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Continuing the Foundry Selection Process

Dave Charbauski

When it comes to selecting a foundry source, ensuring that your prospective choice can produce high-quality castings will be the primary goal for most manufacturing companies. I’ve discussed the top-line quality measurements such as PPM and scrap rates, but what other items should you consider before making your final foundry choice? Based on my experience, the engineering capabilities of the foundry would be the next area to review.

Engineering in the foundry can cover a broad range of topics, but for the purpose of selecting a foundry, let’s look primarily at the areas of process and manufacturing engineering. 

In my opinion, the process of producing a casting begins with the development of the pattern equipment. In this area, you need to meet with the casting engineering team and delve into the tools they employ to engineer the pattern and coreboxes they will be building for you. As a best practice, the foundry should use solidification modeling to develop all their gating and risering systems. Employing this process will ensure that the casting will be free of inclusions and porosity before any pattern equipment is started. The casting engineering team should also be responsible for any chills, gauges, or fixtures used in the production of the castings. Examples of these would be chill patterns (used to promote directional solidification), grinding gauges, and core assembly or setting fixtures.

All patterns and coreboxes should be checked before each production run to make sure they are not damaged or in need of maintenance. There should be a documented process and checklist showing that the tools have been reviewed. There should also be periodic checks for tooling wear that, over time, can cause dimensional issues in the final casting.

The foundry’s metallurgical engineering capabilities should also be reviewed. The foundry should have a metallurgist and an internal metallurgical lab that has the proper equipment capable of checking the materials they pour. Key to proper metallurgical analysis is a spectrometer for chemical analysis of the metal. As with all inspection tools, the spectrometer should be checked and calibrated on a regular basis, and training records should be available that show that the operators have been properly trained in its use and upkeep. 
For microstructural analysis, the lab should have cutting and polishing equipment along with a microscope with photo capabilities. An additional plus is the use of equipment capable of mounting the test lugs in plastic. These mounted samples provide edge retention on the sample and allow the metallurgist to look at the surface of the casting and check for detrimental conditions, such as flake graphite skin in ductile iron castings. The foundry should also have complete traceability records of the materials they pour, which would include pouring dates, chemical analysis, pouring temperature, and other pertinent metallurgical data.

There should also be a dimensional evaluation area, often referred to as a layout room. This area should have inspection equipment capable of dimensionally checking the castings that are produced in the foundry. At a minimum, there should be computer-aided inspection machinery, such as a Romer or Faro arm or a CMM.  If the layout area only has a granite plate and height gages, there will be a lot of room for improvement. Sample records should also be kept that clearly capture everything that was done to produce a sample casting and any changes that were made to the gating system to address any defects uncovered during the sampling process.

Linking all the foundry processes together would be a system to ensure that the entire process is locked and under control. There should be published process documentation that is available to everyone working in the foundry. In this documentation, there should be process sheets showing the steps required to produce the casting, a control plan, a Process Failure Mode Effects Analysis (PFMEA), and process flow documents, to name a few. These documents should be readily available as they are part of the PPAP process, which has become a common standard within the industry.

Reviewing all the engineering processes at a foundry will give you a good idea of their technical capability to potentially produce your castings. Couple this with the quality metrics I discussed in my previous column, and you now have a good idea of the capabilities of your prospective foundry. But there are a few more points to consider. I’ll discuss these soon.   CS