Improving the quality of die castings through optimal plunger motion planning: analytical computation and experimental validation

Abstract

High-pressure die casting is a process widely used to manufacture components with high productivity and dimensional accuracy. Its main disadvantage is the high percentage of scraps, due to a high amount of defects. Thus, the identification of the parameters affecting quality of castings is the current challenge towards an efficient and effective production. In their previous work, the authors have found and statistically validated a novel parameter explaining and forecasting both static mechanical properties and porosity of castings. Such a parameter, defined as the root mean square value of the plunger acceleration in the fast shot stage, represents a measure of the average force transmitted by the plunger to the melt and has been proved to be very effective in predicting casting quality. In order to provide a practical tool for the use of this parameter, this work proposes an analytical method for its computation, starting from the plunger displacement curve or just some notable points. The method formulation takes advantage of the analytical development of the typical motion primitives adopted and also accounts for limitations due to the machine. Hence, the optimization of the process can be achieved by selecting in advance the most suitable plunger motion profile, among those feasible, that allows to improve the casting quality. Besides the theoretical formulation, a meaningful experimental validation is provided to demonstrate the correctness of the proposed parameter and of the analytical approach, as well as its ease of implementation that makes it suitable for industrial applications.

A Tool for Predicting the Effect of the Plunger Motion Profile on the Static Properties of Aluminium High Pressure Die Cast Components

“…To overcome this limitation, [12,13] proposed the use of novel kinematic parameters that account for the time history of the plunger motion, rather than just some instants, to represent physical phenomena that are not instantaneous but last finite intervals. Indeed, integral parameters collect more information than instantaneous parameters and are more meaningful to explain and predict the casting properties.…”

“…Indeed, integral parameters collect more information than instantaneous parameters and are more meaningful to explain and predict the casting properties. Among these parameters, the root mean square (RMS) acceleration of the second stage was proved in [12,13] to be very effective. Such a kinematic parameter is defined as follows:…”

“…A reliable prediction model that accounts for the influence of the process on the static mechanical behavior and the internal quality of castings is still missing in the literature, except for the concepts and the methodology proposed in the previous work of the authors [6,12,13]. Such works propose a scalar parameter that summarizes the time-history of the plunger motion, through its acceleration, and allows for the comparison of different motion profiles having different shapes (i.e., different mathematical primitives), different maximum speed or first-stage speed.…”

“…Hence, an effective tool to optimize HPDC in different plants through the selection of the optimal motion of the injection machine is obtained. For example, the model is useful for evaluating the impact of modifying the motion profile due to different speed and acceleration limits, as well as the scaling-in-time [13,21] of the motion profile.…”

“…Given the availability of the prediction model in Equation (2) and of the knowledge of the injection machine kinematic limitations (see e.g., [13] for a discussion on the effect of the kinematic and dynamic limitations), process optimization is finally performed by looking for the feasible plunger motion profile ensuring higher a RMS .…”