Here, H and W represent height and width as described in Fig. 1.n_CAD and n depicts the detection point of initial CAD and final geometry, respectively. Thus, the averaged aspect ratio of deformation can be described as below.
Equation (15) shows the relative deformation rate in each direction and can be considered as nonuniform shrinkage rate in major axis. The front cover has ribbed structure with large empty space compared to battery cover. Most critical issue for front cover is dissimilar shrinkage along the height. We have defined width difference for front cover as follows:
Here, W1 and W6 represent the width at upper and lower position along the height of front cover as shown in Fig. 1.
In Fig. 3, we have shown the benchmarking results for both battery and front cover. In Fig. 3(a), the ratio of averaged deformation rate of height and width by experiment for battery cover increases as case number increase, and numerical results show similar tendency. In experimental results of Fig. 3(b), we can notice that the dimension at the upper position of front cover is bigger than lower position along vertical direction and numerical result shows qualitatively similar problem. The actual magnitude of width difference for front cover was in the range of 100 lm which is very small.
Fig. 3 Comparison between experimental and numerical result (a) ratio of the averaged height and width of battery cover and (b) size difference between upper and lower position along height of front cover
We have plotted the detailed size distribution in horizontal and vertical direction for battery cover in Figs. 4 and 5. The final dimension of width at each seven detection point for initial CAD design, experimental, and numerical analysis results for case 1 have been described in Fig. 4(a). Similar plots have been generated for cases 2 and 3 in Figs. 4(b) and 4(c), respectively. Both numerical and experimental results show overall shrinkage in width for case 1. By flipping the mold temperature of top and bottom side, final dimension stay more close to initial CAD design. Additional changes in processing parameter other than mold temperature, i.e., injection speed, packing pressure, or injection time, do not affect the final output that much. We also plotted the final dimension of height in Fig. 5 for both experiment and numerical simulation. The final height of battery cover becomes shrunk and the relative changes are very small for all the test cases.
Fig. 4 Width dimension of CAD model, experimental and numerical analysis result of battery cover (a) CASE 1, (b) CASE 2, and (c) CASE 3
Fig. 5 Height dimension of CAD model, experimental and numerical analysis result of battery cover (a) CASE 1, (b) CASE 2, and (c) CASE 3
In general, both results by numerical simulation and experiment are in relatively good agreements despite small discrepancy in its magnitude. Consequently, we can conclude that the developed numerical model combining MOLDFLOW and ABAQUS software can predict the problems in injection molding process followed by thermal deformation relatively well.
3.2 Design of Experiment
3.2.1 Candidate Processing Parameters.
The residual stress created during injection molding process can induce nonuniform shrinkage or warpage phenomena considered as product defects. Therefore, controlling the residual stress would be a key for producing the final part with good quality by injection molding. There can be various factors that build up residual stress in injection molding process. It is difficult to classify them clearly because factors could be coupled and interact with each other. In this study, we tried to separate the factors which cause residual stress into two categories; flow- and thermal-induced stress. Thermal-induced residual stress is caused by the temperature distribution of mold, the properties of molten material, and cooling time, etc. Flow-induced residual stress can be produced by gate and runner system, injection time, packing pressure, etc. In 注射成型模具设计英文文献和中文翻译(5):http://www.youerw.com/fanyi/lunwen_12455.html