With the continuous improvement of aircraft performance, the requirements of aircraft parts are becoming more and more strict. On the premise of meeting the strength and stiffness, aviation parts should be designed to reduce weight and assembly as much as possible. Therefore, the current aviation parts have several typical characteristics, including complex structure, large size and thin-walled parts, most of the materials are aluminum alloy and titanium alloy, extremely strict quality requirements, small batch, many varieties and so on.
The characteristics of the part itself determine the processing method. The structural parts with simple shape can also be processed by 3 axis or 4 axis machine tools. However, due to the limitation of the relative position between the tool and the part, it may require multiple clamping to complete the machining of the part. Every time the clamping is added, an error source will be added, which will affect the accuracy of the final part and increase the processing time. Also limited by the relative position between the tool and the part, the programmer must be very careful to avoid the interference between the tool and the part, and it is usually difficult to use the best cutting position of the tool, and the cutting efficiency is very low. Structural parts with complex shapes cannot be processed by 3 axis or 4 axis machine tools. For the processing mode of the high tech machining, because there are two rotating shafts, the relative position between the tool and the part is greatly flexible, which can realize the overall processing of the part under the condition of one-time clamping. The tool can approach the cutting surface at an ideal angle to achieve the best cutting conditions.
At present, the control technology of China 5 axis CNC machining services, such as interpolation algorithm and coordinate transformation, has developed very mature. The technical difficulty of 5 axis CNC machining center still lies in its structural design. Although in theory, all machine tools with 5 axis CNC machining function can process structural parts, blades, impellers or bladed disks, the machining efficiency, machining accuracy and even clamping times of different machine tools are very different.
The 5 axis machining center suitable for aviation manufacturing industry should have high static and dynamic rigidity to bear the cutting force during heavy cutting. Long term tool life comes from stable and low vibration cutting, which is the key factor of low-cost machining. The structure of 5 axis CNC used in aviation manufacturing industry shall adapt to the characteristics of aviation parts processing technology. For example, when horizontal machining center is used to process structural parts, a rectangular column can be installed on the tray, and the workpiece and fixture are fixed on the four sides of the column.
In this way, four workpieces can be processed at a time, and chip removal is very convenient. Another example is the machining of Aeroengine Blades. The rough embryo is usually a thin-walled forging of titanium alloy. It is necessary to pull the workpiece during clamping to improve the stiffness of the rough embryo. When machining the air inlet edge or air outlet edge of the blade, the tool will quickly convert on the back arc surface and inner arc surface. If the structural design of the 5 axis CNC machine tool makes the tool tip located at or near the center of the swing shaft, the compensation movement of other shafts will be avoided or greatly reduced, so as to improve the machining efficiency and precision.