Investment casting, also known as lost-wax casting, clearly highlights the importance of wax in this process. There are several types of wax used in investment casting, and the choice depends on your specific casting requirements. Wax patterns made from different types of wax can result in varying surface qualities and dimensional accuracies for the castings. Therefore, the type of wax used directly impacts the final quality of the casting. This article will introduce the common types of wax used in investment casting, their properties, and how to select the appropriate wax for your project.
Why Casting Wax is the Heart of Investment Casting
Many people underestimate the critical role of wax in the lost-wax casting process. However, as professionals in the field, we all recognize the importance of wax; as its name suggests, it is the cornerstone of the finished casting’s quality.
The Role of Wax in the “Lost-Wax” Process
The term “lost-wax casting” is highly descriptive. In the investment casting process, we first use an aluminum mold to create a precise wax pattern identical to the target casting. Next, we apply a ceramic slurry to the surface of the wax pattern to the desired thickness; once cooled, this forms a hard ceramic shell. We then melt the wax inside the ceramic shell at high temperatures and pour it out, creating a cavity. Finally, we pour molten metal into the cavity, and once it cools, we obtain the investment casting. This is where the name “lost-wax casting” comes from.
Why Your Foundry’s Wax Choice Matters to You
From the description above, we can see that the finished casting is, to a certain extent, a replica of the wax pattern. Therefore, the quality of the wax pattern determines whether the target casting’s surface quality, dimensional accuracy, and geometric shape can meet project requirements. Consequently, if the wax pattern itself has defects, it is impossible to produce a perfect metal part.
Types Of Wax Used In The Investment Casting Process
Next, I will introduce the five main types of wax used in investment casting, including filled pattern wax, non-filled pattern wax, runner wax, sticky wax, and water-soluble wax.
Filled Pattern Wax
Filled pattern wax is one of the most widely used high-performance waxes in precision casting. It contains fillers added to the wax base, commonly including bisphenol A (BPA), organic fillers, and terephthalic acid. These fillers enhance the mechanical properties of the wax pattern and ensure its dimensional stability. A low coefficient of expansion and low shrinkage rate are the most notable advantages of filled pattern wax. This means that the wax patterns can achieve tighter dimensional tolerances (±0.1%), making them an ideal choice for precision casting of complex, high-value parts and assemblies.
Due to its high performance, filled pattern wax is more expensive. Furthermore, the addition of fillers impedes its flowability, making it more difficult to process and use, and requiring a longer time to completely burn out during dewaxing. Additionally, the recyclability of this wax is limited, depending on the density of the fillers.
Typical Applications: Aerospace components, medical precision casting, automotive castings, pump castings, turbine components.
Non-Filled Pattern Wax
Non-filled, or unfilled, pattern wax contains no solid fillers. Compared to filled pattern wax, it is more cost-effective and easier to process. Because it contains no fillers, unfilled pattern wax has better flow properties and is easier to recycle. A key advantage of unfilled pattern wax is its excellent surface quality, making it widely used in the investment casting process.
However, it should be noted that unfilled pattern wax has lower strength and stability than filled pattern wax and is not suitable for large, heavy-duty structural castings. It is better suited for small to medium-sized castings with complex geometries. Additionally, due to its slower solidification rate, it is more prone to shrinkage and deformation during cooling, which may require a wax cooler to mitigate.
Typical Applications: Small mechanical parts, used in combination with 3D printing.
Runner Wax
Runner wax, also known as gating wax, is a type of wax specifically used in investment casting to construct the gating system. It offers excellent flow properties and adhesion, optimizing the flow of molten metal to ensure it flows smoothly into all parts of the mold cavity, thereby minimizing defects such as incomplete filling and leakage. Runner wax has a lower melting point than other waxes, which helps prevent damage to the mold caused by high temperatures and facilitates demolding after casting. Additionally, runner wax is typically made from recycled wax, making it a cost-effective option.
Typical Applications: Gating systems for investment casting
Sticky Wax
Sticky wax is a type of wax with adhesive properties. It has a low melting point and is easy to shape; it is used to assemble various wax models and secure them within the central runner system. It is intended solely for assembly or repair and cannot be used as a substitute for pattern wax. Its low melting point allows sticky wax to burn completely at high temperatures without leaving any residue.
Water-Soluble Wax
Water-soluble wax is generally used for casting the cores of complex parts. It is first manufactured and placed in the mold; after solidifying together with the pattern wax, the entire wax assembly is immersed in a dissolving solution. Once the water-soluble wax dissolves, a wax part with a structurally intact, smooth surface and complex internal structure is obtained.
For parts with complex geometries, cavities, and features such as undercuts, water-soluble wax offers an excellent solution. Although it is more expensive, water-soluble wax—which optimizes material utilization and enables lightweight designs—will only grow in popularity as environmental concerns become increasingly important.
Typical Applications: Medical investment castings, aerospace castings.
| Wax Type | The Pros | The Cons | Relative Cost |
| Filled Pattern Wax | Low shrinkage Excellent dimensional stability High mechanical strength | Slightly lower flowability More difficult to process Difficult to recycle | Relatively high |
| Non-Filled Pattern Wax | Superior surface finish Good fluidity Easy to recycle | Higher shrinkage rate Inferior mechanical properties | Moderate |
| Runner Wax | High strength for assemblies Low melting point prevents shell cracking | Weaker dimensional stability | Low |
| Sticky Wax | Excellent adhesion | Very brittle Only useful for assembly | Low |
| Water-Soluble Wax | Allows for “impossible” internal geometries | Highly sensitive to ambient humidity | High |
How to Choose the Right Wax for Your Investment Casting Project
When selecting the appropriate wax for a project, the choice typically comes down to either filled pattern wax or unfilled pattern wax; sometimes, it is also necessary to consider whether to use water-soluble wax to assist in mold completion. Since the applications for adhesive wax and runner wax are largely fixed, we will now discuss the appropriate scenarios for filled and unfilled pattern waxes.
Matching Wax to Geometry Complexity
For components with thick cross-sections and substantial weight, wax shrinkage may cause surface indentations in the wax pattern. In such cases, selecting a filling process can stabilize the wax structure, significantly reduce the wax part’s volumetric shrinkage rate, and ensure surface flatness.
For thin-walled structures and castings with fine details, choosing a non-filling wax material allows it to easily fill even the smallest gaps.
Dimensional Accuracy and Shrinkage Allowances
The type of wax affects the dimensional accuracy of castings. If your project has strict dimensional tolerance requirements, filling-type pattern wax is a more reliable choice. Its low shrinkage rate effectively controls dimensional deviations and ensures dimensional consistency in mass production.
However, regardless of the wax type selected, its shrinkage rate (both pattern wax shrinkage and casting shrinkage) must be considered during the DFM process. Specific dimensional allowances must be incorporated into the mold design to ensure the final castings meet project requirements.
Surface Finish Requirements
Non-filled wax outperforms filled pattern wax in terms of surface quality. If your project requires a high level of surface finish for investment castings, it is the ideal choice.
Cost-Effectiveness
Sometimes, to balance quality with the investment casting cost, we can achieve cost-effectiveness by combining new wax with recycled wax. For example, when manufacturing large, heavy castings, the runner system consumes a significant amount of wax, yet these areas do not directly impact the casting’s quality. We can use recycled wax for the gating system, which not only reduces the unit cost of the casting but also ensures the quality of the finished product.
3D-Printed Castable Resins vs. Traditional Casting Wax
With advances in 3D printing technology, pourable resins have become an important complementary material to traditional casting wax in the investment casting field. They make prototype validation and iteration faster and more convenient. For foundries, we view these two technologies as complementary rather than mere substitutes.
Applications of 3D-Printable Castable Resins
Rapid Prototype Casting and Validation: When your design is still in the testing phase and requires frequent revisions, 3D printing eliminates the need for costly and complex mold-making processes, allowing you to directly transform your design into a physical pattern or even a metal part.
Small-Batch Production: Spending thousands of dollars on mold costs for small-batch orders—such as customized parts, artwork, or niche industrial components—is clearly not cost-effective. 3D-printed casting effectively solves this problem.
Ultra-complex Geometries: 3D printing offers unparalleled forming capabilities, enabling the creation of intricate structures that traditional casting techniques—even investment casting—cannot achieve, thereby providing unlimited possibilities for manufacturing design concepts.
Comparison of 3D-Printable Castable Resins and Traditional Casting Wax
Even though 3D printing resins have brought progress and transformation to the casting industry in the areas mentioned above, they still cannot replace the status of traditional casting wax.
| 3D-Printed Castable Resins | Traditional Casting Wax | |
| Tooling Cost | Zero | Relatively High |
| Lead Time | Very Fast (usually 3–5 days) | Slower (2–4 weeks) |
| Unit Price | Relatively High | Low |
| Surface Finish | Good | Excellent |
| Dimensional Consistency | Good | Superior |
| Ash Residual | Nearly Zero | Zero |
| Optimal Application Scale | 1 – 50 Piece | 100 – 100,000+ Piece |
In comparison, traditional casting wax remains superior to 3D printing resins in terms of recyclability, processing speed, surface quality, and consistency in mass production. Therefore, it remains the material of choice for high-precision, large-scale investment casting applications.
Even though 3D printing resins have brought progress and transformation to the casting industry in the areas mentioned above, they still cannot replace the status of traditional casting wax.
In comparison, traditional casting wax remains superior to 3D printing resins in terms of recyclability, processing speed, surface quality, and consistency in mass production. Therefore, it remains the material of choice for high-precision, large-scale investment casting applications.
Conclusion
In short, in investment casting, the type and quality of the wax used directly impact the quality of the final casting, and each type of wax offers its own unique advantages. Choosing the right wax can help you achieve twice the results with half the effort. If you need assistance, please feel free to contact us. Pingheng Machinery has specialized in investment casting for over two decades, offering a wide range of casting services, including stainless steel and copper alloy casting. With our own foundry and precision machining facility, we provide a one-stop solution to meet all your needs. We look forward to hearing from you.
FAQ
What is the difference between virgin wax and reclaimed wax in casting?
Virgin wax is brand-new, unused wax, while recycled wax is reclaimed wax. You can use the former to create wax patterns for mold components, ensuring a flawless surface finish, and use the latter—after filtering—in the central gating system and runner system. This approach ensures part quality while reducing your unit costs.
Why do foundries use filled waxes instead of unfilled waxes for certain parts?
The primary purpose of using filler wax is to minimize volume shrinkage in the wax pattern, prevent the formation of “shrink marks” (surface indentations), and reduce investment casting defects.
Is it cheaper to use 3D-printed castable resin or injected wax for 50 metal parts?
For production runs of 50 units or fewer, 3D-printable resin is a more cost-effective and faster option. It eliminates the lengthy mold-making process typically required in traditional casting. However, when you plan to increase production volume, traditional casting becomes the more cost-effective choice.
How much does investment casting wax typically shrink during cooling?
Depending on the specific formulation of the wax, its volumetric shrinkage generally ranges from 0.5% to 1.5%.
Can wax shrinkage cause dimensional inaccuracies in the final metal casting?
Yes, that is inevitable. In investment casting, the finished casting is virtually an exact replica of the wax pattern. Any deviation or defect in the wax pattern will be fully reflected in the finished casting. Therefore, strict control over all environmental factors is required during the wax pattern fabrication stage.
This may indeed be caused by the wax pattern. In the case of thicker molds, the wax core cools slowly after the wax is poured, causing it to shrink inward. If this issue is not addressed during the wax pouring stage, the final metal casting will exhibit the same problem.
Which type of wax gives the best surface finish for stainless steel casting?
It is undoubtedly the non-filled pattern wax. Free of additives, it perfectly replicates the highly polished inner surface of aluminum molds, producing sharp edges and a flawless finish.
Does 3D-printed castable resin leave more ash residue than traditional pattern wax?
This has indeed been the case in past casting projects. Early castable resins left behind a small amount of ash residue during the sintering process. However, modern casting-grade SLA/DLP castable resins enable clean sintering with virtually zero ash residue.
Are there any other types of casting patterns besides wax patterns?
Of course, if you want to know more about the types of patterns in casting, please browse our blog.
