Thermal treatment method of cam shaft

Abstract

The invention discloses a thermal treatment method of a cam shaft, which solves the problem of non-uniform heating temperature and temperature gradient on a cam profile. The quenching comprises the following steps of: a, preheating: sheathing an induction coil of an induction heating device outside a cam, placing a shielding plate between a cam lifting part and the induction coil, and preheating for 33-45 seconds under the conditions with voltage of 340-480V and current of 160-230A; b, stopping heating, removing the shielding plate, and 5-8 seconds later, continuously heating for 8-14 seconds under the conditions with voltage of 410-500V and current of 200-250A; and c, cooling: cooling the cam with a quenching medium. Through the invention, the quenching hardness range of the produced cam shaft is reduced by 3.5HRC from that of common surface quenching, the depth range of a hardening layer is reduced by 3.7mm, the metallographic structure is obviously improved, and quenching cracks are avoided; and moreover, the wear resistance and fatigue strength of the cam shaft are obviously improved, and the service life of the cam shaft is obviously prolonged.

Description

technical field [0001] The invention relates to a heat treatment method for a camshaft, in particular to an induction heating and quenching heat treatment method for a camshaft. Background technique [0002] The camshaft is one of the key moving parts of the heart of the diesel engine. During the working process, it bears complex stresses such as extrusion, friction, impact, and bending. In order to ensure the safety and reliability of the diesel engine during use, the cam part of the camshaft can be made to have high enough strength, plasticity and toughness through heat treatment, so that the cam profile has high hardness, wear resistance and fatigue strength, so as to ensure the cam shaft life. [0003] In order to make the medium-speed diesel engine camshaft have the above-mentioned properties, according to the different manufacturing materials, there are two methods can be realized: one method is chemical heat treatment, and the other method is surface induction harden...

AI Technical Summary

Problems solved by technology

However, except for the base circle, the shape and size of the cam profile change, and the radius of curvature is different at each place. According to the characteristics of the induced current, the current density distributed in the axial and circumferential directions of the profile is not uniform. Yes, the sharp corner effect at the edge is more obvious, and the heat transfer rate at each place is also inconsistent, resulting in faster heating rate and faster heat transfer rate at the edge of the base circle, while the heat transfer rate at the edge of the lift is faster than that of the base circle. The circle is slow, but the heating rate is faster than the base circle, which causes a large difference in temperature and temperature gradient between the base circle and the lift of the cam, making the quenching hardness and hardened layer depth very uneven, which cannot meet the design requirements , and the metallographic structure is often out of tolerance, and sometimes quenching cracks appear, which will directly cause the wear resistance, fatigue strength and service life of the product to fail to meet the design requirements, and the product scrap rate is high, which significantly increases the production cost

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