Shell Molding-> Die Casting (C) Flashcards
(44 cards)
What is SHELL MOLDING?
Cousin process to sand casting. A mold cavity surrounded by only a very thin layer of refractory material is prepared and filled with molten metal.
What must the PATTERNS used in SHELL MOLDING be made of?
METAL, unlike the wood or plastic used in sand casting.
Since METAL PATTERNS are expensive, when are they used?
They are used if large numbers of the same part are to be produced.
Why are METAL PATTERNS used in SHELL MOLDING?
Because it will be heated during the process steps and generally up to temps unsuitable for thermoplastics. They are usually organically shaped (not easy to 3D print from plastic).
How are the METAL PATTERNS made?
Sand Casting. Only one set of split patterns are required for the production of multiple parts.
What material is used for the SHELL MOLDS themselves?
A mixture of Zircon sand and thermosetting resin.
What is a DUMP BOX?
A box containing the sand and resin mixture and attached to the METAL PATTERN. The dump box is inverted, allowing this sand-resin mixture to coat the pattern. The heated pattern partially cures the mixture, which forms a shell around the pattern.
What are EJECTOR PINS?
Pins on the pattern plate are used to remove the shell from the plate.
What happens after two SHELLS have been made?
The two shells are assembled together in a container that is filled with support material, such as steel shot.
What are CORES in SHELL MOLDING?
CORES can be added to the mold cavity if CORE PRINTS were included in the METAL PATTERN.
What are the ADVANTAGES of SHELL MOLDING (over sand casting)?
Thin shells (fast cooling, flexible, good gas permeability), low sand volume (compared to sand casting), surface finish, lightweight, fewer flaws.
What are the DISADVANTAGES of SHELL MOLDING (over sand casting)?
Limited size and weight (thin walls can’t support large products), metal pattern (too expensive for one-time use), limited core complexity (especially if chaplets are needed).
What is INVESTMENT CASTING/LOST WAX CASTING?
An EXPENDABLE MOLD process that involves wax. Investment means to “DIP”.
What is WAX CARVING?
A process to make wax patterns. Usually for making items such as rings and jewelry with organic shapes. Done by a craftsman.
What is DIRECT 3D WAX PRINTING?
Designing them in 3D CAD modeling software and then printing out the WAX PATTERN with a 3D PRINTER designed for printing wax.
What is 3D PRINTING PLASTIC MOLDS?
Creating wax patterns indirectly using conventional 3D PRINTING of thermoplastics.
What is INJECTION MOLDING?
A method of creating plastic parts and wax patterns in very large numbers. However, the metal molds needed are very expensive.
What is a TREE in INVESTMENT CASTING?
An assembly of wax elements including the patterns, which will eventually become an entire casting system with a pouring basin, sprue, runners, and mold cavities.
How are the TREES assembled?
By softening the individual elements with a fine gas torch and fusing them together.
What are the TREES dipped into?
STUCCO or CERAMIC SLURRY. At first, it is dipped into a mixture of fine particles and water. Then it is dipped multiple times into a course particle mixture and less moisture. Once dry, it forms a thick ceramic SHELL.
After DIPPING, why is the TREE placed into an oven?
To DRY and CURE the ceramic stucco, which provides strength and drives off moisture. The heating also serves to MELT OUT the wax from their surrounding ceramic shells.
What is the result of MELT OUT?
The formation of a hollow shell, with internal passageways where the TREE used to be. The molten wax is collected and recycled.
What is the METAL POUR step of SHELL MOLDING?
When the molten metal is poured into the mold.
What is SHAKE OUT?
A method of separating the ceramic shell and the now metal tree.
