Fit, form and function FAQs

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

Is my part too heavy for investment casting?

Like any other manufacturing process, investment casting has limitations. At multiple stages throughout the investment casting process, the moulds must meet certain weight requirements. The moulds themselves have weight restrictions based on the type of alloy poured, with a maximum of 100 to 120 pounds, in accordance with industry weight standards. At other stages, moulds are handled manually or automatically by Signicast's advanced automation and robotics systems, requiring strict weight and safety restrictions.

Does surface area create limitations?

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

Dip

The greater the part surface area, the more viscous slurry adheres, increasing the sprue weight and creating weight limitations for the robot.

Dewax

Once there is a fully injected and dipped mould, the weight of the wax and the additional weight of the ceramic shell must be considered. At this stage, personnel safety weight limitations apply to ensure moulds can be transported safely within the plant.

Burnout oven

The moulds are fired to 1800℉, and once this temperature is reached, it is essential to ensure that the moulds can still be 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 mould 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 takes up space on a mould, so changes or features can be added to the design at no additional cost, provided the mould footprint remains unchanged.

For example, holes or bosses can be added to the design without increasing the overall footprint of the part. The number of pieces on the mould, as well as the unit part price, will remain the same. Minor cost implications may be added to the tooling cost.

In a recent project, the Signicast Engineering team reduced a customer's unit part price from $23 to $18—a cost reduction of almost 30%. This price reduction was not due to alloy cost, but rather a design change that allowed for more pieces per mould. The initial customer DFM session also leveraged the full benefits of the investment casting process by adding lettering, lot codes, part numbers and logos to 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 use cutting and grinding tools. A knife blade design, initially machined from solid 420 steel, was submitted for review. After discussing the part's function and conducting a DFM review, 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 extensive machining, heat treatment and material homogenisation before machining are recommended to minimise hard spots and broken tools. However, if extensive machining is not necessary, heat treatment may be eliminated entirely.

How can I eliminate machining and ultimately cut costs?

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

The engineering team frequently encounters drawings 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 for a sealing surface, O-ring groove or press fit. The DFM process can often help eliminate one or two machining passes, or even reduce the overall machining cycle time.

How long does a DFM meeting take?

The meeting typically lasts 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 review and conclude with actionable steps to improve the quotation or RFQ.