New Technology Development and e-Manufacturing (Part 1)? After the 2002 Chicago Machine Tool Show

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1 New development of high-speed machining The high-speed CNC machining source was characterized by the application of electric spindle (achieving high spindle speed) and linear motor (achieving high linear movement speed) in the early 1990s. The field of application is first and foremost for the automotive and other mass-produced industries. The aim is to replace the machining center with high spindle speed and high-speed linear feed motion with a single spindle instead of a multi-spindle machine that is difficult to achieve high spindle speed and high-speed feed. The idea is: although the number of spindles is not as large as that of a multi-spindle machine that can simultaneously process, the feed rate of high-speed machining centers can reach 60~80m/min or even higher, that is, several times or even ten times. The feed rate of the combined machine tool, plus the higher speed (100m/min or so) for the return of the lost motion, the time required for the single spindle multiple high-speed reciprocating motion may be less than or slightly higher than the multi-spindle one reciprocating motion It takes time. Therefore, in mass production, it is possible to replace the combined machine tool with a high-speed machining center, which not only achieves high flexibility, but also facilitates rapid product replacement without reducing production efficiency. In actual production, some well-known automobile factories, such as Shanghai General Motors Co., Ltd. in China, have already replaced the combination machine tools with a production line consisting of high-speed machining centers (German GROB products).

At the same time as the application of linear motors, new high-speed precision ball screw drive pairs have emerged. It is characterized by: multi-head and moderately increasing the lead to increase the transmission speed of the lead screw; to increase the diameter of the lead screw, the central hole penetrates the strong coolant to increase the transmission rigidity and reduce the heat; the ceramic ball is used to increase the ball retention. The device (separating the working balls with small diameter balls), the nut raceway and the lead angle direction are the same, and the ball reverse circulation device is improved, so that the d* (screw shaft diameter X screw speed) value can be used up to 150000. For machine tools, the maximum line speed can reach 100m/min and the acceleration can reach 1.5g. In Japan's A55E high-speed machining center, Japan's Makino also uses double-screw and double-servo motor parallel drive to improve transmission rigidity. INA Company of Germany integrates the nut with the servo motor (the motor rotor and the nut are integrated), and replaces the screw rotation with the high-speed rotation of the nut (the slender rod is easy to generate instability at high speed). There are also manufacturers that use the nut and the screw to rotate in the opposite direction at the same time to achieve high-speed linear motion. Therefore, in the current high-speed machining center market, there are two situations in which the transmission modes coexist.

The Japanese Makino company in the United States put forward the idea that the merits of linear motors and ball screws should not be deviated from the specific application requirements and conditions, and this argument is meaningless. This view can also explain a "strange" phenomenon, that is, the same manufacturers such as Germany's Ex-cell-O and Japan's Mazak simultaneously produce two transmission solutions for the high-speed machining of the ball screw). Moreover, Ex-cell-O is the world's first (1993) manufacturer of linear motor high-speed machining centers, and its ball screw type high-speed machining was developed after 1993.

Another area of ​​high-speed machining applications is the use of cubic boron nitride tools for high-speed milling and turning of hardened steel (called "hard cutting") to replace or partially replace EDM and grinding. This is extremely beneficial to the mold industry. In the past, the only processing method available for complex shape hardened molds was electrical machining. The sparks ablated by the spark discharge are extremely small, so the processing efficiency is extremely low, and the processing time is often measured in hours or even 10 hours. However, the efficiency of high-speed hard milling can be increased by several tens of times, thus becoming an alternative to electrical machining. However, when there are deep and narrow grooves on the mold, and there are requirements for small radius fillets and clear angles in the cavity, high-speed hard milling is incapable, so it is impossible to replace all electrical machining. In terms of surface roughness, high-speed hard milling has reached a very high level, but still inferior to electrical machining. Therefore, high-speed hard milling can be used for roughing and semi-finishing, and then machining with electric machining, so that the mold processing cycle can be greatly shortened.

Spiral bevel gears on cars and helicopters require heavy loads, small vibrations and low noise. Therefore, these bevel gears require both high strength and high precision in manufacturing technology and machine tools. In the past, after hardening, because the grinding efficiency is extremely low, or the grinding principle cannot be ground at all (such as contoured spiral bevel gears), only the paired mutual research process can only improve the contact condition. Now, with the high-speed hard milling process, the spiral bevel gear with high precision and excellent surface roughness can be cut out directly from the hardened tooth. The cutting machine of Oelikon of Switzerland, for a hardened tooth with a modulus of 5~6mm and a diameter of about 300mm, can cut a spiral bevel gear with a high profile on the high speed in only 3~5min.

Due to the consideration of heat treatment deformation, the grinding amount of the hardened gear inner hole of the automobile industry is generally above 2~3mm. Germany EMAG's spindle inverted vertical lathe adopts high-speed hard car and boring to process the end face and inner hole of the hardened gear. The end face is finished in one position, while the inner hole only leaves a margin of 0.02 ~ 0.05mm. The internal grinding tool (installed on the interchangeable cutter head) that comes with the machine tool is finally ground in place quickly, which greatly improves the efficiency.

Of course, high speed machining can also be applied to a wide range of fields other than hardened steel to improve efficiency. This is the fundamental reason why machine tools are generally moving toward high speed.

These applications have the following three characteristics: () Generally only high-speed spindles are required, and high-speed feed is not required. For the machining center, the rapid feed rate is generally 40m/min, which is even higher. Mazak's MoldMaker series for mold processing (a total of 3 models), spindle speeds of up to 12,000 ~ 25000i / min, fast feed is only 50m / min (this is already high enough, of course, compared to high-volume processing applications are still low High-speed hard and soft cutting generally does not use coolant, which is extremely beneficial to environmental protection. Therefore, the pursuit of environmental protection requires high-speed machining; high-speed hard cutting generally can obtain a smaller surface roughness value, thus replacing or partially replacing grinding. At the same time, the grinding field is also actively developing high-speed grinding with a line speed of 120m/s or more. It uses cubic boron nitride grinding wheels to replace hard turning and hard milling with large deep and slow feeding. A situation of "competing" with hard cutting.

The aerospace and aerospace industries are extremely important applications for high speed machining. Reasons: First, the main materials are aluminum alloy and titanium alloy, which are suitable for high-speed cutting. Secondly, the parts often have extremely thin walls and ribs, and the rigidity is very poor. Only when the cutting force is high during high-speed cutting, these can be The ribs and walls are processed (there are examples of processing that are as thin as 0.05 to 0.1 mm). The latest trend is: Recently, these industries have used large-scale aluminum alloy billets to make large parts, such as wings and fuselages, to replace multiple small parts with hundreds of rivets, screws and other joints. This not only saves expensive assembly man-hours and assembly tooling, but also increases the strength, rigidity and reliability of the components. In this way, the specifications of the machine tool, especially its X axis, are getting bigger and bigger. As a result, large-scale high-speed milling machines (named HypeiMach(), HVP(), and JoMach159) dedicated to the aircraft industry were exhibited (or exhibited) in this year's company. This type of machine has the following features: further increase of spindle speed and power Because the aircraft industry uses the overall blank "hollow" method to machine parts, the amount of cutting is extremely large.

Therefore, the space in which the spindle speed and power can be increased is also large. According to CINCINNATI, in the past, the spindle speed of the aircraft industry was 15 000 r/min and 22 kW was high speed. With advances in technology, advanced machine tools have increased to 40,000 r/min and 40 kW. Their HyperMach has been increased to 60 000 r/min and 80 kW, which is a new height.

Ultra-long X-stroke and gantry movement Because the "wing" parts are slim, JoMach machine X strokes up to 30m, while the Y-axis is only 2m and the Z-axis is 5m (it is said to be used to process the next generation of European fighters "Typhoon" "The wing." The HypeiMach machine has a "X" stroke of up to 46m and a Y-axis of only 2m. The British Marwin Alumax series has a total length of 1 (1) m. The long X-stroke can only be moved by the gantry (often multiple gantry). It is impossible to move the workbench.

The use of linear motors for high-speed linear drives is not the same as the helical gear racks or worm gears or ball screw drives used in large-scale machine tools in the aerospace industry. Linear motors are also used. This is to meet the needs of the spindle's ultra-high speed, extra power and long X stroke. After the linear motor is used, the Hyper-Mach machine has a feed speed of up to 60m/min, a fast speed of 100m/min and an acceleration of 2g. According to CINCIN-NATI, they have tried to cut a thin-walled aircraft part on HypeiMach. It took 30 minutes for the same parts to take 3 hours on a general high-speed milling machine and 8 hours on a common CNC milling machine. This reduced the processing cost by 85% and fully demonstrated the power of high-speed machine tools.

Another large milling machine introduced by Jobs for high-speed machining in the aerospace and mold industry is LinX. This machine is a bridge gantry layout, and also applies a linear motor with a maximum feed rate of 60m/min and an acceleration of 0.6g. Speed ​​24 for high-speed spindle and high-speed feed, machining time can be reduced by 50%. The machine structure is also simplified, reducing parts by 25% (contrast ball screw drive) for easy maintenance.

The above description shows that linear motor applications have expanded from the initial mass production industries such as automobiles to the processing of the aerospace industry and large molds.

Laser linear displacement measuring device for position measurement and feedback. For example, CINCINNATI applied a laser device at HypeMach to meet high-speed feedback and improve machine accuracy.

(6) The HVP using the fluid dynamic and static piezoelectric spindle bearing INGERSOLL uses its own developed bearing. It is said that the life of this bearing is much longer than that of the ball bearing, and the rigidity is 5-6 times higher than that of the ball bearing, so that heavy cutting can be performed. The machine's electric spindle has a power of 75 kW. At a maximum speed of 20 000 i/min, the metal removal rate can be as high as 6440 cm 3 /min. The bearing has much better vibration resistance than the ball bearing, so the tool life can be longer.

The price is 1.6 million US dollars. The buyer is Brek of Gardena, California, USA, and is a well-known large-scale aircraft manufacturer in the United States. The specifications of the X, Y and Z axes are 21.3m, 3.25m and 0.75m respectively. The spindle speed and power are 18000r/min and 100kW respectively, and the tool interface is H9C100A. The Siemens 840D CNC system is adopted.

CINCINNATI has produced a five-axis CNC milling machine for large aircraft parts (American profiler) for decades. It has produced more than 500 units and distributed all over the world. It can be equipped with 1~3 milling heads, each of which has 3 forms: (1) the bridge moves on the track; the other is the rail mounted on the two concrete walls, the beams without the two legs are directly on the track mobile. The order from Brek is orbital. This type of machine can be equipped with a tool magazine and a tool changer.

The traditional vertical spindle layout, while the floor-mounted boring-type horizontal spindle layout, the workpiece is mounted on a vertical platform. According to INGERSOLL, its HVP production efficiency is 4 to 11 times higher than that of traditional vertical machine tools. For example, a machine spar requires 50 hours on a conventional vertical machine and a little more than 5 hours on an HVP. Another example is the use of 2.500r/min spindle speed for roughing and finishing, only 70min, while on traditional vertical machine tools, it takes 10h. It is said that the high efficiency of HVP comes from the high-rigidity electric spindle and the horizontal machine tool chip discharge. factor. HVP also offers a 40,000r/min, 80kW spindle and automatic change of tray and spindle head.

The key components of high-speed machining, an electric spindle, showcases the following new developments on IMTS: Swiss Fischer Electric Spindle Co., Ltd. has introduced an online automatic balancing device on the electric spindle. In the case of a machining center, the automatic balancing of the tool quality is performed once for each tool change. It is said that within 1 s, 80% to 99% of the vibration caused by dynamic imbalance can be eliminated.

Swiss IBAG has introduced the electric spindle of hydrostatic bearing, which is said to have a service life of more than 20,000h. Swiss IBAG has introduced the electric spindle of the magnetic bearing.

Swiss IBAG is equipped with an electric spindle axial dimension monitoring sensor on its electric spindle components, which can be coupled with the machine numerical control system for axial dimension compensation.

Electric spindles for permanent magnet synchronous motors have emerged. The current motor of the electric spindle is an asynchronous induction motor. The stator heat can be cooled, and the rotor heat cannot be cooled, and the rotor of the synchronous motor is a permanent magnet that does not generate heat. In addition, the synchronous motor of the same power has a smaller outer shape than the asynchronous motor, which is advantageous for realizing small size and high power, thereby improving power density. 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: 1 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. 2 In the case of high speed operation, the life of rolling bearings is limited, that is, low. The main manufacturing technology and the machine tool failure form are due to material fatigue and loss of precision (the electric spindle accuracy is generally radial runout 2 axis 1~). Therefore, it is impossible to open the market without the ability of local maintenance and renovation. Some electric spindle companies recommend that users purchase a spare item because of the general maintenance, the refurbishment cycle is two weeks. In this way, downtime can be minimized.

On the other hand, Kennametal of the United States has introduced a tool holder with automatic balancing to adapt to high speed.

In the case of linear motors, permanent magnet synchronous motors have been used in the early days because of their good transmission quality, but it is difficult to prevent magnetism. Recently, the induction asynchronous motor with vector control is used, the transmission quality is good and the anti-magnetic difficulty is reduced. This may be related to the recent availability of motor-specific DSP chips by companies such as Motorola and TI, which have integrated circuits with vector control algorithms.

2 Five-axis linkage and five-sided machining are more common in the linkage system price difference.

In the past, five-axis linkage programming software (including post-programming inspection software) was technically difficult and extremely expensive, several times as many as three-axis linkage programming software. Although the price is still high, it has fallen sharply.

In the past, the A/C-axis spindle components were complicated in structure and expensive; now, due to the appearance of the electric spindle, the structure is simplified and the cost is greatly reduced.

It can be seen that the spindle drive of the past A/C axis spindle components requires two pairs of bevel gear pairs and one intermediate drive bevel gear (ie a total of five bevel gears) and a pair of spur gear transmission pairs and two countershafts. .

At present, in high-speed, high-power transmission conditions, these gears must be high-intensity and high-precision. Bevel gears must also use spiral bevel gears, which makes manufacturing and assembly difficult and costly. Now, with the electric spindle independently driven, the above 7 gears and 2 intermediate shafts can be omitted, and the cost is naturally reduced.

In the last IMTS, it has given people a more prominent impression than the past five-axis linkage machine. In this session, almost all machining centers and CNC milling machines can achieve five-axis linkage and five-sided machining. The emergence of this phenomenon is not accidental and has the following profound background.

In essence, the use of three-axis linkage for the machining of three-dimensional surfaces is generally not the best choice. Because, in the case of three-axis linkage, it is generally difficult to use the optimum geometrical part of the tool for cutting, which is not only inefficient but also extremely poor in surface roughness. That is to say, the value of the residual height of the ball-end cutting tool is large, and often requires heavy manual polishing, and the manual polishing can reduce the surface roughness value, but the geometric accuracy of the surface is often lost. 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, you can use the best geometry of the tool for cutting, and you can use high-efficiency end mills when machining convex surfaces. When machining concave surfaces, you can use the arc portion with high efficiency of the ball-end cutter for cutting. These are all impossible to achieve with three-axis linkage. In this way, not only the roughness is good, but the efficiency is also greatly improved. CINCINNATI of the United States once claimed that the cutting efficiency of a five-axis linkage machine tool can be equal to two three-axis linkage machine tools, especially the current high-speed milling and hardening process with cubic boron nitride milling cutter, comparable in the case of five-axis linkage. The three-axis linkage exerts greater power. Therefore, in general, five-axis linkage is the best choice for 3D surface machining.

In the past, due to the following reasons, the widespread application of five-axis linkage has been hindered. Now these obstacles have been ruled out: 1 The price of the past five-axis linkage CNC system is extremely high, which is several times higher than that of the three-axis linkage system. This is because the CPU speed is low at the time, when five-axis linkage, it is often necessary to use multiple CPUs or ASICs; now, because the CPU speed is tens of millions of times higher than in the past, of course, except for the above A/ In addition to the C-axis spindle components, there are various other configurations to realize the spindle component structure of the A/B axis. In contrast, the A/C axis spindle component structure is relatively simple, the rigidity is also good, and the range of the A/B axis can be realized, which can be above *90*. In this respect, it has been difficult for some other structures to be larger than *45*.

This A/C structure also has a great advantage, that is, it can realize five-axis linkage and realize five-face machining at the same time, that is, when the A-axis is 0*, horizontal plane processing can be realized; when the A-axis is fixed at 90 * When the C-axis is rotated 90* each time, it is possible to realize the processing of four planes that are perpendicular to each other. This five-axis linkage and five-face machining combined machine tools are not available in the past. Moreover, since the rotation angle of both the C axis and the A axis is arbitrary, the number of planes that can be actually processed can be larger or smaller than 5 planes. Therefore, the name of the machine with the A/C-axis spindle part is now changed to “five-axis and multi-faceted (instead of the past “five-sided”) machining machine”, which is also a brand new thing.

The main disadvantage of this A/C-axis spindle component is that it is part of a relatively coupled (referred to as the A-axis rotary axis) component with poor stiffness. Therefore, when only five-sided machining is required, and five-axis linkage is not required, the machine tool that automatically replaces the spindle component is used, and the rigidity of the peripheral plane is better with the replacement horizontal spindle component. In addition, when the machining needs to replace the electric spindle of different power and the highest shaft speed, it is only automatically replaced together with the entire A/C shaft component, and it is not easy to realize only the electric power spindle itself. Therefore, it is not possible to replace the machine that can automatically replace the spindle parts (replaceable heads).

It can also be seen that after the electric spindle is used, although seven gears can be reduced, two pairs of precision worm gears are retained. At present, some companies, such as ETEL in Switzerland and KOLLMORGEN in the United States, have developed a ring-shaped motor called "BrushlessRingTorqueMotor"*, which can be rotated at an ultra-low speed, large twist and smooth. It replaces the worm gear pair. It has been applied to a multi-axis linkage milling machine, replacing two pairs of precision worm gears with diameters of 0.5m and 2.5m respectively. It is said that after replacement, the machining accuracy and surface roughness are both Improvements. It is expected that such a toroidal motor may be used in A/C-axis spindle components and A/B-axis composite turrets to replace worm gears and worm gears.

In order to upgrade the three-axis machining center and CNC milling machine that are currently in use to achieve five-axis simultaneous machining, TRI-TECH in the United States exhibited the A/C-axis spindle features available for these older machines (see ). Since the electric spindle is not used, the drive is from the spindle of the original machine tool, so the internal structure is estimated to be similar. It uses a 7:24 taper shank to couple with the existing machine tool spindle. Its C-axis range is 360*A axis for ±90* to ensure angular accuracy of 0.01* and repeatability of 0.005*. The company exhibited the 5411 model at the last IMTS exhibition. This year, the improved 5412 model was exhibited. In its website ( there are examples of typical parts processed with five-axis linkage of this part and used in some user companies.

The popularity of five-axis technology reflects the demand for process equipment in the modern aerospace industry, and also reflects the transition of modern mold manufacturing processes from EDM to HSM. Just as 20 years ago, boring and milling machine manufacturers have developed their products to the same processing center. Today they have to complete the transition from three-axis to five-axis, otherwise they will be eliminated due to the loss of the aerospace and mold industry.

(To be continued) First Author: Chen for many years, China Council for the Promotion of International Trade Machinery (edit Zhangfang Li). Book news.

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