Diamond cutting wheels are used for efficient cutting of hard, short-chipping and wear resistant materials such as glass, ceramics and carbide. The current trend towards sintered materials has increased the use of diamond cutting wheels. They are successfully used in the food industry and medical science, due to their clean and almost residue-free cutting ability.
CBN was developed as an addition to diamond. The specific characteristics of this cutting material permit the machining of high-performance high-speed steel and hardened steel from 55 HRC as well as magnetic materials. The cutting wheels consist of a steel core with the cutting layer on the periphery. The cutting layer in sintered metal, resin or electroplated metal bond contains either diamond or cBN. The combination of bond, type of abrasive, concentration and grit size leads to different tool characteristics which are specified to meet the requirements of different processes and applications
1. Which materials can be cut?
As a general rule, diamond cutting wheels are used to cut hard, short-chipping materials such as glass, ceramics (fired and unfired), carbide, graphite, quartz, ferrite and semiconductor materials. Materials with an affinity for carbon, such as iron-based alloys, are cut using cubic boron nitride (cBN). High-alloy steels such as HSS and chrome steel with 12% Cr are typical examples. Ideally, steel should have a minimum hardness of 55 HRC. Soft, long-chipping materials accumulate in the chip space, so they tend to clog. Compromises can be achieved with electroplated bonds.
2. Which cutting layer specification?
The following is indispensable for correct selection of layer specification: full description of workpiece material•cutting edge quality requirements (e.g. maximum size of edge chipping)•machining parameters, range of variants (e.g. speed from/to, feed rate from/to)• details of drive power (see point 4)• details of coolants•
3. Which tool dimensions?
The tool dimensions are determined by the machine and the height of workpiece to be cut. Normally, the flange diameter should not fall below 1/3 of the cutting wheel diameter, i.e. the maximum workpiece height which can be sawn is less than one third of the blade diameter. A stable cutting wheel core is essential for chip-free cutting edges. The directional stability of the blade can also be enhanced by increasing the flange diameter (diameter size required). Proportionately larger flanges are advisable for high cutting rates. A summary of the internationally approved designations for continuous-rim cutting wheels and the associated flanges has been compiled by FEPA.
4. Which machine?
Generally valid principles apply to the highest possible dynamic stability, since any oscillation during the cutting operation can have a negative effect on tool behaviour. Peripheral speed plays an important role in the adaptation of the tool to the cutting operation, and should therefore be adjustable, at least by means of a change of drive pulley. Sufficient motor drive output is essential as an undersized motor will prevent the optimum utilization of the diamond tool. Diamond and bond must be made to work hard if the self-sharpening effect is to occur. Bonds will have greater resistance to wear and will thus be more economical if the spindle drive permits high cutting rates. Cutting wheels with diameters exceeding 300 mm should be used with a drive power of at least 1.5 kW; for ganged wheels, a further 0.5 kW should be allowed for each additional cutting wheel.
5. Which operation parameters?
In the vast majority of cases, the full material thickness is cut in a single pass at a suitably chosen feed rate. However, step cutting rather than full cutting is used for particularly dense materials such as sapphire which wears the diamond layer without simultaneously removing a corresponding amount of the bond. The smaller the ratio of depth of cut to feed rate i.e. the shallower the cut, the greater is the sharpening effect of the cutting process. Feed rate is directly dependent on the spindle drive power and the hardness or toughness of the material to be cut. A general specification of cutting rates cannot be given in view of the large number of different materials which can be cut with the different cutting wheel types. There are optimal ranges of peripheral speed, dependent on the cutting operation. In general, low peripheral speeds (20–30 m/s) are used for dense, fine-debris materials, whereas higher speeds (30–40 m/s) are used for porous, coarse-debris materials.
6. Coolant or dry cut?
Metal bonded cutting wheels are invariably used with coolant (with the exception of the electroplated S-type), resin bond closed-rim blades can also work dry. Different coolants are used for the different workpiece materials, e.g. water, mineral based oils, emulsions, synthetic oils etc. It is important for coolant flow to be sufficient and to be accurately directed to the tool/workpiece interface. The coolant is supplied via coolant nozzles, by a special flange or by emersio