Increasing of part cutting surface quality by tool path optimization.
Key words: milling, CAM, tool paths, Delphi, software application, optimization
Lot of current software products from CAD area deals with problems of milling. There is though few typical ways of tool motion over the machined surface. These characteristic projections of common geometrical shape to the surface of milled area are called manufacturing strategies. These paper deals with importance of selection of suitable milling strategy, it investigate possibilities to improve the assumptions for right selection and thus it comes to optimization of milling strategies in creation process of NC programs and sequences.
Importance of area of milling strategies lies in revealing and using the space for making the milling more technological and economic. Selection of milling strategy can affect final roughness of milled surface. From the viewpoint of additional technological operations there is also chance to affect level of undersurface residual stresses. Greatest and most logical change though can be achieved in value of time that is necessary for machining of milled surface. This paper deals with simple but effective form of software support of suitable milling strategy selection while considering machining time as its evaluation criterion. It brings the information on creating user and hardware undemanding program that realizes calculations of length of tool trajectories for milling with use of different strategies and selects best one from the viewpoint of time. It describes basic input and output characteristics of program. In the end it also deals with application possibilities of program. It considers further improvements and reserves in area of improving the applicability of program in preparation phase for milling of complex surfaces and shapes (Gots et al., 1995).
2. CAM SUPPORT OF MILLING STRATEGIES
Complex soft-ware products from the field of computer aid of manufacturing include in their CAM modules lot of effective tools for optimization of creation of manufacturing sequences. Systems like Pro/Engineer, NX or Catia many years belong to most known and most used in their area. Beside these software there are special CAM systems used in many companies for their better price. Their group grew rapidly in last few years. Examples can be seen in SurfCAM, EdgeCAM and PowerMill. All these programs provide the creator of manufacturing sequences with possibility to affect milling strategy, although only few of them explain (anyway partially) reasons of realized selection. NC programmers could use simple additional application that would on base of basic dimensional parameters of machined surface select suitable way of tool motion.
In are of milling strategies different software products use different names. Although geometrical references of particular trajectories are very similar or very same. For verification of possibility of creation helpful application there were three most used strategies with their usual names selected:
[FIGURE 1 OMITTED]
In strategy of raster type the tool moves along parallels in lengthwise direction while these parallels are connected with transverse value of side step. With box strategy the tool copies the contour of milled surface in successive miniatures connected with trajectory of side step. Spiral Strategy represents set of uncrossing lines or a curve that in spiral way directs from border of contour to its center or contrariwise.
3. SOFTWARE APPLICATION FOR SELECTION OF MILLING STRATEGY
Working name of program is MISTRA, what is abbreviation of milling strategies. It was created in programming environment Delphi from Borland company. It is software building tool that uses syntax of original Pascal language in environment with classical object programming. On the form that represents the window of future application there are objects allocated (buttons, images, editable fields) between which there are action relations or calculations defined. After receiving the input data from user the program is able to realize computations for length of tool trajectories and necessary machining times (Marcincin & Janak, 2008).
After starting the program and removing first screen by clicking the user may choose one of four buttons on the left side so the shape character of machined surface is set. Next he moves to the editable fields for input values of the program:
* Dimension of machined surface.
* Tool diameter and parameters of cutting process (feed rate, side step).
Together with the dimensions of machined surface user can also select whether it is machining of pocket of straight machining of planar surface. This difference then starts or stops keeping of characteristic circle of tool inside the contour of machined shape (Krimpenis et al., 2005).
[FIGURE 2 OMITTED]
Finally after clicking on last button computation is realized for lengths of tool trajectories and corresponding time intervals. In the same time there are trajectories graphically displayed on output panel in from of three different strategies. User is provided with quick chance to check the suitability of existing strategy from the viewpoint of time that is needed for milling.
Situation on figure 2 with use of gauge presents surface with dimensions 180 x 130 mm. Tool diameter was 12 mm, feed rate was 250 mm.min-1, side step over was 10 mm. Final time difference after using strategies spiral and raster is almost 2 minutes. For real removing of layer with thickness of 6 mm and with setting of parameter of maximal thickness of material after one pass to value of 2 mm this time difference would be over 5 minutes. With large numbers of manufactured elements/parts spiral strategy could provide great time savings and influence economical efficiency of production.
4. PROGRAMMING AND COMPUTATIONS OF MISTRA APPLICATION
Basic condition for good application running is defining of objects and their properties and creation of right relations between particular objects allocated on programming form of program. These factors affects the look of application and its chronological functionality.
Most important part of creation of computing application from the viewpoint of content is assuring the problem free run of program- prevention from possibility of unwanted failure or cycling freeze down while preserving utilization of proper calculation methods.
[FIGURE 3 OMITTED]
Calculation and displaying of tool trajectories are achieved by combination of programming cycles with focus to determination of level of repeating of certain geometrical shape in the frame of projected strategy and consecutively stopping of trajectory generation after reaching that repeat level. On the base of running these cycles in necessary repeat number also the final output value of tool trajectory is cumulated, while particular geometrical segments of that trajectory are calculated thanks to known geometrical equations. Example of using the combination of cycle is on Fig. 3. There is part of cycle realizing drawing of tool trajectory for milling with raster strategy. After good input setting of it value, that represents the repeat number, and after its changing until meeting the critical condition of reaching relevant geometrical border the cycle then stops with defined surface being machined (Edling et al., 2002).
Possibility of quick check on suitability of milling strategy belongs to tools for increasing production efficiency from the viewpoint of time and therefore also from economical saving in manufacturing. In field of commonly used CAM systems there is gap in that area. This paper describes one attitude to software solution of these problems via newly created software application. User of CAM product can use it as handy additional software for selection between available milling strategies. This application should be helpful also for users that still realize workshop floor-programming (Norton, 2009).
Space for improving the functional attributes of MISTRA program is in area of more complex surfaces and shapes created for example after joining 4 basic types included in operational version of program. Another possibility of innovation lies in future database of value of residual stresses that are assumed after milling with different strategies. Involvement of this factor though supposes wide series of tests so results can be used for building such program database.
Manufacturing strategies and their righteous choice represents the areas with necessity of further development. Better solutions in that area contribute to ensuring higher productivity of manufacturing.
Ministry of Education, Science, Research and Sport of SR supported this work, contract VEGA No. 1/0036/09, KEGA No. 047-004TUKE-4/2010 and ITMS project 26220220125.
Edling, H.; Harrison, A.K.; Kirkwood, D.; Bauer, H. (2002). Addressing Surface Error Problems Found when Using Multiple Axis Milling for the Manufacture of Turbine Impellers. The International Journal of Advanced Manufacturing Technology, Vol. 19, No. 3, p. 180-185
Gots, I.; Zajac, J.; Vojtko, I. (1995) Equipment for measuring the degree of wear to cutting tools. Technisches Messen, Vol. 62, No. 1, 1995, p. 8-11
Krimpenis, A.; Fousekis, A.; Vosniakos, G.. (2005). Assessment of sculptured surface milling strategies using design of experiments. The International Journal of Advanced Manufacturing Technology, Vol. 25, No 5-6, p. 444-453
Norton, R. L. (2009) CAM Design and Manufacturing Handbook, Industrial Press, Inc., New York, NY, ISBN 9780-8311-3367-2
Marcincin, J. N., Janak, M. (2008). Software Realisation of Proposal for Computer Aided Selection of Suitable Milling Strategy. In: Proceedings of the 12th International Conference Trends in the Development of Machinery and Associated Technology. Istanbul, 2008, p. 365-368
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|Author:||Novak-Marcincin, Jozef; Janak, Miroslav; Kocisko, Marek; Barna, Jozef|
|Publication:||Annals of DAAAM & Proceedings|
|Date:||Jan 1, 2011|
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