Tips For Computer model diecasting shot sleeves to predict distortion.Part-2

The static simulation was conducted for the model in order to compare the deformations in the two sleeves under consideration. It was seen that both the sleeves expanded outwards during the cycle. The deformations in the sleeves were compared at steady state condition.

The maximum deformation of the sleeves took place at the bottom node on the ID of the sleeve. The maximum deformation in the thin sleeve was 0.013 in. (0.33mm) and in the thick sleeve was 0.012 in. (305mm). Hence, the thick sleeve expanded slightly less, but did not show appreciable difference in comparison with the thinner sleeve. However, the thick sleeve expanded more uniformly (circularity) than the thin sleeve. In either case, the models predicted the possibility of blow back of molten metal past the plunger tip due to this excessive clearance.

In diecasting practice, however, cooling water to the tip can be adjusted to control tip expansion and maintain desired tip-to-sleeve clearance. Thus, the uniformity of cylindrical expansion may be the more important factor, and the thicker sleeve would be more desirable to avoid excessive tip clearances or sticking due to out of round sleeve conditions.

The thin sleeve expanded by 0.021 in. (0.533mm) and the thick sleeve by 0.022 in. (0.559mm) on the OD. The clearance between the sleeve and the die was designed to be 0.027 in. (0.686mm) at room temperature. Therefore, model results indicated that the design clearance between the sleeve and the die on the OD of the sleeve was adequate to prevent the die from acting as a mechanical constraint to sleeve expansion.

Conclusions

This project was conducted for the purpose of assessing shot sleeve designs causing problems due to deformation. The results from the simulation model were compared with experimental temperature and deformation data. Using these data, heat transfer coefficients were determined. The models were found suitable for temperature and deformation analysis predictions.

Based on the model developed for verification purposes, the distortions experienced in commercial H-13 shot sleeves were studied. Comparisons of the maximum distortion in the commercial sleeves were made and it was determined that there was not much appreciable difference in maximum distortion between the thin and the thick sleeve at a section halfway between the pour hole and the biscuit.

It also was seen that in both cases the clearance between the sleeve and the plunger tip would ultimately increase, which might lead to "blow back" of molten metal past the plunger tip. Hence, the sleeve distortion at the section under study was not large enough to cause plunger tip sticking. It also was seen that a sleeve of smaller ID (relatively low mass) took fewer numbers of cycles (10) to reach quasi steady state thermal condition in comparison to sleeves of larger ID (275 cycles) having relatively high mass.

The computer simulation method developed in this model would be helpful in designing the optimal clearance between the sleeve and the plunger tip. This was an important parameter in the design of the sleeve-tip system since a large clearance leads to "blow back" of molten metal past the plunger tip and a small clearance leads to plunger tip sticking.

The time averaged heat transfer coefficients attained a constant value at quasi steady state irrespective of the lubricant used. The deformation in the sleeve decreased when a lubricant was used in the casting cycle.

Results indicate that the finite element computer models developed can be used to predict shot sleeve temperature gradients and deformations. Models applied to large diameter commercial sleeves successfully predicted distortion. The models predicted that sleeve distortions could lead to blow back of molten metal along a section halfway between the pour hole and the platen.

In the course of the research, it was seen that the sleeve to aluminum heat transfer coefficient measured experimentally (1200W/sq m x K) did not yield the most accurate computer model predictions of temperatures around the shot sleeve in the test stand. Errors inherent in the method used to measure temperatures in the shot sleeve test stand, or assumptions made in the calculation of time averaged heat transfer coefficient may be causes of this discrepancy. Also, the sleeve to aluminum heat transfer coefficient used to model the large diameter sleeves (275W/sq m x K) varied significantly from what was used successfully for small diameter shot sleeves (1400W/sq m x K).

Factors that may influence the rate of heat flow from the aluminum to the sleeve include the sleeve inside diameter curvature, sleeve surface finish, sleeve surface treatments (nitriding), type of tip lubricant used, initial % fill, alloy type and initial pour temperature. These issues require further investigation.

This article is based on a presentation (T01-05) at the 2001 North American Die casting Assn. (NADCA - National Aboriginal Dance Council Australia
NADCA - National Air Duct Cleaners Association
NADCA - National Animal Damage Control Association
NADCA - North American Die Casting Association
NADCA - North American Draft Cross Association, Inc
..... Click the link for more information.) congress. For more information, contact NADCA at 847/292-3620.

The research this article is based on was supported by the U.S. Dept. of Energy) and the Cast Metals coalition.

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