Part Buyers Authority Issue #2

Figure 2: It took less than 5 minutes to simulate the porosity defect tendency (yellow region) in a tilt pour permanent mold A356 brake caliper casting design. The foundry knew it needed to work on an improved filling and solidification design to avoid defects. Then, what about the melt properties? Casting buyers usually don’t have the expertise in-house to understand porosity tendencies and need to trust their foundry, or decide based on the lowest cost. OEMs often don’t have the measuring instruments to measure the process quality on the spot during the audit or introduction visit in order to compare two or more foundries. Plus, you don’t know what to look for when you visit the foundry; everything will look fine but is it really? Our suggestion is for all OEMs to maintain a team of experts to guide them in these quality processes – to be proactive versus reactive. Your team can include internal engineers as well as outside consultants that can be pulled in on especially difficult projects. Often problems arise because of lack of proactive engineering and process control, or it’s too late and expensive corrective actions needs to be rushed. Cost-effective proactive actions are a must for win-win, long-term relationship between the foundry and OEM. Casting cost is only one variable in selecting the right foundry. Invest in this effort before ordering your next casting. Controlling Melt Variation Figure 3: Shows a foundry is serious about controlling their melt quality variation by using thermal analysis. Is this always a necessity for all foundries–No. Should the OEM care to understand why such technologies are not needed at that particular foundry–Yes. Also shows thermal analysis of a given aluminum A357 melt sample which failed the grain refinement test. The melt needs to be grain refined before molds can be filled with molten A357. How casting buyers can work with foundries to prevent porosity defects Casting buyers and OEMs typically work with several foundries to source aluminum, steel and ductile iron castings not only for transportation industry but also for several sectors. Moreover, OEMs often use foundries to convert their welded assemblies to castings. Casting buyers often seek a one- stop, cost-effective, problem- free, and long-term relationship with foundries, as keeping everything with one foundry under one roof usually yields higher quality. Right? Defects from Porosities Quality variations with castings are frustrating, especially when you don’t understand the root cause. It’s a loss of time and money when you discover porosities during machining or worse, in service. The time to setup and run the CNC machine can be worth more than the casting itself, which still needs to be rejected. The foundry usually replaces the casting, however, this still is a time consuming problem and the question remains, how to correct porosity problems? Understanding the root cause and how the foundry is addressing it is important for everyone to understand in order to properly meet your objectives and future needs. In this particular case study, it was critical for everyone to understand the importance of thermal analysis and casting process simulation. In other cases, sand properties are often the culprit, which is another area for OEMs to understand. 15 Click here to SUBSCRIBE o r CONTRIBUTE a s an author. (image courtesy of Finite Solutions Inc., www.finitesolutions.com ) (image courtesy MeltLab™ Systems, www.meltlab.com ) Continued on page 16