塑料電子表蓋注塑模具設計【含CAD圖紙+三維SW+文檔】

塑料電子表蓋注塑模具設計【含CAD圖紙+三維SW+文檔】,含CAD圖紙+三維SW+文檔,塑料,電子表,注塑,模具設計,cad,圖紙,三維,sw,文檔 with binder nearly a is So, after pr 1 technology cially cate steps molding, The trolled in order to obtain the final components with the required properties. Both injection molding and sintering are the most im- portant steps related to get the green parts and the final ones, respectively feedstock, lines, separation, speed densities binders. nents. amplified the porous sintering ture to ticles component sintered, in the erties, cal simulations for MIM are now in development and are well expected in order to provide a cost effectively alternative to trial and error methods. This paper focuses on the modeling and nu- E nal soc. MPD Journal Downloaded From: http://asmedigitalcollection.asme.org/ on 04/10/2013 Terms of Use: http://asme.org/terms . As in the injection molding process for thermoplastic the defects such as jetting, air trap, dead zones, welding etc., can also occur in MIM. However, the power-binder called phase segregation, happens during the high and high pressure injection molding process due to different associated with metallic powders and thermoplastic It can induce the inhomogeneity of the green compo- All these effects appearing in the injection step are certainly in all next following ones H208512H20852. After the debinding step, binder is removed and the remained component results in a one including both powders and pores. In the following step, the debinded components are treated at a tempera- just below the melting point of the main constituent in order obtain the required final density by bonding the powder par- together through diffusion. The shrinkage between the green resulting after injection molding, debinding and then is typically in the range 10–20% and the final density is the range 95–100%. In order to get the final components with required dimensional accuracy and specified mechanical prop- it is thus necessary to control the defects such as inhomo- merical simulation of the injection molding and sintering steps in MIM. A biphasic model is presented for the fluid-particle flows arising in the injection process H208514,5H20852. Each phase is characterized by its own density, velocity field, and volume fraction. An inter- action term between the powders and the thermoplastic polymers accounted for the momentum exchange between both phases. A new efficient explicit algorithm has been implemented in the finite element H20849FEH20850 software developed in our research team. This newly developed algorithm can solve the biphasic incompressible flow problem explicitly with an excellent efficiency H208516,7H20852. The phenom- enological sintering models based on the continuum mechanics concepts are employed to predict the final component dimensions H208518–10H20852. The material and process parameters in the used visco- plastic constitutive law are identified by the bending tests carried out in sintering conditions and by the dilatometry tests H2085111,12H20852. The model and the identified material parameters are implemented in the ABAQUS ? FE solver in order to perform numerical simula- tions of the sintering step associated with MIM. The powder vol- ume fraction contours resulting from the injection molded compo- nent issued from biphasic injection simulation are then accounted in the following sintering simulations. Based on the simulation results, the final mechanical properties as mechanical strength are then predicted. The experimental investigations on 316L stainless steel have been carried out to verify the proposed modeling and simulations. 1 Corresponding author Contributed by the Materials Division of ASME for publication in the JOURNAL OF NGINEERING MATERIALS AND TECHNOLOGY. Manuscript received August 23, 2007; fi- manuscript received February 8, 2008; published online December 9, 2009. As- Editor: Matthew P. Miller. Paper presented at the Material Processing Defects 5 held in Ithaca H20849Cornell UniversityH20850 on July 2007. of Engineering Materials and Technology JANUARY 2010, Vol. 132 / 011017-1 J. C. Gelin 1 Professor e-mail: jean-claude.gelin@ens2m.fr Th. Barriere J. Song Department of Applied Mechanics, FEMTO-ST Institute, ENSMM Besan?on, 26 Rue de l’Epitaphe, 25030 Besan?on, France Processing Mechanical Metal Injection The paper is concerned properties associated process is a multistep with a thermoplastic polymeric binder, and normally leads to a processing are associated pleted or heterogeneous paper first describes volume fraction after defects. This analysis elastic-viscous analogy associated defects. final powder densities analysis is completed resultant mechanical Keywords: metal injection Introduction Metal injection molding H20849MIMH20850 is relatively new processing used in powder metallurgy industries, which is espe- efficient and beneficial for manufacturing small and intri- metallic components in large quantities. It includes four basic consisting in mixing the powders and binders, injection debinding, and finally sintering the powder skeleton H208511H20852. defects arising in each MIM steps should be properly con- Copyright ? 2010 Defects and Resulting Properties After Molding with occurrence of processing defects and resulting mechanical material processing by metal injection molding (MIM). MIM one that consists first in the injection of metallic powders mixed , followed by a debinding stage that permits to evacuate the then followed by a sintering stage by solid state diffusion that dense component. The main defects arising during MIM with powder segregation during injection molding, and uncom- mechanical properties resulting from solid state diffusion. The biphasic fluid flow approach that can accurately predict powder injection molding and consequently the associated segregation followed and continued by a proper sintering model based on an that predicts the resulting local densities after sintering and also from the two subsequent models, it becomes possible to get the processing and to localize the possible resulting defects. This by an analysis using a porous material model to get the final operties after processing. H20851DOI: 10.1115/1.2931155H20852 molding, defects, segregation, sintering, modeling geneous shrinkages, distortions, cracks, etc. These defects are in- fluenced by the material and processing factors including initial density, heating rate, sintering temperature and atmosphere, fric- tion, gravity, etc. H208513H20852. The experimental investigations concerning the defects arising in MIM process are presented in this paper. The conventional trial and error methods are widely used in the MIM industries to obtain the qualified products by adapting and adjusting tools and processing parameters iteratively. The numeri- by ASME 2 stock Carmel, The structural tronic spherical =1 mixed stock feedstock step make packing molded 22 used steel cesses tions. ing components. to form taining There conventional conventional face front defects one forming is ous H20849 ing, quasicontinuous behavior the fact W ting the The parameters 1. Fig. gas-atomized thermoplastic 01 Downloaded From: http://asmedigitalcollection.asme.org/ on 04/10/2013 Terms of Use: http://asme.org/terms Experimental Investigations 2.1 Materials and Procedures. A 316L stainless steel feed- was provided by Advanced Metal Working Particles, LLC., IN, and wax-based binders were used for the feedstock. powder volume fraction of the feedstock is 62%. A micro- photograph of the feedstock observed by scanning elec- microscope H20849SEMH20850 is shown in Fig. 1. The powders are of shape with a particle size smaller than 45 H9262m and D 80 6H9262m. It can be observed that the powders and binders are well and one has to underline that the homogeneity of the feed- is important in the following processing steps. The injection molding is the step that consists to shape the into the desired geometries in MIM processing. The includes heating the feedstock at a sufficient temperature to it as a melt, forcing melt to flow into the mold cavities, then at high pressure, and finally cooling and ejecting the parts out of the mold cavities. In the experimental work, a ton injection machine was used. The thermal debinding was to remove the wax-based binders from the 316L stainless powder molded parts. The presintering and sintering pro- were conducted in a batch furnace under vacuum condi- Various injection molding, debinding, and sintering process- were tested to investigate their effects on the final 2.2 Jetting Defects During Injection Molding. Jetting refers the phenomena that occur when the melt does not form a uni- flow front, but rather proceeds as a fingerlike steam, main- the geometry of the gate as it enters the die cavity H2085113H20852. are two forms of jetting in MIM described in literature: jetting H20849in liquid stageH20850 and solid-phase jetting. For jetting, a single liquid flow steam moves to the far of the cavity, then upon flow reversal, finally forms a flow that fills the cavity backward. Conventional jetting results in in the final molded part. In the case of solid-phase jetting, solid fingerlike flow steam piles up upon itself instead of a backward flow. The consequence of solid-phase jetting surface irregularities including weld lines and cracking. The glass windows of the mold cavity allow the quasicontinu- monitoring of mold filling using a fast charge coupled device CCDH20850 camera that records the front mixture advances during fill- see Fig. 2 H2085114H20852. Then, image processing software provides a view of the filling stage. In MIM, the rheological of the powder/binder mixture is largely different from rheological behaviors of thermoplastic polymers due to the that the amount of powder is very large, e.g., 60% in volume. e focused here on the analysis of incidents associated with jet- in the cavity with the same thickness as the cross section of gate. For this purpose, different runners and lengths are used. dimensions of the die cavity were also different. The injection used to obtain the components are described in Table These parameters are in agreement with the ones proposed by 1 SEM photograph of the MIM feedstock composed of 316L stainless steel powders and wax-based binders 1017-2 / Vol. 132, JANUARY 2010 the feedstock provider H2085115H20852. Different filling stages are recorded by a CCD camera during injection molding with a frame interval equal to 0.04 s. These records provide an accurate description of the filling patterns dur- ing injection process, as shown in Fig. 2. The injection of original feedstock is shown in Fig. 2H20849aH20850. One can observe that the 316L melt inserts into the cavity like a finger steam at the beginning of the injection stage. Then, the steam reaches the opposite wall in cavity. Afterward, the cavity is filled, mainly along the injection direction, until the filling is completed. It should be mentioned that the melt steam is extremely curved in the middle of the cavity. The steam overlaps cause the problems for continuation of the injection process. Jetting phenomenon is a conventional one in loaded polymer injection molding; this phenomenon is undesir- able as defects may result in the final components. The second column presents a jetting under control with the recycled feed- stock after the first injection stage. It indicates that an initial jet is formed, but it is followed by an acceptable filling result, see Fig. 2H20849bH20850. This phenomenon is called solid-phase jetting in literature. Melt begins to fully fill cross sections of the cavity since middle of the injection process. The frozen tail sticks on the down part of the cavity. The frames also indicate that the components injected with recycled feedstock are more homogeneous compared to com- ponents injected with the original one, due to the fact that the recycled feedstock is more homogeneous than the original one. 2.3 Segregation Defects During Injection Molding. In order to investigate the segregation between the powders and binder during the injection molding, a five-cavity mold has been de- signed and realized for the experiments. With the injection pro- cessing parameters as presented in Table 1, the obtained molded components are shown in Fig. 3H20849aH20850. The molded tensile test speci- men and the wheel component were cut into small segments. A helium pycnometer and an accurate balance were used to obtain Fig. 2 Jetting phenomena arising in mold cavity during the filling stage with 316L stainless steel based feedstock: ?a… original feedstock and ?b… recycled feedstock Table 1 Processing parameters for the injection of 316L based feedstock Parameters Used Injection pressure H20849barH20850 160 Injection velocity H20849mm/sH20850 160 Mold temperature H20849°CH20850 50 Melt temperature H20849°CH20850 185–200 Packing pressure H20849barH20850 45 Injection time H20849sH20850 0.18 Transactions of the ASME the Figs. stock ing gradually parts. during properly nents. specimens with a However implant cracks hip distortion Fig. the cavity shrinkage possible nately temperature test Fig. sured in Journal Downloaded From: http://asmedigitalcollection.asme.org/ on 04/10/2013 Terms of Use: http://asme.org/terms local apparent density of the molded components, as shown in 3H20849bH20850 and 3H20849cH20850. The segregation effect depends on the feed- properties, mold design, and the processing parameters. 2.4 Cracks and Distortions Occurring During the Debind- Stage. In the debinding process, the components become fragile due to the removal of the binder in the molded The defects such as cracks and distortion are prone to occur debinding. The debinding process should be designed accordingly to the feedstock and shape of the compo- The proposed thermal cycle for the tensile and bending test as shown in Fig. 3H20849aH20850 consists in heating up to 130°C a rate equal to 0.625°C/min, then heating up to 220°C with slower rate equal to 0.1°C/min and then holding for 1 h H208517H20852. , when this cycle was employed for the debinding of hip prototype made with the same feedstock as Fig. 4H20849aH20850, the occur, as shown in Fig. 4H20849bH20850H2085116H20852. Simultaneously, when the implant is debinded on the plate support, there is obvious at the contact position due to the gravity, as shown in 4H20849cH20850. In order to avoid these defects, slower heating rates for thermal debinding cycles and a proper support with the half as the injection mold were employed H2085116H20852. 2.5 Uneven Shrinkage and Distortion in Sintering. The of the parts during sintering should be uniform to render the design of the cavity of the injection mold. Unfortu- , the factors such as green inhomogeneity, gravity, friction, gradient, etc., make the shrinkage uneven. A sintering has been conducted for the tensile test specimen, as shown in 5. The mean shrinkages of the sintered tensile specimen mea- by experiments correspond to 13.11%, 14.09%, and 14.55% the length, width, and thickness directions, respectively. The Fig. 3 Inhomogeneous green density segregation defects occurring during less steel: ?a… injection molded components, test specimen, and ?c… density contours segmented parts Fig. 4 Cracks and distortion defects 316L stainless steel MIM hip implants: components, ?b… cracks occurring during curring during debinding of Engineering Materials and Technology defects associated with injection molding and debinding cannot be removed, but are amplified in the sintering process. As an ex- ample, the distortion of the bending test specimen after sintering at 1150°C is shown in Fig. 6. It is due to the green inhomogeneity induced by short shot or under packing in the injection molding. 3 Biphasic Injection Simulation for MIM 3.1 Biphasic Model for Injection Molding. The simulation of the injection stage in MIM is carried out under the frame of the Eulerian description. The injection flow of feedstock mixture is expressed by the flows of two distinct phases, namely, the solid one to express the flow of metallic powder and the fluid one for the flow of polymer binder. Both distinct flows are described by their proper Navier–Stokes equations that are coupled through the momentum exchange terms. At each instant t, the volume fractions of each phase in the filled portion of the mold cavity are defined by two variables H9272 s and H9272 f , named solid and fluid volume fractions, respectively. Due to the mass conservation, H9272 s and H9272 f should continuously satisfy the following saturation conditions: H9272 s +H9272 f = 1 and H11509 H11509t H20849H9272 s +H9272 f H20850 =0 H208491H20850 The flows of solid and fluid phases are described by two distinct velocity fields V s and V f , respectively, and the effective velocity V eff for the mixture is defined as V eff =H9272 s V s +H9272 f V f H208492H20850 The filling front is tracked by the advection effect associated with the effective velocity field. A filling state field variable F is used in the molded components due to step of MIM for 316L stain- ?b… density contours of tensile of the wheel component through occurring during the debinding of ?a… injection molded and debinded debinding, and ?c… distortion oc- JANUARY 2010, Vol. 132 / 011017-3 injection to in filled express is the So, the evolution The the versation saturation tion ally Stokes each and in m flows the where function by Fig. steel ing Fig. steel the 01 Downloaded From: http://asmedigitalcollection.asme.org/ on 04/10/2013 Terms of Use: http://asme.org/terms express the filling stage and corresponds to a value equal to 1.0 the filled part of the mould cavity, while the value in the un- part of the mold cavity is zero. This field variable permits to the front position versus time. A Taylor–Galerkin method used for the treatment of the associated advection equation for flow of the mixture: H11509F H11509t + H11612 · H20849V eff FH20850 =0 H208493H20850 the mass conservation for the flows of each phase results in following equations that can be used directly to evaluate the of volume fractions: H11509H9272 s H11509t + H11612 · H20849H9272 s V s H20850 = 0 and H11509H9272 f H11509t + H11612 · H20849H9272 f V f H20850 =0 H208494H20850 solution of Eq. H208494H20850 directly measures the segregation effects at prescribed instant. Incompressibility of the mixture is equivalent to the mass con- constraints for each phase resulting from the associated for their volume fractions, which leads to a single equa- for the mixture expressed as the incompressibility condition: H11612 · H20849V eff H20850 =0 H208495H20850 In the MIM injection stage, as the Reynolds number is gener- small, it permits to neglect the advection terms in Navier– equations. Then, momentum conservation equations for phase can be reduced to two-coupled Stokes equations: H9267 s H11509V s H11509t =?H11612H20849H9272 s PH20850 + H11612 ·H9268 s +H9267 s g + m s H9267 f H11509V f H11509t =?H11612H20849H9272 f PH20850 + H11612 ·H9268 f +H9267 f g + m f H208496H20850 which P stands for the pressure field in the mixture, and m s and f H20849m s =?m f H20850 terms represent the interaction effects between the of two distinct phases. Both these terms are proportional to difference of velocities between two phases: m s = kH20849V f ? V s H20850 and m f = kH20849V s ? V f H20850H208497H20850 k is an interaction parameter that could be constant or a of the processing and material parameters. The viscous behaviors in the flows of each phase are expressed the following state equations: 5 Comparison of the geometries of the 316L stainless tensile test specimens after injection molding and sinter- indicating the uneven shrinkage in various directions 6 Distortion of the bending test specimen ?316L stainless … occurring in sintering due to the defects associated with injection molding step 1017-4 / Vol. 132, JANUARY 2010 H9268 s =2H9262 s H20849H9255˙ s ,T,H9272 s H20850H9255˙ s and H9268 f =2H9262 f H20849H9255˙ f ,T,H9272 f H20850H9255˙ f H20849