Dynamic Grinding Hub Monitoring during a High Performance Grinding Process with Ceramic CBN on Cold Work Steel

Grinding is a material removing process with undefined cutting edges. The high numbers of grains participating during the chip formation are continuously subjected to non-uniform wear and topography changes. This behavior typifies a highly non-stationary process. Capturing the whole process in a simulation and predicting the work results is difficult. For this reason are In-process monitoring techniques a suitable approach to address this issue. In this paper a wireless In-process monitoring system is presented. The system is mounted on the grinding hub and detects the dynamic behavior of the wheel during the grinding process. A full bridge with strain gauges located close to the abrasive layer has been used to give instantaneous feedback concerning normal force and wheel deformation during each wheel revolution. This technique enables a continuously monitoring and improving of the grinding process, hence a more efficient and sustainable use of the abrasive layer. Experiment results are presented which demonstrate the ability of the ‘intelligent’ wheel to monitor grinding processes and to improve the machine performance.

Disc brake judder considering instantaneous disc thickness and spatial friction variation

Brake judder is a braking-induced vibration. The character of judder is typical of forced vibrations passing through a critical speed. No specific friction characteristic is needed for judder to occur. In two previous models, i.e. a rotor-stator model and a whole vehicle model, the vibration during a brake application was simulated. The vibrations were assumed to be driven by a brake torque variation (BTV) during a wheel revolution. The BTV was assumed to be proportional to the brake pressure variation (BPV) which was measured. Moreover, the proportionality constant was assumed to be independent of the braking conditions. Verifying measurements were made on a street going vehicle with strong disc thickness variation (DTV) on one of its front wheels. The measured vibration variation during braking was predicted almost exactly by the models. However, the maximum measured vibration level could only be approximated. In the present paper a more accurate analysis of the measurements was found to improve strongly the agreement between predicted and measured vibrations. Hence, the deviation in slope between measured and experimentally generated curves was markedly reduced by replacing the overall mean values of brake pressure level, etc. by slowly varying time functions. The new extended model of the present paper takes into account that the BTV may be generated by variations in normal force (i.e. BPV) and other synchronous variations (called BXV), e.g. spatial friction variation and variation of the equivalent brake radius. The result indicates that BXV may be induced by high BPV levels. Even at judder vibrations primarily caused by heavy DTV (20 μm or more in the cold state), there may be considerable contributions to the vibration level from other synchronous disturbances, i.e. BXV. Further, it was found that the pad stiffness increases with the brake pressure. For such a pad stiffness characteristic, an increase of the DTV level (for whatever reason) by 50 per cent might result in more than a 100 per cent increase in the corresponding BPV and BTV levels. Hence, a progressive pad is more sensitive to increases of the DTV level than a linear pad would be.

Ductile-Regime Grinding: A New Technology for Machining Brittle Materials

Because of recent advances in precision engineering that allow controlled grinding infeed rates as small as several nanometers per grinding wheel revolution, it is possible to grind brittle materials so that the predominant material-removal mechanism is plastic-flow and not fracture. This process is known as ductile-regime grinding. When brittle materials are ground through a process of plastic deformation, surface finishes similar to those achieved in polishing or lapping are produced. Unlike polishing or lapping, however, grinding is a deterministic process, permitting finely controlled contour accuracy and complex shapes. In this paper, the development of a research apparatus capable of ductile-regime grinding is described. Furthermore, an analytical and experimental investigation of the infeed rates necessary for ductile-regime grinding of brittle materials is presented. Finally, a model is proposed, relating the grinding infeed rate necessary for ductile material-removal with the properties of the brittle workpiece material.

Abrasive Grain Temperature at the Beginning of a Cut in Fine Grinding

In any grinding operation heat flows periodically into the abrasive grains in the surface of the wheel during wheel-work contact and is extracted during the remaining portion of a single revolution of the wheel. If it can be assumed that all of the heat flowing inward is extracted outward during the cooling portion of a single wheel revolution, then the thermal partition coefficient R=heattowork/totalgrindingenergy may be readily estimated. This paper discusses conditions under which this assumption represents an acceptable approximation.

The Driving Severity Number (DSN) — A Step Toward Quantifying Treadwear Test Conditions

A system, called the “Driving Severity Monitor” (DSM), has been developed for characterizing tire force distribution as related to treadwear in either normal tire use or in tire fleet testing in a convoy. The system consists of an accelerometer for monitoring lateral accelerations, a wheel revolution counter, and a module for signal processing and read-out. The output of the DSM is reduced to a single index, the Driving Severity Number (DSN), which characterizes a vehicle journey. The DSN is equal to the sum of squares of lateral acceleration measured once per tire revolution during a trip, divided by the number of wheel revolutions. The DSN had a high degree of correlation (R ≧ 0.95) with treadwear in two wear programs when pavement abrasiveness was held constant. This supports the concept that the three basic treadwear components: tire force distribution, pavement abrasiveness, and ambient temperature, can be separated for better understanding of tire treadwear.

Paper 5: Some Aspects of Tyre and Vehicle Vibration Testing

Instrumentation techniques are discussed. Particular emphasis is given to those techniques which have been developed to give immediately interpretable results from complex vibration data. The relative merits of various test methods for the evaluation of tyre vibration performance are indicated. Of particular importance in this respect is the difference between rolling and non-rolling testing. This is illustrated during discussion of cross-ply/radial-ply comparisons using various test methods, and also comparisons between radial tyres of slightly different construction. A necessary vibration property of a tyre is its ability to absorb single obstacles such as ‘cat's eyes' or road joints. Attempts have been made to simulate such objects on a drum, and various methods of analysing the resulting impulse to the axle are compared. As yet no generally acceptable method of analysis has been found. The majority of vehicle testing is done using vibrator excitation, as this tends to minimize tyre differences. However, problems involving low frequency excitation due to once per wheel revolution inputs are usually investigated on both drums and vibrators. This type of problem often arises when longitudinal compliance has been introduced in the suspension. Typical curves from suspensions of this type are shown. An example showing one of the principal modes of oscillation of a tyre is given.