The induction hardening and tempering of gears and critical components is traditionally a hot subject in heat treating. In recent years, gear manufacturers have increased their knowledge in this technology for quality gears.
The performance of metal surfaces can be dramatically enhanced by the thermal process of rapid surface melting and re-solidification (RMRS). When the surface of a metal part (for instance, a gear) is melted and re-solidified in less than one thousandth of a second, the resulting changes in the material can lead to:
Increased wear and corrosion resistance,
Improved surface finish and appearance,
Enhanced surface uniformity and purity, and
Sealing of surface cracks and pores.
The quality of the material used for highly loaded critical gears is of primary importance in the achievement of their full potential. Unfortunately, the role which material defects play is not clearly understood by many gear designers. The mechanism by which failures occur due to material defects is often circuitous and not readily apparent. In general, however, failures associated with material defects show characteristics that point to the source of the underlying problem, the mechanism by which the failure initiated, and the manner in which it progressed to failure of the component.
Increased productivity in roughing operations for gear cutting depends mainly on lower production costs in the hobbing process. In addition, certain gears can be manufactured by shaping, which also needs to be taken into account in the search for a more cost-effective form of production.
Quality gear manufacturing depends on controlled tolerances and geometry. As a result, ferritic nitrocarburizing has become the heat treat process of choice for many gear manufacturers. The primary reasons for this are:
1. The process is performed at low temperatures, i.e. less than critical.
2. the quench methods increase fatigue strength by up to 125% without distorting. Ferritic nitrocarburizing is used in place of carburizing with conventional and induction hardening.
3. It establishes gradient base hardnesses, i.e. eliminates eggshell on TiN, TiAIN, CrC, etc.
In addition, the process can also be applied to hobs, broaches, drills, and other cutting tools.
Helical gear pairs with narrow face width can be theoretically classified into three categories over the contact ration domain whose abscissa is the transverse contact ration and whose ordinate is the overlap contact ratio. There is a direct relation between vibration magnitude and shaft parallelism deviation. To clarify the effect of the tooth deviation types on the vibration behavior of helical gear pairs, performance diagrams on vibration are introduced. the acceleration levels of gear pairs are shown by contour lines on the contact ratio domain. Finally, the performance of gears with bias-in and bias-out modifications is discussed considering the effect of the shaft parallelism deviation with use of the developed simulator on a helical gear unit. It becomes clear that there is an asymmetrical feature on the relation between the vibration magnitude of a gear pair and the direction of each deviation.
Designing a gear set implies a considerable effort in the determination of the geometry that fulfills the requirements of load capacity, reliability, durability, size, etc. When the objective is to design a new set of gears, there are many alternatives for the design, and the designer has the freedom to choose among them. Reverse engineering implies an even bigger challenge to the designer, because the problem involves already manufactured gears whose geometry is generally unknown. In this case, the designer needs to know the exact geometry of the actual gears in order to have a reference for the design.
The market demand for gear manufacturers to transmit higher torques via smaller-sized gear units inevitably leads to the use of case-hardened gears with high manufacturing and surface quality. In order to generate high part quality, there is an increasing trend towards the elimination of the process-induced distortion that occurs during heat treatment by means of subsequent hard finishing.
Traditionally, profile and lead inspections have been indispensable portions of a standard inspection of an involute gear. This also holds true for the worm of a worm gear drive (Ref. 1). But the inspection of the profile and the lead is rarely performed on a worm wheel. One of the main reasons is our inability to make good definitions of these two elements (profile and lead) for the worm wheel. Several researchers have proposed methods for profile and lead inspections of a worm wheel using CNC machines or regular involute and lead inspections of a worm wheel using CNC machines or regular involute measuring machines. Hu and Pennell measured a worm wheel's profile in an "involute" section and the lead on the "pitch" cylinder (Ref. 2). This method is applicable to a convolute helicoid worm drive with a crossing angle of 90 degrees because the wheel profile in one of the offset axial planes is rectilinear. This straight profile generates an involute on the generated worm wheel. Unfortunately, because of the hob oversize, the crossing angle between the hob and the worm wheel always deviates from 90 degrees by the swivel angle. Thus, this method can be implemented only approximately by ignoring the swivel angle. Another shortcoming of this method is that there is only one profile and one lead on each flank. If the scanned points deviated from this curve, it produced unreal profile deviation. Octrue discussed profile inspection using a profile checking machine (Ref. 3).
Material selection can play an important role in the constant battle to reduce gear noise. Specifying tighter dimensional tolerances or redesigning the gear are the most common approaches design engineers take to minimize noise, but either approach can add cost to the finished part and strain the relationship between the machine shop and the end user. A third, but often overlooked, alternative is to use a material that has high noise damping capabilities. One such material is cast iron.