An investigation of misalignment effects on the performance of acetal gears

This paper concentrates on the effects of misalignment on meshing behaviour of acetal gears as hardly any misalignment investigations on polymer gears in the existing literatures. The experimental results show that the wear of acetal gears is insensitive to radial and axial misalignments but sensitive to yaw and pitch misalignments which degrade the conjugate contact action. Yaw misalignment leads to ‘scoop’ wear marks near tooth pitch points. Pitch misalignment causes ‘superimposed palisade’ wear marks and micro cracks near tooth roots. Compared with metal gears, the effects of small pitch angle on acetal gears are insignificant which may be linked closely to polymer's low elastic modulus. Strikingly different wear striations and various debris morphologies are observed by using scanning electronic and optical microscope (SEM, OM) and misalignment effects can be noted

Minimization of shrinkage in injection molding process of acetal polymer gear using Taguchi DOE optimization and ANOVA method

Injection molding is one of the very widely used manufacturing process for polymer materials due to its high production rate and low process cost. However, polymer parts manufactured through injection molding process are prone to various defects such as geometrical defect, shape related defect and visual defects. All designers work hard to minimize these defects and increase the quality of the molded part to satisfy the end application through the molding process parameters optimization with help of design of experiments (DOE). The main objective of this paper is to study the effect of various injection molding process parameters on the volumetric shrinkage of a acetal polymer gear part, identifying the most significant parameter causing high volumetric shrinkage and optimizing the process parameters through Taguchi orthogonal array design and analysis of variance (ANOVA) method. The acetal polymer gear injection molding process is simulated using Moldflow adviser ultimate simulation software and the change in volumetric shrinkage is analysed for various process parameters combination. Taguchi optimization and ANOVA method were found to be very useful in determining the most significant molding process parameter that affect volumetric shrinkage and optimizing the control parameters for achieving minimum part shrinkage

Zigzag edge modes in Z2 topological insulator: reentrance and completely flat spectrum

The spectrum and wave function of helical edge modes in Z_2 topological insulator are derived on a square lattice using Bernevig-Hughes-Zhang (BHZ) model. The BHZ model is characterized by a "mass" term M (k) that is parameterized as M (k) = Delta - B k^2. A topological insulator realizes when the parameters Delta and B fall on the regime, either 0 < Delta /B < 4 or 4 < Delta /B < 8. At Delta /B = 4, which separates the cases of positive and negative (quantized) spin Hall conductivities, the edge modes show a corresponding change that depends on the edge geometry. In the (1,0)-edge, the spectrum of edge mode remains the same against change of Delta /B, although the main location of the mode moves from the zone center for Delta /B < 4, to the zone boundary for Delta /B > 4 of the 1D Brillouin zone. In the (1,1)-edge geometry, the group velocity at the zone center changes sign at Delta /B = 4 where the spectrum becomes independent of the momentum, i.e. flat, over the whole 1D Brillouin zone. Furthermore, for Delta/B < 1.354..., the edge mode starting from the zone center vanishes in an intermediate region of the 1D Brillouin zone, but reenters near the zone boundary, where the energy of the edge mode is marginally below the lowest bulk excitations. On the other hand, the behavior of reentrant mode in real space is indistinguishable from an ordinary edge mode.Comment: 19 pages, 33 figure

Friction characteristics of polymers applicable to small-scale devices

A review of the critical features of a published micro-tribometer design, which was intended to improve on the dynamic response of typical commercial instruments, leads to its use with a modified technique. Data post-processing is introduced to partially compensate for some potential systematic errors. This approach is demonstrated by a preliminary study of the coefficient of friction (CoF) in sub-mm length reciprocating sliding motion for samples of polytetrafluoroethylene (PTFE) and an R11 acrylic formulation made by micro-stereo-lithography, with an SiO2-coated silicon wafer used as a control sample. Testing covered normal loads in the region of 10 mN–60 mN, at scan frequencies up to 9 Hz, corresponding to sliding speeds in the broad region of 1 mm s−1. While the control samples closely adhered to Amonton's laws over all the test parameter ranges, the CoFs of the two polymers showed contrasting patterns of dependence on sliding speed and repetition rate. Such results have implications for how polymers might be used effectively in future designs for small mechanical systems. They indicate a clear need for further development of the testing methods and large-scale studies of tribological behaviour and its underlying mechanisms under the specified micro-scale conditions

An extension of the entropic chaos degree and its positive effect

The Lyapunov exponent is used to quantify the chaos of a dynamical system, by characterizing the exponential sensitivity of an initial point on the dynamical system. However, we cannot directly compute the Lyapunov exponent for a dynamical system without its dynamical equation, although some estimation methods do exist. Information dynamics introduces the entropic chaos degree to measure the strength of chaos of the dynamical system. The entropic chaos degree can be used to compute the strength of chaos with a practical time series. It may seem like a kind of fnite space Kolmogorov-Sinai entropy, which then indicates the relation between the entropic chaos degree and the Lyapunov exponent. In this paper, we attempt to extend the defnition of the entropic chaos degree on a d-dimensional Euclidean space to improve the ability to measure the stength of chaos of the dynamical system and show several relations between the extended entropic chaos degree and the Lyapunov exponen

A physical investigation of wear and thermal characteristics of 3D printed nylon spur gears

For particular applications such as automotive and aerospace engineering, polymer gears have unique advantages over metal gears, such as: low cost and weight; high efficiency; quietness of operation; functioning without external lubrication; etc. The characteristics of wear and thermal behaviour of injection moulded gears have previously been studied [1], however, additive manufacturing (AM) and 3D printing processes have become increasingly popular for production of polymer components. It is generally understood that 3D printing is cost effective if production volumes are below 1000 units in comparison with plastic injection moulding [2]. The technology has been applied in wide range of industries, including the automotive, aerospace, medical and architectural industries [3]. The nature of 3D printing means that the process is inherently linked to the materials used and each 3D printing technology has a subset of materials that it is compatible with. For Fused Deposition Modelling (FDM) for instance there are many different materials available on the market including polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), polycarbonate (PC), nylon and many others [4]. Due to the increased interest in 3D printing there is an increasing amount of research regarding the direct mechanical properties and thermal properties of 3D printed materials and their modification. Leigh et al. [5] introduced a low-cost conductive composite material for 3D printing of electronic sensosr. Christ et al. [6] increased the elastic strain of polyurethane through addition of multi wall carbon nanotubes. Blok et al. [7] claimed that adding continuous fibers could further increasing the tensile strength compared with carbon fibre nylon composites. Kalin et al. [8] Claimed that gear performance and durability could be affected by thermal properties with the result showing an increase in operating temperature could decreasing the life cycle of the gear. Hu and Mao [9] investigated misalignment effects on acetal gears together with wear behaviour, with the results demonstrating that acetal gears were most sensitive to pitch misalignment

Thermal simulation modeling of a hydrostatic machine feed platform

Hydrostatic guideways are widely applied into precision and ultra-precision machine tools. Meanwhile, the oil film heat transfer causes thermal disturbance to the machine accuracy. Therefore, it is necessary to study the mechanism of the oil film heat transfer and the heat-transfer-reducing method to improve the machine accuracy. This paper describes a comprehensive thermal finite element (FE) simulation modeling method for the hydrostatic machine feed platform to study methods of reducing machine thermal errors. First of all, the generating heat power of viscous hydraulic oil flowing between parallel planes is calculated based on the Bernoulli equation. This calculation is then employed for the simulation load calculations for the closed hydrostatic guideways, which is adopted by the hydrostatic machine feed platform. Especially, in these load calculations, the changing of oil film thickness (resulted from external loads) and the changing of oil dynamic viscosity (influenced by its temperature) are taken into account. Based on these loads, thermal FE simulation modeling of the hydrostatic machine feed platform is completed to predict and analyze its thermal characteristics. The reliability of this simulation modeling method is verified by experiments. The studies demonstrate that the hydrostatic machine thermal error degree is determined by the oil film heat transfer scale, and this scale is mainly influenced by the relative oil supply temperature to ambient temperature (quantitative comparison of oil supply temperature and ambient temperature). Furthermore, the reduction of the absolute value of this relative oil supply temperature can reduce the oil film heat transfer scale and improve the machine accuracy

A differentiated multi-loops bath recirculation system for precision machine tools

Traditional bath recirculation cooler for precision machine tools always has the uniform and open-loop cooling strategy onto different heat generating parts. This causes redundant generated heat being transferred into the machine structure, and results in unsatisfactory thermal errors of precision machine tools. For the solution of this problem, this paper presents the differentiated multi-loops bath recirculation system. The developed system can accomplish differentiated and close-loop cooling strategies onto machine heat generating parts during its operation. Specially, in order to illustrate the advantages of this system, constant supply cooling powers strategy is presented with its applications onto a certain type of built-in motorized spindle. Consequently, advantages of the proposed strategy based on the differentiated multi-loops bath recirculation system are verified experimentally in the environment within consistent temperature (TR = 20 ± 0.3°C). Compared with room temperature tracing strategy based on the traditional bath recirculation cooler, the constant supply cooling powers strategy is verified to be advantageous in spindle temperature stabilization and thermal errors decrease

The effects of cooling rate (mould temperature) on HDPE gears produced through injection moulding

The effects of mould temperature (cooling temperature) on molten HDPE (Hostalen GC 7260) during manufacture, is evaluated in this paper. HDPE gears were produced at varying mould temperatures using Injection Moulding. Optimised injection values for melt temperature, injection volume, hold pressure, and hold time were obtained, and then held constant while the mould temperature was altered