Investigating a novel approach to reduce transverse weld scrap in aluminum extrusion using profiled dummy blocks and billets

The supply chains of extruded aluminum are materially inefficient, with up to two-fifths of the billet being scrapped before the profile is incorporated into a final product. A significant source of process scrap arises from removing the tongue-shaped transverse weld—also known as the front-end defect or charge weld—that is formed between the consecutive billets being extruded, primarily because of concerns over weld integrity. Optimizing process settings and die geometry can reduce the transverse weld length—and thus the amount of scrapped material—but only by approximately 15%. We investigate a novel methodology for significant scrap reduction, where an initially profiled interface—rather than a flat one—between consecutively extruded billets compensates for the differential velocities of material across the billet cross-section as it moves through the die ports, resulting in shorter welds. This profiled interface is created using profiled billets that fit into a dummy block shaped with the inverse of the billet profile. We present a design process to define the shape of the profiled dummy block and billet. For a given part, we first determine the ideal shape by obtaining the velocity field from finite element simulations of the conventional extrusion process, assuming perfectly rigid tooling and no constraints on the creation of profiled tooling or billets. Next, we rationalize this shape by applying stress and deflection limits to the dummy block, ensuring it avoids plastic deformation and interference with the container wall. Additionally, we consider ductile damage limits for the billet to prevent cracking during a pre-extrusion hot forging stage, which is one method of generating profiled billets. The design process is applied to four profiles of increasing complexity: solid round and rectangular bars, a square-tube hollow, and a complex multi-hollow profile. Extrusion and forging trials using custom-built tooling are conducted to validate the design process. The experimental case studies demonstrate that profiled dummy blocks and billets can achieve weld length reductions of over 50% and that the same tooling can offer scrap savings across a range of similar extruded shapes. In the tests, a profiled dummy block with an air escape vent showed zero-to-negligible plastic deformation and neither air entrapment nor clogging of the vent during extrusion, while a conventional billet was hot-forged to produce profiled ends without cracking or deforming the forging tools. Overall, this study highlights that profiled billet extrusion is a promising technology for significantly reducing scrap from transverse weld removal in aluminum extrusions.