What is the process for designing a pattern?

By C.A. Lawton | January 22, 2020
pattern blog

At The C.A. Lawton Co., the design review process begins when the customer reviews the required casting shape with our casting engineer. This consists of drawings or models of a casting-friendly pattern and one or more core boxes to produce the highest quality casting.

Technical discussions typically include tolerances required, allowable machine stock, machined and non-machined surfaces, and the castablility of the desired casting. Tooling design can vary, depending upon the pattern material, casting production process, and estimated annual usage (EAU) required.

Casting engineers and pattern makers typically utilize solidification modeling software to identify and fix potential internal problem areas.

Here are some essential items to consider when designing pattern tooling.

Pattern and Core Box Materials 

Metal: Materials include aluminum and steel. The advantages are high tolerance and excellent durability. Downsides are long lead times and high costs. Metal patterns are best suited for high-production run parts (EAU 200 castings or more), such as automotive components. They require a temperature-controlled environment for storage.

Red Board: This is a hard urethane material. Advantages include high tolerance, excellent durability, and a lower cost than metal. It’s also long-lasting, less expensive, and requires a shorter lead time than metal. Red board is well-suited to high-production run parts (EAU 100-200 castings or more). Like metal patterns, it requires a temperature-controlled environment for storage.

Wood: Common materials used to create patterns are mahogany and pine wood. Advantages include moderate cost, tolerance, and lead times. Wood’s sweet spot in terms of casting quantity is EAU 10-100 castings. Wood patterns hold up best when stored in a temperature-controlled environment.

Styrofoam: Styrofoam offers the lowest cost and shortest lead time (3-4 weeks), but has a lower tolerance. It’s best suited for prototype projects and EAU of 1-5 castings. Styrofoam is a one-time use material because the pattern and core box tooling are destroyed during the casting production process.

Pattern Bottom or Insert Boards: Wood bottom or insert boards function as a “backplate” for the pattern, which is permanently mounted to the surface of the board. It secures the pattern during the casting production process as well as transportation from storage to production. Bottom or insert boards are not required for styrofoam patterns.

Rigging and Gating

Rigging: Rigging is required, so the pattern and core boxes can be moved around the casting production floor, either with a fork truck or an overhead crane. It includes locking devices or clamps on core boxes or handling straps. Rigging materials and methods are foundry specific, based on the equipment used to handle the patterns.

Gating: Gating delivers molten metal to the sand mold, where it fills the mold cavity and creates the casting. The design of the gating is calculated so that the molten metal fills the features of the mold without voids, hot spots, or other defects. Gating can be mounted permanently to the bottom or insert boards or “loose,” depending upon the pattern design.

Our foundry experts and patternmakers are ready to coach your team through your next project. Why not contact us to discuss your needs?