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Ultimate Guide to Investment Casting Designing

In any manufacturing process, the price of a casting part increases as dimensional tolerances and inspection standards become more stringent. The early involvement and commitment of ACE technicians enable clients to overcome traditional casting tolerances. This was achieved through innovation and technology, with the timely delivery of 100 percent casting specifications at the lowest total cost. The most important rule to remember is to get ACE involved early in the design phase.

Definition of investment casting: Investment casting is a casting process through which metal parts can be produced through ceramic (investment) molds formed with disposable (wax or plastic) patterns. Investment casting is sometimes called lost wax casting or precision casting.

Investment Casting Model Handling And Processing Guidelines

Check for leaks

It is always wise to carefully check the investment casting mold for any type of holes, cracks, or leaks. Even the smallest openings can allow the slurry to flow into the inside of the mold, which can create non-metallic inclusions in the casting. It is recommended to perform both pressure (to locate holes) and vacuum inspection (to find thin line cracks) to ensure that the pattern is sealed. The hole can be sealed with cast wax or light-curable resin.

Create specific patterns

Similar to any molding style, a casting foundry may wish to add wax to the fillet to follow its specific casting design requirements to obtain a sufficient radius. At burnout temperatures, undrained parts below 0.060 inches (1.5 mm) may expand and crack the shell. Always be careful to maintain the size requirements of the pattern, or to machine or grind the excess metal to obtain the desired size.

Accept investment mold

The received pattern must be stored in a cool and dry room to avoid moisture. In addition, in order to prevent water absorption, the pattern should be stored in a sealed plastic bag with a desiccant.

Gating and exhaust

It is recommended that all foundries overuse their mold. This eliminates the possibility of remaking the casting. You can use isopropyl alcohol to clean the gate area to secure the wax door more firmly. Since some surfaces will repel wax, it may be necessary to sand the area with 180 grit sandpaper. This will make a strong bond between the grid and the pattern. Once the gate is fixed, it is recommended to perform pressure and vacuum checks again to ensure a good seal.

Shelling pattern

Most foundries have developed a proprietary process for the shelling mode. The precision casting mold can be used with any of them. Popular shelling materials include fused silica, alumina, aluminosilicate, and zirconium silicate.

When heated above 1650°F (899°C), fused silica will transform into cristobalite, and this will occur during the burnout cycle. This limits the housing to only one thermal cycle. This means that if the shell is cooled to remove its ashes, it cannot be reheated without deterioration.

Fused silica can be used with ferrous metals because the molten metal itself generates extremely high heat. Not only will the pattern burn off the shell, but the high temperature will often cause it to evaporate when poured into ashes. This ensures that this operation is completed in a single thermal cycle when the enclosure does not return to room temperature.

Systems that can be cooled after the burnout period and reheated before casting include alumina, aluminosilicate, and zirconium silicate. After the shell is cooled, the ashes remaining on the investment mold can be removed by washing, vacuuming, or vibration. For non-ferrous materials, this is the preferred housing material because it will withstand multiple thermal cycles.

Many topcoat slurry systems contain surfactants to promote the wetting of the slurry on the wax. Some slurry systems cannot adhere to all resins in use. In this case, it is easy to use aerosol glue to promote adhesion to investment casting and allow it to dry out before starting dipping.

Three typical types of adhesives are used today. Water-based adhesives (such as colloidal silica), alcohol-based adhesives (such as ethyl silicate), and other water-based special adhesives can all be used with precision casting models. The first dip is low in water content and intended to dry quickly, which exposes the investment mold to the minimum amount of water before Shell takes over. Even if the subsequent immersion liquid has a higher moisture content, they will not come into direct contact with the investment casting mold.

Note that if the investment casting mold creates high stresses on the shell, there are several ways to eliminate the problem. By adding an additional primer layer (adding multiple layers to the shell mold), stress can be reduced. Another method used is to add a wire mesh between the coatings. Finally, adding chopped ceramic fiber, a chopped stainless steel wire or chopped stainless steel wool can relieve undue stress on the shell.

Precautions for Investment Casting Design

Size and weight

Part size and weight are the most critical factors that determine the cost of parts because the mold capacity is limited by size and weight. The more parts that can be run on the mold, the lower the cost of the parts. Our design team will work with you to eliminate unnecessary weight to reduce the weight of parts.

Number of doors

Where possible, parts should be designed so that a single gate can supply parts. Generally, this will generate more fragments per mold and help reduce the pouring weight of each mold. Single-gate feed also enhances the dimensional stability of a given part by providing a directional solidification pattern.

Castability

If the designing contains features that will increase the scrap or rework rate (and unit price), the ACE estimation engineer will suggest modifications to the design to reduce the unit price.

With the world’s leading engineering experts, rapid prototyping and delivery, and the world’s most advanced investment casting equipment. ACE is redefining how today’s manufacturers create, refine, and deliver products. If you need high performance, design freedom, and flexibility, we should talk about it.

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If you would like to have a question then get in touch today, we are ready to assist 24/7.
We welcome your cooperation and we will develop with you.

 Factory-direct Connectivity Solutions.
 High quality, Competitive Price.
 Custom-tailored solutions.
 Problem-solving approach.