1、PDF外文：http:/ 附录 2 Integrated simulation of the injection molding process with stereolithography molds Abstract Functional parts are needed for design verication testing, eld trials, customer evaluation, and production planning. By eliminating multiple steps, the creation of the injection mold
2、directly by a rapid prototyping (RP) process holds the best promise of reducing the time and cost needed to mold low-volume quantities of parts. The potential of this integration of injection molding with RP has been demonstrated many times. What is missing is the fundamental understanding of how th
3、e modications to the mold material and RP manufacturing process impact both the mold design and the injection molding process. In addition, numerical simulation techniques have now become helpful tools of mold designers and process engineers for traditional injection molding. But all current simulat
4、ion packages for conventional injection molding are no longer applicable to this new type of injection molds, mainly because the property of the mold material changes greatly. In this paper, an integrated approach to accomplish a numerical simulation of injection molding into rapid-prototyped molds
5、is established and a corresponding simulation system is developed. Comparisons with experimental results are employed for verication, which show that the present scheme is well suited to handle RP fabricated stereolithography (SL) molds. Keywords Injection molding Numerical simulat
6、ion Rapid prototyping 1 Introduction In injection molding, the polymer melt at high temperature is injected into the mold under high pressure 1. Thus, the mold material needs to have thermal and mechanical properties capable of withstanding the temperatures and pressures of the molding c
7、ycle. The focus of many studies has been to create the injection mold directly by a rapid prototyping (RP) process. By eliminating multiple steps, this method of tooling holds the best promise of reducing the time and cost needed to create low-volume quantities of parts in a production materia
8、l. The potential of integrating injection molding with RP technologies has been demonstrated many times. The properties of RP molds are very different from those of traditional metal molds. The key differences are the properties of thermal conductivity and elastic modulus (rigidity). For example, th
9、e polymers used in RP-fabricated stereolithography (SL) molds have a thermal conductivity that is less than one 2 thousandth that of an aluminum tool. In using RP technologies to create molds, the entire mold design and injection-molding process parameters need to be modied and op
10、timized from traditional methodologies due to the completely different tool material. However, there is still not a fundamental understanding of how the modications to the mold tooling method and material impact both the mold design and the injection molding process parameters. One cannot obtain rea
11、sonable results by simply changing a few material properties in current models. Also, using traditional approaches when making actual parts may be generating sub-optimal results. So there is a dire need to study the interaction between the rapid tooling (RT) process and material and injection moldin
12、g, so as to establish the mold design criteria and techniques for an RT-oriented injection molding process. In addition, computer simulation is an effective approach for predicting the quality of molded parts. Commercially available simulation packages of the traditional injection molding proc
13、ess have now become routine tools of the mold designer and process engineer 2. Unfortunately, current simulation programs for conventional injection molding are no longer applicable to RP molds, because of the dramatically dissimilar tool material. For instance, in using the existing simulation soft
14、ware with aluminum and SL molds and comparing with experimental results, though the simulation values of part distortion are reasonable for the aluminum mold, results are unacceptable, with the error exceeding 50%. The distortion during injection molding is due to shrinkage and warpage of the plasti
15、c part, as well as the mold. For ordinarily molds, the main factor is the shrinkage and warpage of the plastic part, which is modeled accurately in current simulations. But for RP molds, the distortion of the mold has potentially more inuence, which have been neglected in current models. For instanc
16、e, 3 used a simple three-step simulation process to consider the mold distortion, which had too much deviation. In this paper, based on the above analysis, a new simulation system for RP molds is developed. The proposed system focuses on predicting part distortion, which is dominating defect i
17、n RP-molded parts. The developed simulation can be applied as an evaluation tool for RP mold design and process optimization. Our simulation system is veried by an experimental example. Although many materials are available for use in RP technologies, we concentrate on using stereolithography (SL),
18、the original RP technology, to create polymer molds. The SL process uses photopolymer and laser energy to build a part layer by layer. Using SL takes advantage of both the commercial dominance of SL in the RP industry and the subsequent expertise base that has been developed for creating accurate, h
19、igh-quality parts. Until recently, SL was primarily 3 used to create physical models for visual inspection and form-t studies with very limited func-tional applications. However, the newer generation stereolithographic photopolymers have improved dimensional, mechanical and therma
20、l properties making it possible to use them for actual functional molds. 2 Integrated simulation of the molding process 2.1 Methodology In order to simulate the use of an SL mold in the injection molding process, an iterative method is proposed. Different software modules have been
21、 developed and used to accomplish this task. The main assumption is that temperature and load boundary conditions cause signicant distortions in the SL mold. The simulation steps are as follows: 1 The part geometry is modeled as a solid model, which is translated to a le readable by the
22、ow analysis package. 2 Simulate the mold-lling process of the melt into a photopolymer mold, which will output the resulting temperature and pressure proles. 3 Structural analysis is then performed on the photopolymer mold model using the thermal and load boundary conditions
23、obtained from the previous step, which calculates the distortion that the mold undergo during the injection process. 4 If the distortion of the mold converges, move to the next step. Otherwise, the distorted mold cavity is then modeled (changes in the dimensions of the cavity after disto
24、rtion), and returns to the second step to simulate the melt injection into the distorted mold. 5 The shrinkage and warpage simulation of the injection molded part is then applied, which calculates the nal distortions of the molded part. In above simulation ow, there are three basic
25、 simulation modules. 2. 2 Filling simulation of the melt 2.2.1 Mathematical modeling In order to simulate the use of an SL mold in the injection molding process, an iterative method is proposed. Different software modules have been developed and used to accomplish this task. The main assumption is that temperature and load boundary conditions cause significant distortions in the SL mold. The simulation steps are as follows:
