The rigid structure of numerical control machine tool

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  • source:AVELLINO CNC Machining
In the first phase that numerical control machine tool develops, the change with its machinery structure and more how old than doing not have photograph of general purpose machine tool, just mix in automatic gearshift, tool carrier the respect such as automatic dislocation and handle operation makes workbench some of change. As the development of numerical control technology, the control way that considers it and use characteristic, just raised taller requirement to precision of the productivity of the machine tool, treatment and life. The main body orgnaization of numerical control machine tool has the following characteristic: 1) because used main shaft of high-powered infinitely variable speeds and servo transmission system, the ultimate drive structure of numerical control machine tool simplifies greatly, transmission catenary also shortens greatly; 2) machine productivity to suit to successive automation is machined and rise, structure of machinery of numerical control machine tool has taller static, dynamic stiffness and damp precision, and taller wearability, and heat is out of shape small; 3) to reduce attrition, eliminate transmission clearance and obtain taller treatment precision, used efficient drive disk assembly morely, be like ball guide screw deputy with scroll slideway, disappear unoccupied place positive drive deputy etc; 4) work for improvement condition, reduce auxiliary time, improvement to operate a gender, improve labor productivity, used cutting tool library of automatic clamp device, knife and trade the auxiliary unit such as knife device and unit of automatic platoon bit automatically. According to the applicable circumstance of numerical control machine tool and orgnaization characteristic, because raise the following requirement,logarithm controls machine tool construction: One, taller machine tool is static, the statement that uses data-in means to offer according to numerical control process designing or hand undertakes use machine tool of stiffness numerical control automatically machining. As a result of rigid structure (wait like machine tool lathe bed, slideway, workbench, tool carrier and main shaft box) geometrical precision and in be out of shape the fixed position error of generation is machining a process, cannot adjust artificially with compensation, accordingly, must everywhere the flexibility that rigid structure part produces is out of shape control is in minimal inside, in order to assure the treatment precision of a requirement and exterior quality. To raise the stiffness of main shaft of numerical control machine tool, not only often use the 3 structures that prop up, and choose the biserial with steel very good sex bearing of short columnar roller and horn contact join with a hinge of afferent thrust bearing to go out believe errorring force bearing, be out of shape in order to reduce the radial of main shaft and axial. To raise the machine tool is big stiffness, use close interfacial lathe bed, use fluid equilibrium to because the position changes positional machine tool is out of shape,reduce mobile part. To raise a machine tool the osculatory stiffness of each component, increase the carrying capacity of the machine tool, use the contact that blows grinding method to increase unit area to go up to nod, bring to bear on between combinative scale enough big increase load beforehand, in order to raise osculatory area. These measure raise osculatory stiffness effectively. To develop the efficient process capability of numerical control machine tool adequately, can undertake stabilizing cutting, below the premise that assures static stiffness, still must raise dynamic stiffness. Commonly used measure basically has the stiffness that improves a system, increase damp and adjust component part wait from Zhen Pin rate. The experiment makes clear, raising damp coefficient is improvement is fought brace up effective method of the gender. Of armor plate solder the structure can increase static stiffness already, reduce structural weight, can increase the damp of component part itself again. Accordingly, used armor plate to solder on numerical control machine tool in recent years structural lathe bed, pillar, beam and workbench. Seal arenaceous cast to also be helpful for oscillatory attenuation, fight to rising brace up the gender also has better effect. 2, below the heats up the heat source outside be out of shape inside effect that reduces a machine tool, each component will produce the machine tool the heat of different level is out of shape, make the opposite motion concern between workpiece and cutting tool breaks ring, also be machine tool quarter drops. To numerical control machine tool, because full treatment process is calculative instruction pilot, hot metabolic effect is more serious. Be out of shape to reduce heat, adopt the following measure normally in structure of numerical control machine tool. 1.

The generation when reducing interior of calorific machine tool to give out heat heats up metabolic main heat source, ought to go out heat source as far as possible from the depart in lead plane. 2.

After control temperature rise was taking a series of step that reduce heat source, hot metabolic circumstance will be improved somewhat. But the heat source of inside and outside that should eliminate a machine tool completely is very difficult normally, it is impossible even. Must be heated up through coming loose goodly so and refrigeration will control temperature rise, in order to reduce the effect of heat source. Its are mid more effective method is the calorific place in the machine tool cools compulsively, also can adopt heating method in part of machine tool low temperature, the temperature that makes the machine tool is nodded each tends consistent, can reduce the warpage that causes as a result of difference in temperature so. 3.

Improve machine tool orgnaization to be below likewise calorific condition, machine tool orgnaization is out of shape to heat also have very big effect. The odd pillar orgnaization that if numerical control machine tool goes,uses is possible be replaced by place of double column orgnaization. Because control semmetry, the main shaft line after be heated of double pillar orgnaization divides the translation that produces perpendicular way outside, of other direction be out of shape very small, and the correction that the axes shift of perpendicular direction can use a coordinate conveniently undertakes compensating. To the main shaft box of numerical control lathe, should make the heat of main shaft is out of shape as far as possible on the perpendicular way that produces in cutting tool to be cut. This can make main shaft heat is out of shape the influence to machining a diameter is reduced minimal. Still should reduce main shaft center and main shaft as far as possible on the structure the distance to the ground, in order to reduce hot metabolic gross, should make the around temperature rise of main shaft box concurrent at the same time, after avoiding main shaft to be out of shape, appear tilt. The ball guide screw in numerical control machine tool often is in predicting load big, rotate speed is high and medicinal powder the job below the condition of hot difference, because this guide screw is easy calorific. The consequence that ball guide screw heats up production to cause is serious, it is especially in open loop system, it can make feed system loses fixed position precision. At present certain machine tool reduces the heat of guide screw to be out of shape with the method that helps beforehand. Be out of shape to adopting afore-mentioned measure to still be heated up indelibly, can try to amend according to measuring a result to give out compensation pulse by numerical control system. 3, reduce motion to chafe and eliminate workbench of machine tool of transmission space numerical control between (or procrastinate board) displacement measures the equivalent in 11 arteries and veins to be most of subsection, ask again normally can move with the speed of base. To make workbench can right the instruction of numerical control device is made accurate answer, must take corresponding step. Slideway of current and commonly used sliding slideway, scroll and static press slideway to existing in respect of attrition damp character apparent difference. Slip guide screw is replaced to also can get similar result with ball guide screw in feed system. Current, numerical control machine tool uses transmission of ball guide screw without an other place almost. Numerical control machine tool (especially the numerical control machine tool of open loop system) treatment precision depends on greatly the precision of feed drive catenary. Besides the machining error that reduces transmission gear and ball guide screw, another important step is to use unoccupied place transmission of very close to each other deputy. The accumulation to pitch of ball guide screw error, use pulse to compensate device to undertake pitch is compensated normally. 4, the life that improves a machine tool and precision maintain a gender to maintain a gender to raise the life of the machine tool and precision, in the wearability that component of airport of mature numerical control answers when the design, especially the wearability of the component of main shaft of chance of port of wait of machine tool slideway, feed main part that affects plan. In use process, should assure numerical control machine tool each part is lubricant and good. 5, reduce auxiliary time and improvement to operate function to be in the sheet of numerical control machine tool in treatment, auxiliary time (be not the time that cut bits) have larger proportion. Want to improve the productivity of the machine tool further, must adopt make utmost ground reduce auxiliary time. At present already machine tool of a lot of numerical control used much main shaft, much tool carrier, and those who take knife library is automatic the device that change a knife, change knife time in order to decrease. To cutting the numerical control machine tool that bits dosage increases, lathe bed orgnaization must be helpful for discharging bits. Advocate of machine tool of numerical control of component of carry motive instrument advocate transmission motion is the transmission motion that shows production cuts bits, for example, the main shaft on numerical control lathe drives the whirligig of workpiece, the whirligig that the main shaft on vertical machining center drives milling cutter, boring cutter and emery wheel to wait. Of numerical control machine tool advocate transmission motion is to pass advocate transmission electric machinery procrastinates those who move. One, advocate the gearshift system that transmission moves is current, of numerical control machine tool advocate the dc timing electric machinery that transmission electric machinery uses electric machinery of common communication asynchronous and convention already basically no longer, they and be replaced by electric machinery of electric machinery of burgeoning servo of communication frequency control and dc servo timing stage by stage. Of numerical control machine tool advocate motion asks to have bigger timing range, the reasonable dosage that cut bits can be chosen in order to assure when treatment, acquire precision of first-rate productivity, treatment and exterior quality thereby. To get used to all sorts of workpiece and the requirement of all sorts of workpiece material, the numerical control machine tool that congratulations to change a knife automatically more and machining center advocate timing scope of motion should expand further. Dictate according to control when the gearshift of numerical control machine tool undertake automatically, because this gearshift orgnaization must get used to the requirement of automata. Because shed the timing system with electric machinery of communication gearshift main shaft to be perfected with each passing day continuously, can realize the infinitely variable speeds of wide range conveniently not only, and decreased among deliver link and raised gearshift pilot dependability, because this is in of numerical control machine tool advocate the advantage that it can show more in transmission system. To ensure the torque when low speed, some numerical control machine tools are communicating and match on the foundation of infinitely variable speeds of dc electric machinery with gear gearshift. As a result of advocate motion used infinitely variable speeds, can realize constant speed to cut bits control when inclined end panel is measured on lathe of large numerical control, so that improve manufacturing efficiency and exterior quality further. Numerical control machine tool advocate transmission basically has kind of 3 kinds of configuration. 1.

Those who contain gearshift gear advocate transmission this is big, kind model numerical control machine tool uses a kind of more means. Pass decelerate of a few pairs of a few gear, expanded to output torque, in order to satisfy the requirement with characteristic to outputting torque main shaft. Course of study of machine tool of small-sized numerical control uses one part way of this kind of transmission, in order to obtain puissant the torque that when cutting bits, needs. The shift of slippage gear uses hydraulic pressure to dial fork mostly or drive gear implementation by hydraulic pressure oil cylinder directly. 2.

Pass belt-conveyor advocate this basically uses transmission on machine tool of small-sized numerical control, can avoiding positive drive is the vibration that cause and noise. But the main shaft that it can use the torque character with the requirement only. 3.

By timing electric machinery of direct drive advocate this plants transmission advocate transmission way simplified greatly the structure of main shaft casing and main shaft, raised the stiffness of main shaft component effectively. But torque of main shaft output is small, electric machinery is calorific bigger to the precision influence of main shaft. 2, the precision of component of main shaft of machine tool of numerical control of component of main shaft of numerical control puncture, stiffness and heat are out of shape to treatment quality has immediate effect. Because machine,machine tool of incorrect numerical control undertakes be adjustmented artificially in the process, these effects are more accordingly serious. At present the main shaft miller of numerical control machine tool should have 3 kinds of type. 1.

Around is propped up before using different bearing, prop up use biserial afferent thrust ball bearing combines bearing of short columnar roller and biserial of contact of 60 ° horn, prop up after use ball bearing of didymous and afferent thrust. This configuration form makes the integrated stiffness of main shaft rises substantially, can satisfy puissant the demand that cuts bits, because this applies generally at machine tool of of all kinds numerical control. 2.

Bearing uses high accuracy biserial before afferent thrust ball bearing is afferent the performance when high speed of thrust ball bearing is good, top rotate speed can amount to main shaft 4000r/min. But, its carrying capacity is small, apply to consequently carry high speed, gently and close together numerical control lathe. 3.

Biserial and sheet list tapered roller bearing radial of this kind of bearing and axial stiffness are tall, can bear heavy load, can bear especially stronger move load, installation and adjust function it may not be a bad idea. But, this kind of bearing restricted the top rotate speed of main shaft and precision, because this uses the numerical control machine tool of medium precision, low speed and burden. On the orgnaization of main shaft, the fixed position of bearing of the discharge carry on one's shoulder that wants the outfit clip that treats good chuck and tool carrier, main shaft, main shaft and clearance are adjusted, of main shaft component lubricate and sealed and on craft other a series of problems. Be opposite to reduce heat of temperature rise of main shaft component to be out of shape as far as possible the influence of precision of machine tool job, the circulatory system that uses lubricating oil normally takes away the quantity of heat of main shaft component, make main shaft component and casing maintain constant temperature. Appropriative refrigeration device is used on boring of certain numerical control, milling machine, idealer realized temperature control. In recent years, the main shaft bearing of machine tool of certain numerical control uses advanced oil, with seal means to undertake lubricating, every add grease to be able to be used 7 years to 10 years. Mix to make lube and grease are not sent, use labyrinthian and sealed means normally. To main shaft of numerical control lathe, because the dynamical chuck of structural ponderosity and clamp oil cylinder are being installed in its two end, so main shaft stiffness must rise further, should design reasonable join end, in order to improve the join stiffness that dynamical chuck and main shaft end spend. To the main shaft of numerical control boring machine or milling machine, assemble and unassemble fast or automatically considering what realize cutting tool, still deserve to cutting tool assembles and unassemble automatically on main shaft, the cleared unit that main shaft stops definitely and bits cuts inside main shaft aperture. Component of feed drive machinery normally, a system of typical feed of closed-loop control of numerical control machine tool, compare by the position, enlarge component, driving unit, mechanical gearing and detect the composition of a few parts such as feedback component. Among them, mechanical gearing is one of positional control important segment. The mechanical gearing that says here, it is to show the whirligig drive source turns into the catenary of whole and mechanical drive of the sharp movement of workbench, include nut of gear plant, guide screw deputy wait for intermediate main transfer machinery. (one) shaft coupling shaft coupling is a kind of returns move to pass torque and motion together unit that two rods that use join to send an orgnaization make. The type of shaft coupling is at present various, have hydraulic type, electromagnetism type and mechanical. The application of mechanical shaft coupling is most wide. Sleeve shaft coupling is tectonic and simple, radial size is small, but it is difficult to assemble and unassemble (the axis needs axial to move) . And in asking two axes are opposite strictly, not radial of be patient of or angle deviation, because of when this is used, be restricted certainly. Circuitous shaft coupling uses cone-shaped clamp ring to deliver load, can make motivation is delivered without directional clearance. Flange type shaft coupling is tectonic of simple, cost, can deliver bigger torque, commonly used at rotate speed low, 5 kinds are reached, axial tigidity reachs good to neuter situation greatly. His main drawback is pair of two axes is very tall to neuter requirement. If exist between two axes displacement and tilt, save add load is caused inside parts, make working state exasperate. (2) decelerate orgnaization 1.

Positive drive of positive drive device is a kind of mechanical drive with very wide application, there is positive drive almost in the gearing of all sorts of machine tools. The end that uses positive drive device in system of feed of servo of numerical control machine tool has two. The servo electric machinery of the torsion that is will high rotate speed (if the pace enters electric machinery, dc and communication servo electric machinery to wait) the execution that outputs a change to be big torsion of low rotate speed input; Another it is to make the moment of inertia of ball guide screw and workbench has lesser proportion in systematic technical secondary school. In addition, still can assure the athletic precision of a requirement to open loop system. Accuse a machine tool to machine the influence of precision to reduce logarithm of tine side clearance as far as possible, often take step on the structure, with reduce or removing gear error of deputy light locomotive trip. If use double a law of gear fault tine, use prejudicial set adjust gear to deputy center is apart from or use axial spacer setting method to eliminate gear backlash. With use synchronous tooth form to take photograph comparing, gear decelerate device is used in catenary of drive of feed of numerical control machine tool, produce low frequency vibration more easily, because middling of this decelerate orgnaization configures damper,will improve dynamic performance. 2.

Synchronous tooth form takes synchronous tooth form to take drive is a kind of new-style belt transmission. As ordinal as the teeth of a cogwheel of belt annulus clench the teeth delivers the tooth form that he uses tooth form to take motion and motivation, hold the advantage that takes positive drive and transmission, catenary drive concurrently consequently, and without relatively slip, average transmission is more accurate, transmission precision is tall, and the strength that tooth form brings tall, ply small, weight light, reason is usable at high speed drive. Tooth form is taken need not special Zhang Jin, reason action is mixed in the axis the load on bearing is small, transmission efficiency is tall also, show wide on numerical control machine tool already application. The main parameter that synchronous tooth form takes and norms are as follows: 1) pitch pitch P is photograph adjacent two tine are apart from in section on-line. The length when working as a result of puissant layer is changeless, the section line that so the central line of puissant layer is taken for tooth form by the regulation (neutral line) , regard tooth form as the nominal length of the belt with the circumference L of section line. 2) modulus modulus definition is M=p/ π , make tooth form takes dimension calculative a main basis. 3) the other parameter that other parameter tooth form takes and dimension and involute rack are basic and identical. Tooth form takes dentiform computation formula and involute rack to differ, because the section line of tooth form belt is on puissant layer, and be absent tooth depth is mid. The tagging that tooth form takes the method is: Tine of * of modulus * width is counted, namely M*b*z. (3) nut of ball guide screw deputy to improve the sensitivity of feed system, fixed position precision is mixed prevent crawl, the attrition that must reduce system of feed of numerical control machine tool reduces the difference of coefficient of static, kinetic friction. Accordingly, form not quite long sharp movement orgnaization guide screw of commonly used ball deputy. Deputy transmission efficiency is as high as ball guide screw 85%-98% , it is common and slip guide screw deputy 2-4 times. Deputy angle of friction is less than ball guide screw 1 ° , because this is not locked up oneself. If deputy drive of ball guide screw rises,fall motion (be like main shaft box or lifting platform litre fall) , must have unit of apply the brake. The coefficient of static, kinetic friction of ball guide screw does not have what difference almost actually. It can eliminate backlash and bring to bear on preload, conduce to raise fixed position precision and stiffness. Ball guide screw is made by special workshop. CNC Milling