Discussion on the skill of ploughing integrated gears


According to the working condition of the gearbox, the material is suitable for 20CrMnTi low alloy carburizing steel. The hardenability and core strength of the steel are high, and the carbon content is low, so the gear core can be good. Toughness, the presence of alloying elements chromium and manganese improves the hardenability, the low-carbon martensite structure is obtained in the core, and the strength of the steel is enhanced. The chromium element also promotes carburization and increases the rate of carburizing. Manganese has a weakening effect. When carburizing, the surface contains too much carbon, and titanium can prevent the growth of austenite grains during heating, which improves the strength and toughness of steel.
Machining Process The quality of the blank of the gearbox is critical, usually in the form of a forged shape, and the strip structure of the steel must be controlled so that it does not exceed level 3. The machining process route is as follows: blank forming a preliminary heat treatment (normalizing) - turning processing - pulling internal teeth - rolling external teeth - carburizing (or carbonitriding) - final heat treatment - shot peening (sand) - grinding inner circle .
Pre-heat treatment and cutting of blanks (1) Pre-heat treatment of blanks - normalizing. In order to reduce the deformation of the machined gear during carburizing and quenching, it is required that the metallographic structure and grain size of the blank are uniform. Therefore, before the cutting process, the 20CrMnTi steel gearbox gear should be arranged with a preliminary heat treatment - normalizing to eliminate The internal stress of the forging and the improvement of the cutting performance of the material. In the case of normalizing, the temperature is first raised to 950,970 ° C, then air cooled or blown, spray cooled. If the hardness is low, measures such as water cooling and air cooling may be adopted. This ensures that the hardness of the tooth blank is between 179,217 HBS, so that evenly distributed sheet-like pearlite and ferrite can be obtained, and the cutting processability is improved.
(2) Machining. The normalized processing of the blank is as follows: roughing - semi-finishing - finishing - pulling internal - deburring - rolling external teeth - deburring - caries - heat treatment - shot peening - grinding inner circle . Machining accuracy should meet the requirements of class 9 gears.
For some gears, the non-carburized surface should be protected (such as the threaded part), and the carburizing protection should be carried out according to the requirements. The commonly used methods are coating protection method, plugging method, reserved machining allowance protection method, steel sleeve bolt protection. Law and copper plating protection method, etc. The final heat treatment process is based on the performance requirements of the gearbox gear and the characteristics of the material. The gear is directly quenched after the carburization of the pit furnace is lowered to 850,860 °C, and then low temperature tempering to improve the internal metallographic structure and reduce the workpiece. The deformation.
Gear inspection and conclusion The gear finished product processed by the above process is processed, the surface hardness test and the metallographic structure analysis. The result is: the machining accuracy fully meets the requirements of the pattern, and the 9-stage gear precision is achieved. The surface hardness is HRC5862, the surface metallography The structure is tempered martensite and uniformly distributed fine-grained charcoal, and the heart is low-carbon martensite and a small amount of ferrite. The gear material of the tillage machine adopts 20CrMnTi low alloy steel, and the heat treatment process adopts a carburizing temperature of 920940 °C. It is suitable to temper at low temperature after quenching. The gears manufactured according to the heat treatment process can meet the requirements of the drawings.

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