Press Quenching Process of Hypoid Gear

Hypoid gears are used to transmit the movement and power between two intersecting or staggered shafts, and are the basic components to realize the movement transmission between the intersecting and staggered shafts. As a surface mesh gear, it is necessary to strictly control the depth of the hardened layer, the quenching hardness of the surface and the core, and the internal and external warpage during the heat treatment process. The production of hypoid gears is carried out on a continuous carburizing and quenching line. After carburizing, the parts enter a constant temperature chamber for heat preservation, and then enter the press at the frequency of two pieces per batch for pressure quenching. The hardness and internal and external warpage of the parts produced in this way are difficult to meet the requirements of the drawings.

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In response to this situation, we use induction heating and pressure quenching to quench carburized gears. However, when purchasing and debugging existing induction equipment, only a few small-sized and light-weight components are considered. As described in this article, the size and weight of hypoid gears are relatively large, and the power required for induction heating has exceeded the capacity of the production line. However, in order to save costs, it is necessary to find a suitable process to meet the needs of such parts without changing the power supply.

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Process difficulties and program discussion:

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The new type of press quenching line is mainly produced by induction heating and press quenching. Therefore, in order to complete the production of such parts on the new press-quenching line, the greater difficulty lies in a series of problems caused by the insufficient power supply of the press-quenching line. In addition to the size adjustment of the equipment tray and the robotic arm gripper, it mainly includes the following two Aspects: ①Under the current conditions, the power grid is debugged, and it takes about 110s for the parts to be heated to the quenching temperature at a time. According to previous production experience, the surface of parts heated for more than 70s is easy to oxidize and decarburize. ②The concave step at the bottom of the part is not easy to heat, which causes the part to be heated impermeably, and the hardness of the step center after quenching is low.

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The debugging scheme is as follows:

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(1) The carburizing process of hypoid gears is completed in the existing box furnace, cooled slowly, and then subjected to induction heating and pressure quenching through a pressure quenching line.

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(2) The parts of hypoid gears need to be heated in sections. After heating for a period of time, stop heating so that heat can be conducted to the inside of the part. By observing the color change of the part during the heating process, the heating temperature can be known.

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(3) After induction heating, the parts are directly put into the quenching press for pressure quenching. When debugging according to the above scheme, in order to shorten the heating time, the power supply of the equipment was debugged, so that the trip often occurred during the second stage of heating. It is observed that the equipment tripping is mainly concentrated in the stage where the induced magnetic field is the strongest, that is, when the heating temperature reaches the Curie temperature of the part, the relative permeability of the part drops sharply, the current increases, and the protection current of the equipment exceeds the protection current, resulting in tripping.

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After the above debugging, the results of the hypoid gear meet the technical requirements, but due to the opacity of heating, there is a large amount of massive undissolved ferrite in the core structure of the gear step. In the induction heating process, the heating efficiency is mainly related to the magnetic flux density. Therefore, a magnetizer is added to the inner loop inductor to concentrate the magnetic flux density and control the direction of the magnetic flux, thereby driving the current from the outside of the magnetic sensor to the inside, thereby improving the heating efficiency.