WO2010094022A1 - Procédé de prototypage rapide - Google Patents

Procédé de prototypage rapide Download PDF

Info

Publication number
WO2010094022A1
WO2010094022A1 PCT/US2010/024274 US2010024274W WO2010094022A1 WO 2010094022 A1 WO2010094022 A1 WO 2010094022A1 US 2010024274 W US2010024274 W US 2010024274W WO 2010094022 A1 WO2010094022 A1 WO 2010094022A1
Authority
WO
WIPO (PCT)
Prior art keywords
product
wire
wedm
input
cutting
Prior art date
Application number
PCT/US2010/024274
Other languages
English (en)
Inventor
Richard A. Wysk
Zhi Yang
Sanjay Joshi
Original Assignee
The Penn State Research Foundation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by The Penn State Research Foundation filed Critical The Penn State Research Foundation
Publication of WO2010094022A1 publication Critical patent/WO2010094022A1/fr

Links

Classifications

    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B19/00—Programme-control systems
    • G05B19/02—Programme-control systems electric
    • G05B19/18—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form
    • G05B19/4097—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by using design data to control NC machines, e.g. CAD/CAM
    • G05B19/4099—Surface or curve machining, making 3D objects, e.g. desktop manufacturing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23H—WORKING OF METAL BY THE ACTION OF A HIGH CONCENTRATION OF ELECTRIC CURRENT ON A WORKPIECE USING AN ELECTRODE WHICH TAKES THE PLACE OF A TOOL; SUCH WORKING COMBINED WITH OTHER FORMS OF WORKING OF METAL
    • B23H9/00—Machining specially adapted for treating particular metal objects or for obtaining special effects or results on metal objects

Definitions

  • the present invention relates to rapid prototyping processes and manufacturing.
  • RP rapid prototyping
  • CAD computer aided design
  • RP/RT/RM rapid tooling
  • RM rapid manufacturing
  • One of the major advantages of RP/RT/RM is the ability of the technologies to permit manufacture of an object, directly from CAD data input, without significant human intervention or skill.
  • researchers have focused on additive processes, those processes are considered as traditional RP processes, such as stereolithography, sheet lamination, laser sintering, adhesive bonding, drop deposition, etc.
  • the generally used materials are powders, plastics, and paper, which are sufficient for concept models, but not for most mechanically functioning parts.
  • Figure IA and Figure IB illustrates an example of two parts with different mass volume.
  • the part in Figure IA would require an excessive amount of machining to remove the material. This part however would be a reasonably efficient candidate for an additive RP process.
  • an additive RP process will spend an excessive amount of time stacking simple layers, whereas the subtractive process would finish the part very quickly from a block of material.
  • RP technologies may be divided generally into additive processes and subtractive processes. The majority of RP research has focused on additive processes, and little effort has gone into subtractive techniques.
  • EDM Electrical Discharge Machining
  • Wire EDM is one such process where a wire is used to produce the spark between the material and wire and perform the cutting operation. Processing on wire EDM is a forceless process and makes WEDM a strong candidate for RP applications. Like other linear cut manufacturing systems, such as abrasive water jet and laser material processing, WEDM has a noticeable line contact characteristic with the part being produced. Unlike traditional manufacturing processes which involve point contact between the tool and the work piece, the contact mode in wire cutting processes is a linear edge.
  • Figures 3 A and 3B illustrates the contact models for traditional machining processes and linear cut manufacturing systems. Generally, metal material fabrication is not performed using traditional RP additive processes.
  • a WEDM processing method is needed for complex geometries suitable for rapid prototyping. Such a process preferably permits utilization of known WEDM processing tools.
  • One embodiment of our method of rapid prototyping a product may include identifying a product geometry to prepare a geometric model, determining fabrication setup orientation, preparing a fabrication process, generating a cutting path based NC code and fabricating the product using a linear cut process.
  • the NC code is numerical control code such as Step-NC code or NC G-code.
  • the cutting path may include one or more paths that require a wire to move along one or more cutting paths or perform one or more cutting passes along a part for fabricating the part into a product.
  • the linear cut process may be wire electrical discharge machining, water jet cutting, laser machining or hot wire machining.
  • the linear cut process is conducted by a wire electrical discharge machine (WEDM) that utilizes a five axis or a six axis electrical discharge machining (EDM) machine.
  • WEDM wire electrical discharge machine
  • EDM electrical discharge machining
  • the linear cut process may also be conducted by a four, five or six axis laser machine.
  • Another embodiment of our method of rapid prototyping may include identifying a product geometry, selecting a rapid prototyping system, preparing a first model for fabrication, preparing a first fabrication process that takes input and generates tangent visibility for each facet identified in the input, identifying a part orientation, generating a modeling process for fabricating the product from stock material, generating at least one cutting path and fabricating the product using a linear cutting mechanism.
  • the input is one or more STL files that provide part or product geometry data.
  • any polygonal part data may also be used.
  • the generation of the modeling process can include determining tangent visibility and wire range based on the input and determining part orientation based on product geometry and information provided in the input for each facet of the product.
  • a three dimensional tool path or wire path will be generated based on tangent visibility results to prepare the first fabrication process or any additional fabrication processes.
  • the first fabrication process is preferably the only process needed to be run to fabricate the product.
  • the preparing of the first model can include adding at least one support to the first model prior to tool path planning for the first fabrication process.
  • the fabrication process may also be run such that the one or more supports are severed to fabricate the part.
  • Embodiments of the method may also include preparing one or more visibility methods to determine if an axis of rotation of the product is feasible.
  • the one or more cutting paths may include multiple wire paths that include convex edges of the product that are generated to minimize the number of setups and number of B-axis orientations for fabrication of the product.
  • Embodiments of the methods may be incorporated in a machining apparatus, such as a machining apparatus configured for rapid prototyping.
  • That apparatus may include one or more linear cutting mechanisms, one or more input devices and one or more controllers.
  • the one or more controllers may include a computer or may include one or more processors operatively connected to memory that has software stored thereon for running by the one or more processors.
  • the input device may be a scanner, keyboard, or other device configured to provide data, such as one or more STL files that may be utilized by the software run by the one or more processors.
  • the one or more controllers are connected to the at least one input device and at least one linear cutting mechanism.
  • the one or more controllers are configured to control the at least one cutting mechanism,
  • the one or more controllers are also configured to identify a geometry of a product, prepare a first model for fabrication; prepare a first fabrication process that takes input received from the at least one input device and generates tangent visibility for each facet identified in the input; identify a product orientation, generate a modeling process for fabricating the product from stock material, generate at least one cutting path, and actuate the cutting mechanism to move along the at least one cutting path to fabricate the product.
  • the input is comprised of at least one STL file.
  • the at least one cutting path may include a plurality of wire paths.
  • the wire paths may include convex edges of the product and may be generated to minimze B axis orientation for the fabrication of a part or product.
  • Figure IA is a perspective view of a part illustrating a part with a mass volume.
  • Figure IB is a perspective view of a part that has a second mass volume.
  • Figure 2 is a chart illustrating a qualitative situation of the direct metal components production relative to usual options.
  • Figure 3 A is a schematic illustrating a contact model of a traditional machining process.
  • Figure 3 B is a schematic illustrating contact model for a linear cut process.
  • Figure 4 is a flow chart illustrating examples of a general approach for using conventional machining as a rapid prototype tool.
  • Figure 5 is a perspective view of a six axis wire electrical discharge machine.
  • Figure 6 A is a perspective view of a toll illustrating conventional visibility from a point.
  • Figure 6B is a perspective view illustrating WEDM visibility.
  • Figure 7 is a flow chart illustrating a present preferred embodiment of a method for rapid prototyping.
  • Figure 8 is a perspective view of an embodiment of a model pagoda.
  • Figure 9A is a perspective view illustrating raw material on an indexer.
  • Figure 9B is a view similar to Figure 9A illustrating a present preferred initial fabrication setup step of a present preferred method of rapid prototyping.
  • Figure 9C is a view similar to Figures 9A and 9B illustrating a present preferred part after a first cut path has been run along the part in accordance with a present preferred method of rapid prototyping.
  • Figure 9D is a view similar to Figures 9A, 9B and 9C illustrating the present preferred part after several rotations on an indexer.
  • Figure 9E is a view similar to Figures 9A, 9B, 9C and 9D illustrating a finished part made by a present preferred method of rapid prototyping.
  • Figure 10 is a flow chart illustrating a present preferred method for data preparation for use in a present preferred method of rapid prototyping.
  • Figure 11 is a flow chart illustrating a present preferred method of rapid prototyping.
  • Figure 12 is a perspective view of a part being fabricated by a present preferred method of rapid prototyping.
  • Figure 13 is a schematic view illustrating relations between cylinder center line 1 and rotational norm RN and rotational orientation R 0 .
  • Figure 14 is a flow chart illustrating a present preferred method of generating a wire path that may be utilized in a present preferred method of rapid prototyping.
  • Figure 15 is a graph illustrating a comparison between production cost of selective laser sintering (SLS) and WEDM prototyping.
  • Figure 16 is a present preferred embodiment of a computer apparatus that may implement an embodiment of our method for rapid prototyping.
  • Figure 17 is a coordinate system defined in this research
  • Figure 18 is a demonstration of rotational Norm R V N and rotational orientation Ro on a six-axis WEDM machine
  • Figure 19 is the flowchart to calculate the optimal set of intermediate coordinate systems
  • Figure 20 is the flowchart to calculate initial R N
  • Figure 21 is the flowchart to calculate initial Ro.
  • Figure 22 is an example of a present preferred intersection graph for a polygon.
  • Figure 23 is a flow chart illustrating a present preferred method for computing the tangent visibility percentage
  • Figure 24 is a fragmentary view of a present preferred cutting path generated for cutting a part using a linear cutting mechanism.
  • Figure 25 is a graph illustrating a present preferred method of determining edges based on a center of mass.
  • Figure 26 is a schematic view illustrating all coverable edges for a given rotational norm are shown in Figure 26
  • Figure 27 is a schematic view illustrating how a rotational norm of a cutting mechanism may be capable of covering certain degree of edges for a part.
  • Figure 28 is a graph illustrating a valid wire orientation perpendicular to a facet norm.
  • Figure 29 a graphical view illustrating coverable polygon norms for a particular orientation product.
  • Figure 30 is a flow chart illustrating a present preferred method for determining an intermediate coordinate system by determining a rotational norm and a rotational orientation.
  • Figure 31 is a graphical illustration of a plurality of rotational norms determined based on a determined rotational orientation.
  • Figure 32 is a graphical illustration of a plurality of rotational orientations determined based on a determined rotational norm.
  • Figure 33 is a flow chart illustrating a present preferred method for calculating an initial rotational norm.
  • Figure 34 is a flowchart of a present preferred method for calculating an initial rotational orientation.
  • Figure 35 is a flowchart showing a present preferred method for classifying tangent visibility results into different coordinate systems.
  • Figure 36 is a flowchart of a present preferred method for determining the intermediate coordinate system for a given edge.
  • Figure 37 illustrates an example of a cutting wire in its intermediate coordinate system.
  • Figure 38 is a flowchart showing a present preferred method of wire path generation.
  • Figure 39 is a flowchart illustrating a present preferred method for determining the intermediate coordinate system for triangle results.
  • Figure 40 is a schematic view illustrating straight lines parallel to a vector orientation product that may be used as a rectangle boundary.
  • Figure 41 is a schematic view illustrating a present preferred manufacturing coordinate system.
  • Figure 42 is a flowchart representing a present preferred method for the generation of the cutting sequence.
  • Figure 43 is a schematic view illustrating Six defined surfaces.
  • Figure 44 is a flowchart representing a present preferred method for a "GOTOZero" function.
  • Figure 45 is a schematic or graphical view illustrating a first present preferred wire path generation process.
  • Figure 46 is a schematic or graphical view illustrating a second present preferred wire path generation process.
  • Figure 47 is a schematic or graphical view illustrating a third present preferred wire path generation process.
  • Figure 48 illustrates an example of a cut off plane for a present preferred part.
  • Figure 49 is a block diagram illustrating a present preferred software structure for the WEDM-RP system.
  • Figure 50 illustrates a present preferred slotted part that may be fabricated via a rapid prototyping process.
  • Figure 51 is a schematic view illustrating setup orientation and rotational orientation results for the slot part shown in Figure 50.
  • Figure 52 is a schematic view illustrating the wire trajectory result for a determined coordinate.
  • Figure 53 illustrates a present preferred inner feature part that may be fabricated via a present preferred rapid prototyping process.
  • Figure 54 is a schematic view illustrating setup orientation and rotational orientation results for the inner feature part of Figure 53.
  • Figure 55 illustrates a present preferred pagoda part that may be fabricated via a present preferred rapid prototyping process.
  • Figure 56 is a schematic view illustrating setup orientation and rotational orientation results for the pagoda of Figure 55.
  • Figure 57 illustrates a present preferred hourglass part that may be fabricated via a present preferred rapid prototyping process.
  • WEDM has some similarity in general approaches as a rapid prototyping process. This process requires a product geometry model, analysis of the product model for producibility, tool path generation and fabrication preparation, and fabrication of the final product.
  • FIG. 5 illustrates the design of a six-axis WEDM.
  • the electric wire in Figure 5 is the cutting tool for WEDM; the electric wire will be kept straight in a line during fabrication. Due to the uncommon fabrication approach of WEDM, the tool path planning for WEDM-RP is not a layer-based approach (neither additive nor subtractive).
  • One flow chart of the entire process for WEDM-RP is illustrated in Figure 7 and can be summarized by the following important contents:
  • Input for the proposed system is a CAD file.
  • One embodiment of this CAD file is in STL format, where the boundary of the part is represented by triangular facets.
  • Part Orientation This part of the problem intends to seek an orientation such that maximum the machinable surface area. This step can also take tangent visibility result and STL file as input and generate the fabrication orientation.
  • Model Process and wire path generation Based on tangent visibility and part orientation results, the manufacturability of the given part can be analyzed and a wire path generated.
  • An example part to fabricate on six-axis WEDM is a small statue of a pagoda, which is illustrated in Figure 8.
  • the pagoda is a symmetric part without cavities in the geometry and can be fully fabricated on six-axis WEDM in one setup with multiple rotation orientations.
  • Figure 8 illustrates one embodiment of a pagoda product made by a WEDM-RP rapid prototype process that utilizes a method such as the method shown in Figure 7.
  • the input of the WEDM-RP is any geometric model.
  • the input is formatted as Stereolithography (STL) files.
  • STL Stereolithography
  • Data preparation can prepare the data for the whole method.
  • the STL file will be translated in to labeled triangles, vertices, concave edges, and convex edges.
  • the steps in one present preferred method of data preparation are presented in Figure 10.
  • FIGS. 6 A and 6B illustrate the difference between regular visibility and WEDM's visibility.
  • the regular visibility is a natural phenomenon in everyday life. Seeing an object means identifying the portions of the object visible from the current position. A point is visible from the current position if the line segment connecting the point and the current position does not intersect with any other part of the same object.
  • FIG 6B the tangent visibility is illustrated.
  • Tangent visibility intends to solve the tangent visibility problem for WEDM.
  • a Stereolithography (STL) file the common RP input, may be used as input for our process.
  • the fundamental elements in the STL file are triangle facets.
  • the tangent visibility will be tested for each triangle facet in the given STL file.
  • the detail flowchart for tangent visibility is presented in Figure 11. This tangent visibility could also be applied to other linear cutting processes, such as a gamma knife operation or laser cutting, to determine the reachable region for those linear cutting processes.
  • Rotational orientation R 0 and rotational norm R N are illustrated in Figure 13. Different rotational norm R N represents different setups.
  • the orientation is preferably chosen such that it maximizes the machinable surface area under the rotational norm R N .
  • the wire needs to move only within the wire movement range in order to fabricate the facet, and straight lines in the range will be produced as a result of the cutting wire orientations for fabricating the facet. A part will be fabricated by completing fabrication of each facet.
  • not all facets can be fabricated in one rotational orientation for a given setup and given rotational orientation; the location of the wire will vary in a two cones, as illustrated in Figure 13.
  • the center line of the cones is located on the vector R 0 x R N passing the center of mass of the input geometry.
  • the relationships of cylinder center line Op , rotation norm R 0 , and rotational orientation R N are illustrated in Figure 13. If the orientations of straight lines for some facets lie in the cones, those triangle facets could be fabricated under given rational orientation R 0 and the setup.
  • the cutting wire In order to cover the tangent visible regions from the tangent visibility result, the cutting wire needs to rotate and translate following the orientations obtained from the visibility results.
  • the cutting wire movement range is restricted.
  • Some wire orientations may require the rotation of the workpiece on WEDM instead of rotating cutting wire.
  • the coordinate system for global tangent visibility results is based on the coordinate system of the input STL geometry. Consequently, the cutting wire orientation is also based on the coordinate system of the input geometry. The rotation of the workpiece will change the cutting wire orientation in the coordinate system.
  • the coordinates required to manufacture the part should be based on the WEDM machines instead of the input part geometry.
  • each coordinate system is defined by three vectors: (1) rotational norm #,v , the physical meaning of rotational norm is the setup orientation for the given geometry; (2) rotational orientation R o and (3) orientation product Op .
  • the origin of the coordinate system is the center of mass of the input geometry.
  • FIG 17 illustrates the relationships among rotational norm R .v , rotational orientation R o , and orientation product O N , Each of these vectors has a physical meaning.
  • Rotational Norm R N is same as the rotational axis on a six-axis WEDM or other rotary axis.
  • the direction of the rotation is defined using right hand rule: the fingers of the right hand are curled to match the rotation motion, and the thumb indicates the direction of the vector.
  • Figure 18 illustrates an example of a rotational norm.
  • a series of R' o S is defined, as illustrated Figure 18.
  • Each rotational orientation Ro is used to indicate the current position of the rotary axis under a certain coordinate.
  • Orientation product °p represents the neutral position of the cutting wire. Based on the physical limitations of a WEDM machine, the cutting wire can only rotate in a restricted area around the orientation product Op . In order to find the optimal set of intermediate coordinates, the most important vectors to define are the rotational norm RNS . With properly defined , all possible cutting wire orientations in 3D space can be covered. Based on the definitions of rotational norm, rotational orientation, and orientation product, an intermediate coordinate system requires at least two out of the three vectors, and the third vector is the cross product resulting from the two known vectors. An overall flowchart on how to determine the intermediate coordinate system by determining the rotational norm -R.v and rotational orientation ⁇ o is presented. The flowchart is illustrated in Figure 19.
  • Each rotational norm obtained from the algorithm results represents a setup orientation for six-axis WEDM.
  • a greedy algorithm is used to classify all visibility result in to all necessary coordinate systems and generate two important vectors: initial K,v and initial R ⁇ .
  • the intermediate coordinates formed by initial R ,v and initial R o will cover most of the tangent visible areas of the given geometry.
  • a series of R ,v s will be generated by rotating initial #,v around initial ⁇ o .
  • Each rotational norm #,v represents one required setup orientations to fabricate the input geometry.
  • ⁇ lV a series of rotational orientation K o will be calculated. Those rotational orientations will be used to guide the rotational axis movement on six-axis WEDM.
  • the manufacturability result can provide wire movement information for each triangle facet in the given STL file. Because the cutting wire can be moved within the machine physical limitation, a number of B-axis orientations R 0 can be calculated based on machine physical limitation and manufacturability result. If the taper angle of the WEDM machine is ⁇ , [90 ⁇ ⁇ ] number of rotational orientation R 0 will be able to cover all necessary tangent visible regions.
  • the wire path generation flowchart is illustrated in Figure 14.
  • a fixture can be designed to hold the part. Because WEDM has the characteristic of a zero cutting force, the function of those fixtures will be clamping the part. Sacrificial fixtures can also be used. Because the part can be fixed on B-axis indexer for each setup, the fixture is preferably located as close to the rotation center as possible. Furthermore, some other issues can be considered: • The sacrificial fixture is preferably not an obstacle for fabrication
  • Simplification of the cut-off surface is preferred. For instance, a planar surface is much easier for cut off than a curved surface.
  • a global tangent visibility problem for a polyhedral model can be simplified into a 2D problem.
  • each planar surface of a product geometry or part geometry must be expanded to obtain an intersection plane with the given geometry. Because the geometry is a polyhedral model, the intersection plane is on a tangent surface of each planar surface. Based on the intersection plane results, a tangent visibility analysis may then be performed and the tangent visible percentage for the planar surface may then be calculated.
  • the first step to computing tangent visibility is to calculate the polygon plane intersection graph.
  • the convex-concave edge property plays of a particular part may play a key role in the tangent visibility definition.
  • the edge property In order to compute the tangent visibility, the edge property must be correctly assigned. Before providing the rules for assigning the edge property, several important definitions are presented first.
  • extended surface for the polygon The extended surface is used to calculate the intersection graph for the polygon.
  • Polygon P ⁇ norm, P ⁇ 5 where norm is the polygon norm, p is the set of points on the polygon boundary.
  • intersection graph for the polygon P is denoted as G PI .
  • G PI ⁇ E, F(E) ⁇ , Where E is the set of all edges of the geometry.
  • the set of non-original edges is noted as E ,v:
  • Figure 22 illustrates an example of an intersection graph for polygon Pi .
  • Edge ⁇ 1 is shared by polygon ⁇ i and Ps , and it is an original edge.
  • e i is a convex edge.
  • Edge e s is shared by Polygon ⁇ s and ⁇ i , and the relationship between -Ps and Pi is concave, so that ⁇ i is a concave edge.
  • Edge ⁇ 3 is the intersection result of the extended surface ⁇ e and the polygon P* .
  • Edge e * is the intersection result of ⁇ - and polygon Ps .
  • Both edge e a and edge e t are original edges; therefore, they are special original edges considering that they do not belong to polygon ⁇ i .
  • a non-original edge, edge ⁇ s is the intersection result of polygon ⁇ e and extended surface ⁇ - and it is a non-original edge.
  • edge e * is shared by polygon A and polygon A .
  • Point Vs on polygon A is located on positive side of polygon A .
  • Point *'i on polygon -Pa is located on negative side of polygon A , so the edge e * is a concave edge on the intersection graph for polygon A .
  • ii except the points on shared edge between P * i and P * 2 , all points on P 5 1 is located on same side of Pi with P S 2 , the edge is a convex edge.
  • An algorithm that may be used to calculate a tangent visibility percentage for a part to be rapid prototyped mat be determined from the result of the intersection graph and the properly defined edge properties, which may be used as input for this algorithm.
  • the input of a present preferred algorithm for use to calculate a tangent visibility percentage may include the following definitions:
  • Intersection Polygon is the polygon we are interested in.
  • Convex edge sets ⁇ vex is all convex edges in the intersection graph ⁇ vex — ⁇ .
  • Stepl Determine whether the edges in G P/ intersect with any concave edges.
  • Step2 If all edges in ⁇ 1 n are convex edges, then use convex edges to form rectangle with points in 1 ⁇ m in order to cover the intersection polygon Pi .
  • Table 2 illustrates a present preferred algorithm to calculate tangent visibility.
  • the sub- functions of the tangent visibility algorithms are illustrated in Tables 3-8
  • the present preferred global tangent visibility algorithm includes three major steps, as illustrated in Table 2.
  • the first major step is the edge intersection test. In this step, an intersection test is performed for the edges in the intersection graph ®pf with all concave edges. The complexity of this operation is ®( m x 0» + " ) ),
  • the second step in the global tangent visibility algorithm of Table 2 is that of performing the polygon-clipping operations for polygons without concave edges.
  • the polygon-clipping operation is finished using the third-party open source package, Computational Geometry Algorithms Library (CGAL).
  • CGAL Computational Geometry Algorithms Library
  • the general polygon-clipping operation has the complexity ° ⁇ T) with x and V being the edge numbers of the arbitrary polygons. Consequently, the complexity of the second step is O ( n * ) ⁇ given that these polygons do not have concave edges,
  • the third step in the present preferred tangent visibility algorithm of Table 2 is that of forming visible regions and performing polygon clippings, The complexity is °( (>n + " ) x ( ⁇ + 0» -I- « )3 ) ).
  • Global tangent visibility results may contain only triangle and rectangle shapes. Due to the fact that the coordinates of the tangent visibility result are based partly on geometry coordinates, those shapes may be classified into intermediate coordinate systems before they are translated into manufacturing coordinates. Present preferred methods of classifying edges and facets into different intermediate coordinate systems are discussed below.
  • Triangle or rectangle shapes usually require edges to cover them.
  • each triangle shape as illustrated in Figure 24, requires two edges to cover the whole triangle. The two edges are the starting cutting edge and the end cutting edge.
  • Several lemmas may be used to classify those edges under a certain intermediate coordinate system.
  • Lemma 1 An edge is coverable for a certain ⁇ N if the edge forms an angle with RN between [90 — a, 90 + a] 5 where a is the taper angle limitation for WEDM machines.
  • the maximum angle between the edge and the neutral wire position is ** .
  • Lemma 2 In 3D space, only F ⁇ O ⁇ ⁇ number of R ,v s are required to cover all possible edges in 3D space, where ff is taper angle limitation for WEDM machines.
  • edges in 3D will form a unit globe with center at center of mass.
  • All coverable edges for a given R ,v are shown in Figure 26.
  • a certain edge orientation for the rectangle shape may need to be determined in order to translate the tangent visibility result into manufacturing information.
  • Several lemmas are introduced in order to classify those polygons without concave edges under a certain intermediate coordinate system.
  • Tangent visibility results may be classified into several intermediate coordinates and then translated into manufacturing coordinates. Based on Lemma 1 and Lemma 2, discussed above, F90 ⁇ a] number of R N S are capable of covering all possible edges in 3D space. Based on Lemma 3 and Lemma 4 ; [90 ⁇ a] number of OpS under any R-N is enough to cover all polygons without concave edges.
  • any set of intermediate coordinate systems can be a feasible solution for WEDM- RP, finding the optimal solution for setup is not guaranteed.
  • an algorithm to determine the optimal set of intermediate coordinate systems is presented such that the number of trial setups is minimized.
  • an algorithm may be applied to calculate two initial vectors, initial ⁇ .v and initial R o ,
  • the intermediate coordinates formed by initial R ,v and initial ⁇ o will cover most of the tangent visible areas of the given geometry.
  • [90 4- d ⁇ norms are calculated by rotating initial # ,v around initial ⁇ o .
  • Each rotational norm forms a 2 ⁇ - angle with its neighbor rotational norms.
  • the taper angle a 20°
  • Each ⁇ lV forms a 4°° angle with its neighbor ⁇ ,v s .
  • FIG. 33 A flowchart for a present preferred method of calculating an initial ⁇ ,v is illustrated in Figure 33.
  • a list of initial fl.v candidates is generated.
  • the facet or polygon norm is used as a potential initial # .v and saved into the ⁇ RnList , ⁇ ne total area that is reachable under each initial ⁇ ,v candidate is calculated, and the final initial R ,v is the one that has the maximum reachable total area.
  • the initial ⁇ .v affects the cut off plane, as discussed in Chapter 6. Consequently, any initial H ,v candidate must have at least one polygon without a concave edge that is perpendicular to the initial ⁇ ,v . This perpendicular polygon is used as the cut off plane.
  • the initial rotational orientation ⁇ & a is a unit vector that is perpendicular to the initial ⁇ ,v .
  • the flowchart for calculating initial ⁇ o is presented in Figure 34. In this procedure, all polygon norms which are perpendicular to the initial ⁇ .v , are candidates for initial R 0 . Those candidates are grouped together if the norms coincide. For each group of polygons, the total area is calculated. The final initial R o is the group norm with the maximum total area. If no polygon has a norm that is perpendicular to the initial R ,v , the initial R o will be an arbitrary vector that is perpendicular to the initial #,v .
  • FIG. 35 illustrates a flowchart of a present preferred method for classifying tangent visibility results into different coordinate systems.
  • each shape is formed by two edges, and an intermediate coordinate can be determined for each edge.
  • a procedure called FindRnRoEdge is defined to determine the intermediate coordinate system for a given edge.
  • a flowchart of a present preferred method of finding the RnRoEdge is illustrated in Figure 36.
  • a third type of tangent visibility result is a polygon without concave edges. There may be an infinite number of feasible solutions to cover these polygons. Based on Lemma 3, only one intermediate coordinate system for these polygons may be found. Due to the fact that any [90 -r ⁇ l number of Ro under any given R N is capable of covering all polygons without concave edges, the initial R N and its first pre-defined F90 ⁇ a] number of ⁇ o will be used to cover all polygons without concave edges.
  • a function named "FindRnRoFct" is defined to classify the polygon without concave edges into different intermediate coordinates.
  • Tangent visibility results may be classified into several intermediate coordinate systems. Under each intermediate coordinate system, the tangent visibility results are stored as rectangle shapes, triangle shapes and polygons without concave edges.
  • Figure 37 illustrates an example of a cutting wire in its intermediate coordinate system.
  • the UV plane and the XY plane are perpendicular to vector Op in the intermediate coordinate system.
  • the distance between the UV plane and the XY plane is C , which is a parameter related to the physical restrictions of a WEDM machine.
  • the distance D represents the physical distance between the upper wire guide and lower wire guide on a WEDM machine. The distances from the origin of the intermediate coordinate system to the UV plane
  • the cutting edge from the tangent visibility result is an edge which covers the polygon in the graph.
  • the extension of the cutting edge will intersect with the UV plane and the XY plane to create the cutting wire trajectory points.
  • FIG. 38 A flowchart for a present preferred method of wire path generation is shown in Figure 38.
  • the tangent visibility results are classified into rectangle results, triangle results, and results for polygons without concave edges. For each result, corresponding intermediate coordinate systems and wire path trajectories are found.
  • a rectangle result may have two cutting edges that have the exact same orientation. Consequently, the rectangle result can be finished using the same intermediate coordinate system.
  • the cutting wire trajectories on the XY plane and the UV plane are used to guide the cutting wire and finish the rectangle coverage.
  • a triangle result may have two cutting wire orientations; the orientation differences may result in a need for different intermediate coordinate systems to cover the triangle result.
  • a flowchart illustrating a present preferred method for determining the intermediate coordinate system for triangle results is illustrated in Figure 39. Based on the result, one or multiple intermediate coordinate systems may be generated to cover the whole triangle area.
  • a polygon without concave edges can be covered using an infinite number of rectangle regions.
  • the straight lines parallel to vector 0 p are used as the rectangle boundary, as illustrated in Figure 40. Because the straight lines covering the polygon have the exact same orientation, the coverage for a polygon without concave edges can be finished using the same intermediate coordinate system as well.
  • the origin of the manufacturing system is at the rotational center of the B-axis on a six-axis WEDM machine.
  • the center of mass (the origin of the intermediate coordinates), may be translated.
  • the rotational norm fi,v needs to be translated to the X-axis. Assuming that the center of mass is Pc si , the trajectory point in the intermediate coordinate is P , the rotational norm of the intermediate coordinate is R ,v , and the rotational orientation is # o .
  • the new trajectory point P» ⁇ w in the manufacturing coordinate can be calculated by:
  • T is the transformation matrix and can be calculated by:
  • T ⁇ s sin ⁇ + O) x (O y (I - cos ⁇ ) cos ⁇ + ⁇
  • Each shape in the tangent visibility result may have a trajectory segment on the UV plane and the XY plane.
  • the wire path generated by this method may be isolated.
  • the separate trajectories should be translated into one connected trajectory.
  • a method is presented to combine separate trajectories into one trajectory and generating the wire path plan automatically.
  • a flowchart representing a present preferred method for the generation of the cutting sequence is illustrated in Figure 42. In this operation, the wire trajectories are classified into trajectories generated by triangle coverage and trajectories generated by rectangle coverage.
  • UV plane is a plane parallel to fl.v ⁇ o plane, and in the area corresponding to negative
  • This plane is used for wire path projection.
  • XY plane is a plane parallel to ⁇ .v-Ro plane, and in the area corresponding to the positive
  • This plane is used for wire path projection.
  • Right Plane is a plane parallel to O P R N plane, and in an area corresponding to the
  • Left Plane is a plane parallel to 0 p R N plane, and in an area corresponding to the
  • Top plane is a plane parallel to R o ⁇ p plane, and in an area corresponding to the positive
  • Bottom plane is a plane parallel to ⁇ o Op plane, and in an area corresponding to the
  • parameter D is the fixed distance from the UV plane to the XY plane. This is a distance related to machine dimensions. Parameter height and width are related to input machine dimension limitations.
  • four edges are defined and illustrated in Figure 43; (1) Top Right Edge is the intersection edge of the top plane and right plane; (2) Top Left Edge is the intersection edge of the top plane and left plane; (3) Bottom Right Edge is the intersection edge of the bottom plane and right plane; (4) Bottom Left Edge is the intersection edge of the bottom plane and left plane.
  • FIG. 44 A flowchart representing a present preferred method for a "GOTOZero" function is illustrated in Figure 44. This function intends to create a lead-in for the wire path from an idle position to the initial cutting point or to create the lead-out for the wire path from the last cutting point to an idle position.
  • Scenario 1 When the starting point of the cutting chain trajectory is formed by coverage of a polygon without concave edges, the last segment in the cutting chain will be extended to intersect with one of the six surfaces defined above. When the starting point of the cutting chain trajectory is not formed by coverage of a polygon without concave edges, the last segment on the cutting chain will also be extended to test any intersection with the six surfaces defined above or any existing cutting chain trajectory.
  • Scenario 2 If the intersection with the surfaces is closer than the intersection with the cutting chain trajectory, then the lead-in/lead-out wire path will follow the rules used for Scenario 1.
  • Scenario 3 If the intersection with the cutting chain trajectory is closer than the intersection with the surfaces, the lead-in/lead-out wire path will follow the intersected cutting chain trajectory.
  • Figure 45 illustrates an example of Scenario 1.
  • the cutting chain "Chain 1" and “Chain 2" are on the UV plane.
  • the extension of the first segment of "Chain 1" intersects with Right Plane on edge Ei .
  • the extension of the last segment of "Chain 1" intersects with Right Plane on edge £2 .
  • the extension of the first segment of "Chain 2” intersects with Left Plane on edge Ei.
  • the extension of the last segment of "Chain 2" intersects with Left Plane on edge E4. Consequently, the cutting chain sequence for "Chain 1" is: Top Right Edge -> El -> Chain 1 ->E2->Top Right Edge.
  • the cutting chain sequence for "Chain 2" is Top Left Edge ⁇ E3 ⁇ Chain 2 ⁇ E4 ⁇ Top Left Edge.
  • Figure 46 illustrates an example of Scenario 2.
  • the projection of a cutting chain, "Chain 1” is on the UV plane.
  • the projection of the first segment of "Chain 1" intersects with Top Plane on edge ⁇ 1 .
  • the projection of the last segment of "Chain 1” intersects with Top Plane on edge £2 . Consequently, the cutting chain sequence for "Chain 1" is: Top Right Edge- ⁇ El ->Chain ⁇ -> E2 -> Bottom Left Edge -» Top Right Edge.
  • Figure 47 illustrates an example of Scenario 3.
  • the last operation of wire cutting may be to cut off the part or product that is rapid prototyped or fabricated by a rapid prototype process.
  • a cut off plane is required.
  • the cut off plane is the plane that is perpendicular to the initial fi,v and is a polygon without concave edges. Because the rotational norm is the initial #,v and the cut off plane is a polygon without concave edges, the intermediate coordinate could be formed by initial R ,v and initial # o .
  • the cut off plane coverage is rectangle coverage.
  • embodiments of our method may be implement on a computer 1 or computer system as shown in Figure 16.
  • software may be configured to be stored on memory 2 and run by a processor 3 that implements an embodiment of our method for rapid prototyping.
  • the software may be configured to receive input from one or more input devices 4 connected to the processor and may send output data via the processor to one or more output devices 5.
  • the input devices may be, for example, scanners, measurement devices, sensors, detectors, keyboards, key pads, or a computer mouse.
  • Output devices may be, for example, speakers, monitors or displays.
  • An example of a computer system that may utilize an embodiment of our method is shown in Figure 16.
  • the processor 3 may be configured to communicate with and control the actions of a WEDM to control rapid prototyping of a part or device.
  • the computer system may be a component of a WEDM system or WEDM,
  • a WEDM-RP algorithms may be implemented in VC++.net 2005 and tested on an Inter® CoreTM2 Duo 2.60GHZ processor personal computer, running Windows XP operating software.
  • the software accepts ASCII STL files as input and outputs the Numerical Control (NC) code.
  • NC Numerical Control
  • the following are also considered as input parameters for the six-axis WEDM: taper angle, the distance between UV and XY planes, STL file accuracy level, maximum height and maximum width, and wire path incremental accuracy.
  • the taper angle may be the maximum angle to which the cutting wire can rotate from its neutral position.
  • the STL file accuracy level is used to deal with round-up errors in the co-planar triangle combination procedure.
  • the distance between the UV and XY planes, and the maximum height and maximum width of the six-axis WEDM are the parameters used to generate wire path. Due to the requirement of a polygon-clipping operation in a tangent visibility algorithm, the polygon libraries in Computational Geometry Algorithms Library (CGAL) may be used to improve computation speed.
  • Figure 49 illustrates a present preferred software structure for the WEDM-RP system. Seven major modules were implemented for this WEDM-RP. The file organization module was used to organize the input ACSII STL file into the data structure used in WEDM-RP.
  • the AAG simplification module was used to simplify the input polyhedral geometry into planar polygons.
  • the intersection graph module was used to calculate the intersection graph for each planar polygon in the input geometry.
  • the tangent visibility module solved the global tangent visibility problem based on the intersection graphs generated from the intersection graph module.
  • CGAL libraries were used to finish the polygon- clipping operations.
  • the manufacturing orientation module determines the optimal manufacturing orientation for the input geometry. NC codes drive the WEDM machines to fabricate the final product.
  • the visualization module was built to help visualize the intermediate and final result in the WEDM-RP system.
  • This module generated Visual Basic for Application (VBA) codes, which were then executed in Solidwork® 2008 software to generate drawings automatically. For example, the drawings for the intersection graphs and tangent visibility results were all generated automatically by the VBA codes produced by the WEDM-RP system.
  • This visualization function is used to help the user understand and verify the algorithms' output.
  • Part orientation algorithms may be used to determine the optimal setup orientations for the given geometry and calculate number of setup required to finish the final product.
  • Figure 50 illustrates a slot part with its coordinate system. The part orientation algorithm may be configured to determine that this slot part requires one setup and two rotational operations. Recall that the number of rotational norms represents the number of setups, and under each rotational norm, the number of rotational orientations indicates the rotational axis movement (see Chapter 5 for detailed information).
  • Figure 51 provides the setup orientation and rotational orientation results for the slot part. The slot part will be setup along R N( 1 ) , and the rotational axis will have two positions, ⁇ o ( ' J- ) and -R o ( 2 ) to finish all fabrication operations.
  • Figure 52 illustrates the wire trajectory result for #,v ( l ) fi ⁇ ( l ) coordinate. The wire trajectory information will be transformed into final manufacturing coordinates in NC generation module.
  • Figure 53 illustrates an inner feature part with its coordinate system.
  • the part orientation algorithm determined that this part required one setup and two rotational operations.
  • Figure 54 provides the setup orientation and rotational orientation results for the inner feature part.
  • the part was set up along K.vU ) , and the rotational axis had two positions, -Ro ( I ) and R o (2 X whereby all the fabrication operations were finished.
  • Figure 55 illustrates a model pagoda, a more complex part, with its coordinate system.
  • the part orientation algorithm determined that this part required one setup and four rotational operations.
  • Figure 59 provides the setup orientation and rotational orientation results for the pagoda.
  • the pagoda was set up along #.v ( i ) , and the rotational axis had four positions, Ko(I) , ⁇ o( 2 ), fio( 3 ) and ⁇ o ( 4 ⁇ whereby all the fabrication operations were finished.
  • Figure 57 illustrates a model hourglass.
  • the global tangent visibility analysis shows that all triangles on the model hourglass are globally tangent visible.
  • a complex pagoda was also evaluated similarly to the hourglass model of Figure 57.
  • Table 9 shows the total computation time for different model geometries.
  • the prismatic geometries require less unit computation per facet than non-prismatic geometries. Because the prismatic geometries do not require the error elimination procedure to deal with incorrectness in edge convexity error in STL file, the unit computation time is much less than non-prismatic geometries.
  • Manufacturing Cost c m, achine + ⁇ r ⁇ maintain A ⁇ - C ⁇ l bor W ⁇ J P ⁇ I ⁇ ⁇ proc a i tool
  • This unit cost model is applicable for both additive processes and subtractive processes.
  • WEDM-RP intends to decrease. WEDM-RP provides methodologies to create tooling plan, tool path and fixtures, and very little to no human interaction is necessary. As a result, the engineering time is trivial .
  • Figure 8 illustrates the selected part for a cost analysis. Two processes are evaluated for producing the pagoda, selective laser sintering, and an embodiment of our WEDM-RP. The main assumptions are provided in Table 10.
  • FIG. 15 illustrates the cost comparison between several sources. The result in Figure 15 shows that WEDM process has cost advantages when the fabrication volume is small, for this pagoda example, the volume is less than 15.
  • Embodiment of our WEDM-RP method provides a possibility for applying conventional process, such as WEDM, as rapid prototyping tools. Use of such embodiments can decrease the total engineering time by automatically generating process plan and decreasing human interaction. Cost comparison results also show that WEDM has cost advantages when production volume is less than 15. Furthermore, WEDM can provide higher accuracy product than normal additive rapid prototyping processes.

Abstract

L'invention concerne un procédé de prototypage rapide d'un produit, consistant : à identifier une géométrie de produit pour préparer un modèle géométrique; à préparer un processus de fabrication; à générer une trajectoire de coupe; et à fabriquer le produit par un processus de coupe linéaire. Des modes de réalisation de l'invention concernent des systèmes de prototypage rapide ou des systèmes informatiques. Par exemple, un appareil d'usinage comprenant au moins un mécanisme de coupe linéaire, au moins un dispositif d'entrée et au moins une unité de commande, peut être configuré pour mettre en oeuvre au moins un mode de réalisation de l'invention.
PCT/US2010/024274 2009-02-16 2010-02-16 Procédé de prototypage rapide WO2010094022A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US15275609P 2009-02-16 2009-02-16
US61/152,756 2009-02-16
US30456510P 2010-02-15 2010-02-15
US61/304,565 2010-02-15

Publications (1)

Publication Number Publication Date
WO2010094022A1 true WO2010094022A1 (fr) 2010-08-19

Family

ID=42115734

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US2010/024274 WO2010094022A1 (fr) 2009-02-16 2010-02-16 Procédé de prototypage rapide

Country Status (1)

Country Link
WO (1) WO2010094022A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114186298A (zh) * 2021-11-15 2022-03-15 广东宏远新科自动化技术开发有限公司 智能机械零件制造营运方法及系统
US20220350835A1 (en) * 2019-11-28 2022-11-03 Mitsubishi Electric Corporation Workpiece image search apparatus and workpiece image search method

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6021358A (en) 1996-09-18 2000-02-01 Sachs; George A. Three dimensional model and mold making method using thick-slice subtractive fabrication
US6627835B1 (en) 2000-02-02 2003-09-30 Purdue Research Foundation Three dimensional object fabrication techniques

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6021358A (en) 1996-09-18 2000-02-01 Sachs; George A. Three dimensional model and mold making method using thick-slice subtractive fabrication
US6627835B1 (en) 2000-02-02 2003-09-30 Purdue Research Foundation Three dimensional object fabrication techniques

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
BOXLER J: "PLATINEN-SCHEIDWERKZEUGE FUER KLEINE STUECKZAHLEN", VDI Z, SPRINGER VDI VERLAG, DE, vol. 132, no. 10, 1 October 1990 (1990-10-01), pages 116,119 - 122, XP000165981, ISSN: 0042-1766 *
WOO T C: "VISIBILITY MAPS AND SPHERICAL ALGORITHMS", COMPUTER AIDED DESIGN, ELSEVIER PUBLISHERS BV., BARKING, GB LNKD- DOI:10.1016/0010-4485(94)90003-5, vol. 26, no. 1, 1 January 1994 (1994-01-01), pages 6 - 16, XP000423003, ISSN: 0010-4485 *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20220350835A1 (en) * 2019-11-28 2022-11-03 Mitsubishi Electric Corporation Workpiece image search apparatus and workpiece image search method
US11580156B2 (en) * 2019-11-28 2023-02-14 Mitsubishi Electric Corporation Workpiece image search apparatus and workpiece image search method
CN114186298A (zh) * 2021-11-15 2022-03-15 广东宏远新科自动化技术开发有限公司 智能机械零件制造营运方法及系统
CN114186298B (zh) * 2021-11-15 2022-09-27 广东宏远新科自动化技术开发有限公司 智能机械零件制造营运方法及系统

Similar Documents

Publication Publication Date Title
US11429076B2 (en) Automatic strategy determination for computer aided manufacturing
Lauwers et al. Optimal and collision free tool posture in five-axis machining through the tight integration of tool path generation and machine simulation
US7930054B2 (en) Method and system for toolpath generation
CN104350437B (zh) 机器的cam集成cnc控制
EP2252954B1 (fr) Procédé et dispositif d'usinage de composites
Ivanov et al. Information Support of the Computer-aided Fixture Design System.
Erdim et al. Offline force control and feedrate scheduling for complex free form surfaces in 5-axis milling
Tunc et al. Extraction of 5-axis milling conditions from CAM data for process simulation
Patil et al. An intelligent feature-based process planning system for prismatic parts
Lasemi et al. A freeform surface manufacturing approach by integration of inspection and tool path generation
Chen et al. Automated post machining process planning for a new hybrid manufacturing method of additive manufacturing and rapid machining
Liu et al. A multi-perspective dynamic feature concept in adaptive NC machining of complex freeform surfaces
Sun et al. Iso-planar feed vector-fields-based streamline tool path generation for five-axis compound surface machining with torus-end cutters
Lim et al. Exact tool sizing for feature accessibility
Krimpenis et al. Assessment of sculptured surface milling strategies using design of experiments
WO2010094022A1 (fr) Procédé de prototypage rapide
Li et al. Machinability analysis for 3-axis flat end milling
Duvedi et al. The edge–torus tangency problem in multipoint machining of triangulated surface models
Luo et al. Optimal tool orientation generation and chip volume/cutting force predictions for 5-axis CNC machining of curved surfaces using flat-end mills
Osman Zahid et al. End mill tools integration in CNC machining for rapid manufacturing processes: simulation studies
Oduola et al. A comparative study of product development process using computer numerical control and rapid prototyping methods
Leo Kumar Automation of tool path generation in multi-process micromachine tool for micromachining of prismatic and rotational parts
Qu et al. Raster milling tool‐path generation from STL files
Epureanu et al. Reconfigurable machine tool programming–a new approach
Li et al. A new approach for uncut detection and automatic design of EDM electrodes

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 10707391

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 10707391

Country of ref document: EP

Kind code of ref document: A1