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abstractGear characteristics are strongly dependent on the quality of the tooth edge of the gears. Therefore,meth-ods for removing defects such as burrs and pits of gears are very important. Burrs and pits are particularlydifficult to remove from small gears due to the small dimensions of the tooth grooves. In addition, theequipment for the removal process should be simple and lowin cost. In the present study, amethod usinga gear-shaped tool made from glass-fiber-reinforced plastic (GFRP) is developed for removing burrs andpits from small gears. A manufacturing method for the GFRP gear-shaped tool is proposed and it wasconfirmed that a conventional hobbing machine and a carbide hob can easily manufacture such a toolwithout defects. The ability of the proposed tool to remove burrs and pits is evaluated experimentallyand the results demonstrate that the burrs and pits of awork gear can be effectively removed by using theproposed toolwith simple equipment based on a lathe. This toolwas then applied to themass productionof gears, and it was confirmed that this tool has the durability to remove the burrs of 16,797 work gears.© 2010 Elsevier B.V. All rights reserved. 1. IntroductionCompact geared motors are used in a wide variety of appli-cations, such as industrial manufacturing, railways, and officeequipment.50904
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These geared motors must be compact, lightweight,and highly reliable. Recently, geared motors have been introducedintomedical equipment and domestic electrical appliances. In suchapplications, in addition to meeting the abovementioned criteria,the geared motors must be noiseless.A compact geared motor consists of a motor and a gearhead.The gearhead is a reduction gearmechanismcomposed of the smallgears of micromodules (hereafter, referred to as small gears). Suchgears must be manufactured with a high degree of precision torealize a noiseless geared motor. Currently, high-precision hob-bing can be applied to small gears. However, hobbed small gearshave the problems depicted in Fig. 1, namely burrs (Fig. 1(a) and(b)) and pits (Fig. 1(c)) at the edge of the gear tooth. Gillespiereports that burrs are generated by hobbing or the shaping pro-cess of a gear and the burr deteriorates the gear quality (Gillespie,1999). These burrs and pits may only be 0.01mm in size but arerelatively large compared to the size of small gears. Thus, thesedefects strongly affect the gear strength, vibration, and noise. Gille-spie and Blotter define four types of burrs: Poisson burr, rolloverburr, tear burr and cut-off burr (Gillespie and Blotter, 1976). In hobbing, rollover burrs are formed at the side of a tooth, as shownin Fig. 1(a). In the manufacture of gears, the rollover burr gener-ated in the hobbing process is usually removed by a deburring toolinstalled in the hobbing machine or a chamfering machine witha disk-shaped whetstone, as shown in Fig. 2(a) (Gillespie, 1999).However, this deburring process generates remaining burrs or newburrs as shown in Figs. 1(b) and 2(c). In the study of burr forma-tion in face milling, Kishimoto et al. (1981) define two types ofburrs: primary burr and secondary burr. The primary burr is theformed normal rollover burr, and the secondary burrs are the oneshort in height that is generatedwhen the rollover burrs separated,and the remaining one on the edge. In the case of gear, for exam-ple,when a tooth edge is chamferedwith a disk-shapedwhetstone(Fig. 2(a)) (Gillespie, 1999), new secondary burrs are generated inthe chamfered region (Fig. 2(b) and (c)). In the removal process ofburr of gear, the secondary burrs protrude toward the tooth grooveside in many cases and are difficult to remove. Such secondaryburrs are removed using a nylon/abrasive filament brush (Fig. 2(d))(Stango, 2001). However, in the case of small gears, burrs oftenremain near the roots of the teeth, as shown in Fig. 2(e), even afterusing a nylon/abrasive filament brush. This is because the toothgroove is narrow, preventing the brush from reaching the roots ofthe teeth.In addition to the secondary burrs, pits are a problem. A pitis composed of a dent and projection due to plastic deforma-tion that is generated when striking another object (Takazawaand Kitajima, 2008). Kawasaki et al. (1984) devised a method thatcrushes pits by applying three gear-shaped vanishing tools. This method has been used in practical applications of automotive gears.However, it is unclear whether this method is effective for smallgears.Several other reports describe gear deburring. However, thesefocus on normal-sized gears, such as automotive gears; to thebest of our knowledge, no studies have investigated the meth-ods for removing burrs and pits from small gears.