Ductile irons are among the most used materials in the automotive industry. One of the critical problems during manufacturing of powertrain components is the fast wear of cutting tools because it can lead to defects in the part. This work investigates the wear mechanisms of TiN coated high-speed steel (HSS) taps when machining GGG50 cast iron under high-speed conditions. SEM images and EDS analysis at the chamfered and cylinder teeth demonstrate that adhesion of iron to the cutting tool is the dominating wear mechanism. Fatigue-fracture and coating removal were also observed in many zones of the tap surface. Furthermore, wear progression is reflected on the evolution on the tapping torque with hole number. An on-line monitoring of this variable could be useful to detect an excessive wear of the tap and prevent the loss of tolerances in the threads.

Additive manufacturing by directed energy deposition is of increasing interest within the scientific community. Over the past decade, this technology has gained ground with the production of parts from SS 316L-Si stainless steel, an industrial product in widespread use. Yet one of the main challenges when extending the use of this technology to the manufacture of medium complexity parts is how to achieve good intersections. This paper focuses on the use of Plasma Arc Welding (PAW) for the additive manufacturing of X-Cross intersections made of SS 316L-Si stainless steel alloy, defining its geometrical suitability and evaluating its productivity. Firstly, two strategies for the production of parts are presented: the energy control strategy on the curved path of a L-shaped wall and the variable amplitude waveform strategy (variable waving) for the continuous production of a X-cross intersection. A metallographic analysis of the samples extracted in the different tests was completed, focusing mainly on the transversal direction. Next, four deposition strategies based on discrete trajectories (cross -over-lapping and cross-waving) and on continuous trajectories (waving and overlapping) are addressed in this paper for the production of cross intersections in a part of medium complexity and for the extension of its use in Near -Net-Shape (NNS) manufacturing. The mechanical properties and microstructure of samples manufactured with these deposition strategies are analysed by means of tensile tests and metallographic characterization. An analysis of the deposition energy and of the productivity is carried out for the four strategies. The productivity is analysed by means of different parameters such as the number of layers, the actual deposition rate and process times (deposition time, waiting time, standby time and idle time). The most advantageous strategies in terms of productivity were cross-waving and waving, achieving torch utilization rates relative to total time of 50 %. Methodologies and conditions for the manufacture of X-cross intersections are established. Finally, a study of the cross-intersection geometry obtained for each deposition strategy is performed. From the geometrical analysis of the crosses produced, it has been observed that the ratio of material used in the cross-overlapping sequence to produce a X-cross intersection in relation to the amount of material deposited is more than 10 % higher than in the other strategies.

In this article, an analytical solution is developed to determine the transient temperature distribution in a rotating finite cylinder subject to a heat source acting on its flat surface with convective cooling. The resolution of the heat conduction problem for the cylinder temperature is carried out by means of the successive application of one-dimensional integral transforms: the finite Fourier transform and the finite Hankel transform. The solution can be applied in different engineering applications such as turning, pin-on-disk devices, bearings and braking systems. Taking this solution into account, a numerical analysis of the transient temperature distribution generated in a rotating cylinder subject to a heat source is performed. In this analysis the effect of the rotation speed and of the convective cooling on the transient temperature distribution of the cylinder and on the time required to reach the quasi-steady state is studied by means of two dimensionless parameters: the Peclet number and the Biot number, which depend on the rotation speed and on the convective heat transfer coefficient, respectively. Finally, different heat source geometries (circular, square and circular trapezoid) are considered.

High temperatures generated in cutting processes significantly affect the surface integrity of machined parts and tool wear, leading to workpiece thermal damage, tensile residual stresses in the workpiece and a reduction in tool life. In recent years, different analytical thermal models to predict cutting temperatures have been developed in literature based on 2D modeling of the cutting process and the assumption that thermal conductivities of work piece and chip are not dependent on temperature. However, this dependence of conductivity on temperature may have a significant influence on predicted temperatures and must be taken into account. In this paper, a thermal model of the orthogonal cutting process that considers thermal conductivity of materials (chip and tool) to be dependent on temperature is developed. A linear variation of thermal conductivity with temperature is assumed for chip (workpiece) and tool materials. The model is based on application of: (1) the Kirchhoff transformation in order to convert the nonlinear heat conduction problem into a linear one, (2) the theory of moving and stationary heat sources in semi-infinite and infinite mediums in order to model primary and secondary deformation zones and (3) imaginary heat sources to meet adiabatic boundary conditions in the chip and tool. Imaginary heat sources were defined in the thermal model proposed in this paper in such a way that the effect of the tool-chip interface dimensions and of cutting tool width on

This paper presents an experimental method for predicting tool wear in drilling Inconel 718 superalloy. The method combines analysis of drilling force signals and tool wear progress. Force characteristics were studied both in time and frequency domains (power spectrum and wavelet decomposition) in order to find best correlation with tool wear progress. These analyses show that the mean value of the thrust force component, the high frequency component of the force, the frequencies that arise during drilling, and the evolution of the wavelet decomposition details are all sensitive to tool wear progress. Therefore, these characteristics can be employed as indicators for drill failure prediction. Among all those indicators, the mean value of the thrust force and the standard deviation of high frequency components of that force have shown the greatest sensitivity to drill wear.

Automotive, railway and aerospace sectors require a high level of quality on the thread profiles in their manufacturing systems knowing that the tapping process is a complex manufacturing process and the last operation in a manufacturing cell. Therefore, a multivariate statistical process control chart, for each tap, is presented based on the principal components of the torque signal directly measured from spindle motor drive to diagnosis the thread profile quality. This on-line multivariate control chart has implemented an alarm to avoid defected screw threads (oversized). Therefore, it could work automatically without any operator intervention assessing the thread quality and the safety is guaranteed during the tapping process.

Thread quality control is becoming a widespread necessity in manufacturing to guarantee the geometry of the resulting screws on the workpiece due to the high industrial costs. Besides, the industrial inspection is manual provoking high rates of manufacturing delays. Therefore, the aim of this paper consists of developing a statistical quality control approach acquiring the data (torque signal) coming from the spindle drive for assessing thread quality using different coatings. The system shows a red light when the tap wear is critical before machining in unacceptable screw threads. Therefore, the application could reduce these high industrial costs because it can work self-governance.

In this work, a model for the prediction of drilling stability against low-frequency lateral vibrations, named as whirling in the literature, is proposed. These vibrations are lateral displacements of the tool that arise at frequencies near multiples of the rotation frequency of the drill. The appearance of whirling vibrations leads to the generation of lobe-shaped holes. In order to predict whirling vibrations, the motion equation of the drill is deduced taking into account the modal characteristics of the drill and the cutting and process damping forces that act on it. In this paper, forces that arise in two different regions of the drill are considered: (1) forces on the main cutting edges and (2) forces on the chisel edge. Different force models are presented for each region that include both the regenerative effect of the vibration on the cutting area and the process damping. An oblique cutting model and an orthogonal model are employed for the calculation of cutting forces acting on the main cutting edges and on the chisel edge, respectively. The cutting force model for the main cutting edges takes into account the cutting angle (inclination angle, rake angle, and chip flow angle) variation along the main cutting edges. For the chisel edge region, where the feed speed is no longer negligible with respect to the cutting speed, the dynamic cutting angles are employed for the force model development. Concerning the process damping force model, previous works in the literature consider a constant value of the clearance angle for the calculation of the process damping coefficient. However, in this work, the variation of the normal clearance angle along the main cutting edges is considered. It is shown that, depending on the clearance face grinding parameters employed, the clearance angle can double its value along the main cutting edges. Considering the force models and through the semi-discretization of the motion equation of the drill, the appearance of low-frequency lateral vibrations is predicted regarding the drill geometry and cutting conditions such as drill rotation speed and feed. In addition, given cutting conditions at which whirling vibrations are expected to occur, the model is able to predict the vibration frequencies that are excited. The drilling model and the stability predictions are experimentally validated by means of drilling tests with different drill diameters and cutting conditions. In comparing the experimentally obtained results and the predictions obtained by the model, it is concluded that the model can reasonably predict the appearance of whirling vibrations as a function of drill geometry and cutting conditions. Generated hole shape is also analyzed through the measurement of hole roundness and bottom surface geometry. It is observed that, when drilling in the presence of whirling vibrations, holes with lobed shape and polygonal bottom surface are generated. It is also noticed that both the number of lobes and the number of sides of the polygonal bottom surface are directly related to the vibration frequencies that arise.

This paper presents a model for predicting the surface topography generated in face milling operations. In these operations, when the face mill inserts remove the workpiece material, they leave marks on the machined surfaces. The marks depend on the face mill geometry, the geometry and runout of the face mill inserts, and cutting conditions, e.g. feed and step over. In order to predict the surface topography, the geometry of the face mill cutting edges must first be modelled. The modelling of the cutting edge geometry is for round insert face mills and for square shoulder face mills. Due to the influence of insert runout on the final surface topography, axial and radial runouts of the face mill inserts are also taken into account in the modelling of the cutting edge geometry. Next, the equations expressing the trajectory of any cutting edge point are derived as a function of the feed value, the rotation angle of the face mill, its axial position, and its radial position with respect to the face mill axis. Finally, given the cutting edge geometry and the trajectory of cutting edge points, a methodology based on the discretization of the milled surface in a grid with a finite number of points is developed in this paper for the simulation of the surface topography. The methodology is based on the fact that at each grid point, the final height of the topography will be the height of the workpiece material remaining at this point after many face mill revolutions. For this reason, the procedure initially estimates the rotation angles of the face mill for which the face mill cutting edges in their front-cutting and back-cutting motion pass by the grid point being considered. In order to achieve this, a transcendental equation that is only dependent on the rotation angle is derived from the cutting edge trajectory equations. This equation is transformed into an equivalent polynomial equation by means of Chebyshev expansions. The transformed equation is solved for the rotation angle using a standard root finder that does not require a starting value. Then, by means of the estimated rotation angles and the cutting edge trajectory equations, the radial positions of the cutting edge points passing by the grid point are obtained. Finally, based on these radial positions and the cutting edge geometry, the heights of cutting edge points, which can generate the surface topography at this grid point, are estimated. The final height of the surface topography will correspond to the lowest value among the estimated height values. The methodology can be easily extended and applied to face mills with other insert geometries or to face mills with central and peripheral inserts. In addition, the simulation of the surface topography generated by lateral passes in face milling operations is simplified. The procedure allows the influence of the face mill geometry, the feed value and the step over between passes to be analysed and the roughness values to be predicted. In order to validate the model predictions, a series of face milling tests are carried out. Predicted surface topographies are compared with measured topographies and a good agreement between them is observed.