Guillaume Fromentin

Precision and surface integrity of threads obtained by form tapping

Largely applied to internal threading of extruded tubes, cold form tapping is now becoming a promising process for internal threading of holes in non ferrous and ferrous solid components, more particularly for mass production in the automotive industry. The aim of this study is to present the surface properties of the threads resulting from form tapping. Geometrical characterization, surface texture, mechanical and metallurgical observations are investigated. The results obtained are discussed according to the input parameters of the process, and are compared to those obtained from cut tapping. The strength of the work material and the influence of the lubricant are the two main parameters affecting the process, and a correlation with the tapping torque is proposed. Finally, the characteristics of the thread surface depend on the parameters of the tapping operation, thus it has to be taken into account in the design approach when this tapping process is chosen.

Analysis of chip formation mechanisms and modelling of slabber process

During the primary transformation in wood industry, logs are faced with conical rough milling cutters commonly named slabber or canter heads. Chips produced consist of raw materials for pulp paper and particleboard industries. The process efficiency of these industries partly comes from particle size distribution. However, chips formation is greatly dependent on milling conditions and material variability. Thus, this study aims at better understanding and predicting chips production in wood milling. The different mechanisms of their formation were studied through orthogonal cutting experiments at high cutting speed for beech and Douglas fir. Under these conditions, ejection of free water inside wood can be observed during fragmentation, particularly on beech. As previously seen in quasi-static experiments, chip thickness is proportional to the nominal cut thickness. Moreover, the grain orientation has a great influence on the cutting mechanisms, so as the nominal cut and the growth ring widths. This chip fragmentation study finally allows the improvement of the cutting conditions in rough milling. In order to optimize machine design as well as cutting geometry, a geometrical model of a generic slabber head was developed. This model allows the study of the effective cutting kinematics, the log-cutting edges interactions and the effective wood grain direction during cutting. This paper describes the great influence of the carriage position on cutting conditions. The results obtained here can be directly used by milling machine manufacturers.

Modeling and Analysis of Five-Axis Milling Configurations and Titanium Alloy Surface Topography

Five-axis milling with a ball-end cutter is commonly used to generate a good surface finish on complex parts, such as blades or impellers made of titanium alloy. The five-axis milling cutting process is not straight forward; local cutting conditions depend a lot on the geometrical configuration relating to lead and tilt angles. Furthermore, the surface quality is greatly affected by the cutting conditions that define the milling configuration. This study presents a geometrical model of five-axis milling in order to determine the effective cutting conditions, the milling mode, and the cutter location point. Subsequently, an analysis of surface topography is proposed by using the geometrical model, local criteria, and a principle component analysis of experimental data. The results show the effects of local parameters on the surface roughness, in relation to the lead and tilt angles.

Flank wear prediction in milling AISI 4140 based on cutting forces PCA for different cutting edge preparations

One of the criteria mastering the choice of a cutting tool is its wear resistance. For coated inserts, prior to the coating process, edge preparation method choice will impact their performance. So, a classification based on its impact on wear resistance is needed. Indeed, the flank wear of three coated cemented carbide inserts presenting differently prepared edges (untreated, dragging and magneto-abrasive machining) is explored experimentally. Those inserts are used to face mill the hardened AISI 4140 low alloy steel. Further, by means of the principal component analysis (PCA), correlations between the online measured cutting forces and flank wear behaviour are investigated. In view of this analysis, for each studied case, the statistical law predicting flank wear relying on cutting forces components is established with fair approximation. However, the experimental results have quantitatively shown that edge preparation could be in some cases not beneficial for tool wear resistance of the milling inserts considering either maximal or average flank wear.