Development of Computer-aided Manufacturing System for a Jewelry-making CNC Machine

Transcription

1 Development of Computer-aided Manufacturing System for a Jewelry-making CNC Machine Ya Miao 1,,4,a, Kai He 1,,b, *, Haitao Fang 1,,c, Zhimin Zhou 1,,d and Ruxu Du 3,e 1 Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China Shenzhen Key Laboratory of Precision Engineering, Shenzhen, China 3 The Chinese University of Hong Kong, Shatin, N.T, Hong Kong 4 University of Science and Technology of China, Hefei, China a ya.miao@siat.ac.cn, b kai.he@siat.ac.cn, c ht.fang@siat.ac.cn, d @qq.com, e rdu@mae.cuhk.edu.hk *corresponding author Keywords: Jewelry-making CNC Machine, CAM, NC Program, Simulation. Abstract. This paper designs a CAM system for a jewelry-making CNC machine. The CAM system not only provides a human-computer interface for setting machining parameters, but also can generate special NC programs automatically and realize the simulation for the machining process. In addition, the paper gives an efficient application for machining an ellipsoidal gold bead. The basic design of the jewelry-making CAM system and the experimental results are presented. Introduction Generally, the special CAM system generates suitable NC program according to each workpiece s shape and the special CNC machine s system. For the jewelry-making CNC machine, there are many well-known jewelry CAD/CAM softwares on the market, such as Artcam Jewelsmith, Jewelcad, MasterCAM ART, etc. All have mature CAD jewelry modeling function, but their CAM post processor hardly could produce suitable NC program for 5 or more axises special NC machine tools actually used. In addition, on account of the high cost of the oversea CAD/CAM copyrighted software, these softwares are not proper choices in jewelry industry applications in china. Thus, it is necessary to develop the special CAM system for jewelry-making CNC machines. With the improvement of people's living standard, more and more beautiful jewelry is required, especially a kind of ellipsoidal gold bead jewelry named lucky bead with simple patterns on its surface. At present, the jewelry-making CNC machines used for machining a pattern on a bead surface have a similar machine structure. It usually has 5 axises or more but lacks a matched special CAM module. In the jewelry industry, manual trial cutting on a bead to get a perfect pattern is the main production mode, which is dependent on the proficiency and experience of operators and results in many problems like poor levels of automation, low production efficiency, low product accuracy and consistency. In order to overcome the shortcoming of manual operation, CAM system of jewelry is needed to develop to improve pattern s quality and machining efficiency, which also reduces the demand of operator s knowledge and experience[1]. In this paper, a simple CAM system is designed for a jewelry-making CNC machine, which is used to cut patterns on the surface of ellipsoidal beads in order to explore a method of quickly developing a CAM system for special jewelry-making CNC machines. Jewelry-making CNC Machine s Structure The designed CAM system is adapted to the our designed jewelry CNC machine shown in the Fig.1. The CNC machine has 9 axises, A, B, C, D, E, X, Z, M01, M0, to coordinate to cut patterns, where X, D, Z are translational axises and C, E, A, B are rotational axises. Axis A, B, D, E, X, M01, and

2 M0 control tool s motion. Axis C, and Z axis control the workpiece s motion. Axis X, and D can drive the tool move horizontally forward and backward, whereas Axis A, and E can make tools rotate about Axis X and D respectively. Axis B can rotate X-D table horizontally. The ellipsoidal workpiece is clamped by the air cylinder, and Axis Z can drive workpiece to move forward and backward perpendicularly to X-D orientation, and Axis C axis can rotate workpieces around Axis Z. Axis M01 and M0 are the tools self-rotating axises. Fig. 1. The jewelry-making CNC machine CAM System Design The CAM system should include three main functions: it must have a human-computer interface to help operators set technological parameters. In the meantime, it should assist operators with calculation and generate NC program by itself. In addition, it can also realize process simulation, which makes operators a better understand of the process results. Based on the above points, the CAM system is divided into 5 modules, including the workpiece definition module, the machining parameters module, the tool path planning module, the NC program generation module and the process simulation module. In consideration of software implementation, the software development kits are MFC Dialog framework in VC++ and OpenGL graph lib, which put friendly interface and graph process into practice. The design of every module of CAM system are introduced in next sections. Workpiece Definition Module. The workpiece is an ellipsoidal bead, and the designed CAM system must provide a graphic interface to guide users to set workpiece s dimensions, then CAM system software automatically models the workpiece. the ellipsoid surface is gridded into limited numbers of small rectangles to render model by OpenGL drawing functions. According to the small rectangles sum and equation (1), it can easily calculate the vertexs of gridded rectangles. x = a sin θcosϕ y = a sin θsin ϕ z = ccosθ, 0 θ π,0 ϕ π. (1) Machining Parameters Module. Process design is mainly based on the analysis and processing of large amounts of information by selection(processing method, machine tool, cutting tool and machining sequence, etc.), computing (machining allowance, dimensions, tolerances, cutting parameters and time quota, etc.), drawing (process chart), as well as by process documents, etc. In general, the process parameters are chosen according to the size and shape of the parts and processing content []. During the process planning of the jewelry CAM system, three main parameters shown in Fig. should be considered. The CAM system offers users system parameters and NC code related

3 parameters setting as well as a patterns library. In the patterns library, operators could choose needed elementary patterns and set elementary patterns parameters, which include shape parameters and position parameters on the bead s surface. Fig.. Technological parameters needed Tool Path Planning Module and NC Program Generation Module. In order to generate NC program, the CAM system needs to plan the tool path, and calculate the cutter location point according to the designed patterns and workpiece s shape feature, then transform the location point which is in the workpiece coordinate system to the machine tool s coordinate system to get the nine axises relative vector displacements simultaneously. Inverse Solution to Axises Relative Vector Displacements. When calculating every axis relative vector displacement from origin state, the CNC machine configuration shown can be considered simply as 5 axises configuration like other jewelry-making CNC machine. Because Axis X, A, and M01 are symmetry with Axis D, E and M0 respectively and the workpiece is a rotational part, Axis M01 and M0 have no influence on calculation. Only calculation of Axis X, A, B, C and Z or Axis E, D, B, C and Z are required. Most postprocessors of special CAM system are based on the workpiece feature technologies[3], and involve inverse kinematics calculation using homogeneous coordinates transformation[4,5,6]. Here, we can simply transform and calculate the inverse solution without homogeneous coordinates: according to the shape of ellipsoid workpiece and motion mode of the mechanical axises, we use following expressions to deal with the inverse kinematics. Fig.3 shows the bead s XOZ plane projection in the workpiece coordinate system. Point O is the origin. Point P1(x1,y1,z1) is the actual machining point on the workpiece surface, every mechanical axis relative vector displacement can be calculated as follows: The projection equation can be expressed as:

4 Fig. 3. Bead s XOZ plane projection in the workpiece coordinate system (z m) c x + a = 1, () Where c is semi-major axis of ellipsoid and a is semi-minor axis. The vector distance PZ calculated by () is: x = a [ c (z m) ] c 1. (3) The vector angle on the point P between the X-axes positive direction in the workpiece coordinate system to the tool 1 movement trail line cc is: (z1 m) a θ = arctan( x c ), π π θ (, ). (4) x in (4) is determined by (3), and it can be inferred that: Axis Z s relative vector displacement is: ( l+ OZ' ) = (l + z1 + x tan θ). (5) l is set by operators, which is related to the start point of cutter location. Because the tools can t move along the Z-axes direction, and the workpiece can do this, Axis Z s relative vector displacement symbol is negative. After the workpiece moves along the Z-axes direction, the machine s Axis B rotating center has became Point z from Point s. Then if we choose tool 1 to machine the Point P, Axis B s relative vector displacement is θ. Axis X s relative vector displacement is: ( CZ' x cos ) = θ ( CS x ) cosθ, (6) where CS is set by the operator. Axis C s relative vector displacement is figured out by (7):

5 y1 = arcsin x c, c [ π, π]. (7) Axis A s relative vector displacement is determined by the cutting direction according to the pattern. If Point P is in the fourth quadrant of the XOZ plane, the x value symbol is opposite to the gotten x by (3). If we use the number tool, the formulas of getting every Axis B, Z, D, C s displacement is similar to the referred Equation (4), (5), (6) and (7). Program Design. Algorithm flow charts of these two modules are shown in Fig. 4 and Fig. 5: The calculation in tool path planning module consists of two main parts. One is the CL point calculation using inverse kinematics introduced in the previous section, and the other is the pattern s theoretical cutting result calculation according to the tool s geometric dimension and process parameters. The development of NC program generation module also includes two main parts. One is the reading and saving of files and filtering fields of the data for all records, the other is the interpreter programm, which interprets the CL point data in ASCII format as the corresponding NC program code. CL point data obtained from calculated CL data files imported Extract a set of CL data Interpret this set of CL data using interpreters Call the generation function of NC framework program Call the NC program generation function of corresponding elementary pattern Extraction finished N Y Save NC program end Fig. 4. Algorithm flow chart of tool path planning module Fig. 5. Algorithm flow chart of NC program generation module Process Simulation Module. This module not only realizes the function of compiling the existing NC program but also offers operators the edit box to manually input NC program. Further, the module provides the interpreter of the NC program corresponding with the graphics programming of tools cutting motion. In the meantime, operators could see the simulation of the machining process.

6 Fig.6 shows the pattern graphic modeling flow and Fig.7 shows the design of tools cutting process simulation flow. The tools cutting process simulation could be well performed by OpenGL double buffering drawing pictures and model transformation. For the reason of quick development s requirement, the patterns on the bead s surface are shown with surface visual effect to help workers analyse the pattern, instead of scraggy visual effect. Fig. 6. Flow chart of pattern modeling Fig. 7. Flow chart of cutting process simulation In the cutting process simulation module, it involves the NC program complier, which effectively checks the error of NC program, filter and interpret the needed NC program into the corresponding simulation animation. Experimental Results In this section, the simulation results and actual results of machining the pattern 米 on a ellipsoidal bead s surface using the designed CAM system for our designed jewelry-making machine (Fig.8) are shown in Fig.9 and Fig.10. In addition, other patterns machined by the proposed CAM system are also exhibited in Fig.11.

7 Fig. 8. The Jewelry-making CNC machine Fig. 9. The simulated 米 pattern Fig. 10. The machined 米 pattern Fig. 11. Other machined patterns From the simulation and experimental results, we can see it is successful to machine the workpiece with the designated pattern with the developed CAM system. Conclusions This paper presents the development of a CAM system for a jewelry-making CNC machine. The system consists of five main parts:workpiece definition module, machining parameters module, tool path planning module, NC program generation module, and process simulation module. The experiments validate that the CAM system design is successful, and it will help to improve the producing efficiency and product uniformity in the jewelry industry. Acknowledgements This research was surpported by the Shenzhen Science and Technology Development Project (CXZZ ), and Guangdong Introduced Leading Talents project as well as Shenzhen Fundamental Research Project(No.JC A). References [1] Yang P.,Chen L.l. et al,computer-aided prosthetic socket manufacturing system based on an advanced manufacture technology, Journal of Clinical Rehabilitative Tissue Engineering Research,Vol.13,No,May 8,009 [] Fugui Wang,Computer aided manufacturing system for Sheet metal,journal of Textile Machinery, 1994, 6. [3] Zhang, H., Zhao, F., Ai, C., & Ze, X. (008, June). The CAM system research of sawing and milling machining center for PVC profile based on feature technologies. In Intelligent Control and Automation, 008. WCICA th World Congress on (pp ). IEEE. [4] My, C. A. (010, October). Integration of CAM systems into multi-axes computerized numerical control machines. In 010 Second International Conference on Knowledge and Systems Engineering. [5] Bohez, E. L., Makhanov, S. S., Munlinb, M., Phien, H. N., & Tabucanon, M. T. (009). On 5-axis freeform surface machining optimization: vector field clustering approach. International Journal of CAD/CAM, 5(1). [6] Makhanov, S. S., & Ivanenko, S. A. (003). Grid generation as applied to optimize cutting operations of the five-axis milling machine. Applied numerical mathematics, 46(3),