模具型腔数控加工计算机辅助刀具选择和研究.docx

MouldtypeofnumericalcontrolprocesscomputerassistthecutterchooseandstudyForewordNumericalcontrolincludecutterproductionandcutteroforbitchoosetwokeyproblemsprocess,.Thefirstproblemhasbeengotandstudiedextensivlyanddeeplyoverthepast20years,alotofalgorithmsdevelopedhavealreadygotapplicationincommercialCAD/CAMsystem.MostCAMsystemscanproducethecutterorbitautomaticallyafterusersinputrelevantparametersatpresent.Comparativelyspeaking,itisstillnotripetoregardquality,efficiencyastheresearchofchoosingtheproblemofcutterofoptimizingthegoalcorrectly,donothavecommercialCAMsystemthatcanofferthepreferreddecisionsupporttoolofcutteratpresent,thereforeitisdifficulttorealizetheintegratingautomaticallyandorganicallyofCAD/CAM.Thecutterischosentousuallyincludecuttertypeandcuttersize.Generallyspeaking,suitableforoneprocessingcutteroftargetformuchkind,onecuttercanfinishdifferentprocessingtasks,soitiseasiertoonlyconsidermeetingthecutterthatbasicallyprocessestherequirementandchoose,especiallytogeometirccharacteristicsofmodelsuchasthehole,trough,etc.Butinfact,itiscommonforcuttertochooseandsureoptimizationgoalinterrelate,forinstancemostheavytocutefficiency,processtime,minimumprocesscost,longestservicelife,etc.atleast,sothecutterischosenitisacomplicatedoptimizationquestion.Suchasmouldtypeoneofparts,becausethegeometircformiscomplicated(usuallyincludecurvedsurfaceoffreedomandisland),influencegeometrythatcutterchooseitrestrainsfromtobecanexplicittosayamongCADmodel,needtodesignthecorrespondingalgorithmtodraw,thereforechoosethecutterspecificationsuitableandcutterassociation,itisnoteasythingsbyimprovingefficiencyandqualityprocessedinnumericalcontrol.Mouldtypegenerallywithpreparationmethodthatnumericalcontrolmill,usuallyincludingroughmachining,halffinishmachining,preciseprocessofprocessingetc.Theprincipleofroughmachiningistosparenoefforttoremovethesurplusmetalwithhighefficiency,thereforehopetochoosethelargercutter,butthecutterisoversized,maycausetheincreaseofthecrudevolume;Halffinishmachiningoftaskstoremoveroughmachiningleaveoverstepthatgetoffmainly;Finishmachiningmainlyguaranteessizeofthepartandsurfacequality.Consider,goon,selectexist,surebycomputerdifficultautomaticallytotallyuptillnow,thereforeassistthecuttertochooseinthecomputerthatwedeveloped(ComputerAidedToolSelection,CATS)amongthesystem,baseon,provideoneaiddecisiontoolforuser,roughmachining,halffinishmachining,precisetoprocessetc.,therealpolicy-makingpowerisstilllefttousers,inordertogivefullplaytotheadvantagesofcomputerandpeople.1 BasicstructureofthesystemCATSsystemisCADmodel,outputforcuttertype,cutterspecification,milldepthofsharpening,enterthegivingamount,rotationalspeedofmainshaft(cutthepace)andprocesssixparameterssuchastime(suchasFig.I),includingchoosingtheaiddecisiontoolincuttertype,roughmachiningcutterchooseaiddecisiontool,halffinishmachiningcutterchooseaiddecisiontoolandfinishmachiningcutterchooseaiddecisiontool,etc.GiventheroughmachininginXingqiangprocessingoftheimportantposition(usuallyrelytime5l0times),roughmachining,thesystemautomaticallyoptimizeportfoliowithcutleryfunctionstoenhanceoverallprocessingefficiency.Inadditiontothedecision-makingtools,thesystemalsohasadetailedlookcutlerynorms,basedonthetypeandsizecutleryrecommendedprocessingparametersandassessthefunctionofprocessingtime,thelastgenerationoftheoverallresultsofchoicecutlerystatements(figure2).Allthedataandknowledgesystemscutlerydonebythebackgrounddatabasesupport.2 Keytechnologiesandalgorithms2.1 CutlerytypechoiceAccordingtoAssistantXingqiangdigitalprocessingpractice,XingqiangXistategeneralprocessingcutleryintomillingcutter,millingcutterradiusmillingcutterandthefirstthreeballs.Dbasedcutlerydiameter,radiusradiusrwhenr=0formillingcutter,0<RCutlerycanbedividedintotheoverallstyleandembedfilmsceremony.Forinlayfilmstyle,thekeyistoselectthematerialsrazorblades,razorbladesmaterialschoicedependsonthreeelements:theprocessingofworkingmaterials,machinetoolsandcutleryjigstabilityofthestatestructures.Processingsystemwillbetranslatedintomaterialsteel,stainlesssteel,castiron,nonferrousmetals,materialsandhardtocutmaterialssixgroups.Machinetooljigstabilityintogood,betterandlessthanthreelevels.Cutleryinvestigationintotheshortandlongcantileverstructurestwo,thesystemautomaticallyreasoningonthebasisofthespecificcircumstancesofrazorbladesmaterials,decision-makingknowledgefromWaltercutlerymanualsystembytheusersfirstchoicecutlerytypeintheworld.Toembedfilmstylecutlery,arules-basedautomatedreasoningsuitablerazorbladesmaterials.Forexample,ifthefinalprocessingofmaterialsforthesteel",machinetooljigforgoodstability,cutlerycantileverstructuresforshort,razorbladesmaterialsforWAP25.RoughmachiningcutleryportfoliooptimizationXingqiangroughmachiningtheaimistomaximizetheremovalofexcessmetalnormallyusedmillingcutter,take-cuttingapproach.Thus,3DmouldXingqiangtheroughmachiningprocess,isactuallyaseriesof2.5DcomponentsXingqiangprocessing.Cutleryoptimizationistofindagroupofcutleryportfolio,allowingformaximumefficiencyremovalofmostmetals.Cutleryportfoliooptimizedbasicmethodsasfollows:A. TodosomelongstepintoknifeinthedirectionofagroupofverticalandhorizontalsearchXingqianganotherentitytoformasearchlayer.B. Deriveclosedtothecontours.C. CalculatedbetweenCentralandoutsidetheislandorislandsandthedistancebetweenthekeythataffectcutlerychoicegeometricconstraintsalgorithmflowAsshowninfigure3D. Accordingtotheprincipleofthemerger(adjacenttothecriticaldistancewillbesmallerthanthedifferencebetweenthethreshold)tosearchlayermerger,graphicprocessingandidentifyingviablecutlerysets,aprocessinglayer.E. Determinetheuseofeachprocessinglayercutlery,cutleryXingqiangprocessingportfolio.F. AccordingcutleryrecommendedprocessingParameterS(cuttingspeed,depthandintoXianxiaotospeed),thecalculationofmaterialremoval.G. Accordingtotheactualremovalofthevolumeprocessinglayer,theprocessingtimeforeachprocessinglayer.H. Xingqiangcalculatingthetotalprocessingtimeandresidualvolume.I. TheoverallportfoliooftheGroupcutleryprocessingefficiencyassessment.J.Repeataiuntilderiveoptimalmixofcutlery.Iftimeisthegoal,calledfortheentireprocessingtimetXingqiangshortestportfoliotooptimizecutlery.2.2 Semi-finishedcutlerychoiceThemainpurposeistoremovesemi-finishedroughmachiningresidualcontoursofthenewwarrants.Tocompletelyremoveheight,depthmustbegreaterthanXianxiaopartsofeachleveltothesurfacedistancex.Itsalgorithmstepsareasfollows:Step1:entitymodelsfrompartsoftwoadjacenttothecrosssectionofthesurfacecontoursandthecorrespondinglength;Step2:Theaveragelengthofcontours;Step3xalculateitswidth;Step4:calculatingheightfloortothesurfaceofpartstothelawdistancex;Step5:steps1repeatsteps4,eachlevelofdecisionXianxiaodepth;Step6:calculatecutlerydiameterD,byorundercutleryexperienceD=x0.6manualrecommended;steps7:chooseXianxiaoxdepththanthesmallestcutlery.2.3 finecutlerychoiceFinecutlerychoiceisthebasicprinciple:cutlerypartssurfaceradiussmallerthanthesmallestsizeRcurveradiusr,thegeneraladmissionR=(0.8-0.9)r.Itsalgorithmstepsareasfollows:Step1:fromthesmallestcurveradiuscalculationmodelpartsentities;Step2:Fromcutlerydatabasesearchradiusoflessthanacutlerycalculatedradiusofthecurveallcutlery;Step3:selectthebestcutlerymeettheaboverequirements;Step4:Ifallcutlerythanthesmallestcurveradius,thesmallestchosenasarecommendedcutlery.3 summaryanddiscussionMouldtypeofcraftofprocessingplan,needhightechnologyandexperienceveryusually,prepareNCtimeofdatanearlyandprocesstimetobelarge.SopersonwhoproduceofcraftofprocessingplanandNCprocessdemandoftheorderrightawayseemfurthermoreurgentautomatically.Thistextsystemresearchmouldtypeofcraftcutterplan,chooseproblem,putforwardmouldofroughmachining,halffinishmachining,finishmachiningprincipleandmethodthatcutterchooses,therealizationalgorithmwithcorrespondingstructure,andhascarriedontherealizationofpreliminaryprogrammingundertheenvironmentofUG/OPENAPI,havedevelopedCATSprototypesystem.Incuttertypeandonthefoundationthatthespecificationisfixed,systemalsocanrecommendparameterofprocessingaccordingtocuttermanual(cutpace,mill,sharpendepth,enterpersonwhogive,etc.),evaluatecorrespondingprocessingtime.FinalpurposeitstorealizeintegrationofCAD/CAMreally,producethroughaftertreatmentnumericalcontrolprocesstheorder.Needtopointout,shouldimprovethemouldtypetotalityofandprocessefficiency,needitfromtheroughmachining,halffinishmachining,considerationonthewholeoffinishmachining,makeupandoptimizemanytargets,thiswillbeworkthatwewanttocarryonnext.模具型腔数控加工计算机辅助刀具选择和研究引言数控加工中包括刀具轨迹的产生和刀具选择两个关键问题。前一问题在过去的20年里得到了广泛而深入地研究，发展的许多算法已在商用CAD/CAM系统中得到应用。目前大多数CAM系统能够在用户输入相关参数后自动产生刀具轨迹。比较而言，对以质量、效率为优化目标的刀具选择问题的研究还远未成熟，当前还没有商用CAM系统能够提供刀具优选的决策支持工具，因而难以实现CAD/CAM的自动有机集成。刀具选择通常包括刀具类型和刀具尺寸。一般来说，适合一个加工对象的刀具通常有多种，一种刀具又可完成不同的加工任务，所以仅考虑满足基本加工要求的刀具选择是较容易的，尤其对孔、槽等典型几何特征。但实际上，刀具选择通常和一定的优化目标相联系，如最大切削效率、最少加工时间、最低加工成本、最长使用寿命等,因此刀具选择又是一个复杂的优化问题。比如模具型腔类零件，由于几何形状复杂（通常包含自由曲面及岛），影响刀具选择的几何约束在CAD模型中不能显式表示，需要设计相应的算法进行提取，因而选择合适的刀具规格及其刀具组合，以提高数控加工的效率与质量并非易事。模具型腔一般用数控铳的加工方法，通常包括粗加工、半精加工、精加工等工序。粗加工的原则就是尽最大可能高效率地去除多余的金属，因而希望选择大尺寸的刀具，但刀具尺寸过大，可能导致未加工体积的增多；半精加工的任务主要是去除粗加工遗留下来的台阶;精加工则主要保证零件的尺寸及表面质量。考虑到目前完全由计算机进行自动选刀还存在一定困难，因而在我们开发的计算机辅助刀具选择（ComputerAidedToolSelection,CATS）系统中，立足于给用户提供一个辅助决策工具，即粗加工、半精加工、精加工等，真正的决策权仍留给用户，以充分发挥计算机和人的优势。1系统基本结构CATS系统的输入为CAD模型，输出为刀具类型、刀具规格、铳削深度、进给量、主轴转速（切削速度）和加工时间等六个参数（如图D,包括刀具类型选择辅助决策工具、粗加工刀具选择辅助决策工具、半精加工刀具选择辅助决策工具及精加工刀具选择辅助决策工具等鉴于粗加工在型腔加工中的重要地位（通常为精加工时间的510倍），粗加工时系统具有刀具自动优化组合的功能，以提高整体加工的效率。除了上述决策工具外,系统还具有查看刀具详细规范、根据刀具类型和尺寸推荐加工参数及评估加工时间等功能，最后生成总的刀具选择结果报表。系统所有的刀具数据及知识均由后台数据库做支持。2关键技术及算法2.1刀具类型选择根据模具型腔数控加工实践，型腔铳加工的刀具一般分为平头铳刀、圆角铳刀及球头铳刀三种。设刀具直径为D,圆角半径为r,当r=0时为平头铳刀，0<R刀具又可分为整体式和镶片式。对于镶片式，关键是选取刀片的材质，刀片材质的选择取决于三个要素：被加工工件的材料、机床夹具的稳定性以及刀具的悬臂状态。系统将被加工工件的材料分为钢、不锈钢、铸铁、有色金属、难切削材料和硬材料等六组。机床夹具的稳定性分为很好、好、不足三个等级。刀具悬臂分为短悬臂和长悬臂两种，系统根据具体情况自动推理出刀片材质，决策知识来源于WALTER刀具手册，系统由用户首先交互选择刀具类型。对镶片式刀具，基于规则自动推理出合适的刀片材质。例如，如果被加工工件的材料为“钢”，机床夹具的稳定性为很好，刀具悬臂为短悬臂，则刀片材质应为WAP25。粗加工刀具组合优化型腔粗加工的目的就是最大化地去除多余的金属，通常使用平头铳刀，采取层切的方法。因此，3D模具型腔的粗加工过程，实际上就是对一系列2.5D模具型腔的加Io刀具优化的目的就是要寻找一组刀具组合，使其能够以最高的效率切除最多的金属。刀具组合优化的基本方法如下：A.以一定的步长做一组垂直于进刀方向的搜索平面与型腔实体相交，形成若干搜索层。B.求出截交轮廓。C.计算内外环之间或岛与岛之间的关键距离，即影响刀具选择的几何约束.D.根据合并原则（相邻关键距离相差小于给定阈值）对搜索层进行合并，确定加工平面和可行刀具集，形成加工层。E.确定每一加工层使用的刀具，即型腔加工的刀具组合。F.根据刀具推荐的加工参数（切削速度、铳削深度和进给速度），计算材料去除率。G.根据加工层实际切除的体积，计算每一加工层的加工时间。H.计算型腔总的加工时间和残余体积。1 .对该组刀具组合的总体加工效率进行评估。J.重复ai,直至求出最优的刀具组合。如以时间为目标，即要求以整个型腔的加工时间t最短来优化刀具组合。2 .2半精加工刀具选择半精加工的主要目的是去除粗加工残留下的台阶状轮廓。为完全去除台阶，铳削深度必须大于每一台阶到零件表面的距离X。其算法步骤如下：步骤1由零件实体模型获得两个相邻截面的表面积以及相应的轮廓长度；步骤2计算平均轮廓长度；步骤3计算台阶宽度；步骤4计算台阶拐角到零件表面的法向距离X;步骤5重复步骤1步骤4,决定每一台阶的铳削深度；步骤6计算刀具直径D,按经验D=xO.6或根据刀具手册推荐；步骤7选择铳削深度大于X的最小刀具。2.3精加工刀具选择精加工刀具选择的基本原则是：刀具半径尺寸R小于零件表面最小的曲率半径r,一般取R=(0.80.9)r。其算法步骤如下：步骤1：从零件实体模型计算最小曲率半径；步骤2:从刀具库中检索出刀具半径小于计算所得的曲率半径的所有刀具；步骤3:选出满足上述要求的最大刀具；步骤4:如果所有刀具大于最小的曲率半径，选择最小的作为推荐刀具。3小结与讨论模具型腔加工的工艺规划通常需要很高的技术与经验，准备NC数据的时间几乎和加工时间一样多。因此，自动产生型腔加工的工艺计划及NC加工指令的需求就显得愈加迫切。本文系统研究了模具型腔工艺规划中的刀具选择问题，提出了模具型腔粗加工、半精加工、精加工刀具选择的原则和方法，构造了相应的实现算法，并在UG/OPENAPI环境下进行了初步编程实现，开发了CATS原型系统。在刀具类型和规格确定的基础上，系统还可根据刀具手册推荐加工参数(切削速度、铳削深度、进给量等)，对相应的加工时间进行评估。其最终目的是真正实现CAD/CAM的集成，继而通过后处理产生数控加工指令。目前CATS系统的界面还是独立于UG的CAM界面，CATS的决策结果还需要用户重新输入到CAMo需要指出的是，要提高模具型腔的总体加工效率，需要从粗加工、半精加工、精加工的整体上考虑，进行多目标组合优化，这将是我们下一步要进行的工作。