Investment Casting Prototypes

Harvest Technologies has been in the product prototyping business for over nine years and we are typically considered to be one of the leading service bureaus in the industry. Our services include SLS® and SLA® rapid prototyping (12 machines total), urethane casting, CNC machining, investment casting prototypes and multiple options for low run tooling and injection molding to best match your product requirements and part volumes. Through the knowledge we have gained over these nine years, we have become a leading source in the US for investment casting prototypes. We supply both SLS CastForm™ and SLA QuickCast™ patterns and we can deliver finished investment casting prototypes in the metal of your choice through our network of quality investment casting partner foundries.

Investment Casting Overview

In investment casting (also known as the lost wax process), a pattern made of wax (or similar) is coated with a refractory material to make the mold, after which the wax is melted away prior to pouring the molten metal. This process is one of the oldest manufacturing processes, dating back some 5000 years to the Egyptians who used it in the time of the Pharaohs to make gold jewelry. The term investment comes from one of the less familiar definitions of the word invest, which is “to cover completely”, this referring to the coating of the refractory material around the pattern. It is a precision casting process because it is capable of making castings of high accuracy and intricate detail. In addition, metals that are hard to machine or fabricate are good candidates for the investment casting process. Investment casting is also used to make parts that cannot be produced by normal manufacturing techniques, such as turbine blades that have complex shapes, or airplane parts that have to withstand high temperatures. Many consumer products and sporting goods, such as golf clubs, are also made exclusively via investment casting.

Let’s take a little closer look at the investment casting process and how investment casting prototypes produced via rapid prototyping (or additive layer manufacturing) can make a positive impact on low volume part requirements. First, traditionally the mold is made by making a pattern using wax or some other material that can be melted away (like an SLS® CastForm™ or SLA® QuickCast pattern). This pattern is dipped in refractory slurry, which coats the pattern and forms a skin. This is dried and the process of dipping in the slurry and drying is repeated until a robust thickness is achieved. After this, the entire pattern is placed in an oven and the wax, or like material, is melted away. This leads to a mold that can be filled with the molten metal. Because the mold is formed around a one-piece pattern, (which does not have to be pulled out from the mold as in a traditional sand casting process), very intricate parts and undercuts can be made. Just before the pour, the mold is pre-heated to about 1000 ºC (1832 ºF) to remove any residues of wax and further harden the binder. The pour in the pre-heated mold also ensures that the mold will fill completely. Pouring can be done using gravity, pressure or vacuum conditions. Attention must be paid to mold permeability when using pressure, to allow the air to escape as the pour is done.

Investment casting tolerances of 0.5 % of length are routinely possible, and as low as 0.15 % is possible for small dimensions. Investment castings can weigh from a few ounces to 80 lb, but the normal size ranges from about 7 oz to 15 lb. Normal minimum wall thicknesses are about 0.020-0.040” for alloys that can be cast easily. These same tolerance ranges can be achieved with quality investment casting prototypes from Harvest Technologies’ rapid prototyping pattern making capabilities.

There are a wide variety of materials that can be used in the investment casting process such as aluminum, bronzes, tool steels, stainless steels, titanium, Stellite, Hastelloys, and precious metals. Parts made with investment castings often only require minimal machining for clean up and finishing because of the close tolerances that can be achieved.

Investment Casting Prototypes Pattern Production

The typical method of producing the wax pattern for investment casting production is to make a metal mold, also know as hard tooling. This gives you a very reliable and repeatable process for making a quality wax pattern. However, the process of having a metal tool made is typically a labor intensive, time consuming and expensive process. It is not unusual for metal tooling to take six to eight weeks to complete and cost anywhere from several thousand to tens of thousands of dollars. And, that is only useful if a part is not overly complicated. But what if your requirements are for only 10 to 100 parts for the life of the product? Or, what do you do if you only want 1 or 2 investment casting prototypes to review before you commit to production tooling? Then our rapid prototyping pattern making technologies are the answer to your investment casting prototypes and/or low-run production requirements.

There are many different processes in the rapid prototyping industry that are capable of producing an investment casting prototype pattern. These technologies include SLS®, SLA®, Ink-jet and 3D printers. The ink-jet and 3D printing technologies are limited by overall build chamber size and slow part building speeds. They are typically focused on producing small, high-resolution parts such as jewelry or larger parts where speed and overall part quality are not important. However, the majority of companies looking to take advantage of additive layer manufacturing processes to produce investment casting prototypes are interested in parts bigger than jewelry and in most cases, they require production-like quality. At Harvest Technologies, we have focused on both the SLS and SLA technologies to produce production-like investment casting prototypes for these types of customer requirements in mainstream industrial product companies, such as the automotive, aerospace, oil & gas and heavy equipment industries. Both the SLS and SLA technologies provide the unique ability to produce investment casting prototypes with a high degree of accuracy and quality. With our skilled technical staff, Harvest Technologies is also capable of building larger parts in multiple sections and then joining them in post-processing to produce large investment casting prototypes that would be difficult or impossible to do with any other pattern making method. There are some differences between the SLS and SLA processes and materials used in each. These differences should be taken into account when choosing the best process for your particular part size and geometry.

For investment casting prototypes in metal, the SLS CastForm™ PS patterns are considered more “foundry friendly” than SLA QuickCast. This is because CastForm patterns can be autoclaved and easily burned out. CastForm is organic in composition, low in ash content and less likely to expand during burnout and thus break the surrounding shells causing loss of production, time and money. SLA QuickCast can produce larger, single-piece patterns with slightly better detail and surface finishing, but the QuickCast patterns require more experience and special processing to cast successfully in the foundry, thus there are far fewer investment casting foundries willing to work with this rapid prototyping pattern material. However, once a foundry defines and perfects a process for QuickCast, the results are generally very good and consistent.

Overall, Harvest Technologies’ skill and expertise in rapid prototyping provides you with a quality partner which you can trust for all of your investment casting prototypes. We are constantly striving to improve the processes involved in producing quality investment cast patterns, making adjustments in the build and finishing procedures for size and geometry complexity to further insure the final product meets with your requirements.

For a quote on your investment casting prototypes, please call us at (254) 933-1000, or submit your RFQ through our online RFQ system via our website at www.harvest-tech.com.