Selecting the Right Casting Process: ZA12 alloy using Graphite Permanent Molding, the Most Cost-Effective process for Annual Quantities Up to 20,000 Pieces
If you are attending the NADCA Die Casting Congress & Exposition 2024, you may be surprised by the significant investment required for the latest die-casting options, especially if you are producing less than 20,000 parts annually.
When deciding on the most cost-effective casting process for producing zinc alloy components, especially when manufacturing 150 or up to 20,000 pieces annually, it’s essential to evaluate various factors to determine the optimal method. Here’s a guide to help you make an informed decision:
1. Part Complexity
For intricate and detailed shapes, die-cast and investment castings are typically preferred due to their ability to handle fine details and complex geometries. However, if the parts are relatively simple, permanent molding is a viable alternative, offering a balance between complexity and cost. Graphite molds can be cut to exacting tolerances in combination with the highly fluid ZA alloys allowing raised graphics and artwork to be cast in fine detail.
2. Production Volume
With an annual production volume of 150 up to 20,000 pieces, permanent molding is a suitable choice. It strikes a balance between high-speed processes like die casting, which is more cost-effective for very high volumes. Permanent molds can be used for years, making them economical for low to medium-sized production runs.
3. Material Selection
Zinc-aluminum alloy components benefit from the precision and durability of permanent molding. The process involves using a graphite mold to create parts with consistent properties and surface finish. This method is ideal for ZA12, as it supports the material’s casting properties while providing reliable net shape results. ZA alloys offer yield strengths from 29,000 to 54,000 psi and tensile strengths from 37,000 to 64,000.They have replaced aluminum, brass, and cast iron castings. Complete alloy information is available here.
4. Surface Finish
Graphite permanent molding offers as good of surface finish as diecasting. For most applications, the surface quality achieved with permanent molding is sufficient and cost-effective. If an exceptional finish is critical, you may consider additional finishing processes.
5. Dimensional Accuracy
Permanent molding provides good dimensional accuracy and can handle tolerances that are generally acceptable for many applications. Tolerances can be held +/-.005” for the first inch of dimension in any direction with an added +/-.002”/inch for each additional inch. 2 degrees of draft is required for inside and outside surfaces perpendicular to the parting line. Small holes can be cored. If your project demands very tight tolerances, secondary machining can be done in house for an additional cost.
6. Time and Speed
Graphite permanent molding is a relatively fast casting process compared to some other methods. Tools can be cut in a week providing the 3D models are available. It allows for quicker production runs and faster turnaround times while still being economical. This speed is advantageous for initiating the launch of a new product, maintaining production schedules and meeting deadlines. We call it rapid production.
7. Cost
Permanent molding is often more cost-effective than die-casting for medium production volumes. Die casting might offer lower costs for very high volumes due to its speed and use of die casting machines. However, permanent molding provides a more economical solution than sand casting or investment casting for quantities as low as 150 and up to 20,000 pieces. In order for the total cost of acquisition to be evaluated, one must include the initial investment in molds and the per-unit cost of production over the product life cycle. Graphite permanent mold has a low cost of entry with a reasonable cost per part.
8. Geometric Features
Zinc aluminum components often involve specific geometric features. Permanent molding supports a wide range of geometries, but it’s essential to ensure that the mold design can accommodate the part’s features. The process is well-suited for parts with moderate complexity and varying section thicknesses up to .375” thick.
9. Achievable Quality
Permanent molding offers a reliable level of quality, including good surface finish and dimensional stability. It is an excellent choice when you need a consistent and high-quality outcome without the high costs associated with other methods. While investment casting might provide a finer finish, permanent molding is generally sufficient for most applications within the specified production range.
Conclusion
For annual quantities of up to 20,000 graphite components, graphite permanent molding stands the test of time as a highly cost-effective and practical casting process. It balances cost, quality, and production efficiency, making it a suitable choice for producing high-quality zinc-aluminum alloy parts with moderate complexity and good dimensional accuracy. By choosing permanent molding, you can achieve reliable results while keeping production costs in check. To see more of our foundry’s casting capabilities and work visit https://albco.com/our-work/.
