University of Nevada Las Vegas
MEG426/626 Manufacturing Processes
Department of Mechanical Engineering
Fall Semester 2000
Fundamentals of Casting
Castingis a process in which molten metal flows by gravity or other force into s mold where it solidifies in the shape of the mold cavity.
Basic Requirements of Casting Processes:
Pattern: an approximate duplicate of the final casting.
Flask: is the box that contains the molding aggregate.
Cope: the top half of the molding aggregate.
Drag: the bottom half of the molding aggregate.
Core: is the sand shape that is inserted into the mold to produce the internal features of a casting.
Core Print: is the region added to the pattern, core, or mold that is used to locate and support the core within the mold.
Mold cavity: is the shaped hole formed by the mold material and core, which the molten metal is poured and solidified to produce the desired casting.
Riser: is an extra void created in the mold that will also fill with molten metal. It provides a reservoir of metal that can flow into the mold cavity to compensate for any shinkage that occurs during solidification.
Gating system: is the network of channels used to deliver the molten metal to the mold cavity.
Pouring cup: is the portion of the gating system that initially receives the molten metal from the pouring vessel and controls its delivery to the rest of the mold.
Sprue: the vertical portion of the gating system.
Parting line (parting surface): is the interface that separates the cope and drag halves of a mold, flask, or pattern and also the halves of a core in some core-making processes.
Draft: is the taper on a pattern or casting that permits it to be withdrawn from the mold.
Core box: the mold or die used to produce casting cores.
Pouring temperature: is the temperature of the molten metal as it is introduced into the mold.
Pouring rate: refers to the volumetric rate at which the molten metal is poured into the mold.
Fluidity: is a measure of the capability of a metal to flow into and fill the mold before freezing.
Solidification of Metals:
Pure Metals: solidifies at a constant temperature.
Most Alloys: freeze over a temperature range (mushy zone).
Eutectic Alloys: solidifies at a constant temperature, such as lead-tin alloys.
Three steps: 1). Liquid contraction during cooling prior to solidification.
2). Solidification shrinkage: contraction during the phase change from liquid to solid.
3). Thermal contraction of the solidified casting during cooling to room temperature.
Pattern shrinkage allowance: the amount by which the mold must be made larger relative to the final casting size.
Directional solidification: in which the solidfication interface sweeps continuously through the material, can be used to assure the production of a sound casting.
Chills: are metal parts that cause rapid freezing in certain regions of the casting.
Internal chills and external chills.
ts = B (V/A)n where n = 1.5 to 2.0
ts = the time from pouring to the completion of solidification, min; V = the volume of the casting, in.3 (cm3); A = surface area of the casting, in2. (cm2); and B = mold constant.
Created by Dr. Wang