For the bearing positions, shaft extension positions, and slip ring positions of motor shafts, most motor manufacturers use grinding to process them. The surface roughness of the metal after grinding is good, which can meet the requirements of precision fit and other requirements of motor performance.
Comparison of turning and grinding
Although mechanical parts have diverse structures, they are all composed of some basic geometric surfaces. The machining process of mechanical parts is essentially the process of obtaining these basic geometric surfaces. Each step of this process is completed by different technological systems according to requirements, and different parts require different machining methods. We will compare some characteristics of the machining processes of turning and grinding.
Turning is one of the most widely used methods in machining, mainly applied to the machining of rotating parts. The surface-forming motion in ordinary external turning consists of two movements: the rotation of the workpiece, which is the fundamental movement for removing excess metal and forming a new surface; and the longitudinal movement of the cutting tool, which ensures the continuous turning process. Depending on the turning action, the workpiece's rotation is called the main turning motion, while the tool's movement is the feed motion.
Grinding is a machining process that uses tools with hard abrasive grains on their surfaces to process the surface of a workpiece at high linear speeds. Grinding is a widely used method in mechanical manufacturing, offering high machining accuracy and broad adaptability to various materials and geometric surfaces. It can process not only common metallic and non-metallic materials but also a variety of high-strength and difficult-to-machine materials.
Precautions for machining on CNC lathes
The machining process of CNC lathe is similar to that of ordinary lathe. However, since CNC lathe completes all turning operations continuously and automatically in one setup, the following aspects should be noted.
● Select appropriate cutting tools. For roughing, choose high-strength, durable tools to meet the requirements of large depth of cut and high feed rate. For finishing, choose high-precision, durable tools to ensure machining accuracy. To reduce tool change time and facilitate tool setting, use indexable inserts and clamped tools whenever possible.
● Select appropriate fixtures. Use general-purpose fixtures to clamp workpieces whenever possible, and avoid using special fixtures; ensure that the positioning references of the parts coincide to reduce positioning errors.
● Determine the machining path. The machining path refers to the trajectory and direction of the tool relative to the workpiece during CNC machining. It should ensure machining accuracy and surface roughness requirements; the machining path should be shortened as much as possible to reduce tool idle travel time.
●Select appropriate cutting parameters. For high-efficiency metal cutting, the workpiece material, cutting tool, and cutting conditions are the three key factors. These determine machining time, tool life, and machining quality. An economical and efficient machining method necessarily involves the rational selection of cutting conditions.
●The relationship between machining route and machining allowance. Under the condition that CNC lathes have not yet been widely used, excessive allowances on the blank, especially those containing forged or cast hard skin layers, should generally be machined on ordinary lathes.
Three elements of cutting conditions
The three key elements of cutting conditions—cutting speed, feed rate, and depth of cut—directly cause tool damage. As cutting speed increases, the tool tip temperature rises, leading to mechanical, chemical, and thermal wear. A 20% increase in cutting speed reduces tool life by half. The relationship between feed rate and flank wear is minimal. However, a large feed rate increases cutting temperature and leads to greater flank wear. Its impact on the tool is smaller than that of cutting speed. While the depth of cut has a less significant impact than cutting speed and feed rate, the formation of a hardened layer in the workpiece during shallow cuts also affects tool life.
Users must select the cutting speed based on the material being machined, its hardness, cutting conditions, material type, feed rate, and depth of cut. The most suitable machining conditions are determined based on these factors. Ideally, tool life should be achieved through regular, stable wear. However, in actual operation, tool life selection is related to tool wear, changes in the machined dimensions, surface quality, cutting noise, and machining heat. Therefore, it is necessary to study the actual situation when determining machining conditions. For difficult-to-machine materials such as stainless steel and heat-resistant alloys, coolants can be used, or a rigid cutting edge can be selected.
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