多功能護(hù)理床的設(shè)計(jì)【含19張CAD圖紙】

多功能護(hù)理床的設(shè)計(jì)【含19張CAD圖紙】,含19張CAD圖紙,多功能護(hù)理床的設(shè)計(jì)【含19張CAD圖紙】,多功能,護(hù)理,設(shè)計(jì),19,CAD,圖紙 Ye Lie-mail: yeliiastate.eduMatthew C. FrankDepartment of Industrial and ManufacturingSystems Engineering,Iowa State University,Ames, IA 50011Machinability Analysis for 3-AxisFlat End MillingThis paper presents a method for geometric machinability analysis. The implementationof the strategy determines the machinability of a part being processed using a plurality of3-axis machining operations about a single axis of rotation for setup orientations. Slicefile geometry from a stereolithography model is used to map machinable ranges to eachof the line segments comprising the polygonal chains of each slice. The slices are takenorthogonal to the axis of rotation, hence, both two- and three-dimensional (2D and 3D)machinability analysis is calculated for perpendicular and oblique tool orientations,respectively. This machinability approach expands upon earlier work on 2D visibilityanalysis for the rapid manufacturing and prototyping of components using CNCmachining. ?DOI: 10.1115/1.2137748?Keywords: machinability, tool accessibility, CNC machining, slice geometry1IntroductionMachinability analysis is taking an increasingly important roleas complex surfaces are used in the design of a wide variety ofparts. Current computer-aided manufacturing ?CAM? software isreadily capable of generating toolpaths given a set of surfaces of apart and a cutting orientation ?3-axis machining?. However, deter-mining the setup orientation can be difficult and moreover, it maybe very challenging to determine if the part can be created usingmachining at all. An appropriate setup orientation can guaranteean effective cutting of the surface, whereas an inappropriate onewill leave too much material in certain regions. The advancementof 5-axis computer numerically controlled ?CNC? milling ma-chines seems to alleviate this situation; however, often the costand/or difficulty of programming a 5-axis machine have limitedtheir widespread use. Three-axis machines, as economical andtechnologically mature pieces of equipment, have been paid spe-cial attention with respect to complex surface machining if as-sisted with multisetup devices ?e.g., a programmable indexer?.Suh and Lee ?1? used a 3-axis machine with a rotary-tilt-typeindexer to provide an alternative to 5-axis ball end milling. Suh etal. ?2? provided a theoretic basis for machining with additionalaxes. Recently, Frank et al. ?3? employed a 3-axis milling centerwith a fourth axis indexer as an effective rapid prototyping ma-chine. End mills have been shown to offer a better match to thepart surface geometry, a higher material removal rate, and a longertool life compared to ball-mills ?4?. Ip and Loftus ?5? demon-strated the competency of an inclined end mill machining strategyon 3-axis machines in producing low curvature surfaces. How-ever, to machine a surface with large curvature variation, it isnecessary to determine a set of machining orientations and carryout multiple 3-axis machining operations in a sequential mannerwith respect to each of those orientations. Therefore, an effectivemachinability analysis is of critical importance to the successfulimplementation of multiple orientation 3-axis machining for cre-ating complex parts.Many researchers have studied machinability analysis and itsclosely related workpiece setup problem. Most of the approachesare based on visibility, which is essentially line-of-light accessi-bility. Su and Mukerjee ?6? presented a method to determine ma-chinability of polyhedral objects. A convex enclosing object isconstructed to make each face of the part orthogonally visible tothe planes of the enclosing object. The part is then considered tobe machinable from the normal-vector directions of the enclosingobject planes. Later, computational geometry on the sphere wasutilized to analyze visibility by Chen and Woo ?7? who performedpioneering work on computational geometry algorithms that couldbe used for determining workpiece setup and machine selection.Tang et al. ?8? formulated the problem of workpiece orientation asfinding the maximum intersection of spherical polygons. Gan etal. ?9? discussed the properties and construction of spherical mapsand presented an efficient way to compute a visibility map from aGaussian map. Chen et al. ?10? partitioned the sphere by spheri-cally convex polygons to solve the geometric problem of deter-mining an optimal workpiece orientation for 3-, 4-, and 5-axis ballend milling. A visibility map is generated by using the normalvectors of a specified portion of the surface of a part; therefore, itcannot guarantee global accessibility. Yang et al. ?11? computedvisibility cones based on convex hull analysis, instead of relyingon visibility maps. Yin et al. ?12? defined complete visibility andpartial visibility, and presented a C-space-based method for com-puting visibility cones.Asculptured surface is approximated by itsconvex hull ?11?, and the spherical algorithms ?7,13? are used inthe approach of Yin ?12?. The convex hull may, in some cases,have a significant deviation from the true surface. Suh and Kang?14? constructed a binary spherical map to compute the point vis-ibility cone in order to algebraically solve machining configura-tion problems, including workpiece setup orientation. The partsurface is decomposed into triangular patches. An occupancy testof the patches is conducted on a triangular-represented unit sphereto generate global visibility. Dhaliwal et al. ?15? presented a simi-lar approach for computing global accessibility cones for polyhe-dral objects, but with exact mathematical conditions and algo-rithms. Balasubramaniam et al. ?16? analyzed visibility by usingcomputer hardware ?graphics cards?. Frank et al. ?17? analyzedtwo-dimensional ?2D? global visibility on stereolithography ?STL?slices and searched the necessary machining orientations forfourth-axis indexable machining by executing aGREEDYsearchalgorithm. All these visibility-based approaches determine thenecessary condition for machinability; however, they ignore toolgeometry and, therefore, true accessibility ?machinability? is notguaranteed. Figure 1 shows that the accessibility cone ?,?based on line-of-light visibility cannot guarantee the true accessi-bility using a sized tool in machining a segment ij.Su and Mukerjee ?6? took into account the cutter information byconstructing a new part model through offsetting the original partsurface by the amount of the cutter radius. Machinability wasfurther guaranteed by checking the topology of this offset partContributed by the Manufacturing Engineering Division of ASME for publicationin the JOURNAL OFMANUFACTURINGSCIENCE ANDENGINEERING. Manuscript receivedOctober 13, 2004; final manuscript received August 8, 2005. Review conducted byD.-W. Cho.454 / Vol. 128, MAY 2006Copyright 2006 by ASMETransactions of the ASMEDownloaded 11 Dec 2009 to 222.190.117.204. Redistribution subject to ASME license or copyright; see http:/www.asme.org/terms/Terms_Use.cfmsurface. This method is effective for the machinability analysis ofa ball end cutter, but not for that of a flat end cutter, because theeffective radius of a flat end cutter is variable with the change oftool tilting angle. Haghpassand and Oliver ?18? and Radzevichand Goodman ?19? considered both part surface and tool geom-etry. However, tool size was not taken into account becauseGaussian mapping does not convey any size information of thepart surface and/or the tool. Balasubramaniam et al. ?16,20? veri-fied tool posture from visibility results by collision detection be-fore interpolating the tool path for 5-axis machining.Over the past years, feature-based technologies have been anactive field among the manufacturing research community. Regli?21?, Regli et al. ?22?, and Gupta and Nau ?23? discussed featureaccessibility and checked it by calculating the feature accessibilityvolume and testing the intersection of the feature accessibilityvolume with the part. Gupta and Nau ?23? recognized all machin-ing operations that could machine the part, generated operationplans, and checked and rated different plans according to designneeds. A comprehensive survey paper on manufacturability byGupta et al. ?24? reviewed representative feature-based manufac-turability evaluation systems. Shen and Shah ?25? checked featureaccessibility by classifying the feature faces and analyzing thedegree of freedom between the removal volume and the work-piece. TheMEDIATORsystem reported by Gaines et al. ?26? usedthe knowledge of manufacturing equipment to identify manufac-turing features on a part model. Accessibility is examined by test-ing the intersection of removal volumes with the part. Faraj ?27?discussed the accessibility of both 2.5-D positive and negativefeatures. Other researchers presented featured-based approachesto determine workpiece setups ?2831?.Although feature-based approaches are capable tools to handlefeature-based design, they cannot lend themselves to free-formsurfaces where definable features may not exist. In addition,feature-based approaches suggest that all the geometric elementscomprising of a feature are treated together as an entity. Thisactually imposes a constraint to the analysis of a part model. Forexample, it might be feasible to machine a portion of a part fea-ture in one orientation and then finish the remaining surfaces ofthe feature in one or more successive orientations. The currentproblem that this paper addresses is based on a rapid machiningstrategy proposed by Frank et al. ?3? whereby a part is machinedwith a plurality of 3-axis machining operations from multiplesetup orientations about a single axis of rotation.The strategy is implemented on a 3-axis CNC milling machinewith a fourth-axis indexer ?Fig. 2?. Round stock material is fixedbetween two opposing chucks and rotated between operations us-ing the indexer. For each orientation, all visible surfaces are ma-chined using simple layer-based tool-path planning. By setting thecollision offset ?b? ?shown in the Fig. 2? on each side of theworkpiece, the implementation of rapid machining can avoid therisk of collision between tool holders and the holding chucks. Thediameter of largest tool ?Dtmax? used to calculate the collisionoffset ?b? makes the setting of collision offset for each new partunnecessary. The feature-free nature of this method suggests thatit is unnecessary to have any surface be completely machined inany particular orientation. The goal is to simply machine all sur-faces after all orientations have been completed. The number ofrotations required to machine a model is dependent on its geomet-ric complexity. Figure 3 illustrates the process steps for creating atypical complex part using this strategy.Currently, the necessary cutting orientations are determined by2D visibility maps with tool access restricted to directions or-thogonal to the rotation axis. Cross-sectional slices of the geom-etry from an STL model are used for 2D visibility mapping. Thevisibility of those slices approximates the visibility of the entiresurface of the part along the axis of rotation since the slices aregenerated orthogonal to that axis. The above literature review sug-gests that existing approaches to machinability cannot calculatethe set of orientations for setups such that one can machine allmachinable surfaces after all orientations, because either ?i? 2D orthree-dimensional?3D?visibilityconesemployedbytheFig. 1Accessibility based on light ray and a sized toolFig. 2Setup for rapid machiningFig. 3Process steps for rapid machiningJournal of Manufacturing Science and EngineeringMAY 2006, Vol. 128 / 455Downloaded 11 Dec 2009 to 222.190.117.204. Redistribution subject to ASME license or copyright; see http:/www.asme.org/terms/Terms_Use.cfmvisibility-based approaches convey no size information of the tooland workpiece and, therefore, cannot guarantee true accessibility;or ?ii? the feature-based approaches cannot cope with complex?free-form? surface machining because few traditional featurescan be identified on parts with free-form surfaces.An effective machinability analysis method is a prerequisite tothe successful implementation of multisetup 3-axis end milling inorder to achieve the needs of 4- and perhaps 5-axis machining. Aneffective machinability analysis method will determine, given amachining orientation and an end mill of a particular size, howmuch of the part surface can be machined with respect to thismachining orientation. The focus of this paper is to present afeature-free machinability analysis that can determine the numberof setups required to completely machine the surfaces of a partwith one-axis-of-rotation setups. The machinability analysismethod presented in this paper is unlike any previous work in itscompletely feature-free treatment of the part geometry. We reducethe surfaces of the part down to simple line segments on theslices; therefore, any CAD model can be exported as an STL fileand studied. This approach is done because we are only assumingthat the part is machined about one axis of rotation; therefore, it ismuch simpler to simply analyze the 2D slices rather than 3Dsurface geometry.The remainder of this paper is organized as follows. In Sec. 2,definitions that are used throughout this paper are presented. Sec-tion 3 discusses the machinability analysis method in further de-tail, and Sec. 4 presents the implementation of the machinabilityanalysis approach. Last, conclusions and future research endeav-ors are provided.2DefinitionsAlthough previous researchers have defined the concepts of vis-ibility and machinability in their work, similar definitions are pro-vided first in this section to clarify the difference between visibil-ity and machinability. Next, the concepts of tool space ?TS?,obstacle space ?OS?, and machinable range ?MR? are introduced.A condition to determine the existence of machinability is alsoderived. The definitions provided in this section are used for thesubsequent discussion in the remainder of this paper.Visibility:Apoint p on a surface S?p?S? is visible by a lightray emanated from an external point q if pq?suffices thecondition of pq?Sp?=?.Machinability: A point p on a surface S?p?S? is machinableby a certain type and size of tool T?CL,? if p?T?CL,?and T?CL,?Sp?=?. T?CL,? represents the tool sur-face at the cutter location CL, approaching from the orien-tation?.By definition, machinability shares the same concept of acces-sibility with visibility, but differs in the sense that machinabilitytakes into account the size and shape of the cutting tool instead oftreating it simply as a line of light. Therefore, machinability canguarantee true accessibility, whereas visibility is only a necessarycondition of machinability. Hence, the aggregate of orientationssatisfying machinability is a subset of that satisfying visibility. Inother words, machinability can guarantee visibility, but not viceversa.Unlike the expression of visibility in angular orientations, thebundle of which forms a cone, there are two parameters used todescribe machinability. They are the cutter location and the ap-proaching orientation, if the type and size of a cutter are specified.Machinability with respect to an approaching orientation?existsonly if there is a cutter location that allows the cutting tool toapproach and touch the point p without intersecting any other partsurface.Similar to the concept of the visibility of a feature, the machin-ability of a feature ?a line, a curve, or a patch of surface that isgeometrically composed of a set of points? is the intersection ofthe machinability of each point belonging to that feature. Similarto the concept of partial visibility ?PV?, partial machinability?PM? of a feature can also be defined in addition to the concept ofcomplete machinability ?CM?.Partial Machinability: A feature is partially machinablealong an orientation?if there exists at least one point onthat feature such that no cutter location CL exists for it tosuffice the condition of p?T?CL,? and T?CL,?Sp?=?.Complete Machinability: A feature is completely machin-able along an orientation?if for each point on that featureat least one cutter location CL can be found to guarantee thecondition of p?T?CL,? and T?CL,?Sp?=?.Note that Complete Machinability may exist for either a pointor a feature, whereas partial machinability exists only for a fea-ture, because a point can only be said to be either machinable ornonmachinable.If machinability exists with respect to an approaching orienta-tion?, the number of feasible cutter locations CLs may vary withdifferent points on a surface. Points with more feasible CLs trans-lates to easier machining because the more possible CLs providemore options for tool-path and setup planning. The need to mea-sure the space of cutter locations leads to the concept of toolspace.Tool Space: The aggregate of all feasible cutter locations tocut a point p from an orientation?forms a region calledtoolspace,writtenasTS?p,?=?CL:p?T?CL,? and T?CL,?Sp?=?.Tool space of a feature F is the union of the tool space of everypoint belonging to F; that is, TS?F?=?TS?p,?:p?F?. A toolspace reaches its maximum value maximum tool space ?MTS?when there is no obstacle around the geometric entity. Here, weconsider the entire part surface except the portion under consider-ation to be obstacles. Thus, the corresponding space for obstaclesis defined as obstacle space.Obstacle Space: The aggregate of all unfeasible cutter loca-tions with respect to an orientation?due to the existence ofan obstacle i ?Obi? is called the obstacle space of obstacle i,written as OS?i,?=?CL:T?CL,?Obi?.The cutter cannot enter the domain of obstacle space because itwill gouge into the obstacle.Tool space can be computed by subtracting all the obstaclespaces from maximum tool space.TS= MTS?iOS?1?If the computed tool space using Eq. ?1? is not empty, thenmachinability exists; otherwise, the geometric entity is nonma-chinable. The machinability analysis method presented in this pa-per is based on Eq. ?1?. Tool space is actually a measure of ma-chinability since it tells the existence of machinability and themagnitude of machinability, if it exists.Once the tool space is determined, the machinable range result-ing from it can be obtained.Machinable Range: The maximum machinable portion of afeature given the tool space is called machinable range ofthat feature, written as MR=?p:p?F and TS?p,?.The above definitions will be used throughout the remainder ofthis paper.456 / Vol. 128, MAY 2006Transactions of the ASMEDownloaded 11 Dec 2009 to 222.190.117.204. Redistribution subject to ASME license or copyright; see http:/www.asme.org/terms/Terms_Use.cfm3Machinability AnalysisThe machinability analysis approach presented in this paper isbased on the concept of configuration space ?C-space?. The con-cept of C-space first applied in robotic spatial motion planningwas documented by the work of Lozano-Perez ?32?. The basicidea of C-space is to find the aggregate of the valid spatial con-figurations for a moving mechanism in an environment with ob-stacles around it. Recently, C-space has been applied in tool-pathplanning for multiaxis machining. Choi et al. ?33? presented aC-space-based approach to generate 3-axis numerically controlled?NC? tool paths for sculpture machining by transforming the de-signed part surface and stock-surface into elements in C-space andtreating the cutter as a moving object in the safe space. TheC-space is represented and computed using a Z-map model of thepart. Choi and Ko ?34? incorporated C-space into computer-automated process planning ?CAPP? for freeform die-cavity ma-chining. Morishige et al. ?35? used C-space to generate tool pathsfor 5-axis ball end milling. Jun et al. ?36? optimized tool orienta-tions for 5-axis flat end milling by a search method in C-space.C-space of the cutting tool, which is defined as tool space in Sec.2, provides the safe space for tool-path planning; therefore, toolpaths based on C-spa