Development of Canned Cycle for CNC Milling Machine

Transcription

1 Development of Canned Cycle fo CNC Milling Machine S.N Sheth 1, Pof. A.N.Rathou 2 1 Schola, Depatment of mechanical Engineeing, C.U SHAH College of Engineeing & Technology 2 Pofesso, Depatment of mechanical Engineeing, C.U SHAH College of Engineeing & Technology Abstact Despite the temendous development in CNC pogamming facilities, linea and cicula cuts paallel to the coodinate planes continue to be the standad motions of moden CNC machines. Howeve, the inceasing industial demand fo pats with inticate shapes cannot be satisfied with only these standad motions. The popotion of pats which ae not coveed by the standad CNC motions is cetainly gowing, due to the inceasing industial demand fo inticate shapes. So fo that we have decided to develop a new CANNED cycle with the help of MACRO (paametic) pogamming on Hypo cycloid, combined EP-hypo cycloid cuve and last fo Bezie suface also. we found that this canned cycle would be useful fo diffeent application such as cycloidal speed educe, lobe pump oto and suface milling without equiing extenal aangement like CAD modeling, CNC intepolato etc. Keywods CANNED cycle, MACRO (paametic) pogamming, Hypo cycloid, EP-hypo cycloid, Bezie suface, cycloidal speed educe, lobe pump oto. 1. INTRODUCTION In poduct development, stages such as conceptual design, pototype making, CAD model constuction, tooling design, etc. ae involved. Eithe fowad engineeing o evese engineeing can be employed. In geneal, in fowad engineeing, a 3D solid model of a poduct is fist designed in a CAD platfom and CAD infomation is obtained. Then coesponding tool-path infomation is geneated and the poduct is poduced using an appopiate manufactuing pocess, such as CNC machining. Howeve, in evese engineeing, geometical infomation is needed to be obtained fom a physical shape diectly and this infomation is conveted into a computable fomat fo othe downsteam pocesses. In most cases, a digitizing device is used to get the data and the output data is usually a set of scatteed points (called a point cloud). Due to the chaacteistics of the digitizing device, the point cloud can be divided into two main types a egula point cloud and an iegula point cloud. In the fome, intevals between adjacent digitizing points ae identical while they ae not in the latte. No matte which type of point cloud is obtained, suface fitting techniques ae usually applied and a suface model is constucted. Based on the suface model, CAM tool-path infomation is geneated accodingly. This pocedue is temed as an indiect machining pocess and the technologies fo fitting sufaces onto a point cloud ae essential. Howeve, suface fitting pocess is usually time-consuming. The tool-path infomation can be achieved diectly fom the point cloud. But, this two technique (fowad & evese) equied making much extenal aangement and so moe money and time. Why we ae not going to use available intenal facility? It means in CNC machine thee is a facility of pogamming the tool path accoding to the equied shape of job and fo that we can use combination of linea, cicula and cuvatue tool path. [1] The aw data could, in a simple case, consist of coodinate fo points which should be connected with staight lines o second degee cuves fulfilling cetain conditions of smoothness. Regadless of complexity, howeve, the tanslation should esult in data fo the complete path in the fom of piecewise epesentation of mathematical cuves. The cuve data obtained fom the tanslato is to be conveted into small unit steps along the fixed axes. This pocess is also known as intepolation. [2] 2. TOOLS TO BE USED Since the advent of the compute, the demand fo complex shapes has been met by constantly upgading the shape geneating capabilities of CNC systems and by developing sophisticated CAD/CAM pocessos, capable of educing complex geometies to long seies of linea cuts. Thus, if a paticula shape cannot be pogammed diectly with the standad CNC motions, it is fist lineaized with the help of a CAD/CAM system, which then encodes the esult automatically into an executable NC pogam.[3] The development and incopoation of tool path geneatos into CNC systems, based on efficient and accuate cuve tacing methods, capable to satisfy the inceasing industial demand fo machining complex shape pats is an impotant goal in the field of computeaided manufactuing. Anothe fequent demand is met in the field of suface machining. A lot of sculptued sufaces as ae the cases of molds, stamping dies, foging tools, olling shapes, etc., ae defined as evolved sufaces with fee-fom pofiles. Despite the paticulaity in the definition and the design of these sufaces the available CAM systems deal with them as with fee-fom sufaces. That is, a sequence of staight lines is used to appoximate the pat suface and voluminous data descibing them must be sent to the CNC machine. [4] Fo boundaies fomed at the intesection of highe degee o fee-fom sufaces, an accuate solution of the bounday machining poblem has hitheto been consideed to be beyond the powe of taditional cuve tacing methods Although elated topics as ae geneal suface intesection methods, poblems aised on suface/ suface intesection and bounday epesentation methods have been extensively addessed by seveal authos. [5] 71

2 Paametic pogamming, mathematical calculations with do-loop suboutines, maco-capabilities and sophisticated canned cycles ae among the stengths of the last CNC geneation lessening the use s dependence on CAD/CAM. Despite this temendous development in pogamming facilities, howeve, basic motions in a thee axis CNC machine continue to be executed only by 2D o theedimensional (3D) linea and 2D cicula intepolatos. Othe types of motions implemented by appoximating the desied path with staight-line segments ae accompanied with the dawbacks of acceleation deceleation cycles on the machine and consequently machining inaccuacies ae aised with the machining time inceasing substantially. 2.1 An Intoduction to CANNED CYCLE Canned cycles povide a pogamming method of a CNC machine to accomplish epetitive machining opeations using theg/m code language. Essentially, canned cycles ae a set of pe-pogammed instuctions pemanently stoed in the machine contolle that automate many of the equied epetitive tasks. Thei use eliminates the need fo many lines of pogamming, educes the pogamming time and simplifies the whole pogamming pocess. [6] All CNC machining contols come with a set of helpful machining canned cycles. These canned cycles ae executed o called up n by enteing a cetain code togethe with any equied vaiable infomation. Once canned cycle has been defined it emain active until cancelled. Dilling, counte-boing, peck dilling, pocket o slot machining ae all examples of standad canned cycles. Howeve, the standad canned cycles ae limited in numbe and capability, being unable to accommodate the inceasing needs of applications with complex geometies. Example of standad CANNED CYCLE Rough tuning cycle: G71 Once the caned cycle has been defined it emains active until cancelled. In othe wod evey time a block has axis movement pogammed, the machining opeation of the canned cycle is active also. Multiple function ae defined as a seies of function which allow a machining opeation to be epeated along a given path. The pogamme will select the type of machining which can be canned cycle o model suboutine. These functions must be defined evey time they ae used. The pogamming of canned cycle is eadily available in the contolle of the NC/CNC machines fo fom activating and geomety. Howeve fo some unknown geomety fo which canned cycles ae not available inpaticula contolle, some can be developed. Milling machine with paticula set of diffeent bounday unde egula manne demands development of new canned cycle. 2.2 Maco pogamming Maco pogamming povides a means of shotening code and doing epetitive tasks easily and quickly. All of you canned cyclesin a contol ae nothing but a maco. Maco is also extemely useful fo families of pats. Repetitive opeations can be made simila to using a sub pogam, but a maco will allow you to change conditions without having to edit multiple lines of code. Vaiables ae used in place of coodinate numbes in the pogam. Vaiables ae expessed in the pogam by a numeical value peceded by the pound sign #100, #500. Values can be input manually into a vaiable egiste Values can also be assigned via the NC pogam #510=1.5, #100=#100+1 Vaiables Can Only be Mathematical Quantities (numbes) Pogam flow function We need to undestand some pogam flow (contol) functions befoe we do ou mathematics because we need some of these functions to quickly pefom the mathematics. These ae the thee most commonly used: IF [compae1 {function} compae2]- GOTO[block]: The if-then statement is a conditional jump. If the statement is tue then the GOTO command is executed and a pogam jump is pefomed. If the statement is false, then pogam flow continues with the next block. Thee ae numeous functions available, the most common ae: EQ - (==) Equals NE - (<>) - Not Equal LT - (<) - Less than GT - (>) - Geate than Example: N40 IF [#500 EQ 0] GOTO If vaiable #500 equals 0 then jump to block 900. WHILE [compae1 {function} compae2] DO END: While the compaison is tue, the blocks between DO and END ae epeated, with the compaison checked each time it loops. Example: N10 WHILE [#530 LT 8] DO N40... N50... N60... N70 END N80... So long as #530 is less than 8, blocks N40-N70 ae executed epeatedly. When #530 is no longe less than 8, pogam execution jumps to block N80 and continues. GOTO {block o label}: This is an absolute jump to a diffeent block. In the Siemens contols the commands ae GOTOF and GOTOB depending on which way you want the contol to seach fo the block. (F= Fowad, B= Backwads) Siemens also suppots labels, while Fanuc style does not. Mathematical Functions: Thee ae quite a few mathematical functions available to us fo maco pogamming. Some contols offe moe extensive opeation sets, but I'll stick with the Fanucese standad set fo now. The standad opeational ode of equations fo Fanucese is: Fist: Functions (Tig Functions, etc) Second: Multiplication, Division, AND Thid: Addition, Subtaction, OR, XOR etc. 3. TOOL PATH GENERATION TECHNIQUE Cuves and sufaces ae mathematically epesented explicitly, implicitly o paametically. Explicit epesentation of the fom y = f(x), although useful in many applications, ae axis dependent, cannot adequately epesent multiple-valued functions, and cannot be used whee a constaint involves an infinite deivative. Hence, these ae little used in compute gaphics o compute aided design. Implicit epesentation of the fom f ( x, y) = 0 and f ( x, y, z) = 0 fo cuves and sufaces, espectively, ae capable of epesenting multiple-valued functions but ae still axis dependent. Howeve, these have a vaiety of uses in compute gaphics and compute aided design. 3.1 Paametic Cuves Paametic cuve epesentation of the fom: 72

3 x=f(t); y=g(t); z=h(t); (3.1) Whee t is a paamete, has exteme flexibility. These ae axis independent, epesenting multiple-valued functions having infinite deivatives. These paametic cuves have additional degees of feedom compaed to eithe explicit o implicit fomulations. To see the late point, an explicit cubic equation is consideed. y = ax 3 + bx 2 + cx + d (3.1.1) Hee, fou degees of feedom exist, one fo each of the fou constant coefficients a, b, c, d. Rewiting this equation in paametic fom, x(t)= t 3 + t 2 t y(t)=kt 3 +lt 2 +mt+n (3.1.2) Whee c 1 t c 2 Hee, eight degees of feedom exist, one fo each of the eight constant coefficients,,,, k,l, m, n. Although not necessay, the paamete ange is fequently nomalized to 0 t SELECTION OF CURVE Fo instance tochoidal milling stategies efficient fo industial applications. A tochoidal tool path is defined as the combination of a unifom cicula motion with a unifom linea motion. As a esult, tajectoy adius is continuous, which ceates favoable milling conditions in tems of tool loads and kinematics. Futhemoe, full-immesion milling configuations ae avoided. Nevetheless, tool path length is much highe compaed to standad tool paths such as zigzag because lage potions ae outside the mateial. Tool path intepolation has also a majo influence on the pocess implementation. Thus, tochoidal tool paths ae well adapted to complex milling cases, such as had mateial oughing.[7] Based on geometic design of cycloidal speed educe [8] and lobe pump oto found that hypotochodal cuve is useful fo the same. 4.1 EPTROCHOID Definition and Paametic Repesentation A cuve taced by a point P fixed to a cicle with adius olling along the outside of a lage, stationay cicle with adius R at a constant ate without slipping, whee the point P is at distance h fom the cente C of the exteio cicle. Fig 4.1.1: Epi-tochoid cuve Repesentation Fig 4.1.2: Epi-tochoid cuve geneation The paametic fom of the cuve is X= cosθ + cosθ - h cos R+ θ (4.1.1) Y= sinθ + sinθ - h sin R+ θ (4.1.2) Whee, R= Fix cicle adius (lage) = Rotating cicle adius (small) The deivation of the equation is given in Appendix 4.2 HYPOTROCHOID Definition and Paametic Repesentation 73

4 A cuve taced by a point P fixed to a cicle with adius olling along the inside of a lage, stationay cicle with adius R at a constant ate without slipping, whee the point P is at distance h fom the cente C of the inteio cicle. The name hypotochoid comes fom the Geek wod hypo, which means unde, and the Latin wod tochus, which means hoop. Fig 4.2.1: Hypo-tochoid cuve Repesentation Fig 4.2.2: Hypo-tochoid cuve geneation The paametic fom of the cuve is X= cosθ - cosθ + h cos R θ (4.2.1) Y= sinθ - sinθ - h sin R θ (4.2.2) Whee, R= Fix cicle adius (lage) = Rotating cicle adius (small) The deivation of the equation is same way as Epi-tochoid in Appendix 4.3 Combination of EPTROCHOID and HYPOTROCHOID It is the cuve taced by the two point P1 and P2 fixed to the cicles with adii olling along the outside and inside espectively of a lage, stationay cicle with adius R at a constant ate without slipping, whee the point P1 and P2 is at distance h fom the cente C1 and C2 of the exteio and inteio cicles. Fig 4.3.1: Epi-tochoid cuve Repesentation Fig 4.3.2: Epi-tochoid cuve geneation 74

5 4.4 Altenation of EPTROCHOID and HYPOTROCHOID It is the cuve taced by the two point P1 and P2 fixed to the cicles with adii olling altenately fo one complete evolution along the outside and inside espectively of a lage, stationay cicle with adius R at a constant ate without slipping, whee the point P1 and P2 is at distance h fom the cente C1 and C2 of the exteio and inteio cicles. Fig 4.4.1: Altenate-Combined Epi-tochoid and Hypo-tochoid cuve Repesentation Fig 4.4.2: Altenate-Combined Epi-tochoid and Hypo-tochoid cuve geneation 5. PART PROGRAMMING AND SIMULATION Finally I found that altenate cycle of Combined EPTROCHOID and HYPOTROCHOID is useful fo designing lobe pump oto. So fo that I have decided to develop a new canned cycle with help of maco pogamming. Hee fou teeth lobe oto cutting is pogammed and simulated Maco Pogam: N10 G54 G90 M05 N12 G28 X0 Y0 Z0 N14 M06 T1 N16 G01 Z0 F(FEED) N18 G41 D1 N20 #501=1 N22 #501=1 N23 #11=0 N25 #1=-1.5 N25 #2=1 N26 #21=(FIX CIRCLE DIAMETER) N27 #22=(ROLLING CIRCLE DIAMETER) N28 #24=(ARM LENGTH) N29 #25=0 N29 #28=6 N30 S (SPINDAL SPEED) M03 N32 #27=#21/#22 N34 #23=#21+#22 N36 #26=#23/#22 N40 #1=#1+1 N42 #31=#26*#1 N44 #10=COS[#31] N46 #3=#10*#24 N48 #13=COS[#1] N50 #4=#13*#23 N52 #14=SIN[#1] N54 #5=#14*#23 N56 #9=SIN[#31] 75

6 N58 #6=#9*#24 N60 IF [#501 LT 0] GOTO68 N62 #7=[#4-#3] N64 #8=[#5-#6] N66 IF [#501 GT 0] GOTO72 N68 #7=[#4+#3] N70 #8=[#5-#6] N72 G01 X#7 Y#8 Z#25 F150 N74 IF [#501 LT 0] GOTO78 N76 IF [#1 LT [360/#27]*#2] GOTO34 N77 IF [#1 GT 360] GOTO100 N78 #501=-1 N80 #23=#21-#22 N82 IF [#502 LT 0] GOTO88 N84 #502=-1 N86 #2=#2+1 N88 IF [#1 LT [360/#27]*#2] GOTO36 N89 #501=1 N90 #502=1 N92 #2=#2+1 N96 IF [#1 GT 360] GOTO100 N98 IF [#1 LE [360/#27]*#2] GOTO34 N100 N101 #27=#21/#22 N102 #501=1 N104 #502=1 N106 #2=1 N108 #1=-1.5 N110 #11=#11+1 N111 #25=# N112 IF [#11 LT #28] GOTO34 N114 G01 Z5 F150 N116 G01 X0 Y0 N118 M30 5.1: Fou Teeth lobe pump oto Tool-Path Fig 5.2: Fou Teeth lobe pump oto 76

7 Fig 5.3: Fou Teeth lobe pump oto Tool Path Fig 5.4: Fou Teeth lobe pump oto Unassigned G code can be adopted to specify tool paths and associated fedeate functions. A block citing the pepaatoy function G contains one o moe wods that communicate infomation on the geomety and tavesal ate of a cuve. Many of the identifies have established meanings within conventional G code pat pogams e.g., angula dimensions about the coodinate axes fo A, B, C; spindle speed fo S; tool selection fo T; fedeate fo F; and seconday dimensions paallel to the coodinate axes fo U, V, W.G blocks be modal i.e., they specify values that will emain in effect until supeseded by wods of the same type in subsequent G blocks [9] 6. CONCLUSIONS In the pesent wok, a CANNED Cycle FOR lobe pump oto has been developed with the paametic pogamming technique using Maco Pogamming. A tool path geneation pogam has also been developed and Simulated in CIMCO Edit v7.0 simulation softwae. Developed canned cycle is useful to poduce any numbe of teeth of lobe pump oto with input of some key paamete of the cuve. To make n teeth of lobe pump oto take compession atio (R/)=2n Selection of adii is depends upon the size of oto Selection of step value decides the smoothness and accuacy of the cuve. Developed CANNED Cycle can be called with G65 at any stage of pat pogamming with input of some key paamete like adii R and, speed, feed etc 7. APPENDIX Deivation of Epi-tochoid paametic equation: As the point C in Fig tavels though an angle ϴ, than its x-coodinate is defined as x= (Rcosϴ -cosθ) and y-coodinate is defined as y= (Rsinϴ - sinθ). The adius of the cicle ceated by the cente point is (R-). As the small cicle goes in a cicula path fom 0 to 2π, it tavels in a counte-clockwise path aound the inside of the lage cicle. Howeve, the point P on the small cicle otates in a clockwise path aound the cente point C. As the cente otates though an angle ϴ, the point P otates though an angle φ in the opposite diection. The point P tavels in a cicula path about the cente of the small cicle and theefoe has the paametic equations of a cicle. Howeve, since ϕ goes clockwise, x= h COSϕ and y=-h SINϕ. Since the inne cicle olls along the inside of the stationay cicle without slipping, the ac length ϕ must be equal to the ac length Rϴ. ϕ=rθ ϕ=rθ/ Howeve, since the point P otates about the cicle taced by the cente of the small cicle, which has adius (R-), ϕ is equal to (R-) ϴ /. Theefoe, the equations fo a hypotochoid ae X= cosθ + cosθ - h cos R+ θ Y= sinθ + sinθ - h sin R+ θ 77

8 7.1 OTHER DEVELOPED CANNED CYCLE HYPOTROCHOID POCKET: The most popula method fo machining a two-dimensional (2D) pocket is the contou-paallel offset method. Contou-paallel machining' is used to efe to pocketing with contou-paallel tool paths. Howeve, we should note that the poductivity of contoupaallel machining is mainly dependent on the tool path inteval, because an incease in the tool-path inteval bings a decease in the total length of the tool paths. Fo die-cavity pocketing, contou-paallel machining is the most popula machining stategy. [10] The geneation of offset cuves is a fundamental and well-known poblem in CNC machining. The pogammed path is the tajectoy of the cutte cente (CNC milling) o the cente of the cutte s ounded tip (CNC tuning), while the machined contou is the envelop of successive cutte positions. The pogammed path is thus offset fom the given contou by the cutte adius o the cutte s tip adius and we ae faced with the poblem of geneating the offset as a eal time tajectoy. [11] Fig 7.1.1: Hypo-tochoid Pocket BEZIER SURFACE Fo geneating a smooth movement in NC machining, paametic cuve intepolato has been developed since 1990s. The input of paametic intepolato is a pogammed tool path associated with an off-line o eal-time scheduled fedeate, and fom this a sequence of efeence commands fo the sevo-contolle can be outputted to coodinate the motion of each dive axis simultaneously. [12] But without equiing extenal aangement like CAD modeling, CNC intepolato etc, we can geneate equied tool path. Paametic pogamming helps to geneate Bezie suface. So fo that I have developed canned cycle fo the same. Fig 7.1.2: Bezie Suface 78

9 REFERENCES 1. Biplab kanti halda: CNC Tool Path Geneation Fo Fee Fom Suface Machining, Thesis submitted in Faculty of Engineeing and Technology, Jadavpu Univesity PER E. DANIELSSON, MEMBER: Incemental Cuve Geneation, IEEE TRANSACTIONS ON COMPUTERS, VOL. C-19, NO. 9, SEPTEMBER Sotiis L. Omiou.,: Space cuve intepolation fo CNC machines, Jounal of Mateials Pocessing Technology 141 (2003) Elsevie. 4. Sotiis L. Omiou, Antigoni K. Baouni: Integation of new pogamming capabilities into a CNC milling system Robotics and Compute-Integated Manufactuing 21 (2005) , 2004 Elsevie. 5. Sotiis L. Omiou: A CNC intepolation algoithm fo bounday machining Robotics and Compute-Integated Manufactuing 20 (2004) , 2003 Elsevie. 6. Sotiis L. Omiou, Andeas C. Neachou: An epitochoidal pocket A new canned cycle fo CNC milling machines, Robotics and Compute-Integated Manufactuing 25 (2009) Elsevie. 7. Matthieu Rauch, EmmanuelDuc, Jean-YvesHascoet: Impoving tochoidal tool paths geneation and implementation using Pocess constaints modeling Intenational Jounal of Machine Tools & Manufactue 49 (2009) Elsevie. 8. Yii-Wen Hwang, Chiu-Fan Hsieh: Geomety Design and Analysis fo Tochoidal type Speed Reduces: with conjugate envelopes, No. 05-CSME-59, B.LC. Accession 2911, Rida T. Faouki, Jaiam Manjunathaiah, Guo-Feng Yuan: G codes fo the specification of Pythagoean-hodogaph tool paths and associated feedate functions on open-achitectue CNC machines, Intenational Jounal of Machine Tools & Manufactue 39 (1999) , 1998 Elsevie. 10. S.C. Pak, B.K. Choi: Uncut fee pocketing tool-paths geneation using pai-wise offset algoithm, Compute-Aided Design 33 (2001) , 2000 Elsevie. 11. Sotiis L. Omiou: A locus tacing algoithm fo cutte offsetting in CNC machining, Robotics and Compute-Integated Manufactuing 20 (2004) 49 55, 2003 Elsevie. Yuwen Sun, Yang Zhao, Yuong Bao, Dongming Guo: A novel adaptive-fedeate intepolation method fo NURBS tool path with dive constaints, Intenational Jounal of Machine Tools & Manufactue 77(2014)74 81, 2014 Elsevie 79