Investment casting is a manufacturing process that involves creating wax replicas of parts, surrounding them in ceramic shells, melting out the wax, and pouring molten metal into the shells. It allows for the production of complex, near-net shape metal parts. Investment castings can be made in a variety of alloys and sizes, from small dental braces to large aircraft engine components. The process provides excellent surface finishes and tight tolerances, reducing machining needs. While tooling costs are higher than other casting methods, investment casting is often more cost effective due to reduced post-casting machining.

1. Investment Casting FAQ
Avalon Precision Metalsmiths
15583 Brookpark Road
Cleveland, OH 44142
www.avalon-castings.com

2. What is investment casting?
Investment casting is a refined manufacturing process.
It consists of several steps, including:
1. Using polished aluminum dies, create injected wax replicas of the part, called “patterns.”
2. Affix the patterns to wax runner bars to create what is known as a “tree.”
3. Dip the tree repeatedly into a slurry to build up a ceramic shell.
4. Remove the wax using steam and pressure.
5. Pour molten metal into the heated ceramic shell.
6. After cooling, remove the shell.

3. Why is it called “investment” casting?
One historical definition of “invest” is “to surround,” so the name “investment casting” refers
to the ceramic shell used to encase the wax replicas of the part to be cast.
Why is it also called “lost wax casting”?
Investment casting is also known as “lost wax casting” because the wax around which the
ceramic shell is formed is melted out, or lost, before the actual part is cast.

4. What are typical investment casting applications?
Investment casting is used to make near-net shape parts with superior finishes
for applications in a wide range of industries, including oil & gas, medical & dental
equipment, aerospace & aviation and military & firearms.
Examples include:
• Dental braces
• Compressor components
• Oil & gas metering bodies
• Components for commercial grills
• Locks and internal lock mechanisms
• Gun triggers, hammers and sights
• Rototiller tines
• Aviation and aerospace cargo systems

5. What tooling & pattern equipment are required?
The main tooling required is the split-cavity aluminum die (with the shape of the final casting)
used to produce the wax mold patterns.
Depending on the complexity of the casting, various combinations of aluminum, ceramic or
soluble cores may be employed to allow for the desired configuration.
Most tooling for investment casting costs between $1,000-$10,000.

6. Is rapid prototyping possible?
Rapid prototypes (RP), including stereo lithography (SLA) models, also can be used.
The RP models can be created in hours and take on the exact shape of a part. The RP parts
then can be assembled together and coated in ceramic slurry and burned out, allowing for a
hollow cavity to obtain a prototype investment cast component.
If the casting is larger than the build envelope, multiple RP subcomponent parts can be
made, assembled into one part, and cast to achieve the final prototype component.
Using RP parts is not ideal for high production but can help a design team examine a part for
accuracy and form, fit and function before submitting a tool order.
RP parts also allow a designer to experiment with multiple part configurations or alternative
alloys without a large outlay of tooling cost.

7. What are the size limits of investment cast parts?
Investment castings can be produced in all alloys from a fraction of an ounce, for dental
braces, to more than 1,000 lbs. (453.6 kg) for complex aircraft engine parts.
Smaller components can be cast at hundreds per tree, while heavier castings often are
produced with an individual tree.
The weight limit of an investment casting depends on the mold handling equipment at the
casting plant.
Most U.S. investment casting facilities cast parts up to 20 lbs. (9.07 kg).
However, many domestic facilities are increasing their capability to pour larger parts, and
components in the 20-120-lb. (9.07-54.43-kg) range are becoming common.

8. What are the design criteria for the tree?
A ratio often used in designing for investment casting is 3:1 — for every 1 lb. (0.45 kg) of
casting, there should be 3 lbs. (1.36 kg) to the tree, depending on the necessary yield and
the size of the component.
The tree always should be significantly larger than the component, and the ratio ensures that
the gas and shrink will end up in the tree, not the part during the casting and solidification
processes.

9. What as-cast dimensional tolerances can be achieved?
Typically, a linear tolerance of ±0.005 in/in (0.127 mm/in.) is standard for investment
castings.
For example, if a 1-ft. component were cast, it likely would have a tolerance of ±0.06 in. (1.52
mm). This would vary depending on the size and complexity of the part.
Post-casting procedures, such as straightening or coining, often allow for tighter tolerances
to be maintained on several specific dimensions.
By working with Avalon Precision Metalsmiths’ engineering staff, an investment casting
drawing can be produced for a part that substantially reduces or completely eliminates the
previous machining requirements to produce an acceptable component.

10. What kind of surface finishes can be achieved?
The final casting finish is excellent.
This is because the ceramic shell is assembled around smooth patterns produced by
injecting wax into a polished aluminum die.
A 125 rms micro finish is standard for investment casting, and even finer finishes (63 or 32
rms) are possible with post-cast secondary finishing operations.
Like other investment casting facilities, Avalon has its own standards for surface blemishes.
Our staff will discuss these capabilities with design engineers/customers before the tooling
order is released.
Certain standards depend on a component’s end-use and final cosmetic features.

11. Is investment casting expensive?
Investment castings generally have higher costs than forged parts or sand and permanent
mold casting methods, because of the costs and labor involved with investment casting
molds.
However, they make up for the higher cost through the reduction of machining that results
from as-cast near-net-shape tolerances.
One example of this is innovations in automotive rocker arms, which can be cast with
virtually no machining necessary.
Many parts that require milling, turning, drilling and grinding to finish can be investment cast
with only 0.020-0.030 inch finish stock.
Further, investment castings require minimal draft angles to remove the patterns from the
tooling (typically ½°); and no draft is necessary to remove the metal castings from the
investment shell.
This can allow castings with 90-degree angles to be designed with no additional machining to
obtain those angles.
Read more about how investment casting can lower the overall cost of ownership.

12. How many parts are needed for investment casting to
be practical?
This number depends on how many casting runs will occur. If there is a run size of 50 that
will be produced 10 times per year, the tooling costs for the wax patterns likely will be well
paid off after the 10th production run.
Generally, machine toolmakers say that the logical part count to pay off a tool is at least 25
castings.
Some investment casting facilities, mainly in the automotive industry, produce more than
100,000 parts per month.
The high part numbers are dependent on how much a metal casting facility is willing to
expand its capacity to produce such high volumes.
For standard orders, the bulk of investment castings produced fall in the range of 100-10,000
pieces per year.

13. Are there porosity and/or shrinkage defects associated
with investment casting?
This depends on how well a metal casting facility degasses a melt and how fast the parts
solidify.
As mentioned earlier, a properly built tree will allow porosities to be trapped in the tree, not
the casting, and a high-heat ceramic shell allows for better cooling.
Also, vacuum-investment cast components rid the molten metal of gassing defects as air is
eliminated.
The integrity of an investment casting can be far superior to parts produced by other
methods.

14. What alloys can be poured with investment casting?
Generally, most ferrous and nonferrous materials can be investment cast. For ferrous
materials, carbon, tool and alloy steel along with the 300, 400, 15-5PH, and 17-4PH stainless
steel alloys are most commonly poured. Also, the rise in ductile iron casting demand has
increased the use of the metal for investment casting.
For nonferrous applications, most aluminum, magnesium, copper-base and other nonferrous
materials can be cast, with aluminum as one of the most common.
Additionally, certain investment casting applications require the use of specialized “exotic”
alloys used primarily in harsh environments. These alloys, such as titanium and vanadium,
meet the additional demands that might not be achieved with standard aluminum alloys.
Cobalt- and nickel-base alloys (with a variety of secondary elements added to achieve
specific strength-, corrosion- and temperature-resistant properties) are additional types of
exotics.
Some examples are Hastelloys, which can endure steam and acids found at chemical
manufacturing plants, and Monels, which have good weldability.

15. Get the Investment Casting Answers You Need
Leading manufacturers across a wide range of industries trust Avalon
Precision Metalsmiths as the full-service, turnkey investment casting
company that will meet their specifications on time and on budget.
To learn why, contact us for your precision component needs by:
Calling 216-362-4100
Submitting a request for quote
Filling out our contact form
You’ll be glad you did.