How to use five-axis linkage high-speed milling machine for automotive molds

1 Status of High Speed ​​Milling Machines in Mould Factory

Our factory has a Rambudi five-axis linkage high-speed milling machine, the maximum clamping tool diameter 20mm, spindle power 12kw, maximum feed 10m/min, spindle speed 1000 to 15000r/min, FIDIA system, the machine automatically decelerates very well, whenever the curvature When the change is sharp, it will decelerate automatically, avoiding the damage of inertia to the machine at high speed. It is a typical high-speed machine tool.

Although the speed of the high speed milling machine can reach 15,000 rpm, it is currently only running at quasi-high speed. The rotational speed of the smooth cast iron parts is 7000 to 8000 r/min, the feed is about 6000 mm/min, and the feed per tooth is 0.3-0.4 (mm/ Tooth) Around, use Walter SΦ20 ball knives: P3202-D20 Tool material: WXK15. According to the "cutting parameters" provided by Walter, the tool has basically reached the upper limit of the cutting speed at 8000 r/min.

2 tool cutting analysis

The cutting speed of the tool is determined by the material of the tool, the material to be cut, and the parameters of the tool such as: front and rear corners. Once the tool is selected, the cutting speed is determined, but we use the ball for machining the mold surface. In the case of a constant knife speed, the linear speed of the tool is different, the speed of the tool tip is zero, the tool radius is the largest, the car mold is often a complex surface, and the cutting point of the tool is changing at any time, so the cutting speed varies widely. This, to a large extent, restricts the high speed machining of automotive molds.

At present, high-speed machining parameters for individual companies have used 0.100-rpm step speeds of 30,000 rpm. However, in terms of automotive molds, high-speed machining is only suitable for flat external plate processing because the higher the rotational speed, the more linear the range of tool speed changes. Large, but the tool allows the cutting speed range is much smaller than this value. The way to solve this problem is to slice processing, isolate the flat areas and process them separately. In order to avoid the disadvantage of zero tool center line speed, it can be processed with proper inclination angle. The outer panel, such as the drawing die of the engine hood, has a flat product part that can be processed at a high speed. The process replenishing part is not suitable for high-speed machining. The inner panel can hardly find smooth surfaces other than the pressing surface. The flat surface mentioned here must be To be large, if it is too small, there will be more knives due to too many slices, and the tool path will be short and turning frequently will not be conducive to high-speed machining. Even if some of the outer plates cannot be separated, for example, the front wall has less exposed surface and less flat areas. The area where the drawing die and punch can be processed at high speed is less than 20%. This 20% can be improved. Efficiency of 30%, then the entire punch to improve the efficiency of more than 5%, such as the hood door and other parts even higher can reach more than 20%. If a part can only be separated into small pieces for high-speed processing, it does not necessarily improve efficiency as a whole.

3 high-speed programming considerations

3.1 Inspection of digital surface quality

The quality of digital-to-analogue plays an important role in high-speed machining. It will directly affect the smoothness of the tool path, which will affect the efficiency and quality. According to our past experience, it is necessary to perform the quality analysis of the surface of the die before the machining of the die surface.

(1) The main content of the analysis:

The smoothness of the product surface, cracks and defects, whether there is a negative angle in the direction of drawing, and whether the supplementary parts of the process are rounded, etc., to ensure the quality of physical processing.

(2) Analysis method:

1) The product surface smoothness analysis with the section curvature comb and the Gaussian radius has revealed the surface quality problem of the product digital mold.

2) Check for defects such as distortions, overlaps, and cracks in the digital module through the view operation and deviation analysis.

3) Analyze the precision of the surface model of the processing model, analyze the tolerance of the model during the production, and predict the influence on the surface processing quality in advance.

4) Enter the UG processing environment, verify the digital model of the machining, and deal with the abnormal surface (dotted box on the processed surface) in advance to prevent the occurrence of the tie-breaker phenomenon. It is very important to analyze carefully, especially the small transitional surface and filleted surface, which is very important. When high-speed machining occurs, such mistakes as overcutting may cause great accidents.

3.2 The principle of slicing and picking

(1) When the mold surface is processed, block programming is used to separate the flat and steep surfaces to improve the processing technology and improve the processing efficiency. As shown in Fig. 1, program 1 in the flat area can be considered for high-speed machining.

(2) Cutting method

For the drawing die of the outer cover, we must pay enough attention to it and try to go along the direction of the car body, as shown in Figure 2.

(3) Feed retraction mode

In the feeding and retracting, circular cutting and cutting are adopted. In order to improve the surface finish and accuracy of the machined surface, no garrote mark is left. In the program design, a circular arc segment is added to the cut-in and cut-out positions to make the arc segment correspond to the initial cutting element at the initial cutting point of machining. Cut, so that the tool cut into the workpiece in a circular manner, to ensure the finish of the surface being machined, as shown in Figure 3.

(4) Selection of ups and downs

Profile machining When the cutting mode is fixed in a fixed direction, crush milling is used.

4. Five-axis linkage function

Our high-speed milling machine has a five-axis linkage function, but I think it is not very suitable in the automotive mold, if the processing of large and regular parts, with five-axis linkage effect is very good, and there is no five-axis linkage processing such as impeller and other parts will It is difficult, but the car mold surface is more complex, it is impossible to always follow the part normal, because if this machine tool swing is too serious, it must interfere with the mold surface, since the tool can not always use the same area to cut, also Loss of the significance of the five-axis linkage. Another important problem is that if three linkages are used, the A-axis and C-axis of the machine tool are locked by the hydraulic system. If 5-axis linkage is used, the A-axis and C-axis of the machine tool are controlled by the drive system of the machine tool itself. This greatly reduces the rigidity of the machine and is extremely detrimental to maintaining five-axis accuracy, and the five-axis interpolation speed is lower than the three-axis.

Recently, our factory began to process inspection tools. This gives a good use of five-axis linkage. The material of the inspection equipment is mainly made of resin and the material is soft, which avoids the disadvantage of poor five-axis linkage rigidity. In the inspection tool with variable angle contours and many inclined holes, the use of five-axis linkage program greatly improves the machining efficiency. If there is no five-axis linkage, the profile of the changing tool shaft is processed by the ball knife in the profiling mode. Five-axis linkage can use side cutters with side cutters, and the machining efficiency varies greatly.