Stable Grinding Force Research Articles

Wear evolution of metal bond diamond tool in grinding of sapphire

The wear characteristics of the metal bond diamond tools changes with the grinding process, resulting in affecting the grinding efficiency, tool's life, and surface integrity of the workpiece. In this study, the wear evolution of a metal bond diamond tool, for the case of grinding of sapphire, is investigated by using a novel design of the grinding setup. The wear characteristics of the diamond grits and the metal bond at a fixed zone of the grinding tool were examined. In addition, the evolution of the grinding process, the grinding force, the grinding ratio, and the surface integrity of the sapphire were also evaluated. As the material removal volume increases, the number of participating diamond grits, the proportion of micro-fractured diamond grits, and the average diamond grit protrusion height increase during the grinding process. And the proportion of newly exposed diamond grits decreases and the distribution of protrusion height of diamond grits becomes narrower during the grinding process. Consequently, a higher grinding ratio, stable grinding force, and excellent ground surface integrity are achieved positively when the wear of the metal bond diamond tool transforms from the initial stage to the stable stage with the material removal volume of up to 3600 mm3.

Wear characteristics of single-layer cBN abrasive tools using ultrasonic vibration–assisted induction brazing techniques

Single-layer brazed superhard abrasive tools have been widely employed in grinding of difficult-to-machine materials in aerospace, aiming at the improvement of the grinding performance and quality. However, the chemical metallurgical reaction during conventional induction brazing (CIB) is severe, and the brazing quality is poor, resulting in a rapid wear and thus reducing service life of abrasive tools. In this case, the single-layer brazed cBN abrasive tools were fabricated using ultrasonic vibration-assisted induction brazing (UVAIB) technology, and the wear comparative experiments of Ti–6Al–4V alloys was carried out using UVAIB and CIB abrasive tools. Results indicate that compared to the CIB abrasive tool, the UVAIB abrasive tool has the higher average exposure height of abrasive grains, lower grinding forces and more stable grinding force ratio during wear processes. Meanwhile, the UVAIB abrasive tool has a slowly decreased exposure height of abrasive grains, a superior wear state and low proportion of macro-fracture as the material removal volume raises. In addition, UVAIB abrasive tool possesses micro-cracks at the top of abrasive grains, leading to micro-fractures of abrasive grains to improve the self-sharpening ability and grinding performance.

Self-sharpening property of porous metal-bonded aggregated cBN wheels during the grinding of Ti–6Al–4V alloys

Grinding process with cubic boron nitride (cBN) superabrasive wheels has been the subject of extensive research during high efficiency and precision machining difficult-to-cut materials in aerospace and aviation industries. However, the grinding performance and tool-life of conventional cBN abrasive wheels are severely affected by the probable macro-fracture and pull-out of cBN grains owing to their anisotropic crystalline structure. In this case, porous metal-bonded grinding wheels coupled with high-performance aggregated cBN abrasive grains were developed to improve tool performance and machined surface integrity. Characterisation of morphologies, including as-sintered aggregated cBN abrasive grains, pore structures and grain wear evolutions, was performed. The grinding ratio, grinding forces, force ratio and ground surface roughness were evaluated through single-grain grinding of Ti–6Al–4V alloys. Experimental results indicated that the porous aggregated cBN wheels had abundant chip storage space and excellent wear resistance. A stable grinding force ratio and small ground surface roughness were obtained during the tool wear tests due to the combined characteristics of microfracture and partial macrofracture of multi-layer cBN particles.

On the grinding performance of metal-bonded aggregated cBN grinding wheels based on open-pore structures

Metal-bonded aggregated cubic boron nitride (cBN) grinding wheels were developed by employing open-pore structures in abrasive layers, aiming to solve the problems, such as severe tool wear, low machining efficiency, and poor quality stability with conventional abrasive grinding wheels. Comparative grinding performances, including grinding forces and force ratio, grinding temperature, specific grinding energy, ground surface roughness were performed between vitrified monocrystalline cBN wheels and porous aggregated cBN wheels. Characterisation of morphologies, such as pore structures and tool wear features were also conducted. Results show that the as-sintered porous aggregated cBN wheels possess the lower grinding forces (reduced by 35.9%–43.3% for Fn′; 3.9%–18.8% for Ft′), a smaller grinding temperature (decreased by 10.4%–71.8%), and a stable grinding force ratio of 2.5 in comparison of vitrified monocrystalline cBN wheels. In addition, the ground surface roughness of porous aggregated cBN wheels ranges from 0.76 to 1.19 μm, whilst the other one possesses over 1.65 μm. Furthermore, the worse ground surface quality is obtained, resulting from the smaller chip storage space and poor self-sharpening ability of vitrified monocrystalline cBN wheels compare to porous aggregated cBN wheels.

Fabrication and wear characteristics of open-porous cBN abrasive wheels in grinding of Ti–6Al–4V alloys

Cubic boron nitride (cBN) superabrasive wheels have been a preferential choice for grinding difficult-to-cut materials (i.e. Ti–6Al–4V alloys) in aerospace and aviation industries. However, the grinding performance and tool-life of conventional cBN abrasive wheels are severely affected by the probable macro-fracture and pull-out of cBN grains owing to their anisotropic crystalline structure. In this case, open-porous sintered cBN abrasive wheels, which are associated with excellent grinding performance and long tool-life, were developed. Pore structures were fabricated using spherical carbamide particles as space holders via the vacuum sintering process. The effects of pore structures, such as pore size and porosity, on the mechanical properties of metallic porous composites were discussed. Characterisation of pore structure and tool wear morphologies was also performed during the grinding process of Ti–6Al–4V alloys. The grinding performances, including grinding force and force ratio, tool wear evolution and machined surface quality, were discussed in detail. Results show that open-porous cBN abrasive wheels featured a desired flexural strength and excellent chip storage space after optimizing the pore size of 0.6–0.8 mm and designed porosity of 40 vol%. The strong bonding strength of porous cBN abrasive wheels was produced due to the chemical reaction in the zone of bonding interface among cBN abrasive grains, Cu–Sn–Ti alloys and MoS2 particles during liquid-phase sintering. The porous cBN abrasive wheels showed a stable grinding force ratio from 1.5 to 2.6 once the grinding speed exceeded 30 m/s. In addition, the sharpness of porous cBN wheels can remain stable in a long duration due to the dynamic changes in the chip storage space provided by the porous parameters and self-sharpening of porous cBN abrasive wheels. Moreover, the ground surface roughness rapidly declined and stabilised due to the stabilisation of the dynamic effective grains number.

Characterisation of the wear properties of a single-aggregated cubic boron nitride grain during Ti–6Al–4V alloy grinding

Single-grain grinding the Ti–6Al–4V alloys is performed to investigate the wear characteristics and material removal mechanism of aggregated cubic boron nitride (AcBN) grains fabricated by multiple monocrystalline cBN grains. An innovative approach entailing the tracking of grains and scratches by using the 3D reconstruction is proposed to investigate accurately the wear characteristics and material removal ability of such grains. Grain wear, which is affected by grinding wheel speed vs and undeformed chip thickness agmax, is characterised. The variations in grinding force and grinding force ratio, volumetric pile-up ratio and volumetric groove removal rate are also studied. Results show that the as-sintered AcBN grains have better self-sharpening ability, higher grinding ratio, and more stable grain wear rate than the McBN grains. In addition, the wear rate of AcBN grains is more sensible in determining the effect of vs compared with the use of agmax. The AcBN grains attained a higher wear volume (nearly thrice the value), a more stable wear rate and a more stable grinding force ratio when vs increases to 120 m/s as opposed to the other smaller vs values regardless of the agmax values.

Effect of grain contents of a single-aggregated cubic boron nitride grain on material removal mechanism during Ti–6Al–4V alloy grinding

Aggregated cubic boron nitride (AcBN) grains were developed by sintering monocrystalline cBN (McBN) grains and inter-abrasive metallic phase. The sintering parameters, including sintering temperature and dwelling time, and volumetric proportions of McBN grains are optimized and correlated with the fracture strength of AcBN grains. Quantitative characterization of the grain and scratches were tracked based on the 3D reconstruction technique to study the grain wear characteristics and material removal ability of AcBN grains. The grinding performance for different AcBN grain types, including grinding force, force ratio, volumetric pile-up ratio and volumetric groove removal rate were investigated. Experimental results indicate that the optimized sintering parameters are 800 °C with a dwelling time of 10 min. The AcBN grains with 90% volumetric proportion of McBN grains possess the more stable grinding force ratio and grain wear rate, better self-sharpening ability, and higher grinding ratio. In addition, the material removal efficiency tends to decline and then increase due to the self-sharpening characteristics through the analysis of the volumetric pile-up ratio regardless of AcBN grain types.

Grinding performance and tribological behavior in solid lubricant assisted grinding of glass-ceramics

High dimensional stability of glass-ceramics is highly attractive to optical and precision engineering industries. This study aims to provide an efficient and stable grinding strategy for realizing high-quality surface and dimensional accuracy of glass-ceramics. The different solid additives (CeO2 and SiC) as lubricants and their performances were investigated regarding the grinding forces, friction coefficient, wheel wear and surface finish during grinding glass-ceramics. Friction and wear mechanism in solid lubricant assisted (SLA) grinding were analyzed. Three-body abrasive wear and chemical mechanical interaction were considered as the predominant lubrication mechanisms. The results showed that the low, stable grinding force and small friction coefficient can be obtained under SLA-SiC grinding. The study proved that the novel strategy can keep the wheel sharpness and improve the process performance.

Effect of grain wear on material removal behaviour during grinding of Ti-6Al-4V titanium alloy with single aggregated cBN grain

Abstract This study aims to explore the grinding ability of as-sintered aggregated cubic boron nitride (AcBN) grains. Single-grain grinding tests of Ti-6Al-4V titanium alloy are conducted, and the wear characteristics of AcBN grains and their corresponding effects on material removal behaviour are investigated. Characterisation of the morphologies and micro-structure of AcBN grains and scratch morphologies is also performed. The grinding force ratio, material removal efficiency and grain wear characteristics of AcBN abrasives are discussed. Results show that the developed AcBN grains have multiple cutting edges and better self-sharpening ability than conventional monocrystalline cBN grains. In addition, AcBN grains feature a more stable grinding force ratio, larger material removal volume, higher material removal efficiency and longer steady-wear regions.

3-D Shape Matching of a Blade Surface in Robotic Grinding Applications

Robotic grinding is a promising technique to generate the final shape of blades. It can relieve human from participating in dirty and noisy environments, improve product quality, and lower production costs. One important task in robotic grinding is 3-D shape matching. However, existing matching methods do not consider the requirements associated with different grinding allowances, which can potentially lead to an unstable grinding force. This paper proposes a novel shape matching method for robotic grinding. The goal is to define a new objective function considering different allowance weights for stable grinding, and address incorrect shape matching from the missing points or uneven density points. The main contribution of this paper is the application of variance minimization to construct an objective function, from which the required shape matching parameters are iteratively calculated. This method balances the contributions of all the measured points, weighs the allowances for the pressure and suction surfaces of a blade, and avoids incorrect matching tendencies for high-density points. It is advantageous to maintaining a relatively stable grinding force. The effectiveness of this method is verified through simulations and scanning/grinding experiments of different blades.

Influence of a Grinding Atmosphere in the Combination Grinding of Steel and WC with a Diamond Wheel

Grinding experiments were carried out in wet, with MQL, in dry, with a spray of dry ice particles and various gases to examine influence of grinding atmospheres on the grinding performance in the combination surface grinding of steel and WC with a diamond wheel. From the experimental results, it was found that the grinding with inert gas injection which reduces an oxygen concentration at the grinding point would proceed a processing at more stable grinding force, resulting in less wear of the diamond abrasives.

Electrical Discharge Truing of a Vitrified Bonded Superabrasive Wheel with Electrical Conductivity

With its high grit retention and easiness to true and dress, the vitrified bond is widely used as a bond material for cBN and diamond grinding wheels. By giving electrical conductivity to the vitrified bond, application of electrical discharge trueing/dressing and detection of a workpiece position by electrical contact sensing will become possible. And moreover, application of the vitrified bonded wheels to various types of electro-assisted grinding processes (electrochemical or electro discharge assisted methods) is expected. In this study, vitrified bonded diamond segments with electrical conductivity were manufactured experimentally by mixing the fine copper powders in the vitrified bond matrix. As a result of investigation into the electro discharge trueing performance in the die sinking and wire electro discharge machining, it was found that a vitrified bonded wheel could be formed by electro discharge machining only because the bond was electrically conductive. In addition, the electro discharge complex grinding utilizing electric discharge machining was applied to the PCD cutting tool materials using the electrically conductive vitrified bonded wheel, and confirmed that the grinding could be continued for a long time maintaining a stable grinding force.

Development of a Vitrified Bonded Superabrasive Wheel with Electrical Conductivity and its Application

A vitrified bonded diamond wheel having electrical conductivity was manufactured on a trial basis. The electrically conductive (EC) vitrified bonded diamond wheel has enabled an electrodischarge truing and an electrical contact sensing. In this study, the EC vitrified bonded diamond wheel is applied to the EDM (Electro Discharge Machining) assisted grinding of PCD materials. The result shows that a lower and more stable grinding force can be realized and a better surface finish is attained compared with those achievable with a metal bonded diamond wheel.

Effect of Complex Electrodischarge Grinding for Electrically Conductive PCD

Polycrystalline Composite Diamond (PCD) is excellent in chipping resistance despite its very high hardness. However, it is not easy to EDM or grind PCD. To realize high efficiency and high quality processing of PCD simply and at low cost, the authors devised new PCD (EC-PCD) by using electrically conductive diamond particles and applied a complex electrodischarge grinding method. In this study, investigation is made on effective grinding condition to realize high efficiency, low and stable grinding force and low wheel wear in complex electrodischarge grinding. As a result, superior grinding property was obtained when the grinding wheel was set at minus polarity, and set peak current of iP = 4 and 6 A was applied. Furthermore it also became clear that additional conventional grinding process followed after complex electrodischarge grinding improved the surface condition.

Complex Grinding Assisted with Electrical Discharge Machining for Electrically Conductive PCD

A new PCD material named EC-PCD (Electrically conductive polycrystalline composite diamond), which consists of electrically conductive diamond grits, has recently been developed. This paper deals with an investigation of a complex grinding assisted with electrical discharge machining (EDM) to realize high efficiency, low and stable grinding force and low wheel wear for the new EC-PCD. The effect of complex grinding assisted with EDM is compared experimentally with the standard PCD (S-PCD). The result shows that, in the complex grinding, lower and more stable grinding force is realized thanks to the material removal action in EDM and that lower wheel wear and better surface finish are attained, just when the EC-PCD is selected as a workpiece.

Processing EC-PCD by Constant-Force Grinding Assisted with EDM

A new PCD (electrically conductive PCD: EC-PCD) consisting of electrically conductive diamond particles has recently been developed. The authors have proposed a complex grinding assisted with electrical discharge machining (EDM) where discharge machining and grinding are used in combination during material removal to realize high efficiency, low and stable grinding force and low wheel wear for the EC-PCD. In this study, the effect of constant-force grinding in a complex grinding assisted with electrical discharge machining of EC-PCD was investigated. As a result, it was found that higher material removal rate, higher grinding ratio and better surface condition were obtained on EC-PCD compared with standard PCD (S-PCD) in the constant-force grinding.

An Investigation of Surface Grinding Characteristics for Titanium Alloy with CBN Wheel

This study performs an experiment to investigate the effect of process variables such as rotational cutting speeds of the wheel, feed rate of the work-table and grinding depth of cut on surface roughness and the fluctuations of grinding forces for Ti-6Al-4V titanium alloy. STP-1623 ADC surface grinding machine, grinding wheel with CBN material sintering and Ti-6Al-4V titanium alloy workpiece are used in the experiment. The roughness of the grinding surface was measured by the roughness measuring instruments and the fluctuations of grinding forces were measured through dynamometer after each surface layer ground from the workpiece in the experiment. The grinding performance can be ascertained from the signal fluctuations phenomena of the grinding forces both along normal and tangential directions, which may also be utilized as an index for the quality of surface finish judgment. The results show that excellent surface quality being always consistent with the stable grinding force fluctuations and can be obtained under the conditions of slow feed rate of the work-table, high revolutions of the wheel and shallow depth of cut.

Analysis of Pin Grinding Mechanism in Twin Axes Synchronous Controlled Cranshaft Pin Grinder

Twin axes synchronous controlled type CNC crankshaft pin grinder has been widely used, but grinding mechanism with this type of pin grinder is not cleared well. In this study, the grinding mechanism is analyzed, and it is found that the cylindrical plunge grinding process carries on. From the investigation of substantial surface speed of both the wheel and the workpiece, grinding speed ratio is formulated. Furthermore, a simulation method, which predicts the grinding results, is developed. In order to realize high precision pin grinding, two methods, which control workpiece rotation speed adequately, are proposed, such as the controlled grinding speed ratio method and the controlled residual stock method. From the analysis, it is made clear that stable grinding force and surface roughness are generated by the controlled grinding speed ratio method, and also high dimensional accracy will be realized by the controlled residual stock method.

Efficient and stable grinding of ceramics by electrolytic in-process dressing (ELID)

In the manufacture of structural ceramic components, it has been well documented that the grinding costs can be as high as 90% of the total cost. Grinding costs can be reduced by maximizing the material removal rates (MRR). A novel grinding technology that incorporates in-process dressing of metal-bonded superabrasive wheels, known as electrolytic in-process dressing (ELID) has been developed. This technology provides dressing to metal-bonded wheels during the grinding process for continuous protrudent abrasive from super-abrasive wheels. High MRR reciprocating grinding operation was performed on silicon nitride materials. Compared with conventional grinding, a significant reduction in grinding force was noted when ELID grinding was performed. The full effect of the ELID process, i.e., low and stable grinding force, was observed only after the grinding was performed for a certain period of time. The investigations have shown that low and stable grinding force can be obtained from the very beginning of the grinding process of ELID grinding combined with modified ELID dressing is performed. The results of this research will be addressed in this paper.