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Cutting speed remains constant during machining of all surfaces, which is impossible with three-axis machining pro- cedures. CAM system must be able to perceive incision sig- nals and to prevent cutter and clamping from collision.
Five-axis post-processor is an important part of a complex of multiple-axis machining and is linking CAM systems with machine-tools. CAM module makes universal, standard NC code, which is further translated (post-processed) into a form, which is understood by specific machine controllers (Fig. 12). Each machine controller has specific post-processor, which transforms different code formats. Five-axis post-processors
Fig. 2. Machining of any shaped surface.
Fig. 3. HSC machining parameters.
contain influence factors of various rotations on variations of zero starting point.
3. Finish machining of heat-treated tool steels
Modern cutting materials, tools shaped as a ‘pencil-tools’, enable small metal removal rate but also much faster machin- ing. It is very important to use right technological parameters for successful machining (Fig. 3).
Fundamental parameter of heat-treated tool steels high- speed finish machining is small cutting depth.
The cutting depth should not exceed 0.2/0.2 mm (ap/ae) value. In this way we prevent tool deflexion/deviation and preserve high level of accuracy (tolerance and geometry).
Cutting tools for finish machining of heat-treated mate- rials should be heat resistant, thus coated (e.g. TiAlN). Re- lating to tool-wear, diffusion is one of the main reasons for
tool-life reduction. Temperatures exceeding 800 ◦C are very
detrimental to all tools, which are not coated with TiAlN and TiCN, or multi-layer coated surfaces (Fig. 4).
4. Some theoretical backgrounds
There are several criteria used for defining high-speed ma- chining, i.e. the criteria for determining the boundary between conventional and high-speed machining.
These include [7], the magnitude of the cutting speed, the revolutions of the spindle or the rotating tool (the spin- dle speed), the DN number (DN is the spindle diameter in mm multiplied by the spindle speed in rev/min), the dynamic behaviour, and the workpiece material. The most appropriate definition of high-speed machining is based on the workpiece material grade (or type) being machined [7], Fig. 5. For ex- ample, the cutting-speed values from 500 to 700 m/min is the high-speed region for machining alloy steels, however, these
Fig. 4. Coating’s heat-resistance.
speeds are considered conventional or low for machining alu- minum.
The microphotos of the chip produced during the machin- ing of X63CrMoV51 (annealed) are shown in Fig. 6. When vcwas 150 m/min (Fig. 6a) the chip looks like the one pro- duced by machining of Ck15, only with a lower chip compres- sion coefficient (λ = 0.17/0.1 = 1.7) and a higher grain texture angle (i.e. the angle between the secondary grain elongation direction and the shear plane). This kind of chip is also a typical example of a steady-state continuous chip.
However, when machining with vc = 1500 m/ min (Fig. 6b) the chip is segmented and saw-tooth shaped.
In this case the chip is formed by an intense shear along the boundaries between adjacent segments, and this is a typical example of a shear-localized segmental chip. These segments are almost of equal width (average 0.06 mm) and shape, which points to the stability of the chip-formation process. The SEM photograph shown in the detail of Fig. 6b also demonstrates this. The other detail of the same figure clearly shows the undeformed and deformed parts of the chip.
On the basis of chip shapes shown in Fig. 6 we can con- clude that a cutting speed of 150 m/min is in the conventional speed range, and a cutting speed of 1500 m/min is in the high- speed range.