September, 14 Overview of Lecture Material • Introduction Casting Processes • Permanent Pattern, Expendable Mold • Expendable Pattern & Mold Casting 530.454 Manufacturing Engineering • Permanent Mold Casting Metal-Casting Processes Types of Casting Processes Mold-Making Clamping Pouring Cooling Removal Trimming Permanent Pattern, Expendable Mold Casting ◼ • • • • Methods of this type include: Sand casting Plaster mold casting Shell-mold casting Ceramic-mold casting September, 14 Expendable Pattern & Mold Casting ◼ Methods of this type include: ❑ Investment casting ❑ Lost-foam casting ❑ Single-crystal Basic investment casting process casting Expendable shell mold and permanent pattern Example investment cast figurines 1 September, 14 Casting ingots in solid form (process) Non-Expendable Mold Casting ◼ • • • • Lecture 3 by Dr. Yury Ronzhes 530.454 Manufacturing Engineering Question ◼ a) b) c) d) e) Methods of this type include: Permanent-mold casting Die casting Centrifugal casting Continuous casting Example of the continuous casting process 7 Sand Casting Overview Which of the following processes involve a mold pattern? Die casting Shell-mold casting Centrifugal casting Investment casting Continuous casting Sand Casting Patterns Casting Pattern • Replica of the object to be cast • Used to make the mold • Made of wood, metal, plastics or other materials ◼ a) b) c) d) Types of casting patterns: Solid pattern Split pattern Match-plate pattern Cope-and-drag pattern Foundry Sands • • • Bigger grain size = worse surface finish. Irregular grain shapes = stronger mold. Larger grain size = better permeability. Permeability is the state or quality of a material that causes it to allow gases to pass through it. September, 14 2 September, 14 Type & Quality of Sand Molds Mold Types • • • • • Greensand mold Dry sand (cold box) mold Skin-dried mold No-bake mold Oil sand Mold Qualities • • • • • • Strength Permeability Thermal stability Collapsibility Reusability Flowability Industrial Sand Casting Horizontal Sand Flask Molding ◼ ◼ ◼ Mold stability is increased by applying hydraulic pressure Improved mold accuracy Further mold handling can be automatic ◼ ◼ ◼ ◼ Pattern pressed into confined sand Reduction of labor costs Improved dimensional accuracy Higher productivity What is a core in sand casting? a) b) c) d) ◼ ◼ ◼ A small structure used to internally support the sand mold A solid piece of sand used to create internal cavities inside the final casting A nickname given to the pattern used in the sand casting A sample of the sand mold used to determine the quality of the mold Industrial Sand Casting (Continued) Match Plate Sand Molding ◼ ◼ ◼ ◼ ◼ Similar to vertical flaskless molding, but oriented horizontally Inexpensive pattern tooling Ease of changing molding tool High molding quality Cleaner, and quieter with reduced safety risks Vacuum Molding ◼ ◼ ◼ ◼ ◼ Plastic film vacuum formed film inside the mold cavity. Absence of moisture-related defects Elimination binder High dimensional tolerances. Relatively slow, and unsuitable for mass production Investment Casting • • • • September, 14 Cores produce internal surfaces in castings. Cores are sometimes supported by chaplets Cores are made of foundry sand and resin Example of the chaplets supporting a core (size is exaggerated) Vertical Sand Flaskless Molding Question ◼ Cores and Chaplets Also known as the lost wax process Can produces complex and intricate parts with good dimensional control. Slurry used is a mixture of plaster of Paris (a binder) and powdered silica Limited by cost, part size, and difficulties using cores. 3 September, 14 Lost Foam Casting ◼ • • • • • ◼ • • Shell Molding Pouring molten metal into a lostfoam mold Advantages: Complex castings without the use of cores Dimensionally accurate Excellent surface finish Requires no draft Has no parting lines Disadvantages High pattern costs Patterns are fragile Example of foam part and resulting cast Investment - Lost Wax (Foam) & Shell Casting Overview A mixture of sand and resin holds the grains together ◼ Advantages: • Good surface finish • Good dimensional accuracy • Suitable for mass production ◼ Disadvantages: • Expensive metal pattern ◼ Area of application: • Mass production of castings weighing more than 10 kg ◼ Question ◼ a) b) c) d) Gravity Die Casting ◼ ◼ 1) 2) 3) 4) Also known as permanent mold casting. Gravity Die Casting Steps: Metal mold is preheated and coated with a die release agent Cores are inserted and the mold is closed Molten metal is poured, and the part solidifies Mold is opened, and the part is removed from the die September, 14 What are the patterns made from in investment casting? Metal Foam Wax Plastic Low-Pressure & Vacuum Die Casting Low-pressure die casting ◼ ◼ ◼ Vacuum die casting Both use pressure to fill a permanent metal die Low-pressure casting pushes molten metal into die cavity with external pressure Vacuum casting pulls metal into die cavity by creating a vacuum in the mold 4 September, 14 Tin, Magnesium, Aluminum Die Casting Overview Lecture 3 by Dr. Yury Ronzhes 530.454 Manufacturing Engineering Centrifugal Casting Hot & Cold Chamber Die Casting Hot Chamber Horizontal Centrifugal Casting Cold Chamber ◼ ◼ • • • ◼ • • Advantages High productivity Close tolerances Good surface finishes Disadvantages Injection system is submerged in molten metal Only simple shapes are possible ◼ • • • ◼ • • Advantages Close tolerances Good surface finishes Injection system not submerged in molten metal Disadvantages Only simple shapes are possible Less productivity ◼ ◼ ◼ Centrifugal casting ◼ Mold rotates to create centrifugal force Force spreads molten metal evenly along mold wall Produces tubular parts Mold can be oriented horizontally or vertically Semi-Centrifugal Casting ◼ ◼ ◼ Produces solid castings Part density is greater in the outer sections than at the center of rotation Used on parts where the is machined away, e.g. wheels and pulleys Centrifugal Casting True centrifugal casting F = mV 2 / R GF = F / W = mV 2 / Rmg = V 2 / Rg 2/g 2 GF = = (R( N/30) GF R N / 30) /g N = 30 / 2 gGF / D ◼ Semi-centrifugal casting Lecture 3 by Dr. Yury Ronzhes 530.454 Manufacturing Engineering September, 14 29 Lecture 3 by Dr. Yury Ronzhes 530.454 Manufacturing Engineering 30 5 September, 14 Question Continuous Casting ◼ a) b) • • • Also called Strand Casting Steel cast directly into semi-finished shapes Increases yield and product quality c) d) e) Which materials are unsuitable for die casting? Steel Zinc Aluminum Copper Tungsten HW-01 ◼ ◼ Submit February 14th See HW-01 in BB The mechanical strength requirements Ultimate tensile strength --130 ksi Yield strength -- 110 ksi Hardness requirements Hardness range requirements for the center lugs and roller path zones were 294 to 327 Brinell hardness (BHN). The pin lug zone hardness range was specified as 286 to 344 BHN. The microstructure in the casting had to be controlled for phase content to produce the desired hardness in the different regions. Lecture 3 by Dr. Yury Ronzhes 530.454 Manufacturing Engineering 33 Lecture 3 by Dr. Yury Ronzhes 530.454 Manufacturing Engineering 35 Where is correct orientation? Option A Option B Lecture 3 by Dr. Yury Ronzhes 530.454 Manufacturing Engineering September, 14 36 6
