Do you know what methods are available for thread processing? General thread processing General Internal Thread: Can be tapped with Tap. According to the processing requirements of the parts, select a standard tap; General External Thread: Can be processed with Dies of different specifications.
Processing threads with a turning tool on a lathe
The method of turning threads is the most widely used. Advantages: The equipment is highly versatile and can obtain threads with higher precision. Disadvantages: Low productivity and high technical requirements for workers. Non-standard threads, large pitch threads and locking threads can all be processed on lathes.
The accuracy of the machine tool, the contour and installation accuracy of the tool, the technical level of the workers, etc. will affect the thread accuracy. The feed method for turning threads is shown in the figure below: Milling of threads
Milling is widely used to process threads in batch and mass production. Comparison between milling and turning: The production cost of milling thread is higher than that of turning thread, and the accuracy is generally 2~3 levels. Due to intermittent cutting during milling, the roughness is higher than that of turning. According to the different milling cutters used, milling threads are divided into the following three types: processing with disc milling cutter, processing with comb milling cutter and whirlwind milling. When using disc milling cutter to process large-sized trapezoidal threads and square threads, the accuracy is not high, and the shape of the thread will change when milling the thread. Therefore, it is generally pre-milled with a disc milling cutter, and then fine-processed with a thread turning tool. When processing large-diameter fine-pitch threads, combined milling cutters (implant cutters) are often used. They can be used for the processing of internal and external threads, can process threads close to the shaft shoulder, do not require a back-off groove, and the processing accuracy is lower than that of disc milling cutters. Whirlwind thread milling is a high-speed cutting method, as shown in the figure below. During cutting, the cutter head equipped with several carbide tools rotates at high speed (1000~3000r/min), and the workpiece is installed in the chuck or on the top and rotates slowly (3~30r/min). The movement trajectory of the tool tip is a circle, and its center has an eccentricity value H with the rotation center of the workpiece. The high-speed rotating cutter head and the motor driving it are fixed on the tool holder slide of the lathe, and the tool holder slide is parallel to the axis of the workpiece for longitudinal feeding. The workpiece advances one pitch for each rotation. Since the center of the cutter head does not coincide with the center of the workpiece, the blade only contacts the workpiece on its arc trajectory, so it is intermittent cutting, and the tool can be cooled in the air. The rotation direction of the workpiece and the cutter head is generally opposite. The rotation plane of the cutter teeth forms an angle with the vertical plane and is equal to the lead angle of the cut thread. When whirling thread, the productivity is high. It should be pointed out that the accuracy of the thread milled by whirling is related to the degree of heat of the workpiece and the wear of the tool. Extrusion thread is a chipless processing method with high productivity and has been widely used in batch and mass production. When extruding the thread, the internal fibers of the metal will not be cut off and damaged, so the thread strength is improved. The tensile strength that the thread can withstand after extrusion is high, and the fatigue strength is 50 times greater than that of cutting. The size range of extruded thread is relatively wide (0.2~120mm). Extrusion can be divided into two categories: extrusion with a washboard and rolling with a roller. Extrusion with a washboard (as shown below) has low processing accuracy, but rolling with a roller can obtain higher accuracy and better surface finish. There are single roller and double roller rolling methods for rolling threads with rollers. The following figure shows the case of rolling threads with double rollers.
Of the two rollers, one is a fixed roller and the other is a movable roller. The movable roller can make radial feeding motion, and both rollers rotate actively while the workpiece is driven to rotate freely. Since the rollers can be ground after heat treatment, the processing accuracy is improved. Thread grinding is mainly used to process threads with higher hardness after heat treatment. The hardness of the workpiece after quenching is higher. Although it can still be cut, the durability of the tool for cutting threads will be greatly reduced. In addition, the thread will cause deformation of the thread profile after heat treatment. Therefore, precision threads must be ground to ensure accuracy and surface finish. The main methods of thread grinding are: grinding threads with single-line grinding wheels, grinding threads with multi-line grinding wheels, and centerless grinding threads.
