Thermal structure interaction analysis was performed to investigate the deformation of the injection product. The thermal structure coupled analysis is conducted on the basis of the heat transfer analysis results. Constraint conditions of thermal structure interaction analysis were fixed to the upper and lower surfaces of the models as shown in Fig. 3. The reason for fixing the upper and lower surfaces of the models is that they are fixed with an injection molding machine.

Experiments were performed under the same conditions as the analysis condition (a) and condition (b). Experimental results were compared to the deformation of the injection molded article. A control module as shown in Fig. 4 was produced, and the condition (b) experiment was performed. Upon cooling to connect the injection molding machine and the control module, it was supplied with water with a temperature of 20°C. The cool- ing time was set to the same as that of the analysis condition.

Fig. 3. Static structural analysis condition of model

Fig. 4. The control module in conjunction with an injection molding machine

3. Results and discussion

The finite element analysis results of this study are as fol- lows. The results of total deformation in condition (a) are shown in Fig. 5. The deformation of the model is small in Base, and it can be seen that the deformation at the corner is large. In addition, a minimum of 0.003 mm deformation is generated from the base, and a maximum of 0.813 mm deformation is displayed at the end portions of the edge. The reason for this is, as shown in Fig. 6, the stress on the corner is concentrated.

Fig. 5. Total deformation of model (50°C, 67 sec)

Fig. 6. Equivalent stress at the edge of model (50°C, 67 sec)

The total deformation results of condition (b) are shown in Fig. 7. The total deformation shows the same trend as in condition (a), and the minimum deformation at the base of the model is 0.002 mm. The maximum of 0.761 mm deformed at the edge of the corner is shown. The deformation at the corner is large, which is the same as in condition (a).

Fig. 7. Total deformation of model (20°C, 46sec)

The results of the experiment show the deformation of the injection molded product. The injection product extracted using molding machine is shown in Fig. 8. The measured displacement to measure the large deformation of the specimen is shown in Fig. 9. In Fig. 10, the injection product was measured using a vernier caliper. This is due to the large deformation of the injection molded article. This was obtained by measuring the error rate for 10 specimens compared to the reference displacement and the measuring displacement. The results are shown in Table 2.

Fig. 8. Injection molding product

Fig. 9. Measuring the deformation of experimental model

Fig. 10. Measuring method of molded product

TABLE 2  Experiment results

50°C 20°C

A 0.150% 0.097%

B 0.177% 0.149%

The average measuring efficiency for displacement A of the condition (a) is 0.150%, and the average measuring efficiency for displacement B is 0.177%. A mean measuring efficiency for displacement A of condition (b) is 0.097%, and displacement B is 0.149%.

From these results, it can be seen that the amount of deformation decreases when the temperature of the cooling water is set to 20°C. in the cooling process. It was found the curing process time speeds up the lower the temperature of the cooling water is, and deformation decreases. The error rate of the reference value was also found to decrease due to the above reason.

4. Conclusions

In this study, using finite element analysis and experiments, the temperature of the mold was found to have the following effects on the molded article. When comparing the simulation results of condition (a) and condition (b), it is possible in condition (b) to shorten the cooling time to 21 sec, and the maximum deformation is decreased to 0.05 mm, and the minimum deformation is decreased to 0.001 mm about total deformation result. In the experiment, the average error rate for condition (b) of displacement A is 0.053% less than condition (a) and displacement B is 0.028%. The following conclusions were obtained. The lower the temperature of the mold in the cooling process is, to the more reduced is the deformation of the injection molded article.