Use of process signals for tool wear progression sensing in drilling small deep holes

Detailed knowledge about the relation between wear progression of a cutting tool and the cutting forces generated is of paramount importance for the development of a tool condition monitoring strategy. This paper discusses the changes in the different process signals with progressing tool wear of small diameter twist drills (D=1.5 mm), when drilling boreholes having a depth of 10 times the diameter in plain carbon steel using MQL. The effect of different wear patterns on the process signals is presented. Furthermore, several features, which evolve over the life of the drills, are identified and extracted from the process signals. Knowledge about the evolution of these features can support the user to determine the final tool life stage, so that the drill can be replaced before the final fracture occurs.     

Flexibility of rectangular beams with abrupt changes of section

The usual strength of materials approach to the calculation of deflexions of stepped beams can incur errors if applied to stepped beams with large and abrupt changes of section. After initial comparison with experimental results, the finite element displacement method was used in an investigation into the properties of such beams, particular attention being paid to the relationships between the geometry and the centre line deflexion curves. Data are presented so that for a beam of any geometry and any loading condition, the centre line deflexion curve can be calculated by using simple bending relationships in conjunction with an equivalent variable second moment of area.     

Investigating the feasibility of DLC-coated twist drills in deep-hole drilling

The ideal coating for twist drills used to drill deep holes should have both a high hardness and a smooth surface. The latter property is considered to ease chip evacuation through the drill’s chip flutes and, therefore, reduces the risk of chip clogging and possible premature drill fractures. For this reason, diamond-like carbon (DLC) appears to be a well-suited type of coating. This paper presents the results of cutting tests using DLC-coated HSS and cobalt-HSS twist drills when drilling deep holes of diameter 1.5 mm into plain carbon steel. Their capability to extract swarf from the borehole as well as their tool lives were investigated and compared to uncoated and TiN- and MoS₂-coated drills. Although the DLC-coated drills showed a very good swarf disposal capability, they did not exhibit a longer tool life when compared to off-the-shelf drills.     

Novel cooling channel shapes in pressure die casting

The pressure die casting involves die designs incorporating cooling channels positioned to facilitate the controlled extraction of energy from a solidifying casting. It is now known that subcooled nucleate boiling can occur in cooling channels and this paper is concerned with novel cooling channel shapes that are optimized to promote and enhance this boiling and thus reduce casting times. Shape sensitivity analysis is applied to a boundary element model using the material derivative adjoint variable technique. Mesh node positions on the cooling channels are used as the design parameters. The sensitivities are used in a conjugate gradient non‐linear optimization routine. It is shown that with this approach cooling channels can be designed to maximize boiling heat transfer whilst at the same time allow some degree of control of spatial temperature variation over the die cavity surface. Simulation and experimental results are presented for a traditional die and an optimized die. A 60 per cent reduction in cycle time is achieved with the optimized die. Copyright © 2001 John Wiley & Sons, Ltd.     

Structural Evolution of PCL during Melt Extrusion 3D Printing

Screw‐assisted material extrusion technique is developed for tissue engineering applications to produce scaffolds with well‐defined multiscale microstructural features and tailorable mechanical properties. In this study, in situ time‐resolved synchrotron diffraction is employed to probe extrusion‐based 3D printing of polycaprolactone (PCL) filaments. Time‐resolved X‐ray diffraction measurements reveals the progress of overall crystalline structural evolution of PCL during 3D printing. Particularly, in situ experimental observations provide strong evidence for the development of strong directionality of PCL crystals during the extrusion driven process. Results also show the evidence for the realization of anisotropic structural features through the melt extrusion‐based 3D printing, which is a key development toward mimicking the anisotropic properties and hierarchical structures of biological materials in nature, such as human tissues.     

An improved procedure for solving transient heat conduction problems using the boundary element method

In employing the boundary element method to solve transient heat conduction problems, domain integrals need to be calculated. These integrals can be calculated either by directly discretizing the domain, or indirectly by utilizing a time-marching scheme which requires the time integrations to be evaluated from the initial time. Although the second approach overcomes the need for domain discretization, it has the disadvantage of requiring large storage and CPU time for increasing number of time steps. This paper is concerned with a procedure which approximates the domain integrals without the need for domain discretization. The time-marching scheme is employed so that the domain integrals can be calculated at a particular time with a known weighting and temperature distribution. These integrals can then be utilized to approximate similar domain integrals with a different weighting. It is shown that the method proposed dramatically reduces the storage requirements and CPU time, even for a small number of time divisions.     

Determination of the radial width of cut and cutting modes in milling

This paper describes a method to calculate the variation in the radial width of cut which occurs when the centre of a milling cutter follows the toolpath segments generated by a postprocessor. This variation is approximated by a stepped curve, thus enabling the toolpath segment to be divided into subsections, the radial width remaining constant over each subsection. The method also enables the cutting modes to be determined. The variation in the width of cut is obtained by performing a 2-D Boolean union between the area swept by the cutter when traversing the current segment and the area already machined. As an example, the actual widths of cut are calculated for the toolpaths for machining a pocket. The example clearly demonstrates that the actual widths of cut vary over a wide range and are very different from the value used to calculate the toolpaths. In fact, for the example considered, slotting occurs over 40% of the distance travelled, and only 10% of the actual widths of cut are approximately equal to the original value used for toolpath generation.     

Automatic tool selection for rough turning operations

A method of automatically selecting cutting tools for rough turning operations on a CNC lathe is presented. While the selection procedure can deal with various economic objectives, only the minimum cost per component is considered in this paper. Selection is made from an appropriate tool library and in order to reduce the search time a heuristic method is employed.

The cost of machining with a given tool is estimated following the determination of the cutting conditions consistent with the constraints acting on the process. From a detailed examination of the constraints it is possible to ascertain whether the next tool in the library will give improved cutting conditions and the possibility of a lower cost. This procedure eliminates the need for an exhaustive search of the library and results in a very fast and efficient algorithm.

The results of ten tool selections are presented. In all cases the computation time for the heuristic approach was less than 5% of that for the exhaustive search. In eight out of ten cases the heuristic method selected the same tool as the exhaustive search; in the two cases where the tools selected were different, those selected by the heuristic method produced only a marginal increase in the operation cost.     

Changes in adolescent online social networking behaviors from 2006 to 2009

As online social networking has become an immersive and pervasive phenomenon, traditional considerations and expectations of personal privacy have been drastically altered. This paradigmatic change has led to adolescents possibly making themselves vulnerable to embarrassment, censure, damage to one’s name or reputation, or even victimization by others because of unwise postings or revelations online. The current study sought to determine the extent to which adolescent information disclosure on MySpace.com has changed between 2006 and 2009. We found significant changes in the nature of personal content made publicly available across the two time points and a trend in which teens are being increasingly more selective and discrete when it comes to what they share and with whom they share it.