An Improved Analytical Modeling of Force System in Ball-End Milling

Effect of Process Parameters and Tool Geometry on Fabrication of Ni Particles Reinforced 5083 Al Composite by Friction Stir Processing

The prediction of cutting force in ball-end milling

The paper presents an analytical method to predict stability lobes in ball end milling. Analytical expressions are based on the dynamics of ball end milling with regeneration in the uncut chip thickness, time varying directional factors and the interaction with the machine tool structure. The cutting force coefficients are derived from orthogonal cutting data base using oblique transformation method. The influence of cutting coefficients on the stability is investigated. A computationally efficient, an equivalent average cutting force coefficient method is developed for ball end milling. The prediction of stability lobes for ball end milling is reduced to the solution of a simple quadratic equation. The analytical results agree well with the experiments and the computationally expensive and complex numerical time domain simulations.

In this paper, a new mechanistic model is developed for the prediction of cutting force system in ball-end milling process. The key feature of the model includes the ability to calculate the workpiece / cutter intersection domain automatically for a given cutter location (CL) file, cutter and workpiece geometries. Moreover, an analytical approach is used to determine the instantaneous chip load and cutting forces. The model also employs a Boolean approach for given cutter, workpiece geometries, and the CL file in order to determine the surface topography and scallop height variations along the workpiece surface which can be visualized in 3-D. Some of the typical results from the model validation experiments performed on Ti-6A1-4V are also reported in the paper. Comparisons of the predicted and measured forces as well as the surface topographies show good agreement.

Micro-milling has been considered as the most promising method to repair the micro-defects on the surface of KH2PO4 (KDP) crystal. However, acquiring an ultra-smooth repaired surface by ball-end milling remains a longstanding challenge for KDP crystal due to its soft-brittle properties. In micro ball-end milling of KDP crystal, tool inclination angle has a remarkable effect on the quality of machined surface. Therefore, picking out an optimal tool inclination angle plays a great role in guaranteeing the ductile-mode machining and improving the surface quality of brittle KDP crystal. In this work, the effect of tool inclination on the brittle–ductile transition and surface quality of micro-milled KDP crystal were investigated. A theoretical model considering the tool inclination direction and angle was proposed to calculate the undeformed chip thickness (UCT) and cutting speed involved in the micro ball-end milling process. Besides, micro groove experiments were conducted to evaluate the change rule of the brittle–ductile transition and surface quality related to the tool inclination. The experimental results agree well with the theoretical results, which shows that the evolution of surface quality with respect to the tool inclination depends on the competitive mechanisms between UCT and cutting speed. Inclining the cutter in the tool feed direction (positive inclination angle) and increasing the tool inclination angle both contribute to the ductile cutting of KDP crystal. A + 45° inclination angle is the optimal angle for the micro ball-end milling of KDP crystal and the best surface roughness value achieved could be up to 35.3 nm.

Effect of milling modes on surface integrity of KDP crystal processed by micro ball-end milling

Chip load prediction in ball-end milling

This paper presents a model for cusp height in the ball-end milling process. In many milling operations, the cutting tool performs step over and makes adjacent cuts to complete machining of any feature. As a result, a small cusp of material, called a cusp height, will remain between these cuts on the surrounding walls or on the machined surface if a ball-end mill is used. This procedure presents application of software to evaluate cusp height in milling process. The height of cusp is examined in surfaces having different curvature ratio and different orientation. The model for the mathematical prediction of the cusp height has been developed in terms of axial and radial depth of cut, surface curvature and tool diameter. The application of the DOE technique by Taguchi gives the process parameter values that lead to the minimum machining time and achievement of the desired surface texture.

Mechanical and technological aspects of micro ball end milling with various tool inclinations

Force coefficients identification considering inclination angle for ball-end finish milling

The Friction Stir Welding (FSW) process has a large industrial potential in the field of joining lightweight alloys. Due to the increasing industrial use of aluminium alloys the benefits provided by this technology are very appealing. However, this potential has not, until this time, become a reality due to the lack of relevant available information concerning the process. The lack of information is especially serious in regards to the welding tools. This component, whose importance in the FSW process cannot be overstated, has not been the subject of extensive published research due mainly to the difficulties related to the modelling of the FSW process, which means that all of the development in this field has to be conducted through a trial and error approach. This approach entails significant costs and success risks, thus reducing the capability of R&D institutions to carry out extensive research. The objective behind the work detailed in this paper is the assessment of the effects of the welding tool geometry and features in the weld quality and process productivity. The work was carried out via an experimental procedure, which consisted of carrying out several welds using different pin lengths, pin diameter, pin geometry and shoulder diameter. The geometries that were used are based on known geometries from literature and new concepts. Due to practical limitations the study was conducted using a 3mm thick AA 6082-T6 butt joint configuration. The quality of the welds was assessed through destructive and non destructive testing, namely a visual inspection, an x-ray and a macrographic examination. These results can then be used to correlate the effects of the different tool geometries with the weld quality and productivity. The process productivity can be, according to [1], directly related to the welding speed, this is due to the near absence of welding consumables in the FSW process, leading to the predominance of fixed costs. The results pertaining to this work enable a better comprehension of the manner by which the tool geometry influences the weld quality and the process productivity, thus providing a stepping stone in the ongoing task of optimizing and modelling of the FSW process. The results presented in this paper may also be useful when extrapolated to other materials and thicknesses.

Chapter 5 - Effects of tool geometry

In this paper, the cutting forces and machine-tool vibrations in ball-end mill process were modeled by using mathematical functions. All derivations of cutting forces are directly based on the tangential, radial, and axial cutting force components. The cutting force and vibration models can be formulated by a function of many parameters such as cutting force coefficients, cutter geometry, cutting conditions, and so on. The proposed cutting force model has been successfully verified by both simulation and experiment with very promising results. Besides, the machine-tool vibrations are also predicted for ball-end mill process.

This study investigates the variation of cutting force coefficients (CFCs) in milling operations and their impact on force predictions and stability analysis. While CFCs are often assumed constant for simplicity, they are inherently dependent on feed per tooth and cutting speed, introducing uncertainties in machining dynamics. Using an oblique transformation model, CFCs are predicted from an orthogonal cutting database, considering chip thickness and cutting speed. The results indicate that variations in CFCs significantly influence cutting force estimations, affecting stability predictions based on the stability lobe diagram (SLD). Assuming constant CFCs may lead to inaccurate force predictions, miscalculated stability limits, and increased risk of chatter. This can result in excessive forces, accelerated tool wear, poor surface quality, and potential scrap part. In this study, cutting forces are compared against predictions from both constant and variable CFC models, revealing the improved accuracy of the latter in dynamic milling conditions. The influence of cutting speed and feed per tooth on tangential, radial, and axial force components is systematically analysed. It is observed that higher cutting speeds tend to reduce CFC values due to thermal softening effects, whereas increased feed per tooth generally amplifies force coefficients because of increased chip loads. A stability model incorporating CFC variations may provide a more accurate representation of process dynamics. The study emphasises the necessity of adaptive force and stability models in machining simulations to enhance predictive accuracy. These findings offer critical insights for optimising process parameters, selecting stable cutting conditions, and designing chatter avoidance strategies in industrial applications.

The effects of tool geometry and properties on friction stir spot welding properties of polypropylene sheets were studied. Four different tool pin geometries, with varying pin angles, pin lengths, shoulder diameters and shoulder angles were used for friction stir spot welding. All the welding operations were done at the room temperature. Lap-shear tensile tests were carried out to find the weld static strength. Weld cross section appearance observations were also done. From the experiments the effect of tool geometry on friction stir spot weld formation and weld strength were determined. The opti- mum tool geometry for 4 mm thick polypropylene sheets were determined. The tapered cylindrical pin gave the biggest and the straight cylindrical pin gave the lowest lap-shear fracture load.