Challenge limit

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  • source:GAENOR CNC Machining
Why the thing develops change inside range of a limit, once exceed this one limit, will produce qualitative leap. Put the small issue that is in so, can become extremely serious big question. When use machining center undertakes metallic cutting, main shaft rotate speed is such to machining the influence of the process. Inside the certain limits of rotate speed of low main shaft or commonly used rotate speed, the treatment process effect that has to its is not big. There is the rule that at present cutting theory announced to be in between cutting speed and treatment process producing change, for example, can cause cutting temperature to lift, spare parts dimension changes a little etc. But, treatment falls in the higher main shaft rotate speed that exceeds some limiting value, of main shaft temperature elevatory, increase and increase the vibration that cause lopsidedly of centrifugal force to happen etc, raise what affected a spare parts to machine precision severely. The some limiting value here is machine tool main shaft commonly top rotate speed 20, 000 Rpm, be located in Yilinuosi Mal Sudhakar of assistant manager of company of Mikron of city Lincoln city says. Exceed this limiting value, main shaft cannot safe production, put the small issue that is in so, can become extremely serious big question. In process of high speed treatment, use measuring instrument of one laser cutting tool to measure volume of cutting tool displacement, undertake to cutting tool compensation is adjusted next. Mikron company is for the mould production offers main shaft one top rotate speed exceeds 20, the manufacturer of high speed machining center of 000 Rpm. The machining center that they produce holds stock highest turn up 40, 000rpm or 60, the main shaft of 000 Rpm. In the article, this company director Mr Sudhakar introduced them to the user is how to be in the design of the machine tool, advanced measurement technology and sensor technology apply at the control system of the machine tool, measuring instrument of use laser cutting tool, use new development to give system of intelligent vulcanize countervail (ITC) control a system with advanced technology (APS) , processing exceeds 20 fortunately, below the rotate speed of highest main shaft of 000 Rpm, occurrence centrifugal force increases, main shaft temperature is elevatory, a few serious effects such as the vibration that causes with lopsided addition machine the solution of the technical difficult problem of the process. Leaving mental efforts to increase centrifugal force is the necessary product that rotate speed of tall main shaft processes. Main shaft rotate speed is higher, of generation from runner shaft coming back outward drawing rotates the force of the spare parts (centrifugal force) bigger. It is especially in finish machining, centrifugal power is very great to influence of main shaft bearing. So, when high speed machining center is designed, main shaft the design is become all by can bear of radial and axial force afferent stop push ball bearing to prop up. But in main shaft rotate speed very tall, below the effect of very great centrifugal power of generation, what meeting general props up main shaft is afferent stop push the ball inside ball bearing to be pulled, make bearing happen be out of shape displacement, main shaft also produced displacement to wait. The displacement of main shaft meant installation to produce displacement in the space in the position of point of a knife of the cutting tool inside main shaft aperture, this will cause the dimension out of tolerance that machines a spare parts to discard as useless even. Of course, this is not the problem of itself of main shaft bearing, the square that is speed of corner of size and main shaft coming back becomes the centrifugal force of direct ratio to cause. According to experience formula computation makes clear as a result, main shaft rotate speed by 10, 000rpm turns into 20, when 000rpm, speed is 2 times original, the centrifugal master piece that has 4 times is used on bearing. And main shaft speed from 10, 000 litres arrive 40, when 000rpm, centrifugal force will add 16 times. Action is opposite in the very great centrifugal power on main shaft the machine tool of tall tigidity, 20, the rough machining under 000 Rpm rotate speed still is affected not quite, but to main shaft rotate speed from 0 to be as high as 40, the finish machining of 000 Rpm, the craft test that makes by Mikron company place makes clear, can make point of a knife arises 0.

The displacement of 05mm. This one phenomenon caused the height of technical personnel to take seriously. Graph 1.

Main shaft is highest rotate speed from 0 to 42, 000rpm, centrifugal force increases the metabolic condition that causes displacement of point of a knife subsequently. Mr Sudhakar introduces to people, mikron company is the machining error that the displacement of space of point of a knife that eliminates cutting tool causes, excogitated have compensatory solution. The measuring instrument of laser cutting tool that they used blame contact to measure in treatment (produce by company of Blum Laser Measuring Technology) . General by Mikron company, the standard accessory that executes high speed cutting as the machine tool provides an user. Measure a tool to differ with contact. Use blame contact measures measuring instrument of laser cutting tool, in the cutting that can rotate in main shaft high speed, the size variation of the point of a knife that causes to be being used in very big centrifugal master piece undertakes metrical. This is meant in every time when cutting speed is changed, should undertake be metricaled again to cutting tool? Laser is measured need to cost 30 seconds, so is very frequent measurement had below a few circumstances necessary? Mr Sudhakar answer is not. The metabolic characteristic of the dimension of point of a knife that because leave mental efforts,causes is to press linear relation to change into scale. Also can use a kind of when develop by manufacturer new algorithm ordinarily, make CNC system can the budget gives the displacement of point of a knife that all sorts of cutting rate fall other to measure. But the quantity of displacement of point of a knife that regretful is classics dope and real value differ too big (if pursue,1 is shown) . The best measure that adopts so is measuring instrument of use laser cutting tool, measure the volume of displacement of point of a knife after going out to alternate every time well and truly quickly, next root Ju measures real measure value, the machine program with modification good collection, undertake self-correcting to cutting tool position, undertake in order to be opposite compensating by the machining error that causes from mental efforts. Main shaft temperature lifts a factor that has not said also is changing the displacement of point of a knife, this is main shaft temperature lifts (or weigh heat to expand) . After main shaft is started, or rate rises very quickly, at this moment the temperature on main shaft will begin to lift by new Rpm worth immediately, undertake stable state of quantity of heat allocates afresh, arrive at quantity of heat all the time till the balance, this new quantity of heat is balanced, need cycle of a time. At the same time main shaft dimension also is in along with temperature change constant change. This means process of a treatment, if mill of essence of life is machined, before cutting tool undertakes adjustment, need has time of a warm-up. According to studying a proof, in mill of essence of life, from main shaft rotate speed lift suddenly, achieve balance of caloric stable state to the machine tool, need to pass about 15 - 25 minutes. But, the system of intelligent vulcanize countervail that uses newest development (ITC) , can decrease to cancel this one latency time even. ITC is actual it is new measurement the result that the new numeration in technology and CNC system combines. When heat expands, computer CNC system can collect concerned data from inside loading the temperature sensor inside machine tool main shaft, the quick consideration that passes new numeration next gives heat to expand with the metabolic rule between main shaft dimension. Like heat expands and leaving mental efforts, it is to be in produce change according to definite pattern, what what differ is it either become scale ground to change by linear relation. The heat of the structure of machine tool main shaft that designing technically to expands the discovery in the imitating test that the process has, its expand the rule is shown 2 times like the graph. Newest development is, we need not be used await main shaft to achieve stable state of quantity of heat to balance again, mr Sudhakar says, use ITC, can be in during warming up, the deflection that adjusting cutting tool ceaselessly with respect to the metabolic rule of the curve in beginning to press a plan is measured, expand to heat the amount of change of main shaft deflection that cause undertakes compensating. Via cutting the experiment proves, use ITC can make precision of spare parts treatment controlled in in 20 micron less than. Graph 2.

Main shaft is highest rotate speed lifts the rule that causes change of dimension of point of a knife pursues. Through main shaft medium temperature sensor and CNC system can make up for this one change, purify before the latency time of warm-up. If can choose the processing plan that awaits 3 minutes, criterion ITC can make machine a spare parts to achieve 10 micron more high accuracy. Why can so short latency time have so good effect? Because be in treatment process, the case is more complex, a few processes cannot be mirrorred correctly by temperature sensor. Below the condition that changing a knife for example, in a process that change a knife, in inserting Leng Daobing very hot main shaft, because it and main shaft photograph are compared, dimension differs bigger, so temperature can rise very quickly. If arrange short time of purpose await, can let knife handle and main shaft achieve hot balance very quickly. Can obtain taller treatment precision consequently. A the biggest to machining quality to affect nothing is more... than in producing vibration to be machined in high speed is oscillatory. It is the result in the interaction between workpiece and cutting tool, or cause below the centrifugal force effect of the lopsided generation that is the quality of a certain spare parts in cutting tool and knife handle component. When cutting rate increases, the interaction between workpiece and cutting tool becomes more apparent. Basis (horn) speed and the concern that show exponential growth from mental efforts, will local quality is lopsided expand, the centrifugal force of generation increases. The vibration of the generation in controlling treatment strictly so also is all in all, just do not improve treatment precision and raise manufacturing efficiency place must, and also be the life place need that rise and lengthens main shaft and cutting tool. What in be being machined to control high speed effectively, arise is oscillatory, mikron company development goes those who be used at HVC report main shaft " advanced technology controls a system (APS) . " it is to pass in main shaft before bearing place installs one acceleration to express (see a picture 3) , provide the concerned information such as vibration for APS. APS is considered as handlers " auditive " , but in be as high as 40, in 000rpm treatment " the ear of handlers " the best means that is control and administrative vibration no longer. Need only now APS and CNC monitor connection, the color of green Huang Hegong that handlers can show according to chromatic monitor judges oscillatory condition (vibration is below in 3G " green " , be below in 6G is " yellow " and exceed 6G to be gules affection alarm) . Machine a process through interpose next, optimize treatment craft, be reduced effectively and eliminate vibration, improve service life of cutting tool machine tool. To remove trouble well and truly, generating breakdown source through diagnosing rapid fish also is a very important segment. Rely on what the acknowledge to vibration mixes above to measure or have limitation very much only. Because of amplitude very tall vibration affects cutting deepness severely, the vibration with very tall frequency will continue to enlarge former some lopsided, so must can diagnose quickly adopt an emergency measures, just be the basic measure that solves a problem. Graph 3.

In main shaft before bearing is in of main shaft before bearing place installs one acceleration watch, provide the concerned information such as vibration for APS. Mr Sudhakar says, advanced technology controls a system to change the effect with also rising very main in the operation in nobody. For example, when it can exceed some limiting value with amplitude in oscillatory frequency, by make up good programme controll to stop machine. Also can dogging with acceleration watch in vibration, undertake in time adjustment to the program with good collection. Still but online collect and put lay aside to concern information data, with these the data can separate the origin position of separate out vibration, eliminate vibration according to them thereby, produce the effect of cutting of machine tool high speed adequately. Mikron Is One Example Of A Company Offering Machining Centers For Die/mold And Production Milling Work That Go Much Faster Than This Threshold Speed.

The Company Has Standard Spindles With Top Speeds Around 40, 000 And 60, 000 Rpm.

Mr.

Sudhakar, vice Resident Of Mikron, describes How The Design Of These Highspeed Machines, as Well As Process For Using Them, relies On Easurement And Ensor Technology To Take Control Of The Effects That Come Into Play At The Highest Values Of Rpm.

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