REGRESSIONS MODELING OF SURFACE ROUGHNESS IN FINISH TURNING OF HARDENED 205Cr115 STEEL USING FACTORIAL DESIGN METHODOLOGY

Transcription

1 REGRESSIONS MODELING OF SURFACE ROUGHNESS IN FINISH TURNING OF HARDENED 05Cr115 STEEL USING FACTORIAL DESIGN METHODOLOGY Alexandru STANIMIR, Marius ZAMFIRACHE, Niolae Cătălin EFTENIE University of Craiova Abstrat In this study, in order to find out a mathematial relation of olynomial seond degree tye whih desribe, in finish turning of hardened 05 Cr115 steel, the roughness arameter Ra deendene on utting edge wear, deth of ut, feed rate and utting seed, a fatorial design methodology was used. The exerimental tests were done aording to a omosed, entral, four-fator five-level fatorial rogram. Key words: roughness, hardened steel, finish turning, regression, fatorial design 1. Introdution A large range of omonents enountered in the aerosae defense and auto vehiles rodution are made from ferrous materials thermal treated, where their hardness usual vary between HRC and whih an be dry roessed using olyrystalline ubi boron nitride utting tools. For many of these arts is imosed a high roess reision and a high level smoothness of funtional surfaes. Some researhers have investigated wear harateristis of PCBN utting tools [1,, 5] and the influenes of work material roerties, tool geometry and utting onditions on surfae integrity of the finish-mahined arts [3, 6, 9]. They reorted hallenges in the identifying various roesses, equiment and tooling related fators affeting surfae quality, tool life and rodutivity. Hard turning with PCBN utting tools demand rudent design of exeriment by reason of the lower toughness than other ommon tools materials, thus hiing is more likely. Also PCBN utting tools designed for hard turning feature negative rake angle and a hamfer and/or a hone of the edge. The effet of edge geometry on surfae quality is signifiant [3, 6]. Due to the hanges in roerties of hardened workiee material, hi formation and shearing roess differ in hard turning [11], and the workiee hardness has a rofound effet on the erformane of the PCBN tools [9], and also on the integrity of the finish mahined surfaes [8]. The utting onditions i.e., deth of ut, feed rate and utting seed influene the erformane of PCBN utting tools and the roughness of the finish mahined surfaes. Inreasing utting seed and deth of ut result in inreased temeratures at the utting zone and at elevated temeratures hemial wear of PCBN beomes a leading wear mehanism and often aelerates weakening of utting edge, resulting in remature tool failure, namely edge breakage of the utting tool [9]. In the mahining of hard materials, the rofile of utting edge is transferred to the mahined surfae with reasonable auray. Then, as long as the flank wear is uniform, it does not inrease the surfae roughness [8]. Another arameter that degrades the surfae roughness and tool life is the vibrations. In order to redue tool vibration it is neessary to rovide suffiiently rigid tooling and work iee fixtures. Extremely rigid, high ower and high reision mahine tools are required for hard turning beause PCBN tools are brittle and rone to hiing. It is also suggested that having higher rigidity in mahine tool-laming-tooling system ahieves better surfae quality on the art [9]. 104 Fiabilitate si Durabilitate - Fiability & Durability no 1(7)/ 011 Editura Aademia Brânuşi, Târgu Jiu, ISSN X

2 . Exerimental equiment Workiee material The work iee material used in this study was the 05Cr115 steel, with the hemial omosition resented in the table 1. Table 1. Chemial omosition of 05Cr115 steel C% Mn% Si% Cr% Ni% 1,8..., 0,15...0,450,15...0,3511,0...13,0 0,35 The ylindrial rings 05Cr115 seimen (fig. 1) that are used in this exeriments had a outside diameter of 6 mm, a inside diameter of 53 mm and a length of 16 mm. The seimens were heat treated at HRC. Fig. 1. Workiee Tehnologial system and aaratus The exerimental mahining tests was erformed on a SP630 CNC lathe and the roughness arameter Ra was measured with a Rank Tailor Form Talysurf Series rofilometer. Also solid to PCBN inserts BZ 435 TPGN were used with a Sandvik Coromant CTENR 55M (ISO 5608) tool holder, that give the following tool geometry: K=60º, α=17º, γ=-6º and λ=-6º. In order to mahining the outside ylindrial surfae of the seimens a seial laming system (fig ) was used. 105 Fiabilitate si Durabilitate - Fiability & Durability no 1(7)/ 011 Editura Aademia Brânuşi, Târgu Jiu, ISSN X

3 Fig.. Claming system for workiee 3. Exerimental design In order to establish the seond degree olynomial relationshi oeffiients for the Ra roughness arameter alulus (1) a four-fator five-level fatorial design was used [4], [7], [10]. R a = b0 + b1 + b f + b3 V + b4 + b5 f + b6 V + b7 (1) + b f V + b f + b V + b + b f + b V + b In the table is resented the lanning of the exeriments, where y reresents the resonse to the studied henomena, in this ase Ra, and x 1, x, x 3 and x 4 are the indeendent variables. The five levels of the indeendent variables odified (-), (-1), (0), (1) and () were: - x 1 the utting seed, V=80m/min; 10m/min; 160m/min; 00m/min; 40m/min; - x the feed, f=0,05mm/rev; 0,050mm/rev; 0,075mm/rev; 0,100mm/rev; 0,15mm/rev; - x 3 the deth of ut, a =0,05mm; 0,10mm; 0,15mm; 0,0mm; 0,5mm; - x 4 the flank wear, VB= 0mm; 0,05mm; 0,10mm; 0,15mm; 0,0mm; 0,5mm. Table. The lanning of exeriments Current no. X 1 Indeendent variables levels X X X 4 VB[mm] 14 Y Ra[μm] V [m/min] f[mm/rev] a [mm] 1 00 (1) 0,05 (-1) 0,1 (-1) 0,05 (-1) 0, (-1) 0,05 (-1) 0,1 (-1) 0,05 (-1) 0, (1) 0,1 (1) 0,1 (-1) 0,05 (-1) 0, (-1) 0,1 (1) 0,1 (-1) 0,05 (-1) 0, (1) 0,05 (-1) 0, (1) 0,05 (-1) 0, (-1) 0,05 (-1) 0, (1) 0,05 (-1) 0, (1) 0,1 (1) 0, (1) 0,05 (-1) 0, Fiabilitate si Durabilitate - Fiability & Durability no 1(7)/ 011 Editura Aademia Brânuşi, Târgu Jiu, ISSN X

4 8 10 (-1) 0,1 (1) 0, (1) 0,05 (-1) 0, (1) 0,05 (-1) 0,1 (-1) 0,15 (1) 0, (-1) 0,05 (-1) 0,1 (-1) 0,15 (1) 0, (1) 0,1 (1) 0,1 (-1) 0,15 (1) 0, (-1) 0,1 (1) 0,1 (-1) 0,15 (1) 0, (1) 0,05 (-1) 0, (1) 0,15 (1) 0, (-1) 0,05 (-1) 0, (1) 0,15 (1) 0, (1) 0,1 (1) 0, (1) 0,15 (1) 0, (-1) 0,1 (1) 0, (1) 0,15 (1) 0, () 0,075 (0) 0,15 (0) 0,1 (0) 0, (-) 0,075 (0) 0,15 (0) 0,1 (0) 0, (0) 0,15 () 0,15 (0) 0,1 (0) 0, (0) 0,05 (-) 0,15 (0) 0,1 (0) 0, (0) 0,075 (0) 0,5 () 0,1 (0) 0, (0) 0,075 (0) 0,05 (-) 0,1 (0) 0, (0) 0,075 (0) 0,15 (0) 0, () 0, (0) 0,075 (0) 0,15 (0) 0 (-) 0, (0) 0,075 (0) 0,15 (0) 0,1 (0) 0,39 4. Results and disussion In order to find the values of the oeffiients from the relationshi (1), the exerimental test results were roessed with the Mathad.5 rogram. The relationshi established for the alulus of Ra roughness arameter is: R a = V f V f V [ μm] f V f V f () 107 Fig. 3. Roughness surfae variation with deth of ut and feed rate Fiabilitate si Durabilitate - Fiability & Durability no 1(7)/ 011 Editura Aademia Brânuşi, Târgu Jiu, ISSN X

5 Fig. 4. Roughness surfae variation with utting seed and flank wear In the figures 3 and 4 are resented the grahi diagrams of the relationshi (), made with the Mathematia 5. software, for the doublets a -f, with ommand (3), and V -VB, with ommand (4). The arameters that don t aear on axis were onsidered at the entral value so: V =160[m/min], VB=0,1[mm], a =0,15[mm] and f=0,075[mm/rev]. Plot3D[ * x * y {x,80,40},{y,0,0.}, AxesLabel Plot3D[ * x * y {x,80,40},{y,0,0.}, AxesLabel * x * y * x^ * y^, { " a[ mm] f [ mm / rev] Ra "}] * x * y * x^ * y^, { " V[ m / min] VB[ mm] Ra "}] (3) (4) These diagrams give an eloquent image about the influene of eah fator studied uon the mahined roughness surfaes. So, from figure 3 we an see that the roughness inrease with the feed and resents a minimum with deth of ut variation. And also figure 4 shows that roughness of mahined surfae resent oints of minimum with the utting seed and the wear utting tool flank variation. The maximum roughness, Ra=0,511μm, orresonds to the following exerimental onditions: a =0,15mm, f=0,075mm/rev, V =160m/min and VB=0,mm and the minimum roughness value in this exerimental study is Ra=0,11μm, obtained in the following exerimental onditions: a =0,mm, f=0,05mm/rev, V =10m/min and VB=0,15mm. However the most small values of roughness,5μm were obtained when the flank wear was VB 0,1mm. The alulated minimum of surfae roughness { , {u , x , y , z 186.5}} resulted from the evaluation of the relation () in Mathematia 5. with the relation: 108 Fiabilitate si Durabilitate - Fiability & Durability no 1(7)/ 011 Editura Aademia Brânuşi, Târgu Jiu, ISSN X

6 Minimize[ x y z u x y x z 1.48 x u x z +.15 y u z u x y z u,{ x, y, z, u}] in with are used the following notations : x= a, y=f, z=v and u= VB. This result show that the minimum Ra=0, μm, an be arhived in the following utting onditions a =0,183896mm, f=0, mm/rev, V =186,5m/min and VB= mm. The last value shows that, the best roughness don t orresond to the new tool If the flank wear is uniform, it does not inrease the surfae roughness [11]. 5. Conlusions The established seond degree olynomial relationshi for the Ra alulus as a funtion of the utting onditions and the flank wear aroximate in a satisfatory way the studied henomena. The main influene on the surfae roughness is exerting by the feed rate and flank wear. However, we have to notie that the utting seed and the deth of ut influene indiretly the roughness surfae beause the inrease of this arameters result in inreased hemial wear of PCBN utting tool. Also, the interations of some arameters as feed rate and flank wear have a great influene on the roughness values of the mahined surfae. Referenes [1] Barry J. Byrne G. Cutting tool wear in the mahining of hardened steels. Part II: CBN utting tool wear. Wear 47/001, [] Benga G. Stanimir Al. Wear atterns of olyristalline ubi boron nitride utting tools when mahining hardened bearing steel. Annals of DAAAM for 007 & Proeedings of the 18 th International DAAAM Symosium 4-7 th Otober, 007, Zadar, Croatia, [3] Chou YK. Evans CJ. Barash MM. Exerimental investigation on CBN turning of AISI 5100 steel, J.Mater. Proess Tehnol. 134/003,.1-9. [4] Cohran. W.G., Cox.C.M., Exerimental Design, Willey, New York, [5] Kishawi, H.A., Elbestawi, M.A. Tool wear and surfae integrity during high seed turning of hardened steel, Pro.inst.Meh. Eng. B, 15/001, [6] Matsumoto Y. Hashimoto F. Lahoti G. Surfae integrity generated by reision hard turning, Annals of the CIRP, 48/1/1999, [7] Mihai.R., Introduere in strategia exerimentarii, u aliaţii in tehnologia himia, Editura Ştiinţifia şi Eniloedia, Buuresti 1976 [8] Nakayama K. Arai M. Kanda T., - Mahining arateristis of hard materials, Annals of the CIRP, 37/1/1988, [9] Ozel T. Hsu T.K. Zeren E. Effets of utting edge geometry, workiee hardness, feed rate and utting seed on surfae roughness and fores in finish turning of hardened AISI H13 steel, Int. J. Adv. Manuf. Tehnol. 5/005, [10] Stanimir. Al., Pasu. I., Ivanus. Radu., Exerimental rogram for the determination of seond degree olynomial funtions with four variables used in the alulus of the surfae roughness International Conferene UNIVERSITY S DAYS, 4-6 mai, Tg-Jiu, 00. [11] Stanimir. Al., Pasu. I., Buzatu St. Geonea I., Chi formation and utting fores in the mahining of hardened Rul1V steel, Annals of the Oradea University, 008. (5), 109 Fiabilitate si Durabilitate - Fiability & Durability no 1(7)/ 011 Editura Aademia Brânuşi, Târgu Jiu, ISSN X