Investment casting, also known as lost-wax casting, is a versatile foundry process for producing metal parts with intricate shapes. From lightweight automotive components to golf clubs to jet turbines to art sculptures, this process spans nearly all industries and is relied upon for highquality and high-integrity metal parts. It enables the production of geometries that cannot be manufactured in any other ways and with a high surface finish.

Investment casting typically involves three main steps: creating an expendable pattern, making a non-permanent ceramic mold from this pattern, and casting or pouring liquid metal inside the ceramic mold. The pattern is traditionally fabricated through wax injection molding using metal tooling. This technique requires multiple operations, specialized equipment, and extensive labor by skilled workers. Metal tooling is usually achieved by CNC machining and comes with high costs and long lead times. As a result, investment casting can be expensive, especially for lowvolume production.

Working with these foundries, Bronze, Brass, Aluminum (A356), 6-4 Titanium, 4140 Steel, 8620 Steel, stainless steel 316, and 17-4 PH were all cast. The parts were burnt out in a furnace between 700 °C and 900 °C in all cases, with no autoclave. Most parts were connected to standard investment casting wax sprues and dipped in each customer’s particular shelling system.

While there are many different exact chemistries and methods used in investment casting and tested with Formlabs’ process, this is how the Foundry 4.0 at the University of Northern Iowa successfully was able to cast parts in Aluminum A356.

Parts were initially made into a tetrahedron lattice using Materialise’s Lattice Module with 0.5 mm walls and 1 mm diameter lattice diameter. This was then printed at 100 micron layer heights with the Form 3L and cleaned following Formlabs’ standard printing process. Once post-processed, the parts were adhered to a stock casting sprue using sticky wax. They then used a 100% silica shelling system, starting with Remet RP-1 flour as a primary coat, and RG-1 for backing coats, typically using 2 primary coat dips and 3 backing coats, with stucco applied after the second primary coat and after each subsequent dip. All of the shelling process was carried out automatically by an automation process to guarantee the most uniform possible coat with a minimal amount of manual labor, taking in total 9-10 hours for a single sprue.

Once dried, the part was flash-fired at 900 °C (1650 °F) for 2 hrs, and then cooled and transferred to the casting facility. Prior to casting, the shell was preheated to 540 °C and then the aluminum was cast when it was 700 °C-750 °C. They then removed the shells via a combination of breaking off the bulk pieces and blasting off the remainder, resulting in a clean final piece.

Based on user feedback, patterns 3D printed with Formlabs Clear Cast Resin can produce investment cast parts with quality comparable to traditional wax patterns. 3D printed patterns may be more brittle than wax patterns and should be handled with care. However, the burnout is clean without any noticeable ash left in the visible portion of the shell. The final metal part does not show any unusual defects.

By allowing the direct production of patterns, Formlabs allows parts to be produced immediately and without tooling, soluble cores, or other complex wax formation techniques. Features like undercuts, tortuous channels, and thin walls that prove difficult to pattern for wax injection are easy to 3D print. The table below illustrates the cost and time savings of using 3D printed tools compared to alternative methods.

This table shows that on many parts, even simple ones, foundries can save tens of thousands of dollars.