THE MOLDFLOW ANALYSE OF THE INJECTION PARTS, AND THE IMPROVEMENT OF THE INJECTION PROCESS.

Transcription

1 THE MOLDFLOW ANALYSE OF THE INJECTION PARTS, AND THE IMPROVEMENT OF THE INJECTION PROCESS. Togan V.C. 1,2, Ioniţă Gh. 1 1 Vaahia University, Facuty of Materia Engineering, Mechatronics and Robotics, 18-24, Unirii Bvd, Targoviste, Romania; 2 S.C. Arctic S.A., Product Deveoment Deartment, Str. 13 December, No 210, Gaesti; Romania; E-mai: vaentin.togan@yahoo.com; ionitateacher@yahoo.com Abstract: Processing by injection is the argest industria way to obtain astic arts. An anayzing accuracy of the injected art execution, imroving the quaity of the injection rocess and of course the quaity of geometrica execution arts and injection rocess, has been erformed with the new 3D simuation rogram Autodesk Modfow Insight. Keywords: Part contractions, injection rocess, materia fow, Modfow anayze. 1. INTRODUCTION. The 3D drawing occurrence, ed to the deveoment of the manufacturing arts made from oymer (using directy the 3D drawing on mods execution). With the modernization of mods execution methods, major imrovements have been made on the execution simuation of various oymers based arts. The new and innovative virtua simuation software brought a variety of toos used to verify any design error. This study case is erformed on an injected oyethyene (a ca) with a comex geometric shae design (fig 1.). Thus, the aim of the virtua simuation is to otimize the art or mod design, in order to eiminate the ossibiity of surface defect occurrence during the injection rocess. On the injection thermoastic after rocessing, to achieve a certain art dimension, severa criteria that must be taken into account, infuence the quaity on injection rocess, incuding the contraction henomena, injection time or the cooing mod time cacuation. 2. ACCURACY ANALYSIS OF INJECTED PART EXECUTION. 2.1 Injected art contraction. Moded art contraction deends in the first ace on the nature of thermoastic injected materia. Processing contracts must be from 24 to 168 hours after remova of the injected art from the mod. After the secified eriod contraction henomena or ost contraction can occur. In the beow figure you can see a section in the mod cavity in which materia is injected at injection rocess runtime. Figure 1: Injected art for anaysis. During the injection rocess it may aear some robems, because the arts made of oymeric materias are rone to surface defects that can be avoided ony if the materia fow and the 3D drawing design are correcty executed. To erform this art anayze wi be used Autodesk Modfow Insight software. Figure 2: The mod cavity where the materia is 110

2 2.2. Contraction cacuating. To understand better the contraction henomena, beow are resented some section images that show us the dimensiona difference between the art (L) and the cavity in which the materia is injected (Lm). L L m Dimensiona difference aeared because of the art contraction. m V V Cv = = 1 (2) Where: V m cavity voume of work art inside the mod at average temerature mod in the injection runtime, (30 60ºC); V iece voume injected at ambient temerature, ( 20ºC ) On the mod construction for a wa thickness of 2mm is taken into account: C 0.6% From equation (1) resut: L (3) =1 C Lm For an isotroic contraction of the three voume directions and reaceing the inear dimentions of the art and mod, voume contraction equation can be deveo: Cv C = (4) 3 Amorhous materias (oystyrene, oyaceta viny, ETC.) are showing a arge isotroic roerties with uniform contraction of rocessing by injection. In Figure 4 can be seen that ost contraction is even greater when the storage temerature is higher. Even if the injection rocess is erformed in otima arameters, is very imortant both storage temerature and storage ocation (some injected arts, such as astic handes, requires after the injection rocess a suort to be aced in order to kee the initia shae unchanged). The cavities of the mod Injected art Figure 3: Mod section injected art. Where: m, L m cavities mod dimensions;, L injected arts dimensions. Regarding the studied art: L = 2 mm Lm = 2.01 mm C m = = 1 m m (1) Poyethyene contraction Poyethyene ost-contraction Where: C inear contraction; m mod cavity size to the average temerature of the mod at injection time; ength of the injected art at room temerature (20 0 C) Because in the injection runtime it is rocessed a met materia voume, after the cooing wi take ace a voume contraction: Figure 4: Contraction and ost contraction of oyethyene injected art. The injected art anayze has been erformed with Autodesk Modfow şi Unigrahics NX5. The anayze urose is to avoid surface defects arising from the injection rocess (deformations, shrinkage cavity, burned area, exfoiations, fow materia shae, defects reated with initia materia humidity. 111

3 Cooing the injected art from maximum vaue of astic materia temerature (during fiing the mod cavities) at room temerature requires a reativey ong time. The formation of hot area with cums of materia, in case of a thick-wa moded art such as this, roong the injection cyce due to increasing cooing time in the mod. The mass concentration of materia and the forming of hot area are made eseciay in the corners or the injected art, where the side was are joining the intersection of severa was. Figure 5: Injection oint osition. As shown in Fig. 5 the injection oint osition is in the midde of the art, but not on the commercia surface. The reason for choosing this oint is to fi the injection mod cavities in a areas and in the same time to reduce the art distortion risk. In Tabe 1 are mentioned the secific arameters of the rocess (mod temerature surface, minimum-maximum meting temerature, mod temerature at removing time the art from it, etc.). 3. COOLING PROBLEM AREA SOLUTIONS. 3.1 Imroved design. As a soution to this robem, the design wi be imroved by eiminating the continuous rib and by aying some oca ribs on injected art as shown in the Fig 7.. Figure 7: Imroved design. Tabe 1. Injection rocess arameters. Figure 6: Cooing robem area. 3.2 Injection rocess infuenced by the mod temerature. The mod temerature is a critica measure for cooing seed vaue and injection art roerties. This critica vaue can be estabished according to heat exchange that takes ace into the mod: - Between the injected thermoastic and the mod materia Q; - Heat exchange between the mod and the environment Q T; - Between the mod comonents and environments Q E. Are considered to be ositive the therma fows that are coming inside the mod and to be negatives those that are eaving it: Q + Q E + Q T = 0 Heat baance exressed in this equation can be considered as a basic equation of the cooing rocess. T M = C Q > 0 Q E < 0 Q T < 0 Where: T M Outut vaue or the mod temerature Thus, the fuid temerature T T wi be adjusted between 30 0 C şi 80 0 C. Fow rate V T of fuid temerature is a 112

4 adjustment contro vaue and its disadvantage is that the fow at ow seeds, the water in the mod is strongy heated, so cooing it at the entrance into the mod is more intense then the outut from the mod. Possibiity that the cooing intensity can be adjusted searatey for each moderation can be considered the strongy advantage. Materia temerature T m is one of the main factors that infuence the dimensiona deviations of an injected art. Thus, it seeks to achieve the desired materia temerature through a theoretica adjustment of the cyinder and nozze heating. 3.3 Injection cyce time cacuation. The tota cyce time t t infuence the eve of cooing (the cooing rocess takes aces in the mod). Tota cyce time can be cacuated with the reation: t t = t u + t r + t d (1) Where: t u fiing time; t r cooing time; t d striing time. Tota time determination t t : t t = t u + t u + t cm + t rm + t rest + t dm + t + t im (2) Where: t u fiing time; t u further ressure time; t cm deay for the screw couing ; Design score t cm screw couing deay time ; t rm - screw rotation time; t R eft time time between ending screw rotation and mod oening start; Striing time can be cacuated as: t d = t dm + t + t im 7.5 s (6) t dm mod oening time; t break time; t im mod cosing time. t u << t r +t d, Process tota time: t t = = 17.5 s (7) Figure 9: Quaitative anaysis designs before soution ay. Mod temerature = 40 0 C; Met temerature C Score resut = 0.82 (Maximum score = 1) Figure 8: Injection tota time. t rm screw rotation time; t rest eft time The time between the end of the screw rotation and beginning of the mod oening ; t dm oening mod time between the end and start of the mod oening; t break time time between the beginning of the oening and the end of mod oening ; t im mod cosing time time between ending and starting mod cosing. To determinate the fi time cacuation, we can use the reation: t u = t u min (t u max -t u min) 2 s (4) t u min minimum fiing time t u max maximum fiing time Cooing time is cacuated as: t r = t u + t cm +t rm + t R 8 s (5) t u further ressure time (comaction ressure) Design score Figure 10: Quaitative anaysis designs after soution ay. Mod temerature = C; Met temerature = C Score resut = 0.89 (Maximum score = 1) 113

5 4. CONCLUSIONS. By means of the injected astic fuidity anaysis software Modfow Autodesk Insight, can be highighted both the injection rocess quaity and injected quaity art. In the diagrams shown in Fig. 8 and Fig. 9 is iustrated quaitative anaysis of the two injection rocesses before and after aying the soution to imrove the rocess execution. The charts are generated by the software according with the inut data. Thus, diagrams can anayze the ratio of fow injection (correct art design) and injection tota cyce time. It has been shown that controing the mod temerature wi increase the art quaity. If the temerature correction can be controed, then wi be avoided the surface defect (that can aear on the commercia surface of the art) from the injection rocess (contractions, deformations, shrinkage cavity, combustion zone, exfoiations, fow materia shae, defects caused by materia humidity) Aso, the imortance of using a seciaized rogram such as Modfow, it foows from the fact that the anaysis made in this software, avoids the design mistakes. In case that design errors occur and verifications with such secia software are not erformed, mod modification for correcting this errors is very exensive or sometimes imossibe. 5. REFERENCES: [1] Ion Sereş - Thermoastic materia injection Pubished Western Printing [2] Mircea Ionescu Musce Iancuescu Mod designing for astic injection arts Bucharest Technica Pubished, [3] Tudose, Z., R., "Processes and equiment in manufacturing macromoecuar comounds" Bucharest Technica Pubished, [4] Mihai R., Poymer rocessing simuation. Bucharest Technica Pubished, [5] Internet: htt:// 114