We produce high-precision cast parts with top-quality surface finishes using the precision casting technique, also known as the lost-wax technique. This traditional casting method is particularly renowned for its high level of dimensional accuracy and advanced creative possibilities. In cases where the precision casting process meets its limits with regard to tolerances, only small material allowances are required for subsequent mechanical machining.
For instance, this precision-casting method can be used to create thin-walled parts similar to sheet metal with sides that are only approx. 2.00 mm thick. These parts are also largely ready for installation and only require slight reworking. This saves both time and money. The method can also be used to manufacture components with thick walls.
The precise definition of this precision casting method is as follows: “The production of cast parts based on lost models and moulds”. The origins of the method go back to approx. 3000 BCE, right back to the Bronze Age.
The technique is made even more attractive by the huge variety of materials that can be used. In precision casting, the end products consist of 100% recyclable materials.
The precision-casting process explained.
How to make the perfect cast component in 14 steps.
Production of wax spraying mold
The mold (wax injection mold) is made in order to be able to design the wax pattern of the casting. A distinction is made between single molds and multiple molds for large series. The materials tool steel and high-strength aluminum are used for tool production. Since there are high demands on the wax mold, attention must be paid during production both to the subsequent demoldability and to the casting fundamentals and tolerance.
Making the wax model
To form the wax model, liquid wax is injected into the wax injection mould. This produces an exact replica of the later cast part. The wax model is sized to compensate for physical shrinkage or any cutting that is required due to the casting process. During this step, the temperature and pressure of the injected wax must be precisely controlled.
Combining wax models to form a tree
With economy in mind, the individual wax models are bonded or welded together to form a tree. This forms the sprue and gates to be used during the subsequent casting process. To produce outstanding precision-cast parts, the tree must be assembled with extreme care and the gating must be highly accurate.
Covering with a ceramic layer
The tree is now dipped into ceramic slurry multiple times to cover the model in a layer of ceramic. It is then coated with casting sand and dried to form a solid ceramic shell.
The wax is then melted out of the ceramic mould under pressure in a steam autoclave. The wax model is lost. To make the process sustainable and as efficient as possible, the lost wax is recycled and reused.
Firing for strength
The green-strength ceramic moulds are then fired at 1100 to 1200°C to achieve their final stability and strength.
The steel alloy is smelted in an induction furnace. The molten material is poured into the hot ceramic moulds that have a temperature of around 900°C to 1100°C. Care must be taken to ensure that the hot molten liquid fills even the finest details of the mould. Paying close attention to accuracy and temperature results in high-quality casting and high-quality material. The casting temperature is between 1580°C and 1680°C.
Removing the ceramic mould
Once the tree of models has cooled and hardened, the ceramic shell is removed using, for instance, an automatically controlled, vibrating pneumatic hammer or chemical baths. The ceramic mould then becomes what is traditionally know as a lost mould.
Separating the cast parts from the tree
The cast parts are carefully separated from the tree. Steel remnants are carefully collected during this step to be recycled and reused.
Removing ceramic residues
The last ceramic residues are removed from the cast part by blasting the surface, for example using steel shot and/or white corundum. After all, top-quality surfaces are vital in precision casting.
Finishing the cast parts can include grinding off sprue remnants, heat treatments appropriate for the various material groups and final surface finishing.
Calibrating the cast parts
When the cast parts solidify, shrinkage of various types can cause slight distortions of the component geometry in the millimetre range. This are compensated for using a calibration process. It is performed using calibration equipment adjusted to the component to ensure excellent repeatability.
In cases where general precision casting tolerances are insufficient, the desired tolerances are achieved in this additional step by using mechanical post-processing on areas of the cast parts. Cutting-edge CNC turning and milling centres with 3 to 5 axes are used for this purpose.
Accurate inspection using sensitive final checks
Final testing involves visual inspection of the cast surface and mechanically reworked areas. Critical dimensions are checked in line with the specified approval guidelines. Gauges are inspected according to agreement or the specifications. The following points are inspected depending on the particular customer specifications: Special declaration of the melt analysis and/or mechanical parameters, leakage inspection, inspection of interior quality and inspection of exterior quality using magnetic particle testing or dye penetrant testing methods.