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.

A model that predicts the appearance of low-frequency lateral vibrations in drilling with pilot hole is proposed in this work. These vibrations, called whirling in the literature, are responsible for the generation of lobe-shaped holes during drilling. The present model considers both the influence of the regenerative effect of vibrations on the cutting forces and the influence of the process damping phenomenon that appears along the main cutting edges. In order to model cutting forces, cutting edges are divided into discrete elements and for each of them oblique cutting model is employed. Specific cutting forces at each cutting edge element are calculated as function of cutting speed and normal rake angle value. A new methodology is developed to analyze the motion equation of the drill in the frequency domain in order to predict the appearance of whirling vibrations during drilling with pilot hole. Regarding the depth of cut and the spindle rotational speed, drilling stability limits against low-frequency lateral vibrations are obtained. Moreover, in the presence of vibrations, the model can predict the whirling frequencies that are excited depending on the established cutting conditions. In addition, the stability model is experimentally validated via drilling tests over pilot holes of different diameters for a wide range of cutting conditions. In order to study the appearance of low-frequency vibrations and to avoid the appearance of other vibrations such as regenerative chatter, the analysis is focused on low spindle speed values. A comparison between predicted vibration frequencies and actual frequencies in measured cutting forces during drilling tests is carried out and a good correlation between them is observed.

The emergence of multitasking machines in the machine tool sector presents new opportunities for the machining of large size gears and short production series in these machines. However, the possibility of using standard tools in conventional machines for gears machining represents a technological challenge from the point of view of workpiece quality. Machining conditions in order to achieve both dimensional and surface quality requirements need to be determined. With these considerations in mind, computer numerical control (CNC) methods to provide useful tools for gear processing are studied. Thus, a model for the prediction of surface roughness obtained on the teeth surface of a machined spiral bevel gear in a multiprocess machine is presented. Machining strategies and optimal machining parameters were studied, and the roughness model is validated for 3 + 2 axes and 5 continuous axes machining strategies.

The geometric tolerances of cylindrical workpieces are highly influenced by clamping forces. This relation is of special importance in slender workpieces such as thin rings. Better tolerances are achieved with lower clamping forces, but the disadvantage is that friction is reduced and the risk of slipping increases. Thus, in order to control the process, a key factor is achieving the lowest possible clamping force while still ensuring safety. Cylindrical parts are usually machined in lathes that have concentric plate chucks that are fixed either mechanically with wrenches or hydraulically by controlling pressure with valves. This paper proposes a method for measuring clamping forces in lathes during the turning process. The method allows the clamping force to be calculated from the torque applied by a dynamometric wrench or from valve controlled hydraulic pressure.

Tapping by cutting is one of the most common operations in manufacturing. This multi-teeth tool, known as a tap, cuts the thread in a hole when the piece has a high added value. The thread quality is ensured when the tap is new or slightly worn, yet when tap wear is high; the quality of profiles exceeds tolerance limits and therefore a defect occurs in the manufacturing line. The aim of this paper is to study the tap wear of titanium nitride coated taps measured on nodular cast iron. The level of tap wear is determined by optical images and the wear mechanics are classified by scanning images and energy dispersion spectroscopy analysis. The results highlight that the critical part in measured taps is between the last chamfer and the first cylinder teeth and, consequently, the thread profile is under-sized. Beside adhesive wear, coating removal and chipping are the main wear aspects during tapping operations

Measuring the clamping forces on cylindrical workpieces is a key factor in the geometrical tolerances of such components, especially if they are slender as the case of thin rings. The lower the clamping force, better tolerances will be achieved, but with the disadvantage of reducing friction and, therefore, increasing the risk of slipping. Therefore, achieving a minimum but safe clamping force is a key factor to control the process. Usually, these parts are made in lathes that have concentric plate clutches and these are fixed mechanically by wrenches or hydraulically through the control of pressure by valves. A simple and economic method is proposed to measure the clamping forces in lathes, although it is necessary the use of a model for the ring deformation. This method allows knowing the clamping force from the torque applied by a dynamometric wrench, or from the hydraulic pressure controlled by valves.

This paper presents a model to estimate the total deformation of turned rings. It takes into account the clamping forces values at different angular positions of the workpiece, and the cutting forces during machining. The model is based on the Castigliano Theorem and uses the Chebyshev polynomials to get a stable solution to the differential equation of deformation. Cutting tests were conducted in a lathe and resultant roundness profiles were measured. The results showed good agreement with the model predictions

Tapping is a widely employed but complex manufacturing process in which a multi-toothed tool, known as a tap, cuts a mating thread when driven into a hole. In this paper, the experiments, statistical analysis and the on-line implementation of a new thread quality monitoring system are presented for a tapping process in high-speed conditions. A multivariate statistical process control chart, for each tap, is presented based on the principal components of the torque directly measured from spindle motor drive. The on-line implementation of the multivariate chart provides tap wear warnings and alarms before the process starts producing unacceptable screw threads. The system is cost-effective since the tapping process can be run automatically without any operator intervention, does not require intrusive sensors, does not result in false negatives (defects) and provides an acceptable number of false positives.

Tapping by cutting is one of the most common operations in manufacturing. It consists of cutting internal threads on the wall of a previously drilled hole by means of a tool called a tap that has cutting edges on its chamfered periphery. When taps are new or slightly worn the process is usually in control and the geometry of the resulting threads on the work piece is correct. But as the tap wear increases the thread geometry deviates progressively from the correct one and eventually the screw threads become unacceptable. The aim of this paper consists on an industrial monitoring application (SPC) to data coming from the current signal of the tap spindle for assessing thread quality. It operates on line and indicates when the tap wear is so critical that, if the process were continued, it would result in unacceptable screw threads. Then the system shows a red light so that the operator could replace the worn-out tap. The system would be very cost-effective since the tapping process could be run without any operator intervention

A tribological test has been designed for analysing the wear behaviour of WC-Co and WC-Ni-Co-Cr alloys in contact with steel at high temperatures (725-775 °C) and pressures (between 113 and 134 MPa). The test, based on a particular block-on-ring configuration, allows to measure wear and friction occurring between a cemented carbide sample and a steel wheel rotating at high speed in absence of lubrication. In general, wear resistance increases with hardness, which, keeping constant the WC grain size, depends mainly on the metallic content of the alloy. Thus, cemented carbides with 15 wt.% of metallic content exhibit lower mass losses than those with 25 wt.% of metal. Nevertheless, when compositions with the same metallic content are compared, it is confirmed that the wear resistance is similar for the compositions based on Ni-Co-Cr binders in spite of their lower hardness. This is likely due to the higher oxidation resistance of these alloys compared to those based on cobalt. Friction coefficients are lower for the compositions with higher metallic content, what is likely due to the formation of continuous oxide tribofilms with lubricant properties.

A method for the identification of the tool parallel axis offset (TPAO) that occurs when the end mill is held in the spindle is developed. The method is based on the analysis of the topography of surfaces machined by peripheral milling and considers the cutter grinding errors. As known from the literature, TPAO causes each cutting edge to be at a different radius from the spindle axis and creates transition bands in the topography of milled surfaces, in which roughness grooves generated by different teeth blend together. In this paper, the TPAO, defined by the distance of the tool axis from the spindle axis and by an angle relating the offset direction to the position of cutting edges, is expressed as a function of the width of the roughness grooves at any height of the transition bands. This expression allows the TPAO to be estimated by measuring the groove widths at only two heights and solving a system of two linear equations. In order to obtain the groove widths, a procedure based on digital image processing is developed. Through this procedure, the groove widths are estimated at more than the two necessary heights without high computational cost. This leads to the resolution of an overdetermined system of linear equations that allows the TPAO to be identified with more accuracy. Finally in order to verify the predictions of the proposed method, a series of cutting tests were carried out. A reasonable agreement between the experimental results and the predicted ones was found. (C) 2010 Elsevier Ltd. All rights reserved.

This paper presents a model for the prediction of heterogeneity bands in the topography of surfaces machined by peripheral milling accounting for tool runout. Ideally, when the tool is clamped in the toolholder, all the cutting edges of the tool are located at a distance equal to the tool nominal radius from the rotational spindle. However, tool runout causes each cutting edge to be at a different radius from the spindle axis and this affects the topography of the milled surfaces. The proposed model includes the effects of two factors that produce tool runout: tool setting error and cutter grinding errors (CGE). The influence of tool setting error on the surface topography in peripheral milling has been widely modelled in the literature in the past but the contribution of CGE has not been investigated so far because these errors were relatively smaller. With the increasing precision of toolholders, the magnitude of both errors is similar and therefore, the influence of CGE on the surface topography can no longer be neglected. In this paper, an expression for the effective radius of the cutting edges taking into account tool setting error and CGE is first derived. Next, a model for the prediction of heterogeneity bands is presented. A detailed study of band formation was carried out that makes it possible to study the influence of tool runout and feed on the band geometry (position and width) and on the roughness variations along the milled Surface. Finally, cutting tests were conducted in order to validate the proposed model by comparing the experimental results with the predicted ones and a good agreement between them was found. (C) 2009 Elsevier Ltd. All rights reserved.