tailieunhanh - Cutting Tool Materials Part 2

Tham khảo tài liệu 'cutting tool materials part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Cutting Tool Materials 11 Figure 5. Cemented carbide powders and typical microstructures after sintering. Courtesy of Sandvik Coromant 12 Chapter 1 The desirable properties that enable tungsten carbide to be tough and readily sintered also cause it to easily dissolve in the iron producing the so-called straight cemented carbide grades. These straight grades normally contain just cobalt and have been used to predominantly machine cast iron as the chips easily fracture and do not usually remain in contact with the insert reducing the likelihood of dissolution wear. Conversely machining steel components requires alternative carbides such as tantalum or titanium carbides as these are less soluble in the heated steel at the cutting interface. Even these mixed cemented carbide grades will produce a tendency to dissolution of the tool material in the chip which can limit high speed machining operations. Today the dissolution tool material can be overcome by using cutting insert grades based on either titanium carbide or nitride together with a cobalt alloy binder. Such grades can be utilised for milling and turning operations at moderate cutting speeds although their reduced toughness can upon the application of high feed rates induce greater plastic deformation of the cutting edge and induce higher tool stresses. These uncoated cutting inserts were very much the product of the past and today virtually all such tooling inserts are multi-coated to significantly reduce the effects of dissolution wear and greatly extend the cutting edge s life - more will be said on such coating technology later. Classification of Cemented Carbide Tool Grades Most cemented carbide insert selection guides group insert grades by the materials they are designed to cut. The international standard for over 30 years used for carbide cutting of workpiece materials is ISO 513-1975E Classification of Carbides According to Use3 -which has a colour-coding for ease of identification of sub-groups.