Precision Casting Wax Injection FAQs
Today's blog focuses on Wax Injection Molding and FAQs about this step in the precision casting process. We'll tackle the basics of wax injection, touch on 3D printing advancements, how tooling progresses to wax injection, recycling, tree and gate building, and more. This is the second blog in this series; if you missed part one on tooling, you can check it out here!
A foundry worker working alongside a wax injection machine
What is Wax Injection Molding?
Wax injection molding is the second major step in the precision casting process. During this step, the tooling of your part is filled with rapidly solidifying wax to form a 1:1 replica of your part. These wax models serve as a blueprint for metal pouring later on.
If you've ever used an ice cube tray, a muffin tin, or played with Creepy Crawlers (die-cast toys where you make rubber insects/arachnids) as a kid you're familiar with the idea of molds and matrices. The molding functions as a negative or inverse of what you are trying to create, and the filling (water, muffin batter, or colorful rubber) eventually forms the final product.
These wax models are highly detailed and can include unique surface patterns, spirals, internal cavities, integrated logos/text, and the net geometry of your finalized part.
Why Use Wax Injection?
You may wonder why wax models are used in investment casting as opposed to direct pouring into a mold or sand casting. Here are a few reasons:
1) Wax models allow extreme precision, unique geometry, and consistent surface finishes.
Other casting methods cannot achieve the same level of complexity that wax affords. For simple parts, sand casting may be the preferred method. But when producing complex parts or parts in bulk, the value of investment casting shines, saving you time and money overall. You can create cavitations, overhangs, integrated logos, unique surface finishes, spiraling, and more with investment casting.
Furthermore, instead of requiring complex and expensive secondary and tertiary finishing work, many precision castings are nearly market-ready in a single action.
2) Identify any imperfections before metal pouring.
Working in wax first allows foundry workers to identify imperfections early. If needed, tooling can be adjusted, or wax models can be manipulated, to create a perfect model of your part. This can provide significant cost savings as wax is cheaper than metal, and even waste wax can be recycled and repurposed for future productions.
3) Prevention of Defects
Instead of pouring molten metal directly into a die or sand cast, wax injection allows founders to use pre-heated ceramic shells for casting.
This minimizes defects like porosity, inclusions, and cold shuts because the molten metal flows smoothly into the heated ceramic mold, reducing thermal shock.
Direct metal pouring is more prone to defects due to turbulence, uneven cooling, and more.
4) Material Versatility
Utilizing wax models allows founders to build ceramic shells that can withstand a wide array of melting points and materials, including low-carbon steels, aluminum, cobalt-base alloys, bronze, stainless steels, and more. Whereas direct metal pouring is limited to the tool's ability to handle high temperatures and thermal shock.
5) Consistency is King
Precision Casting is all about repeatability. Wax injection allows you to create hundreds or thousands of identical parts with unmatched consistency. Other methods can add variability through wear and tear of molds or less precision for complex parts in the case of sand casting.
6) Less Waste
Nearly 100% of wax used in investment casting is recycled and can be reused or repurposed for other uses. Investment casting reduces metal waste and machining waste as it creates near-net geometry upon pouring, creating less metal waste while saving your business money and reducing your footprint.
7) Less Expensive Tooling
Compared to direct metal pouring, precision casting tooling is significantly cheaper because tooling doesn't have to be as robust. Direct pouring requires durable, high-temperature tooling, which can be costly to manufacture and maintain.
Direct pouring is typically only cost-effective for massive volumes of parts.
A foundry worker at IPC Utah affixing a tree and gate system to a wax pattern.
What are Trees and Gates in Casting?
You may have heard of Gates or Trees (see picture above) when researching precision casting. Both are important structural components of wax injection models and provide unique benefits during the investment casting process.
Trees:
Are the framework for the casting process. A tree of parts features a main channel for controlled metal pouring and a variety of gates and wax patterns. They allow multiple parts to be cast at the same time, increasing efficiency and reducing turnaround times.
Trees also serve as the structure for ceramic dipping, but that is beyond the scope of this article.
Gates:
Gates are the pathways that connect each wax pattern to the main tree of parts. They act as conduits for molten metal to flow into the ceramic mold cavity during casting. Gates allow for a controlled flow of metal into each part. They help eliminate imperfections as impurities are forced up and out of your part into the gate. Gates help prevent cold shuts, porosity, and shrinkage.
During onboarding and tooling, foundry workers will work to optimize your production cycle by planning ideal gate and tree combos, allowing for pouring multiple parts in one go while maintaining consistency and quality throughout the process.
What is the difference between 3D printing and Wax Injection Molding for pattern making?
3D printing technology has improved dramatically in the past few years and is becoming increasingly accessible for DIYers, small businesses, and hobbyists. In the professional casting space, it allows engineers to quickly prototype and iterate on designs without the need for expensive and time-consuming tooling. Many foundries, including IPC, use 3D printing to rapidly produce first articles and prototypes to help businesses get functional models in their hands ASAP.
These functional models allow for internal testing and decision-making before a full-scale production run. 3D printing has limitations in material availability, bulk production, and consistency when compared to wax injection molding. Nevertheless, it is an integral part of modern prototyping and small-batch production.
For medium and large-scale production, wax injection is the preferred method as it provides cost savings, consistency, material diversity, and speed in bulk production that 3D printing currently cannot match. At IPC, for example, following onboarding, testing, and prototyping with a 3D print model, our engineers will prepare tooling for traditional wax injection and investment casting.
What Happens to the Wax During Precision Casting?
Following the development of trees and gates, wax injection models will move onto the next step of the precision casting process, ceramic slurry dipping (which will be covered in an upcoming FAQ blog!)
Here, the wax models will be repeatedly dipped in a ceramic slurry that will make a hard outer shell around the wax model. This shell serves as an ideal medium for metal pouring.
Before metal pouring, the wax patterns and ceramic shells will be superheated to "burnout" all of the wax models leaving behind a hollow shell where the wax once was. The ceramic shells will eventually be filled with molten metal later in the process.
During the burnout/dewaxing phase, nearly 100% of wax can be recycled or repurposed for future production runs.
How long does it take to produce a Wax Pattern?
Once prototyping and tooling are complete, wax injection is lightning-fast. Modernized automated injection machines can produce patterns in as little as 10 seconds. There is a good amount of variability in how long a pattern takes depending on geometry and size, but even the largest and most complex parts only take a few minutes on modern equipment.
Following the injection of standard parts, foundries will also produce wax models for gates and trees. Much of this process is fully automated in modern foundries.
How do you ensure dimensional accuracy in wax patterns?
At IPC, we make sure our wax patterns are accurate by:
Using high-quality wax with predictable shrinkage.
Designing and testing our tooling to account for shrinkage.
Maintaining precise control over injection parameters (temperature, pressure, speed, etc.)
Regularly inspecting and calibrating molds and equipment.
Can broken/defective Wax Patterns be repaired?
Depending on the severity of the issue, yes! Many imperfections can be repaired with wax welding tools. Typically small imperfections are fixed when parts are added to gates and trees. If a major issue is detected, the wax is recycled and foundry staff will troubleshoot the wax injection machine, tooling, or both.
A foundry worker using a wax welding tool
Conclusion
Wax injection is the second major step of the investment casting process and it is where projects move from concept to concrete. Modernized equipment allows for extreme precision and consistency when producing parts en masse. We hope this blog helped you learn more about Wax Injection molding and the casting process!
At IPC Foundry Group, we're always focused on investing in our clients with technology that helps you produce high-quality parts faster and more affordably than ever. If you'd like to learn more about casting or how IPC can help your business, Contact Us today!
