Estudo da otimização de um processo de controlo de peso com recurso a controlo estatístico de processo

  • Diana Margarida Andrade Moreira (Student)

Student thesis: Master's Thesis


Quality perception of a product or a service is related with a huge set of characteristics or attributes, which are mostly on the basis of consumer’s choice. The diversity of consumer profiles, the demand for high quality levels and a strong world competitiveness imply that Quality is currently considered a continuous improvement and not a mere compliance with a specification. Therefore, companies are forced to continuously improve Quality, not only of their products or services, but also of their tools, skills, methods and, above all, processes. In practice, it often results in ensuring more effective processes, stable and predictable, since the Quality of a product or service is inversely proportional to its variability. Cerealis Produtos Alimentares S.A. is being sensitive to this reality and as a competitive company that positions itself continuously at the forefront of the agrifood sector, the present study aimed to streamline the process of weight control of pre-packed cookies in order to reduce losses associated with the overweight of the retail units. Thus, the work focused on Integral cookies, minimizing excess of weight in a batch production, fulfilling the legal weight limits per unit and the acceptance criteria of the lot, in accordance with the applicable law and consequently with the limits imposed in Cerealis Group (lower limit: 190,50 g; upper limit: 218,00 g). The weight reduction approach aimed to decrease the upper specification limit (218,00 g) to the upper control limit (209,00 g). The Statistical Characterization of the Process was carried out, which included control charts and process capability studies, applied at the end of the packaging line. Results allowed to conclude that the average weight of Integral pre-packed units was around 204 g. However, the average weight of retail units will be higher, due to weight control system that ensures compliance with the legal requirements, in which non-compliant units are disregarded. The overweight reality directly implies three types of wastes, which are: loss of financial profitability, since the established price considers the nominal weight and is not variable with the effective unit weight; the cost of reprocessing the packages that do not meet the legal requirements, by excess or default, which added new material and human costs; and finally, equipment efficiency losses in the order of 2% for every 4 grams of excess, which results in nominal speed reduction. Therefore, the tested approach to reduce the average weight of pre-packed units by reducing the upper control limit was not feasible, since the control charts of the process studied do not have neither the necessary stabilization or variability to attain a reduction of average weights coupled with commitment of losses listed above.
Date of Award29 Mar 2019
Original languagePortuguese
Awarding Institution
  • Universidade Católica Portuguesa
SupervisorRui Mário da Silva Azevedo (Supervisor)


  • Quality
  • Statistical process control
  • Weight control
  • Process variabiity
  • Cookies


  • Mestrado em Engenharia Alimentar

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