tailieunhanh - Metal Machining - Theory and Applications Episode 1 Part 6

Tham khảo tài liệu 'metal machining - theory and applications episode 1 part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Work material characteristics in machining 93 content gives rise to increasing temperatures for a given cutting speed. This comes from the increasing shear stress levels. This completes this brief survey of the stresses and temperatures generated by different alloy groups in machining. Tool stresses are mainly controlled by the metal being machined and vary little with cutting conditions although the tool rake face area over which they act changes with speed and obviously also with feed . Temperatures on the other hand depend not only on the material being machined both through stress levels and thermal properties but also on the speeds and feeds used. Machining with built-up edge formation In the previous section data were presented mainly for cutting speeds greater than 100 m min. This is because at slightly lower cutting speeds at the feeds considered those steels machine with a built-up edge BUE . In Chapter 2 photographs were shown of BUE formation. Figure shows for a steel what changes in specific force and shear plane angle are typically associated with this. In this example the largest BUE occurred at a cutting speed close to 25 m min. There the specific forces passed through a minimum and the shear plane angle through a maximum. Qualitatively this may be explained by the BUE increasing the effective rake angle of the cutting tool. Built-up edge formation occurs at some low speed or other for almost all metal alloys. It offers a way of relieving the large strains small shear plane angles that can occur at low speeds but at the expense of worsening the cut surface finish. For those alloys that do show BUE formation the cutting speed at which the BUE is largest reduces as the feed increases. Figure gathers data for three ferrous alloys and one Ni-Cr creep resistant alloy Nimonic 80 . One definition of high speed machining is machining at speeds above those of built-up-edge formation. These are the conditions mostly focused on in this .