The Influence of Technological Parameters on the Properties of Castings Produced by the Vacuum Assisted Pressure Die Casting Method

Transcription

1 A R C H I V E S of F O U N D R Y E N G I N E E R I N G Publshed quarterly as the organ of the Foundry Commsson of the Polsh Academy of Scences ISSN ( ) Volume 15 Specal Issue 1/ /1 The Influence of Technologcal Parameters on the Propertes of Castngs Produced by the Vacuum Asssted Pressure De Castng Method A. Zyska*, Z. Konopka, M. Łągewka, M. Nadolsk Department of Foundry, Częstochowa Unversty of Technology, Al. Arm Krajowej 19, Częstochowa, Polska * Correspondng author. E-mal address: zyska@wp.pcz.pl Receved ; accepted n revsed form Abstract The paper presents the results of nvestgatons concernng the mechancal propertes of the AlS9Cu3 alloy castngs n correlaton wth the most sgnfcant parameters of the vacuum asssted hgh pressure de castng technology. Experments were desgned and carred out accordng to the 2 3 factoral desgn. There were found the regresson equatons descrbng the nfluence of the plunger velocty n the second stage of njecton, the de temperature, and the njecton temperature on the tensle strength and the unt elongaton of the examned alloy. It was found that the man parameter affectng the ncrease n mechancal propertes s the plunger velocty n the 2 nd stage of njecton. The hghest mechancal propertes of castngs ( exceedng 280 MPa, and at the level of 9%) are acheved (n the examned range of changes) for the plunger velocty n the second stage of njecton equal to 4 m/s, the de temperature of 210 C, and the njecton temperature of 640 C. Keywords: Innovatve foundry technologes, Alumnum alloys, Vacuum asssted hgh pressure de castng, Mechancal propertes of pressure castngs 1. Introducton Hgh pressure de castng (HPDC) s the one of the most effectve castng technologes and t s appled for mass producton of the hgh qualty castngs made of alumnum, magnesum, and znc alloys, as well as of the low-meltng alloys. Pressure castngs are charactersed by the excellent smoothness of the raw surface, the hgh dmensonal and shape accuracy, and good mechancal propertes. The advantages of the HDPC technology nclude also the refned structure of castngs, the defect-free surfaces, small machnng allowances, the possblty of obtanng the ntrcate thn-walled castngs, and the low producton costs [1-4]. The man defect occurrng n pressure castngs s ther gas porosty, and as far as castngs of ntrcate geometry are concerned both the shrnkage and the gas porosty. The presence of blowholes n castngs s related to the character of lqud metal flow durng the frst and the second stages of fllng the pressure de. Durng the frst stage, an occluson of gaseous phase present n the njecton sleeve takes place, whle durng the second phase the ar trapped n the de cavty s occluded or absorbed. The artght walls of the metal de along wth a very short njecton tme result n the mnmal effectveness A R C H I V E S o f F O U N D R Y E N G I N E E R I N G V o l u m e 1 5, S p e c a l I s s u e 1 / ,

2 of cavty ventng. Moreover, the hgh plunger velocty n the second phase of njecton causes the turbulent flow of metal and the compresson of the gaseous phase n the de cavty [4-6]. As a result, the soldfed castng contans a large amount of hghly dspersed blowholes [6, 7]. Ths man defect of pressure castngs not only prevents them from beng appled under the condtons of elevated temperature, but also precludes ther thermal treatment and restrcts the possblty of ther machnng to a very narrow range. Varous solutons are used n order to lmt the porosty of pressure castngs: there can be appled the mult-phase njecton systems, whch allow to control both the plunger velocty and the ntensfcaton pressure by means of modern dgtal systems [8, 9], or the atmosphere of actve gases can be generated n the de cavty [1, 2, 6]. One of such solutons s also the applcaton of the lowered pressure to the de cavty whle t s flled wth molten alloy [1, 2, 7-13]. Ths method can be employed for producton of the hgh-qualty castngs of alumnum, magnesum, znc, and copper alloys. Its broad perspectves of applcaton are suggested by the results of several reports [7, 10, 11, 14-16]. Applcaton of the negatve (relatve) pressure n the de cavty causes that the porosty of castngs drops down to the level occurrng n squeeze cast castngs [15]. The presented method, as compared wth the conventonal HPDC process, requres some changes n the constructon of the de and some adjustments n workng parameters, concernng both the njecton system and the cavty fllng [7, 11-13]. Ther proper selecton gves defnte economc profts due to the rsen mechancal propertes, the reducton of castng wall thckness, the mprovement n the process stablty, the prolonged pressure de lfe, the reduced quantty or even total elmnaton of overflows, the reduced values of njecton velocty and pressure, the possblty of achevng pressuretght and weldable castngs, whch can work n elevated temperature wthout the rsk of surface deformaton because of the expanson of gases contaned n vods [7, 12-14, 16]. Takng the above nto account, a comprehensve study was undertaken concernng the optmzaton of technologcal parameters for the vacuum asssted HPDC producton method. The presented work was amed to determne changes n the mechancal propertes of AlS9Cu3 alloy castngs wth respect to the changes n the pston velocty n the second stage of njecton, the changes n the njecton temperature, and n the de temperature. The ntal optmzaton of varables was carred out accordng to the 2 3 factoral desgn. 2. Methods and results of nvestgaton The expermental nvestgaton was carred out for castngs made of standardzed AlS9Cu3 alloy (EN AB or DIN 226). The castng process was performed on the cold chamber vertcal pressure de castng machne VERTACAST 400. A modfed njecton system was used, and the machne was also equpped wth a vacuum system consstng of a vacuum pump and vacuum valves, n order to remove the ar contaned n the mould cavty and the njecton sleeve. The vacuum system was connected to the ventng system n a way preventng the flow of metal nto the vacuum system. The system constructon allowed to control both the pressure n the de cavty and the rate of fllng the de wth molten alloy. The VERTACAST machne was equpped wth the horzontally parted two-cavty pressure de desgned for castng soleplates of clothes ron (Fg. 1). A castng selected for examnaton should meet the requrements adequate for tems workng wthn the range of elevated temperature, exceedng 100 C. The good qualty of castngs, and partcularly ther low gas porosty, s the man crteron of ther acceptance. Eght njecton sequences were carred out n order to determne the nfluence of negatve pressure n the de cavty on the mechancal propertes of castngs, a seres of castngs beng produced durng each of them. Fg. 1. The examned cast soleplate of clothes ron The optmzaton studes were planned and carred out accordng to the 2 3 factoral desgn applyng the followng ndependent varables and ther ranges of change: Table 1. The ndependent varables and ther ranges of change The ndependent varable, X Centre pont, Range of X 0 change, X X 1 plunger velocty n the 2 nd stage of njecton, m/s 3 1 X 2 de temperature, C X 3 njecton temperature, C Two quanttes descrbng the mechancal parameters of castngs were assumed as the dependent varables (responses): the tensle strength and the unt elongaton. The codng of varables was done accordng to the followng formula: x X X 0 X The realsed expermental desgn s presented n Table 2 n detals. It ncludes all combnatons of varables at the lower and the upper level. For each pont of the desgn the same number of equvalent measurements were taken. The followng quanttes were accepted as constant durng the experment: total volume of castngs (two soleplates cast together) wth gatng system and overflows, equal to V 0 = 373 cm 3 ; the dameter of the njecton plunger, d k =58 mm; the plunger velocty n the frst stage of njecton, v k1 =0.3 m/s; the (relatve) negatve pressure n the de and n the shot sleeve, p = 0.5 atm.; tme of molten metal sucton through the feed tube, t Z = 18 s; (1) A R C H I V E S o f F O U N D R Y E N G I N E E R I N G V o l u m e 1 5, S p e c a l I s s u e 1 / ,

3 the degree of njecton chamber fllng, equal to 60%; the machne clampng force, N z = 2000 kn, the total area of gates for both soleplate castngs, equal to Σf W = 2 75mm1.5mm = 225 mm 2 ; the average castng wall thckness d = 5 mm. The examnatons concernng the mechancal propertes of castngs were carred out for the standardzed tensle bars wth length-to-dameter rato of 5:1, accordng to the PN-EN :2001 Standard, by means of the ZWICK-1488 testng machne. The data obtaned from the test were used to determne the characterstc quanttes, (Table 3) for specmens representng all the combnatons ncluded n the desgn of the experment. Table 2. The appled desgn of experment Independent varables Plunger velocty n the 2 nd stage of njecton X 1 De temperature X 2 Injecton temperature X 3 Centre pont Range of change Upper level (1) Lower level (-1) Symbol of coded varable x 1 x 2 x 3 Experment No Table 3. Average results of tensle strength and unt elongaton of the EN AB alloy Exp. No. Tensle strength, MPa Standard devaton ( ), MPa Elongaton Standard devaton ( ), %, % The factoral desgn appled durng the experment gves a possblty of determnaton of the ncomplete quadratc equaton descrbng the nfluence of the ndependent varables (plunger velocty n the second stage of njecton, de temperature, and njecton temperature) on the tensle strength and the unt elongaton of the EN AB alloy castngs. The general form of the equaton s as follows: ˆ b b x b x x (2) y 0 j j where: b 0, b, b j regresson coeffcents, x ndependent varables, x x j nteractons of the ndependent varables. The results of the strength and the elongaton measurements were statstcally elaborated, fndng frst the varances of expermental data, next the values of the regresson coeffcents, whch were n turn assessed wth respect to ther statstc sgnfcance, then the adequacy of the regresson equatons was checked. These calculatons allowed to fnd two equatons whch descrbe the average tensle strength and the average unt elongaton for the examned ranges of ndependent varables: ˆ X1 3 X X R (3) m X1 3 X A X ˆ The equaton 3 ndcates that the tensle strength depends n a lnear manner on all of the examned parameters of castng producton, and s most strongly nfluenced by the plunger velocty n the 2 nd stage of njecton and the de temperature. The regresson coeffcents standng by the successve examned varables reveal that the nfluence of the plunger velocty on the value s four tmes as large as the nfluence of the njecton temperature, and by 30% greater than the nfluence of the de temperature. The nfluence of the examned ndependent varables on the tensle strength of castngs s presented n Fgure 1. The postve values of coeffcent by the x 1 and x 2 ndcate that an ncrease n these parameters leads to the ncrease n tensle strength, whle the negatve value by the x 3 denotes ts correspondng decrease. The lack of the nteractons x 1 x 2, x 1 x 3, x 2 x 3 n the equaton 3 means that they are statstcally nsgnfcant. The analyss of the obtaned relatonshp (3) and the curves n Fg. 1 also reveals that an ncrease n plunger velocty n the 2 nd stage of njecton by 1 m/s results n the ncrease n by about 13 MPa, and an ncrease n the de temperature by 30 C leads to the growth n by about 10 MPa. On the other hand, the rse n the njecton temperature equal to 30 C causes the drop n the tensle strength whch amounts to about 4 MPa. (4) 166 A R C H I V E S o f F O U N D R Y E N G I N E E R I N G V o l u m e 1 5, S p e c a l I s s u e 1 / ,

4 Tensle strength, MPa Unt elongaton, % (X 1 ) (X 2 =180, X 3 (X 2 =3, X 3 (X 3 =3, X 2 =180) X 1 - Plunger 2.8 velocty, 3.2 m/s X 2 - De temperature, C X Injecton temperature, C 700 Fg. 1. The nfluence of the plunger velocty n the 2 nd stage of njecton, the de temperature, and the njecton temperature on the tensle strength of EN AB alloy castngs (X 1 ) (X 2 =180, X 3 (X 2 =3, X 3 (X 3 =3, X 2 =180) X 1 - Plunger 2.8 velocty, 3.2 m/s X De temperature, C X Injecton temperature, C 700 Fg. 2. The nfluence of the plunger velocty n the second stage of njecton, the de temperature, and the njecton temperature on the unt elongaton of EN AB alloy castngs It also results from the equaton 4 that the unt elongaton lkewse depends on all the examned parameters of producton of the castng, and the most sgnfcant nfluence comes from the plunger velocty n the 2 nd stage of njecton. The plunger velocty affects the unt elongaton of the alloy almost three tmes as much as the njecton temperature, and by 50% stronger than the de temperature. For that case the lnear coeffcents b 1, b 2 are also postve,.e. the unt elongaton s drectly proportonal to the respectve varables they stand by, and the coeffcent b 3 s negatve. An ncrease n the plunger velocty n the 2 nd stage of njecton results n an ncrease n elongaton by about 1%, the rse n the de temperature by 30 C causes the growth n the value by about 0.7%, and an ncrease n the njecton temperature by 30 C results n the drop n the unt elongaton of about 0.3% (Fg. 2). 4. Fnal conclusons 1. The applcaton of the 2 3 factoral desgn allowed to determne the regresson equatons descrbng the changes n mechancal propertes of the EN AB alloy castngs n relaton to the technologcal parameters of the castng process. 2. The tensle strength and the unt elongaton of the EN AB alloy castngs depend on all the ndependent varables n ther examned ranges of change. 3. The man parameter affectng the mechancal propertes of castngs s the plunger velocty n the 2 nd stage of njecton. The obtaned relatonshps ndcate that an ncrease n the plunger velocty n the 2 nd stage of njecton by 1 m/s rses by about 13 MPa, and by about 1%. 4. The hghest mechancal propertes ( exceedng 280 MPa and at the level of 9%) are acheved for the plunger velocty n the 2 nd stage of njecton equal to 4 m/s, the de temperature of 210 C, and the njecton temperature of 640 C. References [1] Perzyk, M. Waszkewcz, S. Kaczorowsk, M. Jopkewcz, A. (2000). Foundry. Warsaw: WNT. (n Polsh). [2] Górny, Z. Sobczak, J. (2005). Non-ferrous metals based novel materals n foundry practce. Cracow: Za-ps. (n Polsh) [3] Bonderek, Z. Chromk, S. (2006). Pressure de castng of metals and njecton moldng of plastcs. WN Akapt. (n Polsh). [4] Bałobrzesk, A. (1992). Pressure de castng. Machnery, equpment and technology. Warszawa WNT. (n Polsh). [5] Dańko, J., Dańko, R. & Stojek, J. (2008). Cognsable effects of model nvestgatons of de castng processes. Archves of Foundry Engneerng. 8, [6] Bałobrzesk, A. (2002). Specal de castng technologes. Foundry Research Insttute. Cracow. (n Polsh). [7] Nu, X.P., Hua, B.H., Pnwlla, I. & Lb, H. (2000). Vacuum asssted hgh pressure de castng of alumnum alloys. Journal of Materals Processng Technology. 105, [8] Belecka, A., Konopka, Z., Zyska, A., Łągewka, M., (2007). Investgaton of pressure de castng of the alumnum alloy matrx compostes wth SC partcles. Archves of Metallurgy and Materals. 52, [9] Bałobrzesk, A., Słowk, P. Wojtarowcz, A. (1984). Research determnng the desrablty of Vacuum asssted hgh pressure de castng. Work program, order 7087/I, II. Foundry Research Insttute. Cracow. (n Polsh). A R C H I V E S o f F O U N D R Y E N G I N E E R I N G V o l u m e 1 5, S p e c a l I s s u e 1 / ,

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