Vacuum Investment Casting – a new era in manufacturing aluminium cast parts

Introduction

Aluminium, often referred to as the "metal of the future," has become an indispensable part of our modern world. Its lightweight, corrosion resistance, and excellent electrical conductivity make it a versatile material for a wide range of applications, from aerospace and automotive industries to packaging and construction. As the demand for aluminium continues to rise, understanding its production and consumption dynamics on a global scale is important.

Aluminium is the second most important commercially used metal in the world. In volume terms it is second only to Iron & Steel. As per the International Aluminium Alliance primary Aluminium production in 2022 was over 68 MMT with Chine contributing almost two-thirds i.e 40 MMT.

In recent years, there has been a shift towards recycling aluminium to meet sustainability goals. Aluminium is infinitely recyclable, and recycling requires significantly less energy compared to primary production. As environmental awareness grows, industries and consumers alike are increasingly focusing on recycling and sustainable practices.

Aluminium parts fabrication processes:

Aluminium parts are manufactured through various processes depending on the specific requirements and the complexity of the part. Here are some common manufacturing processes used to fabricate aluminium parts:

Extrusion: Extrusion is a process where aluminium billets are heated and forced through a die to create a desired shape. This process is often used for creating complex cross-sectional profiles like rods, bars, tubes, and structural components.

Casting: Aluminium can be cast using various methods, including sand casting, die casting, and investment casting. Die casting is used for producing complex shapes with high precision and surface finish.

Machining: Aluminium parts can be manufactured using machining processes such as milling, turning, drilling, and grinding. This is especially common for creating precision components and prototypes.

Sheet Metal Fabrication: Thin aluminium sheets can be cut, bent, and formed to create a variety of parts, including panels, enclosures, brackets, and more. Processes like laser cutting, bending, and stamping are often used in sheet metal fabrication.

Welding: Aluminium parts can be joined together using various welding techniques, including TIG (Tungsten Inert Gas), MIG (Metal Inert Gas), and spot welding. Proper welding techniques are essential due to aluminium's high thermal conductivity and susceptibility to distortion.

Forging: Forging involves shaping heated aluminium billets using a die and hammer or press. It is used for creating parts with improved mechanical properties and strength.

Powder Metallurgy: Aluminium powder can be pressed and sintered to create parts with complex geometries. This is often used for producing small, intricate components.

Additive Manufacturing (3D Printing): 3D printing technologies, such as selective laser melting (SLM) and fused deposition modelling (FDM), can be used to create aluminium parts layer by layer. This is useful for rapid prototyping and the production of highly complex, customized components.

After the fabrication process, aluminium parts may undergo surface treatments such as anodizing, electroplating, or powder coating to enhance their appearance, corrosion resistance, and durability.

The choice of manufacturing process depends on factors such as the part's size, complexity, required tolerances, material properties, and the volume of production. Engineers and manufacturers select the most appropriate method to achieve the desired quality, functionality, and cost-effectiveness for the aluminium parts they are producing.

Die Casting – a preferred process.

Die casting is a widely used manufacturing process for producing high-precision aluminium parts with complex shapes. It involves forcing molten aluminium into a reusable metal mold or die under high pressure. Here's an overview of the die casting process for aluminium:

The mold can be reused for multiple cycles, making die casting a cost-effective production method for high-volume production runs.

Die casting offers several advantages for aluminium parts production, including high dimensional accuracy, excellent surface finish, and the ability to produce complex shapes with tight tolerances. It is commonly used in industries such as automotive, aerospace, electronics, and consumer goods where precision and efficiency are critical. Different types of die casting, such as cold chamber and hot chamber die casting, are used depending on the specific aluminium alloy and part requirements.

Aluminium die casting plays a significant role in the automotive industry due to its numerous advantages, including lightweighting, cost-effectiveness, and the ability to produce complex components with high precision. Here's how aluminium die casting is used in the automotive sector:

Overall, aluminium die casting has become integral to the automotive industry's efforts to reduce vehicle weight, improve fuel efficiency, and meet stringent environmental and safety standards. It allows automakers to achieve a balance between light-weighting, performance, and cost-effectiveness in their vehicles.

Some Limitations of Die Casting:

As stated above, Die Casting is a versatile process and has many advantages – but it also has certain limitations, which are enumerated below.

High Initial Tooling Costs: Creating the molds (dies) for die casting can be expensive. This makes die casting less economical for small production runs.

Limited Part Size: Die casting is most effective for small to medium-sized parts. Larger parts can be challenging to produce and may require specialized equipment.

Material Limitations: While die casting can work with a range of materials, it is not suitable for all alloys. Some alloys may have properties that make them difficult to cast.

Surface Imperfections: Although die-cast parts generally have a good surface finish, they can still have minor defects such as porosity or air bubbles.

Not Suitable for Thin Walls: Extremely thin-walled parts can be challenging to produce via die casting due to the high pressures involved.

Limited Design Flexibility: Design changes to the die-cast part can be costly and time-consuming because they require modifying the molds.

Environmental Concerns: The high energy consumption required for melting and casting metals can have environmental implications, especially if the energy source is not sustainable.

Limited Alloy Mixing: Combining different alloys in a single die-casting process is complex and can lead to inconsistent results.

Attempts have been made to overcome the limitations of Die Casting and some manufacturers have used Investment Casting to address the limitations.

Investment Casting – Advantages and Limitations:

Investment casting, also known as the lost-wax casting process, can be used to create complex and precision aluminium parts. While investment casting is more commonly associated with materials like steel, bronze, or stainless steel, it is possible to use this process for aluminium as well. Here's how investment casting works for aluminium:

While aluminium investment casting is possible, it's worth noting that aluminium has unique characteristics and properties that can present challenges in the investment casting process. These challenges include its high thermal conductivity, which can affect mould filling and solidification, and the need for proper gating and cooling designs to prevent defects. However, with proper process optimization and expertise, aluminium investment casting can produce high-quality and complex aluminium parts for various applications.

Vacuum investment casting, also known as vacuum-assisted investment casting or vacuum precision casting, is a specialized variation of the investment casting process that uses vacuum technology to improve the quality and consistency of castings. Recent advances in vacuum investment casting have focused on enhancing process control, efficiency, and sustainability. Here are some notable advances:

Improved Casting Quality - Advanced vacuum systems with precise control mechanisms are being used to achieve higher levels of vacuum during the casting process. This results in reduced gas porosity and improved overall casting quality.

Reduced Oxidation and Gas Porosity - Vacuum investment casting helps minimize oxidation of molten metal and the formation of gas porosity by removing air and gases from the mold cavity. Recent advances in vacuum technology have led to more efficient gas removal, resulting in cleaner and more reliable castings.

Enhanced Alloy Capabilities - Vacuum investment casting allows for the production of a wide range of alloys, including those that contain elements which are highly reactive to the environment or are susceptible to oxidation and loss. Such alloys and other high-performance materials used in aerospace, automotive, and medical applications, can be easily melted in vacuum and/or under cover of inert gases, without making any change in the vacuum casting machines. This makes it possible to produce high integrity and precision castings of the most complex alloys of Aluminium and other low temperature alloys via vacuum casting.

Additive Manufacturing Integration - The integration of 3D printing and additive manufacturing techniques with vacuum investment casting has opened up new possibilities. Complex internal geometries, lattice structures, and conformal cooling channels designed via the 3D generative design methodologies and topology optimisation, can be incorporated into patterns, enabling the production of highly customized and optimized parts.

This capability of AM integrated Vacuum Casting process can become a big boon to the automotive and aerospace industry, in its never-ending quest for light-weighting. Some generatively designed parts have proven to be upto 70% lighter than the conventional parts, without any loss of performance or strength. In fact many structural parts can be optimally designed and produced from Aluminium alloys which meet the twin but conflicting demands of light weight and desired structural strength of the part.

Rapid Prototyping - Vacuum investment casting has become more adaptable and is becoming the preferred process for rapid prototyping and short production runs. This allows for quicker turnaround times and cost-effective testing of new designs. The castings produced by this approach are high integrity and production ready castings without any compromise, that is necessary with the current prototyping methods. This process can also be scaled up to meet volume production requirements during the initial product launch stages and improve the time-to-market of the manufacturers.

Environmental Considerations – Vacuum Casting is a much cleaner process than the conventional die casting processes, as all the melting and casting takes place in closed chambers. Advances in vacuum systems and controls have led to further improvements in energy efficiency, reducing the environmental impact of the casting process. More environmentally friendly foundry practices, such as reduced emissions and waste, are being incorporated.

Process Simulation - Computational modelling and simulation tools have become more advanced and accurate, allowing foundries to predict and optimize the vacuum investment casting process. This helps in reducing defects, improving yield, and minimizing material waste.

Industry-Specific Applications of Vacuum Investment Casting:

Vacuum investment casting is gaining prominence in industries like aerospace, where complex and high-performance parts are required. Recent advances are catering to the specific needs of these industries, including the development of proprietary vacuum casting techniques.

These recent advances in vacuum investment casting are driving innovation and expanding the applications of this technology, making it a valuable method for producing high-quality, precision components for various industries. Manufacturers continue to invest in research and development to further improve the efficiency, sustainability, and capabilities of vacuum investment casting processes.

Prototyping of aluminium parts is a critical step in product development, allowing engineers and designers to test and refine their designs before committing to full-scale production. There are several methods for prototyping aluminium parts, each with its own advantages and limitations.

Vacuum Investment Casting is an excellent process to manufacture high integrity precision parts very quickly without investment in expensive tooling. These parts are production-ready, and the designer does not need to make any compromised during prototyping stage. Combined with AM patterns, this process eliminates the need of any tools and just one part can be manufactured quickly. Such parts can be used for fitment and other trials and changes can be incorporated rapidly and modified parts can be made within days rather than months with other conventional processes.

This is a huge benefit and can compress the product development cycle manifold. If the designer wishes to use different alloys and desires castings to be evaluated before he makes the final decision, this can be easily achieved by the vacuum investment casting process. This process can produce castings of the same geometry in different alloys, which the designer or product development engineer can use in real applications and field trials before finalising and releasing the part for mass production.