Plastic Mold High-Speed Cutting

Plastic Mold High-Speed Cutting

Because high-speed cnc machining technology has many characteristics and mold parts have complex profiles, the high-speed machining technology of molds puts forward higher requirements on the machine tools, tools, and numerical control systems in the processing system.

1. High-speed spindle

The key to the high-speed cutting of the machine tool is the high-speed spindle of the machine tool. The high-speed cutting machine tools currently used for mold processing are mainly high-speed machining centers, high-speed milling machines, etc., which require the spindle speed to be 10000r / min ~ 40000r / min (higher speeds are still under study, will reach 100000r / min), in addition also require The main shaft can quickly accelerate and decelerate, that is, it has high acceleration and deceleration. The key to the high-speed spindle to achieve high speed is the bearing support of the spindle. High-speed rotating spindles require bearings with high load-bearing capacity, high rigidity, high rotation accuracy and long service life. High-speed spindles often use static pressure bearings, magnetic suspension bearings and other supporting structures.

High-speed electric spindle technology has developed rapidly in the past ten years. The electric spindle is the most important spindle unit of high-speed machine tools. The electric spindle is also called a built-in motor spindle unit. Its main feature is that the motor is placed inside the spindle, and the spindle is directly driven by the driving power supply to work, thereby achieving the integrated function of the motor and the spindle. There are already professional manufacturers of electric spindles in China. The products can be supplied in series. For example, Luoyang Bearing Research Institute, Wuxi Bohua, Jiangsu Star Wheel, Luoyang Shuaiqi, Shanghai Futian and other companies all produce different series of high speed electric spindles. The main characteristics of the electric spindle are:

The air bearing and magnetic bearing have no friction, no lubrication, high speed, wide application range and long service life;

Adjustable speed, stable speed of variable frequency power supply, reliable quality;

Good starting performance, large torque, stable operation, high efficiency and high precision;

The automatic bit changer motor can replace the drill bit and milling cutter, so that it is convenient, rapid and accurate positioning.

2. Dynamic characteristics of high-speed machine tools

High-speed cutting machine tools have high requirements on the static and dynamic characteristics of their support parts. The machine bed must have high static stiffness, dynamic stiffness, and thermal stiffness, good structural rigidity, sufficient support strength, and high-level damping characteristics, so that The natural frequency of the machine tool is far away from the frequency of chattering during high-speed cutting, which in turn makes the machine tool have good dynamic response characteristics. At present, the bed materials of high-speed machine tools are mostly non-metallic damping materials, such as polymer concrete (or artificial granite). The damping characteristics of this material are 7 to 10 times that of cast iron, and the specific gravity is only one third of that of cast iron. ; Reduce the friction damping of the guide rail and ball screw motion pair as much as possible, so that the moving part adapts to the requirements of fast movement and high acceleration and deceleration.

3. High-speed cutting tools

The key to high-speed cutting tools is the tool structure and tool material. The structure of the high-speed cutting tool mainly adopts the double positioning type shank with the hollow cone part and the end surface of the spindle contacting at the same time (such as the KM tool shank of Kenenatal company in the United States, the HSK tool shank of the German OTT company, etc.), and its axial positioning accuracy can reach 1 μm. When the tool rotates at high speed, the centrifugal force makes the clamping of the tool holder more secure, and its radial runout does not exceed 5 μm.

The use of new tool materials can greatly increase the cutting speed, thereby increasing productivity and extending tool life. The commonly used tool materials for high-speed cutting are: cemented carbide and its coatings, ceramics, cubic boron nitride (CBN), polycrystalline cubic boron nitride (PCBN), superhard material diamond, polycrystalline diamond and diamond Coating etc.

In the high-speed cutting tool technology, in addition to the reasonable choice of tool materials, it must also solve the tool body material and structure, tool geometry parameters, blade clamping structure, tool and machine tool clamping method, high-speed spindle tool clamping measures, and rotation For the dynamic balance of cutting tools, the rake angle of high-speed cutting tools is about 10o smaller than that of ordinary cutting tools, and the rake angle is about 5-8o larger.

Compared with ordinary cutting tools, high-speed CNC cutting tools should have the following characteristics:

Good rigidity, small thermal deformation, high cutting precision;

Good vibration resistance, less chatter during the cutting process, and good quality of the processed surface;

The cutter has a reasonable structure design, which can reliably break chips and facilitate chip removal;

The tool has high durability and good cutting performance;

The design of the tool holder structure is reasonable, which is convenient for rapid tool change, and the tool adjustment is convenient, which improves the efficiency of tool change adjustment;

Serialization, standardization, good interchangeability, easy for NC programming and tool management.

4. CNC programming of high-speed cutting machine tools

As the cutting-edge technology of mold processing, high-speed processing technology is applied to mold manufacturing to make CAD / CAM technology develop rapidly. Due to the complex shape of the mold, the mold design is usually modeled using CAD three-dimensional design software, that is, the three-dimensional design software such as Pro-E and UG is first applied to the three-dimensional solid modeling of the product to make the product design faster and more convenient. CAM technology converts the three-dimensional model into CNC machining codes and transmits them to high-speed CNC machining milling machines or CNC machining centers for processing. Based on this requirement of CAD / CAM, high-speed processing machine tools have the following functions:

The numerical control system has the function of high-speed programming calculation;

The CAM system must have the function of optimizing the tool path, as well as the intelligent full-cut protection function;

Can maintain maximum and stable cutting speed, avoid discontinuous and sudden acceleration changes;

The tool trajectory should be kept stable to avoid sudden changes in the direction of the tool trajectory, so as to avoid over-cutting and damage to the tool or equipment

Maintain a constant feed rate during cutting to keep the cutting feed as smooth as possible;

The cutting width should be properly controlled to avoid full-width cutting to avoid damage to the tool and cutting chatter;

For the processing of residual quantities, a series of tools should be used for processing in large to small order to achieve the required size and avoid the completion of one processing. Residual processing method is an effective measure to improve processing quality and processing efficiency;

The tool path should avoid redundant empty tools, and can avoid repeated calculation by mirroring, copying and rotating the tool path. The functions of such tool path editing, transformation and optimization processing of high-speed machine tools are very important;

The high-speed machine tool should have the function of cutting and repairing the tool path. It can be accurately cut to reduce or avoid the empty knife, at the same time reduce the impact of the tool when cutting into the material, and improve the cutting safety.

High-speed cutting technology is the direction of future cutting. The development of high-speed cutting technology is not only reflected in the progress of its key technologies such as high-speed machine tool equipment, numerical control software, electrical control, and cutting tool technology, but also promotes the rapid development of other related technologies. The global manufacturing market economic environment has created conditions for the rapid development of high-speed processing technology. High-speed processing technology will be widely used in many manufacturing enterprises. Although compared with industrially developed countries, China is still in its infancy in the field of high-speed cutting processing technology and applications, and some technical fields are almost blank, but in recent years, this technology has attracted widespread attention from many manufacturing companies including mold companies in China. . For China to occupy a place in high-speed processing technology, it must develop in a leap-forward manner. Since the development and application of high-speed machining technology must integrate and optimize knowledge in various subject areas and implement system technology engineering, China should increase investment and effectively organize the development and application of high-speed machining technology. Only in this way can we shorten the gap between us and the advanced foreign level as soon as possible and improve the level of China’s manufacturing industry.

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