reliability design system
1 The significance of reliability design
As we all know, the reliability of a product is designed first and then manufactured.. According to statistics, the contribution rate of product design stage to reliability can reach 70% to 80%. It can be seen that the inherent reliability of products is mainly determined by design, and the design process endows products with the essential characteristics of “innate advantages and disadvantages”. The safety and reliability of products is one of the main indicators that must be met in the design of electromechanical products. Only when the reliability is fully considered in the product design stage, and then guaranteed by manufacturing and management, can the reliability of products be effectively improved, costs reduced, Achieve product structure optimization and improve product availability.
In order to achieve the purpose of reliability design, in addition to the basic contents of reliability design such as reliability modeling, reliability analysis and reliability distribution, it is necessary to establish a systematic and comprehensive reliability design system in the enterprise, and realize the system’s reliability. Works efficiently.
The establishment and operation of a reliability design system need to be closely integrated with the product development process. Its main contents include the establishment and application of reliability design criteria, the collection and analysis of reliability data, the establishment of reliability models, and the allocation and prediction of reliability indicators. , Analyze the reliability characteristics, review and verify the reliability of the design scheme, etc. The first two are the preparatory work for the reliability design system, and then carry out reliability modeling, reliability prediction and distribution, reliability analysis and other work on this basis, and finally carry out reliability review and verification after the product design is completed. Weak links and feedback to product design for cyclical improvement and optimization. With the help of reliability-related software and tools in the reliability design process, the accuracy and efficiency of the design work can be improved, the design cost can be reduced, and the inherent reliability characteristics of the product can be guaranteed to the greatest extent.
2 Reliability design system framework
The reliability design of products is from the perspective of prevention, combined with the product development process (see Figure 1), and uses reliability design criteria, reliability prediction and distribution, reliability analysis, reliability review, and reliability testing in the product development process. and other technical and management means to ensure the inherent reliability of the product. In order to achieve this goal, the product reliability design system architecture shown in Figure 2 can be established in the enterprise. The dotted line in the figure indicates that the corresponding reliability work needs to be carried out on the basis of the current engineering design, and the arrow indicates the relationship between each reliability work. data flow.
Combining Figure 1 and Figure 2, it can be seen that there is extensive data interaction between reliability design and product engineering design: on the one hand, basic information required for reliability work, such as reliability modeling, FMECA and FTA technologies must be carried out on the basis of the engineering design scheme; on the other hand, the reliability design analysis results are fed back to the engineering design of the product, such as the reliability index of the whole machine is reasonably allocated to each It consists of units, uses FMECA and FTA technology to find weak links in the product design scheme, takes remedial measures such as design changes to further optimize the design scheme, passes reliability reviews and tests, and finally forms manufacturing process documents, process specifications and standards.
3 Reliability work and application tools in each link of product design
Reliability design and analysis work is an integral part of product design and development, which should be reasonably and effectively integrated into product development. The reliability design process runs through every link of product design and development. At different stages of the product design and development process, there are different reliability design contents and different application tools.
3.1 Reliability work and application tools in the technical decision-making stage
The technical decision-making stage needs to complete the preparation of the market research report and the product project feasibility analysis report. The main contents of the reliability work in this stage are as follows:
(1) Investigate and analyze the reliability requirements of the market and users, and formulate a research report on product reliability requirements of the market and users; investigate and understand the reliability status of similar products in the market, and formulate a reliability status survey report for similar products.
(2) Collect on-site data from users, formulate on-site data research reports; conduct statistics and analysis on on-site data, and put forward plans and suggestions for products to be developed based on the reliability requirements of the market and users and the reliability status of similar products on the market, The reliability data analysis process is shown in Figure 3.
(3) Quantitative and qualitative requirements for product reliability based on user needs, formulate the main content of product reliability work based on the analysis conclusions and suggestions of various research reports, combined with the historical data of the enterprise (product failure data, technical means and experience) , and initially formulate a reliability work plan to achieve user reliability requirements.
(4) Carry out feasibility analysis. Feasibility analysis shall include technical feasibility analysis and economic feasibility analysis of reliability indicators, and review the feasibility analysis report of reliability indicators.
Tools used in the technical decision-making phase:
(1) Data statistics tools: SPSS and EXCEL (histogram and pie chart), mainly used to preliminarily analyze the distribution law of fault data and count the proportion of each fault location.
(2) The failure data analysis methods in the research report include the primary and secondary diagram method, the cause and effect diagram method (fishbone diagram or tree tree diagram), etc. The above methods are suitable for analyzing the main reasons, main modes and key parts of existing failures of products.
(3) The technical feasibility analysis process of reliability indicators is mainly the process of predicting indicators, using some related analysis and prediction methods such as performance parameter method, similar product method, failure rate method and Monte Carlo method, etc. In the demonstration and preliminary design stage, the system reliability is predicted based on the initially determined system performance and structural parameters.
(4) JB/T is mainly used for reliability review in the technical decision-making stage
7517-1994 “Reliability Design Review of Mechanical Products” and GB7828-87 “Reliability Design Review” and other standards for review; use the preliminary design stage reliability work content checklist for inspection and control.
3.2 Reliability work and application tools in the preliminary design stage
In the preliminary design stage, a technical task book (including general drawings and sketches of main components) should be prepared, and a preliminary design review report should be prepared. The reliability work in this stage is as follows:
(1) Specify the reliability requirements of purchased parts and outsourced parts to ensure compliance with the specified reliability requirements;
(2) Establish a Failure Reporting, Analysis and Corrective Action System (FRACAS).
(3) Preliminary design reliability review, the reliability review flowchart is shown in Figure 4.
Reliability tools used in the preliminary design phase include:
(1) Refer to GJB450A “General Requirements for Equipment Reliability Work” and GJB841 “Failure Reporting, Analysis and Corrective Action System” to establish and run a product failure reporting, analysis and corrective action system (FRACAS).
(2) JB/T 7517-1994 “Reliability Design Review of Mechanical Products” and GB7828-87 “Reliability Design Review” and other standards are used for review.
(3) Use the work content checklist for inspection and control; use the review checklist for reliability design review.
3.3 Reliability work and application tools in the technical design stage
In the technical design stage, firstly apply for product model, formulate product component design requirements and comprehensive product standardization requirements, and then identify product environmental factors and hazard sources, and finally draw general drawings, assembly drawings of major components, product identification, and conduct technical design review and compilation. relevant review reports. The reliability work at this stage is as follows:
(1) Propose the reliability design related standards (technical standards, management system documents) that should be implemented in the product design stage.
(2) List various bases in the process of product reliability design, including some general requirements, manuals, guidelines, technical terms and other related documents, and determine various factors affecting product reliability, including various stresses and strengths;
(3) Determine the use conditions, limit states and failure criteria of the product, determine the source of danger, identify it, and formulate corresponding protective and remedial measures.
(4) Establish a product system-level reliability block diagram and mathematical model, and write a product reliability modeling report; according to the product reliability model, assign the reliability indicators of the whole machine to the system level, write a reliability assignment report, and report on each sub-system. Predict the reliability level of the system and the whole machine, and prepare a reliability prediction report;
(5) With reference to the drawn general drawing (draft), sketch (draft) and the structure and function of similar products, conduct preliminary D-FMEA, write D-FMEA report, and based on the results of D-FMEA and the failure of similar products Data, preliminary fault tree analysis (FTA), preparation of fault tree analysis (FTA) report.
(6) Reliability modeling report review, reliability assignment report review, reliability prediction report review, failure mode, effect and criticality analysis (FMECA) report review, fault tree analysis (FTA) report review, general parts and critical Parts list review, critical reliability design process and method review; preparation of reliability design review report.
The reliability-related tools applied at this stage are:
(1) Application Manual of Reliability Design Criteria, its implementation flow chart is shown in Figure 5.
(2) Relevant software developed by Relex, reliasoft and other companies.
(3) Product reliability modeling tools or methods: traditional probability models, Boolean truth table models, logical graph models, Markov modeling methods, and Monte Carlo simulation methods.
(4) The commonly used reliability distribution methods in the preliminary design stage of products include equal distribution method and comprehensive score distribution method; the distribution method of reliability index, which method to choose should be based on the data, materials and information at hand. Use, convenience, economy and other aspects are considered comprehensively, and the best distribution scheme is selected.
(5) The commonly used reliability prediction methods in the preliminary design stage of the product include the similar product prediction method, the correction coefficient method and the graphical approximate calculation method; the preliminary finalization design of the product is carried out according to the reliability design criteria.
(6) FMECA analysis of product design is mainly carried out in the form of filling in forms; product FTA analysis is mainly carried out with the help of fault tree.
(7) Adopt JB/T
7517-1994 “Reliability Design Review of Mechanical Products” and GB7828-87 “Reliability Design Review” and other standards for review; application design content checklist for inspection; application design review checklist for reliability design review.
3.4 Reliability work and application tools in work diagram design stage
Working drawing design mainly includes drawing a complete set of engineering drawings, compiling process allocation table, outsourcing parts list, compiling product target cost accounting table, compiling acceptance technical conditions, qualification certificate, compiling instruction manual and assembly list. The reliability work related to this stage is as follows:
(1) Establish product zero and component level reliability block diagrams and mathematical models, and write corresponding reliability modeling reports.
(2) According to the reliability model of zero and components, assign the reliability indexes of each sub-system to each component level, up to the bottom component level, and write the reliability assignment report accordingly; The reliability level is predicted and the corresponding reliability prediction report is prepared.
(3) Carry out detailed D-FMEA analysis on parts and write corresponding D-FMEA reports; carry out detailed fault tree analysis (FTA) on product failures and write corresponding FTA reports.
(4) Determine the general parts and critical parts of the product (critical or important parts), and list the general parts and critical parts of the product, carry out reliability design for the critical parts, and draw sketches of main parts.
(5) Design general parts, draw sketches of all parts, determine the main parts that have a significant impact on product cost, and carry out reliability optimization design.
(6) Develop product reliability acceptance test program, test procedures and other documents.
The tools applied at this stage are:
(1) Relevant reliability software developed by Relex, Reliasoft and other companies.
(2) Product reliability modeling tools or methods: traditional probability models, Boolean truth table models, logical graph models, Markov modeling methods, and Monte Carlo simulation methods.
(3) The commonly used reliability allocation methods in the product detailed design stage include the redistribution method, the proportional combination allocation method and the dynamic programming allocation method; First order second moment method and stress intensity interferometry.
(4) The detailed qualitative design of parts is carried out according to the reliability design criteria; the FMECA analysis of product design is mainly carried out in the form of filling in the D-FMECA form, and the main fault tree analysis of product FTA analysis is carried out.
(5) When determining the position of the dangerous section of the product, traditional calculation methods in mechanical design, such as physical calculation of strength, wear, corrosion, stiffness, etc., can be used, or finite element analysis software such as Asays, Nastran, etc. can be used for direct finite element analysis.
(6) The conventional mechanical design mainly adopts the safety factor method. Generally, the reliability qualitative design can refer to the past successful design experience for standardized design and mature technical design. Rangi multiplier method, dynamic programming method, etc.
(7) Basis of reliability acceptance test: GJB 899-2009 “Reliability Appraisal Test and Acceptance Test”.
3.5 Reliability work and application tools in prototype trial production stage
Prototype trial production requires the preparation of process plan, review, process design requirements, product technology, tooling task book, tooling design, preparation of product manufacturing cost breakdown table, prototype trial production, prototype type test, preparation of type test report and identification documents, and prototype trial production identification , Compile design improvement suggestions for rectification, and draw a full set of working drawings and design documents for small batch trial production. The reliability work that needs to be carried out in each link is as follows:
(1) Formulate a process plan that affects product reliability, and conduct verification and review to clarify the impact of the process on product reliability, determine key process control points, and perform prototype assembly according to the assembly process checklist;
(2) According to the user’s suggestion, comprehensive funds, progress and other conditions, select the project that needs to carry out the reliability development test, formulate the prototype reliability development test plan, and try to combine it with the product development test to formulate the prototype reliability development test report;
(3) Determine the project for reliability growth test, formulate the prototype reliability growth test outline, clarify the growth target, growth model and test profile, carry out the reliability growth test (RGT) as planned, write the reliability growth test report, and propose growth Test Conclusions;
(4) Compile product prototype reliability appraisal test plan, product prototype reliability appraisal test outline, product prototype reliability appraisal test procedure, and conduct reliability appraisal in accordance with the standard GJB899-2009 “Reliability Appraisal Test and Acceptance Test” Test, according to the results of the reliability appraisal test, evaluate whether the reliability level meets the design requirements, provide information for production decisions, and compile the reliability appraisal test report;
(5) Review the test plan, outline, pre-test preparations, test process and test completion.
The relevant tools applied at this stage are:
(1) Process FMECA (PFMECA), assembly process checklist;
(2) The test methods of reliability development test include reliability growth test (or reliability test), reliability enhancement test (RET) or highly accelerated life test (HALT), etc., or combined with performance test and environmental test, The reliability growth test adopts the modeled reliability growth test, and the relevant requirements and manuals include GJB450A-2004 “General Requirements for Equipment Reliability Work”, GJB1407-92 “Reliability Growth Test”, and GJB/Z77-95 “Reliability Growth Management” Manual, etc.;
(3) Before entering mass production at the end of the development stage, specific test plans, outlines and procedures should be formulated in accordance with the standard GJB899-2009 “Reliability Appraisal Test and Acceptance Test”;
(4) Carry out the corresponding tests in accordance with the relevant standards of reliability identification test, such as GJB450A-2004 “General Requirements for Equipment Reliability Work”, GJB899-90 “Reliability Identification and Acceptance Test”, GJB899A-2009 “Reliability Identification and Acceptance Test” “Wait.
(5) Improve and improve according to PDCA cycle.
3.6 Reliability work and application tools in small batch trial production stage
The small batch trial production stage includes process and tooling rectification, small batch trial production, small batch trial production type test and preparation of test reports, preparation of identification documents for identification, preparation of design improvement proposals for correction, preparation of a full set of working drawings and design documents for finalized production, preparation of Product quality characteristic grading table and preparation of product maintenance parts production catalog and atlas, the reliability work content of each link is as follows:
(1) Analyze and study the defects and weak links of the product process, and provide a basis for the improvement of the product process design;
(2) Carry out assembly and quality control according to the assembly process checklist;
(3) Use the reliability analysis method to analyze the problems related to product structure and performance in the process of small batch trial production, and summarize the solutions;
(4) Compile product reliability identification test plan, identification test outline, and identification test program. In accordance with the standard GJB899-2009 “Reliability Appraisal Test and Acceptance Test”, the reliability appraisal test shall be carried out, and the test plan, outline, pre-test preparations, test process and test completion shall be reviewed.
The relevant tools applied at this stage are:
(1) Fault tree analysis (FTA), finite element analysis;
(2) Standard for small batch trial production type test (comprehensive performance test);
(3) Prepare the prototype identification documents and conduct the corresponding tests according to the relevant standards of reliability identification test, such as GJB450A-2004 “General Requirements for Equipment Reliability Work”, GJB899-90 “Reliability Identification and Acceptance Test”, GJB899A-2009 “Reliable Performance appraisal and acceptance test”, GB5080.5-85 “Verification test plan for equipment reliability test success rate”, GJB150-86 “Environmental test method for military equipment”, etc.;
(4) Improve and improve according to PDCA cycle.
3.7 Reliability work and application tools in the finalized production stage
The finalized production stage includes process rectification, tooling rectification, and finalized production. The reliability work related to each link is as follows:
(1) Analyze and study the defects and weak links of the product process, and provide a basis for the improvement of the product process design;
(2) Formulate and improve process documents, including processing, assembly, debugging and other process documents, form final formal process specifications and standards, formulate and improve tooling documents, and form final formal tooling specifications and standards.
(3) Understand and master the product quality information in product processing, assembly, debugging, storage and transportation, etc., and deal with and improve it in a timely manner.
The relevant tools applied at this stage are:
(1) PDCA cycle;
(2) “Product Reliability Management System Document”.
4 Establishment and operation of reliability design system
Combined with the established reliability design system framework, taking the automatic pallet exchange and transposition of a horizontal machining center in a machine tool factory as an example, the reliability design analysis workflow is analyzed. Automatic pallet change (APC, automatic pallet change) is one of the key functional components of the machining center. Its function is mainly to realize the automatic exchange between the processed parts and the parts to be processed, and its working reliability must be guaranteed.
4.1 Preliminary structural performance analysis of the product
According to the analysis of the functional requirements of the product and the preliminary investigation, it is preliminarily determined that this type of horizontal machining center is equipped with a dual-station pallet automatic exchange device, that is, two pallets are arranged, and they are arranged symmetrically at 180° with the support column as the center, which can achieve relatively high efficiency. For mixed-flow processing that runs unattended for a long time, the pallet change time is 15 s automatically. The pallet automatic exchange device has the functions of ascending, descending and 180° rotation around the middle support column, so as to realize the automatic exchange of the processed workpiece and the workpiece to be processed. Its structure diagram is shown in Figure 6.
4.2 Carry out reliability design analysis work on the basis of the preliminary scheme
(1) Function analysis of target products
The changing process of the automatic pallet changer is as follows: the carriage is raised, then rotated, and then lowered. These three actions only complete the half cycle of the automatic pallet changing device. In the second half cycle, the lifting and lowering actions of the bracket remain unchanged, but the rotation direction of the bracket is opposite to the first half cycle, thus realizing the cycle of the workpiece. exchange.
(2) Preliminary preparations for reliability
According to the use requirements of the product, the reliability design index of the horizontal machining center is determined as: MTBF reaches 1500h. Then collect and sort reliability data for reliability data analysis according to Figure 3, and then formulate a reliability work plan. The main contents include: ① the overall requirements and schedule of the reliability work; ② the management organization of the reliability work and its responsibilities are clear ; ③ The implementation organization of the reliability work and its responsibilities are clear; ④ The arrangement of the supervision and control of the supplier; ⑤ The requirements and arrangements of the reliability review work.
(3) Reliability modeling
Draw functional block diagrams and reliability block diagrams to establish basic reliability models and task reliability models for quantitative allocation, prediction and evaluation of product reliability. This can be done through the software Isograph.
Through further analysis of the function and structure of the automatic pallet changer, the task reliability block diagram is obtained (see Figure 7).
(4) Reliability allocation prediction and verification
Combining the reliability index MTBF=1500h with other reliability data and the established reliability model, carry out reliability allocation and prediction, and then carry out verification. If the reliability requirements are not met, use FMECA and FTA analysis techniques to find weak links, and then Information is fed back to engineering for improvement and refinement. This was done using the Isograph software.
(5) Failure Mode Effect and Criticality Analysis (FMECA) and Fault Tree Analysis (FTA)
① Failure mode analysis
Through in-depth analysis of the structure and operation principle of the automatic pallet changer, and with reference to the opinions of experts in actual engineering experience, all possible failure modes of the automatic pallet changer are determined, such as the bracket rising, falling and rotating out of place; At the moment of deceleration and when it rotates in place, there will be large shaking and noise; the exchange frame is not running smoothly, etc.
② Failure cause analysis Failure modes can only describe the manifestations of product failures, but cannot explain why these failures occur. Specific measures should be taken in the aspects of type, processing, assembly, adjustment, user use and maintenance to achieve the purpose of improving the reliability of the automatic pallet exchange device. For example, the reasons for the failure mode bracket to rise, fall and rotate in place are as follows: hydraulic oil leakage occurs due to wear or damage to the sealing device of the lifting cylinder, resulting in insufficient oil pressure; the sealing device of the rotary cylinder is worn or damaged, resulting in hydraulic oil leakage and rotation. The installation position of the induction switch is unreasonable.
③ Failure impact analysis
Through the analysis of the failure modes of the automatic pallet changer, it is concluded that the occurrence of various failure modes is localized, and the foothold of the analysis of the automatic pallet changer and FMEA is to propose corresponding improvement measures and compensation measures for different failure modes. Eliminate or mitigate the effects of failures, thereby increasing product reliability. For example, for the rise of the exchange rack, the impact on the safety of the whole machine, the integrity of the equipment, the success of the mission, and the maintainability.
④Analysis of fault detection methods
The selection of fault detection methods, means or tools should be determined based on a comprehensive analysis of specific failure modes, causes and other factors. For the fault detection of the automatic pallet exchange device of the horizontal machining center, it is generally visual inspection, instrument detection, and numerical control system Display alarm inspection.
⑤Design improvement and use of compensation measures to analyze the failure of falling in place, and the improvement measures taken are: improving the sealing structure of the lifting hydraulic cylinder, using high-reliability seals; regularly dredging the solenoid valve and oil return pipeline; optimizing the installation position of the proximity switch and structure.
⑥Hazard Analysis (CA)
According to the statistical analysis of reliability test information, user information and similar product failure information, all possible failure modes of automatic pallet changer are obtained by FMEA analysis. Due to the lack of corresponding failure rate data, the risk priority number is used for hazard analysis.
⑦ Failure Mode Criticality Ranking
According to the final risk priority number, the hazard degree of the failure modes of the automatic pallet changing device is sorted from large to small, and then the potential failure mode with higher hazard degree is selected as the improvement object.
⑧ Output FMECA report
Through the analysis and summary of the above steps, the FMECA report of the automatic pallet changer can be obtained, and then the FTA analysis can be carried out.
4.3 Feedback information to engineering design
Use FMECA and FTA technology to find weak links in product design, determine key parts and important parts, and for general parts, conventional mechanical design methods and reliability qualitative design can be used for direct design. However, for the reliability design of key and important parts, a combination of qualitative and quantitative design methods can be used. If quantitative design is adopted, the given design requirements and reliability index requirements must be clearly defined. Perform stress analysis and thermal analysis on critical parts. Ansys software can be used to complete stress analysis and thermal analysis.
4.4 Selection of electronic Components
According to the relevant selection principles, electronic components are selected and controlled to ensure that qualified electronic components are selected in the design, and the composite requirements of the components used in the manufacturing are ensured, and the supply is stable to ensure the reliability of the product.
4.5 Structural reliability design
Combined with reliability design criteria such as electromagnetic compatibility design criteria, thermal design criteria and “three-proof” design criteria to carry out structural reliability design.
4.6 Reliability test
According to the reliability indicators of the system and product, determine the reliability test plan and formulate corresponding test procedures. If the product fails during the test, the failure mechanism should be analyzed, remedial measures should be taken, and real-time records should be recorded. After the test is completed, the form can be submitted reliability test report. Run the Fracas function Module in the Isograph software during the test to analyze the failures in the test, determine the cause of the failure, and review the effectiveness of the corrective measures. Finally, the designer summarizes the reliability design work and forms a reliability design manual.
This paper mainly builds the reliability design system framework based on the product design and development process, and expounds the reliability work and related application tools of each link of product design. The reliability design system lays a solid foundation for ensuring the reliability design work is carried out in an orderly and efficient manner. The implementation of this system framework plays a preventive role in eliminating potential failures, and also ensures the safety, reliability and economy of products when optimizing product structure design. sex.
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