Plunger Kinematic Parameters Affecting Quality of High-Pressure Die-Cast Aluminum Alloys
- PDF / 2,795,639 Bytes
- 13 Pages / 593.972 x 792 pts Page_size
- 23 Downloads / 157 Views
RODUCTION
HIGH-PRESSURE die casting (HPDC) is a cost-effective process widely used to manufacture components with high productivity and dimensional accuracy for automotive and other industries. The main disadvantages of this process are gas entrapment and oxide formation due to the highly turbulent flow of metal in the chamber and die cavity. The entrapped gas remains in the casting in the form of gas porosity which hinders the casting suitability for conventional heat treatment and deteriorates the casting quality sometimes to such a degree that it must be rejected.[1] Meanwhile, oxides worsen the tensile properties of the casting and cause premature failure.[2] HPDC can be basically described through the sequence of three stages that can be easily recognized by analyzing the plunger motion profile and the pressure exerted by the hydraulic actuator. The first stage of the process, also called slow shot stage, requires usually constant and low speed for filling the shot sleeve and for avoiding turbulence in the melt and consequent generation of defects in the casting. The second stage, also called fast shot stage, is the filling of the die cavity, which should be performed at higher speed in order to avoid premature solidification at the gate and incomplete castings. Finally, the third stage, also called upset ELENA FIORESE, Postdoctoral Fellow, and FRANCO BONOLLO, Full Professor, are with the Department of Management and Engineering, DTG University of Padova, Stradella S. Nicola 3, 36100, Vicenza, Italy. Contact e-mail: fi[email protected]. Manuscript submitted October 27, 2015. Article published online April 28, 2016 METALLURGICAL AND MATERIALS TRANSACTIONS A
pressure stage, consists in applying an upset pressure on the solidifying melt in order to prevent the formation of shrinkage defects and the expansion of previously entrapped air. The recent survey questionnaire addressed to the European foundries[3] and the extensive literature review[4] carried out by the authors have highlighted some critical issues that are yet unsolved. On the one hand, there is the actual need to improve the HPDC technology, since an average of 10 pct scrap is typically manufactured by this process due to the presence of porosity and oxides, which deteriorate the quality of castings.[3] On the other hand, there are no reliable methods in the existing literature to overcome this trouble and the available results are sometimes fragmented and conflicting.[4] Several works in the literature attempt to investigate this relevant issue, by examining the effect of different types of process characteristics on the final outcome. Among the different critical process characteristics, several papers focus on the study of the so-called ‘‘process parameters’’ that are the modifiable settings of the injection machines. This approach aims at optimizing the quality of castings through the selection of the optimal machine settings, within those feasible, to ensure the best achievable performances given the melt chemical composition and the die geometry. Among the
Data Loading...
