Casting Design Improvement for Permanent Mold

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Have you ever wondered how to design a casting? Perhaps you’re curious about the cost savings of converting a machined part into a casting. Let us be of some assistance! This article discusses some suggestions for casting design for permanent mold.

Simple is better

When designing parts for permanent mold, we believe the goal is to make the part perfectly suited to its intended use with as simple and strong of a form as possible. Simpler designs are more likely to cast well, maintain trueness of shape and generally provide better tool longevity. So as you create your part, consider which pieces of the form are necessary for functionality.

Consider parting line placement carefully

Parting lines are placed where the two halves of your mold will come together. Placing the parting line correctly can eliminate undercuts and reduce the number of risers and gates needed during casting. This will result in a stronger part with less wasted material.

The simplest way to decide where to place your parting line is to use the tools built into your CAD program – in SOLIDWORKS (our preferred program). There’s an option called “Parting Line Analysis” that can help you decipher the best placement.

Use At Least a 3° Draft Angle

Draft is a small angle on the parting line that allows the removal of a casting from the mold. Straight, 90° sides will stick and drag in a permanent mold, affecting not only ease of production but also the quality of your casting surface finish. We recommend a minimum of 2-3 degrees draft and 5+ degrees where possible. Five degrees or more will facilitate production and enhance tool life.

It is often helpful to use the “Draft Analysis” tool in SOLIDWORKS to get a feel for where draft may need to be added or removed.

Think In The Negative

The outside edge of the part you design becomes the inside edge in a mold cavity. Make sure to add fillets and rounds where possible on flat surfaces to make the cast easier to remove from the mold. Some features in a part could become undercuts in the mold depending on how they’re designed.

Avoid Undercuts

Undercuts are features designed into your part that will lock your part into the mold. Sometimes undercuts can be resolved by adjusting the placement of a parting line. Other times you may want to consider removing undercuts if they’re an aesthetic feature that doesn’t affect how the part is used. Be sure to consider how the casting will be removed from the tool or where problem areas may lie.

Once you feel you have predetermined your parting line, you may want to try using the “Undercut Analysis” tool in SOLIDWORKS. This tool highlights any undercut areas that may need to be addressed.

Use At Least 0.125” Wall Thickness

When casting walls are too thin the aluminum cools unevenly and may leave holes in your final part. We recommend a minimum thickness of 0.125” on all parts to ensure both strength and quality.

Identify machining/post-processing requirements

Once the part is cast, consider the locations of where you may require some machining. You may need to add stock on your part for full machine cleanup. Depending on which surface requires machining, we generally recommend up to .030” stock on.

Identify part surface requirements

Consider the type of finish required for your part – heavy-duty, commercial, or personal use – since this can also affect surface requirements. If the cast part will be visible on your final product, you may desire the part to be finished or painted.

We offer a variety of finish options including powder coat and lettering/trademark services. For a full list, view our downloadable Finishes pdf and RMS surface finish scale.

Once your part is designed to the functionality you need, be sure to get in touch with your foundry for a review. Although the basic design considerations above will often bring you 90% of the way, the experience and knowledge of your foundry will help give you a superior product in the most cost-effective way.

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Need some casting design assistance? We’re happy to help! 

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