•A new approach is proposed to predict the temperature of spur gear transmissions.•It is suitable for transmissions with any gear geometry, material or lubrication.•The new approach can be applied ...under steady state and transient thermal conditions.•The performance of the approach is illustrated with several numerical examples.•The accuracy of the results is proved by comparing them to experimental results.
This article describes a new numerical approach to determine the temperature field of polymer spur gears during their operation. The approach is based on an uncoupled procedure in which a mechanical problem is solved to determine the amount of heat that is generated by friction during the meshing of the gears, and then this heat is considered as a thermal load to perform a thermal analysis of a finite element model of the transmission.
The amount of heat generated by friction is determined from the results of a numerical loaded tooth contact analysis of the transmission, which is based on the finite element method. The generality of the finite element method enables this approach to be applied to any kind of spur gear transmission, regardless of the geometry and the material of the gears and lubrication conditions.
The resulting approach is applied to determine the temperature field of a spur gear transmission where polymer and metallic gears are combined, under several different operating conditions. The results obtained from this approach are compared to those obtained from experimental analyses, showing a good degree of similarity between them.
•Developed thermo-mechanical model produces results consistent with exp. measurements.•Model enables the consideration of any type of spur gear tooth profile.•High-speed thermography offers detailed ...insight into thermal response of polymer gears.•Tooth flash temperature gradient quickly dissipates after meshing cycle completion.•Geometric tolerance deviations influence the temperature rise on a given tooth pair.
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The presented work is focused on the development of a comprehensive thermo-mechanical model for predicting the temperature rise in thermoplastic polymer spur gears with any desired profile geometry while running. The specific constitutional behavior of thermoplastics influences the gear-meshing pattern, which can deviate substantially from ideal gear meshing, as typically exhibited by metal gears in moderate-loading conditions. Taking this aspect into account is of paramount importance if realistic temperature-rise predictions are to be made. The thermal response of the considered gear pair is studied thoroughly from both the analytical and experimental standpoints. Good agreement was found between the results of the model and the experimental measurements performed using a high-speed thermal imaging infrared camera, although it was also observed that the real-life temperature rise can increase noticeably if large geometric tolerance deviations from the ideal profile geometry are present. The presented experimental approach also offers the possibility to observe the temperature rise inside and outside the meshing cycle.
•The injection molding lunker defect is detected by X-ray CT and the polymer gear fatigue model considering lunker is established considering the thermal-elastic-plastic constitutive behavior.•The ...effects of loading condition and the lunker defect on the POM gear fatigue life are studied numerically and experimentally.•The failure mode competitive mechanism of POM gears reveals that the final failure mode is more sensitive to the loading condition, but the presence of injection molding lunker rises the possibility of tooth root breakage.
Polymer gears manufactured with injection molding have been widely used in many industries, but the unavoidable injection molding lunker defects limit the loading capacity and the further use of polymer gears in power transmissions. In this work, injection molding lunker defects are detected by X-ray CT and a polymer gear fatigue model with lunker defect is established considering the thermal-elastic-plastic constitutive material behavior. Durability tests are also conducted, and the fatigue lives correspond well with simulation results. Results reveal that the lunker defect jeopardizes the loading capacity of tooth root under medium or heavy loading conditions, while the tooth flank failure is significantly influenced by the loading condition.
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Heat convection is an important phenomenon in the process of cooling polymer spur gears running in dry conditions, which ultimately affects the strength of the gears. In order to gain some insight ...into this phenomenon, a numerical heat convection model for polymer spur gears is proposed in this work, which is based on a detailed CFD simulation of the gears in operating conditions and it allows us to investigate the heat convection through their external surfaces.
The performance of this numerical model is illustrated with several examples, in which a parametric study has been conducted to observe the variation of the heat transfer coefficients with the face width and the angular speed of the gears. The results obtained from this parametric study are compared to those obtained from a representative classical heat convection model, observing that the relative differences between them in terms of heat transfer coefficients can be as high as 125%.
Finally, a new optimized heat convection model for polymer spur gears running in dry conditions is proposed, in which the convective heat transfer coefficients for the external surfaces of the gears are calculated from empirical equations based on the Newton’s law of cooling. This optimized model has lower computational cost than the numerical one, while it provides an important increase of the accuracy of the classical heat convection models, reducing the maximum relative differences to 10%.
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•In-depth study of the heat convection (HC) in dry-running polymer gear transmissions.•Proposition of a numerical HC model based on a CFD analysis of the transmission.•Variety of numerical examples with variations in the face width and angular speed.•Comparison of obtained results with those calculated from classical HC models.•Proposition of an optimized HC model that enhances the accuracy of classical models.
•Definition of tooth surface topologies in plastic-metal helical gear drives.•Proposition of a FE model for the loaded tooth contact analysis of the transmission.•Proposition of a FE model for the ...steady state thermal analysis of the transmission.•Performance of a parametric study to assess the impact of contact pattern design.•Improvement of the durability and running performance of the transmission.
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This article describes an investigation that has been conducted to assess the effects of the contact pattern design on the mechanical and thermal behaviors of plastic-steel helical gear drives. The maximum contact pressure, frictional power loss, transmission error function and operating temperature are determined for different designs of the pinion tooth surfaces. Several numerical examples based on loaded tooth contact analyses and steady-state heat transfer analyses are carried out considering different types of micro-geometry modifications of the involute tooth surfaces. The obtained results show that an appropriate design of the pinion tooth surfaces can help reducing the maximum contact pressure and the maximum operating temperature, increasing the durability of the transmission. The frictional power loss and the peak-to-peak transmission error can be diminished, improving the performance of the transmission and increasing its efficiency. Also, it has been shown that the design of the pinion tooth surfaces can provide some capability to the transmission to absorb angular misalignments.
The use of 3D printing to manufacture nylon polymer gears is evaluated in this paper. More specifically, Nylon spur gears were 3D printed using Nylon 618, Nylon 645, alloy 910 filaments, together ...with Onyx and Markforged nylon proprietary materials, with wear rate tests performed on a custom-built gear wear test rig. The results showed that Nylon 618 provided the best wear performance among the 5 different 3D printing materials tested. It is hypothesised that the different mechanical performance between nylon filaments was caused by differences in crystallinity and uniqueness of the Fused Deposition Modelling (FDM) process. SEM (Scanning Electron Microscopy) revealed dramatically different wear behaviour for the 3D printed gears when compared to literature reports of injection moulded gears. Monitoring with a thermal camera during wear tests was used to analyse the thermal performance of gears during wear tests and together with SEM was used to analyse gear failure mechanisms. The performance results showed that gears 3D printed using Nylon 618 actually performed better than injection moulded nylon 66 gears when low to medium torque was applied.
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•Spur gears produced using 3D printing and a selection of nylon filaments to determine differences in wear behaviour.•Somewhat unexpectedly, 3D printed Nylon 618 gears performed better than injection moulded gears when torque applied below 12Nm.•The causes of different mechanical performance between nylon 3D printing filaments has been investigated.
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.
Analysis on how the mould temperature affected peak melting points and crystallinity were then carried out using differential scanning calorimetry (DSC). These revealed that crystallinity improved as the mould temperature was increased from 22 °C to 65 °C. Gears produced at similar cooling temperatures were then meshed on a gear test rig and run at 1000 rpm, using different torque loadings. Their wear rates, and modes of failure were then analysed, and comparisons were made to ascertain how the differing mould temperatures employed during the injection moulding manufacturing process affected their wear characteristics. Topographical analysis of worn gear teeth was performed using scanning electron microscopy (SEM). It was noted that gear tooth wear and failure was dependent on the mould temperature employed during the manufacturing process. Gears produced at 65 °C showed improved tooth surface wear resistance at lower loads (0.5 Nm and 1 Nm) compared to those produced at 22 °C, but were more likely to fail through tooth fracture at the pitch line due to excessive material removal. Gears produced at lower mould temperatures, on the other hand, exhibited better wear resistance for higher loads (3 Nm and 4 Nm), compared to those produced at higher mould temperatures, and were more likely to fail due to material flow. The results show a correlation between mould temperature, crystallinity, and gear performance. Based on wear rate responses of gears produced at differing mould temperatures to the application of varying torque loadings, a Mould Temperature to Torque Reference Chart for HDPE is presented.
•HDPE gear performance is affected by injection moulding input parameters.•The mode of gear failure is dependent on mould temperature and torque loading.•At 0.5 Nm and 1 Nm, wear rates decrease as mould temperature is increased.•At 2 Nm, 3 Nm and 4 Nm, wear rates increase with mould temperature.
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•A high-power-density design method via adaptive NSGA-III and surrogate sub-models for polymer gear systems is outlined.•The key factors affecting the operating performance of polymer ...accessory gearbox are explained.•Compared with metallic design scheme, the polymer scheme achieves a 49 % weight reduction and power density with 22.5 kW/kg.
There is a growing and prevalent trend in the power transmission field of high-performance polymers replacing metallic materials given the strict light-weight requirement. Polymer gears exhibit a low elasticity modulus, high-temperature sensitivity, and increased geometric design flexibility, presenting technical challenges to the straightforward application of metallic design methods to polymer gear systems. This study is centred on the development of a high-power-density polymer gear transmission system for the accessory unit of a gas turbine engine, utilising an adaptive NSGA-III algorithm and surrogate sub-models. A comprehensive assessment indicator for the operating performance of the transmission system is suggested, encompassing gear strength, bearing temperature, and shaft torsional stiffness. The model made it possible to simultaneously optimise forty-six structural parameters, including gear tooth module, web thickness, and bearing clearance. In contrast to the original steel design scheme, the optimised polymer gear transmission system indicated a 49% reduction in weight and a 1.96-fold increase in power density. This presents a method for substituting steel with polymers for effective power transmission.
This study investigates the potential of three different thermoplastic materials viz. Acrylonitrile Butadiene Styrene (ABS), High Density Polyethylene (HDPE) and Polyoxymethylene (POM) to be used in ...plastic gearing applications. The gears are manufactured by injection molding process. Thermal and wear behavior of these gears are examined at different torque levels of 0.8, 1.2, 1.6 and 2.0 Nm along with different rotational speeds of 600, 800, 1000 and 1200 rpm. Also, steady state analysis of the gears is carried out at a torque of 1.4 Nm and a rotational speed of 900 rpm to measure the reduction in the gear tooth, durability and failure modes occurring in these gears. ABS gear fails due to excessive wear of the teeth whereas HDPE gear failure is caused by the cracking at the root of gear teeth. ABS and HDPE gears complete 0.5 and 1.1 million cycles, respectively before failure whereas POM gear completes 2 million cycles without any sign of failure.
•Thermal and wear behavior of polymer based gears have been investigated.•Three different materials viz. ABS, HDPE and POM are used for manufacturing of gears.•Performance of these gears has been compared to verify their potential in gear applications.•Durability and failure modes occurring in these gears have also been investigated.
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