一种逐步铣削的新型数控机床控制装置@中英文翻译@外文翻译

Int J Adv Manuf Technol (2001) 18:399403 2001 Springer-Verlag London LimitedA New NC Machine Tool Controller for Step-by-Step MillingJ. BalicUniversity of Maribor, Faculty of Mechanical Engineering, Intelligent Manufacturing Laboratory, Maribor, SloveniaThe paper describes the design solution, operation and analysisof a new NC controller for a new step-by-step milling pro-cedure. A step-by-step milling device ensures that the millingof workpieces by end or conical milling cutters, where theratio between the depth of milling a (mm) and the millingcutter diameter D (mm) is greater than 1.5 (a/D H11022 1.5) resultsin the increased wear resistance of the cutting edge. Breakingof the milling cutter is minimised and is not frequent and themilling forces are reduced, which results in smaller deflectionsof the milling tool and higher accuracy of machining. Themachine tool use is better.Keywords: NC machine tool controller; Step-by-step milling1. IntroductionTechnological problems occur when machining some compo-nents using end or conical milling cutters of small diametersat large cutting depths. According to the recommendation oftool manufacturers the depth of milling should be within therange of 11.5 D, where D is the milling cutter diameter.Frequently, the depth of milling required for the manufactureof the parts may be as much as 6D.This problem is particularly severe when machining parts(dies and moulds) with a conical milling cutter (cutting depthsis 4D, conical angle 3 to 6), where rough milling with aspecial rough milling tool is not possible and in the case ofmachining dies (the material of the dies is steel according toDIN 1.23430.4% C, 1% Si, 5% Cr, 1.3% Mo, 1% V), forthe extrusion of aluminium bars, pipes, and beams.2. State of the Art and Existing SolutionsThe state-of-the-art technology in the area of machining offerssatisfactory solutions for almost all types of machining. TheCorrespondence and offprint requests to: Professor J. Balic, Laboratoryfor Intelligent Manufacturing, University of Maribor, Faculty of Mech-anical Engineering, Smetanova 17, SI-2000, Maribor, Slovenia.E-mail: joze.balicL50560uni-mb.simain problem arises when, for the industrial use, it is necessaryto optimise the choice of technological solutions with respectto the manufacturing time, resistance to tool wear, quality ofsurface, geometrical precision and manufacturing costs.The literature contains some solutions concerning this areafor ensuring higher quality of NC milling 111. That literaturecontains discussions of step-by-step milling carried out by toolsof special shapes. For each shape to be made by step-by-stepmilling, a specially shaped tool is used. In this process theprogrammed motion of the tool does not change, only themanufactured shape changes, influenced by the predeterminatedstep shape of the milling cutter. The US patent 12 proposesa very high-speed adiabatic face milling machine. Theefficiency of the chip removal system is such that chip recuttingis nearly eliminated and the tool life is improved. This solutionrequired a new machine tool and a high investment.The above mentioned devices and methods for milling donot include the new solution for step-by-step milling describedin the paper.3. Step-by-Step Milling MethodThe step-by-step milling method features the step motion ofthe milling cutter (f1) in the direction of cutting and the relatedFig. 1. Milling by the step-by-step procedure. a, depth of milling; f1,motion in the direction of machining; f2, motion in the directionopposite to machining; D, diameter of milling cutter.400 J. BalicFig. 2. New tool path generated along the programmed trajectory. f1,motion in the direction of machining; f2, motion in the directionopposite to machining; Pst-t, start-point of the motion trajectory; Pend-t, end-point of the motion trajectory; Pst, start-point of each movementforward; Pend, end-point of each deviation; Pint, intermediate point(end-point of the previous deviation and start-point of the nextmovement).movement of the milling cutter (f2) in the direction oppositeto the cutting direction (Fig. 1) 13,14.4. NC Machine Tool Controller4.1 Description and OperationThe step-by-step NC control consists of an input communi-cation module, a generator of the step code, an appropriatecontrol program, an output communication module and amicroprocessor. The generated path of the milling cutter issuch that a ratio of the depth and milling cutter diameter ofup to 5D is achieved, which cannot be achieved using conven-tionally controlled milling machines.Fig. 3. Flowchart for the generation of a new tool path. 1, reading ofinput NC sentence; 2, start of the block; 3, identification of functionsG17, G18, G90, G91; 4, transformation of the system of coordinates;5, definition of parameters f1 and f2; 6, rapid movement (G00); 7,writing record of NC sentence; 8, end-point of trajectory Pend-t H11021 f1;9, movement to pend-t; 10, generation of movement f1 and f2; 11,writing record of the sentence for approaching and deviation; 12,transformation of coordinates; 13, writing record of the sentence; 14,the last sentence.The device reads the program lines of the CNC programfor a certain product, identifies the desired start-point Pst-t(Fig. 2) and end-point (Pend-t) of the step-by-step machiningprocess and its parameters f1 and f2. The parameter f1 is themotion in the direction of machining, the parameter f2 is themotion in the direction opposite to machining and a is thedepth of cut. The parameters f1 and f2 were determined byextensive tests in the laboratory and in real-time productionand assure all the advantages of step-by-step machining. Theoptimal values found were f1 = 0.20.8 mm, f2 = 0.050.4 mm,and the two parameters must fulfil the condition f1 H11021 f2; thestoppage time Ts= 0.011 s. Then the device transforms thevalues of the current position of the tool so that it correspondsto the desired limit values, and to the requirements of the newstep-by-step milling method.The generated path characteristic of the device, based onthe invention 13,14, is a cyclic repetition of the step motion inthe program trajectory. The tool moves f1 in the predetermined(desired) direction, stops in that position for the valueTs= 0.011 s and then moves f2 in the opposite direction. Thisstep motion is repeated along the specified trajectory of thetool motion.4.2 Computer AlgorithmThe NC controller automatically performs the transformationof the tool motion and coordinates.Fig. 4. Methods of incorporation of the stepbystep controller intothe CNC unit of a machine tool (the layout of the CNC control unitis taken from 15). 1, manual input; 2, input with punching tape; 3,4, decoding; 5, computer; 7, positions memory (x,y,z,. . .); 8, functionsmemory (S, T, M,. . .); 9.1, step-by-step unit (in computer); 9.2, step-by-step unit (before memory); 9.3, step-by-step unit (before NC input);10, interpolator; 11, function execution unit; 12, interpolated data flow;13, comparison unit; 14, 15, conversion unit; 16, CNC unit, 17,position data; 18, measuring data; 19, functions data; 20, machinetool; 21, interface; 22, tacho-generator; 23, stepping (or servo) motor.New NC Machine Tool Controller 401Fig. 5. Workpieces and direction of machining.The computer model of the solution is based on the followingassumptions and requirements:Machining without correction (G40).The programmer programs the NC machining “conventionally”;the start and the end of step-by-step machining are determinedby two records in text form.The program comprises the machining functions G17 and G18.The program recognises all the functions having an influenceon the machining process (G90, G91, G54 G59, G00, G01,G02, G03).Fig. 6. Graphical representation of forces.The program includes simultaneous machining of all threecoordinates (x, y, z).The program changes only the statements inside the markedblock.Renumbering of statement numbers.Creation of output data file.The program contains checking of machining correction.The algorithm of operation for the computer program is shownin Fig. 3. Checking of the deviation from the desired positionsis performed automatically.4.3 Methods of Incorporation into Existing NCControl UnitsThe control can be incorporated onto the milling machine inthree ways (Fig. 4):Into the milling machine tool control unit, between the memoryof positions and the interpolator as shown by position 9.1.Into the NC control unit closely behind the reading-in of datamodule, as shown by position 9.2.Before the NC control unit where it intercepts the input dataof the NC program and suitably processes them, as shown byposition 9.3.5. Experiments and Tests5.1 GeneralTests with the step-by-step device were carried out for millingby the conventional and the new methods. The tests wereexecuted in the laboratory 16 and in the real production oftools for the extrusion of aluminium 17.A horizontal 4-axis machining centre (Heller BEA-05) witha pallet system and a tool magazine was used. Tool clampingwas performed with ISO 50 clamping cones. Machining ofworkpieces was horizontal (G17).A Kistler measuring device for measuring cutting forces wasfixed to the machining centre table. The measuring equipmentand the software used for processing the measurement resultshad been developed at the Faculty of Mechanical Engineeringin Maribor 18, 19.The test material was aluminium AlMgSil (AC30T6 pro-ducers factory designation) and steel with the designationaccording to DIN standard 1.2343.Table 1. Two planned tests for tool wear resistance for aluminiumAlMgSil.Tool Depth Spindle Feed Stepof cut speed (mm min1)(mm) (min1)10 6 20g 20pg1A 15 2000 80 Off1A 15 2000 240 On1A 40 1500 30 On1A 40 1500 20 Off402 J. BalicFig. 7. Deviation of the real shape (dotted line) from the ideal shape(solid line). Conventional milling process: (a) slot 3.1; (b) slot 3.2.Step-by-step milling: (c) slot 6.1; (d) slot 6.2.Table 2. Measuring of surface roughness.Material AlMgSi1Procedure Step off Step onWorkpiece 3.1(break) 3.2 6.1 6.2MeasurementsRa1 4.14 4.28 6.98Ra2 6.10 5.68 4.55Ra3 11.51 5.17 6.80Ra4 4.99 3.73 4.31ResultsRa 6.6850 4.7150 5.6600H9268n 2.8711 0.7579 1.2345H9268n1 3.3152 0.8751 1.4255For machining we selected four types of KESTAG endmilling cutters of cutter material: HSSCo8 (of diameters10 mm, 47mm conical, 20 mm and 20 mm for roughmachining). The depths of milling were 1.5 D4 D. Coolingby emulsion was used. The lengths of cutter paths for eachtest piece were two cuts of 50 mm long.The shapes of the machining and the workpieces are shownin Fig. 5.Fig. 8. (a) Conventional milling; (b) step-by-step milling.The plan of tests for measuring the cutting forces and theselected parameters are given in Table 1. The tests comprisedthe measurements of cutting forces, wear, and resistance towear, of the tool cutting edge, geometrical accuracy of machin-ing, roughness of machined surfaces, and visual analysis ofworkpieces.5.2 Analyses of Cutting ForcesAverage values of the measured Fx, Fy, and Fzwere calculated.Maximum forces were determined and the standard deviationof cutting forces was calculated; then the results were diagram-matically evaluated for the average cutting forces, maximumcutting forces, standard deviation of cutting forces, feeding andcutting speeds (Fig. 6).5.3 Measurement on the 3D Coordinate MeasuringMachineMeasurements of the shapes of the slots were carried out inthe laboratory on a UMC 850 (universal measuring centre) forall workpieces, and then compared with the ideal and/or desiredshape of the slot. A programming package KUMVDA, whichNew NC Machine Tool Controller 403automatically senses the points of the desired curve was used.Figure 7 shows the deviation of the real shape (dotted line)from the ideal shape (solid line) of the slot in the conventionalprocess and when milling with the step-by-step method.5.4 RoughnessThe measurements of the surface roughness were carried outby means of a MITUTOYO SURF TEST 211. The results areprocessed by the mini processor DIGMATIC DP1-HS. Themeasurement results are given in Table 2 and show the differ-ence between the surface roughness in the case of the conven-tional milling process and that of step-by-step milling.5.5 Visual AnalysisThe results of conventional and step-by-step milling can beseen in Fig. 8.6. ConclusionBy using the step-by-step milling device, ratios of the depthand the diameter of the milling cutter of up to 5D wereachieved. These cannot be achieved on conventionally con-trolled milling machines. This method can machine componentswhich previously could not be machined. The research showsthat when step-by-step milling with the same machining para-meters, the cutting forces on the tool cutting edge are smaller,the deflection of the milling cutter is also smaller and thegeometrical precision of machining is greater. These are posi-tive “side” effects of the use of the step-by-step milling device.The device mentioned is particularly useful in the tool andmetal-processing industry where a large removal of material isrequired and the products have complicated shapes. It couldbe incorporated as an integral part in a system for cuttingcondition optimisation 20.References1. A. Klimov, B. Krutov, A. Korolev et al., Face step milling cutter,Patent number: SU1558573, 1990.2. V. Baranchikov, A. Zaharinov, O. Ivashkovich et al., Face stepmilling cutter, Patent number: SU1207651, 1986.3. V. I. Malygin, V. V. Matvejkin, A. D. Shustikov et al., Face andend step milling cutter, Patent number: SU1053983, 1983.4. J. H. Roettger, Milling cutter with step-by-step radially dis-placeable cutting elements, preferably for working wood andsimilar nonferrous metals, Patent number: DE3625234, 1988.5. N. Kuraoka, Step cutting type milling cutter, Patent number:JP58217211, 1983.6. E. Feldcamp, Improvements in or relating to milling machines,Patent number: GR63578, 1979.7. P. M. Coetzee, Milling apparatus, Patent number: ZA8400630,1984.8. M. C. Turchan, Milling system, Patent number: US5803683, 1998.9. H. Pauser, Programme-co