Research On Process Reliability For Manufacturing

Product reliability is produced by design, by manufacture and management. The target value of product reliability that was determined in product design stage must be implemented and ensured by manufacturing process, for if the impacts of various factors in manufacturing are underestimated and are out of control, reliability indices of finished products will more likely fall short of requirement. Therefore, ensuring product reliability in manufacturing process becomes an essential problem to be solved. This dissertation focuses its research on ensuring product reliability in mechanical manufacturing process which is most familiar in manufacuting domain.In the context of fast response manufacturing, manufacturing enterprises have to deal with problems such as short developing time, uncertain technical factors, delay of technical reform, short of validation for product reliability, and insufficient management experiences. In order to solve these problems, we should emphasize on the application of reliability engineering, research on process reliability, enhance technical foundation and management, and combine techniques with management. Ensuring product reliability is the research target of process reliability. Therefore, motivated by the requirement, this dissertation summarizes related research, based on which, the concept of mechanical manufacturing process reliability and its analysis methods are proposed. Corresponding models are constructed to instruct effective control of mechanical manufacturing process. The purpose of this dissertation is to provide technical support for ensuring product reliability in mechanical manufacturing process.This dissertation researches on following issues:1) Concept of mechanical manufacturing process reliability and evaluating indicesAccording to the requirement of analysis and control of the capability to ensure product reliability for mechanical manufacturing process, this dissertation summarizes related researches and proposes the concept of mechanical manufacturing process reliability. To completely evaluate mechanical manufacturing process reliability, the dissertation also presents applicable evaluating indices, such as process reliability, frequency of process faults, mean time to repair process fault, process stability, process capability of self-correction, process transmissibility, etc. Corresponding calculating methods for these indices and their selecting principles are also proposed.2) Modeling of mechanical manufacturing process reliabilityAs product reliability indices are gradually shaped during the manufacturing of holes and positions, to ensure product reliability, the key holes and positions, whose manufacturing determine the product reliability indices should be confirmed first. This dissertation synthesizes judgments of experts by means of Bayes theory, to identify the key holes and positions. After the key holes and positions are identified, this dissertation constructs models of process reliability, according to the relations between the machining processes of the key holes and positions and their impacts on process reliability.3) Analysis and control of impacting factors for process reliabilityAs machining processes of key holes and positions usually determine the inherent reliability of product, this dissertation regards the machining processes as main impacting factors for process reliability. Hence, process reliability can ensure product reliability only by enhancing analysis and control of these impacting factors. Therefore, this dissertation first presents a fuzzy method to evaluat factors that affect key holes and positions. Then, based on measure data of product's holes and positions, it applies multivariate analysis methods to implement analysis and control, according to the control requirements of multiple holes and positions and single hole or position in multiple processes, respectively. In order to reduce the chance of process fault occurrence and hence ensure that indices of process reliability meet requirement, the dissertation takes the loss of process faults and cost of preventive maintenance into accounts, presents a decision approach for preventive maintenance, based on proportional hazards model. The proposed approach can effectively reduce the cost of operation for mechanical manufacturing process and guarantee the frequency of process faults will not exceed requirement.4) Process reliability evaluationThis dissertation classifies evaluation of mechanical manufacturing process reliability as system level and index level. In the system level of process reliability evaluation, from the poitview of evaluating process reliability's performs on ensuring product reliability, it is implemented by compare the reliability index of manufactured products with target value, which requires precise estimating of product reliability. However, before the products are handed over to customers, the number of products that can be put into reliability test is small or zero failure is obtained when test time is short, due to limts of time or cost. It is hard to estimate product reliability in such situation. Therefore, this dissertation researches on product whose lifetime follows Weibull distribution, which is popular in practice. It presents the method to estimate product reliability by use of reliability data of similar product and comparison of key holes and positions data between the two kinds of products, in the case of zero failure result obtained in product reliability test with small sample size. It can precisely evaluate mechanical manufacturing process reliability by comparing product reliability index with target value. In the index level of process reliability evaluation, this dissertation proposes that process reliability index evaluation should be combined with data from trial manufacturing. It presents an evaluation approach for frequency of process faults based on Bayes fusion method and a sequential posterior odd test method to evaluate mean time to repair process faults. The proposed methods are incorporated with trial manufacturing and hence are capable to precisely evaluate process reliability indices and offer effective support for improving processes and equipments.This dissertation, motivated by manufacturing requirements, explores theory and methods for mechanical manufacturing process reliability and obtains initial research results. It is grateful to provide references for designing and improving process route, shortening developing period and producing products that match the reliability requirements.