In this paper, a model-based micro-end milling process planning guideline for machining micro mold cavities was proposed. The goal is to facilitate proper selections of the process parameters. Specifically, the axial depth of cut, the feed per tooth are critical in achieving performance objectives in terms of cutting forces, surface accuracy, tool life, etc. To this end, the finite element modeling was used to provide a comprehensive understanding of the underlying science base for the micro-machining (e.g., chip formation mechanisms, minimum chip thickness effect, material deformation flows, stress, strain and temperature distributions). Further, a mechanistic time-domain simulation model was utilized to provide predictive capability in practical machining performance, such as cutting forces, tool vibrations, surface accuracy, and surface roughness. The generalized process planning strategy consists of two steps: roughing and finishing. In roughing, the objective is to control the cutting force within a predefined threshold to prevent premature tool breakage and to maximize the material removal rate. In finishing, the primary objective is to control the form error within the tolerance and to obtain satisfactory surface roughness. The proposed process planning strategy was applied for micro-milling of a mold cavity in AL2024-T6.
In this paper, we develop a methodology to determine flow stress at the machining regimes and friction characteristics at the tool-chip interface from the results of orthogonal cutting tests. We utilize metal cutting analysis originally developed by late Oxley and present some improvements. We also evaluate several temperature models in calculating the average temperatures at primary and secondary deformation zones and present comparisons with the experimental data obtained for AISI 1045 steel through assessment of machining models (AMM) activity. The proposed methodology utilizes measured forces and chip thickness obtained through a basic orthogonal cutting test. We conveniently determine work material flow stress at the primary deformation zone and the interfacial friction characteristics along tool rake face. Calculated friction characteristics include parameters of the normal and frictional stress distributions on the rake face. Determined flow stress data from orthogonal cutting tests is combined with the flow stress measured through split-hopkinson pressure bar (SHPB) tests and the Johnson-Cook work material model is obtained. Therefore, with this methodology, we extend the applicability of Johnson-Cook work material model to machining regimes.
This paper presents investigations on machining of a nickel-based alloy. Orthogonal cutting tests using uncoated carbide inserts with 10 and 25 micron edge radius and 0 and 3 degree tool rake angles are performed. Forces, chip geometry and tool edge conditions are measured. An analytical model is introduced to identify average strain, strain rate, shear stress and temperature for segmented chip formation and friction conditions exerted on the tool during cutting process. Johnson-Cook material model related flow stress data are modified using the experimental data. Finite Element simulations are conducted to investigate the influence of tool geometry on predicted stress, strain and temperature distributions on machined surfaces.
Laser assisted machining is an alternative to conventional machining of hard and/or difficult-to-process materials which involves pre-heating of a focused area with a laser beam over the surface of the workpiece to cause localized thermal softening along the path of the cutting action. The main advantage that laser assisted machining has over conventional machining is the increased material removal rate and productivity. Laser assisted micromilling is a scaled down derivative of laser assisted machining assuming that the process effectiveness potentially exists at the meso/micro scale. It is well-known that continuous-wave (c.w.) lasers generate a wide and deep heat affected zone, and can cause microstructure alterations, potentially making laser assistance counter-productive at the meso/micro scale. The novel use of a pulsed laser in assisting micromilling enables processing of die/mold metal alloys that are typically hard and/or difficult-to-process in micro scale, while reducing the heat affected zone. A fairly innovative technique is introduced by thermally softening only the focused microscale area of the work material with induced heat from a pulsed laser, and material removal is performed immediately with micro mechanical end milling. The focus of this paper is to present a fundamental understanding of the pulsed laser assisted micromilling (PLAM), in particular, to investigate the influence of pulsing on microscale localized thermal softening by coupling with the finite element simulation of the micromilling process. Experiments and Finite element method-based process simulations for micromilling of AISI 4340 steel with and without the laser assistance are conducted to study the influence of the pulsed laser thermal softening on the reduction in cutting forces and its influence on the temperature rise in the cutting tool.
Laser micromachining has the capability to fabricate very small and basic 2.5-D geometric features on a range of materials in the form of laser ablation or irradiation. Short pulsed lasers that can achieve wide range of wavelengths in the form of harmonics of infrared laser beam at 1064 nm wavelength have been a very effective micro-machining tool used for hole drilling, cutting, scribing, trimming and marking. A review of laser processing of materials is given in this paper. Direct laser ablation can be performed by controlling laser beam properties such as laser energy, intensity, pulse duration and wavelength in micro-machining 3-D geometric features. However, this method requires additional capabilities for a typical laser beam generating and delivery system. When the laser beam properties cannot be altered, Hole Area Modulation (HAM) method becomes alternative solution by controlling the density of the holes and the step size in a mask to improve the accuracy of the 3-D geometric feature. In this paper, we perform modeling, planning and simulation of laser micromachining with hole area modulation method to produce spherical and elliptical objects 3-D geometrical features that are typical for aspheric and or refractive micro-lenses. A computational methodology is developed to design a mask with varying density and diameter of the holes. The masks are created using micro-drilling and utilized in laser micromachining of 3-D objects on polycarbonate polymer substrates.
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