Selection of fixtures and tools
1. Clamping and positioning of workpiece
In the process of NC turning, all or most of the surface to be machined can be machined after one clamping as far as possible, and the clamping times shall be reduced as far as possible to improve the processing efficiency and ensure the processing accuracy. For shaft parts, the outer cylindrical surface of the part itself is usually used as the positioning datum; For sleeve type parts, the inner hole is the positioning datum.
In addition to the universal three jaw automatic centering chuck, four jaw chuck and hydraulic, electric and pneumatic fixtures, CNC lathe fixtures also have a variety of special fixtures with good versatility, such as those specially used for clamping shaft parts. Reasonable selection shall be made in actual operation.
2. Tool selection
The service life of the tool is not only related to the tool material, but also to the diameter of the tool. The larger the tool diameter is, the greater the cutting amount it can withstand. Therefore, if the part shape allows, using the largest tool diameter is an effective measure to extend tool life and improve productivity. The commonly used tools for NC turning are generally divided into three categories, namely, sharp turning tools, arc turning tools and formed turning tools
(1) Pointed turning tool.
Turning tools characterized by linear cutting edges are generally called pointed turning tools. The tool tip is composed of linear main and auxiliary cutting edges, such as excircle cutter, end turning tool, cutter, etc. When this kind of turning tool is used to machine parts, the contour shape of the parts is mainly obtained after the displacement of an independent tool tip or a linear main cutting edge.
(2) Arc turning tool.
In addition to turning the inner and outer round surfaces, it is especially suitable for turning various smooth connected formed surfaces. It is characterized by that the shape of the cutting edge constituting the main cutting edge is an arc with very small roundness error or line profile error. Each point of the arc edge is the tip of the arc turning tool. Therefore, the tool point is not on the arc, but on the center of the arc.
(3) Formed turning tool.
That is, the contour shape of the machined part is completely determined by the shape and size of the turning tool blade. In NC turning, the commonly used formed turning tools include small radius arc turning tools, grooving tools and thread turning tools.
In order to reduce the tool change time, facilitate tool setting, and facilitate the standardization of mechanical processing, the machine clamp indexable turning tool should be used as far as possible in NC turning.