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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.
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.
Surface roughness parameter | Polycrystalline diamond cutter | Natural diamond cutter |
---|---|---|
R a (μm) | 0.1068 | 0.0778 |
R y (μm) | 0.812 | 0.496 |
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.
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 |
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 surfaceIn 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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