Investment casting of complex metal alloy parts

All high-tech industries that need help implementing innovative technologies using complex, robust, precise and exceptional quality metal parts turn to investment casting foundries like Vestshell.

Such industries include:

• Defence/armament
• Aerospace
• Medical
• Nuclear power
• Industrial
• Transport
• Commercial 
• Telecoms 

What types of metal alloys can be used in investment casting?

The most used metal alloys fall into two groups:

Ferrous

• Cast iron
• Carbon and low-alloy steel
• Austenitic stainless steel
• Martensitic stainless steel
• Precipitation hardening steel

Non-ferrous

• Aluminum, titanium, copper, nickel or cobalt based

Even if the alloy you require isn’t available when you submit a project to a precision foundry, in many cases, equivalents exist. Specialists are available to advise you and provide support whether you need a single part machined, a new prototype developed, or a first production run executed.

Complex metal alloy parts that can be produced

Considering that investment casting can produce parts from just a few grams to several hundred kilograms, with thin walls, minute details and high levels of complexity, the range of possibilities is endless.

Products designed using investment casting include aircraft engine parts, weapons components, highly sophisticated prostheses and delicate jewellery.

Parts that are unfeasible or not advantageous to produce

The investment casting technique isn’t suitable for all parts. When you need to design large parts – non-repeatable or rather simple parts – industry specialists will help you choose the right forge or advise you on another more cost-effective casting method.

The most efficient investment casting process

Not all precision foundries use the same investment casting process. 

This process draws on the expert skills of many experienced specialists. It also requires equipment that allows maximum production speed, while maintaining the highest level of quality required for the specific steel, aluminum or other metal alloy part. 

The technique ensures that parts are of the highest quality and comply in every respect to the engineering drawings and the highest standards of high-tech industries. 

Moreover, parts can take 30 days to several months to produce, depending on their complexity. However, moulding allows for subsequent repeatability and therefore optimal production speed and shorter delivery times.

Overview of the investment casting process 

Over time, we’ve adapted, tested and perfected every step of the process. The technique goes back thousands of years. However, thanks to today’s skilled resources and precise, complex equipment, the result we can achieve is unmatched. 

1. Automated wax mould design
2. Robotic dipping and shell creation
3. Direct pour casting* 
4. Automated cutting 
5. Complete elimination of casting paths
6. Various NDT tests during the manufacturing process
7. Multi-directional rectification

*Unlike direct pouring, the intermediate casting process leads to steel losses, contamination and oxidation.

Additional detail about the technique

A close-up look at the process details reveals how rigorous the process is to achieve the type of finished product that high-tech industries require. The parts meet the dimensions, angles and other tolerances that testify to the precision of investment casting. 

1. Refractory wax mould creation and clustering

The injection of wax into an aluminum die creates a second mould of the part to be reproduced, this one in ceramic. An assembly of wax components is added to the mould to ensure the metal is poured into each of the cavities. 

2. Robotic dipping to create the ceramic shell

The assembly is then dipped in a liquid ceramic solution (grout). This is followed by many sand coatings (from 7 to 15) depending on the size of the cluster. Each step involves: 

• A grout dipping
• A layer of refractory sand
• Several hours of drying before the next coat is applied

The end result is a mould with a hardened ceramic wall that can accommodate molten metal heated to 1200°C. 

3. Autoclave dewaxing

This shell will hold the cast metal alloy. However, first it has to undergo two more preparation steps. It is sent to the autoclave to melt the original wax mould and then sent to sintering.

4. Sintering

During sintering, the moulded part is heated for a few hours before the metal alloy is applied. This last preparatory step prevents the ceramic mould from breaking under the heat.

5. Casting

At this stage, molten metal is poured into the ceramic mould.

6. Cooling

Cooling is then done at room temperature for a few hours and varies according to the alloy (steel, aluminum, etc.).

7. Demoulding and removal of clusters

The mould is then removed mechanically with a vibrating hammer or water jet, and the part is cleared of its original metal entry paths. These are cut away with a specialized saw or by automated processing.

8. Removal of casting paths, rectification and calibration

Metal alloy parts made using this technique are usually part of larger components, or at least need to be machined to be properly assembled. Therefore, they are coarsely polished and passivated, as required. 

IMPORTANT: Be aware that casting paths can hide defects. Look for a foundry that can offer you a streak-free, well-graded finish with flawless dimensional stability.

9. Quality control through NDT tests

Each foundry has its own quality control methods; however, these are all carried out using a range of non-destructive tests (NDT). 

At Vestshell, we’ve set up rigorous manufacturing quality control processes. Precision casting is a meticulous process. By checking for exactness at every stage, we avoid casting should a test prove inconclusive. 

All phases of the manufacturing process, including NDT control, add up to a lengthy list of benefits: 

• Lesser manufacturing costs 
• Increased profitability
• Improved production and delivery times
• Elimination of irregularities and imperfections
• Quality control
• Contamination and oxidation minimization
• Metal waste minimization
• Easier remanufacturing and repeatability
• Greater employee safety 

Other casting processes: sand, continuous and centrifugal

Other metal part manufacturing processes, such as assembly, forging or welding, are either too error-prone, lack precision or are otherwise unsuitable for this type of part.

Likewise, other metal casting techniques such as sand casting, continuous casting or centrifugal casting aren’t precise enough for high-tech industries and parts and cannot produce parts of the complexity possible with investment casting. 

Investment casting technique prototyping

The investment casting method is ideal for creating your next steel, aluminum or other metal alloy prototype, no matter how complex. Also, experts are often on hand to assist with shop drawings to ensure optimal part performance. 

Sometimes only small changes are needed to improve the stability or performance of the final product. An outside eye can make all the difference.

When submitting your project, it’s essential to understand that the repeatability of an existing part greatly increases the speed of order completion, but a new design can take up to a year to execute. 

The start-up process for manufacturing a new investment casting technique part requires many validation steps and is impacted by many factors including the part’s complexity.

Conclusion: your precision foundry project

When you need to make a metal alloy part using the investment casting technique, be sure to contact a reputable investment casting company and feel free to ask questions and discuss what can be produced. 

Precision foundry is a specialized field that requires a great deal of knowledge. Understanding the process and knowing that the onsite staff are competent, qualified and experienced is key to your peace of mind.