How does 'investment casting' (lost-wax) work? An overview of the steps and phases involved is given below.
Fluid wax is injected into a mould. After the wax hardens, the wax model is removed from the mould. A wax tree (casting mould) is made using the wax models.
In the lost wax casting process, the first step is the engineering and production of a mould into which fluid wax is injected. This mould is developed in-house and is a negative of the cast piece that ultimately comes out of the mould. The moulds are made of aluminium or steel. The series size determines whether the mould is installed on a manual press or on an automatic press. The mould must be made precisely since this largely determines the tolerances and surface irregularities of the moulded piece.
The mould is filled with fluid wax. After cooling, the wax model is pushed from the mould using ejectors in the mould. A wax model has now been formed with the same shape as the final cast piece. These wax models are then racked up into a "tree" by heating the attachment point until it becomes fluid and sticks to a wax branch. This creates the casting mould, sometimes called the "wax tree" or "runner". As many products as possible are stuck to the wax tree. The top of the wax tree is equipped with a casting funnel through which steel will be poured later in the process.
The wax tree (casting mould) is given a fire-resistant ceramic coating. Once the wax has melted and been poured off, a ceramic casting mould is formed.
Once the wax models have been built up into a wax tree, they are rinsed. This removes any surface contamination. This rinsing process guarantees proper adhesion of the ceramic to the wax tree.
A fire-resistant ceramic coating is created by plunging the wax tree multiple times into a fluid sludge and then sprinkling it with ceramic powder. After the application of every ceramic layer, the casting mould must be dried in a drying chamber under atmosphere conditions.
Once all the layers have been applied and dried, the wax in the ceramic mould is melted in an autoclave using steam. This is why this process is called the lost wax casting method: the wax model disappears; the product shape is then taken over by the ceramic coating. Most of the melted wax is reused after regeneration.
The ceramic mould is fired in a furnace (sintered) at a high temperature (approximately 1.100°C) and achieves its ultimate strength after this sintering process. Any remaining wax burns off in the high temperature of the furnace during this process.
The heated trees are removed from the kiln by a robot and then poured full with the desired fluid steel alloy.
The desired steel alloy is melted in a smelting furnace and brought up to a casting temperature of (approximately) 1600 °C. At the same time, the ceramic mould is heated in a kiln to (approximately) 1.100°C. The hot mould is then removed from the kiln and poured full. Heating the ceramic mould prevents a thermal shock during casting. This also allows thin walls to be cast. Since the fluid steel is poured into a hot mould, it takes some time before solidification starts. Once the trees have been filled, they cool off in on a cooling lane under controlled conditions: the solidification process takes place in a controlled manner.
CIREX performs the finishing processes, heat and surface treatments and final inspection. The final product is ready for immediate installation by the customer.
The ceramic skin is removed from the steel casting moulds by breaking the shell with an automatic hammer. This removes the majority of the ceramic. The cast pieces are sawed off or vibrated away from the steel tree. Pieces of steel that remain are sorted according to their alloy type and can be melted again for reuse.
In the finishing department, the last remains of ceramic are removed using steel, sand and/or water blasting. Any edges remaining on the sawn-off cast piece are sanded off. A sanding mould is often used to sand the product neatly.
All products are visually inspected for casting errors using a quality standard sheet. This ensures that a high-value casting is always inspected according to the same procedure.
CIREX has the in-house facilities needed to perform processes such as drilling holes, tapping screw threads, lathing and milling. Heat treatment is sometimes needed to obtain certain mechanical properties (hardness, tensile strength, elasticity). Standard heat treatments are performed in our own factory. More complex heat treatments are outsourced. We can also perform surface treatments either in-house or externally. For example, a coating can be applied to a steel component for beautification of the final product or to protect it from wear or corrosion (rust formation).
The last step in this process is once again a visual inspection and, if necessary, drawing up a dimensioning report and material analysis. If so desired, extra product-specific inspections can also be performed for the formation of cracks (penetrex), porosities (X-ray) or for specific dimensioning (100% dimension inspection with camera or gauge). After the final inspection, the products are ready for packaging and shipment.