Reducing production scrap is vital for decarbonizing the aluminum industry. In extrusion, the greatest source of
scrap stems from removing profile sections containing transverse (charge) welds that are deemed too weak for
their intended purpose. However, until now, there has been no predictive transverse weld strength model. This
article establishes a transverse weld strength model as a function of billet properties and extrusion parameters. It
extends the film theory of solid-state welding by enhancing Cooper and Allwood’s plane strain model to consider
non-plane strain deformations at the billet-billet interface. These enhancements are informed by analyzing oxide
fragmentation patterns through shear lag modeling and microscopy of profiles extruded from anodized billets.
Model predictions are assessed through shear tests on welds from single and two-piece billets, extruded into rod,
bar, and multi-hollow profiles. The experiments reveal that negative surface expansions at the weld nose cause
interface buckling and weaker welds, but both surface expansions and weld strengths increase with distance from
the nose. In non-axisymmetric profiles, deformation conditions and strengths vary across, as well as along, the
weld. Two-piece billet welds are longer but reach bulk strength long before weld termination. The model predicts
these trends and shows that die pressures are sufficient for micro-extrusion of any exposed substrate through
interface oxide cracks. This underscores the significance of interface strains in exposing substrate and determining the weld strength. The model can help increase process yields by determining minimum lengths of weak
profile to scrap and aiding process optimization for increased weld strength.
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Exploring a Novel Process for Reducing Aluminum Extrusion Process Scrap
Extruded aluminum supply chains are materially inefficient with around 40% of the billet likely to be scrapped before the profile is embedded in a product. One of the largest sources of scrap is the removal due to weld integrity concerns of the tongue-shaped transverse weld(s) that forms between consecutively extruded billets. Process setting and die geometry optimization can decrease the weld length (and hence scrapped material) by modest amounts. We explore a process for significant scrap savings using profiled dummy blocks to generate shorter welds by compensating for the differential metal flow velocities across the billet cross-section as it flows through the die ports. We develop a design process for defining the profiled dummy block shape. For a given part and press, we first define an ideal dummy block shape by extracting the velocity field from finite element simulations of the conventional process and assuming perfectly rigid tooling. Next, we rationalize the tool shape using stress and deflection limits (preventing plastic deformation and interference with the container wall) and ductile damage limits for the billet to prevent cracking. We then simulate the likely effect of the rationalized dummy block design on back-end defect removal. The methodology is demonstrated for four profiles of increasing complexity. The process’ potential is evaluated experimentally using billets machined to match the ideal dummy block shape. The results show that profiled billets can achieve weld length reductions >50% for simple shapes. We demonstrate that multi-profile tooling can deliver scrap savings across a family of similar profiles.
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- Award ID(s):
- 2122515
- NSF-PAR ID:
- 10447058
- Date Published:
- Journal Name:
- Proceedings of the 14th International Conference on the Technology of Plasticity - Current Trends in the Technology of Plasticity
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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