Investment Casting: Definition, Process, Advantages, Disadvantages, and Comparison with Other Manufacturing Methods

Dating back to 3700 BC, investment casting is an ancient manufacturing legacy that remains a suitable method especially for complex components of modern industry. Often referred to as lost-wax casting, the process is defined by its name: a sacrificial wax pattern is 'invested' (surrounded) by a refractory ceramic material. Once the shell hardens, the wax is melted away to create a hollow cavity for molten metal. This method offers remarkable freedom in part size and material selection, achieving a standard precision of ±0.1mm. It is the go-to solution for complex surfaces, intricate internal cavities, and medium-to-large components. With tooling costs lower than die casting and accuracy far superior to sand casting, investment casting provides a perfect middle ground. However, for ultra-precise features like threaded holes or tight-tolerance bores, secondary CNC machining is essential. This article explores the investment casting process, its pros and cons, suitable materials, and how it compares to other manufacturing techniques.

 

 

 

 

 

What is Investment Casting? 

 

 

 

 

At its core, investment casting involves creating a sacrificial wax pattern that is "invested" (encased) in a refractory ceramic shell. Once the shell is hardened, the wax is melted away, and molten metal—such as stainless steel or aluminum—is poured into the resulting cavity. After cooling, the ceramic is removed to reveal a metal part in the desired shape.

 

Among various casting methods, investment casting is a well-suited solution for mass-producing complex parts: it offers a moderate cost with good dimensional precision(0.1mm) among various casting processes. While extreme tolerances (±0.01mm) still require secondary CNC machining, investment casting is ideal for complex geometries or hard-to-machine materials.

 

This process is indispensable across several high-stakes industries:

 

• Medical: Producing orthopedic implants using biocompatible materials like Cobalt-Chrome alloys.
  
• Aerospace: Manufacturing turbine blades and engine components from high-strength 7075 alloy and 7050 Aluminum.
  
• Automotive: Delivering mass-produced sensor housings, rocker arms, and exhaust manifolds using 5754 Aluminum.
  
• Industrial & Food Machinery: Crafting high-durability pumps and valves from materials like 316 Stainless Steel or 2205 Duplex Stainless Steel.
  
• Jewelry Invest Cast: Creating intricate jewelry designs in gold, silver, platinum, or glasses.
  

 

 

 

 

The Step-by-Step Investment Casting Procedure

 

 

 

 

For mass-produced items, the process usually begins with a steel tool to create the wax patterns. Here is how a part moves from a digital file to a metal component:

 

• Step one(Wax Injection): Molten wax is injected into a metal die to create a high-fidelity replica of the part.
  
• Step two(Tree Assembly): Multiple wax patterns are attached to a central wax sprue, forming a "casting tree."
  
• Step three(Shell Building): The tree is dipped into ceramic slurry and coated in fine sand. This is repeated until a thick shell is formed.
  
• Step four(Dewaxing): The shell is placed in an autoclave; the wax melts out, leaving a precision ceramic mold.
  
• Step five(Metal Pouring): The shell is preheated and filled with molten metal (Stainless steel, Aluminum, or Cobalt alloys).
  
• Step six(Knockout): Once cooled, the ceramic shell is broken off to reveal the investment casting parts.
  

 

 

 

What are Advantages of Investment Casting

 

 

Investment casting is favored by engineers because it bridges the gap between design freedom and production efficiency. Its primary strengths include:

 

• Complex Geometries: It can produce intricate shapes—such as internal cooling channels or thin-walled fins—that are impossible to achieve with sand casting or traditional machining.
  
• Superior Surface Finish: Compared to other casting methods, it offers a much smoother surface (typically Ra 1.6 to 3.2μm), significantly reducing the need for intensive polishing.
  
• Material Versatility: It supports a vast range of alloys, including hard-to-machine metals like Cobalt-Chrome, Duplex Stainless Steel, and Superalloys.
  
• Reduced Material Waste: As a "Near-Net Shape" process, it uses only the metal necessary for the final part, leading to major cost savings on expensive raw materials.
  
• Dimensional Consistency: It provides tight tolerances (approx. ±0.1mm) that remain consistent across high-volume production runs.
  

 

 

 

 

What are Disadvantages of Investment Casting

 

 

Despite its versatility, the process has specific limitations that you may consider:

 

• Higher Initial Tooling Costs: The metal dies required to create the wax patterns are more expensive than the patterns used in sand casting (although lower than die casting).
  
• Lengthy Production Cycle: The multi-stage process—dipping, drying the shell, dewaxing, and pouring—means lead times are usually longer than die casting or direct CNC machining.
  
• Size Limitations: While medium-sized parts are common, extremely large components are difficult and costly to "invest" in ceramic shells.
  

 

 

 

 

What’s the CNC Machining Role in Investment Casting

 

 

Investment casting is a formative process (shaping molten material), whereas CNC machining is a subtractive process (cutting from solid material). CNC-machined parts are far more precision(0.01mm) than any casting methods including the investment casting(0.1mm) but expensive for CNC machining requires high machine operating cost and there is materials waste problem. For hard-to-machine or expensive materials to make complex parts but must require 0.01mm precision, you can combine these two ways: first investments casting and then secondary CNC machining.

 

 

 

 

The Necessity of Secondary CNC Machining

 

• Achieving Extreme Tolerances: Casting usually hits a limit at ±0.1mm. For critical components like engine valves or medical joints, VMT CNC machining brings that precision down to ±0.01mm.
  
• Threading and Tapping: Cast sharp and functional screw threads are hard to achieved by investment casting. CNC machining is required to tap holes and mill precise threads for assembly.
  
• Perfect Mating Surfaces: For parts that must be airtight or watertight (like pump housings), CNC milling ensures that the mating surfaces are perfectly flat.
  
• Boring and Reaming: Critical internal diameters, such as bearing seats, must be bored with CNC equipment to ensure perfect circularity and fit.

 

 

 

 

Investment Casting vs. Die Casting vs. Sand Casting 

 

 

Among casting methods, investment casting, die casting, and sand casting stand out for their unique surface finish, cost difference, parts precision, etc. Below table shows their (investment casting vs die casting vs sand casting) unique characteristics:

 

 

Table 1: Investment Casting vs. Die Casting vs. Sand Casting

 

 

            

 

            

1. Dimensional Tolerance and Surface Finish

 

The precision of a cast part is directly determined by the stability and rigidity of the mold material. Die Casting offers the highest precision because it utilizes machined steel molds and high pressure to force molten metal into every corner, acting as a high-precision stamp where the metal must follow the exact dimensions of the steel. Investment Casting also provides high accuracy, but because it uses a ceramic shell that can slightly expand or contract during the firing and cooling process, it has a higher variance than a solid steel die. Sand Casting provides the lowest accuracy and a grainy finish because it relies on compressed sand; the large grains and the tendency for the mold to "shift" slightly under the weight of the molten metal result in looser tolerances.

 

 

2. Geometric Complexity and Design Logic

 

The ability to produce complex or hollow shapes depends on whether the mold is permanent or sacrificial. Investment Casting is the clear winner for complexity because the ceramic shell is broken to remove the finished part, allowing for "impossible" internal shapes and intricate geometries to be cast. In contrast, Die Casting is significantly more limited; because the steel mold must open to eject the part, the design cannot include undercuts or internal traps that would prevent the rigid mold halves from sliding apart.

 

 

3. Metal Compatibility 

 

Compatibility is dictated by the melting point of the mold compared to the pouring temperature of the metal. Die Casting is limited to "softer" non-ferrous metals like Aluminum and Zinc because a steel mold would melt or warp if subjected to the extreme temperatures (approx. 1500°C) required for molten steel. However, Sand and Investment Casting are considered universal methods. They utilize refractory materials—sand or ceramic—that can withstand extreme heat, making them perfectly capable of handling Stainless Steel, Superalloys, and other high-temperature metals.

 

 

4.Production Cost and Volume

 

The financial viability of each method is a balance between upfront tooling investments and ongoing labor. Die Casting requires very high tooling costs because the molds are machined from expensive blocks of H13 tool steel, necessitating massive production volumes to recover the investment. Sand Casting is the most cost-effective because sand is inexpensive, and patterns can be quickly made from wood or 3D-printed materials. Investment Casting occupies the middle ground; it involves higher labor costs because every single part requires a unique wax pattern and a hand-dipped ceramic shell.

 

 

 

 

Conclusion

 

 

In this guide, we have explored the versatility of investment casting, from its ability to handle complex geometries to its compatibility with high-strength, hard-to-manufacturing materials. Among many casting methods, investment casting remains good economical for most of the complex parts while there is no need expensive mold cost like die casting, no sand-like surface like sand casting, and far less material waste like CNC machining.

 

 

 

 

 

 

VMT CNC Machining Case Study: Precision Finishing for Medical Valve Bodies 

 

 

A medical device manufacturer required a complex valve body made from 316L Stainless Steel. The part featured intricate internal flow chambers that could only be produced via lost wax investment casting. However, the valve required three internal bores to have a tolerance of ±0.015mm and a mirror-smooth surface finish —specifications the casting process alone could not meet. The client shipped the "Near-Net Shape" castings to the VMT CNC Machining Factory.

 

 

Our Solution:

 

• Precision Secondary Finishing: We utilized our 5-axis CNC machining centers to precisely bore the internal valve seats.
  
• Automated Threading: We added high-precision threaded ports that are impossible to cast with enough accuracy for medical-grade seals.
  
• Surface Refinement: Using high-speed milling, we brought the critical mating faces to the required Ra 0.4μm finish.
  

 

By combining the geometric freedom of stainless steel investment casting with the extreme accuracy of VMT CNC machining, tolerance and surface smoothness have met the requirements while ensuring 100% assembly pass rates. 

 

 

 

 

FAQs

 

 

Is investment casting expensive? 

 

Investment casting is considered moderately expensive. While the initial tooling costs are significantly lower than die casting, the high per-unit cost stems from its labor-intensive nature—every part requires a unique wax pattern and a hand- or robot-dipped ceramic shell that is destroyed after one use. However, it often saves money in the long run by producing "near-net shapes" that eliminate the need for expensive secondary CNC machining on complex parts. 

 

 

How long does it take for investment casting to finish?

 

A typical production cycle can take 4 to 8 weeks, depending on the complexity of the shell-building and cooling phases. Secondary CNC machining at VMT can then be performed quickly to finalize the parts.

 

 

Can you use 3D printing for investment casting? 

 

Yes. 3D printing investment casting patterns (printing the "wax" or a resin equivalent) is a popular way to skip the expensive tooling stage for prototypes or small batches.

 

 

Which is stronger: CNC-machined parts or investment cast parts?

 

Generally, CNC machined parts from forged or extruded billets are stronger and more consistent, as they do not have the risk of internal casting defects like gas porosity.

 

 

What is the difference between "Invest" and "Investment" casting? 

 

There is no difference; they are the same process. The name comes from the pattern being "invested" (surrounded) by the ceramic shell.

 

 

Why do I need CNC machining for my investment cast parts?

 

Casting cannot accurately produce features like threaded holes, tight-tolerance bearing seats (±0.01mm), or extremely smooth mating surfaces. CNC machining is the standard "second process" to achieve these requirements.