1ère étape fondamentale: le tronçonnage

Metallographic Cutting Abrasive cutting is the most widely used method of material sectioning for microscopic examination. Good cutting means freedom from burn, distortion and disturbed material. It is essential, therefore, to select the correct wheel for the specific application and to provide adequate specimen cooling while using the correct cutting technique. Silicon carbide is preferred for non-ferrous metals and non-metallics while aluminium oxide is best for ferrous metals. Coarse grits usually cut heavier sections faster and cooler while fine grits produce better surfaces and less burning on delicate pieces. Hard wheels break down more slowly, wear longer and are generally recommended for the softer materials. Soft wheels break down faster, exposing new cutting surfaces more rapidly, and are preferred for hard materials. Buehler offers selected abrasive wheels particularly developed for different groups of materials. They result in a smooth-cut, clean surface that is to a large extent free from surface deformation. Our abrasive discs have been developed especially for the materialography cutters. Abrasive Cutters are an integral part of the modern metallographic laboratory and are preferred over dry cutting and other more damaging techniques. A heat-damaged zone can alter the structure of the sample and is avoided by the use of a suitable cutting fluid. This cooling helps to prevent sample deformation and also washes away the swarf; surface roughness is reduced and wheel life extended. The optimal cut will allow the specimen to be prepared in a fewer number of steps and in a shorter time. The abrasive cut is therefore of fundamental importance to ensure high quality in the final preparation. Abrasive cut-off wheels Abrasive wheels are frequently classified according to their degree of hardness. Wheels with a hard bond wear out more slowly, have a higher life and thus are mainly used for softer materials. Wheels with a softer bond wear out faster, revealing new sharp abrasives and are recommended for cutting harder materials. Cutting with abrasive cuto-off wheels Abrasive cut-off wheels come in two bonding materials: resin bond and rubber bond. Resin-bonded abrasive wheels are used with most materials. The hardness of the bonding agent depends on the material being cut. The rubber-bonded wheels are characterised by a particularly thin cut and no-burn sectioning. The sample must be firmly and evenly clamped, in order to prevent breaking the wheel and damage to the sample. The cutting force should be applied with care and in relation to the material. The table on the next page highlights the main problems that can occur during the cutting process, and the actions required to remedy these. Diamond and Boron Nitride (CBN) blades As the development and use of modern engineering materials increases, so does the demands placed on the technology required to prepare these materials for analysis. Diamond and CBN (boron nitride) abrasive wheels are able to section through hard metals, composite materials, plastics, glass and mineral fibres, ceramic(s), glass or bone without any problem. Whether a diamond or a boron nitride disc is to be used, depends essentially on the hardness or brittleness of the sample material. Following is a general guideline: Metal bonded diamond discs:
Aggressive sectioning of metals, general sectioning of composites materials with hard phases, PCB’s, ceramic coatings, glass and electronic packages Resin bonded diamond disc:
Hard metals, tungsten carbide, gentle cutting of hard brittle materials (ceramic(s), glass etc.) CBN discs:
Hard ductile materials (highly alloyed steel, cobalt and nickel based alloys, lead alloys) Buehler's AcuThin Cut-off Wheels have been formulated for fast sectioning of small, delicate specimens, as well as large sturdy specimens. These blades give the user a versatile cutting option that proves effective over a variety of specimen types.