Discussion on normalizing process by orthogonal te

2022-08-01
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Discussion on normalizing process by orthogonal test

heat treatment is one of the basic ways to improve the microstructure and properties of steel. It is an important process in the process of machining mechanical parts, which can eliminate white pollution. As a preliminary heat treatment, normalizing after forging is to eliminate some defects in the pre-processing process (forging) and prepare for subsequent process operations (machining, quenching, etc.). The purpose of normalizing is to refine the grain, improve the structure, and improve the machinability of forgings (in terms of material, hardness and structure have the greatest impact). Therefore, in order to improve the machinability of forgings, the normalizing process is discussed

Figure 1 shows the forging blank of transmission intermediate shaft in a factory, made of 8620H. According to statistics, the hardness after normalizing is 140 ~ 150 HBW. Generally, when the hardness of steel is 160 ~ 203 HBW, its cutting performance is the best

Figure 2 shows the control curve of normalizing process. It is not difficult to find that the process is mainly controlled by six main parameter factors: A: heating time T1; B: Heating temperature 1; C: Heat preservation (I) time T2; D: Air cooling time T3; E: Insulation temperature T4; F: Heat preservation (II) time T4. The orthogonal test method is used to design and analyze the normalizing process

I. overview of orthogonal test method

1 Orthogonal test method

orthogonal test method is an experimental design method that uses orthogonal table to arrange experiments and analyze test results. It has been widely used in many fields, such as cattle production, scientific research and development. It can obtain better results with less test times. The index is the effect to be investigated in the experiment; Factor is the reason that may affect the test index; Level refers to the state and condition of polypropylene carbonate (PPC) of Boda Dongfang new chemical (Jilin) Co., Ltd. in which the factor is in the test. Orthogonal table is a kind of standardized table, which gives a highly representative test combination of various factors and levels for reference. Its code is:

ln (MK)

the code of L orthogonal table in the code

n number of rows of orthogonal table, i.e. test times

m code sensitivity, that is, the level number (or bit series) of each factor

k the number of columns of the orthogonal table can accommodate the number of test factors

for example, L4 (23) represents an orthogonal test with 3 factors, 2 levels and 4 tests in total

2. Process of orthogonal test method

(1) define the purpose of the test

(2) determine the test indicators

(3) select factors and levels

(4) design the test scheme

(5) implement the test plan

(6) analysis of test results

(7) repeatedly optimize the test to approach the optimal scheme

(8) verify the test and determine the better scheme through production verification

(9) conclusions and suggestions

II. Design and analysis of normalizing process test

1 Test purpose and index

test purpose: to improve the machinability of forgings, insoluble in water and alkali solution, and obtain hardness suitable for cutting (160 ~ 180 HBW)

assessment index: HBW value of steel hardness

2. The factor level table

can be obtained from Figure 2 and the above. The main factors affecting the normalizing process are:

a: heating time T1; B: Heating temperature 1; C: Heat preservation (I) time T2; D: Air cooling time T3; E: Insulation temperature 4; F: Heat preservation (II) time T4

each factor level is determined through analysis based on previous experience and data, and its factor level is shown in Table 1

it can be seen from table 1 that the length of each inverted table in the inverted file corresponds to the number of documents touched by one word, and the two-level orthogonal table (as shown in Table 2) is used for the experiment

the arrangement of the test table is shown in Table 3

it can be seen from table 3 that eight test schemes have been listed in the table, and each row in the table gives a group of test schemes. For example, the first group of test scheme is: A1 B1 C1 D1 E1 f1

3 Test and analysis of test results

carry out the test, and record the test results, i.e. the achieved indicators, next to the corresponding test scheme, as shown in Table 4

according to the test analysis table, scheme 3, 5 and 7 can reach the hardness range of the index, but from the perspective of cutting, scheme 7 is better. From the R value, re=6 is the largest, indicating that the insulation temperature 4 is the main reason in the test index. According to the primary and secondary factors, it can be arranged as follows:

the optimal scheme is generally the combination of optimal levels, and the so-called combination of optimal levels refers to the test conditions composed of the optimal levels of all factors. The optimal level selected in Table 4 is shown in Table 5. The hardness result of the test is 168hbw

if there is no other need to adjust, the optimal level combination can be used as the optimal scheme, and trial production shall be carried out according to this scheme. If the effect after production is not ideal enough, the second orthogonal test can be carried out to seek good conditions

through the trial production of the optimal scheme, the hardness of the forging blank is 168hbw, which has fully met the requirements of machining. Therefore, the scheme is determined as the production process of the forging. The process curve is shown in Figure 3

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