OPTIMIZATION OF THE PLASTIC INJECTION PROCESS THROUGH THE MODIFICATION OF THE PROCESS FUNCTIONAL PARAMETERS

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1 OPTIMIZATION OF THE PLASTIC INJECTION PROCESS THROUGH THE MODIFICATION OF THE PROCESS FUNCTIONAL PARAMETERS Teodor - Daniel Mîndru, Ciprian Dumiru Ciofu &, Dumiru Nedelcu Gheorghe Asachi Technical Universiy of Iasi, Faculy Machine Manufacuring and Indusrial Managemen, mindru.daniel@gmail.com Absrac: The paper presens he opimizaion of he plasic injecion process hrough he reducion of he cooling and removing imes. For he deploymen of he experimen he PA 6 polyamide will be used. The SolidWorks and Moldflow sofware packages will be used for CAD and process simulaion, he maerial flow ino he mold, as well. The experimen aims o obain he opimal varian of PA 6 polyamide injecion hrough he modificaion of he mold as well as he mel emperaure in order for he mold filling o be complee and he cooling ime o be as shor as possible, herefore generaing an increase of produciviy. Keywords: cooling channel, flow, mel, mold, emperaure 1. Inroducion In order o plan a plasic injecion process was aken ino consideraion ha he mos imporan echnological parameer is he emperaure of he mold. We may consider ha he process develops under normal condiion only he emperaure of he mold is saionary and may be conrolled. Depending of he plasic maerials used, he injecion molds can be heaed [1]. The plasic injecion process is a cyclic one, formed by several operaions such as: - The gauging [2]; - The heaing and he meling of he maerial in he machine cylinder; - The mold clamping; - The mold charge wih under pressure maerial; - The solidificaion and he cooling of he maerial; - The opening of he mold; - The removal of he injeced piece from he mold. This paper will sudy he injecion operaion as well as he charging and he cooling operaions of he maerial from a mold hrough he opimizaion of he inle emperaures of he injecion process. Cooling of he injeced piece from he maximum value of he emperaure o he room emperaure value is an operaion deermined by he hermal conducibiliy of he plasic maerial. Afer he mold is opened, he cooling operaion coninues. In plasic injecion cycle, he cooling imes are he longes, geing up o 68% of he oal period of he process [2]. The injecion echnology aims o obaining he shores cooling ime possible ha assures he prescribed qualiy of he piece. The figure 1 presens he emperaure variaion inside a plasic componen during he cooling operaion. Figure 1. Temperaure variaion inside a plasic piece during cooling operaion; T c environmenal emperaure, T D mold release emperaure; T r cooling emperaure.[2] 87

2 As a resul of he analysis of figure 1, we may express he calculus formula of he oal ime of he injecion process as: u r d (1) Take ino consideraion he relaion (2): (2) u r d K (3) and replacing relaions (2) and (3) ino relaion (1), his one may be wrien as: K (4) - Cycle ime - Injecion ime u r - Cooling ime d - Time Cleaners K - Consan r 2. Simulaion process, resuls and discussions The cooling sysem of he mold mus be designed according o he overall dimensions of he injeced pars or, as he curren analyzed siuaion, when he injecion is made in caviy disribuion channels, hus obaining six componens, he cooling channels mus cover he enire surface of he model. The piece used for process opimizing is presened in figures 2a and 2b. The figures are realized using he SolidWorks sofware package. d I was considered he cold ype of sprue. The iniial parameers are as follow: - Conical ledge: 23 mm; - Inle diameer: 5 mm; - Oule diameer: 9 mm; - Semicircular runners ype: 10 mm; - Conicalgae: inle diameer 5 mm. oule diameer 3mm; - Dimensions of mold acive pars: 165x105x50mm; - Used maerial for mold: P20. Figure 3: The 3D general view fo injecion mold The maerial used during he simulaion is PA6 polyamide. In figure 4 i may be seen he variaion of he viscosiy depending on he working emperaure. In figure 5 is presened he variaion of he specific volume by emperaure. a) Figure 4: The viscosiy variaion by emperaure b) Figure 2: The bushing ype piece drawing, a) 2D Model, b) 3D Model The six caviies along he disribuion channels and heir placemen in he mold are represened in Figure 3. Figure 5: The specific volume by emperaure In order o obain accurae componens, special aenion mus be applied o he placemen of he cooling channels in relaion o he componen, o 88

3 he injecion sies, he filling direcion of he mold ec. For a beer cooling here were realized several ypes of runners: wih recangular shaped secion, square shaped secion and riangular shaped secion. As a resul of he experimens, i was noiced ha he mos efficien runners are experimenally he square shaped ones and heoreically he recangular ones, see figure 6, a and b. Consrucively speaking, he easier o make are he circular ones, because hey are jus drilled, see figure 7 [2]. Figure 6: Runners. a) Recangular shaped runner; b) Square shaped runner. Figure 7: Drilled runners The mos ofen used cooling circui is made ou of sraigh runners. The connecions beween he runners are made wih he help of supplemenary runners, applied o he mold plaes. The role of he runners in he injecion process is o mainain he emperaure of he mold plaes a he esablished value, wihou considerable variaions. The injecion process s inle parameers are: mold emperaure o C, meled maerial emperaure o C and maximum injecion pressure 180 MPa. 2.1 Process simulaion The analysis wih Auodesk Moldflow of he injecion process offers he possibiliy of visualizing he process evoluion wihou being necessary o build he mold and o solve he evenual problems ha can occur in he designing process of new pars [3]. Due o he fac ha he simulaion is made for an injecion cycle, he experimenal plan will no ake ino consideraion he runners bu only he emperaure variaion of he mold and of he meled maerial. The mechanical properies of he maerial used for he simulaion par are presened in able 1. In able 2 are presened he process parameers recommended by he manufacurers [4]. Table 1 The mechanical proprieies of he used plasic maerial Elasic modulus 2910 MPa Poisson raio Shear modulus 1050 Table 2 The process parameers Mold emperaure range minimum 70 o C Mold emperaure range maximum 110 o C Mel emperaure range minimum 230 o C Mel emperaure range maximum 300 o C Absolue maximum mel emperaure 340 o C Ejecion emperaure 133 o C Maximum shear sress 0.31 MPa Maximum shear rae /s Table 3 highlighs he parameers of he simulaion and he number of experience. As i may be noiced, during he firs nine experimens he emperaure of he meled maerial is consan and we varied he emperaure of he mold. During he following 8 experimens he emperaure of he mold is consan and we varied he emperaure of he meled maerial 10 o like sep adh 5 o for mold heaing emperaure. Table 3 Parameers and experimens number Mold Mel Mold Exp. emp. emp. emp. [ o C] [ o Nr. C] [ o C] Exp. Nr. Mel emp. [ o C] The paper presens he highlighs experimens from able Resuls of he simulaion Following he simulaion, we may analyze he resul presened in ables 4, 5, 6, 7 and 8 as well as in he figures aached o each experimen. 89

4 Table 4 The simulaion resuls Experimen 1 Figure 8,9,10 Acual filling ime 0.32 (s) Acual injecion pressure (MPa) Max. clamp force during filling (on) Velociy/pressure swich-over a (%) Velociy/pressure swich-over a 0.31 (s) ime Esimaed cycle ime 7.38 (s) Toal par weigh (g) Sho volume Caviy volume Runner sysem volume (cm^3) Figure 11: The filling ime disribuion Figure 12: The emperaure a flow fron Figure 8: The filling ime disribuion Figure 9: The emperaure a flow fron Figure 10: The pressure a end of fill Table 5 The simulaion resuls Experimen 5 Figure 11,12,13 Acual filling ime 0.31 (s) Acual injecion pressure (MPa) Max. clamp force during filling (on) Velociy/pressure swich-over a (%) Velociy/pressure swich-over a 0.31 (s) ime Esimaed cycle ime 8.37 (s) Toal par weigh (g) Sho volume Caviy volume Runner sysem volume (cm^3) Figure 13: The pressure a end of fill Table 6 The simulaion resuls Experimen 9 Figure 14,15,16 Acual filling ime 0.32 (s) Acual injecion pressure (MPa) Max. clamp force during filling (on) Velociy/pressure swich-over a (%) Velociy/pressure swich-over a 0.31 (s) ime Esimaed cycle ime 7.36 (s) Toal par weigh (g) Sho volume Caviy volume Runner sysem volume (cm^3) Figure 14: The filling ime disribuion Figure 15: The emperaure a flow fron 90

5 Figure 16: The pressure a end of he ime Esimaed cycle ime Toal par weigh Sho volume Caviy volume Runner sysem volume 7.56 (s) (g) (cm^3) Table 7 The simulaion resuls Experimen 10 Figure 17,18,19 Acual filling ime 0.70 (s) Acual injecion pressure (MPa) Max. clamp force during filling (on) Velociy/pressure swich-over a (%) Velociy/pressure swich-over a 0.64 (s) ime Esimaed cycle ime 8.35 (s) Toal par weigh (g) Sho volume Caviy volume Runner sysem volume (cm^3) Figure 20: The filling ime disribuion Figure 21: The emperaure a flow fron Figure 17: The filling ime disribuion Figure 18: The emperaure a flow fron Figure 22: The pressure a end of fill 2.3 Discussions As a resul of he experimens we can draw graphics for he variaion during he injecion process. In he figure 23 is presened a graphic for he firs 9 experimens, during which he emperaure of he mel emperaure is consan. The figure 24 presens he graphic display of he variaion during he las 8 experimens, for which he emperaure of he mold is consan. Figure 19: The pressure a end of he fill Table 8 The simulaion resuls Experimen 17 Figure 20,21,22 Acual filling ime 0.16 (s) Acual injecion pressure (MPa) Max. clamp force during filling (on) Velociy/pressure swich-over a (%) Velociy/pressure swich-over a 0.16 (s) Figure 23: The variaion of he process ime by he mold emperaure. 91

6 During he simulaion of he 10 h and he 11 h experimen appeared a producion faul, named incomplee filling, presened in figure 27. As a resul of hese wo experimens, we had wasage. Figure 24: The variaion of he process ime by he mel emperaure. Analyzing hese graphics we may observe ha he opimal varian for designing he injecion process is by seing he echnological parameers o: mel maerial emperaure, 265 o C mold emperaure, 90 o C. The opimal values were used while performing five experimen. The values for all he inle parameers of he process may be found in able 5. The simulaion may be visualized in figures 11, 12 and 13. If go back o Eq. 1, and se he experimenal daa ino his formula, he cooling ime for he injecion process using PA 6 polyamide may be expressed as: r d (5) Applying Eq. 3, we obain: r K (6) Following here are several informaion resuled from he simulaion of number 5 experimen during he muli-caviy injecion process. Figure 25 graphically presens he variaion of he emperaure during he injecion process. The difference beween he maximum value of he emperaure and he minimum is 3,735 o C. Figura 25: The emperaure variaion Figure 26 presens he variaion of he cooling ime. The difference beween he maximum and he minimum obained values is 0,5337 s. Figura 26: The cooling ime disribuion Figure 27: The incomplee filling 3 Conclusions Afer he experimenal research he main conclusions are as follow: - The ime of deploymen for an injecion process is increasing by mainaining consan he emperaure of he meling maerial and he increase of he mold emperaure; - When he mold emperaure is consan and he meling maerial emperaure is increasing, he deploymen ime is decreasing; - The injecion ime, as minimal value could be obain using he overlap of figure 23 and 24 and hus resul he process parameers; - The obained resuls confirm ha he injecion pressure decreases by he increase of he injecion ime if he meled maerial emperaure is consan. The value of he pressure in his case decreases from MPa down o MPa; - If he mold emperaure is consan, he injecion pressure decreases by he meled maerial emperaure from MPa down o MPa. Acknowledgemen This paper was realised wih he suppor of POSDRU CUANTUMDOC DOCTORAL STUDIES FOR EUROPEAN PERFORMANCES IN RESEARCH AND INOVATION ID79407 projec funded by he European Social Found and Romanian Governmen. 4 References [1] Feec u, C., Injecarea maerialelor plasice, Buchares, 2005, pp [2] eres, I., 1996, Injecarea maerialelor ermoplasice, Imprimeria de Ves Publisher, Oradea (1996), pp [3] Feecau C., e all. Overmolding injecion molding simulaion of ensile es specimen, Inernaional Journal of Modern Manufacuring Technologies, Vol. II, No. 2/2010, Poliehnium Publishing House, ISSN [4] *** Plasics Daa Chars - Accesed: