半閉環(huán)數(shù)控車床總體設(shè)計【含3張CAD圖紙】
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英文原文
CNC machine tools
While?the?specific?intention?and?application?for?CNC?machines?vary?from?one?machine?type? to?another,?all?forms?of?CNC?have?common?benefits.?Here?are?but?a?few?of?the?more?important? benefits?offered?by?CNC?equipment.
The?first?benefit?offered?by?all?forms?of?CNC?machine?tools?is?improved?automation. The operator?intervention?related?to?producing?work?pieces?can?be?reduced?or?eliminated.?Many?CNC?machines?can?run?unattended?during?their?entire?machining?cycle,?freeing?the?operator?to?do?other tasks.?This?gives?the?CNC?user?several?side?benefits?including?reduced?operator?fatigue,?fewer? mistakes?caused?by?human?error,?and?consistent?and?predictable?machining?time?for?each? workpiece.?Since?the?machine?will?be?running?under?program?control,?the?skill?level?required?of? the?CNC?operator?(related?to?basic?machining?practice)?is?also?reduced?as?compared?to?a?machinist?producing?workpieces?with?conventional?machine?tools.?
The?second?major?benefit?of?CNC?technology?is?consistent?and?accurate?workpieces.?Today's?CNC?machines?boast?almost?unbelievable?accuracy?and?repeatability?specifications.?This?means? that?once?a?program?is?verified,?two,?ten,?or?one?thousand?identical?workpieces?can?be?easily? produced?with?precision?and?consistency.
A?third?benefit?offered?by?most?forms?of?CNC?machine?tools?is?flexibility.?Since?these? machines?are?run?from?programs,?running?a?different?workpiece?is?almost?as?easy?as?loading?a? different?program.?Once?a?program?has?been?verified?and?executed?for?one?production?run,?it?can? be?easily?recalled?the?next?time?the?workpiece?is?to?be?run.?This?leads?to?yet?another?benefit,?fast? change?over.?Since?these?machines?are?very?easy?to?set?up?and?run,?and?since?programs?can?be? easily?loaded,?they?allow?very?short?setup?time.?This?is?imperative?with?today's?just-in-time?(JIT)? product requirements.?
Motion?control?-?the?heart?of?CNC?
The?most?basic?function?of?any?CNC?machine?is?automatic,?precise,?and?consistent?motion? control.?Rather?than?applying?completely?mechanical?devices?to?cause?motion?as?is?required?on? most?conventional?machine?tools,?CNC?machines?allow?motion?control?in?a?revolutionary?manner2.?All?forms?of?CNC?equipment?have?two?or?more?directions?of?motion,?called?axes.?These?axes? can?be?precisely?and?automatically?positioned?along?their?lengths?of?travel.?The?two?most?common?axis?types?are?linear?(driven?along?a?straight?path)?and?rotary?(driven?along?a?circular?path).?
?Instead?of?causing?motion?by?turning?cranks?and?handwheels?as?is?required?on?conventional?machine?tools,?CNC?machines?allow?motions?to?be?commanded?through?programmed?commands.?Generally?speaking,?the?motion?type?(rapid,?linear,?and?circular),?the?axes?to?move,?the?amount?of?motion?and?the?motion?rate?(feedrate)?are?programmable?with?almost?all?CNC?machine?tools.?
A?CNC?command?executed?within?the?control?tells?the?drive?motor?to?rotate?a?precise?number?of?times.?The?rotation?of?the?drive?motor?in?turn?rotates?the?ball?screw.?And?the?ball?screw?drives? the?linear?axis?(slide).?A?feedback?device?(linear?scale)?on?the?slide?allows?the?control?to?confirm? that?the?commanded?number?of?rotations?has?taken?place3.
Though?a?rather?crude?analogy,?the?same?basic?linear?motion?can?be?found?on?a?common?table?vise.?As?you?rotate?the?vise?crank,?you?rotate?a?lead?screw?that,?in?turn,?drives?the?movable?jaw?on?the?vise.?By?comparison,?a?linear?axis?on?a?CNC?machine?tool?is?extremely?precise.?The?number?of?revolutions?of?the?axis?drive?motor?precisely?controls?the?amount?of?linear?motion?along?the?axis.?
How?axis?motion?is?commanded?-?understanding?coordinate?systems?.
It?would?be?infeasible?for?the?CNC?user?to?cause?axis?motion?by?trying?to?tell?each?axis?drive?motor?how?many?times?to?rotate?in?order?to?command?a?given?linear?motion?amount4.?(This?would?be?like?having?to?figure?out?how?many?turns?of?the?handle?on?a?table?vise?will?cause?the?movable?
jaw?to?move?exactly?one?inch!)?Instead,?all?CNC?controls?allow?axis?motion?to?be?commanded?in?a?much?simpler?and?more?logical?way?by?utilizing?some?form?of?coordinate?system.?The?two?most? popular?coordinate?systems?used?with?CNC?machines?are?the?rectangular?coordinate?system?and? the?polar?coordinate?system.?By?far,?the?more?popular?of?these?two?is?the?rectangular?coordinate? system. The?program?zero?point?establishes?the?point?of?reference?for?motion?commands?in?a?CNC? program.?This?allows?the?programmer?to?specify?movements?from?a?common?location.If?program?
zero?is?chosen?wisely,?usually?coordinates?needed?for?the?program?can?be?taken?directly?from?the?
print.?
With?this?technique,?if?the?programmer?wishes?the?tool?to?be?sent?to?a?position?one?inch?to?the?right?of?the?program?zero?point,?X1.0?is?commanded.?If?the?programmer?wishes?the?tool?to?move?to?a?position?one?inch?above?the?program?zero?point,?Y1.0?is?commanded.?The?control?will? automatically?determine?how?many?times?to?rotate?each?axis?drive?motor?and?ball?screw?to?make?
the?axis?reach?the?commanded?destination?point?.?This?lets?the?programmer?command?axis?motion?
in?a?very?logical?manner.All?discussions?to?this?point?assume?that?the?absolute?mode?of?
programming?is?used.?The?most?common?CNC?word?used?to?designate?the?absolute?mode?is?G90.?
In?the?absolute?mode,?the?end?points?for?all?motions?will?be?specified?from?the?program?zero?point.?For?beginners,?this?is?usually?the?best?and?easiest?method?of?specifying?end?points?for?motion?
commands.?However,?there?is?another?way?of?specifying?end?points?for?axis?motion.
In?the?incremental?mode?(commonly?specified?by?G91),?end?points?for?motions?are?specified?
from?the?tool's?current?position,?not?from?program?zero.?With?this?method?of?commanding?motion,?the?programmer?must?always?be?asking?"How?far?should?I?move?the?tool?"?While?there?are?times?
when?the?incremental?mode?can?be?very?helpful,?generally?speaking,?this?is?the?more?cumbersome?and?difficult?method?of?specifying?motion?and?beginners?should?concentrate?on?using?the?absolute?mode.
Be?careful?when?making?motion?commands.?Beginners?have?the?tendency?to?think?incrementally.?If?working?in?the?absolute?mode?(as?beginners?should),?the?programmer?should?always?be?
asking?"To?what?position?should?the?tool?be?moved?"?This?position?is?relative?to?program?zero,?
NOT?from?the?tools?current?position.?
Aside?from?making?it?very?easy?to?determine?the?current?position?for?any?command,?another?
benefit?of?working?in?the?absolute?mode?has?to?do?with?mistakes?made?during?motion?commands.?
In?the?absolute?mode,?if?a?motion?mistake?is?made?in?one?command?of?the?program,?only?one?movement?will?be?incorrect.?On?the?other?hand,?if?a?mistake?is?made?during?incremental?movements,?all?motions?from?the?point?of?the?mistake?will?also?be?incorrect.
Assigning?program?zero?
Keep?in?mind?that?the?CNC?control?must?be?told?the?location?of?the?program?zero?point?by?
one?means?or?another.?How?this?is?done?varies?dramatically?from?one?CNC?machine?and?control?to?another8.?One?(older)?method?is?to?assign?program?zero?in?the?program.?With?this?method,?the?
programmer?tells?the?control?how?far?it?is?from?the?program?zero?point?to?the?starting?position?of?
the?machine.?This?is?commonly?done?with?a?G92?(or?G50)?command?at?least?at?the?beginning?of?
the?program?and?possibly?at?the?beginning?of?each?tool.?
Another,?newer?and?better?way?to?assign?program?zero?is?through?some?form?of?offset.?Refer?
to?fig.4.?Commonly?machining?center?control?manufacturers?call?offsets?used?to?assign?program?
zero?fixture?offsets.?Turning?center?manufacturers?commonly?call?offsets?used?to?assign?program?
zero?for?each?tool?geometry?offsets.
A?flexible?manufacturing?cell?(FMC)?can?be?considered?as?a?flexible?manufacturing?
subsystem.?The?following?differences?exist?between?the?FMC?and?the?FMS:
1. ?An?FMC?is?not?under?the?direct?control?of?the?central?computer.?Instead,?instructions?from?
the?central?computer?are?passed?to?the?cell?controller.?
2. ?The?cell?is?limited?in?the?number?of?part?families?it?can?manufacture.?
The?following?elements?are?normally?found?in?an?FMC:???Cell?controller?
??Programmable?logic?controller?(PLC)???More?than?one?machine?tool?
??A?materials?handling?device?(robot?or?pallet)?
The?FMC?executes?fixed?machining?operations?with?parts?flowing?sequentially?between?
operations.??
High?speed?machining
The?term?High?Speed?Machining?(HSM)?commonly?refers?to?end?milling?at?high?rotational?
speeds?and?high?surface?feeds.?For?instance,?the?routing?of?pockets?in?aluminum?airframe?sections?with?a?very?high?material?removal?rate1.?Over?the?past?60?years,?HSM?has?been?applied?to?a?wide?
range?of?metallic?and?non-metallic?workpiece?materials,?including?the?production?of?components?
with?specific?surface?topography?requirements?and?machining?of?materials?with?hardness?of?50?
HRC?and?above.?With?most?steel?components?hardened?to?approximately?32-42?HRC,?machining?
options?currently?include:?Rough?machining?and?semi-finishing?of?the?material?in?its?soft?(annealed)?condition?heat?treatment?to?achieve?the?final?required?hardness?=?63?HRC?machining?of?electrodes?and?Electrical?Discharge?Machining?(EDM)?of?specific?parts?of?dies?and?moulds?(specifically?
small?radii?and?deep?cavities?with?limited?accessibility?for?metal?cutting?tools)?finishing?and?
super-finishing?of?cylindrical/flat/cavity?surfaces?with?appropriate?cemented?carbide,?cermet,?solid?carbide,?mixed?ceramic?or?polycrystalline?cubic?boron?nitride?(PCBN)?
For?many?components,?the?production?process?involves?a?combination?of?these?options?and?in?the?case?of?dies?and?moulds?it?also?includes?time?consuming?hand?finishing.?Consequently,?
production?costs?can?be?high?and?lead?times?excessive.?
It?is?typical?in?the?die?and?mould?industry?to?produce?one?or?just?a?few?tools?of?the?same?
design.?The?process?involves?constant?changes?to?the?design,?and?because?of?these?changes?there?is?also?a?corresponding?need?for?measuring?and?reverse?engineering?.
The?main?criteria?is?the?quality?level?of?the?die?or?mould?regarding?dimensional,?geometric?
and?surface?accuracy.?If?the?quality?level?after?machining?is?poor?and?if?it?cannot?meet?the?
requirements,?there?will?be?a?varying?need?of?manual?finishing?work.?This?work?produces?
satisfactory?surface?accuracy,?but?it?always?has?a?negative?impact?on?the?dimensional?and?
geometric?accuracy.
One?of?the?main?aims?for?the?die?and?mould?industry?has?been,?and?still?is,?to?reduce?or?
eliminate?the?need?for?manual?polishing?and?thus?improve?the?quality?and?shorten?the?production?
costs?and?lead?times.
Main?economical?and?technical?factors?for?the?development?of?HSM?Survival?
The?ever?increasing?competition?in?the?marketplace?is?continually?setting?new?standards.?The?demands?on?time?and?cost?efficiency?is?getting?higher?and?higher.?This?has?forced?the?development?of?new?processes?and?production?techniques?to?take?place.?HSM provides?hope?and?solutions...?
Materials?
The?development?of?new,?more?difficult?to?machine?materials?has?underlined?the?necessity?to?find?new?machining?solutions.?The?aerospace?industry?has?its?heat?resistant?and?stainless?steel?
alloys.?The?automotive?industry?has?different?bimetal?compositions,?Compact?Graphite?Iron?and?an?ever?increasing?volume?of?aluminum3.?The?die?and?mould?industry?mainly?has?to?face?the?
problem?of?machining?high?hardened?tool?steels,?from?roughing?to?finishing.
Quality?
The?demand?for?higher?component?or?product?quality?is?the?result?of?ever?increasing?
competition.?HSM,?if?applied?correctly,?offers?a?number?of?solutions?in?this?area.?Substitution?of?
manual?finishing?is?one?example,?which?is?especially?important?on?dies?and?moulds?or?components?with?a?complex?3D?geometry.
Processes?
The?demands?on?shorter?throughput?times?via?fewer?setups?and?simplified?flows?(logistics)?
can?in?most?cases,?be?solved?by?HSM.?A?typical?target?within?the?die?and?mould?industry?is?to?
completely?machine?fully?hardened?small?sized?tools?in?one?setup.?Costly?and?time?consuming?
EDM?processes?can?also?be?reduced?or?eliminated?with?HSM.
Design?&?development?
One?of?the?main?tools?in?today's?competition?is?to?sell?products?on?the?value?of?novelty.?The?
average?product?life?cycle?on?cars?today?is?4?years,?computers?and?accessories?1.5?years,?hand?
phones?3?months...?One?of?the?prerequisites?of?this?development?of?fast?design?changes?and?rapid?
product?development?time?is?the?HSM?technique.
Complex?products?
There?is?an?increase?of?multi-functional?surfaces?on?components,?such?as?new?design?of?
turbine?blades?giving?new?and?optimized?functions?and?features.?Earlier?designs?allowed?polishing?by?hand?or?with?robots?(manipulators).?Turbine?blades?with?new,?more?sophisticated?designs?have?
to?be?finished?via?machining?and?preferably?by?HSM?.?There?are?also?more?and?more?examples?of?
thin?walled?workpieces?that?have?to?be?machined?(medical?equipment,?electronics,?products?for?
defence,?computer?parts)?
Production?equipment?
The?strong?development?of?cutting?materials,?holding?tools,?machine?tools,?control sand?especially?CAD/CAM?features?and?equipment,?has?opened?possibilities?that?must?be?met?with?new?production?methods?and?techniques5.?
Definition?of?HSM?
Salomon's?theory,?"Machining?with?high?cutting?speeds..."?on?which,?in?1931,?took?out?a?
German?patent,?assumes?that?"at?a?certain?cutting?speed?(5-10?times?higher?than?in?conventional?
machining),?the?chip?removal?temperature?at?the?cutting?edge?will?start?to?decrease..."?
Given?the?conclusion:"?...?seems?to?give?a?chance?to?improve?productivity?in?machining?with?
conventional?tools?at?high?cutting?speeds..."?
Modern?research,?unfortunately,?has?not?been?able?to?verify?this?theory?totally.?There?is?a?
relative?decrease?of?the?temperature?at?the?cutting?edge?that?starts?at?certain?cutting?speeds?for?
different?materials.?
The?decrease?is?small?for?steel?and?cast?iron.?But?larger?for?aluminum?and?other?non-ferrous?metals.?The?definition?of?HSM?must?be?based?on?other?factors.?
Given?today's?technology,?"high?speed"?is?generally?accepted?to?mean?surface?speeds?between?1?and?10?kilometers?per?minute?or?roughly?3?300?to?33?000?feet?per?minute.?Speeds?above?
10?km/min?are?in?the?ultra-high?speed?category,?and?are?largely?the?realm?of?experimental?metal?
cutting.?Obviously,?the?spindle?rotations?required?to?achieve?these?surface?cutting?speeds?are?
directly?related?to?the?diameter?of?the?tools?being?used.?One?trend?which?is?very?evident?today?is?
the?use?of?very?large?cutter?diameters?for?these?applications?-?and?this?has?important?implications?
for?tool?design.?
There?are?many?opinions,?many?myths?and?many?different?ways?to?define?HSM.?Maintenance?and?troubleshooting?
Maintenance?for?a?horizontal?MC?
The?following?is?a?list?of?required?regular?maintenance?for?a?Horizontal?Machining?Center?as?shown?in?fig.5.?Listed?are?the?frequency?of?service,?capacities,?and?type?of?fluids?required.?These?
required?specifications?must?be?followed?in?order?to?keep?your?machine?in?good?working?order?and?protect?your?warranty.?
Daily?
Top?off?coolant?level?every?eight?hour?shift?(especially?during?heavy?TSC?usage).?Check?way?lube?lubrication?tank?level.?Clean?chips?from?way?covers?and?bottom?pan.?Clean?chips?from?tool?
changer.?
Wipe?spindle?taper?with?a?clean?cloth?rag?and?apply?light?oil.?Weekly?
??Check?for?proper?operation?of?auto?drain?on?filter?regulator.??
On?machines?with?the?TSC?option,?clean?the?chip?basket?on?the?coolant?tank.?Remove?the?
tank?cover?and?remove?any?sediment?inside?the?tank.?Be?careful?to?disconnect?the?coolant?pump?
from?the?controller?and?POWER?OFF?the?control?before?working?on?the?coolant?tank?.?Do?this?
monthly?for?machines?without?the?TSC?option.?
Check?air?gauge/regulator?for?85?psi.?
For?machines?with?the?TSC?option,?place?a?dab?of?grease?on?the?V-flange?of?tools.?Do?this?
monthly?for?machines?without?the?TSC?option.?
Clean?exterior?surfaces?with?mild?cleaner.?DO?NOT?use?solvents.?
Check?the?hydraulic?counterbalance?pressure?according?to?the?machine's?specifications.?
Place?a?dab?of?grease?on?the?outside?edge?of?the?fingers?of?the?tool?changer?and?run?through?
all?tools".?
Monthly?
Check?oil?level?in?gearbox.?Add?oil?until?oil?begins?dripping?from?over?flow?tube?at?bottom?of?sump?tank.?
Clean?pads?on?bottom?of?pallets.
Clean?the?locating?pads?on?the?A-axis?and?the?load?station.?This?requires?removing?the?pallet.?
??Inspect?way?covers?for?proper?operation?and?lubricate?with?light?oil,?if?necessary.?Six?
months?
Replace?coolant?and?thoroughly?clean?the?coolant?tank.?Check?all?hoses?and?lubrication?lines?
for?cracking.?Annually?
??Replace?the?gearbox?oil.?Drain?the?oil?from?the?gearbox,?and?slowly?refill?it?with?2?quarts?of?Mobil?DTE?25?oil.?
??Check?oil?filter?and?clean?out?residue?at?bottom?for?the?lubrication?chart.?Replace?air?filter?
on?control?box?every?2?years.?
Mineral?cutting?oils?will?damage?rubber?based?components?throughout?the?machine.?Troubleshooting?
This?section?is?intended?for?use?in?determining?the?solution?to?a?known?problem.?Solutions?
given?are?intended?to?give?the?individual?servicing?the?CNC?a?pattern?to?follow?in,?first,?
determining?the?problem's?source?and,?second,?solving?the?problem.?
Use?common?sense?
Many?problems?are?easily?overcome?by?correctly?evaluating?the?situation.?All?machine?
operations?are?composed?of?a?program,?tools,?and?tooling.?You?must?look?at?all?three?before?
blaming?one?as?the?fault?area.?If?a?bored?hole?is?chattering?because?of?an?overextended?boring?bar,?don't?expect?the?machine?to?correct?the?fault.?
Don't?suspect?machine?accuracy?if?the?vise?bends?the?part.?Don't?claim?hole?mis-positioning?if?you?don't?first?center-drill?the?hole.?
Find?the?problem?first?
Many?mechanics?tear?into?things?before?they?understand?the?problem,?hoping?that?it?will?
appear?as?they?go.?We?know?this?from?the?fact?that?more?than?half?of?all?warranty?returned?parts?are?in?good?working?order.?If?the?spindle?doesn't?turn,?remember?that?the?spindle?is?connected?to?the?
gear?box,?which?is?connected?to?the?spindle?motor,?which?is?driven?by?the?spindle?drive,?which?is?
connected?to?the?I/O?BOARD,?which?is?driven?by?the?MOCON,?which?is?driven?by?the?processor.?The?moral?here?is?don't?replace?the?spindle?drive?if?the?belt?is?broken.?Find?the?problem?first;?don't?
just?replace?the?easiest?part?to?get?to.?
Don?tinker?with?the?machine?
There?are?hundreds?of?parameters,?wires,?switches,?etc.,?that?you?can?change?in?this?machine.?Don't?start?randomly?changing?parts?and?parameters.?Remember,?there?is?a?good?chance?that?if?you?change?something,?you?will?incorrectly?install?it?or?break?something?else?in?the?process6.?Consider?for?a?moment?changing?the?processor's?board.?First,?you?have?to?download?all?parameters,?remove?a?dozen?connectors,?replace?the?board,?reconnect?and?reload,?and?if?you?make?one?mistake?or?bend?one?tiny?pin?it?WON'T?WORK.?You?always?need?to?consider?the?risk?of?accidentally?damaging?the?machine?anytime?you?work?on?it.?It?is?cheap?insurance?to?double-check?a?suspect?part?before?
physically?changing?it.?The?less?work?you?do?on?the?machine?the?better.
中文譯文
數(shù)控機(jī)床
雖然各種數(shù)控機(jī)床的功能和應(yīng)用各不相同,但它們有著共同的優(yōu)點。這里是數(shù)控設(shè)備提供的比較重要的幾個優(yōu)點。?
各種數(shù)控機(jī)床的第一個優(yōu)點是自動化程度提高了。零件制造過程中的人為干預(yù)減少或者免除了。整個加工循環(huán)中,很多數(shù)控機(jī)床處于無人照看狀態(tài),這使操作員被解放出來,可以干別的工作。數(shù)控機(jī)床用戶得到的幾個額外好處是:數(shù)控機(jī)床減小了操作員的疲勞程度,減少了人為誤差,工件加工時間一致而且可預(yù)測。由于機(jī)床在程序的控制下運行,與操作普通機(jī)床的機(jī)械師要求的技能水平相比,對數(shù)控操作員的技能水平要求(與基本加工實踐相關(guān))也降低了。?
數(shù)控技術(shù)的第二個優(yōu)點是工件的一致性好,加工精度高?,F(xiàn)在的數(shù)控機(jī)床宣稱的精度以及重復(fù)定位精度幾乎令人難以置信。這意味著,一旦程序被驗證是正確的,可以很容易地加工出2個、10個或1000個相同的零件,而且它們的精度高,一致性好。大多數(shù)數(shù)控機(jī)床的第三個優(yōu)點是柔性強(qiáng)。由于這些機(jī)床在程序的控制下工作,加工不同的工件易如在數(shù)控系統(tǒng)中裝載一個不同的程序而己。一旦程序驗證正確,并且運行一次,下次加工工件的時候,可以很方便地重新調(diào)用程序。這又帶來另一個好處—可以快速切換不同工件的加工。由于這些機(jī)床很容易調(diào)整并運行,也由于很容易裝載加工程序,因此機(jī)床的調(diào)試時間很短。這是當(dāng)今準(zhǔn)時生產(chǎn)制造模式所要求的。?
任何數(shù)控機(jī)床最基本的功能是具有自動、精確、一致的運動控制。大多數(shù)普通機(jī)床完全運用機(jī)械裝置實現(xiàn)其所需的運動,而數(shù)控機(jī)床是以一種全新的方式控制機(jī)床的運動。各種數(shù)控設(shè)備有兩個或多個
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