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11 B - METAL CASTING , permanent mold


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Permanent mold process
CASTING A METAL INTO A PERMANENT, PREHEATED MOLD with or without cores, a process that produces good dimensional control and high rates of part production that come at the expense of expensive machinery. Used to produce precise parts - automotive and airspace components, missile parts. Variations: Slush casting, low-pressure casting, vacuum permanent-mold casting >>> PERMANENT MOLDS SMOOTH OUT ANAL BEADS
Slush casting
A METHOD TO CAST A HOLLOW FIGURE, allowing the walls to solidify and pouring out the excess metal, producing a nice surface finish with a hollow interior, a method used for producing trinkets: statues, trinkets, lamp pedestals, by having an nice exterior and saving on material costs >>> SHINY, HOLLOW STATUE ATTRACTS VASTS EMPTINESS
Low pressure casting
Filling a mold using air pressure driven metal - the clean metal fills the mold, driven by air pressure, pressure pressing down on the surface of a molten metal container, forcing the clean, non-oxidized metal from the bottom into the mold, thereby minimizing oxidation and gas porosity defects, a method with high dimensional accuracy and fit for high rates of production - rail road wheels are cast in graphite molds >>> DIRTY AIR PROPELS CLEAN METAL.
Vacuum permanent mold casting
Using vacuum to draw metal into the mold, a technique that holds an advantage of even less porosity and greater strength than in low pressure casting, and it's also fit for high production output, producing good dimensional accuracy, surface finish, and mechanical properties. >>> EMPTY AND LIFELESS VACUUM SUCKS IN FAST AND PRECISE METAL
Die casting
INJECTION OF MOLTEN METAL INTO A DIE USING A PLUNGER at high rates and high pressures, around 7 to 350 MPa, quickly producing a lot of parts with good surface finish, dimensional control, thin sections up to 0.5 mm, small grains due to fast cooling, and low part costs at high production rates. Two types exist: [1] Hot chamber machines, [2] Cold chamber machines >>> HIGH PRESSURE PLUNGER MAKES SHINY, THIN RIBS.
Hot chamber die casting machines
Part of the machine is submerged in a liquid metal, usually a metal with low melting temperatures that is forced into the die by a plunger, a machine that can output great number of parts, a machine that can't be used for aluminum and copper alloys, since they will attack the molten metal pot. >>> FAST HEAT FEARS CHEMICAL BROTHERS
Cold chamber die casting machines
The molten metal is poured into an unheated chamber and forced into a die by a plunger, a process that is a bit slower since it requires feeding the metal into the machine's chamber, yet it still manages to produce quite a bit of precise parts >>> FIRST LADLE, THEN PLUNGER
Flash
A thin portion of metal at the exterior of a casting that results from molten metal being squeezed into the spaces between the die halves of the mold at the parting line, or into the clearances around the cores and ejector pins. >>> HOT FLASH CLOGS HEAVY DIES
Common die materials
COMMON MATERIALS FOR DIE CASTING DIES are hot-work tool steels, mold steels, maraging steels, and refractory metals such as tungsten alloys or molybdenum alloys.
Squeeze casting
A COMBINATION OF CASTING AND FORGING which is sometimes called liquid-metal forming, a process that squeezes the molten metal in a preheated lower die by by the upper die, after solidification begins, thus completely filling the cavity and producing good surface finish, low porosity, low shrinkage, a process commonly used for alluminum and magnesium alloys, due to their low melting temperatures, producing things like automotive parts >>> LIQUID FORGE SHAMES EVEN THE MIGHTY HEPHAESTUS
Semisolid metal casting
MOLDING OF A SEMISOLID ALLOY, a slurry formed between solidus and liquidus, the mushy liquid/solid mix is constantly agitated to prevent the formation of dendrites, since it needs to have granular grains. --Advantages: [1] Complex part geometries, [2] Thin walls in parts, [3] Close tolerances, [4] High strength due to zero or low porosity. Forms of semisolid metal casting: [a] Thixocasting, [b] Rheocasting, [c] Thixomolding >>> MUSHY METAL MAKES STRONG PARTS.
Rheology
Science that relates deformation and flow of materials.
Thixocasting
Heating up an aluminum, non-dendritic billet and injecting the mushy, semi-solid matter into die.
Rheocasting
Agitating an alluminum slurry between the solidus and the liquidus temperature, in order to prevent dendrite formation, and injection of it into a die.
Thixomolding
Creating a magnesium slurry by heating up and mixing particles with a rotating screw, before injecting them into a die.
Centrifugal casting
Rotating the mold at a high speed, in order to distribute the metal to all the regions of the die. Has at least three varieties: [1] True centrifugal casting, [2] Semicentrifugal casting, [3] Centrifuge casting.
True centrifugal casting
ROTATING MOLTEN METAL IN A VERTICAL OR HORIZONTAL TUBULAR DIE, eliminating defects and porocity due to constant force applied to metal, producing parts with good outer surfaces - bushings, tubes, pipes by the application of a centrifugal force that must be bigger, by about a factor of 60 to 80, then the metal's weight (GF - G Factor), a process that produces parabolic inner surfaces when casting vertically. >>> ROUND ROTATOR CREATES TUBULAR TUBES
Semicentrifugal casting
Production of solid castings, such as wheels and pulleys, by rotating the mold with G-Factors of bout 15, creating parts with good metal density on the outside and usually removing the inside portions. Quite often the process uses expendable molds. >>> ROTATED WHEEL MAKES A STRONG EXTERIOR.
Centrifuge casting
Rotating a mold with smaller, non symmetrical parts on the exterior, thus ensuring good metal density and reduced defects. >>> CENTRIFUGED CLUTCH CATCHES DENSE METAL
Furnaces
A furnace heats and melts the metal. We cover following: [1] Cupolas, [2] Direct fuel-fired furnaces, [3] Crucible furnaces, [4] Electric arc furnaces, [5] Induction furnaces. >>> ELECTRIC CUPOLAS DIRECT INDUCTIVE CRUCIBLES
Cupola furnaces
VERTICAL CYLINDRICAL FURNACES equipped with a tapping spout near base. Melts cast irons and CONVERTS PIG IRON TO CAST IRON.
Direct fuel fired furnaces
Melts non-ferrous metals like aluminum and copper based alloys, heating the metal charge in a small, open-hearth by burning natural gas through burners on the side of the furnace, DIRECTLY APPLYING FLAME TO METAL.
Crucible furnaces
HEAT THE METAL INSIDE OF THE CRUCIBLE, avoiding direct contact with flame. Three types exist: [1] Lift out crucible, [2] Stationary pot, [3] Tilting pot furnace.
Electric arc furnaces
Melt high quantities of metals, primarily steels, by means of electric arc. Fit for high production rates, yet consumes much energy.
Induction furnaces
Melt metals, any metals, by running an alternating magnetic field through them, rapidly heating the material while avoiding any contamination by contact with it. >>> ALTERNATING MAGNET MELTS EVERYTHING
Pouring molten metal
Pouring or metal is done by ladles, big or small pots of refractory materials that sometimes have filters to remove oxides or fluxes to retard oxidation, since the metal on the surface oxidizes, and that can produce defects in the mold, and even ladles that can pour metal from the bottom, leaving all the oxides at the top, have been developed. >>> SMART LADLE LEAVES OXIDES TO RUST
Cleaning and heat treating
After the casting is removed, it's "cleaned" and heat treated: [1] Trimming - removing excess sprouts of solidified metal: runners, risers, flashes; [2] Removing cores; [3] Surface cleaning - removal of sand and surface finish enhancement; [4] Inspection - check that there no defects; [5] Repair - if the casting is damaged, it's fixed by welding, grinding, and other salvage methods; [6] Heat treatment - increase qualities of part by heat treating. >>> TaCo SIR Hugs: TRIMMING, CORE_REMOVAL,,, SURFACE_CLEANING, INSPECTION, REPAIR,,, HEAT_TREATMENT