Assessment of Force-Induced Errors in CNC Turning

This paper describes a procedure to evaluate the force-induced errors occurring in cylindrical turned components. This procedure is based on a model which represents the real-time stiffness of the spindle-bearing system and the rotational clamping stiffness of the component held in a chuck. The stiffness values are determined from a single cutting test in which the deflection of a test bar is measured. The model also takes into account the stiffness of the component and toolpost. The model is validated by comparing the predicted error in the cylindricity of a machined bar with the measured value.     

Process‐Driven Microstructure Control in Melt‐Extrusion‐Based 3D Printing for Tailorable Mechanical Properties in a Polycaprolactone Filament

3D printing techniques are utilized to produce biomaterial scaffolds with porous architectures that enable cell attachment, biological factors, and appropriate mechanical strength. As the basic building block of a scaffold, the individual filaments should have sufficient mechanical properties, comprising high compressive loading, and fracture resistance to mimic the natural tissue organisation. In this contribution, process–structure–property relationships in melt extruded polycaprolactone filaments are investigated by considering crystalline features, tensile properties, and an array of processing parameters. The tensile properties of the filaments are improved significantly with relatively higher screw rotational speed and relatively lower processing temperature resulting in considerable increase in Young's modulus. The favorable properties are attributed to the increased crystal volume fraction and anisotropy. Thus, this study provides initial pathways for the potential control of mechanical properties of bioscaffolds via engineering crystalline structural features in printed filaments.     

Cyberbullying myths and realities

Bullying has long been a concern of youth advocates (e.g., educators, counselors, researchers, policy makers). Recently, cyberbullying (bullying perpetrated through online technology) has dominated the headlines as a major current-day adolescent challenge. This article reviews available empirical research to examine the accuracy of commonly-perpetuated claims about cyberbullying. The analysis revealed several myths about the nature and extent of cyberbullying that are being fueled by media headlines and unsubstantiated public declarations. These myths include that (a) everyone knows what cyberbullying is; (b) cyberbullying is occurring at epidemic levels; (c) cyberbullying causes suicide; (d) cyberbullying occurs more often now than traditional bullying; (e) like traditional bullying, cyberbullying is a rite of passage; (f) cyberbullies are outcasts or just mean kids; and (g) to stop cyberbullying, just turn off your computer or cell phone. These assertions are clarified using data that are currently available so that adults who work with youth will have an accurate understanding of cyberbullying to better assist them in effective prevention and response. Implications for prevention efforts in education in light of these revelations are also discussed and include effective school policies, educating students and stakeholders, the role of peer helper programs, and responsive services (e.g., counseling).     

An Optimum Two-tool Solution for Milling 2½D Features from Technological and Geometric Viewpoints

This paper describes a procedure to determine the optimum pair of tools that can machine a milling feature with soft and/or hard boundaries. The optimum cutting conditions, as well as the actual distances traversed by the two tools, are used in the determination of the total machining cost. In addition to technological constraints such as machine tool power, geometrical constraints including minimum concave radius, bottleneck width and entry distance are determined from the Voronoi diagram. The paper also describes a novel method to determine the stock machined by the larger tool. An example is included to illustrate the method.     

Determination of optimum cutter diameter for machining 2 -O pockets

Tool paths in milling are calculated using user-defined values of the radial width of cut (b) and the cutter diameter (D). When calculating the other cutting parameters, most researchers and practising engineers assume that the ratio of the radial width of cut to the cutter diameter i.e. b/D remains constant over the entire tool path length. However, in practice, when machining pockets and many other features with window-frame type toolpaths, b/D does not remain constant. In this paper, the optimum cutter diameter is chosen following a consideration of the variation of b/D throughout the cutter path. It is shown that while a smaller cutter diameter gives a more favourable variation, it leads to a longer toolpath. Hence the final optimum cutter diameter is a compromise between the increased costs of a larger diameter with a shorter toolpath and the lower costs of a smaller diameter with a longer toolpath.     

The onset of nonlinear viscoelasticity in multiaxial creep of glassy polymers: A constitutive model and its application to PMMA

A physically based, isostructural, constitutive model is described for simulating the onset of nonlinear viscoelasticity in multiaxial creep of glassy polymers, as needed in stress analyses of load-bearing components. In the linear viscoelastic limit, shear response reduces to that of a generalized Maxwell model, while hydrostatic response is Hookean. Nonlinearity enters through Eyring-type rate process kinetics. The equations of the model are solved numerically using a pseudo-linear approximation through each time step, leading to an incremental equation for stress that would be convenient for use in finite element analyses. The model and its assumptions were tested using tension, shear and combined tension/shear creep experiments on well-aged poly(methyl methacrylate) at 70°C. Reproducibility tests confirmed the assumption of constant glass structure for strains up to ～ 1.5 × 10^?2. Shear and pressure activation volumes were obtained by fitting the dependence of the shear compliance on stress invariants. The data showed unequivocally that shear activation volumes vary with log(relaxation time), and excellent agreement was obtained for a linear variation, consistent with the “compensation rule” of polymer thermo-viscoelasticity. The activation volumes are large (many monome units), indicating the cooperative nature of the elementary flow process. Interestingly, they are of the same order as those applying to yield and plastic flow. Although the model finds success in simulating creep, it fails to describe so accurately the strain recovery on unloading. Possible explanations are suggested.     

Estimation of biometric parameters from cattle rump using free-hand scanning and a 3D data processing algorithm

The quantity and quality of phenotypic data recovered from farm animals became a bottleneck for breeding programmes, and new tools are required to overcome this problem. This study evaluated the use of a portable structured light scanner and a 3D modelling to recover biometric information of the rump region in cattle. Virtual 3D models were created based on coordinates extracted from the points-cloud obtained through reverse engineering. A MATLAB algorithm was implemented to identify reference points, which were used to automatically calculate rump width, length, and angle. Results were compared to measurements performed directly in vivo and in the 3D models. There was no difference among rump parameter values obtained among biometry methods, though an interaction with body condition score was observed for rump width. The algorithm allowed evaluating correlations within biometric parameters, as well as extracting silhouettes of selected areas to evaluate differences caused by the mobilisation of subcutaneous fat.     

A plasma-assisted bioextrusion system for tissue engineering

A challenge for tissue engineering is to produce synthetic scaffolds of adequate chemical, physical and biological cues effectively. This paper describes a plasma-assisted bio-extrusion system to produce functional-gradient scaffolds; it comprises pressure-assisted and screw-assisted extruders, and plasma jets. This paper also describes how the system conducts plasma surface modification during the polycaprolactone scaffold fabrication process. Water contact angle and in vitro biological tests confirm that the plasma modification alters the hydrophilicity properties of synthetic polymers and promotes proliferation of cells, leading to homogeneous cell colonization. The results suggest this system is promising for producing functional gradient scaffolds of biomaterials.     

Modelling the pressure die casting process with the boundary element method: Steady state approximation

This paper describes a model which can predict the temperatures on the cavity surfaces of a die. The time varying boundary conditions are averaged so that the process can be modelled as a steady state problem. Since the model considers only thin components, it is reasonable to assume that the melt has totally solidified before ejection, and therefore the quantity of heat energy entering the die over the casting cycle can be estimated. This and other assumptions relating to the boundary conditions also enable the value of thermal resistance between the melt and the die to be estimated. Under certain conditions, subcooled nucleate boiling takes place in the cooling channels of the die. An iterative procedure is used to take account of this, which involves the repeated calculation of global heat transfer coefficients for the cooling channels, with the criteria that the total energy transferred through the channels is equal to that transferred due to boiling and convection. The boundary element method is used to predict the cavity temperatures. In die casting, only the temperatures on the cavity surfaces are of interest since the surface quality of a component is related significantly to the temperature distribution over the cavity. Since only thin components are considered herein, it is not necessary to model the solidifcation process and discretize the cast. These factors make the BEM ideally suited for the work described in this paper. To verify the model, the predicted temperatures for two components are compared with experimental values measured using thermocouples and a thermal imaging camera. It was found that there is fairly good agreement between the two sets of results.     

Influence of the process variables on the temperature distribution in orthogonal machining using the finite element method

The temperature distributions in the workpiece, tool and chip during orthogonal machining are obtained numerically using the Galerkin approach of the finite element method for various cutting conditions. The effect of a number of process variables such as speed, feed, coolant, rake angle, tool flank wear and tool material on the temperatures has been investigated.