Cost Drivers for Casting from an Engineering and Design Perspective
Let’s say you were in need of a vehicle and had a family of 5, were living on a single income, and had a budget of $20,000. Would you start by going to the local Chevrolet dealership and start pricing a new Corvette ZR1? On the other hand, if you were single, making $150,000 plus a year with a need for speed, then the Corvette may be a perfect fit for your needs.
Now let’s apply this same thought process to casting needs. The difference is that the casting engineers and designers have greater control over the cost of casting cost than you may have thought.
Here are the major cost drivers for large castings (500-10,000 lbs.), and what you can do from the engineering and design perspectives to optimize your investment in them:
Lack of casting knowledge in your design/engineering department. A lack of casting knowledge is at the root of nearly every cost driver for large castings. To complicate matters, even if you have general knowledge or experience in casting, every foundry uses different processes. What works to reduce cost in one operation can drive cost up in another.
Even if you have personnel who have general casting knowledge, it is always best to get the foundry involved as early as possible in the design process.
Understanding the capabilities of a particular foundry’s process. If you need several castings that range from 50 lbs. to 5,000 lbs. for a project, they may not be designed the same way. Large foundries often need to do multiple cavity tooling to reduce the cost of smaller parts. They also need different configurations and setups than the larger castings.
Improper casting design, such as defining parting surfaces, planes and draft, can very easily hinder the foundry from being able to leverage the design to produce it cost effectively.
This is an area where getting the foundry involved early on will help to solve these issues, long before the castings reach the foundry floor.
Tolerances: A common challenge happens when design engineers call for overly tight tolerances where they are not needed to provide fit, form and function. Global dimensions and tolerancing (GD&T) is a system for defining and communicating engineering tolerances through the use a symbolic language on engineering drawings (click here to view an article that provides a deeper discussion of GD&T). It explicitly describes the part geometry and its allowable variations. If a design engineer uses it without fully understanding its principles and best practices, it can complicate the part and mold design process
Complexity: Some parts require extensive cores or, in some cases even specialty or 3D printed cores, which are very expensive. In general, the more cores a part requires, the higher the cost.
Quality requirements: Excessive quality requirement can drive up part costs. Examples include:
- Full layouts and scans of every part,
- Drawings that declare that every dimension is critical, or
- All parts need part specific chemical and mechanical testing.
Tooling design, if patterns already exist and are being transferred to a new foundry operation. In every case, existing tools need to be repaired, modified or reinforced to work within our foundry processes. Lawton uses a four-step process (click here to read all about it) to help ensure that this process goes smoothly.
Every foundry is different when it comes to the metal casting process. What works great in one foundry may not work in another. So be sure you get your foundry involved as early as possible in the casting design process.
You’ll be glad you did!