The performance of guide rail directly affects the machining accuracy, bearing capacity and performance of the machine tool. The common guide ways of machine tools include sliding guide, rolling guide and hydrostatic guide.
1、 Characteristics of sliding guide, rolling guide and hydrostatic guide
1 slide guide
Sliding guide has the advantages of simple structure, convenient manufacturing, good stiffness and strong seismic resistance. It is widely used in general machine tools, and is often made of cast iron or steel inlaid guide rail. In order to improve the wear resistance and accuracy of the guide rail, the surface of the guide rail is generally quenched and then ground.
2 Rolling Guide
The rolling guide rail is a rolling element installed between the working faces of the guide rail. The rolling element can be ball, roller and needle. The contact between the rolling guide rail and the guide rail is point contact or line contact. Therefore, the friction coefficient of the guide rail is small. The static and dynamic friction coefficients are basically the same, the starting resistance is small, the low-speed motion stability is good, the positioning accuracy is high, the micro displacement is accurate, the wear is small, the accuracy retention is good, and the service life is long. Its disadvantages are poor seismic resistance and high protection requirements. Rolling guide, especially linear rolling guide, has been widely used in recent years. With the development of CNC machine tools to high speed, linear guide rail is more and more widely used.
3 hydraulic guide rail
The hydraulic guide rail used on the machine tool is mainly hydrostatic guide. Hydrostatic guideway is usually filled with pressure oil between two relative moving guide surfaces to make the moving parts float. The oil pressure can be adjusted automatically with the change of the external load to ensure that the friction between the guide surfaces is always in the pure liquid state. Therefore, the friction coefficient of the hydrostatic guide is the minimum and the power consumption is small. This kind of guide rail is not easy to wear, and has good precision retention and long service life. Its oil film thickness is almost not affected by the speed. The oil film has large load-carrying capacity, high rigidity, good shock absorption, stable operation and no creeping phenomenon. The structure of hydrostatic guideway is complex, and the hydraulic device with good filtering effect is needed, so the manufacturing cost is high.
It is very important to select NC tools correctly. The general requirements of NC tools are convenient adjustment, good rigidity, high precision and good durability. On this basis, the cutting performance of workpiece materials, the machining capacity of machine tools, the types of NC machining processes, cutting parameters and many factors related to the working range of machine tools and CNC devices are comprehensively considered.
When compiling the sequence.
- The factors affecting the selection of NC tools
When selecting the type and specification of cutting tools, the following factors are mainly considered:
- Production property here refers to the batch size of parts, mainly considering the influence of processing interest on tool selection. For example, it may be cost-effective to use special tools in mass production, while it is more suitable to select standard tools for single piece or small batch production.
2 machine type
The NC machine tool used to complete the process affects the selected tool type (drilling, turning or milling). Under the condition that the rigidity of workpiece system and tool system is good, high productivity tools such as high speed cutting tool and large feed rate turning tool are allowed.
3 NC machining scheme
Different types of cutting tools can be used in different NC machining schemes. For example, drilling and reaming drills can be used for hole processing, as well as drills and boring cutters.
4 dimension and shape of workpiece
The size and shape of workpiece also affect the selection of tool type and specification, for example, special tool is used to process special surface.
- Surface roughness
For example, rough milling cutter can be used in rough milling, and fine tooth milling cutter is better used in finish milling.
- Machining accuracy machining accuracy affects the type and structural shape of finishing tools. For example, the final machining of holes can be processed by drilling, reaming, reaming or boring tools according to the accuracy of holes.
7 workpiece material
Workpiece data will determine the selection of tool data and cutting local geometric parameters. Tool data is related to the machining accuracy and hardness of workpiece.
- Performance requirements of NC tools
Due to the characteristics of high machining accuracy, high efficiency, centralized processing procedures and less clamping times of parts, higher requirements are put forward for the CNC tools used. In terms of tool performance, CNC tools should be higher than those used in ordinary machine tools.
When selecting NC tools, first of all, we should give priority to the selection of standard tools. When necessary, we can choose various high-efficiency composite tools and special special tools. When selecting the standard NC tools, we should combine the actual situation and select various advanced tools as far as possible, such as indexable tools, integral cemented carbide tools, ceramic tools, etc.
The following problems should also be considered when selecting cutting tools for CNC machine tools
- The type, specification and accuracy grade of NC tools shall meet the processing requirements, and the tool data shall be compatible with the workpiece data.
- Good cutting performance. In order to adapt to the large back feed and high feed rate when the tool is used in rough machining or workpiece processing of difficult to machine materials, the tool should be able to accept high-speed cutting and powerful cutting. At the same time, the same batch of cutting tools must be stable in terms of cutting performance and tool life, so as to realize tool change according to tool life or manage tool life by CNC system.
- High precision. In order to meet the requirements of high precision and automatic tool change in NC machining, the tool must have high accuracy. For example, the radial dimension accuracy of some integral end mills is as high as 0.005mm
- High reliability. To ensure that the NC machining will not occur unexpected damage and potential defects affecting the processing
About the author