Fit Form Function FAQs

Part design is crucial to the success of any component. It's essential for the overall success of a project to remain on track in terms of timelines and deliverables. A supplier requesting a design for manufacturing review may seem like a potential hindrance, but an initial design review at the project's outset could save costs related to the fit, form, and function of the part, thanks to input from design experts. Below are some frequently asked questions about the investment casting process and how our team of highly trained engineers can enhance the design of parts.

Is my part too heavy for investment casting?

Just like any other manufacturing process, there are limitations with investment casting. In multiple steps throughout the investment casting process, the molds must meet certain weight requirements. Molds themselves have weight restrictions based on the type of alloy poured, maxing out at 100 to 120 pounds and meeting the industry weight standard. At other stages, molds are handled manually, or even automatically by Signicast’s state-of-the-art automation and robotics systems, requiring strict weight and safety restrictions.

Does surface area cause limitations?

There are three areas in which surface area has limitations—dip cells for the ceramic shell-building process, dewaxing where steam pressure is used to remove the wax from the shell, and then the burnout ovens.

Dip

The more surface area the part has, the more viscous slurry sticks, increasing the weight of the sprue and causing weight limitations for the robot.

Dewax

Now that there is a fully injected and dipped mold, there is the weight of the wax and the added weight of the ceramic shell. In this stage, there are personnel safety weight limitations to safely transport the molds in the plant.

Burnout Oven

The molds are fired to 1800℉, and once the temperature is reached, it's essential to ensure that the molds are still handled safely. 

How do I take full advantage of the investment casting process?

As previously mentioned, almost every design will likely encounter a geometry, pour weight, or shell weight limitation during the initial mold design phase.

However, through a Design for Manufacturing (DFM) meeting, the Signicast engineering team collaborates to address potential limitations, increasing the value of the part from the outset. The part effectively "rents" space on a mold, so any changes or features added to the design are essentially free, as long as the footprint of the mold remains unchanged.

For instance, holes or bosses can be added to the design without increasing the overall footprint of the part. The number of pieces on the mold, as well as the piece part price, will stay the same. Small price implications might be added to the tool cost.

In a recent project, the Signicast Engineering team reduced a customer's piece part price from $23 to $18—a cost reduction of almost 30%. This price reduction wasn't due to the alloy cost, but rather a design change that allowed for more pieces per mold. The initial customer DFM session also leveraged the full benefits of the investment casting process by adding lettering, lot codes, part numbers, and logos on the parts at no additional cost.

When should I consider alloy and heat treatment selection?

Alloy selection and heat treatment are often considered early in the design process and not revisited later.

Some customers utilize cutting and grinding tools. A knife blade design, initially machined from solid 420 steel, was brought in for review. After discussing the part's function and conducting a DFM call, the in-house metallurgist suggested D2 tool steel. The result was a sevenfold increase in wear resistance, significantly extending the part's service life.

Considering heat treatment is also crucial. For parts requiring heavy machining, heat treatment and homogenization of the material before machining are recommended to minimize hard spots and broken tools. However, if extensive machining isn't necessary, heat treatment might be eliminated entirely.

How can I eliminate machining and ultimately cut costs?

By simply designing an investment casting with certain features, machining can be avoided, eliminating a significant cost associated with the part.

The engineering team frequently encounters prints with surface finish callouts. This often adds unnecessary costs. Many features machined on the casting are for size, position, or flatness. A surface finish callout is only necessary if it's for a sealing surface, O-ring groove, or a press fit. The DFM process can often help eliminate one or two machine passes, or even reduce the overall machining cycle time.

How long does a DFM meeting take?

The meeting duration typically ranges from 15 minutes to an hour, depending on the part's complexity and the potential areas for improvement identified by the engineering team. Within this timeframe, the team can conduct a comprehensive DFM call and conclude with actionable steps to enhance the quote or RFQ.