Investment Casting with 3d Printing

Investment casting is a process that is also known as the "lost-wax" process or precision casting. In this process a wax pattern must be made for every casting and gating system; i.e., the pattern is expendable. This process offers the end-user good value for money where a good surface finish, complex geometry, and cast features are desirable without the necessity of extensive machining or other fabrication/ finishing work required to provide a usable end item. 

Traditionally investment casting uses wax patterns. These patterns are made using metal molds, making the tooling is an expensive process and can take several weeks.

3D printing patterns for investment casting is increasingly becoming the go-to solution for artisans, engineers, and industry professionals alike.

Traditionally low volume and prototype orders tend to make the investment casting process less effective because of the high tooling costs and long lead times for wax pattern tooling. SLA 3D Printed investment casting patterns flip this age-old problem on its head and opens the door for much smaller quantity orders of investment cast parts to begin to make economic sense for manufacturers.

3D printing offers an effective tool-less solution for investment casting patterns with Stereolithography (SL). As an alternative to wax and wood, SL builds patterns with a UV laser that cures and solidifies thin layers of resin. Yifei Machinery direct builds SL investment casting patterns in a nearly hollow structure with a sparse internal lattice structure and thin walls. This proprietary build style translates to proportionately less ash and minimized thermal expansion forces during flash firing.

Investment casting process when using SLA 3D printed investment casting patterns:

1. First, the investment casting pattern is designed on a 3D CAD system and saved to an STL which is then uploaded to Forerunner 3DP's SLA 500 machine where it is produced in a matter of hours out of WaterShed XC 11122.

2. Each investment casting pattern component is sealed and leak checked once it comes off of the SLA 500 and has its build support removed. It is recommended that leak-checking also be completed at the foundry after gating and sprue assembly, before the first dip.

3. Once the assembly gets to the foundry the investment casting patterns are secured to a central wax bar with gates, called a sprue.

4. A shell mold is created by dipping (investing) the cluster into a very fine ceramic slurry. The first layer, the face coat, allows for the reproduction of finely detailed features.

5. After the first layer, the shell is layered with a fine ceramic refractory grain like sand. Upon drying, the process of dipping the shell mold into the slurry and layering the sand is repeated (with coarser grains) to obtain the desired shell thickness.

6. After the shell mold dries, it is typically flash-fired in a furnace to sinter the mold and remove the investment casting pattern from the shell.

7. The mold is preheated before pouring in the molten metal.

8. The ceramic shell is removed from the solid metal through mechanical vibration, chemical cleaning, or water blasting depending on the particular metal used.

9. The original parts are now cut from the sprue and gates and ground smooth so that they are ready for additional processes.

Using 3D printing for investment casting can help to

• Reduce lead times from weeks to days

• Eliminate high tooling costs

• Give designers more freedom when creating highly complex patterns

While 3D printing casting will by no means signal the end of traditional foundry methods, the technology can help to bypass the costly and time-consuming aspects of creating patterns, cores, and molds, enabling greater flexibility and cost-effectiveness for low-volume, highly complex castings, and prototypes.