1 Introduction Refers generally to precision machining dimensional accuracy of 0.1 ~ 1μm, surface roughness R
a of 0.02 ~ 0.1μm of cutting. Precision machining technology is one of the most important basic technologies in the mechanical manufacturing industry, and to some extent represents the overall level of a country's manufacturing technology. However, in most production processes, in order to obtain high processing precision, the precision machining cutting speed is usually lower than the conventional machining cutting speed. For example, the cutting speed of precision machining aluminum alloy parts in actual production is mostly about v=100m/min. It is lower than the cutting speed of ordinary processing of aluminum parts (v=200～300m/min). This results in lower precision machining of precision parts, higher production costs, longer product development cycles and longer manufacturing time. With the increasing application range of precision machining, modern precision machining technology should not only achieve high machining accuracy, but also require high production efficiency and product qualification rate at lower processing costs. Therefore, it is of great practical significance to study precision machining under high-speed cutting conditions. To this end, we used a diamond tool on a high-speed CNC lathe to perform precision cutting tests. By optimizing the amount of cutting, we obtained a high-precision machining surface, and discussed the tool condition, cutting method (dry or wet cutting), cutting amount and other factors. The influence of the surface roughness on the surface.
2 high speed precision cutting test
Test conditions
Workpiece material: LY12 high-strength aluminum alloy, workpiece size Ø140×150mm.
Cutting tool: 1 polycrystalline diamond tool: R a <0.02μm after grinding, straight wiper b e =0.11mm; 2 natural diamond cutter: R a <0.02μm after grinding edge, arc type The tip r e = 0.9 mm.
Machine tool: Hawk150 high-speed CNC lathe, the cutting fluid is a special emulsion;
Cutting amount: ap=0.025 to 0.1 mm, f=0.005 to 0.02 mm/r, and v=400 to 1200 m/min.
Machined surface roughness measurement The surface roughness of the workpiece was measured using a microcomputer-assisted profilometer. The profiler performs stylus scanning on the machined surface, and the surface microscopic unevenness information is output in the form of electrical analog quantity (voltage), and then a set of discrete surface microscopic unevenness data is obtained by sampling and A/D conversion, and processed by computer-specific software. Printouts R a , R z , R y , s, s m measurement results and contour plots.
3 Influence of cutting conditions on the surface roughness of the machined surface
Tool material, blade shape and grinding quality
Natural single crystal diamond has high hardness and wear resistance, good thermal conductivity, low friction coefficient, and can sharpen sharp edges. It is an ideal tool material for high-speed ultra-precision cutting aluminum alloy. Synthetic polycrystalline diamond can not grind a sharp edge of r ≤ 1μm, so it is difficult to achieve ultra-precision mirror cutting requirements, but can be used for high-speed precision cutting of non-ferrous metals and non-metallic materials, and the tool cost is much lower than natural diamond tools ( The price ratio of natural diamond tools to synthetic polycrystalline diamond tools used in this test is 7: 1). In order to obtain a high-precision machined surface, the primary and secondary cutting edges of the diamond tool must be ground to a straight or circular transition edge (shadow). The straight line wiper blade can theoretically obtain a lower surface roughness than the arc wiper, but the blade direction and the feed direction are strictly consistent, so it is difficult to tool the cutter; the arc wiper is easy to use and easy to use. It is more suitable for processing high-precision revolving surfaces, but the manufacturing process of the tools is poor and the cost is relatively high.
In this cutting test, the surface roughness values of the two diamond tools obtained under the same high-speed cutting conditions (v=800m/min, f=0.01mm/r, a p =0.01mm, plus emulsified cutting fluid) are shown in the table. 1.
Table 1 Machining surface roughness values obtained by the two tools | Surface roughness parameter | Polycrystalline diamond cutter | Natural diamond cutter |
|---|
| R a (μm) | 0.1068 | 0.0778 |
| R y (μm) | 0.812 | 0.496 |
It can be seen from Table 1 that the surface roughness R
a of the natural diamond tool with the arc wiper is reduced by 27% compared with the artificial polycrystalline diamond tool using the straight line wiper, and the R
y value is decreased. Then up to 40%. In the subsequent cutting tests, the R
y values decreased by a large margin. It can be seen that the natural diamond tool can not only reduce the peak-to-valley mean value of the contour curve of the machined surface, but also significantly reduce the maximum height of the surface profile curve fluctuation. The reason is that the natural diamond tool has sharper cutting edge and small cutting deformation, and the cutting edge The boundary extrusion is reduced. Therefore, in high-speed precision machining, the influence of the edge sharpness of the tool on the surface roughness of the machine is more important than the geometry of the tool transition edge.
In high-speed precision machining, regardless of the type of diamond tool, the grinding quality (sharpness, integrity, finish, etc.) of the cutting edge and the front and back flank surfaces have an important influence on the surface roughness of the machined surface. Same as the machining at normal cutting speed. Table 2 shows the roughness of the machined surface obtained by cutting the polycrystalline diamond tool with different grinding quality in the cutting edge area at three different cutting speeds (cutting conditions: v=500,800,1100 m/min, f=0.01) Mm / r, a p = 0.05mm, straight line polishing edge be = 0.2mm, plus emulsion cutting fluid). From the test results, the influence of the tool grinding quality is very significant.
Table 2 Machining surface roughness of polycrystalline diamond tools with different grinding quality | Tool grinding quality | Machined surface roughness R a (μm) |
|---|
| v=500m/min | v=800m/min | v=1100m/min |
|---|
| Grinding (▽12) | 0.210 | 0.180 | 0.235 |
| Fine research (▽14) | 0.109 | 0.102 | 0.132 |
The effect of dry and wet cutting methods When machining aluminum alloy at high speed, dry and wet cutting methods have a great influence on the surface roughness of the machined surface. In the case of dry cutting (especially when the backing amount a p <5μm), the chips are thin and flocculent. Due to the high cutting speed, the cutting and bonding of the machined surface are very obvious, indicating that the built-up edge is serious. In wet cutting (additional emulsified cutting fluid), the surface roughness of the machined surface is significantly improved, and the same effect as the normal speed precision cutting (lubricating) can be achieved.
4 The effect of cutting amount on the surface roughness of the machined surface In high-speed precision cutting, the choice of cutting amount is the main factor affecting the processing quality and processing efficiency. Corresponding to different process conditions, a cutting test is required to determine a reasonable amount of cutting. In this cutting test, according to the performance characteristics of high-speed CNC lathes, and for comparison, the cutting speed range is from 200m/min to 1200m/min for ultra-high-speed cutting; the feed range is 0.002-0.02mm/ r; LY12 aluminum alloy (plus emulsion cutting fluid) is cut by precision ground diamond tool. By means of the preferred amount of cutting, a highly smooth surface with a R a = 0.04 to 0.10 μm is obtained, i.e. a machined surface equivalent to a ▽11 finish is obtained under cutting conditions eight times higher than the usual cutting speed. The effect of each cutting amount on the surface roughness of the machined surface is analyzed below.
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