Investment casting

What is investment casting?

Investment casting, also known as lost wax casting or precision casting, is a versatile and precise method of producing complex metal parts and cast objects. In contrast to vacuum casting, investment casting is an atmospheric casting process - i.e. it is cast under normal air and pressure conditions. Investment casting can be used to produce extremely precise, small castings with complex geometries and structures. It is characterised by high surface quality, dimensional accuracy and attention to detail.

In simple terms, investment casting is a casting process in which a model is made from wax, which is then coated with a ceramic layer to form a mould. Once the wax has melted out, the mould is filled with molten metal. The result is high-precision castings with complex geometries and fine surfaces.

History

The roots of investment casting go back thousands of years. Originally, this method was used in ancient civilisations such as Mesopotamia, Egypt and China to produce art objects and jewellery. In the 20th century, investment casting was rediscovered and further developed industrially. The process became particularly important during the Second World War, as it enabled the production of complex components for aviation.

Usage

Today, investment casting is indispensable in many industries, including

  • Automotive
  • Medicine
  • Dentistry
  • Mechanical engineering
  • Chemical industry
  • Jewellery
  • Art
  • Aerospace
  • Electronics

Characteristics of investment casting

High precision

Enables the production of castings with very fine details, thin wall thicknesses and tight tolerances.

Complex geometries

Enables the production of castings with complex shapes and undercuts that would be difficult or impossible to produce using other casting processes.

Surface quality

The resulting cast objects have smooth surfaces that often require little or no post-processing.

Versatility

Suitable for a wide range of metals and alloys.

Advantages and disadvantages of investment casting

Advantages

Freedom of design
Enables complex and intricate designs that cannot be realised with other processes.

Precision
Very high dimensional accuracy, thin wall thicknesses and low tolerances.

Variety of materials
Can be used with almost all casting alloys.

Low material loss
The precise design minimises material loss.

Cost-effective even for small series
Particularly economical for small and medium quantities.

Disadvantages

Costs
The production of wax patterns and ceramic moulds can be expensive, especially for large series.

Time consuming
The process is complex and time consuming compared to other moulding methods.

Size limitations
Not ideal for very large or massive castings.

Materials for investment casting

Investment casting is an extremely versatile process that is suitable for a wide range of metals and alloys. This flexibility makes it particularly valuable in various industries, as it offers the possibility of producing castings with specific mechanical and physical properties.

Copper and copper alloys

Copper

Provides excellent electrical and thermal conductivity and is widely used in the electronics industry.

Bronze

An alloy of copper and tin, known for its hardness and corrosion resistance, often used in art for sculptures and design objects and in bearing and gear components.

Brass

An alloy of copper and zinc, used for decorative applications as well as for fittings and valves.

Aluminium and aluminium alloys

Aluminium

Lightweight, corrosion-resistant and offers good electrical conductivity. Ideal for the aerospace, automotive and electronics industries.

Aluminium alloys

Improve mechanical properties and are often found in structural applications.

Steel

Stainless steel

Corrosion-resistant and ideal for applications in the food industry, medicine, chemical processing and in maritime environments.

Precious metals

Gold

Used in jewellery manufacturing and in certain electronic applications.

Silver

Also for jewellery and for applications that require high electrical conductivity.

Other materials for investment casting are:

  • Carbon steel
  • Titanium & titanium alloys
  • Nickel & Nickel Alloys
  • Cobalt & cobalt alloys
  • Zinc & zinc alloys
  • Magnesium & magnesium alloys
  • Platinum

What investment casting processes are there?

Investment casting processes comprise several specialised casting processes, all of which share the principle of the pattern and the ceramic mould to produce precise and complex castings.

Lost wax process

The traditional lost wax process is the most commonly used investment casting process. It uses a wax model that is coated with a ceramic shell and then melted out before the metal is cast.

Lost wax process

Ceramic Shell Casting

A special process in which a ceramic shell is formed around the wax model. This shell is thinner and more flexible than conventional ceramic moulds and enables an even finer level of detail.

Plaster Mold Casting

This process uses a plaster material instead of ceramic to make the mould. Plaster moulds can produce very smooth surfaces and detailed contours, but are less heat-resistant than ceramic moulds and are therefore better suited to low-melting-point metals.

Resin Investment Casting

In this process, a resin model is used instead of a wax model. The resin model is embedded in a ceramic mould and then burnt to make room for the molten metal. Resin casting is particularly useful for the production of prototypes and small series.

Sol-Gel Casting

A modern approach in which a sol-gel coating is applied to the wax model to create a very fine and highly precise ceramic mould. This process offers advantages in terms of mould thickness and quality control.

Vacuum Casting

An extension of investment casting in which the metal is cast under vacuum conditions. This reduces the risk of air inclusions and improves the surface quality and mechanical properties of the cast part.

RP Investment Casting

Here, a rapid prototyping model (e.g. using 3D printing) is used to produce the wax model. This technique enables models with complex geometries to be produced quickly and cost-effectively, which are then further processed in the investment casting process.

Micro Investment Casting

A specialised investment casting process for the production of very small and precise parts that are often used in medical technology, watchmaking or the electronics industry. It requires extremely precise control over pattern and mould production.

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