Advantages of CNC Thread Milling
Traditional thread processing methods mainly use thread turning tools to turn threads or use taps, dies for manual tapping and threading. With the development of CNC machining technology, especially the emergence of three-axis linkage CNC machining systems, a more advanced thread processing method, CNC milling, has been realized. Compared with traditional thread processing methods, CNC thread milling has the following advantages.
During thread milling, the part does not move and the tool performs rotary milling, while traditional turning is the rotation of the part. In traditional turning, the thread processing of non-rotating bodies will have the problem of inflexible clamping, but the milling method will solve this problem. At the same time, the fixed processing parts also reduce the motion load of the machine tool and improve the positioning and processing accuracy.
Thread CNC milling is not limited by the thread structure and thread rotation. The same thread end mill can process internal and external threads of different rotation directions with the same pitch but different diameters.
The same thread end mill can process the thread to any tolerance zone by modifying the tool radius compensation value. In the traditional method, the tap cannot be used anymore after it is worn and the thread size is less than the tolerance, and it can only be scrapped. However, when the thread milling cutter is worn and the thread hole size is less than the tolerance, the necessary tool radius compensation adjustment can be made through the CNC system to continue to process the thread with qualified size.
Since the thread milling cutter has no guide part, it can process the thread with precise depth close to the bottom of the thread without the need for a back groove or transition buckle.
The durability of the thread milling cutter is more than ten times or even dozens of times that of the tap.
The CNC milling of threads is efficient. At present, the manufacturing material of the thread milling cutter is cemented carbide, and the processing line speed can reach 80m/min~200m/min. The processing line speed of the high-speed steel tap is only 10m/min~30m/min, so the CNC milling of threads is suitable for high-speed cutting, which improves the processing efficiency.
he CNC milling method of threads can extend the service life of milling tools. The thread processing of high-hardness materials and high-temperature alloy materials, such as titanium alloys, nickel-based alloys and molybdenum alloys, has always been a difficult problem. This is mainly because the tool life is short when high-speed steel taps are used to process the threads of the above materials. However, the use of carbide thread milling cutters is more ideal, and the cutting force of the tool is greatly reduced, solving the problem that the machine tool is too overloaded and cannot drive the tap for normal processing.
Compilation of NC Program for Thread Milling
The main principle of thread milling program compilation is to use G02 and G03 arc interpolation instructions, that is, adding the third axis linear interpolation while the two-axis circular interpolation to form a spiral interpolation motion. There are many ways to compile the CNC program for thread milling.
Manual Programming
For thread machining with simple tool paths, we can perform manual direct programming through simple calculations. For example, when machining threads with multi-tooth thread cutter inserts whose effective length is greater than the thread length, the entire thread machining can be completed by moving one pitch in the thread axis. The following is a CNC program for machining M16×1.5 external threads with a length of 9mm.
G00 G42 X100 Y0 Z15
M03 S3000
G0 Z-9 (down to the thread length) G01 X14.376 F100 (the tool processes to the thread bottom diameter)
G02 X14.376 Y0 I-14.376 J0 Z-7.5 (helical interpolation movement, while the Z direction increases by 1 pitch 1.5)
G01 G40 X100 Z15
M30
Programming with General-purpose Software
NX is a software system that integrates CAD/CAM/CAE produced by Siemens. It is widely used in the automotive, aerospace and mold processing industries. The thread milling function we use is one of its CAM programming functions.
First enter the “plane milling” or “drilling” processing environment, and select the “THREAD_MILLING” subtype in the “Create Operation” dialog box. Then set the relevant options and parameters as needed, and the system will generate the corresponding processing program.
Programming with Dedicated Software
Each tool generally provides a set of special programming software according to its own thread milling cutter. These special software are all very good thread milling programming software. You can choose different special software for thread milling CNC programming according to your own characteristics in actual application.
Practical Application of CNC Thread Milling Technology
Due to the many advantages of thread milling, many manufacturing companies have widely adopted CNC thread milling technology. When we processed the nozzle thread of a complex engine part, we also adopted the thread milling method after experimental research and achieved good results. The following is a brief introduction to this process and process.
Characteristics and Processing Difficulties of Parts
A complex part is an important part of the engine. If the nozzle thread part is turned, the main body of the part and the nozzle are not at the same rotation center, which brings certain difficulties to clamping and positioning. However, the method of milling the thread can be easily clamped and processed.
Selection of Thread Milling Tools
In thread milling, three-axis linkage CNC machine tools and thread milling tools are two essential elements. The following introduces several common types of thread milling cutters.
Cylindrical Thread Milling Cutter
The spiral lift of the cylindrical thread milling cutter in processing is achieved by machine tool movement. Due to this special structure, the tool can process both right-handed and left-handed threads, but it is not suitable for processing large pitch threads. It is suitable for milling small and medium diameter threads, with stable cutting and high durability. The disadvantage is that the tool manufacturing cost is high and the price is expensive.
Machine Clamp Thread Milling Cutter and Inserts
Machine clamp thread milling cutter is suitable for processing threads with larger diameters (such as D>25mm). Its characteristics are that inserts are easy to manufacture and the price is low. The advantage of machine clamp thread milling cutter is that inserts are easy to replace, thereby reducing processing costs.
Combined Multi-station Special Thread Boring Milling Cutter
The combined multi-station special thread boring end mill is characterized by one tool with multiple blades, completing multi-station processing at one time, saving auxiliary time such as tool change, and significantly improving productivity. This combined tool can complete the internal thread, chamfer and platform required for workpiece processing at one time.
