Manufacturing Processes - General Investment Casting
Lost Wax or Investment Casting Handbook
Investment casting comes under the general category of casting as a manufacturing process and uses expendable moulds and patterns.This process is sometimes referred to as the lost wax process and is one of the oldest metal forming processes around dating back nearly 5000 years.
There are approximately 5 general stages to the component casting program.
1. A wax pattern is produced by injecting molten wax into a metal or rubber die that can be split to remove the pattern.
2. The wax patterns are then assembled onto a tree with feeding and gating systems built in. Once assembled the tree is dipped into a refractory slurry and is then coated or stuccoed with refractory powder and set using either an investment drying process or chemicals to chemically set it. The dipping, coating and setting stage is repeated several times to build up a ceramic layer that is about 5 to 10mm thick.
3. The wax is removed from the ceramic shell that has been formed by heating it in a furnace or steam autoclave.
4. For the casting stage the ceramic mould that has been created is fired in a mould and pre-heated to accept the molten metal. The metal is then poured into the feeder until the mould is full and then allowed to cool. To access the castings the ceramic shell has to be chiseled off revealing the metal version of the tree that has replaced the original wax version.
5. The components are now fettled from the tree and put through any further required operations to prepare them for final purpose. this could include machining,grinding and or heat treatment.
The process is best suited for small, or relatively small, complex 3D components. It is also suitable for most metals including reactive metals that require the casting to be done under vacuum. Larger components can be produced using this process and have been, but it is normally because the complexity of the shape dictates it.
- Very accurate and repeatable with good surface finish
- Wax can be recycled
- Less need for secondary operations i.e. minimal post casting machining
- Equipment costs are relatively high, particularly with respect to vacuum systems required for reactive metals
- Production rates slow due to multiple process stages
- Refractory materials are expensive and cannot be recycled
- Micro-structures are relatively coarse
Investment casting is used extensively in the aerospace and power generation industries for the production of turbine blades, being a process that lends itself perfectly to the requirements for production of complex 3D shapes.
It also lends itself very well to the production of items of jewelry, one of the original uses of the process from its conception when beeswax was used to create the pattern and clay was used as the investment.
Investment Casting or Lost Wax Casting Process
Manufacturing Processes - Further Resources
- Manufacturing Processes and Methods
The selection of a manufacturing process is done very much on the basis of a manufacturer choosing the process that best suits his needs. Consideration must be given to a number of factors before deciding on...
- Materials Selection versus Manufacturing Processes
Material selections can determine what manufacturing processes are available, form can determine what materials can be used and manufacturing processes can determine what form can be created. So what you...
- Casting Process Problems
The main problem to overcome in a casting process is porosity, of which there are 2 types
- Manufacturing Processes - Sand Casting
Sand casting comes under the general category of casting as a manufacturing process and is a permanent pattern process.In other words the sand moulds are produced using a reusable pattern that is removed...
- Manufacturing Processes, Full Mould Evaporative Pattern Casting
Full mould casting, otherwise known as full mould evaporative pattern casting, comes under the general category of casting as a manufacturing process and is an expendable mould and pattern process....
- Manufacturing Processes - Gravity Die Casting
Gravity die casting is a simple casting process which utilises reusable metallic moulds. The process is primarily used for simple shapes with some basic coring possible. It is mostly suited to casting light...
- Manufacturing Processes - Pressure Die Casting
Pressure die casting is a process that fits under the general category of casting as a manufacturing process. It utilises a permanent mould where molten metal is forced into the die cavity through a system of...
- Manufacturing Processes - Squeeze casting
Squeeze casting fits in the general category of casting as a manufacturing process. Casting has been around for approximately 6000 years, so squeeze casting is a relatively new development.being introduced...
- Manufacturing Process-Centrifugal Casting & Rotational Molds
Centrifugal casting fits under the general category of casting as a manufacturing process and utilities a permanent mould. Typically this process is used for the production of long, hollow components that...
- Manufacturing Processes - Injection Moulding
The injection moulding process fits under the general category of casting as a manufacturing process. This may seem surprising as the process is dedicated to the production of plastic, rubber and composite...
- Manufacturing Processes - Reaction Injection Moulding (RIM)
This is a permanent mould process that fits in the general category of casting as a manufacturing process and is sometimes abbreviated to the RIM Process. The general mode of operation of this process is to...
- Statistical Process Control versus Acceptance Sampling
There are two types of product quality control approaches that are going to be compared and contrasted in this article, namely: Acceptance Sampling Statistical Process Control. (SPC) The purpose of...
More by this Author
Electrochemical Machining involves removal of material from a workpiece using electrolysis. The material for this process to work has to be electrically conductive.
The extrusion process applies to a variety of processes that involve confining a material in a container and applying a force to push the material through an orifice to produce a required shape.
The selection of a manufacturing process is done very much on the basis of a manufacturer choosing the process that best suits his needs. Consideration must be given to a number of factors before deciding.
Investment Casting or Lost Wax Casting Process - Your Thoughts
No comments yet.