This prevents stagnation of the material at the die. Each profile die requires production testing and modification to perfect its shape. The shape of the profiles is unlimited. Large or thick profiles are normally extruded with hollows, ledges and projections. A profile with a uniform wall thickness throughout the cross section is the easiest to produce.
Uneven walls cause materials flow variation between the large and small portions of the profile.
A die with uneven wall thickness is called an unbalanced die. The thinner wall sections cool faster than the thick ones, causing a bow, or warp, toward the heavy side. Changing to uniform wall thickness improves flow, cooling and warp characteristics. In the design of hollow profiles that require a leg projection inside the hollow, that projections of leg from the wall be held to a maximum length equal to the thickness of the wall. Figure 5-27 illustrates how extruded profiles can be redesigned to achieve a balanced die.