Casting Processes

Casting Processes

1. Sand Casting

   • Unbonded Sand
     • Lost Foam Casting
       • Advantages
         • No size limitations, improved surface finish, no fins, excellent dimensional tolerances
       • Molding Process
         • Pattern coated with a refractory coating, placed onto a compaction table, dry sand is poured into the flask and pattern, molten metal is poured replacing EPS pattern after solidification sand is dumped
       • Materials
         • Patterns are made of EPS beads
     • V-Processes
       • Materials
         • Plastic film and dry sand
       • Molding Process
         • Heat a thin plastic film, vacuum-formed over a pattern on a hollow carrier plate, fry sand fills the special flask set, slight vibration compacts the sand, flask covered with a second sheet of plastic film, the vacuum is drawn on the flask and the sand becomes rigid
   • Chemical Bonded
     • Coldbox Systems
       • Materials
         • Sand is coated with bentonite clay, water and other additives
       • Molding Process
         • Sand is coated, then compacted by hand of mechanical force around the pattern
       • Advantages
         • Cost-effective, adjustable properties
     • Airset Systems
       • Molding Process
         • Sand is mixed with one or two liquid resin and a liquid catalyst, the binder gets harder by chemical reaction, the mix is placed against the pattern, compaction is used to provide densification, then coated to protect the sand from heat and erosion
       • Advantages
         • Good casting dimensional tolerances, good casting finishes, easy shakeout
     • Shell
       • Materials
         • The resin contains a hexamethylenetetramine catalyst
       • Molding Process
         • Sand is pre-coated with a phenolic novalac resin, resin-coated snad is dumped into a metal corebox that has been heated to 450-650F
       • Advantages
         • Excellent core, good dimensional accuracy, storage for indefinite periods of time, high-volume production
   • Green Sand
     • Molding process
       • Catalysts in the form of gas is added to the sand and resin, the mixture is blown into a corebox to compact the sand, catalytic gas is permeated through the sand mixture, the resin component hardens the sand
     • Advantages
       • Dimensional accuracy, excellent surface finish, short production cycles, excellent mold shelf life

2. Permanent Mold Processes

   • Die Casting
     • Materials
       • Produced in nonferrous alloys with limited amounts of cast iron and steel castings
     • Molding Process
       • 1. Metal molds are coated with mold surface coating and preheated
         • 2. Molten metal is forced into the permanent mold under extreme pressure (over 15,000 psi)
     • Advantages
       • Excellent mechanical properties
         • Dimensional tolerances of 0.005-0.01 in
           • Thin-section castings
   • Permanent Mold Casting
     • Materials
       • Cast iron or steel
     • Molding Process
       • 1. Mold is made in two halves
         • 2. Halves are preheated
           • 3. Internal surfaces are coated with a refractory
             • Statin pouring
               • Set vertically
             • Tilt pouring
               • Set horizontally
     • Advantages
       • Superior mechanical properties
         • Uniform shape
           • Excellent dimensional tolerances
             • Control of solidification
   • LPPM
     • Materials
       • Nearly all LPPM castings produced are made of aluminum, other light alloys or copper-base alloys
     • Molding Process
       • Internal passageways made by mechanically actuated metal inserts or sand cores
     • Advantages
       • Control of the solidification rate, good surface finish
         • In case of directly fed into the casting: excellent yield and little need for additional handwork

3. Ceramic Processes

   • Ceramic Processes
     • Materials
       • Graded refractory fillers
     • Molding Process
       • Refractory fillers are blended to a slurry consistency, the slurry is poured over a pattern, a gel is formed in a pattern and stripped from the mold, then heated to a high temperature
     • Advantages
       • Effective with smaller size casting, excellent surface finish, good dimensional tolerances
   • Investment Casting
     • Advantages
       • Excellent surface finishes, tight dimensional tolerances, reduction of machining, can produce titanium castings
     • Molding Process
       • 1. Production of heat-disposable wax
         • 2.Assembly pf attern onto a gating system
           • 3.Covering of the assembly with ceramic to produce a monolithic mold
             • 4.Melting of the pattern assembly
               • 5.Firing of the ceramic
                 • 6.Pouring
     • Materials
       • For refractory aggregate
         • Silica, zircon, aluminum silicate sand
   • Plaster Molding
     • Materials
       • Calcium sulfate in the slurry
     • Molding Process
       • A slurry is poured into a flask that contains a pattern, pattern and flask are removed, the moisture from is removed from the mold, core and mold are assembled, mold is preheated
     • Advantages
       • Well-suited for short run and prototype work

4. Rapid Prototyping

   • Investment Casting
     • Materials
       • Photopolymer, thermopolymer and polystyrene for RP printed parts
     • Molding Process
       • Convert a 3-D CAD model into a .STL file, file is printed then attached to a gating system and processed through typical investment casting
   • Sand Casting
     • Materials
       • RP-generated parts used as patterns
     • Molding Process
       • Build the cores and molds layer-by-layer by fusing either polymer-bonded sand together
     • Advantages
       • Molds are created in a fraction of the time
   • Plaster Molding
     • Molding Process
       • Create a rubber mold from an RP-generated pattern, then rubber mold is used to create plaster molds