Investigation of the manufacturing processes of recycled aluminum pots: A lean six sigma approach for sustainable and efficient production

This study investigates the artisanal manufacturing process of recycled aluminum pots, employing Lean Six Sigma tools to identify major sources of non-conformity. Conducted in Sub-Saharan Africa, primarily across five representative workshops in Cameroon, the study reveals that melting 1 kg of aluminum waste requires an average of 8640 s significantly exceeding typical industrial benchmarks. Value Stream Mapping (VSM) indicates an average cycle time of 12,731 s for mechanical finishing and 14,713 s for manual finishing, with corresponding Process Cycle Efficiencies of 73 % and 75 %. Molding sand quality deteriorates after 90 reuse cycles, reducing cleanliness to 79.85 % and impairing the surface quality of cast parts. Chemical analysis of 45 samples shows that 66.6 % of productions exceeds the regulatory lead limit of 0.05 %, with concentrations reaching up to 0.152 % in some cases. However, the dimensional characteristics (thicknesses ranging from 3 to 6 mm) and Leeb hardness values (289.25 – 367.35 HL) align with normative requirements (NF EN 12983 and NF EN 601). Impact Strength (1.2 – 3.6 J/m²) also falls within acceptable thresholds for industrial cast alloys. Multivariate analysis reveals a significant influence of waste type (η² = 0.564; p = 0.016) and melting treatment (η² = 0.472; p = 0.041) on lead content. Lastly, the process capability regarding health safety is critically low (Cp = 0.20; Cpk = 0.166), indicating a non-compliance rate of 97.7 %.