Application of Five-axis High Speed Machining Center in Automobile Panel Mould
With the development of CNC machining equipment and high-speed machining tool technology, high-speed cutting theory is more and more accepted by people. High-speed cutting is a comprehensive concept covering various technical fields. Its appearance has fundamentally changed the traditional machining concept. In the face of these new processing technologies, how to effectively use them is a new challenge in the automotive mold manufacturing process.
The automobile panel mold has the following unique manufacturing characteristics.
The working part of the mold is composed of non-mathematical curved surfaces, and its surface is required to be smooth, smooth, without ripples, and clear edges. Automotive panels usually require several pairs of molds to complete, and each working profile must conform to the same mathematical model. Therefore, the requirements for surface roughness and shape accuracy are high. Wedge-shaped molds have multiple stamping directions, and manufacturing equipment requires a rotation angle.
The performance of high-speed milling equipment
The main technological performance of five-axis high-speed milling equipment: the maximum spindle speed is 18000r/min. The maximum feed speed of the spindle is 25 m/min. The rotation angle of the A axis is ±110 degrees. The rotation angle of the C axis is ±360 degrees. Axial and radial cutting depth ≤ 0.3 mm. The length of the installation tool does not exceed 300mm, the weight does not exceed 5kg, and the 5-axis can be linked.
High-speed milling function: Due to the high speed, fast feed speed, small cutting amount, small cutting force, low cutting temperature, small tool deflection, high surface roughness can be obtained, and processing efficiency is high. However, the cutting load must be uniform.
High-speed milling process design
The molding of the car cover is mainly based on profiles. According to different processing purposes, it can be divided into three stages: rough machining, semi-finishing and finishing.
1. Rough machining
No surface quality or shape accuracy is required to maximize the amount of material removed per unit time. Since most of the workpieces are cast, the working surface is hard and uneven, and there are few high-speed milling devices. Rough machining Use powerful milling numerical control equipment and tool selection Φ63 R8 ring milling for contour cutting.
2. Medium finish
The error left by rough cutting is eliminated, the shape reaches a certain accuracy, the finishing allowance is more uniform, and high-speed finishing becomes possible. The remaining margin after rough machining is sawtooth, especially the corner margin is large, so traditional CNC will continue to be used, and Φ30 ball end milling cutter will be selected for semi-finishing. The process is as follows: first use a small-diameter ball-end milling cutter to flatten the corners, and then use a Φ30 ball-end milling cutter to combine the large surface.
Remove the semi-finishing allowance to meet the technical requirements of the profile. The precision milling cutter is used for finishing, and the parallel line cutting uses Φ20 ball end milling cutter. The quality of the machined surface is high and the fit is poor.
Three-axis simultaneous milling and 5-axis simultaneous milling can be selected for finishing:
Since the surface processing is a point contact milling method, the curvature of the mold surface varies greatly. When a ball end mill is used for 3-axis simultaneous milling, the contact point between the tool and the workpiece changes with the curvature. The cutting speed at the cutting point is zero and the cutting force is the smallest. Participating in cutting at this time will reduce the quality of the machined surface, increase the wear of the blade, and increase the Z direction of the machine tool spindle. The cutting point at the radial point of the tool is the largest and the cutting force is the largest. At this time, cutting also accelerates the blade wear at this point. (The picture shows the failure mode of the insert during the 3-axis simultaneous cutting process.) That is, the cutting force changes continuously throughout the cutting process. The larger the tool diameter, the greater the change in cutting force. Therefore, choose a small diameter ball nose tool to reduce the change in cutting force. However, when machining steep walls, small diameters and long mandrels are not suitable for high-speed machining.
Compared with 3-axis simultaneous milling, 5-axis simultaneous milling has several advantages. The movement of the two rotating shafts maintains a specific (or range) angle between the workpiece surface and the tool axis. By avoiding the cutting speed to reach the maximum cutting speed point and zero point, the cutting force remains stable, and there is no need to extend the tool post when machining steep walls. For contours and holes with different punch directions in the mold, 5-axis simultaneous milling can also simplify the machining process and reduce tool setting assistance time.
However, the main shaft of the 5-axis linkage is too large, and the diameter of the clamped tool is small and short, which will interfere with the workpiece during processing. This limits the rotation angle and makes it difficult to machine parts such as narrow and deep grooves and deep cavities.
Therefore, the 5-axis milling method is mainly used for the manufacture of automobile shell molds, and is now mainly used for mold parts with relatively flat contours, small curvatures and little changes. Automobile outer cover molds, etc. However, the shape of automobile outer cover parts is complicated, and the curvature changes greatly.
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