Operating behavior and performance of oil-lubricated plastic gears

Plastic gears and their numerous applications have become an integral part of industrial practice. In particular, the ability to produce large numbers of gears cost-effectively using injection molding techniques is making a significant contribution to growing market shares. Compared to conventional steel materials, however, the material properties of thermoplastics differ fundamentally. In particular, the high temperature dependence of the material properties and the lower strength pose challenges for designers. Against this background, theoretical and experimental studies on the operating and service life behavior of different thermoplastic materials have been conducted and evaluated. In addition to theoretical investigations on the tooth flank load carrying capacity, comprehensive measurements on temperature behavior were carried out and compared to common methods of temperature calculation for plastic gears. Experimental investigations on the tooth flank load capacity by means of back-to-back tests of different materials and their evaluation show the potential of thermoplastic materials for the application in power transmitting drivetrains. This contribution will give an overview of the performed research work and summarizes main results of these studies.

Statistical Analysis for Transmission Error of Gear System with Mechanical and Thermal Deformation Uncertainties

We establish a robust algorithm to analyze the influence of system uncertainties on the transmission error of a spur gear pair under 2D simplification. The algorithm provides a way of generating smooth cutter profiles with machining uncertainties and measuring the thermal deformation through the uncertainties in material properties. Then, it produces realizations of gear tooth profiles based on the analytical method for accuracy and computational efficiency. Numerical investigations show the statistical analysis on the tooth contact analysis by comparing steel and plastic gears. It is worthwhile remarking that the plastic gear is susceptible to the geometric error caused by thermal deformation. Moreover, although the impact of thermal deformation on steel gear may seem slim, it can have a noticeable influence when it exists with mechanical uncertainties together.

A Practical Numerical Approach to Characterizing Non-Linear Shrinkage and Optimizing Dimensional Deviation of Injection-Molded Small Module Plastic Gears

This paper was aimed at finding out the solution to the problem of insufficient dimensional accuracy caused by non-linear shrinkage deformation during injection molding of small module plastic gears. A practical numerical approach was proposed to characterize the non-linear shrinkage and optimize the dimensional deviation of the small module plastic gears. Specifically, Moldflow analysis was applied to visually simulate the shrinkage process of small module plastic gears during injection molding. A 3D shrinkage gear model was obtained and exported to compare with the designed gear model. After analyzing the non-linear shrinkage characteristics, the dimensional deviation of the addendum circle diameter and root circle diameter was investigated by orthogonal experiments. In the end, a high-speed cooling concept for the mold plate and the gear cavity was proposed to optimize the dimensional deviation. It was confirmed that the cooling rate is the most influential factor on the non-linear shrinkage of the injection-molded small module plastic gears. The dimensional deviation of the addendum circle diameter and the root circle diameter can be reduced by 22.79% and 22.99% with the proposed high-speed cooling concept, respectively.

The investigation of wear on three-dimensional printed spur gears

Gears are commonly used in every field of industry as power and motion transmission elements. According to the usage areas, they are manufactured from materials such as steel, aluminium, plastics, cast and bronze. There are different manufacturing methods according to material type. Plastic gears are preferred in textile, automotive and aviation industries where the supported load is low, and corrosion and lightness are considerably important. They work more quietly than metal gears. Plastic gears are manufactured by an injection moulding or hobbing method. The disadvantages of the plastic injection method are high cost of the injection moulds and strength losses in the moulded parts due to the internal clearance faults, whereas the disadvantage of the hobbing method is defects in tooth profiles due to operational faults. In this study, wear strengths of plastic spur gears manufactured via a three-dimensional printer with the fused deposition modelling technique as an alternative manufacturing method were experimentally examined. In the experimental studies, polylactic acid pinion gear manufactured with the three-dimensional printer was subjected to wear tests with St37-2 gear. Wear strengths of plastic spur gears were compared in wear tests performed with Forschungsstelle für Zahnrader und Getriebebau equipment under various loads and rotational speeds. Wear depths that occurred in plastic gears were examined via coordinate measuring machine equipment. As a result of the experimental studies, it is found that wear is increased with the increase of load affecting the gear, and wear is decreased with the increase of rotational speed. As a result of this study, it was shown that plastic spur gears manufactured with three-dimensional printers can be used in areas where lightness and corrosion resistance is important under low loads.

Experimental And Numerical Studies of Shrinkage and Sink Marks On Injection Molded Polymer Gears

Injection molding is an efficient and most economical process employed for the mass production of plastic gears and helps to reduce the processing time and cost required to produce the desired geometry. However, significant process and product qualification of plastic gears face the shrinkage and sink marks issues during cooling and after ejection. In present work, the best gate locations and flow resistance analysis along with a polypropylene (PP) were carried out using Autodesk Moldflow Insight 2019.05. The numerical and experimental study was conducted to evaluate the effect of packing pressure, packing time, and melt temperature on diametric shrinkage, mass, and sink marks of PP gear. The results show that by increasing packing pressure and packing time, the diametric shrinkage decreased but mass increased. However, as the melt temperature increased the diametric shrinkage also increased but the mass decreased. The minimum diametric shrinkage of 0.562% was found in numerical analysis and 1.619% found in an experimental analysis at the same injection molding process parameters. Mostly, the sink marks were observed in the gear surface between hub and dedendum circle.