Squeeze Casting and Lost Foam Casting
Squeeze China precision machining casting also known as liquid metal forging, is a combination of casting and forging process The molten metal is poured into the bottom half of the pre-heated die. As the metal starts solidifying, the upper half closes the die and applies pressure during the solidification process. The amount of pressure thus applied is significantly less than used in forging, and parts of great detail can be produced.
Coring can be used with this process to form holes and recesses. The porosity is low and the mechanical properties are improved. Both ferrous and non-ferrous materials can be produced using this method.
Fig. 6.12 Schematic of squeeze casting process
Lost Foam Casting
Lost foam casting allows the production of complex parts. The process produces complex parts and reduces finish machining of the part produced by lost foam casting.
To make lost foam casting, a foam pattern of the finished part is made.
The pattern is dipped into a water solution containing a suspended refractory. The refractory material coats the foam pattern leaving a thin heat resistant layer. Sand is poured around the pattern and provides mechanical support to the thin refractory layer. 。 Molten metal is then poured into the mold, and the molten metal melts and vaporizes the foam. When the metal becomes solid, it is removed from the sand, thus the name lost foam casting. Lost foam castings may be of any shape or size. Materials commonly used in lost foam casting are Aluminum, iron, steel and nickel alloys. The Lost Foam casting process originated in 1958 when H.F. Shroyer was granted a patent for a cavity-less casting method,China precision machining using a polystyrene foam pattern embedded in traditional green sand.
The polystyrene foam pattern left in the sand is decomposed by the poured molten metal. The metal replaces the foam pattern, exactly duplicating all of the features of the original pattern. Like other investment casting methods, this requires that a pattern be produced for every casting poured because it is evaporated (“lost”) in the process.
The basic steps to the process include (Fig. 6.13):
1. A foam pattern and gating system are made using a foam molding press
2. The foam pattern and the gating system are glued together to form a cluster of patterns
3. The cluster is coated with a permeable refractory coating and dried under controlled conditions
4. The dried, coated cluster is invested in a foundry flask with loose, unbonded sand that is vibrated to provide tight compaction
5. The molten metal is poured on to the top of the gating system which directs the metal throughout the cluster and replaces the foam gating and patterns
6. The remaining operations such as, shake out, cut-off,
grinding, heat treat, etc. are straightforward and similar to other casting processes.
Fig. 6.13 Schematic of lost foam casting process
Generally, all ferrous and non-ferrous materials can be successfully cast using the Lost Foam process. Because the foam pattern and gating system must be decomposed to produce a casting, metal pouring temperatures above 1000°F are usually required. Lower temperature metals can be poured, but part size is limited. China precision machining In addition, very low carbon ferrous castings will require special processing.