IOP Conference Series: Mterils Science nd Engineering PAPER OPEN ACCESS Effect of High-speed Milling tool pth strtegies on the surfce roughness of Stvx ESR mold insert mchining Relted content - Reserch concerning optimum cutting prmeters ccording with tool pth strtegy for finishing procedures A E Pen, F D Anni nd M Zpciu To cite this rticle: A. Mebrhitom et l 216 IOP Conf. Ser.: Mter. Sci. Eng. 114 126 View the rticle online for updtes nd enhncements. This content ws downloded from IP ddress 46.3.22.198 on 23/12/217 t 21:
Effect of High-speed Milling tool pth strtegies on the surfce roughness of Stvx ESR mold insert mchining Mebrhitom A. 1, Rizun D 1., M. Azmir 1 nd M.Nssif 1 1 Fculty of Mnufcturing Engineering, University Mlysi Phng, 266 Pekn, Mlysi E-mil: mebrhitom@ump.edu.my Abstrct. High speed milling is one of the recent technologies used to produce mould inserts due to the need for high surfce finish. It is fster mchining process where it uses smll side step nd smll down step combined with very high spindle speed nd feed rte. In order to effectively use the HSM cpbilities, optimizing the tool pth strtegies nd mchining prmeters is n importnt issue. In this pper, six different tool pth strtegies hve been investigted on the surfce finish nd mchining time of rectngulr cvities of ESR Stvx mteril. CAD/CAM ppliction of CATIA V5 mchining module for pocket milling of the cvities ws used for process plnning. Keywords: CAD/CAM, CATIA, High speed mchining, Inserts, tool pth strtegies, Surfce finish 1. Introduction High speed mchining (HSM) is one of the promising technologies which re typicl for reduced mchining time by pplying smll side nd down step combined with high spindle speed nd feed rte. It hs been used in the mchining processes of moulds nd dies which require high surfce finish nd geometric ccurcy. However, it ws only the spindle speed, cutting speed nd other cutting prmeters tht hve been the subject of previous reserches [1, 2]. Due to the high mrket demnd nd competition, mould nd die mkers re fcing the stringy requirement to meet the customers expecttions in terms of surfce qulity. Mchining Stvx ESR (AISI 42 modified) used for mold insret is topic of gret interest in plstic industries nd scientific reserch [1]. It is corrosion resistnt mold steel, with very good polishbility. For exmple, STAVAX plstic mold stinless steel is one of the mold mterils tht ply n essentil role in the forming nd shping processes due to its high hrdness, toughness, corrosion resistnce, nd wer resistnce [2]. The precision nd the surfce qulity of the mold re the primry concerns becuse they directly ffect on the ppernce of the plstic products. Min pplictions cn be found s insert mteril for blow molds inserts with demnds on high surfce finish nd where low mintennce is needed. A high proportion of production costs re involved in mchining, s lrge volumes of metl re generlly removed nd finishing cuts must meet strict work piece surfce roughness nd dimensionl ccurcy requirements. As such, the use of high speed milling (HSM) for the production of moulds nd dies is becoming more widespred. Significnt dvntges of HSM re high metl removl rtes, good surfce finish since high cutting speed voids built-up edges, low cutting forces, miniml work piece distortion, lbour reduction by unttended mchining [3], reduced prt counts into monolithic component, bility to mchine thin-wlled sections nd simple fixturing. Other dvntges include product repetbility, improved ssembly techniques, comprble 1 mebrhitom@ump.edu.my. Fculty of Mnufcturing Engineering, University Mlysi Phng, 266 Pekn, Mlysi Content from this work my be used under the terms of the Cretive Commons Attribution 3. licence. Any further distribution of this work must mintin ttribution to the uthor(s) nd the title of the work, journl cittion nd DOI. Published under licence by Ltd 1
mss nd reduced production costs. To chieve significnt impct on overll mchining efficiency nd process relibility, the selection of cutting tools, cutter pth strtegies nd mchining prmeters is criticl [4-6]. In pocket milling there re minly two tool pth strtegies clled contour prllel nd direction prllel which re used to generte some fetures [6]. The contour prllel tool pths re generted by successive offsets of input profiles wheres, the direction prllel pth line segments re prllel to n initilly selected reference line. Any of the tool pth strtegies do hve the effect on the mchining time, cutting forces, length of tool pths nd surfce roughness. Due to the need for high performnce mchining of free form surfces with optimized CNC, ppliction of CAD/CAM softwre hs become vitl for the design nd process plnning. In this pper, CATIA softwre ws used for generting the process pln to mke pocket. Three types of tool pth strtegies were used to study the effect on the surfce roughness of the mchined surfce. 2. Experimentl procedure 2.1 Work piece mteril nd tooling The work piece mteril used in this experiment ws Stvx stinless tool steel. It is premium grde stinless tool steel with nominl composition of.38% C,.9% Si,.5% Mn, 13.6.% Cr,.3% V nd Fe blnce. Prior to milling process, the work piece ws wire electro dischrge cut in rectngulr shpe of 1x6x3 mm 3. A 4-flute ultr-fine grin solid bulls end mills were used coted with monolyer (Al,Ti)N film with thickness of bout 2.5 lm. The cutter hs dimeter of 6 mm, helix ngle of 45 nd rdil rke ngle of 14. 2.2 Equipment setup The experimentl studies were performed on 3-xis verticl prismtic high speed mchining centre from Roders RXP 3. This hs continuously vrible speed of 2 2, rpm with mximum spindle power of 15 kw nd vrible feed rtes up to 15 m/min. All mchining tests were conducted dry. In ddition, high-pressure ir blst delivered through nozzle ws directed t the cutting zone for ll mchining tests conducted. For this experiment the spindle, feed rte nd depth of cut were fixed t 7196 RPM, 12.88IPM nd.2 mm respectively. All cutters were checked prior to mchining to ensure tool run out of less thn 1 lm [6]. These were ssessed using dil indictor with resolution of.1 mm [6]. 2.3 Tool pth strtegies using CATIA mchining workbench The chllenge to the CAD/CAM system is to mke psses with very smll stepovers t very high feed rtes. And this must be ccomplished without forcing the tool to mke shrp turns, becuse the lookhed fetures of HSM controls will utomticlly reduce the feed rte when they detect corner pproching. In this work, three of the tool pth strtegies nmely; inwrd helicl, outwrd helicl nd bck nd forth ws used. Helicl or spirll milling s shown in Figure 1, is strtegy divided into two different wy of cutting where in the outwrd the cutter my strt t the center then proceeds spirlly outwrds. In inwrd helicl s shown in Figure 1b, the cutter strts t the edge of the pocket nd proceeds spirlly inwrds. In bck nd forth milling s shown in Figure 1c, the cutter drws zigzg cutter pth by moving bck nd forth cross the work piece in the xy plne. The mchining plnning nd tool pth selection ws used suing CATIA mchining work bench s shown in Figure 2. 2
b c d Figure 1. Tool pth strtegies ()Bck nd Forth (b)inwrd Helicl (c)outwrd helicl (d) Both Inwrd nd outwrd helicl Figure 2. Mchining simultion using CATIA One fctor t time (OFAT) pproch is method in design of experiment where ll the mchining prmeters re kept constnt nd one prmeter hs been fluctuted from minimum to mximum vlues. It is very useful in nlyzing the optimum condition of prmeters, min effect, nd the significnce of specified prmeter to surfce integrity. In this experiment for ech tool pth strtegy, kipping the cutting prmeters constnt, the tool dimeter rtio ws vried from 5-5% t five percent intervl while the mchining time nd surfce roughens (R) ws mesured. The surfce roughness of the mchined surfce of ech specimen ws mesured using Perthometer ZEISS (SURFCOM 13/48 A). Specimens surfce were clened before ny surfce roughness mesurement is done. This is becuse oil sticking on specimen surfce my disturb surfce roughness reding thus producing wrong surfce roughness vlue. The surfce roughness which is mesured by the centrl line verge (R) ws used to ssess the surfce qulity of the mchined surfce. Ech specimen will hve three surfce roughness vlues nd the verge from those three reding ws tken. The microstructure of mchined surfce ws viewed lso by using metllurgicl microscope. Ech specimen is undergoing through this process for ech element tht re mchined for ech tool pth strtegies. 3
3. Results nd discussion In die or mold mnufcturing, the min purpose of high-speed milling is to reduce or even eliminte mnul polishing nd reduce the time for surfce finish mchining. An improved surfce finish cn be chieved through selection of the best tool pth strtegy nd pproprite tool dimeter rtio. Figure 3, 5 nd 7 show the chnge in surfce roughness nd mchining time when used the outwrd helicl tool pth strtegy. The tool dimeter ws vried from 5-5% tool dimeter rtio so tht it covered the whole rnge of psses during mchining. It cn be observed tht s the tool dimeter rtio incresed, the surfce roughness vlue decresed nd the mchining time ws incresed t high rte. This is due to the fct tht, s higher tool dimeter rtio removes smll size of the surfce, cutting forces will be reduced nd hence leding to better surfce finish. The trde-off between the surfce roughness nd the mchining time ws between 2-25% tool dimeter rtio. However, s the surfce microstructure in Figure 4 of the pockets t the different overlp rtio shown, none of this optimum combintion (2-25%) hs the better surfce. The 4% tool dimeter rtio is better smoother tht the optimum rnges of tool dimeter rtio. 11 Tool strtegy: Outwrd Helicl.1 Mchining time (s) 18 16 14 12 1 98 5 1 15 2 25 3 35 4 45 5 Tool dimete rtio (%) Figure 3. Effect of tool dimeter rtio on the mchining time nd surfce roughness using the outwrd helicl strtegy.8.6.4.2 Surfce roughness, R (um) Mchining time( s) Surfce roughness, R(um) b Figure 4. Outer surfce using opticl microscope for the outwrd helicl mchined surfce () overlp rtio t 2% (b) overlp rtio t 3% The effect of inwrd helicl pocketing on the surfce finish vlue nd mchining time is shown in Figure 5. The trend is the sme s the outwrd helicl but the rnge of the optimum percentge for both mchining time nd surfce roughness is bit higher of 5-1 percent. Around the sme percentge of tool dimeter rtio (3%), it showed the lowest surfce roughness smoother surfce s shown in Figure 6. This phenomen my be due to the constnt force pplied lone the inwrd direction of the tool pth. 4
112 Too pth strtegy: Inwrd helicl.12 Mchining time (s) 11 18 16 14 12 1 5 1 15 2 25 3 35 4 45 5 Tool dimeter rtio (%) Figure 5. Effect of tool dimeter rtio on the mchining time nd surfce roughness using the inwrd helicl strtegy.1.8.6.4.2 Surfce roughness, R (um) Mchining time( s) Surfce roughness, R(um) b Figure 6. Outer surfce using opticl microscope for the inwrd helicl mchined surfce () overlp rtio t 2% (b) overlp rtio t 3% The generl trend of the effect of tool pth strtegy on the surfce roughness of the bck nd forth lso showed the sme trend s the previous methods. However, the bck nd forth tool pth showed the lowest surfce roughness nd poor microstructure t ny combintion of tool dimeter rtio compred to the tow methods s shown in Figure 7 nd 8 respectively. This is becuse the bck nd forth tool pth strtegy my not crete stble cutting force long the pths. 5
Mchining time (s) 12 1 8 6 4 2 Tool pth strtegy: Bck nd forth 5 1 15 2 25 3 35 4 45 5 Tool dimeter rtio (%) Figure 7. Effect of tool dimeter rtio on the mchining time nd surfce roughness using the bck nd forth strtegy.25.2.15.1.5 Surfce roughness, R (um) Mchining time( s) Surfce roughness, R(um) b Figure 8. Outer surfce using opticl microscope for the bck nd forth mchined surfce () overlp rtio t 2 % (b) overlp rtio t 3% 4. Conclusions From the experiment, it ws shown tht different tool pth strtegies, with different tool dimeter rtion resulted in to different surfce roughness vlues. Using the inwrd helicl, the finest surfce roughness ws observed better when the tool pth rtio ws 3%. However, this strtegy tkes high mount of time which my incur higher mnufcturing cost for the mold inset compnies. In moulding industry, the most criticl prmeter is cvity nd core insert of the mold surfce finish, hence this experimentl work cn the indictor for selecting the best surfce finish with the type of tool pth strtegy implemented. Acknowledgment This experimentl work ws supported by the RDU13312 grnt from University Mlysi Phng. References [1] Logins, A. nd T. Torims, Procedi Engineering. 1: p. 1253-1261. [2] Mjerik, J. nd J. Jmbor, Procedi Engineering. 1: p. 45-459. [3] Lpez de Lclle, L.N., et l., Journl of Mterils Processing Technology, 22. 123(2): p. 292-32. [4] Brcly, J., V. Dhoki, nd A. Nssehi, Procedi CIRP. 33: p. 49-495. [5] Monrel, M. nd C.A. Rodriguez, Computer-Aided Design, 23. 35(4): p. 395-41. [6] Toh, C.K., Mterils & Design, 25. 26(6): p. 517-533. 6