Not only that, in the IMTS2000 exhibits, sheet metal stamping machines and laser sheet cutting machines also use linear motors, such as Alabama's laser cutting machine, which uses a linear motor with a speed of 150 m/min and an acceleration of 1.3 g. In addition, linear motors are also used in coordinate measuring machines, such as Helmel's Mierostar HS products, with linear movement speeds of up to 30 m/min, so that the probe can make more than 120 contact measurements per minute.
Speeding up another key feature – the electric spindle has recently made the following new developments:
(1) Swiss company Fischer has introduced a product with an online automatic balancing device on the parts of the electric spindle. It is applied to the machining center, and the automatic balancing of the tool quality is performed once for each tool change. It is said that 80 to 90% of the vibration caused by dynamic imbalance can be eliminated in one second.
(2) Swiss IBAG Company introduced the electric spindle of hydrostatic bearing, which is said to have a service life of more than 20,000 hours.
(3) Ingersoll Corporation of the United States introduced the electric spindle of the hydrostatic bearing as a separate component.
(4) Swiss IBAG company introduced the electric spindle of the magnetic bearing.
(5) Swiss IBAG company is equipped with an axial size monitoring sensor on its electric spindle components, which can be coupled with the CNC system for axial dimension compensation.
(6) The electric spindle of the permanent magnet synchronous motor has also appeared. Previously, the motors of the electric spindles were all asynchronous induction motors. The stator heats up to cool, while the rotor heats up and cannot cool. However, the rotor of the permanent magnet synchronous motor does not generate heat for the permanent magnet. In addition, the synchronous motor of the same power has a smaller external size than the asynchronous motor, which is advantageous for achieving small size, high power, and high power density (PowerDensity). However, only a few machine tool companies (such as Mazak) are currently in development. The professional electric spindle company has not seen any product supply.
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 form of failure is the loss of accuracy due to material fatigue (the accuracy of the electrospindle 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 to repair and renovate locally. Some electric spindle companies recommend that they 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.
Five-axis simultaneous machining is fashionable; five-axis linkage and five-sided machining are combined into one
At the IMTS2000 exhibition, people were given a prominent impression that the five-axis linkage machine tool is more than ever. 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 spindle head with a composite A (B) and C axis (hereinafter referred to as a 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. Ultra-low speed, high torque and smooth rotation have always been a big problem in motor drive technology. Therefore, a mechanical reducer of various configurations is necessary. However, with the rapid development of power electronics and microelectronics, especially DSPO (Digital Signal Processor) chips and permanent magnet materials, this big problem has been broken. Recently, ETEL of Switzerland and KOLLMORGEN of the United States have introduced "BrushlessRingTorqueMotor". ETEL has supplied a large-scale astronomical telescope with a toroidal torque servo motor with a diameter of 2.5 m and a thickness of only 40 mm and a torque of 10,000 Nm. Under the condition that the turning speed is less than 1 rev / 56 days, it is still incredible to rotate extremely smoothly and evenly. The company also applied a toroidal torque servo motor with diameters of 0.5m and 1m to replace the worm gear pair on the multi-axis linkage milling machine used in the aerospace industry. The machining accuracy and surface roughness were greatly improved. Currently, both companies offer a range of ring torque servo motors in size and size. Taking ETEL as an example, the available motor outer diameter range is from 120mm to 1260mm, the torque is from 1Nm to 18000Nm, the positioning accuracy is up to 0.5′′, the repeatability is up to 0.01′′, and the minimum speed is up to 0.001r/min. It is foreseeable that in the near future, the worm gears in the A and C (B) axis servo drives of the composite turret and the composite spindle head will be replaced by these ring servo torque motors. The worm gear pair and the spiral bevel gear pair will gradually withdraw from the field of CNC machine tools after the spur gear pair. This will be another breakthrough change.
In order to meet the increasing popularity of five-axis linkage processing, TRI-TECH of the United States now sells the functional parts of the composite spindle head (model 5411). Therefore, any existing three-axis linkage machine can be changed into a five-axis linkage machine (using a 7:24 taper shank and the connector provided by the company, the composite spindle head can be coupled with the spindle of the existing machine tool), and its C axis The range is 360°; the A(B) axis is ±90°, the angular accuracy is 0.01°, and the repeatability is 0.005°. Naturally, the existing machine tool must have a five-axis linkage function CNC system and five-axis linkage programming software. In addition, the company also offers five-axis post-processing software.
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