Advanced method of NC programming for 5-axis machining

Transcription

1 Available online at Proceia CIRP (0 ) th CIRP Conference on High Performance Cutting 0 Avance metho of NC programming for 5-axis machining Sergej N. Grigoriev a, A.A. Kutin b, V.V.Pirogov c * a Department of High-effective Machining echnologies, State echnological University SANKIN, Vaovsy per., Moscow 7994, Russia b Department of Manufacturing Engineering, State echnological University SANKIN, Vaovsy per., Moscow 7994, Russia c Department of Manufacturing Engineering, State echnological University SANKIN, Vaovsy per., Moscow 7994, Russia * Corresponing author. el.: ; fax:. aress: aa@stanin.ru. Abstract his paper presents a metho to simultaneously increase the accuracy an ecrease the calculation time for complex tool path programming in multi-axis machining centers. Examples of complex parts requiring such complex tool paths inclue various ins of turbine blaes, pump-forcing augers, teeth surfaces, etc. It explains the creation of topological structures on the basis of analytical spline curves with floating range efinitions. he metho for tool path calculation accommoates the specific requirements for multi-axis milling. he algorithms evelope are the founation for the CAD/CAM software that allows for NC programming an machining on 5-axis centers employing any esign moel. Inustrial tests reveal a 70-80% reuction of NC programming time of parts with complex surfaces, reuce machining time of approximately 40-50% using basic high-spee cutting methos an custom-mae tools. he avance methos of NC programming result in substantially increasing machining accuracy. 0 he Publishe Authors. by Publishe Elsevier BV. by Elsevier Selection B.V. an/or Selection peer-review an/or peer-review uner responsibility uner responsibility of Prof. Konra of Professor Wegener Konra Wegener Open access uner CC BY-NC-ND license. Keywors: NC programming, multi-axis milling, CAD/CAM software, machining accuracy. Introuction Recently, computer capabilities have substantially increase the programming spees which in turn enable a 90% reuction of machining time for components using a variety of methos [, ]. However, implementing high spee an multi-axis machining in manufacturing requires new software for complex surfaces. At the same time, evelopers continuously improve an evelop more elaborate proucts that cause aitional ifficulties in manufacturing. hese problems cannot be solve by using toay's mainstream algorithms. As an example, consier a turbine wheel with blaes of ouble curvature (fig ). In orer to increase the exerte force of the wheel, esigners have ouble the number of full an truncate blaes. hus blae thicness has ecrease. Real machining time of such a wheel shoul be ouble, but actually time of manufacturing has increase almost 0 times. Previously the machining time of one channel too hour, but with the new esign 6 hours an 0 minutes is require. his is cause by: using the tool of smaller iameter reuce the fee rate from 00 mm/min to 80 mm/min; the introuction of aitional operations because of reuction of blae thicness resulte in a high level of material removal, resulting in increase part eformations. For machining time reuction, high-spee cutting an new technological methos of multi-axis milling are require. his has require the evelopment of new methos of NC programming to increase accuracy an spee of tool path calculation he Authors. Publishe by Elsevier B.V. Selection an/or peer-review uner responsibility of Professor Konra Wegener Open access uner CC BY-NC-ND license /j.procir

2 Sergej N. Grigoriev et al. / Proceia CIRP ( 0 ) choice of value of number N: N max( nx, ny, nz) (4) Proceeing from the accepte equations () an (3), the general computing structure can be written: Fig.. urbine wheel with change blaes. Use of topological structures for the creation of mathematical moels for 5-axis machining Increase of accuracy an geometrical complexity of moern proucts emans further evelopment of software for 5-axis programming of CAM systems. Calculations show that for an increase in the accuracy of approximation 0 times, the calculation time increases 00 times. Because these problems arise uring tool path moeling, permanent moel recalculation is necessary an time for such recalculation is very long. he generalize equations for efinition of a curve as an analytical spline are [3]: C( x y z nx ( a x + ( a cos( + b sin( ) 0 ny ( a y + ( a cos( + b sin( ) 0 nz ( a z + ( a cos( + b sin( 0 ) () Consier () from the point of view of algorithmic maintenance of functions of a mathematical moel. Having obtaine the general computing metho for all ins of curves, matrix proucts are the most convenient way for the settlement base of the software. he sets of factors, namely a vector factors a () an a vector of factors b (3) can be etermine as: a c 0 ( a x 0, a y 0, a z 0 ) a c ( a x, a y, a z ) acn ( axn, ayn, azn b c 0 (0,0,0) b c ( b x, b y, b z ) bcn ( bxn, byn, bzn ) ) () (3) N C( a c + ( a c cos( + b c sin( 0 ), (5) where N max( nx, ny, nz). Having generate matrixes of factors as vectors of N - measurement an having mae the amenment which maes /, insie of a vector a co, can be etermine: Ac ( a c, a c,, acn ) Bc ( b c, b c,, bcn ) ( a, ac x 0, a y 0, a z 0 ) (6) For a settlement part vectors of N- - measurement cosine an sine: (cos(,cos( 4π,,cos( N π (sin(,sin( 4π,,sin( N S (7) From (6) an (7) the common mathematical structure of calculations can be obtaine: C( ac + ( Ac Cc) + ( Bc Sc) Having etermine (8) as the mathematical basis for calculation of geometrical parameters of curves on all part moels, is possible to inclue all settlement algorithms on all elements in a parallel moe. Forming vector matrixes C c an S c, an further, using their scalar multiplication with vector matrixes A c an B c an amening on a vector a c it is possible to calculate all eges insie a cycle an on all cycles simultaneously. Such a moe of calculations allows a reuction number of repeate operations to the least amount of the same eges in part moel. As a result the real gain in time of calculation will be approximately 80 per cent. It enables the process of preparation of computing structures A c an B c for the curves. Representation for a surface base on u an v curves can be presente as follows: (8) Logically to apply a rule of the maximum factor for

3 04 Sergej N. Grigoriev et al. / Proceia CIRP ( 0 ) 0 07 S( (9) x( y( z( n ( a x0 c x0 a x0 )) + (( a + v( c a )) cos( u) + ( b b )) sin( u) n ( a y0 c y0 a y0 )) + (( a + v( c a )) cos( u) + ( b b )) sin( u) n ( a z0 c z0 a z0 )) + (( a + v( c a )) cos( u) + ( b b )) sin( u) ocumentation an moels resulting from esign process. his in of initial information is the basic for machining moeling. he ientification of similar tass is realize in the special program moules execute together with program complex -Flex CAD/CAM 0.0 [4, 5]. For emonstration of parameters an the operations which are carrie out by these moules consier an example of NC programming for parts with spatially complex surfaces (SS). he spatial complexity of surfaces of consiere parts is etermine by the following features (fig. ): where a x l ( )cos( ) ; b x l ( )sin( ) c xr( )cos( ) ; xr( )sin( ), 0; nx 3. Creation of topological moel of surfaces association for tool path calculation he create moel of tool path calculation is focuse on 5 axis milling with an opportunity of the parametrical issue of technological parameters. he share of five-axis milling among other ins of metal machining increases every year. However, alongsie with requirements of machining for one set up without change of technological bases, there are also a number of essentially new problems. All these problems can be ivie on three basic groups: obtaining the maximal machining spee an reuction in machining time; reuction the number of technological operations ue to the increase of accuracy of the intermeiate stages of machining; increasing machining accuracy of a prouct to meet customers. All these tenencies shoul to be taen into account aequately uring process planning. hus, the CAD/CAM system within which NC programs are being create, shoul escribe precisely part geometry, have flexibility for the tas of relative position of the tool an worpiece an also be able to tae into account features of cutting process. hus, in the system structure shoul be taen of features governing all electronic Fig.. Example of spatial complexity of surfaces. Geometrical complexity. Parts will consist of surfaces of ouble curvature an smooth interfaces specifie by the hyroynamic or aeroynamic analysis of parts specifications. his oes not allow tool path calculations on a basis of linear transitions on the similar contours. It is necessary to tae into account coorinates of each point on a surface an the irections of normal to them for the exact calculation of coorinates of the position an inclination of the tool. It is also necessary to tae into account continuity up to the secon erivative at least, in orer to be able to analyze the change of curvature from one set point to the other.. echnological complexity. Some parts have a relative positioning of surfaces that is resulting in the formation of "shaow zones an narrowing. he technological effect of cutting tool sliing from the surface can also result in the surface being cut off. In this case it is necessary to set position of the tool to exclue the contact of peripheral part of the tool with other surfaces. 3. Joint geometrical an technological complexity which is a ratio of the geometrical sizes of a part

4 Sergej N. Grigoriev et al. / Proceia CIRP ( 0 ) elements (for example, the height an thicness of blaes), an also a transition point of base forming surfaces result in a non-uniform istribution of rigiity along all machining surfaces. Various sizes of the pliability of a part o not allow cutting force to be constant which in turn maes it impossible to achieve constant technological parameters such as cutting epth, fees etc. his maes it necessary to provie continually variable technological parameters uring NC programming. he -Flex CAD/CAM system inclues specialize algorithms, which allow taing into account these features. he preliminary stages of parametrical processing are the functions which carry out calculation of the base areas of efinitions of each surface forming tool path. For use of this algorithm it is necessary to mae a 3D contour on the basis of limiting sies, an then to procee to the tas of geometrical parameters for NC programming. Consistent choice of a part moel an specifying it, irecting the 3D path of the top contour an limiting the 3D path of the bottom contour enables the efinition of a geometrical component of tool path. he further steps of calculation are the following: the surfaces limite to chosen ways, by software combine in a uniform surface; equiistance is esigne to a surface an isplacement is etermine by the raius of the tool; epening on type of the chosen passes, it is possible to obtain a set of close coils of a tool path in which each point goes from a constant component on V const: "loop" or "zigzag", or on a coil, where each point will go with a constant epth an a component on V V+V, which is a spiral line with constant step of epth (where V stans for isoparametrical line). his not only obtain a cutting tool path with precisely certain position, but also taes into account the form of the limiting contours which set the form of passes. It allows at a part manufacturing stage to tae into account its functional features. he avantages of this metho of efining cutting tool movement when machining a spiral trajectory are as follows:. Continuous an constant material removal.. Machining time is etermine by cutting process. Auxiliary transitions from one height on another are exclue an there is no necessity to upating of surfaces interfacing the basic geometrical elements. 4. Calculation of the cutting tool path in five-axis milling It is possible to attribute various parametrical ways to set off an avancing angle, parametric item milling an parametric efinition of an allowance to the features of 5-axis milling. rue part geometry influences the correct calculation of the cutting tool position. For correct ajustment of the equipment uring five-axis machining, NC programs are usually positione on the center line of the cutting tool. However, while manufacturing on machine tools, the surfaces quality epens on cutting parameters, an also from angular position of the tool. his gives the highest importance to a metho for ealing with corners an also of their efinition concerning the current area of movement of the tool. One more question at the esign of algorithms is that the angles of an avancing tool, which are epenent on the machine-tool. For the calculation of avancing angles in -Flex CAD/CAM system there are some opportunities of efinition of the inclination of the tool:. Avancing angles are set as an inclination lengthways an perpenicularly to a irection of movement;. he inclination of the tool is set by a focusing metho; 3. Avancing angles are as ual equiistance. In this case the axis of the tool passes through corresponing points on two spatial curves (fig. 3). Fig. 3. An example of esigning a focusing curve tool path. he first curve is a movement of the center of the tool sphere. he secon curve is a spatial line receive by transformation of the first curve to the following sequence. Vector etermines equiistant shift of a line in a irection of a normal to the initial surface. Vector sets the size of rise of the shifte path, relative to the flat

5 06 Sergej N. Grigoriev et al. / Proceia CIRP ( 0 ) 0 07 sie of the part. hus the obtaine secon curve is similar to the first, an the inclination of the tool taes into account the irection of a normal at a point of contact of the tool an the moel. Such an approach allows setting of a constant angle of the tool inclination to a machine surface in a irection perpenicular to tool movement, instea of starting position of the tool on a path that istinguishes this way from traitional approach. 5. Position milling Machining is conucte on the five-axis equipment with the fixe angular coorinates ue to linear movement. he moule 5D-zone Milling of CAD/CAM -Flex system supports simultaneous use of position an five-axis machining uring tool path calculation. In a ialogue moe it is possible to set ranges an values of change of avancing angles. he range is etermine parametrically as an interval of length of the first chosen path. In case of ventilating wheels machining the following characteristic zones (fig. 4) has been establishe:. Lateral blae surfaces - three-axis milling with fixe in-angle coorinates (3D+D);. Rouning surfaces five-axis milling (5D). From the technological point of view the optimal machining is coorinate 3D milling an forming of spiral path by 5-axis machining. During tool path calculation there is an opportunity to ecrease the influence of machine tool ynamic components on prouct quality. his is achieve by the ability to smoothly vary the fee rate in all coorinates an by elimination of sharp path trajectories, which is especially important for machining of thin wall structures. Fig. 4. An example of a five-axis milling Scanner consists of ental 3D-camera, a 3D-camera holer an 3-coorinate table with linear coorinates an angular coorinate. he ental moel is locate on a coorinate table. Moving of a ental moel allows registering an reconstructing of its separate parts. hen separate reconstructe surfaces of the ental moel are unifie by the software. Dental CAD/CAM system inclues the following units: Scanner; Software for woring with scanner an restoration moeling; NC milling machine, (fig.5); Software for woring with the NC milling machine. 6. Examples using of the evelope methos in ental CAD/CAM systems Last years fast rates began to be evelope in ental practice CAD/CAM systems for moeling the teeth an their manufacturing on multi-axis CNC estop machine tools. 3D-Software is use to moel restoration. he ental CAD/CAM-system inclues the scanner. he scanner is opto-mechanical evice for non-contact optical measurement of ental moel surface. Fig. 5. Wor area of the ental CNC milling machine he main characteristics of such a system are:

6 Surface measurement accuracy 5 m; Restoration manufacturing 40 m; NC programming time is 0 minutes. ime of restoration manufacturing is less than 30 minutes. Size of CNC milling machine mm; Weight of CNC milling machine is less than 50 g. Sergej N. Grigoriev et al. / Proceia CIRP ( 0 ) Summary Woring with specialize CAM moules a minimum quantity of geometrical elements is necessary for a choice of machining strategy, which is impossible to carry out, using the stanar approach of moeling in CAM-system. It allows more than half NC programming time reuction for machining of components with complex surfaces, ue to improve tool path calculation capacity. For maintaining geometrical accuracy of machine parts, the process of tool path calculation is necessary in orer to obtain a continuous moel with the use equiistant surfaces that allows increasing accuracy of machining. In the CAM-system the basic criterion of technological flexibility is the opportunity for tool orientation epening on technological features of machine part. hus it is possible to use all of the avantages of five-axis machining on CNC machine tools. Maintenance of the set of machining accuracy an minimization of efective proucts is solve at two stages of the path calculations removal of trajectories in the mile of an amission fiel an the account of a variable pliability of a etail in two irections. References [] Bringmann B., Maglie P. A metho for irect evaluation of the ynamic 3D path accuracy of NC machine tools. Annals of CIRP, 009, v.58, i., p [] Bua E., Oztur E., unc L.. Moeling an simulation of 5-axis milling processes. Annals of CIRP., 009, v.58, i., p [3] Symplectic Geometry an opology, 008, 44 p., ISBN [4] Kutin A. CAM -Flex became reality: SAPR I Graphia, 9, 999, (in Russian). [5] Kutin A., Weigle E. High Spee Machining an CAD/CAM echnology, Human Resources Development Institute, South Korea.,00. [6] Grigoriev S.N., Kutin A.A. Innovative evelopment of high-tech manufacturing on the basis of computer integrate systems./ Automation an moern technologies,. [7] Kutin A.A., urin M.V. he structural optimization criterion of the complex parts manufacturing process in mechanical engineering. Journal of manufacturing engineering, 0, 0, ISSN