An apparatus for casting material, comprising: first and second opposing side walls; first and second end wall assemblies (230; 240) extending between the first and second side walls, wherein the first and second opposing side walls cooperate with the first and second end wall assemblies (230, 240) to form a profile of the mold cavity which is in the shape of the perimeter of the generally rectangular shaped mold cavity; wherein at least one of the first and second opposing side walls comprises two or more force receiving members (310, 510), each of the two or more force receiving members (310, 510) secured to the at least one of the first and second opposing side walls at two or more attachment points disposed along a height of the at least one of the first and second opposing side walls, wherein each of the two or more force receiving members (310, 510) are configured to be displaced relative to a straight line between a first end of the at least one of the first and second opposing side walls and a second end of the at least one first and second opposing side walls in response to receiving a respective force applied externally from the mold cavity to the two or more force receiving members (310, 510), wherein the respective displacement at a first of the two or more force receiving members (310, 510) relative to the straight line is different from a displacement at a second of the two or more force receiving members (310, 510) relative to the straight line, and wherein a respective force at each of the two or more force receiving members (310, 510) changes a curvature of the at least one of the first and second opposing side walls between the first end and the second end of the at least one first and second opposing side walls. first and second opposing side walls; first and second end wall assemblies (230; 240) extending between the first and second side walls, wherein the first and second opposing side walls cooperate with the first and second end wall assemblies (230, 240) to form a profile of the mold cavity which is in the shape of the perimeter of the generally rectangular shaped mold cavity; wherein at least one of the first and second opposing side walls comprises two or more force receiving members (310, 510), each of the two or more force receiving members (310, 510) secured to the at least one of the first and second opposing side walls at two or more attachment points disposed along a height of the at least one of the first and second opposing side walls, wherein each of the two or more force receiving members (310, 510) are configured to be displaced relative to a straight line between a first end of the at least one of the first and second opposing side walls and a second end of the at least one first and second opposing side walls in response to receiving a respective force applied externally from the mold cavity to the two or more force receiving members (310, 510), wherein the respective displacement at a first of the two or more force receiving members (310, 510) relative to the straight line is different from a displacement at a second of the two or more force receiving members (310, 510) relative to the straight line, and wherein a respective force at each of the two or more force receiving members (310, 510) changes a curvature of the at least one of the first and second opposing side walls between the first end and the second end of the at least one first and second opposing side walls.