New trends in the development of machine tool technology (3)
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At least three well-known electric spindle companies in Europe (Fischer, IBAG, GMN, Germany) are rushing to the US market, and they have established branches in the United States for sales, repair and refurbishment. The reason is that the core technology of the electric spindle is precision machining and precision assembly, which requires high level of skill for workers. These are the strengths of Switzerland and Germany; in the case of high speed operation, the life of rolling bearings is low. The main failure mode is the loss of accuracy due to material fatigue (the accuracy of the electric spindle is generally 2 μm in the radial direction and 1 μm in the axial direction). Therefore, it is impossible to open the market without the ability of local maintenance and refurbishment. Some electric spindle companies recommend that users purchase a spare item because the general repair and refurbishment time is two weeks. In this way, downtime can be minimized.
In addition, Kennametal of the United States has introduced a tool holder with automatic balancing to adapt to high speed.
The five-axis linkage machining was fashionable; the five-axis linkage and the five-face machining combined into one at the IMTS2000 exhibition gave people a prominent impression that the five-axis linkage machine tool is more than before. According to incomplete statistics, there are about 50 units. The emergence of this phenomenon is not accidental and has the following profound background.
(1) In essence, for the machining of 3D curved surfaces, triaxial linkage is generally not the best choice, because in the case of three-axis linkage, it is generally difficult to cut with the optimal geometry of the tool, which is not only inefficient but also has surface roughness. Extremely poor, often requires heavy manual polishing. Hand polishing can improve surface roughness but often loses the geometric accuracy of the surface. For this reason, some companies use subsequent EDM, which not only takes a long time but also manufactures electrodes with complicated shapes.
With five-axis linkage, the tool's optimum geometry can be used for cutting, including the use of the arc portion (non-tip portion) of the ball-end milling cutter for cutting. In this way, not only the surface roughness is good but also the efficiency is greatly improved. CINCINNATI of the United States once claimed that the efficiency of a five-axis linkage machine is equal to two three-axis linkage machines. Especially in the current popular cubic boron nitride milling cutter high-speed milling hardened steel process, the five-axis linkage can exert greater power than the three-axis linkage. Therefore, in general, five-axis linkage is the best choice for 3D surface machining.
(2) The widespread application of five-axis linkage is hindered for the following reasons:
1 The price of the past five-axis linkage CNC system is extremely high, several times higher than the three-axis linkage system. Now, the price difference between the two linkage systems is small.
2 In the past, the five-axis linkage programming software (including the post-programming inspection software) was technically difficult and the price was extremely high, which was several times that of the three-axis linkage programming software. Although the price is still high, it has fallen sharply.
3 Five-axis linkage There are two ways to realize the movement of two rotary axes other than X, Y and Z. One is to use the composite A and C (B) axis rotary table on the workbench (hereinafter referred to as the composite turntable); It is a composite A (B), C axis spindle head (hereinafter referred to as composite spindle head).
At present, due to the appearance of the electric spindle, the structure of the composite spindle is greatly simplified, and no spiral bevel gear pair, toothed belt or wheel drive chain is required, and the manufacturing difficulty is greatly reduced. Most of the five-axis linkage machines exhibited at IMTS2000 are composite spindle head types.