Multi-stage Cost Evaluation Of Laser Deposited Metal Parts Based On Fatigue Life Characteristics

Laser direct metal deposition(LDMD)has been widely applied for fabricating complex parts due to its capability of high-design freedom and high-precision forming.However,highly complex thermal behavior during LDMD results in the generation and randomness of parts’ internal defects such as pores,lack of fusion and unmelt particles,which often become the key factor affecting the parts’ fatigue life during the servicing process.In particular,the defect-induced parts’ fatigue life too short or too long,resulting in the mismatch and imbalance between resource consumption and benefit output during the parts whole process from deposition manufacturing to service failure.Apparently,how to reveal the relationship between the random internal defects inducedfatigue life characteristics and multi-stage cost economy is critical to realize mutual matching between the parts fatigue life and each stage cost economy.Therefore,this paper systematically carried out the research on the mutual matching between the defect-induced fatigue life characteristics and the multi-stage cost economy for LDMD metal parts.First,the key factors affecting the parts’ fatigue life among the deposit defects were identified and quantified.Subsequently,with analyzing the relationship among the fatigue life-related reliability and failure rate during servicing process and multi-stage cost,a parts’ fatigue life-related multi-stage cost model was established.The main research contents of this paper are as follows:(1)Based on literature research,the key factors affecting the fatigue life of additive parts during servicing process were analyzed,and the maximum defect occurring in the part was rendered to be the key variable for parts’ fatigue life estimation during the manufacturing and servicing process.Subsequently,two groups of repeated orthogonal experiments were designed to obtain LDMD-316 L parts with different defect characteristics,and the block maximum(BM)defect sampling method was used to identify the maximum defect appearing in the cutting plane for parallel cross-section from parts.Accordingly,the maximum defect identified was quantitatively characterized by defect projection area,and the hardness of the parts sampling crosssection was also measured.(2)Aiming at the problem for the identification and estimation of the parts’ random maximum defect and the time-consuming for BM defect sampling method,an extremum probabilistic estimation method from small sample size was proposed in this research,and with the accurately estimated maximum defect occurring in the parts as driving force,a defect-related fatigue life prediction model was subsequently established at the critical state of parts’ fatigue failure.Accordingly,based on the defect sampling in two groups of repeated orthogonal experiments,combined with the extreme value statistic(EVS)theory and the approximate identically distributed characteristics of defects,the defect samples’ characteristics in the process interval was probabilistic evaluated to infer the Gumbel distribution characteristic parameters for LDMD-316 L parts under each process level,and the parts’ maximum defect size was accordingly estimated and the parts’ fatigue life was predicted as well.Subsequently,the accuracy of parts’ maximum defect estimation and fatigue life prediction was verified.(3)Based on the parts’ fatigue life during servicing,the parts fatigue life characteristic parameters such as defect-induced failure rate and reliability were quantified.Subsequently,taking these fatigue life characteristics parameters to be rendered to be the driving force,the activity characteristics and cost elements of LDMD parts during the manufacturing and service process were analyzed,and the variable for the manufacturing cost including material and electricity and the servicing cost under different service scenarios including maintenance,repair,and fault disposal were further analyzed.Consequently,a fatigue life-related manufacturing and servicing cost model was established to provide guideline for matching the parts’ fatigue life characteristics with the cost economy of each stage.(4)Based on the fatigue life-related manufacturing and servicing cost model,a case study for LDMD-316 L bearing seat parts under the aviation service background was carried out.Subsequently,the parts’ fatigue life was obtained according to the defectrelated fatigue life predication model,and the manufacturing and servicing cost evaluation of parts was completed.Furthermore,the correlation between parts’ fatigue life characteristics and manufacturing and service cost was analyzed,and the fatigue life economic interval for LDMD-316 L parts with relatively low cost of each stage was obtained,which was used as the feedback to guide the LDMD process to output the process defect tolerance for realizing the mutual matching between the parts’ fatigue life characteristics and the cost economy of each stage.