THE PROCESS
HISTORY OF THE PROCESS
The investment casting, or lost wax, process originates from ancient times. A number of Chinese bronze artefacts, dating from the Shang Dynasty, were created using investment casting techniques.
Investment casting has been used down the ages to produce various works of art, the versatility of the process allowing intricate and delicate objects to be cast.
Designers of metal components are keen to use the process, as it offers reliability coupled with the ability to produce most design requirements.
DIMENSIONAL TOLERANCES
Close dimensional tolerances on castings can be achieved of + or - 0.005 inches per inch (metric equivalent 0.125mm per 25mm).
This level of accuracy is usually sufficient to eliminate the need for further machining on many components, as the process gives an excellent finish on dimensions and surface texture.
In addition, the majority of alloys can be investment cast, including many that prove problematic to machine.
Versatility and flexibility are key advantages of the investment casting process. The shape and size of components is not a problem.
The technique produces castings as a single unit, thereby eliminating the need for welding and assembling.
By using investment casting, mould joint lines can be avoided. Complex pieces and accurate dimensions can easily be accommodated.
The nature of the process also means it is easily adapted to producing small or large quantities.
VERSATILITY & FLEXIBILITY
MAKING
THE WAX
The initial phase in the investment casting process is to produce an aluminium or steel die cavity from the customer's design and specifications. Once this has been produced it is then possible to make an accurate wax pattern.
The wax is heated until liquid and then injected under pressure into the die cavity. The process is repeated until all the wax patterns have been made for a particular order.
Once the wax has set and has been removed from the die cavity, it is visually inspected. On passing inspection the wax is stuck onto runner bars; this allows multiple wax patterns to be stuck on a 'tree' and hence will allow molten metal to flow into the cavities.
MAKING THE
CERAMIC SHELL
The waxes are coated with a fine ceramic slurry and stucco capable of reproducing the detail and smooth surface of the wax pattern.
The coated assembly is then dried and the process repeated several times. At each stage a progressively coarser stucco is used. This helps build the strength into the shell.
PREPARATION
FOR CASTING
Once the shelling process is finished and the mould is dry the wax has to be removed. This is where the process starts to reverse itself and where the term 'Lost Wax' comes from.
The wax is removed from the moulds by using steam; however, the wax is not lost as we recycle it for future use.
The mould, which is in a 'green state', then has to be cured. The mould is heated to a temperature in excess of 800ºC. This burns out out any wax residue and develops the strength of the mould. The now empty ceramic shell is ready for casting.
CASTING
The metal is melted using an induction furnace in comparatively small quantities, varying from as little as 4.5kg up to 14kg.
The moulds are preheated and filled under gravity with the required type of molten metal alloy, which is then left to solidify.
FINISHING
Once the mould has been cooled, the ceramic is mechanically removed. The runners and feeder are removed from the components by means of a circular cut-off saw.
The parts are then finished by the use of abrasive belts and, depending on customer requirements, there is little evidence of where the metal entered the mould.
All the parts are then shot-blasted and passed on to inspection.
INSPECTION
The final stage in the investment casting process is inspection. Here the component is checked to the customer's specifications. All castings are 100% visually inspected for any defects and any critical dimensions can be gauged if necessary.
Castings are then dispatched to the customer. We also offer heat treatment, machining, electropolishing, plating or painting services.