The machine tool spindle is a typical shaft part. It is one of the key parts of the machine tool. It transfers the whirling motion and torque through the furniture at the end of the spindle to the workpiece or tool. Therefore, the spindle is subjected to torque and bending moments during operation, and high rotation accuracy is also required. Therefore, the manufacturing quality of the spindle will directly affect the working accuracy and service life of the entire machine. A series of technical requirements, such as dimensional accuracy, shape position tolerance, surface roughness, contact accuracy and heat treatment requirements, are specified on the spindle part drawing. These are to ensure that the spindle has high rotation accuracy and rigidity, good wear resistance and dimensional stability. The requirements for the development of the machine tool spindle machining process are as follows:
First, the division of the processing stage
Spindle machining is usually divided into three stages, namely roughing, semi-finishing and finishing. The division of each stage is roughly bounded by heat treatment. The stage of division and the rational arrangement of the process are to ensure the quality of the process, to achieve higher production efficiency and the least cost of production.
The spindle of general precision, fine grinding can be used as the final process. For the spindle of a precision machine tool, there should also be a finishing stage to obtain a small surface roughness value, sometimes to achieve higher dimensional accuracy and fit requirements.
Second, the heat treatment process arrangement Heat treatment process is an important process of spindle machining, which includes:
(1) Heat treatment of the blank. After the spindle is forged, it is subjected to normalizing or annealing to eliminate the internal stress of forging, improve the metallographic structure, refine the grain, reduce the hardness, and improve the machinability.
(2) Preparatory heat treatment. It is usually treated by quenching and tempering, arranged after roughing to obtain a uniform and fine tempered sorbite structure, so that the spindle can obtain both hardness and strength, good impact toughness, and also eliminate coarse Processing stress. After the precision spindle is quenched and tempered, the cutting pattern is required for metallographic examination.
(3) Final heat treatment. Generally arranged before coarse grinding, the purpose is to improve the surface hardness of the spindle, and to maintain the toughness of the core, so that the spindle neck or working surface can obtain high wear resistance and fatigue resistance to ensure the working precision and service life of the spindle. . The final heat treatment method includes local heating and quenching, tempering, carburizing, nitriding, etc., depending on the spindle material. After carburizing and quenching, low-temperature tempering is also required. For those who do not need carburizing, they can be protected by copper plating or pre-released and then removed to the carbon layer.
(4) Qualitative treatment For spindles with high precision requirements, qualitative treatment is required after quenching, tempering or rough grinding. The qualitative treatment methods include low temperature artificial aging and ice cooling treatment, etc., in order to eliminate quenching stress or processing stress, promote the transformation of austenite into martensite, stabilize the metallographic structure, thereby improving the dimensional stability of the main shaft and keeping it long-term. Precision.
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