The first step of CNC lathe processing is to determine the technical requirements of parts and the batch of processed workpieces, formulate the functions that CNC lathe should have, make preparations in the early stage, reasonably select the conditions of CNC lathe, and satisfy the technical requirements of typical parts. The technical requirements of typical parts are mainly the structural dimension, processing range and accuracy requirements of parts. The control accuracy of CNC lathe is selected according to the accuracy requirements, that is, the requirements of scale accuracy, positioning accuracy and surface roughness of workpiece.
Lathe processing is a part of mechanical processing. There are mainly two processing methods: one is to fix the turning tool to process the unformed workpiece in rotation, and the other is to fix the workpiece to process the precision through the high-speed rotation of the workpiece and the lateral and longitudinal movement of the turning tool (tool holder). In the lathe can also be used to drill, reamer, reamer, tap, die and knurled things such as the corresponding processing. Lathe is mainly used to process shaft, disc, sleeve and other workpieces with reverse appearance. It is the most widely used machine tool in machinery manufacturing and repair factory.
There are several points in machining tools
The reasonable or unreasonable selection of machining skills will directly affect the machining accuracy, output power and economic benefits of the workpiece. The selection of technical equipment should be based on local production type, detailed processing conditions, workpiece structure characteristics and technical requirements.
- Selection of fixture.
For single piece and small batch production, all kinds of general fixtures and machine tool accessories should be selected, such as chuck, flat vise for machine tool, division number one; for large-scale and large-scale production, special high-efficiency fixtures should be selected to improve the production rate; adjustable fixtures or group fixtures can be selected for multiple types of medium and small batch production.
- Selection of cutting tools
Standard cutting tools are usually preferred. If mechanical convergence is selected, various efficient special tools, compound tools and multi edge tools can be selected. The type, standard and accuracy level of the cutting tool should be suitable for the machining request.
- Selection of measuring tools.
General measuring tools, such as vernier caliper, micrometer and dial indicator, should be widely used for single piece and small batch production; limit gauge block and efficient special inspection fixture and gauge should be used for large-scale and large-scale production. It is necessary to adapt the accuracy of measuring tools to the machining accuracy.
The selection of the best span l of the spindle and the supporting span l of the spindle. The distance between the front bearing point of the spindle and the rear bearing point of the spindle is called span L. The support span of the spindle assembly has a great influence on the stiffness of the spindle itself and the support stiffness.
(1) Spindle bore diameter. The diameter of the inner hole of the spindle is used to fix the tool through the tool clamping device, drive the pneumatic or hydraulic chuck, etc. The larger the diameter of the spindle, the lighter the relative weight of the spindle components. The aperture size of the spindle is mainly restricted by the stiffness of the spindle.
(2) Spindle diameter. The larger the diameter of the spindle is, the higher its stiffness is, but the size of the bearing and other parts on the shaft increases accordingly. The larger the diameter of the bearing is, the larger the tolerance value of the bearing with the same grade accuracy is, and the more difficult it is to ensure the rotation accuracy of the spindle.
The determination of the spindle overhang a of CNC machining center, the spindle overhang a refers to the distance between the action point of the radial support reaction force of the front support of the spindle and the front end of the spindle, which has a great influence on the stiffness of the spindle assembly. According to the analysis and experiment, shortening the overhanging amount can significantly improve the stiffness and vibration resistance of the spindle assembly. Therefore, on the premise of meeting the structural requirements, the overhanging amount a should be shortened as much as possible.
CNC machining center spindle span diagram, discusses the structure design and progress of CNC machining center mechanical spindle, the influence of span L on the comprehensive stiffness K is not unidirectional. If l is larger, the deformation of the spindle is larger; if l is smaller, the deformation of the bearing has a greater impact on the displacement of the front end of the spindle. Therefore, l has an optimal value. If l is too large or too small, the comprehensive stiffness will be reduced. There is an optimal span l0 for the support span of the spindle, which can minimize the displacement of the front end of the spindle assembly. Due to the structural limitation and the guarantee that the center of gravity of the spindle assembly falls between the two supports, the actual support can be greater than the optimal support span.
Material selection and heat treatment of CNC machining center spindle
When the main shaft bearing of CNC machining center adopts rolling bearing, the journal can not be hardened. However, in order to improve the contact stiffness and prevent knocking from damaging the matching surface of the journal, many 45 steel main shaft journals are still subject to high-frequency quenching. When using sliding bearing, in order to reduce wear, the journal surface must have high hardness. Therefore, high frequency quenching is usually carried out at the journal; flame quenching can also be used for large diameter spindle to improve its surface hardness; 15 or 20 steel can be used for spindle with large impact, and carburizing, quenching and tempering can be carried out on the journal surface. 45 steel, GCr15, etc. are often used for spindle materials, which need nitriding and induction hardening.
The selection of spindle material is mainly based on the stiffness, load, wear resistance, heat treatment deformation and other factors. The stiffness of the spindle of CNC machining center is related to the elastic modulus E of the material, and the E value of the steel is larger, so the steel should be considered first. Moreover, the value of elastic modulus E of steel has nothing to do with the type of steel and heat treatment method. Therefore, the cheap medium carbon steel should be selected first. Alloy steel should be considered only when high load and large impact or when material deformation is reduced and high strength and wear resistance are required
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