Micro Milling in Mold Making (2)

It should be mentioned here that for three-axis machining or when the milling cutter shaft is not tilted, when the ball-end milling cutter is milling, the actual cutting speed at the working diameter of the milling cutter is required because the amount of the back-feeding knife is small. It is much smaller than the speed of the nominal diameter of the milling cutter. In order to achieve a better cutting process for micro-milling, the actual working diameter of the milling cutter should be taken into account when selecting the cutting speed. For example: 0.5mm ball end mill, the cutting speed is 160m/min, (the corresponding spindle speed is 102000r/min) and the backing knife is 0.05mm. It is calculated that the working diameter of the milling cutter is only 0.3mm, and the corresponding cutting speed is only 96m/min. If the cutting speed is cut at a cutting speed of 160 m/min, the spindle speed is increased to 170,000 r / min.

Figure 1 Small tool: Solid carbide micro-milling cutter (Source: Phom)

Figure 2 Microfabricated core: A forming die for indexable inserts (S224 and S229 models) manufactured by micro-milling. (Source phom company)

image 3

Fine limit cutting of stamping die

Very high spindle speed

Fine milling with very small diameter tools requires a high spindle speed to achieve the cutting speed determined by the workpiece material. For example, milling a steel with a 0.5 mm diameter milling cutter requires a spindle speed of 115,000 r/min when a cutting speed of 180 m/min is used. The smaller the tool diameter, the higher the spindle speed required.

At present, the common machining center commonly used in mold manufacturing has a spindle speed of 18,000 to 42,000 (r/min), which is suitable for machining with an end mill of 2 mm to 12 mm diameter. The diameter of the tool used for micro-milling is smaller (0.1mm ~ 2mm). Since the cutting speed depends on the workpiece material to be machined, if the micro-machining is performed on such a conventional machine tool, it is obviously impossible to obtain a better cutting process.

In order to adapt to the rapid development of micro-milling, the development of new higher-speed electric spindles is of particular importance. A few years ago, some electric spindle manufacturers have produced spindle parts at 160,000 r/min. A team of several spindle component manufacturers and the Fraunhofer Institute of Production Technology has been working on the development of air bearing bearings and synchronous motors driven by synchronous motors at a speed of 300,000 r/min. Currently, Precise Precision Spindle Components has introduced a high-speed electric spindle specifically for micromachining. It can be seen from these electric spindles that the electric spindle supported by the air bearing can achieve a high rotational speed. In addition, the advantage of the air bearing is that the operation is stable, the round runout error can reach <1祄, and the bearing is not easy to wear, so it has a long service life. This type of bearing is particularly suitable for fine cutting due to the small cutting forces generated by micro-milling itself.

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