The requirements of high-speed cutting (HSC) technology for tooling manufacturing on machine tool control systems provide many new options for machining high-hardness materials and alloy tool steels. After the classic EDM machining technology, high-speed cutting technology directly processes high-hardness materials and shows more and more excellent economy. One of the prominent advantages of HSC technology is its temperature distribution and heat removal during processing. High-speed cutting, high-speed feed, and low depth of cut allow the chips to carry a large amount of heat away from the workpiece.
Figure 1 Freeform Machining (Hyperboloid)
The feed rate of HSC machining is large, and the acceleration of the contour of the workpiece surface is higher. It can highlight the mechanical and electrical properties of the machine. If the acceleration of the feed drive increases, the structure of the machine will inevitably undergo greater acceleration. In addition, it is also easy to cause vibration of the machine and affect the surface quality. This requires that the numerical control system has the ability to achieve the best surface quality of motion control while minimizing the processing time and meeting the accuracy requirements. The CNC system must provide machine tool manufacturers and users with the best path control methods.
Machine tool builders need CNC systems to optimally control the characteristics of the machine. The CNC system should provide parameters for the motion control and feed drive motor control loops, and have a reasonable structure. The machine tool often evaluates the performance of the final machined part. Every machining task must be performed to ensure that high dynamic response does not cause machine vibration. Therefore, the CNC must work closely with the machine to ensure high dynamic performance for any machining task.
CNC machine users demand that the CNC system can reduce the processing time on the premise of meeting the accuracy of the workpiece. To achieve the required accuracy without requiring time-consuming testing, the first piece of processing must be able to meet the requirements. These requirements must be defined in the NC program to ensure mass production requirements. Moreover, free-form surfaces are often milled using a reciprocating path in order to control the processing time of the mold within an acceptable range. In this way, the CNC must also be able to generate reproducible tool paths that process contours from opposite directions. Otherwise, the surface quality will be damaged.
The influence of data processing ability on the surface quality of workpieces. Processing of parts with metal cutting involves a large number of intermediate steps. Through these steps, CAD model geometry is converted into a tool path; CAD (Computer Aided Design); CAM (Computer Aided Manufacturing); CNC ( Computer digital control); electromechanical systems.
Optimizing the machining time, surface quality and workpiece accuracy puts forward the following basic requirements for the CNC system: effective monitoring of contour tolerances; accurate repetition of adjacent paths after the direction of movement is reversed; high dynamic motion will not cause vibration. For 2D tool motion, the influence of the data processing chain capability on the accuracy of the workpiece can be detected with a KGM182 2D encoder from HEIDENHAIN. The motion control features of the HEIDENHAIN iTNC 530 system can be displayed using the demonstration unit on the portal milling machine. KGM is the basic inspection tool that can finally achieve contour accuracy.
Figure 2 Ball cutter TCP tool path
An NC program that effectively controls contour tolerance free-form surfaces is usually generated using the CAM system, which consists of a large number of simple line segments. HEIDENHAIN controls automatically smooth the transition shape while maintaining continuous movement of the tool on the workpiece surface. This system internal function for detecting contour deviation can automatically control the smoothing process.
On a free-form surface, the deviation of the CAD geometry model includes the defined contour tolerance value and the difference in chord height defined by the CAM system. The final effect on the workpiece depends on the machine's overall characteristics and the feed axis acceleration adjustment and acceleration.
The path control function of the iTNC 530 smoothes the acceleration and satisfies the contour tolerance requirements, even when the contour machining speed changes drastically (Figure 3). If you can define larger tolerances, you can significantly reduce the processing time. In this example, the contour machining tolerance was relaxed from 0.01 mm to 0.02 mm, and the machining time was shortened by 12%.
Fig. 3 is a partial enlarged view showing TCP's profile monitoring nominal path
Fig. 4 Multi-knife milling of commutation motion, repeatability of adjacent cutting paths
4a: Decrease in surface quality due to adjacent path deviations 4b: Milling results for the iTNC 530 system: Surfaces of forward and reverse motion machining are the same
The smooth movement control of acceleration and acceleration is the outstanding feature of HEIDENHAIN CNC system. It can suppress machine vibration very effectively. According to need, the numerical control system can also automatically reduce the programming feed rate to minimize the risk of vibration. Effectively preventing machine vibrations allows part programs to be executed at higher speeds, thus significantly reducing machining time.
Figure 5 The actual position is measured and recorded at the corner using a 2D encoder, and a NC filter is used to process the NC data.
Another unused nominal filter (5a and 5b, respectively)
Fig. 6 Effect of machine vibration on workpiece surface: 6a: No speed-up smoothing, Z-axis vibration causes surface scratch
6b: The motion control function of the iTNC 530 system effectively avoids surface quality problems caused by vibration
In addition, the iTNC 530's adjacent milling paths are highly repeatable, ensuring that the user can achieve high-quality workpiece surface machining and reduce the machining time with a reciprocating multi-knife milling process. The iTNC 530 has set a new standard for the coordination of CNC, drive and machine tool structures. Makes the user's batch part production from the first piece can achieve high-quality processing results.
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