The choice of the best span l of the computer gong processing spindle, the bearing 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.
Composite material is a new type of material which has two or more kinds of different physical and mechanical properties by composite processing. For example, glass, graphite (carbon), boron, plastics and other non-metallic materials can be composite into a variety of fiber reinforced composites. Plastic composite steel plate with high strength and corrosion resistance can be obtained by sticking plastic on the surface of common carbon steel plate. Its main advantages are high strength and elastic modulus, and its mass is very small. However, it also has the disadvantages of poor heat resistance, poor thermal conductivity and conductivity. In addition, the price of composite materials is more expensive. So at present, composite materials are mainly used in aviation, aerospace and other high-tech fields. In civil products, composite materials also have some applications.
Nonmetallic materials refer to polymer materials such as plastics, rubber, synthetic fibers and ceramics. Polymer materials have many advantages, such as rich raw materials, low density, good elasticity in the appropriate temperature range, good corrosion resistance and so on. Its main disadvantage is that it is easy to aging, and many of the materials have poor flame retardancy, generally speaking, poor heat resistance. The main characteristics of ceramic materials are high hardness, wear resistance, corrosion resistance, high melting point, high stiffness and low density than steel. At present, ceramic materials have been used in seals, rolling bearings and cutting tools. Its main disadvantages are brittleness, low fracture toughness, high price and poor processing technology.
Metal materials are divided into ferrous materials and non-ferrous materials. Processing ferrous materials include all kinds of steel, cast steel and cast iron, which have good mechanical properties (such as strength, plasticity, toughness, etc.), are relatively cheap and easy to obtain, and can meet the requirements of a variety of properties and applications. In all kinds of ferrous metals, CNC machining is often used to manufacture important parts because of its excellent properties. Nonferrous metal materials include copper alloy, aluminum alloy, bearing alloy, etc., which have the advantages of low density, good thermal and conductive properties, and can also be used in the occasions with requirements of antifriction, wear resistance and corrosion resistance.
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