First, the introduction of the crankshaft
Take the crankshaft shown in Figure 1 as an example. The raw material of the crankshaft is made of bar forgings, the material is 40Cr, the mechanical properties are: σ b ≥ 736MPa, σ s ≥ 490MPa, δ 5 ≥ 14%, ψ ≥ 4 5 %, A K ≥ 39J, the overall quenching and tempering hardness For 270 ~ 300HBW, the position of the crank and the holding sleeve should be subjected to high frequency induction quenching treatment to 42~48HRC. The surface quality and geometric tolerance dimensions of the workpiece must be strictly guaranteed.
Second, crankshaft processing process analysis
From the forging bar of raw materials, it is processed through 16 processes. The specific process flow is shown in Table 1.
Note: Each order is very critical, and the order pass rate must be guaranteed.
Note: After all the tests, the workpiece was not found to have cracks after high frequency induction hardening.
Third, find the cause of the crankshaft crack
1. Coloring penetration detection of the crankshaft
In our company, we use the method of coloring and non-destructive testing to detect the crankshaft in the system. Eight crankshafts are selected (6 of them are quenching process, 2 are quenching and tempering processes, 6 are 40Cr materials, and 2 are 42CrMo. Material) unfolding detection, the specific test results are shown in Table 2.
(1) Through the non-destructive testing of the eight crankshafts in Table 2, it is concluded that all the quenched workpieces have cracks in the joints between the quenched and non-quenched parts, and the cracking phenomenon is more serious.
(2) The cracking phenomenon of the workpiece of 42CrMo material after quenching is slightly less than that of the workpiece of 40Cr material after quenching.
(3) It is found that there is a serious crack at the joint between the quenched part and the non-quenched part of the workpiece, as shown in Fig. 2. Determine the ring-shaped hemp crack generated by the crankshaft in the heat treatment-high frequency induction hardening process.
2. Magnetic particle testing
The non-destructive testing professional of the 12th station of the Quality Supervision Bureau came to our company for magnetic particle testing, and selected a scrapped crankshaft for destructive non-destructive testing. The specific results are shown in Table 3 (40Cr for quenching, grinding position at both ends) The main tile is installed at the cover).
Destructive non-destructive testing of the crankshaft results in a crack depth of 2.2 to 2.5 mm due to quenching, and a surface hardness of 52 to 56 HRC after grinding.
Fourth, heat treatment test on the sample
Choose 3 kinds of specifications, 2 pieces each, a total of 6 pieces, the materials are 40Cr, and the length is 100mm. The specific specifications are shown in Table 4.
Process: After roughing, the workpiece is quenched and tempered to 240~280HBW→grinding the workpiece (see light), do penetration testing, measure the surface hardness of the workpiece → finish the workpiece to the finished car size of Table 4 Requirements → Measure the hardness on the surface of the workpiece, high-frequency induction quenching up to 42 ~ 48HRC → grinding the workpiece to meet the refining size requirements of Table 4 → do the penetration test, measure the surface hardness of the workpiece. The results after the test are shown in Table 5.
Note: Each order is very critical, and the order pass rate must be guaranteed.
Fifth, determine the high frequency induction quenching process
Through the adjustment of the quenching process parameters, the ideal high-frequency induction hardening process is obtained, as shown in Table 6.
About the author: Du Haowei, Tianjin Liugong Machinery Co., Ltd.; Wu Yapeng, Tianjin Changrong Printing Equipment Co., Ltd.
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