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Proceedings of CAD'15, 2015, 360-365
Automatic Post-processing for Tolerance Inspection of Digitized Parts Made by Injection Molding

Michele Bici, Francesca Campana, Università di Roma La Sapienza, Italia
Alessio Trifirò, ABB SpA – Automation Products Division, Pomezia

Abstract. Injection molding is one of the most widespread manufacturing systems for high volume production. In case of electromechanical components (dimensional range between 25-150 mm, shell thickness 0.5-0.8 mm), Reverse Engineering (RE) may play an important role to understand weakness of the product-process design. Arrangement of the cavities on the die may locally change injection and cooling parameters, producing sinks, weld lines, burrs or global shape defects (warpage). Residual stresses induced by shrinkage are major responsible of these defects and, of course, they affect dimensional and geometrical tolerances of the parts. For this reason, in electromechanical assemblies, inspection of functional tolerance represents a relevant aspect to validate die design, in particular if a large amount of parts is made as multiple cavities on a single die. Although the injection molding process has a tolerance compatible with laser scanner measurements (±0.05 mm versus an accuracy of 0.025 mm) or other enhanced solutions (e.g. grey code and phase shift systems), RE applications concerning the evaluation of dimensional and geometrical tolerances are not a well-established industrial tool yet. It is due to methodological problems associated to: (1) the post-processing of the cloud of points, (2) the assessment of the measurement protocol; (3) the hardware set-up according to the acquisition paths and conditions.

Keywords. RE, Tolerance inspection, Hierarchical space partitioning, Plastic injection molding

DOI: 10.14733/cadconfP.2015.360-365