Question

The dimensional accuracy and the residual stress formation tendency in casting is affected by

Answer 1

What are residual stresses
Residual stresses or locked-in stresses can be defined as those stresses existing within a body in the
absence of external loading or thermal gradients. In other words residual stresses in a structural
material or component are those stresses which exsist in the object without the application of any
service or other external loads.
Factors that cause residual stresses
Residual stresses can be present in any mechanical structure because of many causes.
Residual stresses may be due to the technological process used to make the component.
Manufacturing processes are the most common causes of residul stress. Virtually all manufacturing
and fabricating processes such as casting, welding, machining, molding, heat treatment, plastic
deformation during bending, rolling or forging introduce residual stresses into the manufactured
object. Residual stress could be caused by localized yielding of the material, because of a sharp
notch or from certain surface treatments like shot peening or surface hardening.
Among the factors that are known to cause residual stresses are the development of deformation
gradients in various sections of the piece by the development of thermal gradients, volumetric
changes arising during solidification or from solid state transformations, and from differences in the
coefficient of thermal expansion in pieces made from different materials.
Thermal residual stresses are primarily due to differential expansion when a metal is heated or
cooled. The two factors that control this are thermal treatment (heating or cooling) and restraint.
Both the thermal treatment and restraint of the component must be present to generate residual
stresses.
When any object is formed through cold working, there is the possibility for the development of
residual stresses.
A good common example of mechanically applied residual stresses is a bicycle wheel. A bicycle
wheel is a very light and strong because of the way in which the components are stressed. The wire
spokes are radial aligned and tightening the spokes creates tensile radial stresses. The spokes pull
the rim inward, creating circumferential compression stresses in the rim. Conversely, the spokes
pull the tubular hub outward. If the thin spokes were not under a proper tensile preload load the
thin wire spokes could not adequately support the load of the rider.

Answer 2

Temperature is known to be the main function to affect the dimensional accuracy and residual stress forming tendency during metal casting.

The dimensional accuracy of a casting metal is affected when the metal in the liquid form cools down to form solid metal.  

The residual stress forming tendency is affected during the weld joints are heated and cooled in various temperature.