Acoustic emission in dressing of grinding wheels: AE intensity, dressing energy, and quantification of dressing sharpness and increase in diamond wear-flat size
Graphical abstract
Introduction
Acoustic emission (AE) has been applied to various aspects in grinding, most notably in contact and collision detection. Oliveira et al. [1] used AE to determine the wheel shape and Jayakumar et al. [2] reported on its use in contact detection when fine-grinding lenses. It has also been used to assess wheel imbalance and wheel and part roundness, as reported by Xue et al. [3]. Aguiar et al. [4] used AE to detect thermal damage, where severe burn coincided with a significant increase in the AE RMS value. Sutowski and Plichta [5] used the AE RMS value to evaluate grinding-wheel wear progression and also to detect grinding burn on the machined surface. Hundt et al. [6] gave the sources of AE energy as elastic impact, bond fracture, grain fracture, indentation cracks and friction and showed different frequencies for bond fracture and grain fracture (Fig. 1). Mokbel and Maksoud [7] found lower AE amplitude when grinding with sharper wheels. In dressing, Lee et al. [8] used AE to build a map of the circumferential wheel topography. Inasaki and Okamura [9] took a more microscopic view of AE in dressing and found that AE intensity increased with dressing depth and dressing lead and correlated this empirically with grinding power and workpiece surface finish. Oliveira et al. [1] showed an increase in the AE intensity with dressing depth and highlighted the challenges associated with sensor positioning. Kim et al. [10] also used the AE RMS signal to determine the optimum dressing depth.
In spite of this, several fundamental relationships are not understood when using AE in dressing, namely: 1) how repeated diamond/grit contact and its possible associated interactions – grit/bond fracture, plastic deformation, elastic impact and friction – affect AE intensity; 2) the correlation between AE intensity and dressing energy; 3) whether AE can be used to predict dressing efficiency; 4) whether AE can be used to quantify wheel sharpness; and 5) whether AE can be used to evaluate changes in dressing-diamond geometry, which can be detrimental to grinding performance.
Therefore, an investigation was made into these fundamental concepts. The relationships between dressing forces, dressing energy and AE intensity was established. Then, how the contact mechanisms between the diamond tool and the grit affect AE intensity was explored. The relationship between AE intensity and dressing energy was quantified experimentally and this was used to predict wheel sharpness and, in turn, grinding energies. It was then investigated whether AE could be used to measure the increasing diamond flat width with wheel wear, which is a major problem in industry that contributes to unstable grinding operations and increased risk of grinding burn.
Section snippets
Background
In dressing of conventional-abrasive and cubic-boron-nitride grinding wheels, diamond dressers are used in the form of stationary tools (single-point, clusters, logs and blade tools), plunge diamond rolls and diamond traverse discs. The resulting sharpness of the grinding wheel depends greatly on dressing parameters. Numerous studies have shown that more aggressive dressing conditions create a sharper wheel, resulting in lower grinding forces and temperatures [11]. One important parameter is
Experimental set-up
Dressing and grinding investigations were undertaken on a Jones and Shipman 540 surface grinder (ds,i = 200 mm, ωs = 2880 RPM). The dressing diamond was mounted in a holder affixed to a Kistler, three-axis piezoelectric dynamometer which measured forces in three directions at 10,000 samples/second. A Kistler 8152B AE sensor (50–400 kHz) was mounted on the diamond dresser toolholder 45 mm from the point of wheel/dresser contact (Fig. 2). Data was sampled at 1 MHz with a time-constant of 1.2 ms,
AE intensity
The first step was to determine the effect of residual noise originating from the grinding wheel, spindle bearings, coolant and other possible sources. The AE intensity was measured with the wheel and coolant on, and then during dressing. The result is shown in Fig. 3, indicating that residual noise is negligible.
In addition, a Fourier transform (FFT) was performed on several signals to determine if certain frequencies might be dominant and if they could be associated with a particular energy
Discussion
The results indicate that the AE intensity is directly proportional to dressing power. Considering that Malkin found dressing energy is proportional to grinding energy, it should be possible to use AE to predict grinding power and evaluate wheel sharpness. Inasaki and Okamura [9] measured AE during dressing and grinding, power during grinding and workpiece surface finish after grinding at different dressing depths and dressing leads. If the grinding power is converted to grinding specific
Conclusions
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Acoustic-emission intensity during dressing is proportional to dressing power.
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This proportionality appears to be true regardless of dressing parameters, abrasive grit type, or the AE energy source, be it grit/bond fracture, plastic deformation, rubbing, or other possible sources.
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A new concept was introduced, the specific AE dressing energy, in volts/mm3/s, which is proportional to the specific dressing energy via the AE power factor. Once the power factor is determined, AE can be used to
Acknowledgements
Funding for this project was provided by The Grinding Doc Consulting and Element Six under the auspices of the IRCSET Enterprise Partnership framework, and in part by a research grant from Science Foundation Ireland (SFI) under Grant Number SFI/12/RC/2278.
Nomenclature
- ad
- μm dressing depth
- bd
- mm diamond wear spot width
- C
- points/mm2 cutting point density
- ds
- mm wheel diameter
- ds,i
- mm new wheel diameter
- eae
- V/mm3/s specific AE dressing energy
- ed
- joules/mm3 specific dressing energy
- ed,ae
- joules/mm3 converted specific AE dressing energy
- ed,ae,ic
- joules/mm3 specific AE dressing energy at contact ic
- fc
- collisions/s collision frequency
- FT
- Newtons tangential force
- iae
- volts AE signal intensity
- ic
- dressing contact number
- Pd
- Watts dressing power
- Pd,c
- Watts converted dressing power
- PFae
Jeffrey A. Badger, Ph.D. is an expert in grinding. He works independently as “The Grinding Doc”, a consultant in grinding. He continues to do research in the field and has strong ties to Trinity College, Dublin, where he did his Ph.D. His is widely published in the academic journals and in CIRP. Contact: +1-512-934-1857 // [email protected].
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Jeffrey A. Badger, Ph.D. is an expert in grinding. He works independently as “The Grinding Doc”, a consultant in grinding. He continues to do research in the field and has strong ties to Trinity College, Dublin, where he did his Ph.D. His is widely published in the academic journals and in CIRP. Contact: +1-512-934-1857 // [email protected].
Stuart Murphy received his Ph.D. from Trinity College Dublin in 2015. His research areas are in the field of grinding including eccentricity, loading, process monitoring via acoustic emission, force and power measurements. Contact: [email protected].
Dr. Garret O'Donnell is a University lecturer in the Department of Mechanical and Manufacturing Engineering in Trinity College Dublin and an associate member of CIRP. Garret's research activity in Trinity College Dublin is based on advancing manufacturing technologies that underpin sectors such as biomedical, automotive, aerospace, and ICT. His principal research area is the process monitoring of machining processes with goals of understanding the fundamental science, developing new sensor concepts, signal processing algorithms, intelligent decision making strategies and adaptronic control systems for high performance cutting processes. Contact: [email protected].