Once you have received your casting quotes and performed your cost analysis, it is time to choose the foundry you want to produce your castings. Many questions likely pop into your mind: How do I choose which foundry should produce my castings? Are there specific criteria for selecting a foundry? What points should I consider first when choosing a foundry? These are all important and valid questions for the casting buyer to review. Some buyers may consider the quoted price of a casting to be the ultimate factor in choosing a casting supplier. While price is important, it is typically not the primary consideration.  

The first item on many OEM sourcing decision lists is quality. If you currently do business with a supplier, you should have a good handle on their level of delivered quality and know if they meet your business criteria. If you haven’t done business with this supplier in the past, how do you determine their level of quality? To answer this question, you’ll need to perform a bit of investigation into the data provided to you by the prospective foundry.

All manufacturing companies will be able to tell you their internal scrap rate—this will be the total percent of scrap that has occurred through their entire manufacturing process. With foundries, this number will vary greatly depending on manufacturing process, casting size, complexity level, and several other factors, but an internal scrap rate of less than 4% is generally considered to be a fair scrap percentage, although foundries strive to bring this level to zero. This number shows you what their internal fallout rate is running but doesn’t reflect what their customers are seeing. A better measure of their performance as a supplier will be their customer scrap rate.

Customer scrap rates are most often reported as PPM (parts per million), which is an industry standard measurement. In lower volume or small batch manufacturing, some manufacturers will measure parts per thousand, which they may feel is a more accurate measure that is in line with their limited production runs. Foundries that produce numerous small volume casting orders may suffer from higher PPMs since one casting rejected in a 100-piece order equates to 10,000 PPM, whereas one casting rejected from a 1,000-piece order equates to 1,000 PPM. The point here is that you need to make the determination of what foundry rejection levels you will deem to be acceptable for your specific casting design, manufacturing process, and annual volume.

Researching the internal and external scrap rates of the foundry is only part of the selection process, as the subject of quality goes deeper than just a review of the historic numbers. The second portion will require you to schedule a visit to the foundry to audit and review their operation and processes. Understanding how the foundry intends to produce and process your casting, as well as seeing the foundry for yourself will tell you a great deal about their quality capabilities.

During your audit, check into areas that aren’t normally associated with quality, such as machine maintenance, employee training, cleanliness, management depth, and general material flow. While these aren’t strictly quality related, they are indicators of how a manufacturing company views their operation and the steps they take to make it efficient and highly productive.   

When you are performing the foundry audit, a strategy that has served me well over the years is to start your walk through the foundry in the shipping area and work backwards through their process. Look at the finished castings the foundry intends to ship to their customers—the parts the foundry has processed through all their quality gates and have deemed to be acceptable. Do the castings you see appear to conform to your expectations of cleanliness, surface finish, and visual inspection? I use this method to tell me how well their processes are working. Do castings flow through their operation with little fallout, or do they need to perform a large amount of inspection and rework to obtain saleable castings.

Many other factors need to be considered when selecting a foundry, and quality-related items are highly important. I will be discussing additional topics in the selection process in future columns.    CS