There are many differences between high speed CNC machining center and ordinary machining center, such as spindle, tool magazine, tool, CNC system, etc., mainly depends on spindle speed and cutting feed. A standard high-speed cnc machining center must meet the requirements of the standard high-speed CNC machining center.
Requirements Of High Speed CNC Machining Center For Spindle
The high-speed spindle of the high-speed machining center shall have the characteristics of high precision, good rigidity, smooth operation and small thermal deformation. There are several types of spindles popular in machining centers: belt type, gear type, straight joint type and electric spindle. High speed CNC machining center can use direct spindle and electric spindle, the rest of the spindle basically can not meet the basic speed requirements of high speed cnc machining center. The spindle speed of high-speed CNC machining center shall not be lower than 10000rpm at least, which is basically achieved only by direct connection spindle and electric spindle.
The maximum speed of the direct connected spindle is not as high as that of the electric spindle. In foreign countries, some manufacturers of high-speed CNC machining centers have developed ultra-high speed CNC machining centers. It is very simple for the spindle speed of such machining centers to exceed 100000. But we all know that the higher the spindle speed is, the less the cutting force is. Therefore, the cutting force of the direct connected spindle is far better than that of the electric spindle.
Cutting Feed of High Speed CNC Machining Center
In numerical control machine tools, it can be said that improving the cutting feed of machine tools is equivalent to improving the processing efficiency. This is especially true for high-speed CNC machining centers. The cutting feed of high-speed CNC machining centers is generally 20-40m/min, of course, there is no lack of faster cutting feed. The cutting feed of several high-speed CNC machining centers of Shandong Haite CNC exceeds 40m/min.
The mature use of linear motor makes high-speed cnc machining center have a qualitative leap, in the processing efficiency and processing accuracy have been comprehensively improved. The drive mode of linear motor is non-contact direct drive mode, with few moving parts and no distortion. With this technology, the machine tool manufacturing has reached the level that the traditional ball screw cannot reach. The linear motor has the characteristics of high acceleration and deceleration. The acceleration can reach 2g, 10-20 times of the traditional drive device, and the feed speed is 4-5 times of the traditional drive device.
CNC System of High Speed CNC Machining Center
The CNC system of high speed CNC machining center has higher requirements than that of general machining center. The cnc system of high speed cnc machining center must have faster data processing capability and higher functionality. This is especially true for four or five axis high-speed cnc machining centers. The 32-bit or 64 processor numerical control system is preferred. These two kinds of numerical control systems are very strong, which are incomparable with ordinary numerical control systems.
High Speed CNC Machining Center Tools
High-speed CNC machining center tool is not the type of tool, but the tool material of high-speed CNC machining center. The commonly used tool materials for high speed CNC machining centers are polycrystalline diamond, cubic boron nitride, and hard coated tools. A good tool can make the cutting speed develop to a higher level.
To perform dynamic balancing on the tool structure, especially the tool with a long tool handle extension, dynamic balancing must be performed to prevent the tool handle or blade with low bending strength and fracture toughness from breaking due to centrifugal force caused by high speed, which is dangerous to high-speed CNC machining centers and operators. The selection of tool holder system will also affect the repeatability and cutting rigidity of automatic tool change. At present, the tool holder system is generally a one side clamping tool holder system with a 7:24 taper.
CNC Programming for High Speed Machining
The CNC programming of high speed machining is different from that of common machining. In high-speed machining, programmers must be able to predict how the cutting tool cuts into the workpiece due to the fast feed speed and processing speed. In addition to using small feed rate and shallow cutting depth during machining, it is also very important to avoid sudden changes in the machining direction when compiling CNC codes, because sudden changes in the feed direction will not only reduce the cutting speed, but also may cause “crawling” phenomenon, which will reduce the quality of the machined surface, and even cause over cutting or residue, tool damage and even spindle damage, In particular, in the process of 3D contour machining, it is more advantageous to machine complex surfaces or corners separately than to machine all surfaces at once with zigzag machining method, straight line method or some other general machining methods.
During high-speed machining, it is recommended that the tool slowly cut into the workpiece, and at the same time try to avoid cutting into the workpiece again after cutting out. Therefore, it is better to slowly enter from one cutting layer into another cutting layer than to suddenly enter after cutting out. Secondly, keep a stable cutting parameter as far as possible, including maintaining the consistency of cutting thickness, feed rate and cutting line speed. When encountering the possibility of increasing the cutting depth at a certain place, reduce the feed rate, Because the change of load will cause the tool deflection, which will reduce the machining accuracy, surface quality and shorten the tool life.
Therefore, in many cases, it is necessary to pretreat some complex parts of the working profile, so that the high-speed finishing small diameter tools will not cause the sudden increase of cutting load due to the “machining residue” left by the larger diameter tools used in the previous procedure. At present, some CAM software has the function of “machining residual analysis”, which enables the CAM system to accurately know the location of machining residual after each cutting, which is the key to keep the tool load unchanged, and this key is crucial to the successful realization of high-speed machining.
In short, the simpler the tool path is, the better. In this way, the machining process is more likely to reach the maximum feed speed without slowing down due to dense data point clusters and sudden changes in the machining direction. In the zigzag cutting path, using “arc” (or similar arc line segment) to connect two adjacent straight line segments will help reduce the frequent calls and conversions of acceleration/deceleration programs.
In high speed machining, the automatic over cutting (residual) maintenance function of the CAM system is essential both in terms of machining accuracy and machining safety. Because the damage to the workpiece caused by over cutting (residue) is irreparable. The destruction of the tool is also disastrous, which requires an accurate and continuous digital model of the geometric surface to be machined and an efficient tool path generation algorithm to ensure the integrity of the machining profile. Secondly, the ability of the CAM system to verify the tool path is also very important. On the one hand, it allows programmers to verify the correctness of the programming before sending the processing code to the workshop. On the other hand, it can also optimize the program and automatically adjust the feed speed according to different processing paths to always maintain the maximum safe feed speed.