1 The traditional thread processing method mainly uses the thread turning tool to turn the thread or the tap, die manual tapping and buckle. With the development of NC machining technology, especially the emergence of three-axis CNC machining system, a more advanced thread machining mode -- CNC milling of thread can be realized. Thread CNC milling processing compared with the traditional thread processing method, in the processing accuracy, processing efficiency has great advantages, and processing is not subject to the thread structure and thread rotation restriction, such as a thread milling cutter can process a variety of different rotation of internal and external threads. For threads that do not allow transition buckle or retreat groove structure, it is difficult to process by traditional turning method or tap, die, but it is very easy to achieve by CNC milling. In addition, the durability of thread milling cutter is more than ten times or even tens of times of the tap, and in the process of CNC milling thread, it is very convenient to adjust the diameter of thread size, which is difficult to do by using tap and die. Because of the advantages of CNC milling, CNC milling technology has been widely used in mass thread production in developed countries.
2 thread CNC milling
The numerical control milling example of M6 standard internal thread is shown. Workpiece material: aluminum alloy; Tool: carbide thread drilling and milling cutter; Thread depth 10mm; Milling cutter speed: 2,000r/min; Cutting speed: 314m/min; Drilling feed: 0.25mm/min; CNC milling feed: 0.06mm/ tooth; Processing time: 1.8s per hole. The process of processing station is:
(1) position, threaded drilling milling cutter quickly run to the workpiece safety plane;
(2), thread drilling milling cutter drilling to hole depth size;
(3) bit, the thread drill milling cutter is quickly lifted to the thread depth size;
(4), thread drill milling cutter to arc cut thread starting point;
(5), the thread drilling and milling cutter makes interpolation motion in X and Y directions around the thread axis, and makes motion in the +Z direction parallel to the axis. That is, it runs 360° around the thread axis, and rises one pitch along the +Z direction, and the three-axis linkage running trajectory is a spiral line.
(6), the thread drill milling cutter with the arc from the starting point (is also the end point) back tool;
(7), threaded drilling milling cutter quickly back to the workpiece safety plane, ready to process the next hole. The machining process includes drilling, chamfering, internal thread milling and thread root groove CNC milling, using a tool to complete, machining efficiency is very high.
3 Thread milling cutter main types
Three axis CNC machine tool and thread CNC milling tool are two essential elements in thread CNC milling. The following are some common thread milling cutter types:
(1) cylindrical thread milling cutter
The shape of cylindrical thread milling cutter is very like the combination of cylindrical end milling cutter and thread tap, but its thread cutting edge is different from tap, there is no spiral lift on the tool, and the spiral lift in the processing is realized by the movement of the machine tool. Because of this special structure, the tool can process both right and left screw threads, but it is not suitable for the processing of larger pitch threads.
(2) The commonly used cylindrical thread milling cutter can be divided into two kinds of coarse thread and fine thread
For the consideration of processing efficiency and durability, thread milling cutter is mostly made of carbide materials, and can be coated with various coatings to meet the processing needs of special materials. Cylindrical thread milling cutter is suitable for CNC milling of medium and small diameter thread of steel, cast iron and non-ferrous metal materials, with stable cutting and high durability. The disadvantage is that the cutting tool manufacturing cost is high, the structure is complex, the price is expensive.
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