Development of new feeding-distance rules using casting simulation: Part I. Methodology
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I. INTRODUCTION
THE consequences of a low casting yield are well known in the foundry industry: lower profits due to increased production costs and decreased capacity. Additional melted metal and heats, as well as the increased labor and materials costs required for production, are the primary reasons for the increased costs. Furthermore, it is recognized that a higher casting yield has the side benefit of lowering casting cleaning costs. Essentially, when a foundry achieves the highest possible yield, it can operate at maximum capacity, maximizing its revenues. Computer simulation of the casting process is becoming an indispensable tool in the effort to achieve increased casting yield. Simulation enables more experimentation with the casting process, since a design can be modified, simulated, and analyzed to determine the effects of the modifications, without having to actually produce the casting. In addition, simulation enables better use of feeding aids such as sleeves and chills, which can sometimes be difficult to apply effectively without numerous trial runs in the foundry. However, computer simulation is applied on a case-by-case basis. Also, to be used effectively, simulation requires expertise and accurate data for numerous process variables. Therefore, in spite of the power of simulation, a recent survey indicates that simulation is used for less than 10 pct of the tonnage of steel castings produced.[1,2] The same survey indicated that feeding rules (or rule-based software) were used to rig about 80 pct of the tonnage produced. This 80 pct was comprised of 50 pct “rules developed in-house;” 20 pct feeding rules given in the Steel Founders’ Society of America (SFSA) handbook, Risering Steel Castings; and 10 pct “non-SFSA published rules.” Due to the prevalence of rules-based KENT D. CARLSON and RICHARD A. HARDIN, Assistant Research Engineers, SHOUZHU OU, Postdoctoral Researcher, and CHRISTOPH BECKERMANN, Professor, are with the Department of Mechanical and Industrial Engineering, The University of Iowa, Iowa City, IA 52242. Contact e-mail: [email protected] Manuscript submitted December 3, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS B
rigging in the steel casting industry, any attempt to increase casting yield in a general sense must begin with these rules. Furthermore, casting simulation does not provide the initial riser design for a casting, nor does it automatically optimize the risering. Thus, even if simulation is used, feeding rules are useful to develop a reasonable starting point for simulation and to shorten the iterative optimization cycle by providing insight into, for example, the maximum distance between risers. The first rules governing the riser feeding distance were developed empirically, based on extensive casting trials that were performed in the early 1950s. Most notably, there is the substantial body of experimental work from the Naval Research Laboratory (NRL) by Pellini, Bishop, Myskowski, et al. for determining feeding distances[3–7] and adequate riser dimensions.[8
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