Capability Study and Measurement System Analysis: A Case Study at Bosch Rexroth AB
Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Measurement System Analysis helps, along with statistical methods, provide deep knowledge about the capability of a company’s measurement system. Through a better understanding of how measurement systems perform, companies can base decisions on facts to promote quality work. This study examines the capabilities of Measurement System Analysis and examines how well a test bench performs while testing motors at Bosch Rexroth AB in Mellansel. The study examines both the repeatability and the reproducibility of the measurement system, i.e., the variability that occurs when the same operator is doing repeated measurements on the same motor and when different operators perform measurements on the same motor. Bosch Rexroth AB manufactures high torque hydraulic motors. The case study covered the motor type CA 50, which is the most produced motor today at the company. The tests were made at one of the two existing test benches. The DMAIC method within Six Sigma was selected to get a structured workflow in the case study. Three parameters were examined for the motor type CA 50 – high pressure, external leaks, and cleanliness – and touched on Destructive Testing. It was clear from the Measurement System Analysis that the operators did not have a significant impact on the variability of the motor tests for any of the three parameters. The precision of the measurement system differed between the parameters. Concerning the parameter high pressure, the measurement system could be considered to be acceptable, but with room for improvement. The parameter external leaks showed an excellent measurement system with strong margins. The parameter cleanliness, however, showed an unacceptable measurement system. The capability study regarding the same three parameters showed different results. The parameter high pressure showed a decent capability (C_pk^ = 1.17). Parameter external leaks showed a high capability (C_pk^ = 1.17), but cleanliness showed a poor capability (C_pk^ = 1.09, 1.0 respectively 1.13) for the three different particle sizes 4µm, 6µm and 14µm. This thesis resulted in four main suggestions for improvement concerning both the test bench facility and motor type CA 50. The recommendations could help reduce the uncertainty in the measurements of the parameter cleanliness and the precision of the parameter high pressure. Furthermore, the thesis presents a suggestion on how outliers of parameter high pressure might be handled and suggestions for adjusted tolerances on the parameter external leaks.
Place, publisher, year, edition, pages
IdentifiersURN: urn:nbn:se:ltu:diva-170OAI: oai:DiVA.org:ltu-170DiVA: diva2:971935
Industrial and Management Engineering, master's level
Lovén, Erik, Universitetsadjunkt
Garvare, Rickard, Professor