Vacuum Carburizing And Gas Quenching Process For The Input Shaft Of Precision Reducer

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Vacuum low pressure carburizing and high pressure gas quenching process for the input shaft of industrial robot precision reducer

Shaft tooth parts have a very wide range of applications in industrial technology. The structure of the input shaft of the industrial robot reducer is complex. One end has a toothed structure, and the other end has a blind hole. There is a keyway in the hole. Its main function is to transmit torque, and the working conditions are relatively harsh. It is required to have excellent wear resistance. , Contact fatigue strength and bending fatigue resistance. Carburizing and quenching is a common heat treatment process to obtain high hardness on the surface of the workpiece to improve service reliability and wear resistance. In order to obtain good wear resistance of the shaft tooth parts of the industrial robot reducer, it is also necessary to carry out carburizing and quenching treatment. The most commonly used carburizing process for such shaft and tooth parts is gas carburizing, which is carried out in a protective atmosphere for heating and heat preservation. The surface quality of the carbon layer is easy to control and so on.

However, in the traditional gas carburizing process, nitrogen-methanol is usually used as the carrier gas. Due to the potential safety hazard of explosion in the low-temperature pyrolysis of methanol, when gas carburizing is carried out in a multi-purpose furnace or a pit furnace with a controlled atmosphere, the temperature is below 750 °C. The workpiece cannot be preheated and held in a protective atmosphere, and it usually needs to be quickly heated to above 800 °C before carburizing treatment. This results in possible heating distortion of the workpiece during the heating process from the low temperature stage. In this case, the keyway deformation and tooth shape distortion of the shaft tooth parts of the industrial robot reducer can even reach 0.03~0.05mm, which cannot meet the technical requirements of heat treatment for precision machinery. Moreover, the gas carburizing process cannot guarantee the formation of a sufficient depth of the carburizing layer in the blind hole of the part, and the carburizing quality is not easy to control.

Vacuum low pressure carburizing is an upgrade of the traditional gas carburizing process, and it is an inevitable trend for the development of high-quality heat treatment and low-carbon development. Using acetylene vacuum carburizing technology and high-pressure gas quenching technology network to carburize and quench the surface of steel parts, not only does not have carbon emissions, but also because higher carburizing temperatures can be used, the carburizing speed of parts can be accelerated, and the predetermined speed can be reached quickly. It has the characteristics of safety, low carbon, high efficiency and environmental protection, and the blind hole carburization of the parts can effectively avoid internal oxidation on the surface of the carburized layer, which is a unique advantage of vacuum low pressure carburizing. The precision requirements of the shaft tooth parts of the industrial robot reducer are very high, and the tooth shape distortion is required to be controlled within 0.015~0.025mm, and the existing vacuum and low pressure carburizing technology has the problem of excessive keyway and tooth shape distortion. There is no ready-made solution. Therefore, according to the structural characteristics and precision requirements of such shaft tooth parts, it is necessary to carry out targeted development of the existing vacuum low pressure carburizing process, and carry out less distortion-free vacuum low pressure carburizing and high pressure carburizing of typical robot shaft tooth parts. Research on the gas quenching heat treatment process, optimize the heat treatment process, complete the demonstration application of vacuum low pressure carburizing and high pressure gas quenching process for typical robot shaft tooth parts, and at the same time achieve the goal of reducing carbon emissions.

The manufacturing process of the input shaft is: blanking – rough turning – normalizing – inspection – machining – carburizing, quenching and tempering – inspection – shot blasting – grinding – inspection – cleaning – Packaging and storage. The final heat treatment of the gear shaft is carburizing and quenching, and the depth of the hardened layer is required to be 0.425~0.725mm, the surface hardness is 58~62HRC, and the core hardness is 30~40HRC.

The equipment used is a double-chamber vacuum low-pressure carburizing high-pressure gas quenching furnace. The carburizing and quenching process is as follows:

In the heating stage, the vacuum degree in the furnace is controlled below 1Pa, and the workpiece is heated to (300±5)℃ for 30min in turn; to (480±5)℃ for 30min; then to (680±5)℃ , the temperature was raised to (780±5) ℃ for 30 minutes, and the temperature was averaged for 30 minutes; the temperature was raised to (850±5) ℃, and the temperature was averaged for 30 minutes; the temperature was raised to 950℃, and carburizing was carried out after multi-stage heating and temperature averaging.

In the carburizing stage, the furnace pressure was controlled at 850~880Pa. In the strong infiltration stage, acetylene gas was introduced for 10 s and then nitrogen gas was introduced for 20 s. As a carburizing pulse cycle, the entire intensive infiltration stage consisted of 5 carburizing pulse cycles. In the strong infiltration stage, nitrogen gas is used to exhaust the exhaust gas generated in the furnace. After carburizing, it was cooled to 830°C in the furnace and quenched with nitrogen at a pressure of 1.8 MPa (18 bar). The quenching fluid flow direction, flow rate, process transformation, etc. are automatically controlled by the software attached to the vacuum carburizing high-pressure gas quenching furnace.

The input shaft fully meets the requirements after being quenched by vacuum low pressure carburizing and high pressure gas. At the same time, after vacuum low-pressure carburizing, there is no internal oxidation on the surface of the parts, and the carburizing quality is significantly improved. The carburizing time is 30% shorter than that of the controlled atmosphere carburizing, the cleaning process is eliminated, the production electricity, gas cost and total man-hours are reduced, and the benefits are obvious. Compared with oil quenching, the input shaft is quenched by high pressure gas, the hardness is up to standard, and the distortion is small.

Equipment selection: The RVGQ series double-chamber vacuum heat treatment furnace produced by SIMUWU is a high-quality product for the vacuum heat treatment of tooling and molds. The good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum heat treatment process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.