With the popularity of CNC machine tools, thread milling technology is increasingly used in the machinery manufacturing industry. Thread milling is a process of forming threads by helical interpolation milling using a thread milling cutter through the three-axis linkage of a CNC machine tool. The cutter moves one pitch in a straight line in the vertical plane for every circular motion on the horizontal 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 analyzes seven common thread milling cutters from the perspective of application characteristics, tool structure, and processing technology.
Ordinary Machine Clamp Thread End Mill
The machine clamp thread milling cutter is the most commonly used and inexpensive tool in thread milling. Its structure is similar to that of an ordinary machine clamp milling cutter, consisting of a reusable toolbar and an easily replaceable insert. If you need to process a tapered thread, you can also use a special tool bar and insert for processing tapered threads. This insert has multiple thread cutting teeth.
The tool can process multiple thread teeth at a time by processing along the spiral line. For example, if you use a milling cutter with 5 2mm thread cutting teeth, you can process 5 thread teeth with a thread depth of 10mm by processing along the spiral line. In order to further improve the processing efficiency, you can use a multi-blade machine clamp thread milling cutter.
By increasing the number of cutting edges, the feed rate can be significantly improved, but the radial and axial positioning errors between each insert 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 insert for processing.
When selecting a machine clamp thread milling cutter, you should try to use a tool bar with a larger diameter and an appropriate blade material based on factors such as the diameter, depth and workpiece material of the thread to be processed. The thread processing depth of the machine clamp thread milling cutter is determined by the effective cutting depth of the tool bar. Since the insert 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 insert length, it needs to be processed in layers.
Ordinary Integral Thread End Mill
Integral thread milling cutters are mostly made of integral 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 tapered threads. This type of tool has good rigidity, especially the integral thread milling cutter with spiral grooves, which can effectively reduce the cutting load and improve processing efficiency when processing high-hardness materials.
The cutting edge of the integral thread milling cutter is covered with thread processing teeth. The entire thread processing can be completed by processing along the spiral line for one circle. There is no need for layered processing like machine-clamped tools, so the processing efficiency is high, but the price is relatively expensive.
Integral Thread End Mill 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 of the cutting edge, which can be used to process the chamfer of the thread end while processing the thread. There are 3 ways to process chamfers. When the tool diameter is large enough, the chamfering edge can be used directly to countersink the chamfer. This method is limited to processing the chamfer of the internal thread hole.
When the tool diameter is small, the chamfering edge can be used to process the chamfer through circular motion. However, when using the chamfering edge at the root of the cutting edge for chamfering, it should be noted that there should be a certain gap between the tool thread cutting part and the thread to avoid interference. If the thread depth to be processed is less than the effective cutting length of the tool, the tool will not be able to achieve the chamfering function. Therefore, when selecting the tool county, its effective cutting length and thread depth should be matched.
Thread Drill End Mill
The thread drill milling cutter is made of solid carbide and is an efficient tool for processing small and medium diameter internal threads. The thread drill milling cutter can complete the drilling of thread bottom holes, chamfering of hole mouths and internal thread processing at one time, reducing the number of tools used. However, the disadvantage of this tool is that it has poor versatility and is relatively expensive. The tool consists 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 drilling part is the bottom diameter of the thread that the tool can process. Limited by the diameter of the drilling part, a thread drill milling cutter can only process one specification of internal thread. When selecting a thread drill milling cutter, not only should the specifications of the threaded hole to be processed be considered, but also the matching of the effective processing length of the tool and the depth of the hole to be processed should be noted, otherwise the chamfering function cannot be achieved.
Thread Spiral Drill End Mill
The thread spiral drill milling cutter is also a solid carbide tool for efficient internal thread processing, and can also process the bottom hole and thread at one time. The end of the tool has a cutting edge like an end mill. Since the helix angle of the thread is not large, when the tool performs a spiral motion to process the thread, the end cutting edge first cuts off the workpiece material to process the bottom hole, and then the thread is processed by the rear of the tool. Some thread spiral drill milling cutters also have chamfering edges, which can simultaneously process the chamfer of the hole mouth. The tool has high processing efficiency and better versatility than the thread drill milling cutter. The internal thread aperture range that the tool can process is d~2d (d is the diameter of the cutter body).
Deep Thread Milling Tool
The deep thread milling tool is a single-tooth thread milling cutter. A general thread milling cutter has multiple thread processing teeth on its blade, and the contact area between the tool and the workpiece is large, the cutting force is also large, and the tool diameter must be smaller than the thread aperture when processing internal threads. Since the cutter body diameter is limited, the rigidity of the cutter is affected, and the cutter is subjected to force on one side when milling threads.
When milling deeper threads, the cutter is prone to let go, which affects the thread processing accuracy. Therefore, the effective cutting depth of a general thread milling cutter is about twice the diameter of its cutter body. The use of a single-tooth deep thread milling cutter can better overcome the above shortcomings. Due to the reduction of cutting force, 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 cutter body.
Thread Milling Tool System
Versatility and efficiency are a prominent contradiction of thread milling cutters. Some tools with composite functions have high processing efficiency but poor versatility, while tools with good versatility are often not efficient. To solve this problem, many tool manufacturers have developed a modular thread milling tool system. The tool is generally composed of a tool holder, a countersink chamfering blade and a universal thread milling cutter. Different types of countersink chamfering blades and thread milling cutters can be selected according to processing requirements. This tool system has good versatility and high processing efficiency, but the tool cost is high.
The above outlines the functions and characteristics of several commonly used thread milling tools. When milling threads, cooling is also crucial. It is recommended to use machine tools and tools with internal cooling functions. When the tool rotates at high speed, it is difficult for external coolant to enter under the action of centrifugal force. In addition to cooling the tool well, the internal cooling method is more important because high-pressure coolant helps to remove chips when machining hole threads. When machining small-diameter internal threaded holes, higher internal cooling pressure is especially required to ensure smooth chip removal. In addition, when selecting thread milling tools, specific processing requirements should be comprehensively considered, such as production batch, number of screw holes, workpiece material, thread accuracy, size specifications and many other factors, and tools should be selected comprehensively.
