Based on this situation, in recent years, the research and technical development of cutting experiments on glass materials by mechanical processing methods have been increasing. Recently, Professor Takeuchi and others in Japan reported the research on machining three-dimensional shapes of glass with end milling cutter, and its feasibility and practicability are worth looking forward to. According to the cutting mechanism of end milling cutter, the groove machining test of glass material above 10μm was carried out to study its cutting characteristics. This paper introduces the cutting characteristics and application examples of glass materials processed by ball end milling cutter.
Plastic-brittle composite cutting of glass by end milling cutter
From the cutting edge trajectory on the vertical section corresponding to the cutter shaft and the interference curve pattern between the cutting edge trajectory and the subsequent cutting edge trajectory, it can be seen that the end milling cutter moves from bottom to top while rotating, and a part of material will be cut off every time it rotates. In this process, the cutting edge continuously cuts in and out (separates) the material. Therefore, every time the cutting edge rotates, the cutting thickness increases from 0 to the maximum cutting thickness, and then gradually decreases to 0. As the cutter moves, the rest is also cut. If the cutting thickness of glass is below 1μm, chips will be generated like metal, and the material will be removed without brittle fracture. Therefore, keeping the cutting thickness below 1μm can protect the machined surface from brittle damage. In the actual machining process, due to the influence of spindle vibration and tool bending, it is impossible to obtain an ideal cutting path. The same is true for the creation mechanism of cutting edge and machining surface near cutting edge. Therefore, it is necessary to set appropriate spindle speed and feed speed to realize the plastic processing of glass.
When machining with ball-end milling cutter, the rotation radius of cutting edge trajectory increases with the increase of tool axial height. Therefore, according to the above mechanism, when the machined surface is formed from the bottom of the groove to the upper part of the groove, even if the cutting depth in the axial direction is large, the machined surface will not become brittle. However, the radius of rotation at the bottom of the cutting edge is too small and the cutting speed is very low. Therefore, in order to improve the cutting performance, the tool is inclined at a certain angle in the feed direction to maintain a certain cutting speed for machining.
Cutting characteristics
The glass slide (lead-free glass, composition: 72%SiO2 _ 2, 18%K2CO2, 10%CaCO2) of the sample was observed by optical microscope for cutting test, and the characteristics of ball-end milling cutter during machining were observed. In the cutting test, in order to realize the inclined cutting mode, the precision spindle driven by brushless motor is inclined 45 degrees to the tool feed direction. In the cutting test, the tool system is usually installed on the spindle head of the machining center to clamp the tool, and the tool is inclined. The tool used in the experiment is a cemented carbide ball-end milling cutter with a diameter of 4mm and a radius of curvature of 0.2mm, and the surface of the tool is coated with TiAlN coating. In order to provide enough cutting fluid for the cutting edge, it is necessary to put the glass workpiece in the water tank on the workbench and cut it in the water.
Under the processing conditions of 80000rpm, 0.06mm/min feed rate and 65438 08 μ m cutting depth, the surface conditions of optical glass processed by dry cutting and underwater cutting were compared. The cutter is fed from bottom to top, and the cutting edge cuts in from the left side and cuts out from the right side. The results show that the surface quality of dry cutting is worse than that of wet cutting, brittle damage occurs in the groove, the cutting surface is incomplete and the groove width is unstable. Different from the glass materials used in the above experiments, the Vickers hardness of the timely glass ground after drying and water immersion was compared. The comparison curve on weibull probability paper shows that the mechanical strength of glass decreases after moisture is attached compared with that when it is dried. Therefore, it can be considered that when cutting in water, the mechanical strength of glass decreases, so the machinability can be improved.
After the ball-end end milling cutter processes the optical glass with 0 inclination (i.e. no inclination) and 45 inclination along the feed direction (cutting conditions: rotating speed of 20000rpm, cutting depth of 0.0 18mm, feed speed of 0.48mm/min；; ; Wet cutting), the comparison of surface quality between the two shows that the latter can obtain better machining effect. When the ball-end milling cutter obliquely cuts optical glass (cutting conditions: rotating speed 80000rpm, cutting depth 0.020mm, feed speed 0.48mm/min；; ; Wet cutting), if the double-edged ball-end milling cutter is used for non-inclined machining, when one blade cuts out the material, the other blade starts to cut into the material. However, if the tool is inclined, when the cutting depth is less than the radius of the tool, the cutting force is zero, that is, the two blades are not machined and the material is not in contact with the tool, and the tool will cool down at this time. In addition, because the actual cutting time is short, the time for cutting heat to enter the tool is also short. If the tool is inclined, although the cutting area of the cutting edge increases, the cutting time is shortened and the cooling time is increased, so the temperature rise of the tool can still be suppressed.
From the comparative results of the influence of spindle speed on the processing quality of optical glass surface (cutting conditions: cutting depth 0.0 18mm, feed per tooth 12nm/ tooth; Wet cutting) shows that when the rotating speed increases, the cutting edge is prone to brittle failure, and chip adhesion can be seen when the rotating speed is 40000 rpm and 80000 rpm. From the comparison of tool wear of 50mm cutting at different www.flm8.com speeds, it can be seen that the tool wear is serious at 40000rpm and 80000rpm, and the shape of the cutting edge has changed. But at 20000 rpm, the tool wear is small and the cutting edge shape is stable.
From the machined surface obtained by wet cutting optical glass with a cutting depth of 20000rpm and 20μm, it can be seen that the brittle damage area on the right side of the groove increases with the increase of feed speed. Under the same cutting conditions, the machined surfaces on the forward milling side and the reverse milling side were cut with FIB, and the observation section showed that no cracking was observed on the forward milling side, and the machined surfaces were in good condition. On the reverse milling side, cracks extending in the cutting direction can be seen in the depth range of several microns of the surface layer. Therefore, when the end milling cutter is used to carve the glass groove, the reverse milling method with reduced cutting thickness is easy to cause brittle failure.
According to the change of surface roughness of optical glass processing at different feed speeds (cutting conditions: rotating speed 20000rpm, cutting depth 0.018 mm; ; Wet cutting) shows that the smaller the feed speed, the better the surface roughness. However, when the feed speed is less than 0.24 mm/min, the quality of the machined surface deteriorates. By comparing the quality of the machined surface when the feed speed is 0.06mm/min and 0.48mm/min respectively, it can be seen that when the feed speed is 0.06mm/min, a large area of scratches can be seen on the machined surface. That is to say, if the feed speed is too small, the cutting will be missed due to the bending of the cutter, and the rotating cutting edge can not cut off the material at one time, so it is necessary to remove the material irregularly for many times. Therefore, if the feed speed is too small, the machining effect is not good.
Application of Vertical Milling of Glass
In an example of processing optical glass with a right-angle groove composed of a longitudinal groove with a depth of 20μm (width 196μm) and a transverse groove with a depth of 15μm (width 152μm), the tools used are ball-end milling cutters with diameters of 0.4mm and 0.5mm, with a spindle speed of 20000rpm and a feed speed. This product is made to improve the detection accuracy of DNA microarray (a certain amount of DNA will be attached to the10x010 micro-surface equivalent to the remaining area after groove treatment, and the excess DNA will overflow from the groove). It can be seen that the machined surface after cutting has no brittle loss and is in good condition.
The depth of micro-grooves required to inspect the substrate is usually about 100-200 microns ... If the curvature of the tool itself is ignored, the axial height cannot be considered according to the cutting mechanism. Therefore, it is necessary to set appropriate cutting conditions, even if the glass is cut more than 100μm at one time, it can be processed without damaging the glass.
An example of high-efficiency vertical milling of glass materials is introduced above. Compared with general metal cutting, the cutting feed speed used for processing glass is quite low. However, compared with the cutting methods such as scratch test, the glass can be processed efficiently in one-step deep cutting.
It has never been considered before that the end mill can mill glass materials by cutting in and out the blade. However, as shown in this paper, as long as the cutting mechanism is used correctly and flexibly, the glass can be cut without damaging it.
In order to improve the practicality and processing efficiency of glass vertical milling, we need to pay attention to the following two points:
(1) Reasonably design the cutting edge shape of end milling cutter suitable for glass cutting.
(2) The tool should keep an inclined posture along the cutting feed direction and flexibly process various groove types.
For the first point, in 2006, we developed an 8-edge ball-end milling cutter with Hitachi Tools. For the second point, in 2005-2006, the processing machinery was trial-produced by the subordinate units of the Ministry of Economy, Trade and Industry, which proved its feasibility. The main task in the future is to study the tool materials (especially the coating materials) to improve the wear resistance of the tool.
As long as there are facilities that can tilt the tool, the cutting method introduced in this paper can be easily introduced into the processing and production site without using other special equipment.