With the popularity of CNC machine tools, thread milling technology is increasingly used in the machinery manufacturing industry. Thread milling is a three-axis linkage of a CNC machine tool, which uses a thread milling cutter to perform spiral interpolation milling to form threads. The cutter makes a circular movement on the horizontal plane, and linearly moves a thread pitch in the vertical plane. Thread milling has many advantages such as high processing efficiency, high thread quality, good tool versatility, and good processing safety. There are many types of thread milling tools currently in use. This article intends to analyze and introduce several common thread milling cutters from the perspectives of application characteristics, tool structure, and processing technology.
1 Ordinary machine clamp type thread milling cutter
The clamp-type thread milling cutter is the most commonly used and low-cost tool in thread milling. Its structure is similar to that of the ordinary clamp-type milling cutter. It consists of a reusable toolholder and a blade that can be easily replaced. If you need to machine taper threads, you can also use special tool holders and blades for taper threads. This blade has multiple thread cutting teeth. The tool can process multiple thread teeth at a time along the spiral line. For example, use one A milling cutter with 5 2mm thread cutting teeth can process 5 thread teeth with a thread depth of 10mm along the helical line. In order to further improve the processing efficiency, a multi-blade machine clamp thread milling cutter can be used. By increasing the number of cutting edges, the feed rate can be significantly increased, but the radial and axial positioning errors between each blade distributed on the circumference will affect the thread processing accuracy. If you are not satisfied with the thread accuracy of the multi-blade machine clamp thread milling cutter, you can also try to install only one blade for processing. When selecting a machine-clamp thread milling cutter, according to factors such as the diameter and depth of the thread being machined, and the material of the workpiece, try to choose a larger diameter shank (in order to improve the rigidity of the tool) and an appropriate blade material. The thread processing depth of the clamp-type thread milling cutter is determined by the effective cutting depth of the tool holder. Since the blade length is less than the effective cutting depth of the tool bar, when the depth of the thread to be processed is greater than the length of the blade, it needs to be processed in layers.
2 Ordinary integral thread milling cutter
Integral thread milling cutters are mostly made of solid carbide materials, and some are also coated. The integral thread milling cutter has a compact structure and is more suitable for processing medium and small diameter threads; there are also integral thread milling cutters for processing taper threads. This kind of tool has good rigidity, especially the integral thread milling cutter with spiral groove, which can effectively reduce the cutting load and improve the processing efficiency when processing high-hardness materials. The cutting edge of the integral thread milling cutter is covered with thread processing teeth, and the entire thread processing can be completed along the spiral line for one week. There is no need for layered processing like a clamp-type tool, so the processing efficiency is higher, but the price is relatively expensive .
3 Integral thread milling cutter with chamfering function
The structure of the integral thread milling cutter with chamfering function is similar to that of the ordinary integral thread milling cutter, but there is a special chamfering edge at the root (or end) of the cutting edge, which can process the thread end chamfer while processing the thread . There are three methods for chamfering. When the tool diameter is large enough, the chamfering edge can be used directly to make the chamfer. This method is limited to the chamfering of the internal threaded hole. When the tool diameter is small, the chamfering edge can be used to process the chamfer through circular motion. But when using the chamfering at the root of the cutting edge for chamfering, pay attention to the clearance between the cutting part of the tool and the thread to avoid interference. If the processed thread depth is less than the effective cutting length of the tool, the tool will not be able to realize the chamfering function. Therefore, when selecting the tool, ensure that the effective cutting length and the thread depth match each other.
4 Thread drilling and milling cutter
The thread drilling and milling cutter is made of solid carbide, which is a high-efficiency machining tool for small and medium diameter internal threads. The thread drilling and milling cutter can complete the drilling of threaded bottom holes, hole chamfering and internal thread processing at one time, reducing the number of tools used. But the disadvantage of this tool is its poor versatility and relatively expensive price. The tool is composed of three parts: the drilling part of the head, the thread milling part in the middle, and the chamfering edge at the root of the cutting edge. The diameter of the drilled part is the bottom diameter of the thread that the tool can process. Limited by the diameter of the drilled part, a thread drilling and milling cutter can only process internal threads of one specification. When selecting thread drilling and milling cutters, not only the specification of the threaded hole to be machined should be considered, but also the matching of the effective machining length of the tool and the depth of the machined hole should be taken into consideration, otherwise the chamfering function cannot be realized.
5 Thread auger milling cutter
Thread auger and milling cutter is also a solid carbide tool for efficient processing of internal threads, and it can also process bottom holes and threads at one time. The end of the tool has a cutting edge like an end mill. Because the helix angle of the thread is not large, when the tool makes a spiral motion to process the thread, the end cutting edge first cuts the workpiece material to form the bottom hole, and then the thread is processed from the back of the tool. Some thread auger milling cutters also have a chamfering edge, which can simultaneously process the hole chamfer. The tool has high processing efficiency and has better versatility than thread drilling and milling cutters. The internal thread aperture range that the tool can process is D～2D (D is the diameter of the cutter body).
6 Milling deep thread cutter
The deep thread milling cutter is a single-tooth thread milling cutter. A general thread milling cutter has multiple thread processing teeth on the cutting edge. The contact area between the tool and the workpiece is large, the cutting force is also large, and the diameter of the tool must be smaller than the thread aperture when processing internal threads. Because the diameter of the cutter body is limited, which affects the rigidity of the cutter, and the cutter is forced on one side when milling threads, it is easy to give up the tool when milling deep threads, which affects the accuracy of thread processing. Therefore, the effective cutting depth of general thread milling cutters is about 2 times the diameter of the knife body. The use of single-tooth milling deep thread cutters can better overcome the above shortcomings. As the cutting force is reduced, the thread processing depth can be greatly increased, and the effective cutting depth of the tool can reach 3 to 4 times the diameter of the tool body.
7 Thread milling tool system
Versatility and efficiency are a prominent contradiction of thread milling cutters. Some tools with compound functions (such as thread drilling and milling cutters) have high processing efficiency but poor versatility, and tools with good versatility are often not efficient. To solve this problem, many tool manufacturers have developed modular thread milling tool systems. The tool system generally consists of a tool holder, a counter-boring chamfering edge and a general thread milling cutter. Different types of counter-boring chamfering edges and thread milling cutters can be selected according to the processing requirements. This tool system has good versatility and high processing efficiency, but the tool cost is relatively high.
The functions and characteristics of several commonly used thread milling tools are briefly introduced above. Cooling is also very important when milling threads. It is recommended to use machine tools and tools with internal cooling. Because when the tool rotates at a high speed, the external coolant is not easy to enter under the action of centrifugal force. In addition to the internal cooling method, which can cool the tool well, it is more important that the high-pressure coolant can help chip removal when machining blind hole threads. In particular, a higher internal cooling pressure is required when machining small-diameter internal threaded holes. Ensure smooth chip evacuation. In addition, when selecting a thread milling tool, the specific processing requirements should be considered comprehensively, such as production batch, number of screw holes, workpiece material, thread accuracy, size specifications and many other factors, and the tool should be selected reasonably.
Post time: Nov-30-2021