, tangential thread rolling, and rolling head thread rolling
- Radial thread rolling: Two or three thread rolling wheels are installed on parallel axes. The workpiece is placed on the support between these wheels. Both wheels rotate in the same direction and at a constant speed. One of them also performs radial feed motion in the same direction. As the rolling wheel drives it, the workpiece rotates and the surface is extruded radially to form threads. For some screws that don't require high precision, similar methods can also be used for roll forming.
- Tangential thread rolling: Also known as planetary thread rolling, the rolling tool consists of a rotating central rolling wheel and three fixed arc-shaped wire plates. During thread rolling, the workpiece can be fed continuously, so the productivity is higher than that of thread rolling and radial thread rolling.
- Thread rolling with rolling head is a process that is commonly used to create short threads on a workpiece. This process is performed on an automatic lathe. The rolling head consists of 3 to 4 rolling wheels that are evenly distributed around the periphery of the industrial cnc machining workpiece. During the process, the industrial cnc machining workpiece rotates while the rolling head feeds axially to roll the workpiece out of the thread
- Radial thread rolling: Two or three thread rolling wheels are installed on parallel axes. The workpiece is placed on the support between these wheels. Both wheels rotate in the same direction and at a constant speed. One of them also performs radial feed motion in the same direction. As the rolling wheel drives it, the workpiece rotates and the surface is extruded radially to form threads. For some screws that don't require high precision, similar methods can also be used for roll forming.
- Thread rolling is a process that involves the use of two plates with threaded tooth profiles. These plates are arranged in a staggered manner, with a 1/2 pitch difference between them. The fixed plate remains stationary, while the movable plate moves back and forth in a straight line parallel to the static plate.
8. Common data for ordinary thread processing
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