Mistakes in the world of metalcasting can kill a project, so you can’t take any chances from start to finish.
Understanding the critical aspects of casting design and production will help you create the best process for your parts, giving you a leg up on less-informed competitors.
In this article, we’ll describe metalcasting principles like wall thickness requirements for a sound part, how tooling accounts for everything from cost to product lifecycle and why secondary finishing impacts lead time and investment.
Here are the ten questions you’ll need to answer to perform this complex manufacturing process with speed and confidence.
It’s critical to create your production process around the goals for your final product. Quality standards and production volumes should be in the books before the planning phase.
The sweet spot for permanent mold casting is 500 to 35,000 units produced annually. Low volume parts are better suited for a process like sand casting. If it is a high-volume part, it’s usually best to invest in a diecast tool, unless there are design criteria that diecasting cannot control, such as pressure tightness. Many permanent mold projects fall in the 3,000 to 12,000 range.
Permanent mold tooling must be built to keep pace with the long-term production goals. As the person specifying the production method and casting source, you need to know the return on investment for your tooling and how long your operation can wait to realize those investments.
You won’t know the best way to make a part unless you know how it will be used.
If the product doesn’t work in the field, projects have to be abandoned or reimagined. Your set up costs substantially contribute to your final piece price. Maintaining product quality across longer runs with greater quantities can also lower piece prices.
Project engineers without metalcasting experience may not know what to ask the foundry to assure the parts are strong or aesthetically pleasing enough to serve their purpose.
Does it need to have a clean finish? Does it need to be leakproof? Does this industry fall under any regulations?
We stand behind the drawing specifications to ensure that the part is made to the quality standards dimensionally and metallurgically. If the part is to be pressure tight, the foundry should understand the quality standard or testing parameters.
To put this in perspective, recently a purchasing manager came to us after struggling with a couple of suppliers to produce a cover piece for the transportation industry. They couldn’t find a way to make the part structurally strong enough to meet requirements while maintaining a pleasing aesthetic.
The part had to be structurally sound and leak-proof, but appearance was perhaps the most important aspect.
We worked with the customer to find the perfect permanent mold solution for all of their problems, because we took the time to ask the client the right questions at the beginning of the process, such as their surface finishing and cast strength requirements.
There’s a pretty big sweet spot for sizing permanent mold casting products. It can be anywhere from 2 ounces to 110 pounds, though a lot of our products are in the 3- to 30-pound range.
Large products can cause design constraints and few permanent mold foundries have the equipment necessary for those jobs. Sand castings are more common for large castings.
But we can make fairly heavy parts.
A healthcare provider needed a heavy base to provide a better center of gravity to its medical carts.
We created the base with zinc, which is twice as dense as aluminum, offering a smaller but heavier product.
Background information, like if a product is completely new or already available for purchase, is key information to share with your casting supplier. If the part is already in production, how is it manufactured, and could the process be improved within budget?
Batesville Products Inc. works with fabricators to rethink their existing products. A Carolina manufacturing company asked the foundry to turn a formerly fabricated part into a single permanent mold casting. By combining multiple parts into one casting, the foundry cut costs and created a more robust product.
The customer paid off its tooling in just a few months, and only had to use one part and one supplier to produce and control it.
Working with a dedicated metalcasting foundry during the design phase will allow you to make parts with better lead times. After all, this is what they do all day, every day.
While it’s best to approach a foundry before the part has been fully designed, customers sometimes look for a foundry after they have completed their specifications but don’t know how to make them a reality.
A good supplier will be able to take the product apart, run tests and perform finite element analysis on the casting process to help aid in designing the production system. 3D-printed prototypes help provide a sense of the structure before you invest in tooling.
A good supplier will also review the molten metal flow as it’s poured into the casting, watching it take shape. Analyzing the flow of molten metal for turbulence allows foundry’s engineering team to identify possible imperfections in the casting. Once the process is perfected, you should be confident everything is ready for production.
Scanning technology can also be used to digitally recreate existing parts on the computer so engineers can look for new improvements to old designs.
Before a foundry can work on a project, it needs to know your lead time expectations and production schedule to decide if a permanent mold solution can fit your timeframes.
All of expectations for the job need to be presented upfront, especially if you’re working with a tight production schedule.
For example, an engineering manager needed a part for the boating industry that was already designed as for permanent mold. However, it was almost Christmas, and the company wanted parts in a very short time. The product had pressure tightness specifications and required internal cavities, which had to be created with a sand core. Permanent molding is great at creating pressure-tight castings but the foundry had to be creative and adjust the process to semi-permanent molding in which sand cores are used. The foundry went on to make 350 of the boating parts per week for 20 years, and still serves this customer today.
Sometimes the appearance of a product is a major consideration. Castings should have a nice smooth surface right out of the mold if mold coatings and draft angles are used effectively.
Scabbing and blemishes can occur if the mold coating breaks down. Draft angles must be adjusted upfront to maintain the coating throughout an entire shift. Insufficient drafting creates a greater chance for metal-on-metal interaction. Increasing draft lets applied coatings remain consistent across continued pours.
The wall thickness of a casting must be just right to limit weight while allowing metal flow.
Generally, the minimum wall thickness for a permanent mold is about 0.18 inches to ensure there’s enough space for the molten metal to settle as air escapes the mold. However, some permanent mold facilities can go down to 0.125 inches in select portions of a casting, and the walls also can be trimmed down in secondary operations.
The thicker a portion of the molding is, the longer it will take to cool. Parts that are consistently portioned throughout the mold will cool evenly, improving throughput.
The draft angle refers to the angle at which the part will smoothly eject from the mold with a high-quality finish. The minimum functional draft angle is three degrees, but it can be increased to five degrees to help maintain mold coatings.
Foundry workers can occasionally take parts out of the mold, saw off the gate, trim it up and put it right into the assembly.
Understanding the secondary processes needed to turn the casted product into the end application should be taken into account at the beginning of the project.
We make it a point to perform all of the work in our facilities, but not every foundry takes this approach. That’s why you need to know if the foundry can perform secondary machining in house or if they will need to outsource operations, adding time and money to the production.
A good portion of every project’s budget goes toward tooling, so you need to be aware of how long it will take to make a return on that investment as compared to its expected lifetime, especially for long-term projects.
We recently completed a job for a cereal company that had experience with a variety of casting methods. But their engineers didn’t have our specialized experience in permanent mold casting.
Our engineers helped them compare permanent molds to other forms of metalcasting and discussed what the process can consistently offer their operation.
Moving to a permanent mold solved porosity and air entrapment issues experienced using sandcasting and die casting processes on other units.
These 10 questions encapsulate a textbook’s worth of information in a blog-sized package, so if you’d like to dig deeper into the permanent mold casting process, please reach out to us. We love talking shop.
If you’re considering a metalcasting project, we can offer valuable insight that could save your company time, money and resources.