Towards an Objective Classification of Extruded Aluminum Surfaces – A Literature Review and Case Study

Abstract

Large costs and lead-time losses are created by returned aluminum products - to a great extent unnecessarily. Much of the metal product complaints are due to visual surface defects. Today, the aluminum industry relies on several non-standardized classification systems for surface quality assessments which provides far too much scope for subjective and non-repeatable surface estimations. To challenge this situation, a common toolbox to describe and define surface quality in a more objective way needs to be developed. A first step towards such standardization is to speak the same language, thus this study is based on a state-of-the-art survey covering terminology and descriptions of surface defects in literature, and a round-robin assessment collecting terms used by employees at seven companies within the aluminum industry. The literature study showed that most attempts to catalog and categorized various types of defects on commercial aluminum extrusions are based on the origin of defects and how to prevent and/or reduce them, thus the vocabulary is production-oriented and most terms are not useful from the customers’ nor the designers’ point of view when coming to describe desired surface effect, i.e. perceived surface quality. The round-robin assessment confirmed the large variation of terminology used, and that defects were judged differently also within the same company due to experience and field of work. A common vocabulary is suggested to be based on the relationships between used expressions; from general terms at stages linked to consumers, designers and sale, tracing towards more technical terms the closer the stage where the origin of the defect can be found. This structure, in combination with e.g. manufacturing cost, is expected to guide customers towards more sustainable surface quality choices that, together with more consistent surface assessments along the production chain, is expected to strongly reduce unnecessary scrapping.