Optimization of Runner Design in Pressure Die Casting

Abstract

In order to produce high quality parts with high pressure die casting, computer aided simulation has been used to optimize mold designs. Finite difference (differential), finite volume and finite element methods have been used in the filling process simulation and significant progress has been made for general problems. Further work on mold design optimizations is still desired to address specific issues. In die casting, the die often has more than one cavity with multiple cavities producing the same or different parts. Multiple cavities require the application of branch runners connecting to a main runner. The design of the runner system has always been a topic for die casting, since it is important for the designer to ensure that multiple cavities start filling at the same time and have the same fill time. A key factor in the design is to adjust the cross section area of each branch runner according to the cavities’ volumes; however, this may not be enough to fill the cavities simultaneously. The angle between the branch runner and the main runner has been observed to have effects on the filling pressure, filling time and residual stresses, but the observations were limited to very simple lab level die design rather than practical castings. Keywords— Runner, Gate, High pressure die casting, Fill time INTRODUCTION Die casting can be described as a process by which hydraulic energy from an injection system of a die casting machine is applied to molten metal to convey kinetic energy to the metal to achieve a fast filling of the die cavity. There are several die casting systems in use. Although they have distinctive characteristics, these die casting methods have similar mechanical design of the die, thermal control and actuation. The main two die casting processes are the hot chamber process and cold chamber process. We are dealing with the problems in runner of Cold chamber high Pressure Die due to which there was jet marks on the product. A die in a production run has a feed system which is inaccurately designed such that flow causes erosion on the runner walls due to jet pressure formed by molten metal flowing through it. After considerably long production run a local runner area on runner wall gets wear out to form local depression which eventually causes further change in the flow direction. A solution is required with which runner shall be designed to create a molten metal flow with very less or no jetting on runner side walls to minimize wear out of runner side walls. In order to design runner we are using P-Q diagram [2] which is an important tool for the die casting design process. With help of diagram we get the maximum and minimum velocity and filling time which is an operational window and their effects on the production of castings. We consider a value which fits in the operational window as a factor for deciding whether the design is matching the requirement or not. By using the simulation software we will be comparing the results of different iterations of design of die. Design Methodology First we will be establishing the metal flow or desired filling pattern. Then we will calculate the filling time and decide the gate velocity. Establish the minimum and maximum gate depth. Match the machine and die requirements. Determine the final plunger size and slow shot velocity. Calculate the final gate and runner dimensions. The above mentioned steps are methodology proposed by Herman for designing the gating system of castings. The design process begins with the selection of the filling pattern i.e. the desired flow of metal though the cavity. Although some guidelines and ideal filling patterns exist, the procedures are far from well understood or formalized in mathematics or a set of rules. The filling time is considered the time interval between when the molten metal starts to enter the cavity until the cavity and overflows are completely filled. Often it takes values between 0.01 and 0.06 seconds and is higher for larger castings. Also, shorter filing times provide good surface finish. Since the molten metal does not completely fill the shot sleeve, a bigger shot sleeve means that a larger volume of air has to be exhausts through the air exhausts. The extra air increases the possibilities of gas pockets and porosity in the casting and demands a better control of the slow shot speed. Then using the Simulation Software we can know whether the proposed design is meeting the requirements or not and then only we can proceed for production of High Pressure die Casting Die. Design Considerations and Calculation High pressure die casting (HPDC) die gating system consists of a biscuit or a sprue, a runner, a gate, overflows and vents. There are two basic runner types: tangential and fan runner. Runner is a carefully designed part of the HPDC die. It controls the metal flow by accelerating and directing it to the right places inside the die. So while designing we need to decide which type of runner should be used. Selection of the best place for the gate on one side of the casting and vents on the opposite side is one the important consideration while designing. Calculation of a Maximum Die Cavity Fill Time and Selection of a Gate Velocity is another consideration which is taken. The casting should have enough space on the parting International Journal of Engineering Research & Technology (IJERT) ISSN: 2278-0181 http://www.ijert.org IJERTV6IS030413 (This work is licensed under a Creative Commons Attribution 4.0 International License.) Published by : www.ijert.org Vol. 6 Issue 03, March-2017