Gravity die casting - Nguyen Ngoc Ha

e) Part weight can range from .1 kg to 300 kg but typically weigh less than 25 kg Medium quality surface finish, porosity, shape complexity High dimensional accuracy Good to average cost for equipment and labor Can produce 5-50 parts/mold hour Typically requires 1000 parts before being used 1.2. Process Procedure 1- The molds are clamped together by mechanical means and heated to about 150- 200 ˚C to facilitate metal flow and reduce thermal damage to the dies. 2- The molten metal is then poured through the gating system 3- After solidification, the molds are opened and the casting is removed. 4- Special means employed to cool the mold include water or the use of fins, similar to those found on motorcycle 1.2. Process Procedure Graphite+oil 1.2. Process Procedure Steps in permanent mold casting: (1) mold is preheated and coated 1.2. Process Procedure Steps in permanent mold casting: (2) cores (if used) are inserted and mold is closed, (3) molten metal is poured into the mold, where it solidifies. 1.3. Advantages of Gravity Mold Casting • Near- net shapes • Little finish machining • Reusable molds • Good surface finish • Consistent dimensions • Directional solidification • Fast cooling rate to produce a strong structure • Core can be used to increase complexity 1.4. Disadvantages of Gravity Mold Casting • Limited to lower melting temperature alloys • High mold costs – Mold life is strongly tied to cost – Mold life is dependent on the following factors: • Alloys being cast, especially melting temperature • Mold material • Pouring temperature • Mold temperature • Mold configuration – High production runs can validate high mold costs • Limited mold complexity 1.5. Common Characteristics 1.5. Uses • This process is used mostly for aluminum, magnesium, and copper alloys and gray cast iron because of their generally lower melting points. Steels can also be cast using graphite or heat-resistant metal molds. Products Gravity die casting Sand casting Products Products 2. PARTING LINE 2.1. Vertical Parting Line 2.2. Horizontal Parting Line 2.3. Mix-Parting Line 2.3. Mix-Parting Line 3. VENT 4. GATE SYSTEM 5. To increase the life of the permanent molds • The surfaces of the mold cavity are usually coated with refractory slurry, such as sodium silicate, and clay, or sprayed with graphite every few castings. This coating also serves as parting agents and as thermal barriers, controlling the rate of cooling of the casting. Mechanical ejectors, such as pins located in various parts of the mold, may be needed for removal of complex castings. Ejectors usually leave small round impressions on the castings. Mold Cooling 6.CORES FOR GRAVITY DIE CASTING 6.1. Core materials • To produce castings with internal cavities, cores made of metal or sand are placed in the mold prior to casting. Typical core materials are oil-bonded or resin-bonded, plaster, graphite, gray iron, low carbon steel, and hot- work die steel. Gray iron is the most commonly used, particularly for large molds of aluminum and magnesium castings. 6.2. Sand Cores Sand-resin Cores 6.3. Metal Cores 7. Design Considerations in Gravity Die Casting 8. Mold Filling 9.CASTING MACHINES 9.1. Casting Machine with vertical parting line 9.2. Casting Machine with horizontal parting line