Investment casting by “lost wax”
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PRECISION INVESTMENT CASTING process is a technological procedure for the production of mechanical parts with complex geometry. Materials can be stainless steel, carbon steel, nickel alloy, titanium, etc.
If the mechanical piece to be machined has complex shapes, indentations, grooves, undercuts, the other technological processes such as cold and hot forging, forming or other forming technologies do not allow or allow it only by welding more parts together, here the lost wax casting finds its perfect use.
Here below we have showed by pictures the “lost wax” precision investment casting process (the photos were taken in our foundry and then bound by copyright):
1. Wax injection
First step of Lost Wax Process is wax moulding. Wax is then injected in the fitting mould, lending wax the shape of the item to be produced.
2. Assembling the “tree”
A number of wax patterns created thanks to wax injection are assembled around a common gating system, also made of wax. The assembled shape looks like a tree and is named as such.
3. Making ceramic shell
This step consists by dipping the tree of the pieces to be reproduced in a slurry made of special ceramics in order to create an inert shell that may be resistant to high temperatures. A number of coats+drying periods are repeated on the same tree until the needed shell thickness is achieved.
4. De-waxing the shell (“lost wax”)
The dry tree is ready to be de-waxed: shells are dipped into a bath at high temperatures which melts the inner wax and takes it out. Wax is then collected for a new process.
5. Steel melting, by gravity
Shells are fragile, that’s why they are cured in a shell baking furnace to make them nearly glossy while simultaneously liquid metal is prepared in a melting furnace. Once the metal is ready, this is poured in the shells by gravidity.
6. Breaking ceramic shell
Once the ceramic shells are cooled, a vibrating device breaks the shells and casted pieces are finally under our eyes.
Raw castings are then cut and separated from the gating system.
8. Finishing & delivery
Castings are then grinded, blasted and, under request, CNC machined. After inspection and final quality checks they are ready for delivery.
First of all an aluminum mold is prepared, at low cost, within which the NEGATIVE of the piece that has to be produced has been obtained (the actual size will consider both the oversize necessary for following processing steps and any shrinks), then it is injected with wax at about 130°C and after a few seconds it is open so getting the piece identical shape to the metallic original one you wanted.
At this stage the wax model is coated with ceramic layers and allowed to dry for a few days. Finally this "ceramic" container is opened on one side to allow the leakage of the wax (hence the name of the process "lost wax") and inside it will remain the NEGATIVE cast of the item to be produced.
The last stage, the proper melting, sees the pouring of the molten steel (1600°C) in the ceramic container made before. The molten steel will fill all the areas, gaps and undercuts, and after the final cooling can crack the ceramic shell thus obtaining the mechanical part which then will bear all the further processing (heat treatment, CNC machining, polishing, painting, etc.).
The precision investment casting “lost wax” is an ancient technique with its origins 5,000 years ago in the Far East. Today it is an industrial process with still a strong handcraft connotation that allows to make products with a high details precision and finishing that other types of melting do not allow.
The word "precision" must not be misleading with “lighter casting” (against the heavier “sand casting” weight) as in our foundry we have reached such high level that today beside traditional casting of a few grams or a few Kg, we can produce items up to 120 kg! This allows us to make products that may be used for different industrial sectors:
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- Industrial/Sanitary valves and pumps
- Mechanical parts
- Land movement and agriculture
- Furniture accessory
- Food Industry