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Investment Casting Successes: Offering more design freedom than other methods of metal forming, investment casting's advantages are used in many different ways.

Investment casting offers more design freedom than other methods of metal forming because of the near-net-shape advantages that can be attained in a wide variety of alloys. This near-net-shape allows metals not readily machined to be investment cast.

The investment casting process can eliminate some costly machining operations by incorporating detail not readily available from other metal forming methods. However, a design intended for one manufacturing method must be redesigned for investment casting to take full advantage of the process' benefits.

On the following pages are three castings that took full advantage of everything investment casting has to offer.

Pump Housing

Designed by AFS Corporate Member O'Fallon Casting (O'Fallon, Missouri), the pump housing for the aerospace industry weighs 9.6 lbs. and was converted from a multi-piece assembly.

The multiple core passages, tight tolerances and grade B metallurgical requirements made investment casting the ideal process for creating this part. The ability of the process to take what would have to be multiple parts in a different process and turn them into one casting also showed the process' strengths.

The number and complexity of the internal core passages in this casting allowed O'Fallon's customer to decrease the overall size and number of pieces in the engine pump. Instead of multiple pieces with less-complex geometries being assembled together, this one-piece investment casting saved weight and eliminated future failure points at the assembly location.

The pump casting contains 12 interconnected core passages throughout the inside of the casting, with varying diameters and depths. The combination of thin walls in certain areas, large masses of metal in others and the grade B metallurgical requirements make this casting a challenge, something ideally suited for the investment casting process.

Along with the intricate core passage areas, the casting has a very tight profile tolerance, grade B metallurgy and high-pressure tightness requirements.

Drone Frame

The drone frame, a production of AFS Corporate Member Aristo-Cast (Almont, Michigan) and AutoDesk, was cast in magnesium and converted from a solid assembly. Weighing just 0.628 lbs., the frame is much lighter than the previous model. It also maintained the required strengths in the areas of the drone where needed.

Aristo-Cast was asked if they could cast this in magnesium (AZ91E) material to again reduce the weight by 1/3 over the previously used aluminum frame.

The generatively designed frame, coupled with the material change to magnesium, reduced the overall weight by 50% from the original design, while maintaining the strength required to perform their tasks. Just the material change from aluminum to magnesium saved 35% in overall weight. Drone frames created in metal are much stronger and will last longer than plastic frames.

Stator Housing

The casting produced by AFS Corporate Member Carley Foundry (Blaine, Minnesota) in A357 was converted from a two-piece hogout with a pressed-in insert. The switch allowed for a one-piece casting that could incorporate a cast-in steel insert.

Produced for commercial aerospace, the casting created approximately a 17-20% cost reduction in previous designs.

The cast housing includes extensive external mounting features. They act as attachment and support points lor the components of an electronic system and dual-motor controller. The base casting includes precision aerodynamic stator vanes, a motor case with ventilation holes, and a bearing liner. The casting also includes an integrated fan impeller containment ring and mounting brackets that support the installation into the aircraft.

INVESTMENT CASTING RESEARCH

Industry researchers are doing important work regarding investment casting. Every year, crucial papers are published detailing the latest developments around investment casting, helping the ages-old process stay on the cutting edge.

Below are three recent examples of the research. The entire papers are available through the AFS Library (www.afsinc.org), which is free for members.

Firing Time/Temperature Effect on Investment Shells Thermos-Mechanical Properties (2018)

Mingzhi Xu, Joe Govro, Madison Wooley, Scott Vogel, Wayne Pugh

Fused silica is widely used in investment casting shell molds as flour, stucco and binder for its superior properties, such as low linear thermal expansion coefficient and high thermal shock resistance. The fused silica devitrifies at elevated temperature during firing, preheating or the metal casting process. It was found by the authors that firing history plays a significant role on the available total specific surface area of the fused silica. The lack of surface area inhibits the devitrification due to availability of surface energy and favorable kinetical path. The amount of silica devitrified affects the thermo-mechanical properties of the investment shell molds.

What Impact will 3D Metal Printing Have on Investment Casting? (2018)

Tom Mueller

In the past few years, the number of manufacturers of metal additive manufacturing systems has ballooned from less than 10 to more than 30 and new ones seem to appear every month. Some have forecast that metal printing will become the dominant method of creating metal parts. Will metal printing make investment casting obsolete? In this study, investment foundries and metal printers were asked to quote 75 different scenarios covering a range of investment casting cases. Quoted prices were averaged for both investment cast and printed metal and in each case, the lowest cost method was determined. The analysis was then repeated assuming that metal printing prices declined to determine what ground metal printing may gain as costs come down. The results provide some insight to both metal printers and investment casters and can guide them on where to focus their efforts in the future.

Reclamation and Reuse of Shell Ceramics in Investment Casting (2017)

Victor Okhuysen, Michael Landeros, Hiten Shah

In this report on investigations on the reclamation and reuse of shell ceramics in investment casting, bars of ceramic (6x3/4x3/8 inches [150x18x9 mm]) were mixed using recipes based on fused silica and alumino silicates common to investment casting. The bars were tested for green strength and hot strength at two temperatures, 760C and 1100C (1400F and 2012F). All heated specimens were then crushed manually and broken down in a ball mill. The sieve size distribution of the milled material was compared to that of the virgin material. Then, the reclaimed material was remixed and retested, and the results were compared to the virgin mixes. The more promising mixes were run for several cycles. The alumino-silicates were successfully reclaimed at the highest temperature while the fused silica materials were not successful at any temperature except for partial reclamation of flour at 760C (2012F, aluminum processing temperatures).

A MODERN CASTING STAFF REPORT

Caption: This bronze investment casting of a thermostat cover helped add authenticity to the restoration of the Henry and Eleanor Ford estate in Dearborn, Michigan.

Caption: Designed by O'Fallon Casting, the pump housing for the aerospace industry weighs 9.6 lbs. and was converted from a multi-piece assembly.

Caption: Weighing just 0.628 lbs., the frame was much lighter than the previous model. It also maintained the required strengths in the areas of the drone where needed.

Caption: Produced for commercial aerospace, the casting reduced cost by approximately 17-20% from previous designs.
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Publication:Modern Casting
Date:Jan 1, 2020
Words:1159
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