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Ultra-high speed machining and machine tool zero rotation

Article source:admin Popularity:time:2017-07-07 17:39

         Ultra high speed machining is a advanced manufacturing technique of 10 times the normal cutting speed and the speed of the machine processing of the parts.Developed countries have developed very fast in the past years.Enter the 1990s.The process of high speed machine tool is very rapid, group after group of high speed machining center and other kinds of high speed nc machine tools are following the international market, that the high and new technology has now entered a new stage of industrial application from theoretical research [RLL. If of gentle sex manufacturing automation is numerical control technology, due to save a lot of auxiliary area, make traditional manufacturing technology for the first time a revolutionary changes have taken place. As the first milestone of modern manufacturing technology; it? Greatly saves the precision cutting hours and achieve efficient production of ultra-high speed machining technology, is the second milestone of modern manufacturing technology. Is internationally recognized as one of the four advanced manufacturing technology Is a systematic project of the 21st century.

The research and development of high - speed machine with excellent performance is the precondition and key factor to realize ultra-high speed machining.The most important of these are the design and manufacture of high-speed, high-power spindle units and feed units.And eliminate all intermediate driving links. Realize the direct transmission of the power source to the working parts of the machine (spindle, table, and slabs, etc.).The length of the transmission chain is zero. This is known as the zero drive.

The zero drive greatly simplifies the transmission and structure of the machine, but it also significantly improves the dynamic sensitivity, machining accuracy and reliability of the machine.This is a new kind of transmission mode to meet the requirements of superfast machining, which is a breakthrough in machine tool design theory and manufacturing technology in the 1990s.Some people call this zero-transmission machine tool called "next-generation new machine tool" high speed high-power electric spindle.

Under the condition of high-speed operation. Traditional gear Lord system can not meet demand, with wide speed ac frequency conversion motor to realize the machine tool spindle speed, so that the main drive of machinery structure is greatly simplified.In this way, the main shaft parts of the machine can be set up as a functional component - "spindle unit", which is produced by a series of specialized factories.

Spindle unit has a variety of forms [' :. On ultra-high speed CNC machine tools, almost without exception, has now adopted the Spindle Motor and the structure of machine Spindle in one bed, using shell Motor, the hollow rotor directly set on the machine tool Spindle, the stator with a cooling jacket is installed in the Spindle unit housing. The formation of the so-called "built-in Motor Spindle (Build in Motor Spindle). Jane says" motorized Spindle ". In this way, the Motor rotor is the main shaft of machine tool. Shell is the Motor of the machine tool Spindle unit. To achieve "' variable frequency Motor and the integration of machine tool Spindle. This kind of motorized Spindle and early use in grinding machine of the built-in Motor Spindle main E % is: workers have a wide speed range; (2) has a larger drive power and torque; (3) a series of monitoring shaft vibration, bearing operating parameters such as temperature sensor and the test control system, in order to ensure the reliability of the ultra-high speed running with safety. Motorized Spindle is a modern.} 5. Can type features, widely used in high speed machining center and CNC lathe.

In foreign countries, this kind of bulk high-speed motor has been serialized.The machine can be ordered according to your request.

Motorized spindle of compact structure, light weight, small inertia, good response, also can avoid the vibration and noise, is an ideal structure, high-speed spindle unit has being widely used in all kinds of high-speed machine tools.

When designing the main shaft of the motor, except for selecting the appropriate non-shell motor.

Heat sink for internal motor

The finite element analysis of the temperature field of the main shaft and its drive and cooling system shows that the heat output of the main shaft is generated by the stator after the electric power.Can design a pass into the cooling liquid (oil or water) set of Jane, them into the stator winding, by circulating cooling liquid absorption and take away the heat generated by the motor, maintain uniform temperature distribution in the spindle unit light body.

The calculation and measurement show that 1/3 of the heat in the spindle is produced by the rotor of the motor.Because the rotor heat dissipation condition is poor, take away directly.Is the electric spindle heat dissipation line.Cooling fluid

Correct selection of spindle bearing

The bearings of high - speed and high power spindle are mainly in three forms: magnetic floating shaft bearing, liquid static pressure bearing and ceramic rolling bearing.The high speed performance of magnetic floating bearing, high precision, easy to realize real-time diagnosis and on-line monitoring.In the early stage of the development of ultra-high speed machine tools (mid-1980s), the magnetic bearing has been considered as the sole choice for the spindle bearing of the super-high speed machine tool.However, the practice of more than ten years shows that this kind of bearing is complicated by electromagnetic measurement and control system, which is very expensive and high in length. Therefore, it has not been widely used.Liquid static pressure bearing comprehensive absorbed the dynamic pressure bearing and the advantages of hydrostatic bearing, avoids hot under hydrostatic bearing the severe disease and complex oil supply system, and overcome the dynamic pressure bearing can happen when the start and stop the dry friction, also has very good high speed performance, and wide speed range and is suitable for high power rough machining, and is suitable for high speed finish machining.But this kind of bearing must be designed according to specific machine tool, production separately, low standard degree, maintenance is difficult.

Now the most popular is ceramic rolling bearing.This shaft bearing structure is identical to the size series and ordinary steel rolling bearing, only replacing the material of the rolling body with Si, N 'ceramic, with the requirements of super high speed operation.The density of the ceramic materials of silicon nitride (S1, N) is only 40, and the thermal expansion coefficient is only 25% of steel, while the elastic modulus is 1. 5 times of steel and 2. 3 times hardness of steel.Therefore, using this material as a rolling body can greatly reduce centrifugal force and gyro moment in the high-speed operation of the bearing, and obtain a new generation high-speed bearing of low temperature rise, high degree and long life [6]

The test results of the high speed machining and machine tool study room for a maximum speed nm. = 48 OOOr/min.The temperature rise and thermal deformation of ceramic rolling bearing are lower than that of steel rolling bearing.The higher the speed, the greater the superiority of ceramic bearing.Ceramic bearings also have a shorter time to reach thermal equilibrium.In addition, the standardization of ceramic rolling bearing is high, and the structure of the machine is small and easy to maintain, and the price is much lower than that of his two high-speed bearings.

In order to realize ultra-high speed machining, the machine tool should not only have high speed main shaft, but also have high-speed advance to give fast travel.This is not only in order to improve the production efficiency, but also to maintain the high speed cutting tools necessary for normal work, otherwise it will cause rapid wear of cutting tool and the temperature rise, damage the surface of the workpiece processing quality.At the same time, due to machine the straight line trip is short, so only at high speed and in a flash moment in the high speed travel must stop, high speed linear motion is of practical significance, it not only requires high speed feed components, and for acceleration.

Linear motor feed unit profile

In order to meet the requirement of high-speed feed, a new linear motor feed unit comes into being.
In 1845, Charles Wheastone invented the world's first linear motor [m, since the linear motor in the transport machinery, apparatus and meters, computer peripheral equipment and maglev trains and so on all have been applied in various industry [8].
A few years ago, also someone with high frequency small line Routine transverse cylindrical Linear Motor to drive the lathe tool post, to realize non-circular cross-section parts, such as elliptical piston turning processing [Csl. But in work centers and other large stroke nc machine tool feed system driven by Linear Motor, or in the recent 3 years, Germany in 1993 Ex - cel l - O company exhibited for the first time in the international machine tool fair (Hanover) XHC - 240 type high speed machining center, the three coordinate party up all sense of communication should be adopted the German Indramat company type Linear Motor, Linear Induction Motor), table travel 630 ^ - 710 mm, the feed rate is as high as 60 m/min, feed force 800 N 2. When the feed speed of 20 m/min position precision can be up to 4 umVol. The successful application of Linear Motor on the machining center, stir the world machine tool industry, by peer expert evaluation for international machine tool industry in the 90 s peak, a new technology is the theory of machine bed design a major breakthrough.
A single - element schematic diagram of a large - stroke induction linear motor is presented.
The electric winding (primary) of the iron core is mounted on the lower part of the machine tool table, which is the moving part of the linear motor.
There is no electric winding between the guide rails of the bed, each turn in each winding is short circuit, which is equivalent to the expansion of the ac induction rotating motor cage, which is the fixed part of the linear motor.
It can be seen that the linear motor and the rotary motor are opposite, the primary is the moving parts, the secondary is the setting.
After the linear motor is energized, the middle class has a powerful magnetic field, which relies on the magnetic force to push the moving parts (machine tool table) into a rapid linear motion.
Unlike the traditional "rotary machine + ball screw", there is no direct mechanical contact between the linear motor and the machine tool table. Instead, it relies on magnetic connections.
Linear servo motor drives the high-speed feed unit
In the movement of machine tool, the linear motor has the following advantages: it can achieve very high speed and acceleration.
Linear motor feed unit cancelled all intermediate transmission link, realizes the motor to perform component machine bed (workbench, slip board, etc.) of direct drive, transmission chain length of the feed drive is also reduced to zero, this is the machine tool feed system of "zero transmission".
When the start motor, variable speed and thus be avoided Because of the elastic deformation of intermediate transmission link, clearance and wear caused by the movement hysteresis, available feed rate as high as 200 m/min bao and 1 m/s, the acceleration.
With high thrust, high rigidity, fast dynamic response and high positioning accuracy, it is especially advantageous to improve the machining accuracy and surface quality of the parts in high-speed machining, and improve the service life of the tool.
Tests show that when using small 20 mm cylindrical milling cutter milling industry, but the linear motor's magnetic field is wide open, especially the synchronous linear motor to be installed on machine tool bed rows of powerful permanent magnets, magnetic force and machine of metal scraps, machine tool parts, processing, and the assembly tools are magnetic materials, is easy to magnetic field of linear motor to absorb, interfere with the normal work.
When the magnetic dust in the cutting and air is sucked into the small gap between the moving parts of the linear motor and the fixed parts (usually only 0.15 mm), the motor can't work when it is blocked.
Therefore, the magnetic field of the linear motor is enclosed with a 3d folding seal.
Dead heat q while
The linear motor is installed in the machine tool table and the bed guide rail. It is in the "abdomen" of the machine tool. It is difficult to heat the heat and must take special cooling measures.
Linear motor drives directly into the structure of the workbench.
The primary (moving parts) of the linear motor pass a cooling plate to the top of the workbench.
The secondary (fixed) of the linear motor is mounted on the base by a cooling plate.
When the machine is working, the cooling fluid is used in the cooling plate and hole to absorb and take away the heat amount generated in the linear motor parts and the fixed coils.
In the feed servo system of nc machine tool, the negative charge of the workbench can bring external disturbance to the stability of the work.
If the automatic regulating function of the system is not strong, it can cause concussion and destabilize the system.
For linear motor drive, only full closed loop control can be used, which requires that its position detecting element has high data acquisition power, resolution and quick response capability.
The laser detection and feedback control system is usually used.
In addition, in order to reduce the negative of the servo system load and linear motion, the resistance of the ultra high speed machine tool workbench with a new type of lightweight high strength materials (such as fiber reinforced plastic or aluminum qin or inductive synchronous type, linear motor compared with the traditional ball screw feed system, the price is expensive. Along with the advance of production technology, linear motor is a large number of applications, cost will decrease, as a new way of feed drive, linear electric opportunity to show its strong vitality, will be with the development of the ultra-high speed machining technology and gradual popularization and application.
China has not yet attracted enough revision for ultra-high speed processing technology.
Nearly l0 years, the domestic many people engaged in the original processing technology research to make the automation, because the flexible automation is a new hotspot in the research of the domestic outside, easy to get, but from the global perspective, but ignores the process improvements and improve itself, so that the processing technology of our country still stay in low level, the workshop now field using cutting speed almost one over ten of the advanced industrial countries.
We believe that for manufacturing technology, only the advance sex of the process is inherent and essential, and any advanced automation system can only make the process stable and accurate.
If there is a problem with the art itself, no sophisticated automated system can make an essential improvement to it.
From this point of view, we have discussed the tendency of the competent authorities to readjust the policy, change the technology for a long time, and pursue automation.
You know, shorten the auxiliary time and shorten the processing time, to improve the production efficiency, is be short of one cannot, the two complement each other aspects, which on the one hand, can cause serious consequences to ignore. Low processing speed of numerical control technology is by no means the advanced manufacturing technology, not speed up the development and application of ultra-high speed machining technology, automation is not likely to achieve good overall efficiency.
Based on the above understanding, in recent years our school has established a special "ultra-high speed machining and machine tool research room".
First of all, current situation of the development of the advanced manufacturing technology at home and abroad to compare system and in-depth investigation and study, widely collect and organize the relevant literature, and with the close cooperation with closed factories, in the national natural science fund committee and provinces and cities under the support of scientific research departments
Actively carry out the study of the theory of the ultra-high speed machining, vigorously supported institute of institutions of higher learning and the high speed machining mechanism of various materials and related technology in-depth and systematic experimental research work, the basis of a comparatively complete theory system and database.
To guide production practice.
Vigorously developing a new type of cutting tool materials used in high speed machining, the material has a high melting point, hardness and strength, research and improvement of high speed cutting tool geometric parameters and reasonable handle structure, improve the service life of the cutting tool and the work reliability.
The development and research of supporting technology.
For example, it is proposed to develop a linear motor with no shell high speed rotary motor and large stroke force.
The electronic control department is recommended to develop high power and wide speed ac frequency conversion drive system and fast servo control system.
The construction of the bearing industry to develop the ceramic rolling bearing and the new products of magnetic bearing.
Actively conducting academic exchanges and international cooperation.
In the wide open exhibition research, test and application. On the basis of the ultra-high speed machining nationwide academic conference, the organization panel investigates serious for ultra-high speed machining technology abroad, invited foreign experts in the field Give lectures in China, do a good job in personnel training and team building.
After fully prepared, when conditions are ripe, the establishment of a national "ultra-high speed machining research In the center ", the introduction of advanced equipment and instruments. And make it become the research base of open type, solve some technical problems, overall and comprehensive to catch up with the international advanced level.

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