Vacuum heat treatment of aerospace materials

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Generally speaking, the ex-factory and incoming inspection of materials is carried out by cutting a small amount of physical and chemical materials from the rough material.

The heat treatment system is carried out according to the system or strength grade requirements specified in the material standard. while the parts (or parts) are hot.

It needs to be checked again on the part body or on the sample with the furnace when it is processed. The heat treatment system is based on the heat treatment process standard of the part.

The properties specified in the material standards and the in-factory inspection properties are used to determine whether the raw materials meet the requirements and the design to analyze the strength of the parts (in some cases, the A benchmark value or the B benchmark value is used). The standard of heat treatment process of parts is used as the basis for the actual heat treatment of parts. Theoretically, the two should be consistent, but in practice, it is found that the heat treatment requirements for some materials are not completely consistent, which may cause the actual performance of the parts to be inconsistent with the design requirements. For example, the final heat treatment of Cr16Ni6 is in the strength range of ob=1080~1370MPa, the material specification requires a tempering temperature of 420℃, and the process standard requires a tempering temperature of 350~380℃. Since the re-inspection of incoming materials and the heat treatment inspection of parts in the aviation plant are often under the responsibility of different departments, such inconsistencies are difficult to find unless there is a part failure problem for back-checking.

For such issues, on the one hand, it is recommended that the design should pay attention to and evaluate whether the impact of these differences on the performance of the parts is acceptable; on the other hand, it is recommended that the standard setting agency study and revise these inconsistencies to ensure consensus; it is difficult to reach consensus When formulating the heat treatment process, the aviation factory needs to take into account the requirements of the two to ensure that the actual performance of the parts is consistent with the design requirements.

Heat treatment inspection data potential is underutilized

Since the heat treatment process is a special process, the parameters of its execution are closely related to the results, it is very important to establish the relationship between the monitored heat treatment parameters and the material properties. Through statistical analysis, the characteristic parameters and their influence laws that affect the performance of parts under specific process or specific equipment conditions can be obtained, which can not only be used to optimize process parameters, analyze heat treatment failures, predict equipment failures, etc., but also provide design information. The multi-batch performance value of the part provides a strong support for design optimization and material potential.

Since the heat treatment process of materials or parts in the aviation factory is the execution layer, the purpose of a large number of heat treatment performance tests is to determine whether they are qualified or not. The unqualified data will be used for reason analysis or submitted to the technical department for out-of-tolerance use, and qualified data will be used. will be archived and rarely used for statistical analysis. And these data are often kept in paper form, so it becomes very difficult to analyze and utilize the data. In fact, these performance data based on statistics under production conditions are as important as the data obtained from the process tests in the development stage, and their data are often more representative and have a larger sample size, which is often ignored by the technical department of the aviation plant.

To do this, the following three aspects need to be carried out:

(1) By establishing a process parameter recording and collection system, the enterprise heat treatment process resource library is constructed. At present, the data collection of the aviation factory is only the automatic recording of a single device, such as the time and temperature curve recording of the heat treatment furnace. The correlation between the recorded data and the results is often poor, and it is not easy to analyze and use. How to realize the correlation between process parameters and detection results is the key of the system.

(2) Make full use of statistical analysis methods to determine the influence law of heat treatment characteristic parameters, and establish a heat treatment process decision-making resource library. At present, most aviation factories only conduct statistical analysis on the product qualification rate, which is relatively extensive. However, few quality analysis methods are used, such as the use of process capability index (CPK), sigma level and other quality methods. It is the core of enterprise heat treatment process research to analyze the key characteristics of heat treatment, find out the key elements and influence rules of heat treatment process, and establish a decision-making resource base for heat treatment process of enterprises.

(3) Based on the above two points, a simulation system based on computer-aided process design (CAPP) is established.

The utilization of the potential of heat treatment inspection data is a systematic project, covering the effective monitoring, statistical analysis, improvement and optimization of data, etc. It requires top-level design, process-level planning, and effective implementation at the execution level.

The heat treatment work in aviation plants is gradually being paid attention to. Based on the importance and rigor of the heat treatment process, the adoption of new technologies and the optimization and modification of existing technologies should be based on sufficient experimental verification and analysis.

Faced with the rapidly developing new heat treatment technology, the aviation factory should establish its own heat treatment resource system and decision-making system while closely following it to meet the rapidly growing aviation manufacturing needs.

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