Development of Multi-grit cBN Grinding Wheel for Crankshaft Grinding

A crankpin, part of a crankshaft, has a complex profile that is difficult to grind. The process often causes challenges such as excessive heat on the crankpin sidewall and wheel wear on the radius, causing reduced dressing interval. Different solutions were proposed to overcome these challenges, mainly focusing on the process, i.e. grinding strategies. However, the work presented in this thesis is concerned with optimising the superabrasive grinding wheel.A novel analytical assessment framework was developed for evaluating grinding wheel performance that can account for the effects of grit properties and dressing conditions on the wheel topography and, in turn, grinding performance. Based on the model of cutting and sliding grinding force components, a set of performance indicators were derived and then used to evaluate the effect of the wheel topography on the grinding process. Results showed that grit toughness, thermal stability, size and concentration affect the intrinsic specific grinding energy via grit protrusion and sliding component via wear flat area. On the other hand, the grit shape only affects the wear flat area but maintains the intrinsic specific grinding energy regardless if the grit has a higher or lower aspect ratio (blockier or elongated). To complement grinding performance information, wear was evaluated via grinding and lapping tests. The analyses revealed that wheels containing grits with a higher aspect ratio (elongated grits), lower toughness, lower concentration, or smaller size generate lower grinding forces; however, they wore faster. On the other hand, wheels featuring grits with a lower aspect ratio (blocky grits), higher toughness, higher concentration or coarser grit had the opposite effect. They generated higher forces and wore slower, exhibiting longer tool life. Findings from laboratory-based trials resulted in two crankpin wheel designs. One aimed to reduce heat generation, while the other targeted less wheel wear. Industrial tests at the end user demonstrated that the favourable design contained elongated and smaller grits at a lower concentration, because it reduced heat generation despite the higher wheel wear. This was confirmed via the Barkhausen noise measurements, which showed a 20% reduction in intensity compared to the reference wheel and a 30% reduction in intensity compared to the wheel design containing blockier and larger grit at higher concentration

Development of Multi-grit cBN Grinding Wheel for Crankshaft Grinding

Crankshaft is a geometrically challenging component to grind. Over the years a number of grinding strategies have been developed to overcome thermal damage issues and excessive wheel wear. Radial and angular plunge processes have been adopted on some of the production machines. Recently a new, temperature-based strategy, has been proposed. A continuation project was launched, focusing on grinding wheel development and the initial work is presented in this thesis.A series of grinding trails have been used to correlate the grit properties with the grinding performance. The two evaluated grit characteristics are newly proposed aspect ratio (\u1d434\u1d445) and the concentration in the grinding wheel. The results show that blockier particles (lower\u1d434\u1d445) generate high forces and lower grinding wheel wear. On the other hand, the elongated particles require less power for grinding and act more free-cutting, improving the grindability. Further trials using higher concentration grinding wheels, exhibit similar behavior as grit(s) with lower \u1d434\u1d445. The two properties that are driving this performance are the contact area between the grinding wheel and the workpiece and the undeformed maximum chip thickness ℎ\u1d45a which changes with process and wheel design parameters

A lapping-based test method to investigate wear behaviour of bonded-abrasive tools

Grinding-wheel wear is a critical factor affecting grinding performance and tool cost. Unfortunately, wear tests – particularly with superabrasives – can be notoriously time-consuming. Therefore, a novel lapping-based method is proposed for investigating wear behaviour of the grit-bond system. Wear tests were performed in (i) lapping, (ii) surface grinding, and (iii) cylindrical grinding for a range of grit-shape aspect ratios and grit-toughness values for the same grit-bond systems. Results showed that all three methods yielded similar trends. This indicates that the lapping tests could be a viable substitute for lengthy grinding tests, resulting in shorter testing times and smaller specimen sizes

A comparison of polymer film and glass collectors for concentrating solar power

This paper describes work to compare the optical properties and surface texture of glass and polymer film collectors. We also present the results of experiments designed to simulate collector cleaning processes (both contact and non-contact), and the degradation of glass and polymer reflecting surfaces owing to sand and dust abrasion. Finally we present initial results on the applicability of anti-soiling and self-cleaning coatings on glass and polymer film collector surfaces. Measurements, which include specular and hemispherical reflectance, surface roughness, and electron microscopy, indicate the excellent performance of currently available polymer film in terms of its optical performance and robustness in comparison with traditional glass collectors in CSP applications

Effect of the grit shape on the performance of vitrified-bonded CBN grinding wheel

This paper deals with the effect of the CBN grit shape on the grindability of a low alloy chrome steel, 100Cr6. Firstly, a simple wheel-workpiece interaction model is introduced to investigate the grinding response. The formulation considers the global grinding forces, which embodies all the properties of the wheel acting at the interface. The use of this approach eliminates the need to consider the interaction of each individual grit with the workpiece during the grinding process. Next, a series of tailored grinding tests conducted with a creep-feed grinding machine are used to evaluate the grinding performance and the wheel wear. The results have shown that the specific grinding energy (ue) is affected by the CBN grit shape, and the wheel wear is proportional to the ratio of the CBN shape factor (Aspect Ratio) and the overall bearing surface of the wheel-workpiece contact area (af)

The effects of grit properties and dressing on grinding mechanics and wheel performance

This paper introduces an analytical assessment framework for evaluating grinding wheel performance derived from the model of cutting and sliding grinding force components. Four new parameters are proposed based on wheel topography. These parameters are normalized through the aggressiveness number, which circumvents the influences of grinding geometry and kinematics. The framework is validated through experiments with different wheel topographies obtained by changing dressing conditions and grit properties (toughness, thermal stability and shape). The framework and experiments quantify how wheel wear flat area influences the sliding component and how grit protrusion influences the intrinsic specific grinding energy. This framework provides a rational basis for evaluating grinding-wheel performance and abrasive-grit selection

Superabrasive applications in grinding of crankshafts: a review

The crankshaft grinding process has evolved remarkably over the years, from plunge grinding processes run on several machines to completing a crankshaft on a single grinding machine featuring multi-spindles, where rough and finish grinding increments can be determined based on predicted grinding temperatures to avoid thermal damage and reduce wheel wear while simultaneously shortening the grinding cycle time. This paper reviews the important developments of the crankshaft grinding process, primarily by analysing patented grinding methods. The technology advancement, however, is not only process related, since it extends to grinding wheel innovation which necessitates the modification of CBN abrasive grits and optimisation of dressing

A methodology for the evaluation of CBN abrasive grits

A better understanding of the grinding process is essential for newly developed grit types. Mapping the effect of grain properties to the application performance is the ultimate goal of every grit manufacturer. The challenge is, however, to provide crucial information about the grit and, at the same time, distinguishes it from other possible effects such as: porosity, adhesion and bond strength. A series of grinding tests have been conducted using different grit types and bond systems and a novel testing methodology implemented. The results have shown good sensitivity with respect to the grain properties and, consequently, the potential application of this method to grinding process optimization