Analysis of heat treatment technology in Industrial Development -- Part I
preface
American aerospace material specification AMS 2750 "high temperature measurement", the current relevant specification is SAE AMS 2750 g, which is the basis for NADCAP certification of aviation system. Now the heat treatment evaluation of the automotive industry is also carried out in accordance with AMS 2750g. AMS 2750 mainly covers temperature sensors, instruments, heat treatment process equipment, system accuracy verification, furnace temperature uniformity measurement, test furnaces, records, etc. There are clear provisions on classification verification, verification methods and frequencies.
In recent years, the rapid development of aerospace has greatly improved the convenience of people's travel, but also made people pay attention to the importance of aviation equipment, which is related to everyone's travel safety. The aviation industry produces all kinds of high-strength aircraft, selects all kinds of new high-strength materials, and develops precision manufacturing technologies such as near zero allowance forming technology, precision and ultra precision machining technology, and flexible machining production lines. In order to adapt to the development of new materials and precision manufacturing technology, the important development direction of aviation heat treatment is precision heat treatment guided by ams2750e/f/g quality standard, so as to realize precise shape and size control and Zhun precise structure and performance control.
1. Development of aviation heat treatment in recent years
(1) Adopted heat treatment technology. Vacuum heat treatment is increasing at a rate of about 30% per year. Nitrogen based atmosphere heat treatment has become an excellent choice for controllable atmosphere. Controlled carburization has replaced the traditional drop carburization, accounting for about 50%. Nitriding controlled by hydrogen probe or hydrogen analyzer (or ammonia analyzer) has developed rapidly, with 5~-10 sets added every year. Air circulation electric furnace for aluminum alloy has been widely used and has become the main furnace type for aluminum alloy heat treatment. The application of organic quenching medium in aluminum alloy quenching has made a breakthrough, showing obvious effects in reducing heat treatment deformation and environmental pollution. High energy beam heat treatment, such as laser heat treatment and ion implantation, has been applied in the aviation industry. Intelligent instruments and computers are widely used in process control. Computer networks have begun to appear in the aviation heat treatment workshop, which makes the heat treatment workshop present a modern atmosphere.
(2) Implement the quality control of heat treatment, and pay attention to the technical transformation of traditional heat treatment while adopting heat treatment technology. Ordinary electric furnaces have achieved energy saving, improved furnace temperature uniformity, double couple temperature measurement, and intelligent instruments, raising the ordinary electric furnaces to a higher level. The detection and management of furnace temperature uniformity are realized, and the quality control level is improved.
(3) The standardization system of aviation heat treatment is more perfect and. With "aviation heat treatment quality control" as the leader, the heat treatment process standards and quality inspection standards of various aviation materials have been supplemented and improved, a series of heat treatment process material standards have been established, and new process standards such as vacuum heat treatment, nitrogen based atmosphere protection heat treatment, aluminum alloy conductivity measurement have been formulated. At present, there are more than 40 aviation heat treatment standards, which have formed a complete system and have been seriously implemented.
2. Quality control and furnace temperature uniformity detection
(1) Quality control. Heat treatment is a process to achieve the safety and reliability of mechanical parts or products by changing the structure of materials. One of the characteristics of hyperthermia is "internal medicine". Generally, the quality of heat treatment needs to be tested by using instruments of parts or furnace samples. Due to the limitation of detection rate and detection position, for each batch of heat-treated parts, even for each part, the detection is only individual and partial, and in any case, the detection of heat treatment cannot be achieved. The inspection cannot reflect the heat treatment quality of the whole batch of parts or the whole part. Another feature is that the heat treatment quality has a great impact, and the heat treatment production is put into batch and continuous production. Once the quality problem of heat treatment occurs, it will have a great impact on production and products. On the other hand, the objects of heat treatment are mostly semi crystalline or finished parts. If there is a problem with the quality of heat treatment, it will cause great losses. More importantly, when heat treatment defects are omitted, it is easy to cause serious mechanical accidents and greater losses. Therefore, from the perspective of quality control, heat treatment is a special process. Special measures should be taken to implement quality control and formulate special process procedures and inspection procedures. The quality control of heat treatment refers to the control of all influencing factors in the whole process of heat treatment.
All staff participate in the quality of heat treatment. Quality control runs through every link of the heat treatment process, including basic condition quality control, quality control before heat treatment, quality control during heat treatment, and quality control after heat treatment, mainly including personnel quality control, equipment and instrument control, process material and tank liquid control, process control, technical documents and data control.
The implementation of heat treatment quality control is to change the traditional concept and system of quality only relying on passive inspection of final inspection in the past, implement the active quality control mode of focusing on prevention and combining prevention and inspection, shift the focus to the control of quality formation process, and eliminate the defects of heat treatment in the quality formation process. Heat treatment quality control is a systematic project, which integrates professional technology, management technology and scientific methods.
(2) Temperature uniformity of heat treatment furnace
In order to make the heat treated parts achieve the expected service performance, during the heat treatment heating process, all parts and all parts of the parts should be within the temperature range required by the heat treatment process parameters. Therefore, the heat treatment furnace should be able to accurately control and record the heating temperature and make the furnace temperature uniform throughout the working area in the furnace chamber.
The degree of temperature uniformity in the working area of the furnace of the heat treatment furnace is generally shown by "furnace temperature uniformity" (also known as insulation accuracy). The so-called furnace temperature uniformity refers to the large temperature difference between the temperature indicated by the automatic temperature recording instrument and the temperature of each detection point in the working area when the furnace is in a thermal stable state. Heat treatment furnaces are divided into five categories according to the uniformity of furnace temperature, and their technical requirements are shown in Table 1.
Table 1 Classification and technical requirements of heat treatment furnace according to furnace temperature uniformity
Category effective heating zone furnace temperature uniformity / ℃ temperature control accuracy / ℃ instrument accuracy grade instrument accuracy grade
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表1 热处理炉按炉温均匀性分类及技术要求
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Category
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effective heating zone furnace temperature uniformity / ℃
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temperature control accuracy / ℃
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instrument accuracy grade
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Recording paper reading/℃·mm-1
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Not less than
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Not more than
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Ⅰ
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±3
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±1.0
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0.25
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2
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Ⅱ
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±5
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±1.5
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0.3
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4
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Ⅲ
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±10
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±5.0
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0.5
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5
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Ⅳ
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±15
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±8.0
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0.5
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6
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Ⅴ
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±20
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±10.0
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0.5
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8
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