MACHINING BEHAVIOR WITH MAGNETIC FIELD ASSISTANCE

Machining is a process matter with complex dynamics, including an economic dimension and the physical aspect generated by the cut. Performance, productivity, quality of generated surfaces, time and manufacturing costs are the most important criteria in adequate manufacturing processes. Material removals rates with the uncut chip thickness, feeds, cutting speeds provide adequate tool live. This segmentation phenomena influences in the chip morphology, tool forces, chip-tool interface temperatures, and the dynamic behavior of the cutting system.

A chip formation mechanism is modified (plastic deformation within the chip by the tool contact under magnetic field) and the joint effects by hard contact between tool-chip-material. Wear on the flank face appears to be from tear out that typically occurs when welded asperity junctions between the work material and tool face are fractured by a shearing force. Tool wear are noticeably different when a magnetic field is introduced. Minuscule fragments of the tool material are torn out. This may involve some chemical interaction of the tool surface with the surrounding atmosphere. A valid explanation is founded by pinning effect of the dislocations alone cannot account for the strong degradation of the magnetic properties observed at the very beginning of the strain-hardening. Therefore, considerations on the magnetoelastic anisotropy induced by the long-range internal stresses have been proposed.

This research explores the magnetic field application as assistance in machining process. The study proposes necessary elements to understand the cutting mechanisms under magnetic field. Results of orthogonal cutting tests carried out on dry cut of magnetized AISI 1045 steel using nonmagnetic carbide insert; it shows the increasing lifespan of the cutting tools by magnetic field assistance. The study is separated into two groups: (i) a change in the mechanics of cutting (shear angle, shear strain and cutting ratio) and (ii) tribological surface modifications of the tool-chip contact in the presence of magnetic field.

Tribological investigations show that magnetic field has significant influence on the friction and wear of the materials. The magnitudes of coefficient of friction and wear rate are strongly dependent on the magnetic field intensity; Oxide films are generated as result of exposure to magnetic field. The nature of oxide film governs the change in friction and wear. Magnetic field assistance improves the machined surface quality and the manufacturing process.

The effect of cutting and tangential force on magnetic field influence has been identified through the changed measured during the experiments. Cutting forces measurements performed in 2D cutting with magnetic field influence and different speeds revealed a decrease in cutting forces when magnetic field influence was augmented. Using a confidence level of 96%, (Shapiro-Wilk test) an average cutting force diminution of 3.4% and tangential force of 15% were measured (results presented in appendix A). Magnetic field modifies the mechanics of cutting at the tool chip interface in three ways as reported. The magnetostriction effect, heat augmentation and microstructure variation are possible explanations for the enhanced performance of materials under magnetic field.

Scanning electron microscope (SEM) images and optical microscope images were taken for obtaining zoom-in look at the wear and microstructure and to better understand the phenomenon involved behind the result. The variation of chip morphologies as a function of cutting speed and magnetic field produces an effect on tool wear. Figure 34 depicts the damage of tungsten carbide inserts after the contact, for cutting speed of 54.6m.min-1, tangential feed of 0.1mm.rev-1 and magnetic field of 2kA.m-1 representing typically SEM observations of the worn threat resulted after the experiments.