When using five-axis machining, it must be considered to use the shortest cutting tool possible to complete the entire mold processing, so as to obtain a good surface quality, to avoid rework, while reducing the amount of electrode used, shorten the EDM processing time.
Successful five-axis machining applications are not just about buying five-axis machining centers and some five-axis CAM software. Machining centers must be suitable for machining dies. Similarly, CAM software must not only have five-axis functions, but must also have suitable tooling. The function.
Using short cutting tools is the main feature of 5-axis machining. A short tool will significantly reduce tool misalignment, resulting in good surface quality, avoiding rework, reducing the amount of electrode used, and shortening the EDM processing time. When considering five-axis machining, the goal of using a five-axis machining tool must be considered as follows: Use the shortest cutting tool possible to complete the machining of the entire workpiece, and also reduce the time required for programming, set-up, and machining to obtain a more perfect surface quality. .
Triaxial and 3+2-axis machining
As long as the workpiece cavity is not very deep (in relation to the tool diameter), the three-axis tool path (2, 3, 5) is sufficient. If the workpiece cavity is deep and has a very narrow area, it is not enough to use a pure three-axis tool path to complete the entire finishing process. In this case, poor surface quality and long processing time follow. Figure 1 shows the case of a three-axis toolpath, where the shortest tool must be long enough to be machined to all areas of the workpiece in the vertical direction.
Figure 1 Three-axis machining path (Image courtesy of Sescoi)
When using a short tool, the spindle should be tilted to ensure that the special area of ​​the workpiece can be machined. 3+2 axis machining is usually considered to set a constant angle to the main axis. Complex workpieces may require many tilted views to cover the entire workpiece, but this can lead to overlapping tool paths, which increases processing time.
In addition, all tilted views are difficult to combine accurately, so the amount of manual grinding work will increase, but also greatly increase the in and out of action, often leading to surface quality problems and more tool movement.
Finally, programming in this way interferes with each other and is time-consuming, and the sum of all views often does not cover the entire geometry. Figure 2 shows four workpiece views, but there is still an area that is not covered by the center of the workpiece. This area still requires an additional tilted view.
Figure 2 3+2 Axis Tool Path
In order to overcome the disadvantages of 3+2 axis machining, five-axis linkage machining may be a better choice, not to mention that some five-axis machine tools also have some functions specifically designed for the mold industry. Five-axis linkage machining can coordinate three linear axes and two rotation axes to make them operate at the same time, which solves all the problems of machining of three-axis and 3+2 axes. The tool can be very short, no overlapping of views occurs, and the processing area is omitted. The possibility is smaller, processing can be continuous without additional import and export (see Figure 3).
Figure 3 Five-axis tool path
Five-axis milling machine
Five-axis milling machines come in many different configurations, such as:
â–¡ The workpiece can be rotated freely with two degrees of freedom by rotating the table, in which case the spindle can only move in the axial direction.
â–¡ Spindle mounting provides two degrees of freedom to rotate the milling cutter. In this case, the workpiece cannot move.
â–¡ The system can be a combination of the above two conditions - one rotary axis is the rotary table and the other axis is the spindle.
In general, when purchasing a three-axis milling machine, several different characteristics must be considered, such as horsepower, spindle speed, axial feedrate, working range, and weight limit. When evaluating a five-axis machine tool, in addition to these, the following aspects must be considered: Repeated positioning accuracy, speed, angular limits, mill control system selected for five-axis machining, and other options.
1, repeat positioning accuracy
Repositionability refers to the ability of 5-axis machines to return to the same point and maintain vector consistency. For the repeatability of the 5-axis machine tool, not only the accuracy of the axial position, but also the angle value.
2, speed
Speed ​​actually means the speed of the tool relative to the workpiece. The faster this value is, the faster the machine will cut the ground. Many older five-axis machine tools have slower speeds, which of course do not meet the productivity requirements of high-performance machining.
Speed ​​is an important factor for processing molds. Many 5-axis milling machines have a C-axis, which by default rotates around the Z-axis. If you are milling a deep groove workpiece with a short tool, you must tilt the tool through the A/B axis and rotate the C axis to cut around the workpiece. In this case, the C-axis speed performance is the key to success.
3, the angle limit
The limit of the angle is the physical limit of the rotation angle allowed by the milling head of the milling machine, which is based on the design of the special machine tool. If the milling head is required to be tilted by 50° to use the shortest tool or chamfer, then if the milling head only has a rotation limit of 30°, then the machining task under the clamping condition cannot be completed.
When considering the C axis, the angle limit is very important. The angular motion of the C axis of many 5-axis milling machines is unlimited, and there are of course many limitations.
For example, milling may only achieve +360° and -360° rotations. If a tiltable tool is used to machine the wall, the tool must move around the workpiece's machining path. In this example, the main movement is produced by the continuous motion of the C-axis. If there is a limited C-axis, then it will require the machine to finish machining the entire part at regular intervals.
4, work environment
Programmers may already be familiar with the three-axis work environment, but for five-axis machining, programmers must still reconsider their working environment. When the workpiece or spindle rotates, does the actual working range become smaller? In order to confirm this problem, it is possible to clamp an ordinary milling cutter on the spindle and measure the working range in the vertical direction of the tool and the working range when the tool is tilted to the maximum.
Different five-axis machines use different five-axis controllers. The best operating point for some controllers is that when the origin of workpiece clamping coincides exactly with the intersection of the axes of rotation, some controllers perform best when fed in opposite directions.
Many five-axis controllers with logic control know exactly where the tool origin is relative to the workpiece, regardless of how many times it rotates. This function is often referred to as "Rotary Tool Origin (RTCP)". Many users find that advanced RTCP capabilities make 5-axis applications easier.
Five-axis CAM software
With the use of five-axis machining, the problem of 3+2-axis machining may not have been completely solved. The programming problem has turned into a problem with the CAM system. Vibration control has also become the most important consideration. The CAM system only finds that the vibrations between the workpiece, the tool, and the taper shank are insufficient. It must also be able to automatically eliminate these vibrations so that the CAM programmer does not need to manually adjust the tilt angle of tens or millions of data points. Now. In addition, the five-axis automatic programming of the CAM system results in the most optimized tool application, which is the shortest tool length (Fig. 4).
Fig. 4 The tool with smaller diameter is milling the remaining material in the corner of the workpiece, thanks to the five-axis automatic programming for optimal results, which is the shortest tool length
Unlike five-axis functions of special workpieces such as turbine blades, airfoil faces and thrusters, moldmakers do not have to “vertically†cut all faces shown in the CAD file, they simply rotate enough tilt angles to automatically eliminate them. The vibration between the tool, taper shank and workpiece can be. Figure 5 shows that the combination of automatic shank vibration cancellation and more forms of cutting offers greater efficiency and flexibility in five-axis tooling.
Figure 5 is not just a simple taper shank vibration inspection, automatic tool holder vibration elimination is very much needed for deep cavity processing, especially high-efficiency machining, automatic tool holder vibration elimination and more types of cutting methods make five-axis mold processing Higher efficiency and flexibility
When evaluating CAM software for tooling, especially for deep-cavity tooling, there are many factors to consider, such as the flexibility of five-axis functions, the reliability of five-axis cutting paths, ease of use, and the limits of five-axis milling machines. , can not use the five-axis situation.
1, flexible
In a five-axis milling strategy, flexibility is an important feature to consider. If users are using a three-axis CAM package with multiple strategies, why consider using several five-axis strategies?
One of the most recent ways to provide flexibility is to use CAM software modules that automatically generate toolpaths for tooling, punching, and tool applications. In short, this module automatically converts the three-axis cutting path into a five-axis machining path so that the angle of rotation of the rotating tool is sufficient to avoid vibrations. This also brings greater flexibility because of all the three-axis finishing paths. Both can be converted into five-axis environments.
2, reliability
The reliability of the five-axis machining tool path is very important, because the two rotating motions are added to the five axes, and the possibility of vibration is greatly increased. Therefore, the vibration detection and avoidance measures must be reliable, otherwise the expensive equipment may be damaged.
3, ease of use
Easy to use and five-axis programming were once considered mutually exclusive, and five-axis programming was considered difficult, time-consuming, and very interference. But if you want to stay competitive, ideas must change. If you use CAM software that can automatically generate toolpaths in surface or solid tooling, creating a five-axis toolpath is as easy as creating a three-axis toolpath, because such CAM software can perform five-axis programming of complex deep-cavity tooling artifacts. And it can avoid vibration.
4, the limitations of five-axis equipment
The limitations of five-axis equipment can affect how to choose the five-axis machining of the mold. The CAM software must be able to simulate a specific five-axis device and adjust the tool path to avoid movement to the limit of rotation. If a five-axis device has a limit in the C-axis, the CAM software must be able to insert intermittent motion into the tool path while maintaining a tool path that is vibration-free.
In addition, many 5-axis configurations have different limits on their A/B axes. For example, a machine tool may rotate at -90° on the A axis, but only +15° rotation is allowed on the positive direction. Therefore, it can be understood that CAM software automatically Limits are taken into account to avoid exceeding the positive limit.
5, can not use the five-axis situation
In some cases, it is not advisable to use a five-axis solution. For example, if the tool is too short, or if the tool holder is too large, vibration cannot be avoided under any operating conditions. Does the CAM system stop at this point? Is it not possible to generate a tool path at all? Did you show the problem area?
If you let the user take a lot of trial and error, or recalculate the entire tool path, it is bound to have an adverse effect on the entire production. It is best if the CAM system can find the problem area. Use longer tools, shorter tool holders or simply edit these points.
Figure 6 shows the vibrational range of some of the marked points. These vibrations can then be automatically eliminated (Figure 7) so that most of the workpiece can still be cut with a short tool.
Figure 6 The vibration of the marked point is replaced by radial motion
Fig. 7 Using the automatic anti-vibration device for the tool to create a simultaneous five-axis tool path for the complete milling of the workpiece with the shortest tool possible
in conclusion
Synchronous five-axis toolpaths use a short tool to machine the entire workpiece without the need for long tools in a three-axis environment. Five-axis machining can reduce the amount of electrode used and the operation steps of EDM processing. Synchronous 5-axis machining reduces problems with 3+2-axis machining, such as creating multiple tilted views and merging all tilted views.