See. also Machining of aluminum
Cutting tool design
The influence of the design of the cutting tool on the surface quality lies in its ability to form the “right” chip. Important, so that the chips can smoothly pass the cutting surface of the tool. It means, that the front angle of the tooth should be large enough, grease should be sufficient, and the surface of the cutting tool is quite smooth. A good smooth surface cannot be obtained when working with worn cutting tools..
Key factors, which affect the surface quality during machining of aluminum, define four distinct areas of machining quality (figure 1):
- Область I: Из-за налипания на режущую кромку качество поверхности является неудовлетворительным; вместо резания материал подвергается разрывам. This parameter area should be avoided..
- Area II: Roughness decreases with increasing cutting speed.
- Area III: Increasing the influence of tools and equipment, for example, vibration of the cutter or saw, in that area, which, basically, favorable for machining aluminum. therefore, in order to achieve better results at this cutting speed it is necessary to use equipment, designed specifically for aluminum.
- Area IV: Poor surface quality. The chips are collected on the workpiece and stick (welded) to the cutting tool, causing damage to the work surface. Such, for example, occurs during machining of cast alloys using worn cutting tools and high cutting speeds.
Cutting tool wear
Cutting tool wear and scratch, as is typical for machining steel, not observed during machining of aluminum and aluminum alloys. Tool wear during machining of aluminum occurs due to abrasion of the cutting surface. Therefore, the decisive criterion for evaluating the life of the cutting tool is objectively the wear width VB, shown in the figure 2. The wear of the cutting surface depends on temperature and occurs mainly by abrasion. When using a tool with carbide tips, the maximum value 0,3-0,5 mm for the amount of wear VB is considered normal.
The wear of the cutting tool is influenced as the material of the workpiece, so cutting parameters.
The material of the workpiece has a particularly large influence on the wear of the cutting tool:
- Depreciation increases with the amount of large particulate matter., which are embedded in an aluminum matrix. These particles are, for example, primary precipitation of silicon particles in a hypereutectic aluminum alloy. For this reason, aluminum castings cause severe wear on the cutting tool.. This wear is particularly high in the case of foundry hypereutectic piston aluminum alloys.. On the other hand, low silicon wrought alloys cause minimal wear.
- Wear increases with increasing strength of aluminum alloys.. solid particles, which are in a soft aluminum matrix, quite easily break out of it, without causing much harm to the instrument. However, if the aluminum matrix has increased hardness, then inclusions break out harder and therefore cause greater wear and tear on the tool.
- Finally, tool wear depends on the wear resistance of the tool itself.
Effect of cutting speed on tool wear
Regarding cutting conditions, then cutting speed has the greatest impact on the life of the cutting tool. The figure 5 presents an example of the dependence of the life of a cutting tool in the machining of aluminum alloys for die casting. In the case of wrought aluminum alloys, the life of the cutting tool is measured rather in shifts or days., than in minutes, as for high silicon casting alloys.
Since the wear of the cutting tool also depends on other machining parameters, then the service life can only be estimated for a specific set of parameters. Other parameters, which affect the wear of the cutting tool are:
- Lubricating and cooling emulsions - effective cooling reduces tool wear.
- Intermittent cutting, for example, if there are pores in the material, increases tool wear.
- Feed rate and depth of cut. Tool wear increases with increasing cross-sectional thickness of the chip.
Cutting force for machining aluminum
To assess the influence of the material on the cutting conditions, the so-called specific cutting force is used.. This specific cutting force is correlated with cutting force., material and chip size. In general, the following provisions apply:
- Different aluminum alloys have differences in specific cutting forces., but relatively small.
- usually take, that the specific cutting force for aluminum and aluminum alloys is 30 % from such an effort for steel.
- The specific cutting force of an aluminum alloy cannot be deduced from its chemical composition or physical properties..
- Specific cutting force must be determined experimentally for each individual case..
The required cutting force depends not only on the size of the chip, but also from the cutting lubricant and the design of the cutting tool:
- The lubricating-cooling emulsion has two opposite effects.. One side, cooling reduces the temperature in the cutting zone and thereby increases the required cutting force. On the other hand, lubrication facilitates chip movement and reduces the amount of required cutting force.
- The geometry of the cutting tool affects the cutting force through the rake angle γ. The larger this angle, the less the chip compression and the lower the cutting force (figure 3).
- The degree of wear on the cutting edge has a relatively large effect.. Therefore, during prolonged machining, the amount of cutting force increases.
A source: TALAT 3100