Reliability Technology Design System of CNC Machine Tool

1  Significance of reliability design

As we all know, the reliability of a product is first designed, and secondly manufactured [1]. According to statistics, the contribution rate of the product design stage to the reliability can reach 70% to 80%. It can be seen that the inherent reliability of the product is mainly determined by the design, and the design process gives the product the essential characteristics of “innate advantages and disadvantages”. Product safety and reliability 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 the product be effectively improved, and the cost can be reduced. Realize the optimization of product structure and improve the usability of products.

In order to achieve the purpose of reliability design, in addition to the basic content of reliability design such as reliability modeling, reliability analysis and reliability distribution, it is also necessary to establish a systematic and comprehensive reliability design system in the enterprise, and realize the system Effective operation.

The establishment and operation of the 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 and review and verify the reliability of the design scheme. The first two are the preliminary preparations for the reliability design system, and then reliability modeling, reliability prediction and distribution, reliability analysis, etc. are carried out on this basis. Finally, reliability review and verification are carried out after the product design is completed. Weak links and feedback to product design for cyclic improvement and optimization. In the process of reliability design, with the help of reliability-related software and tools, 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 the product is based on the prevention point of view, combined with the product development process (see Figure 1), the reliability design criteria, reliability prediction and distribution, reliability analysis, reliability review, and reliability test are used in the product development process And other technical and management methods 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 reliability work between Data flow.

Combining Figure 1 and Figure 2, it can be seen that there is a wide range of data interactions between reliability design and product engineering design: on the one hand, the basic information needed to carry out reliability work is obtained according to the current engineering design plan, such as reliability modeling, FMECA and FTA technologies must be based on engineering design schemes; on the other hand, the reliability design analysis results are fed back to the engineering design of the product, such as the reliability of the whole machine is reasonably allocated to each The component unit uses FMECA and FTA technology to find the weak links in the product design plan, adopts remedial measures such as design changes to further optimize the design plan, and passes reliability reviews and tests, and finally forms manufacturing process documents, process specifications and standards.

3  Reliability work and application tools in all aspects of product design

Reliability design and analysis work is an organic part of product design and research and development, and it must be rationally and effectively integrated into product research and 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 content 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 market research reports and product project feasibility analysis reports. The main contents of reliability work at this stage are as follows:

(1) Investigate and analyze the reliability requirements of the market and users, and formulate research reports on the reliability requirements of the market and users of products; investigate and understand the reliability status of similar products on the market, and formulate research reports on the reliability status of similar products.

(2) Collect user’s field data, formulate field data research report; conduct statistics and analysis of field data, combine the reliability requirements of the market and users and the reliability status of similar products on the market to propose plans and suggestions for the products to be developed, The reliability data analysis process is shown in Figure 3.

(3) According to the quantitative and qualitative requirements of product reliability determined by user needs, based on the analysis conclusions and recommendations of each research report, combined with the historical data of the enterprise (product failure data, technical means and experience), formulate the main content of product reliability work , Preliminarily formulate a reliability work plan to achieve user reliability requirements.

(4) Carry out feasibility analysis. The feasibility analysis shall include the technical feasibility analysis and economic feasibility analysis of the reliability index, and the feasibility analysis report of the reliability index shall be reviewed.

Tools used in the technical decision-making stage:

(1) Data statistical tools: SPSS and EXCEL (histogram and pie chart), mainly used to initially 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 primary and secondary diagrams, causality diagrams (fishbone diagrams or tree branches), etc. The above methods are suitable for analyzing the main causes of product failures, the main failure modes and key parts.

(3) The technical feasibility analysis process of the reliability index is mainly the process of predicting the index, using some related analysis and prediction methods such as performance parameter method, similar product method, failure rate method and Monte Carlo method, etc., in order to 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; application of 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 content at this stage is as follows:

(1) Specify the reliability requirements of purchased parts and outsourcing parts to ensure compliance with the specified reliability requirements;

(2) Establish a fault reporting, analysis and corrective action system (FRACAS).

(3) Preliminary design reliability review, the reliability review flowchart is shown in Figure 4.

The reliability tools used in the preliminary design stage include:

(1) Refer to GJB450A “General Requirements for Equipment Reliability Work” and GJB841 “Fault Reporting, Analysis and Corrective Action System” to establish and run the 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, first apply for product models, prepare product component design requirements and product standardization comprehensive requirements, then identify product environmental factors and hazards, and finally draw general drawings, assembly drawings of major components, product identification, and conduct technical design review and compilation Relevant review report. The reliability work at this stage is as follows:

(1) Put forward the reliability design related standards (technical standards, management system documents) that should be implemented in the product design stage.

(2) List the various basis in the product reliability design process, 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, mark it, and formulate corresponding protective and remedial measures.

(4) Establish product system-level reliability block diagrams and mathematical models, and compile product reliability modeling reports; according to the product reliability model, assign the reliability indicators of the whole machine to the system level, compile reliability distribution reports, Predict the reliability level of the system and the whole machine, and compile a reliability prediction report;

(5) With reference to the general drawings (drafts) and sketches (drafts) that have been drawn and the structure and functions of similar products, preliminary D-FMEA and preparation of D-FMEA reports, based on the results of D-FMEA and failures of similar products Data, preliminary fault tree analysis (FTA), compile a fault tree analysis (FTA) report.

(6) Reliability modeling report review, reliability distribution report review, reliability prediction report review, failure mode, impact and criticality analysis (FMECA) report review, fault tree analysis (FTA) report review, general parts and critical importance Part list review, critical parts reliability design process and method review; preparation of reliability design review reports.

The reliability-related tools applied at this stage are:

(1) Reliability design criteria application manual, its implementation flow chart is shown in Figure 5.

(2) Related software developed by companies such as Relex and reliasoft.

(3) Product reliability modeling tools or methods: traditional probability models, Boolean truth table models, logical graph models and Markov modeling methods, Monte Carlo simulation methods.

(4) The commonly used reliability distribution methods in the preliminary design stage of the product include the equal distribution method and the comprehensive scoring distribution method; the distribution method of the reliability index, which method is used, should be based on the data, materials and information that you have mastered. Use, convenience, economy and other aspects are considered comprehensively, and the best distribution plan is selected.

(5) The commonly used reliability prediction methods in the preliminary design stage of the product include similar product prediction method, correction coefficient method and graphical approximation calculation method; the preliminary product design is based on the reliability design criteria.

(6) FMECA analysis of product design is mainly carried out in the form of filling out forms; product FTA analysis is mainly carried out by means of fault tree analysis.

(7) adopt JB/T
7517-1994 “Reliability Design Review of Mechanical Products” and GB7828-87 “Reliability Design Review” and other standards are reviewed; the design content checklist is used for inspection; the design review checklist is used for reliability design review.

3.4  Reliability work and application tools in the design stage of work drawing

The work drawing design mainly includes drawing a full set of engineering drawings, drawing up a process allocation table, a list of purchased parts, drawing up a product target costing sheet, drawing up technical conditions for acceptance, qualification certificates, drawing up instructions for use and assembly sheets. The relevant reliability work content at this stage is as follows:

(1) Establish product parts and component-level reliability block diagrams and mathematical models, and write corresponding reliability modeling reports.

(2) According to the reliability model of parts and components, assign the reliability indicators of each sub-system level to each component level, up to the lowest part level, and compile reliability distribution reports accordingly; for parts, components, subsystems and the whole machine Predict the reliability level of the company, and prepare a corresponding reliability prediction report.

(3) Carry out detailed D-FMEA analysis on parts and components, and compile corresponding D-FMEA reports; Carry out detailed fault tree analysis (FTA) on product failures, and compile corresponding FTA reports.

(4) Determine the general parts and critical parts (critical or important parts) of the product, and list the general and critical parts of the product, carry out reliability design on the critical parts, and draw the main parts sketches.

(5) Design general parts, draw all parts sketches, determine the main parts that have a significant impact on product costs, and conduct reliability optimization design.

(6) Develop documents such as product reliability acceptance test program and test procedures.

The tools used at this stage are:
(1) Relevant reliability software developed by companies such as Relex and Reliasoft.

(2) Product reliability modeling tools or methods: traditional probability models, Boolean truth table models, logical graph models and Markov modeling methods, Monte Carlo simulation methods.

(3) Commonly used reliability distribution methods in the product detailed design stage include redistribution method, proportional combination distribution method, and dynamic programming distribution method; in the product detailed design stage, the commonly used reliability prediction methods include component counting method, failure rate prediction method, etc. First-order second-moment method and stress intensity interference method.

(4) The detailed qualitative design of parts is carried out according to the reliability design criteria; the FMECA analysis of the product design is mainly carried out in the form of filling in the D-FMECA form, and the product FTA analysis is analyzed in the form of the main fault tree.

(5) When determining the position of the dangerous section of the product, you can use traditional calculation methods in mechanical design, such as physical calculations of strength, wear, corrosion, and stiffness, or use finite element analysis software such as Asays, Nastran, etc. to directly perform finite element analysis.

(6) The conventional mechanical design mainly adopts the safety factor method. The reliability qualitative design can generally refer to the previous successful design experience for standardized design and mature technical design, and the reliability optimization design method, such as the least costly optimized distribution method, Lager Lange multiplier method, dynamic programming method, etc.

(7) Basis of reliability acceptance test: GJB 899-2009 “Reliability Appraisal Test and Acceptance Test”.