Elliptical torus cutter tool path generation based on minimum distance computation

In mould manufacture the elliptical torus cutters are used for their high cutting velocity, but the special geometry also brings issues in tool path generating and machining quality controlling. In this paper a guide curve tool path generating method for elliptical torus cutters is presented with the cutter location points computed by a minimum distance algorithm and the path spacing determined by an adaptive method. In the minimum distance algorithm, the calculation is resolved into an iterative process from point to freeform surface and an algebraic calculation process from point to elliptical torus surface considering the geometry of the cutter, which reduces the iterative process and improves the computing speed. In the adaptive path spacing method, the contacting geometry between the elliptical cutter and the workpiece surface is analysed and the relations among the scallop height, the tool tilt angle and the path spacing are deduced, based on which the guide curves are adjusted in advance to control the scallop height. Calculating examples and experiments are carried out, showing that the consuming time of cutter location (CL) points computation algorithm is reduced by 30% comparing to earlier method, and the adaptive path spacing method performs better than constant method in both scallop height controlling and tool path shortening. The results indicate that the presented tool path generating method can help to reduce both the machining and machine waiting time as well as ensuring the machining quality.

Surface Texturing of Fan-blade Body by Random-orbital Polishing With in-line Aqueous Mist

Airfoil structures such as fan blades have free form geometry which require a high level of precision in order to create a uniform finish for ideal gas path flow. Challenges in machining of such parts have led to rework in order to remove defects and conform to dimensional requirements at the same time. Mechanical polishing is the most common method to remove surface irregularities on fan blades such as scallop height, while maintaining the required dimensions. After the polishing process, the part will undergo shot peening, vibratory finishing and later, painting and coating at the final stages. It is therefore essential for the fan blade surface to pre-treated with rough, uniform textures in order to promote good surface-to-surface adhesion at the end of the manufacturing cycle. Generally, the polishing process is assisted by an external cooling medium applied on the part surface at intervals. This method of removing heat is not effective, as the polished surface may experience scratches or distortion, especially around thin-walled sections of the leading edge in fan blade. The existing polishing method uses a single-axis rotary tool can produce average surface roughness, Ra, of 1.2 µm that satisfies the requirement. However, this form of aggressive polishing has a high material removal rate, resulting in excessive reduction in material thickness which leads to the rejection of costly fan blade.This study a new localized polishing method and examines its effect on the surface topography of an airfoil component made of aluminum alloy. The area of interest is focused on the leading edge of a fan blade at which polishing is carried out using a random-orbital polishing tool with modified features to incorporate internal cooling capability. Experimental trials are conducted to study the effects of surface finish with fixed grain abrasive disks under four conditions. A cold gun is connected in-line to guide cold air inside the internal passages of the tool and out onto the surface of the part directly. A secondary cooling source by water nozzle spray is integrated in the tool to mix with the cold air jet and form an aerosol mist during tool activation. Surface topography of the samples are determined by arithmetic mean deviation, maximum height and root mean square of the profile. Surface roughness was performed using an optical profilometer. The localized polishing method achieved a desirable surface roughness, Ra of 0.8 µm, while removing all traces of scallop height and maintaining the leading-edge thickness within tolerance. The study showed that the new method produced a topography that is uniformly textured. This method can improve the manufacturing cycle time.

Optimisation of Planning Parameters for Machining Blade Electrode Micro-Fillet with Scallop Height Modelling

Aero-engine blades are manufactured by electroforming process with electrodes. The blade electrode is usually machined with five-axis micromilling to get required profile roughness. Tool path planning parameters, such as cutting step and tool tilt angle, have a significant effect on the profile roughness of the micro-fillet of blade electrode. In this paper, the scallop height model of blade electrode micro-fillet processed by ball-end milling cutter was proposed. Effects of cutting step and tool tilt angle the machined micro-fillet profile roughness were predicted with the proposed scallop height model. The cutting step and tool tilt angle were then optimised to ensure the contour precision of the micro-fillet shape requirement. Finally, the tool path planning was generated and the machining strategy was validated through milling experiments. It was also found that the profile roughness was deteriorated due to size effect when the cutting step decreased to a certain value.

Characterizing the Effect of Cutting Condition, Tool Path, and Heat Treatment on Cutting Forces of Selective Laser Melting Spherical Component in Five-Axis Milling

Additive manufacturing (AM), partly due to its compatibility with computer-aided design (CAD) and fabrication of intricate shapes, is an emerging production process. Postprocessing, such as machining, is particularly necessary for metal AM due to the lack of surface quality for as-built parts being a problem when using as a production process. In this paper, a predictive model for cutting forces has been developed by using artificial neural networks (ANNs). The effect of tool path and cutting condition, including cutting speed, feed rate, machining allowance, and scallop height, on the generated force during machining of spherical components such as prosthetic acetabular shell was investigated. Also, different annealing processes like stress relieving, mill annealing and β annealing have been carried out on the samples to better understand the effect of brittleness, strength, and hardness on machining. The results of this study showed that ANN can accurately apply to model cutting force when using ball nose cutters. Scallop height has the highest impact on cutting forces followed by spindle speed, finishing allowance, heat treatment/annealing temperature, tool path, and feed rate. The results illustrate that using linear tool path and increasing annealing temperature can result in lower cutting force. Higher cutting force was observed with greater scallop height and feed rate while for higher finishing allowance, cutting forces decreased. For spindle speed, the trend of cutting force was increasing up to a critical point and then decreasing due to thermal softening.