Predicting Parting Plane Separation And Tie Bar Loads In Die Casting Using ComputerMODELING AND DIMENSIONAL ANALYSIS
Die Casting dies and machines are high performance products that are subjected to clamp load, cavity pressure loads and thermal loads during normal operation and the dies and machine deflect under the action of these loads. The ability of the dies to withstand loads and preserve the integrity of the cavity dimensions depends on the structural design of the dies. Die castings dies are expensive products with long production lead times and the structural behavior of the dies has to be predicted at the design stage. The other common problem in die casting is the tie bar load imbalance. The machine clamp load is distributed among the four tie bars depending upon the location of the dies and the location of the cavity center of pressure on the platen. Tie bar load imbalance causes the die parting surface to close unevenly and leads to problems such as flash and premature tie bar failure. The problem is over come by adjusting the length of the tie bars between the machine platens until all the tie bars carry equal loads. Tie bar load predictions are necessary to determine the individual length adjustments needed on each tie bars.
Numerical methods such as the finite element method are the most effective way to predict the distortion of the dies and the machine at the design stage. Performing a full FEA during the initial stages of the die design is time consuming and it is not cost effective. So off the shelf design tools such as closed form expressions, design charts and guidelines are needed to make design improvements during the initial stages of the design.
In this dissertation research work the relative contribution of the major structural design variables of the die casting die and machine to the mechanical performance of the dies and machines was investigated using computational (FEA) experiments. The maximum parting plane separation was chosen as the performance measure for the structural behavior of the dies and the machine. The computational experiments were designed using Design of Experiments approach and closed form power law models were developed to predict the maximum cover and ejector side parting plane separation. The functional form for the power law model was obtained using dimensional analysis based on Pi-theorem. These power law models were then used to explain the sensitivity of maximum parting plane separation to the design variables. The power law models can also be used to compare the performance of different dies and machines and make structural design improvements of the die. In addition a methodology to characterize the stiffness of the machine platens is also developed.
In the second part of the research power law models were developed based on dimensional analysis to predict the loads on the tie bars of the die casting machine as a function of the die location, the location of the cavity center of pressure, clamp load and the magnitude of cavity pressure. The power law model to predict die bar loads can be used to determine the length adjustments needed on the tie bar to balance the tie bar loads. The relative contributions of the die location and cavity location on tie bar load imbalance were also studied using the exponents and coefficients of the power law model. The adequacy of the model was also studied by using tie bar load measurements from a die casting machine.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:die casting mechanical performance structural design machine stiffness characterization finite element modeling dimensional analysis tie bar loads empirical correlation parting plane separation
Date of Publication:01/01/2008