METAL CASTING PROCESSES Sand Casting Expendable Mold Casting Processes Permanent Mold Casting Processes Foundry Practice In-class Assignment ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Overview of Sand Casting Most widely used casting process Nearly all alloys can be sand casted Castings range in size and production quantity A large sand casting weighing over 680 kg (1500 lb) for an air compressor frame (photo courtesy of Elkhart Foundry) ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Sand Casting Production Sequence Cavity formed by packing sand around a pattern Gating and riser system Core used for internal geometry New sand mold for each part ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Types of Patterns Patterns slightly enlarged to account for shrinkage Patterns made of wood, metal or plastic solid split match‑plate cope and drag ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Core in Mold (a) core held in place in the mold cavity by chaplets (b) possible chaplet design (c) casting with internal cavity ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Molds & Sands Typical mix: 90% sand, 3% water, and 7% clay Desirable Mold Properties Strength Permeability Thermal stability Collapsibility & reusability Foundry Sands Silica (SiO2) Small grain  better surface finish Large grain  more permeable Typical mix: 90% sand, 3% water, and 7% clay ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Shell Molding ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Shell Molding Disadvantages: Expensive metal pattern Difficult to justify for small quantities Advantages of shell molding: Better surface finish Good dimensional accuracy ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Vacuum Molding ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Expanded Polystyrene Process (Lost Foam) Advantages Pattern need not be removed Simplifies and speeds mold‑making Disadvantages A new pattern is needed for every casting Economic justification of the process Application Automotive engines ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Investment Casting (Lost Wax Process) ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Investment Casting (Lost Wax Process) A one‑piece compressor stator with 108 separate airfoils made by investment casting (photo courtesy of Howmet Corp.) ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Permanent Mold Casting (1) mold is preheated and coated (2) cores (if used) are inserted and mold is closed (3) molten metal is poured into the mold Application – automotive pistons ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Low-Pressure Casting ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Hot-Chamber Die Casting Low melting‑point metals that do not chemically attack mechanical components Casting metals: zinc, tin and lead ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Casting metals: aluminum, brass, and magnesium alloys Cold Chamber Casting Casting metals: aluminum, brass, and magnesium alloys ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Cold Chamber Die Casting Machine Mold usually made of tool steel or mold steel Tungsten and molybdenum (good refractory qualities) used to die cast steel and cast iron ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

True Centrifugal Casting ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Cupola For Melting Cast Iron "charge," consisting of iron, coke, flux, and possible alloying elements ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Buoyancy in Sand Casting Operation During pouring, buoyancy of the molten metal tends to displace the core Force tending to lift core = weight of displaced liquid less the weight of core itself Fb = Wm ‑ Wc Fb = buoyancy force Wm = weight of molten metal displaced Wc = weight of core ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

In-class Example An aluminum‑copper alloy casting is made in a sand mold using a sand core that weighs 20 kg. Determine the buoyancy force in Newtons tending to lift the core during pouring. Sand core density = 1.6 g/cm3 Al-Cu density = 2.81 g/cm3 ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

SME Video ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

In-class Assignment A sand core used to form the internal surfaces of a steel casting experiences a buoyancy force of 225.63 N. What is the volume of the sand core in cm3? Steel density = 7.82 g/cm3 Sand core density = 1.6 g/cm3 ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Extra Credit – hand in before test 1 Caplets are used to support a sand core inside a sand mold cavity. The design of the caplets and the manner in which they are placed in the mold cavity surface allows each caplet to sustain a force of 10 lbs. Several caplets are located beneath the core to support it before pouring; and several other caplets are placed above the core to resist the buoyancy force during pouring. If the volume of the core = 325 in3, and the metal poured is brass, determine the minimum number of caplets that should be placed (a) beneath the core, and (b) above the core. Brass density = 0.313 lb/in3 ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Manufacturing Economics ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Time Permitting Content ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Semicentrifugal & Centrifuge Casting Semicentrifugal Casting Centrifuge Casting Density of part greater in outer sections Used for smaller parts Application: wheels and pulleys ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Metal is melted without direct contact with burning fuel mixture Crucible Furnaces Metal is melted without direct contact with burning fuel mixture lift‑out crucible stationary pot tilting-pot furnace ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Electric‑Arc & Induction Furnaces Heat generated by electric arc High power consumption for high melting capacity Primarily for melting steel Alternating current passing through a coil Develops magnetic field in metal Induced current rapidly heats and melts ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Ladles & Additional Steps Transfer of molten metal to mold Trimming Removing the core Surface cleaning Inspection Repair, if required Heat treatment crane ladle two‑man ladle ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Casting Quality - General Defects ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Sand Casting Defects ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Product Design Considerations Original design Redesign Draft = 1 for sand casting Draft = 2 to 3 for permanent mold Allow 3 mm stock for machining Corners on the casting – source of stress concentration ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e