The design of experiments has been widely used for product and process development based on Quality by design (QbD) approach to achieve quality product. Sources of variability are identified and controlled during manufacturing. However, uncertainty due to uncontrollable variables in the process leads to quality issues and the need for reprocessing in some cases. This study proposes a systematic approach to determine the robust design space for process parameters embraced with the variation of initial and reprocessed materials to ensure that the tablet will meet the specification. The Taguchi L36 experiment design is applied to determine suitable tableting parameters for different granules to ensure physical specifications. Four types of calcium carbonate granules were produced with different moisture contents (ZM) and manufacturing conditions (ZT). Additionally, three critical parameters of tablet compression process—filling volume (XV), compression force (XF), and turret speed (XS)—each encompassing three levels, were selected as input variables. The responses were derived from the product specification, namely weight (YW), tensile strength (YTS), and disintegration time (YDT). The experiment results were embedded into two models: the single independence response model (SRM) and the multiple dependent response model (MRM). After a confirmation experiment using predicted parameters, a comparison of their %MAPE (mean average percentage error) revealed that MRM has lower accuracy in terms of YTS but dominates SRM in terms of the region of design space. This finding relates to the effect of data transformation capturing non-linear relationships between these factors and responses. The design space derived from the models allows manufacturers to adjust critical process parameters for getting desired specification tablets and also provides a framework for continuous improvement by enhancing their original design space and providing a rigorous reprocessing plan.
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