Learn The Investment Casting Process

For more than 70 years, Hitchiner Manufacturing has been manufacturing parts used by the country's leading industries. The process we use to create parts is called investment casting, a highly effective and efficient way to produce complex parts. While many people have some understanding of how casting works, this post will cover the investment casting process and how Hitchiner uses it to make high-quality, high-volume parts.

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Investment casting is a method of manufacturing parts by pouring molten metal into a hollow mold shell. The shell is made by an “investment” of ceramic materials built around a wax model.  Sometimes called precision investment casting or lost wax casting, investment casting begins by creating wax replicas, or patterns, of the desired castings by injecting hot wax into a die. The patterns are attached to a wax stick, called a sprue, to form a casting cluster or assembly. Next, a shell is built around the wax patterns by immersing the assembly in a liquid ceramic slurry and then into a bed of fine sand. At Hitchiner, we use specialized shell building robots during this step for a consistent build and to allow for larger molds than could be built by manual methods. Once the ceramic is dry, the wax is melted out, creating a negative impression of the assembly within the shell. Molten metal is then poured into the shell. At Hitchiner, we use our exclusive Countergravity Casting process. Instead of pouring in the metal, molten metal is drawn into the mold cavity in a controlled fashion, resulting in superior products. Once the metal begins to harden, the vacuum is released, and the ceramic is then broken away to leave the metal part. 

A wide range of industries use investment casting because it offers designers and engineers the ability to create parts using a wide range of alloys. It is also capable of producing precise detail in parts weighing many pounds or just a few ounces. 

What Is Created Using The Investment Casting Process

Investment casting creates high-quality products and gives companies the flexibility to design and produce a wide range of parts in a cost-efficiently way. This versatility is why so many companies, and so many industries, use the technology to create parts, including the automotive, biomedical, and aerospace industries.

The ability to make precise parts is one reason the automotive industry has utilized investment casting. Hitchiner's processes can help companies develop parts that are high-performance and increase fuel efficiency. When parts programs call for ready-to-use or fully finished and assembled investment castings in high, moderate, or low volumes, Hitchiner has the capabilities to meet customers' needs.

Fuel-efficient, high-performance automotive components created using Hitchiner's countergravity processes are uniquely well-suited for these parts and applications areas:

• Turbocharger wheels

• Wastegate

• Fuel rail function blocks

• Actuator rods

• Rocker arms

• Intermediate levers

• Steel pistons

• Fuel cell

• Direct injection system

• Variable valve timing

• Exhaust gas regeneration

In the aerospace industry, Hitchiner has worked with companies such as Bodycote, TCC, Elison Surface Technologies, HiTemco, and many other OEM-qualified suppliers. Whether for commercial airlines of defense contractors, Hitchiner's investment casting process is excellent for parts such as:

• Compressor

• Combustor

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• Turbine

• Augmenter/nozzle

• Fan

• Landing gear

• Structural components

• Auxiliary power unit components

• Defense armament applications

• Missile canard & fin

• Rocket motor case

• Valves

• Propulsion components

What is Investment Casting?

Investment casting is a manufacturing process in which a wax pattern is coated with a refractory ceramic material. Once the ceramic coating material is dry and hardened, the wax is melted out and leaves an internal cavity the shape of the final product’s geometry. Molten metal is poured into the cavity where the wax pattern was. The metal solidifies within the ceramic cavity, cools, and the ceramic is removed from the metal casting. The result of this process is a net to near-net precision metal component which can be used for a broad range of applications in various industries.

Why is it Called Investment Casting?

The ancient art and science of investment casting is also known as the lost wax process. Investment casting was developed over years ago and can trace its roots back to both ancient Egypt and China. Parts manufactured in industry by this process include dental fixtures, gears, cams, ratchets, jewelry, turbine blades, machinery components and other parts of complex geometry.

What is the Investment Casting Process?

Investment casting is a manufacturing process in which a liquid material is poured into a ceramic mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is the casting, which is broken away from the ceramic mold to complete the process. The steps within the investment casting process are as follows:

 Step 1: Engineering Review

• The first step of this manufacturing process begins with a full Design For Manufacturing (DFM) review with the customer.
• This would include an evaluation of print dimensions as it relates to the investment cast process, wax injection mode build considerations such as gate placement, post-case material requirements and expected tolerances for fit, form and function of the part, and final inspection criteria to determine a mutually acceptable part.

 Step 2: Mold Design & Build

• The process begins with a precision-engineered wax injection mold to produce wax patterns representing the final part.
• These design considerations are discussed with the mold builder and a mold design is created.
• Our wax injection molds are built here at Aero Metals at our in-house mold shop.
• The molds are designed and built to reproduce millions of wax parts over its lifetime.

 Step 3: Wax Pattern

• The wax injection mold is quantified to run production and brought to the Wax Room for injection and assembly.
• Anywhere from one to 100 patterns are injected and placed or glued onto a pre-fabricated wax runner system known as a “tree” in our process.
• The populated tree of wax parts is also known a cluster (of parts).
• The tree cluster is then sent to the Dip Room for the next part of the process.

 Step 4: Ceramic Mold Construction

• The wax tree is dipped and completely enveloped into ceramic slurry, taken out, then completely coated in sand to create the first layer of shell, and then dried.
• This enveloping process of dip and sand is repeated 6 or 8 times with a drying period between each one.
• By repeating this process, it creates a lamination effect building a strong ceramic shell around the wax pattern as known as “investment”. The shell now runs through our drying system for 24 to 36 hours before removing the wax from the shell.

Step 5: De-waxing

• The shell, which consists of the wax pattern and its coating of ceramic and sand, is placed into an autoclave to quickly remove the wax under extremely high pressure and steam heat.
• This vessel helps to hold the shell in place and the steam heat quickly melts the wax out creating an empty ceramic mold, hence the name “lost wax” casting.
• The ceramic shell is then moved to the foundry ovens to start the casting process.

Step 6: Foundry & Pouring

• The mold is then placed into a high temperature oven, approximately °C (°F), to cure (cristobalite) the ceramic mold and prepare it for accepting molten metal.
• The cured ceramic mold is removed from the hot oven and molten metal is immediately poured into the mold cup and its subsequent gating system, completely filling out the mold cavity with metal.

Step 7: Shell & Casting Removal

• After the metal has cooled to the touch, the ceramic mold shell can be broken away from the part(s), and the casting(s) removed from, the now metal, tree.
• The ceramic shell is brittle and typically broken free by using water jets, vibration, and other methods.
• Once the tree is clean of the ceramic, the parts are removed from the gating system by either cutting off with a saw with vibration or liquid nitrogen.

Step 8: Finishing

• Often, the part’s gate is removed by a grinding or machining post-cast operation.
• Further finishing such as heat treatment to anneal before machining, plating, or harden is completed before final inspection and shipping to the customer.

Click here for a downloadable walkthrough of the investment casting process

In addition, within the post-casting stage Aero Metals is fully equipped to handle any finishing, if necessary.

Contact us to start the informal engineering discussion about your project, or request a quote on your precision metal component and we’ll get back to you with a proposal.

What Materials can be Investment Cast?

Aero Metals can create precision metal components through investment casting using nearly any metal. However, the advanced quality materials we most commonly use, include:

What is Investment Casting Used For?

The investment casting process is most beneficial for casting metals with high melting temperatures that cannot be forged, pressure casted, or molded in plaster or sand. Typical investment castings include parts with complex geometries, such as turbine blades, firearm components, marine parts, and other industrial components.

What are the benefits of Investment Casting?

There are many benefits associated with investment casting in the manufacturing of precision metal components, some of which include:

The company is the world’s best lost wax casting services supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.

• Mold design versatility
• Increased complex design capabilities
• Provides for a smoother surface (125 RMS)
• Highly accurate, repeatable-designs
• Time & cost savings versus fabrication and machining
• Produces numerous types of products
• Numerous types of metal alloys can be used

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