In my new job, I oversee the preparation and clean-up of all our
cast pieces, though the boss does the actual casting off-premises. I
have not done a whole lot of casting in the past, and all of it was
in silver. At work, we cast silver and several colors and carats of
golds.
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I am not very pleased with the way the castings are coming out, and
I&#;m hoping to get some help understanding what might be done to
improve them.
First-- almost everything we cast is injected. Is it hopeless to get
a good polish on injection waxes, pre-casting? I am not producing
these waxes myself, and I do not want to pressure the wax person
unfairly, but the finish is not what I am used to, on hard carving
wax. There is quite a lot of clean-up after casting.
Second-- Recent castings have had what the boss says is called
"spalling"-- networks of raised ridges that look almost like veins.
What can be done to correct this?
Last, today&#;s silver flask contained 8 pieces-- 2 rings and 6 flat,
coin-like charms-- and they came out with varying degrees of pitting
on the surface. Some were hardly affected; one was so bad in places
that the pits were too large/deep to be sanded out without wrecking
the piece. This was pretty evenly distributed through the flask, and
did not look like a typical porosity problem. The porosity I am
familiar with is generally close to the main sprue, and is not
confined to the surface. Though, in fairness, I don&#;t actually know
what causes the familiar porosity, either. Thoughts?
The silver is de-ox, 50-50 new and old; the investment is new; the
other flasks in the casting (various golds) did not have this
problem.
Oh-- and one more question-- Is it really an absolute no-no to get
even the tiniest bit of metal with solder on it in a casting? What
does it do, other than potentially lowering the karat or degree of
purity you can claim?
Thanks a lot,
Noel
The process of choosing the right metal casting supplier should not be the same as choosing your supplier for bolts, manufacturing equipment, or office supplies. While some may treat metal castings as a commodity, they are far from it and the process of selecting the right supplier for a specific application requires careful consideration.
Supplier qualification is the most important part of the purchasing process. Traditionally, a purchaser&#;s primary responsibility was to find qualified and responsive suppliers. In some cases, purchasers assumed that any supplier willing to contractually meet the purchase requirement was qualified. However, using low cost and unqualified suppliers can cause quality issues, and wasted time and money in the long run.
To help you through the process, here are some things to consider when choosing the right metal casting supplier.
When selecting the right foundry to work with, determine if they have experience in your market. A metal supplier that truly understands your products, applications, terminology, and pain points can anticipate needs and potential problems. This is especially important in defense, nuclear, aerospace or other high compliance markets. The good news is that most casting manufacturers will publish their key markets on their websites, making it easy to determine when considering a supplier.
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Companies try to sell you what they have to offer and some casting suppliers only offer one type of casting process. For example, a company that only uses the investment casting process will try to sell you on why that process is best for your application. But what if using the sand casting process is best for you and your needs? Instead, look for a supplier that offers a range of casting processes so the best option for YOU is selected.
If your components have a range of designs, applications, and sizes, it is likely that the best casting process is not the same for every part. If working with a single source for all of your casting needs is important to you, the supplier needs to be diverse in its capabilities. When combined with other integrated capabilities, this can help simplify and compress the supply base.
When selecting the right casting supplier, careful consideration should be given to quality, service, and price. Take an internal audit on what really is important to you, noting that most companies may be acceptable in all areas but can probably only truly excel in one. If the lowest price possible is most important, for example, the supplier will likely not be world class in quality and service. Which are your &#;Must haves&#;? Lowest price? Meet the spec? Quick response? Easy to do business with?
Does your application require that the casting supplier have proper certifications such as ASME, Nadcap, or PED? If so, confirm that your potential supplier has the proper certs. Granted, a supplier could go through the process to obtain the required certifications but more than likely, time does not allow for that. Most casting suppliers will list their certifications on their website, and companies are searchable by certification. Be diligent.
Do you require non-destructive testing (NDT), mechanical testing, or chemical testing? While all metal casting suppliers can outsource any needed testing, some have all those capabilities in-house which can potentially save time and money. If your application does not require any testing, a casting supplier specializing in high compliance work with in-house capabilities may not be the right fit either.
Buyers increasingly select casting suppliers who have machining capabilities. This can avoid conflict if defects are discovered during machining. If a third party is machining, it may result in &#;finger-pointing&#; about who is at fault. Is it a casting issue or a machining issue? If the casting supplier discovers an issue during machining, the problem is resolved faster with no dispute over whose fault it is. The foundry &#;owns it&#; and there is less time needed for processing, shipping, and handling or replacing. Problem or no, integrated machining simplifies the supply chain and reduces handling time and shipping cost before the product makes it to the customer.
What do you need from your casting supplier? Are you looking for someone to just deliver a metal component to your doorstep or do you need more? For example, if you do not have in-house metallurgy expertise, confirm that the supplier can provide guidance in selecting the proper alloy based on your specific application. Do you have a need to raise the expertise of the overall metal in your company through training or information sharing?
Do you want a supplier who can review your design and material selection and provide recommendations to make your products last longer or save money? Some suppliers may do a great job producing a product to spec but have few other capabilities. Others will exceed the letter of the PO to help you save time and money.
Do you have requirements for both ferrous and non-ferrous alloys? Some foundries are limited or specialized. Make sure the supplier can meet all your material or alloy requirements to eliminate the need for multiple suppliers.
What better way to determine if someone is the right casting supplier than to see their operations firsthand with a plant tour? Most manufacturers are more than happy to have you as a guest in an effort to gain your business. If, by the end of the tour, you have doubts about operations, capability or culture, they are probably not the right supplier for you.
While some may treat metal castings as a commodity, they are far from it, and therefore, the process for selecting the right supplier for your specific application requires careful consideration. Take an internal audit of your company&#;s needs and wants, and determine what is most important. Research the supplier&#;s website. Talk to a sales rep or business associate. Ask a lot of questions. Visit their facility. Get an understanding of what they can do for you and if you can see yourself building a strong, mutual relationship with them.