機械外文文獻翻譯-一種支持機床和工藝計劃聯(lián)合設計的綜合方法 【中文7810字】【PDF+中文WORD】

機械外文文獻翻譯-一種支持機床和工藝計劃聯(lián)合設計的綜合方法 【中文7810字】【PDF+中文WORD】,中文7810字,PDF+中文WORD,機械外文文獻翻譯-一種支持機床和工藝計劃聯(lián)合設計的綜合方法,【中文7810字】【PDF+中文WORD】,機械,外文,文獻,翻譯,一種,支持,機床,工藝,計劃,聯(lián)合 An integrated approach to support the joint design of machine toolsand process planningM.Leonesio,L.Molinari Tosatti,S.Pellegrinelli,A.Valente*Institute of Industrial Technologies and Automation(ITIA),National Research Council of Italy(CNR),Via Bassini 15,20133 Milano,Italy1.IntroductionThe design and configuration of machine tools is instrumentalfor European manufacturing competitiveness 1.Coherently withthe mass customization principles and the traditional Europeanknow how in the field of instrumental goods production,machinetools should result from a configuration process tightly related tothe analysis of the families of products and process qualityrequirements rather than being a standard and rigid catalogueequipment.This makes the machine configuration and the processplanning as two steps of the same problem where the machine toolgeometric and kinematics features influence the accessibility tothe workpiece operations along with the fixturing systemconfiguration and the machine dynamic impacts on the finalquality and costs of the workpiece.The relationships between machine tool configuration andprocess planning have been widely investigated by the scientificliterature with reference to the following topics:the evaluation ofmachine capabilities to statically realize a process plan 2,theexecution of a process plan across several resources 3,the energyefficient process planning 47 and,finally,evaluation of theimpact of machine tool dynamic behaviour on the process planningdefinition 8.However,the interest of these works is mostlyfocused on the impact of a specific machine tool architecture andperformance on the process planning problem.The current paper presents an integrated approach to supportthe joint design of machine tools and process planning.Theproposed approach is structured in four major steps as illustratedin Fig.1.The first step consists in the analysis of the workpiece CADmodel.The workpiece is analysed according to the STEP standard9 through the identification of machining feature(geometricaldescription of the region of the workpiece to be machined),machining operations(selection of cutting tools,machiningparameters and strategies)and machining workingsteps(MWS association between a machining feature and a machiningoperation).On the basis of a number of alternative MWSs,Step 1identifies the MWSs that globally better match the productionrequirements and machine behaviour.The geometric and technological information related to thefamily of products together with the data about the productiondemand and the forecasts about possible product evolutions areutilized in Step 2 related to the machine tool design.The outcomeof this step is a domain of general-purpose machine tools that fitthe production requirements from both the dynamic and staticpoint of view Steps 1 and 2 are traditionally handled asindependent phases as general-purpose machine tools arenormally configured with no knowledge of the actual productsto machine and the process planning is usually developed startingfrom an existing machine catalogue.Step 3 regards the dynamic simulation of the machine toolsolutions resulting from Step 2 while executing the MWSsidentified in Step 1.The dynamic behaviour of machine tools isevaluated against a number of Key Performance Indicators(KPIs)dealing with the energy consumption,tool wear,surfaceCIRP Journal of Manufacturing Science and Technology6(2016)181-186A R T I C L E I N F OArticle history:Available online 9 April 2015Keywords:Process planningMachine tool kinematics and dynamicsMachine designSTEP-NCA B S T R A C TThe configuration of machine tools and process planning problem are traditionally managed asindependent stages,where the process plan is designed by considering a number of machine toolsolutions available from catalogue.This strategy presents a number of disadvantages in terms of processresults and machine capabilities fully exploitation.The current paper proposes an integrated approachfor jointly configuring machine tools and process planning.The approach is structured in 4 majorrecursive steps that eventually ensure the accomplishment of the best trade-off between the machinetool static and dynamic behaviour,the process quality and the resulting economic efficiency.Thebenefits of the approach have been evaluated for a test case application in the railway and automotivesectors.?2013 CIRP.*Corresponding author.Tel.:+39 0223699917;fax:+39 0223699941.E-mail address:r.it(A.Valente).Contents lists available at SciVerse ScienceDirectCIRP Journal of Manufacturing Science and Technologyjou r nal h o mep age:w ww.els evier.co m/lo c ate/c irp j1755-5817/$see front matter?2013 CIRP.http:/dx.doi.org/10.1016/j.cirpj.2013.03.002roughness,maximal required spindle power and torque.The KPIsare concurrently relevant to the MWS assessment as they coulddrive the adjustment of process parameters and to the machinetool design by leading to the tuning of the kinematic and dynamiccharacteristics.The last step of the approach concerns the selection of one ormore fixtures and the definition of workpiece orientations as wellas the association of the operations to a given orientation(workpiece setup)10,11.The outcome of this phase is thegeneration of alternative process plans feasible from the workpiecequality requirements 12.Production time and costs areinvestigated and optimized on the basis of the MWS KPIs.The following section of this work will provide the reader with amore comprehensive description of each step of the proposedapproach(from Sections 2 to 6).Section 7 will present an industrialtest case considered to evaluate the approach benefits.Section 8will outline the conclusions and future work.2.Workpiece analysisThe workpiece analysis is the first activity in feature-basedprocess planning 13 and aims at defining the operations that arenecessary for the complete machining of the workpiece.As statedin Section 1,the workpiece analysis is based on the STEP-NCstandard,leading to the definition of the machining feature(geometric description of the region to be machined),machiningoperations(strategy of machining)and machining workingstep(association between a feature and an operation).As a region canbe machined on the basis of alternative strategies in terms ofcutting tools,machining parameters or tool path,the same featurecan be realized by alternative operations and,consequently,alternative MWSs.The complete realization of a workpiece impliesthe identification of the technological constraints among theMWSs to be executed.The proposed approach considers twodifferent kinds of technological constraints:precedence andtolerance constraints 14.Precedence constraints impose anorder of execution between two MWSs whereas toleranceconstraints require the execution of two MWSs in the same setupto ensure the accomplishment of quality requirements.On thebasis of these technological constraints,a network of operationscan be built by taking into account the precedence constraints andthe alternative strategies to process a specific feature.This networkwill be employed during the last step of the approach dealing withthe fixture selection and setup planning.3.Machine tool designThe configuration of the machine tool is an extremelyarticulated process that,coherently with the proposed approach,starts from the collection of data about the family of products to beprocessed.These data include the geometrical and technologicalcharacteristics of products synthesized in the workpiece analysisstep along with the production volumes.The configuration process involves the identification of theminimum set of machine tool requirements that accomplish theprocess constraints(such as the minimum working cube,thenumber of axes,the spindle orientation and power).On the basis ofthis minimum set,other types of constraints can be taken intoaccount such as the productivity,the reliability,the availablebudget,the energy efficiency as well as the machine global size(inthe case it should be integrated in a predefined shop-floor).In thecase the demand is expected to be variable over time,additionalevaluations can be done with regard to the customization of themachine flexibility degree to match the forecasted changes.All this information leads to the identification of a domain ofalternative machine solutions characterized by different archi-tectures,performance and costs.At this stage,the machine designprocess requires the evaluation of machine performance whileexecuting the process.The analysis of machineprocess dynamicinteractions enables the evaluation of the machine criticalities andpossible improvements.The next section outlines the dynamic cutting simulation as ameans to assess the machine tool design and the workpieceanalysis as part of the process plan.4.Dynamic cutting simulationIn the metal cutting strategy,the objective of decreasingmanufacturing time and costs is strictly connected to the need forensuring the requested level of quality.The quality can concerndirectly the workpiece geometrical properties,or it may refer tothe process,for instance,its efficiency in terms of energyconsumption.The workpiece quality is affected by all the phenomena thatdetermine an undesired displacement of the tool with respect tothe nominal path.A comprehensive assessment of workpiecequality entails an analysis of four major categories of phenomena:thermal deformations of machines and parts;volumetric position-ing errors of the tool tip;dynamic interaction among machine,process and workpiece;trajectories errors due to CNC and/or feeddrives performance.Due to the high demanding performance interms of material removal rate(MRR),the modelling andminimization of vibrations,either forced or caused by chatterinstability,represents a major limitation for improving productiv-ity and part quality in metal removal processes.Vibrationsoccurrence has several negative effects:poor surface quality,outof tolerances,excessive noise,disproportionate tool wear,spindledamage,reduced MRR to preserve surface quality,waste ofmaterials,waste of energy and,consequently,environmentalimpact in terms of materials and energy 15.Besides the surfacequality and the violation of tolerances,the other effects deal withprocess quality and have a direct impact of the overall productionefficiency.The key for evaluating the level and the effects ofvibrations onset is the so-called dynamic cutting process simula-tion,able to couple the forces originating from the materialremoval with the relative dynamic and static response betweentool tip and workpiece 16.While the simulation of singleprocesses or machine characteristics is state of the art,theintegration of process and the machine tool modelling in thesimulations is particularly innovative.The interactions betweenmachine tool,the workpiece and the process surely represent agreat challenge as their modelling must be evaluated to addressthe forced vibrations onset and regenerative chatter instability.The discontinuous cutting forces produced by the machiningprocess excite the tool tip causing a chip section modulation1.WORKPIE CE ANALYSIS2.MACHINE TOOL DESIGN3.DYNAMIC CUTT ING SIMULATIONWorkpiece CAD ModelMWSsMachine Too l Dynamic and Kinema?c 4.FIXTURE SELECTION AND SETUP PLANN INGKPIsMachine too l design ass ess mentMWS ass ess mentAlterna?ve Process PlansLong-term produc?on requ irementsFig.1.The integrated approach.M.Leonesio et al./CIRP Journal of Manufacturing Science and Technology 6(2013)181186182influencing the cutting force itself.In order to incorporate thedescribed effects,the architecture of the dynamic cuttingsimulation approach should integrate the following functionalmodules:?A part program interpreter able to provide the tool path with therelated velocity law,together with the cutting parametersdefining the operation(for instance,spindle speed and feed rate);?A geometric engine for computing the workpiece-tool engage-ment and the chip geometry computation;?A force model relating the chip geometry with the cutting forcesexpressed by each engaged cutter and their summation;?A representation of the tool tip and workpiece relative dynamics;?A time-domain integrator for the overall dynamic simulation.In most of existing commercial applications,the dynamic loopbetween machine and process is not closed,as cutting forcesdisturbances are supposed to not affect tool position andconsequently chip section.Actually,the complexity of the modelseverely reduces the existing commercial applications:the uniquecommercial application realizing a proper Virtual Machiningtaking into account dynamic cutting is MachProTMby MALINC.The dynamic simulation results contribute in evaluating thequality of the machining process.This means to identify a numberof KPIs to be measured and tracked over time.4.1.Key Performance Indicators(KPI)The KPIs considered in the proposed approach are interpretedas a measure of the machine tool dynamics with respect to therequired machining operations.On the basis of the value of theseindicators some instrumental choices can be realized withreference to the machine structure and control system.In thefollowing part of the current section,the most importantconsidered KPIs are briefly introduced.4.1.1.Energy consumptionThe mechanical energy necessary to perform the machiningoperation can be obtained by computing the integral of themechanical power over machining time,namely:Etot Es pindle EaxesZTMWS0Vs pindleTs pindletdt ZTMWS0v*feedt?Fctdt(1)where Vspindleis the spindle velocity,Tspindleis the spindle torque,vfeedis the instantaneous feed velocity,Fcis the cutting force andTMWSis the MWS duration.The computation of electrical energy consumption can be moreprecisely computed by keeping separated axes and spindlemechanical power since the efficiency of the corresponding drives(whose estimation is out of scope)is usually different.Moreover,inorder to compare the copper losses in spindle winding for differentMWSs,the Root Mean Squared value(RMS)of spindle torque canbe computed as well,starting from torque time history.In literature,cutting energy consumption is commonlyestimated by a constant volumetric specific energy associated tothe material type:this approximated approach conflicts with theexperimental data,whereas the specific energy changes with tool,process parameters and machines 17.The specific spindle powerconsumption(SSPC)is inversely related to cutting speed,feed pertooth,depth of cut and width of cut.The situation can be different ifthe process becomes unstable(chatter occurrence):as the spindlecopper losses are proportional to the RMS of the torque,thepresence of a dynamic component in cutting force may cause anincrease of SSPC.All the above-mentioned considerations are automaticallytaken into account by the developed SW module.4.1.2.Spindle bearings loadSpindle bearings usually face a progressive wear duringmachining and most of the spindle maintenance time is devotedto bearings substitution.The bearing catalogues report a stan-dardized formula to compute bearing life by referring to thedynamic equivalent load,able to synthesize in a single numberthe effort requested to a bearing during a complex load history.Assuming that spindle bearings load is proportional to the spindleshaft bending moment,the dynamic equivalent load can becomputed for each MWS,and used to compare the induced bearingstress.In formula:BL Ltool?ZTMWS0ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiF3xytTMWSdt3s(2)where Ltoolis the tool length and Fxyis the cutting force resultant inthe milling plane(xy).4.1.3.RoughnessSurface roughness depends on several factors related to cuttingkinematic and vibration onset.In the proposed approach,the toolvibrations and deflection are directly addressed as a surfaceroughness indicator.They are crucial in determining an acceptablelevel of surface roughness and comparing the influence of differentdynamic responses on this parameter.Thus,the indicatorbecomes:R maxTMWSxtooltk k (3)wherextoolt is the tool tip displacement over time.4.1.4.Tool cutter loadTool chipping occurs when the shear pressure on the cuttingedge overcomes the mechanical resistance of the material.Theshear stress is proportional to the cutting force expressed by thesingle cutter Fcutternormalized with respect to the cutting edgeengagement(b).Therefore,the corresponding indicator is:Cl 1bmaxTMWSFcuttert(4)The other KPIs consist in an estimation of the tool wear exploitingby Taylor formula,the maximum spindle power and maximumspindle torque requested to cut the material,as well as themaximum load requested by machine tool axes to provide feedmovement.They are directly available from simulation andrepresent constraints that the machine tool must respect to beable to perform a given operation.5.Machine tool design and MWS assessmentCoherently with the proposed approach,the interpretation ofKPIs can drive the improvement choices both for the processplanning and the machine tools.Based upon the KPIs values,a number of MWSs can be updatedto obtain a more performing and feasible process.For example,incase the KPI expressing the surface roughness indicates that theprocess is not compliant to the workpiece quality constraints,some MWS such as feed rate or spindle speed can be adjusted;similarly,according to maximum spindle power,feed rate,spindlespeed or cut of depth can be modified in order to reduce the costassociated to the manufacturing process.The impact of KPIs on the machine tool choices is morecomplex to be addressed.The KPIs expressing the requiredM.Leonesio et al./CIRP Journal of Manufacturing Science and Technology 6(2013)181186 183maximum spindle power and maximum spindle torque canbe directly exploited to size the proper motor,while the spindlebearings load can be used to choose the proper bearingsguaranteeing the desired component life.On the otherhand,the KPIs associated to energy consumption,tool life,toolcutter load,may be wrongly related to the sole processparameters,whereas,together with surface roughness indicator,they strictly depend on machine tool dynamic performance,being severely degraded by vibration onset.Therefore,theenhancement of these latter KPIs can be traced back to theassessment of the best MT dynamic performance able to preventchatter occurrence.A method to carry out this task is outlined inthe following.The relationship between chatter occurrence and the KPIs canbe analysed by exploiting a reduced set of variables;for example,adopting the 0th-order approach described in 16.Under thefollowing hypothesis:?Milling operation in X and Y plane,characterized by a straightline trajectory,?No regeneration in Z direction,?No low immersion angles,the relationship between chatter instability occurrence and machinetool is analytically expressed by the characteristic equation of thedynamical system machine tool+milling process:det1 LA0?Gtool-WPv 0(5)where L is an eigenvalue whose real part must be positive toassure the stability;A0 is a matrix that takes into account theorientation of the average cutting force with respect to the axisfeed;Gtool-WP is the relative dynamic behaviour observedbetween tool tip and workpiece.As the eigenvalue L also dependson stable depth of cut(b),radial and tangential cutting pressures(Ktand Kr)and the number of teeth(N),it can be used to map thestability limit,knowing the process parameters.Based on Eq.(5),a first consideration is that the critical depth ofcut(i.e.,the maximum depth of cut ensuring process stability forall spindle speeds)is strictly related to the minimum of the realpart of the relative dynamic compliance between tool tip andworkpiece in a frequency range that depends on Tooth PassingFrequency(TPF),while matrix A0 indicates which compliancedirection is more critical.Hence,the machine tool dynamicassessment can be reduced to the computation of boundaries in aspace defined by:frequency,Re(Gxx(v)and Re(Gyy(v),where thevariables represent the real part of the tool tip dynamic compliancealong the