On the prediction of shrinkage defects by thermal criterion functions

TL;DR

This paper critically analyzes existing thermal criterion functions for predicting shrinkage defects in metal casting, identifies their limitations, and introduces a new theoretically derived method for better prediction of shrinkage locations in low freezing range alloys.

Contribution

A new theoretically based method for predicting centerline shrinkage in metal castings, addressing shortcomings of existing empirical criterion functions.

Findings

Existing criteria are scale/shape-dependent and cannot distinguish cold- from hot-spots.

The new method shows improved prediction accuracy when compared with experimental data.

The method is applicable specifically to low freezing range alloys.

Abstract

The indirect prediction of shrinkage induced solidification defects is considered in this study. The previously suggested criterion function methods, in particular the Pellini and Niyama criteria are analyzed in details, and their shortcomings are shown as a result of our analysis (e.g. the scale/shape-dependency of critical values and the inability to distinguish between cold- and hot-spots). To moderate limitations related to criterion function methods, a new method is introduced to predict the location of centerline shrinkage in metal castings. Unlike the alternative methods which are derived more empirically based on the result of experimental observations, the suggested method in this study is derived theoretically based on a heuristic two-scale, macro-meso-scale, approach. The application of the suggested method is limited to low freezing range alloys. The feasibility of the presented method is studied by comparing numerical results against the available experimental data.