Some problems about hollow dies and die corrections
1.Twisting and side bending of square and round tube dies
The causes of torsion and side bending defects of aluminum extrusion profiles are mainly caused by uneven flow velocity caused by uneven metal supply. The picture below is a schematic diagram of twisting and side bending of a square pipe. Apart from the technological factors (such as the billet and other aluminum extrusion tooling temperature), the main reasons for the uneven flow rate are the unreasonable design of the working belt, especially for multi- cavity dies .
The improper arrangement of the die cavity and the imbalance of the supply of the cavities to the metal. In the picture, the area of diverging cavity 3 and 4 is unequal. Although the area of diverging cavity 1 and 2 is equal, the area of diverging cavity 2 is farther away from the center than 1. Therefore, the metal supply and frictional resistance of the four cavities are not equal, reasonable aluminum extrusion die design is crucial.
2. Convex on the profile surface
Possible reasons: After multiple extrusion or other reasons, the tongue working band of the aluminum extrusion die is worn and pits appear (see below FIG), which impedes the metal flow along the tongue surface and causes the lateral velocity of the profile to be faster than the inner one, thus causing the protrusion of the four walls. If only one wall or two or three walls protrude, it may also be caused by improper coordination between the tongue working belt and the die cavity working belt, that is, the tongue working belt protrudes the die cavity working belt for too long, or it may be caused by local wear of the "tongue".
Correction: When the thickness of the aluminum profile is small, file the tongue working band pits to reduce friction resistance, or block the die working band. If the wall thickness dimension does not allow filing the tongue, then ask the aluminum extrusion die manufacturer, a new die must be replaced. When only individual wall thickness protrudes, the working band at corresponding wall can be obstructed.
3. Concave on the profile surface
In most cases, for customized aluminum extrusion die, due to the insufficient rigidity of the die, elastic deformation occurs during extrusion (see figure below), shortening the actual working band of the tongue and increasing the flow rate, resulting in the concave of the four walls. If only one wall or two walls, three walls produced this situation, then, may also be the tongue and die working belt mismatch caused by the flow rate.
Die correction: add the appropriate thickness of gasket between the tongue and the die, and then remove the same thickness as the gasket from the outer face of the upper and lower die to keep the total thickness of the die unchanged. If the wall is concave, the tongue working band can be obstructed or the die working band can be thinned at the corresponding place.