Analysis and die design of flat-die hot extrusion process 2. Numerical design of bearing lengths

CAD implementation of design rules for aluminium extrusion dies

“…An important reason is that it already takes a lot of effort to produce data about the relationship of a single input parameter (such as profile thickness) to a single output parameter (such as exit velocity). Even if a simple design rule can be derived, such as the bearing length formula by Lee and Im [24], its applicability at other extrusion plants is questionable, because the effect of parameters such as alloy composition and die radius is not included.…”

“…Increasing the length of the bearing channel increases the resistance to flow and therefore decreases the exit velocity [24,33,34]. Some simple design rules for bearing lengths are found in literature [24,33].…”

“…Aside from the compensation for the container effect that they provide, they state that bearing length should increase linearly with profile width in order to achieve a uniform exit velocity. Lee and Im [24] even acknowledge that a shorter bearing is called for in places where there is a bigger bearing surface slowing down the flow, such as at the ends of legs of the profile.…”

“…Design rules for bearing length variations can be found in literature, such as those given by Miles [33] and Lee & Im [24] (see also section 3.1). However, these design rules do not take into account the presence of a sink-in that already balances out the flow to a large extent.…”

“…The resulting extra friction is not modelled in the sink-in formula (3.1), which expresses flow resistance (without a sink-in) only as a function of the thickness T and the distance to the centre R. To compensate for this the formula needs to be overridden. Lee and Im, when faced with the same problem in their design rule for calculation of bearing lengths, added a factor to their formula that shortens the bearing length near leg tips [24]. Boalgroup adapts the same practice, but in some cases they also locally elongate the sink-in to enhance the feed of leg tip sections.…”