Iron Castings - Nov 16, 2021
THROUGH THE EYES OF A METALCASTERDave Charbauski | American Foundry Society
When you are in the casting design process, you go to great lengths to make sure the resulting casting meets your needs. You spend time making sure the material selection meets your strength and durability criteria, you make sure the shape of the casting meets your load constraints, and the dimensions satisfy all your assembly and fit requirements. Your final design meets all your needs when viewed through the eyes of your manufacturing and engineering teams. So, you send out the casting design to your foundry source for a production quote. Now comes the time when your design is evaluated through a different set of eyes—the eyes of the foundry team. But did you ever wonder what your casting design looks like to the foundry? What do their manufacturing and quality teams look for? I’ll give you a hint, it’s a lot more than you might think.
Most importantly, the foundry wants to know if they can make your casting on a day-to-day basis, and within this framework is the basic question: ‘does it fit my process?’ The casting process has many steps; let’s examine a few of the major ones that the foundry considers when they evaluate a customer’s casting design.
Molding: Does the casting fit in the available mold sizes the foundry produces? If the casting does fit, is there enough space to accommodate the proper gating and risers required to produce a defect-free casting? Are the mold heights enough to provide sufficient riser height above the casting to properly feed it and produce sound castings? Is the correct amount of room provided to support the core and venting? Will chills or chaplets be required?
Cores: Are there internal or external features on the casting that require cores? What coring process will need to be used to make the core, and does the foundry even have that process available? If multiple cores are required, can they be combined into one core? Will cores need special processing, such as assembly, refractory coating, internal support or venting?
Tooling: This topic impacts both molding and coring. What type of pattern and core equipment need to be built? Wooden, plastic, and metal are all possibilities. How many cavities can be placed on the pattern? Can the patterns be mounted or cast integrally into a matchplate? Is an offset parting line needed or will it be flat? Will provisions for chills, ram-up cores, or chaplets be required?
Metal and casting weight: What type of metal is required for the casting? Is it produced by the foundry on a regular basis? Are any special in-mold inoculants required to provide metallurgical integrity? Does the casting weight range fall within the guidelines for the chosen molding line? Is the metal-to-mold ratio in line with the foundry’s target? Is there enough cooling time on the molding line to allow the casting to be shaken out at the correct time?
Cleaning and finishing: Can the casting withstand the rigors of shotblasting, or will it require special handling so it does not become broken or warped during the shotblast cycle? Can the casting be ground by hand or will special lifting and grinding fixtures be needed? Can core material (sand, ceramic, etc.) in the internal cored passages be easily removed? Are there any special visual surface requirements or quality inspections needed? Are any other processes needed, such as straightening, coining, coating, or machining?
After all these questions (and many more) are answered, the foundry will evaluate the estimated mold yield, internal scrap percentage, the annual number of castings required, and their level of available capacity to determine a cost and selling price for your casting design. Their aim is to provide a competitive price for the casting while still making a fair profit. You can readily see several factors need to be reviewed by the foundry team to ensure they give you the best and most accurate casting price possible. To help the foundry meet their requirements while meeting all of yours and creating a win-win situation, make sure to get your engineering team involved with the foundry as early in the design process as possible. Doing so will help both parties see the projects clearly from each other’s point of view.