Coarse-grained Diamond Wheels Research Articles

Precision dressing of arc-shaped coarse-grained diamond wheels via electrical discharge aided grinding technology

Precision dressing of arc-shaped coarse-grained diamond wheels via electrical discharge aided grinding technology

Influence of Carbon Nanotubes on Electrolytic Dressing Grinding Performance of a Multi-layer Brazed Coarse-grained Diamond Wheel

Influence of Carbon Nanotubes on Electrolytic Dressing Grinding Performance of a Multi-layer Brazed Coarse-grained Diamond Wheel

Surface and Material Modifications of Tempered Steel after Precision Grinding with Electroplated Coarse Grained Diamond Wheels

One particular kind of engineered grinding wheels are precisely profiled grinding tools with flattened coarse diamond grains, primarily used for machining of brittle materials. Because of their grain geometries, they are also expected to introduce mechanical strains into steel workpieces generating a work hardening effect. Also low surface roughnesses combined with favorable compressive residual stresses are targeted. In this paper the feasibility of this process technology is investigated and possible adverse aspects are identified. These findings can be used in future to further develop the process towards higher forces and speeds and thus conditions close to industrial applications in conventional grinding of steel parts.

Surface micro-structuring of coarse-grained diamond wheels by nanosecond pulsed laser for improving grinding performance

The conditioned coarse-grained diamond wheels are able to achieve the identical surface roughness, higher form accuracy and larger grinding rate when compared to the traditional fine-grained diamond wheels. However, deeper subsurface damage could be inevitably introduced due to the flat tops of the coarse diamond grains. This work presents a micro-structuring method for coarse-grained diamond wheels by means of nanosecond pulsed laser, which allows the generation of micro grooves arrays on the coarse diamond grains distributed on the whole grinding wheel cylindrical surface. The influence of laser parameters such as focal point shift, laser power, scanning speed and scanning passes on micro-structured surface was investigated, and then the laser machining process was optimized in fabricating uniform and continuous micro-structures. The grinding experiments indicate that, when compared to the non-micro-structured grinding wheels, the subsurface cracks depth of ground optical glass was reduced effectually by using the micro-structured coarse-grained diamond wheels.

Ultra-precision grinding of optical glasses using mono-layer nickel electroplated coarse-grained diamond wheels. Part 2: Investigation of profile and surface grinding

After finishing the precision conditioning of mono-layer nickel electroplated coarse-grained diamond wheels with 151μm (D151), 91μm (D91) and 46μm (D46) grain size, resp., profile and surface grinding experiments were carried out on a five-axis ultra-precision grinding machine with BK7, SF6 optical glasses and Zerodur glass ceramic. A piezoelectric dynamometer was used to measure the grinding forces, while an atomic force microscopy (AFM), white-light interferometer (WLI)) and scanning electron microscope (SEM) were used to characterize the ground surface quality in terms of micro-topography and subsurface damage. Moreover, the wear mechanics of the coarse-grained diamond wheels were analyzed and the grinding ratio was determined as well, in aiming to evaluate the grinding performance with the conditioned coarse-grained diamond wheels. Finally, the grinding results were compared with that of the fine-grained diamond wheels with regard to the ground specimen surface quality, process forces and wheel wear as a function of stock removal. The experimental results show that the precision conditioned coarse-grained diamond wheels can be applied in ductile mode grinding of optical glasses with high material removal rates, low wheel wear rates and no dressing requirement yielding excellent surface finishes with surface roughness in the nanometer range and subsurface damage in the micrometer range, demonstrating the feasibility and applicability of the newly developed diamond grinding technique for optical glasses.

Ultra-precision grinding of optical glasses using mono-layer nickel electroplated coarse-grained diamond wheels. Part 1: ELID assisted precision conditioning of grinding wheels

In order to realize ultra-precision grinding of optical glasses with mono-layer nickel electroplated coarse-grained diamond grinding wheels, a novel conditioning technique was developed using copper bonded diamond grinding wheels with grain sizes of 15μm (D15) and 91μm (D91), respectively, as conditioners for truing of diamond wheels with grain sizes of 46μm (D46), 91μm (D91) and 151μm (D151), respectively. During the conditioning process, the conditioners were continuously dressed by means of electrolytic in-process dressing (ELID). A force transducer was used to monitor the conditioning force while a coaxial optical distance measurement system was used to monitor the wheel run-out. In addition, a white-light interferometer (WLI) and a scanning electron microscope (SEM) were used to characterize the successively modified diamond grain morphologies of the conditioned wheels both directly and by a replication technique. The experimental results show that with optimized conditioning parameters, the developed conditioning technique can be applied for truing of coarse-grained diamond wheels within the abrasive layer achieving a constant wheel peripheral envelop surface exhibiting flattened diamond grains with a run-out <2.5μm, which is a prerequisite for introducing coarse-grained diamond wheels into ultra-precision machining of brittle and hard-to-machine materials.

Precision grinding of optical glass with laser micro-structured coarse-grained diamond wheels

This paper presents a series of micro-structured coarse-grained diamond wheels for optical glass surface grinding aiming to improve the grinding performance, especially subsurface damage. The 150μm grit size, single layer electroplated diamond grinding wheels with different interval micro-groove arrays were manufactured by nanosecond pulsed laser, successfully. The influence of micro-structures on surface roughness and subsurface damage was investigated. Compared with conventional coarse-grained diamond wheel, the subsurface damage depth was reduced effectually from 5 to 1.5μm, although the better surface roughness was not obtained by the micro-structured coarse-grained diamond wheel. In addition, the surface roughness and subsurface damage depth were both reduced with the decreasing interval of micro-groove arrays.

Precision grinding of BK7 glasses using conditioned coarse-grained diamond wheel

For precision machining of large-sized optical elements, more attention is being paid to the ground surface quality, the processing costs and the machining efficiency. Besides the commonly used fine-grained diamond wheels, the coarse-grained diamond wheel is now also expected to be a promising tool with lower wheel wear rate and higher efficiency. However, conditioning of this kind of wheel is always a difficult issue to deal with. In this article, the efficient conditioning of the electroplated diamond wheel and precision grinding of BK7 glasses were investigated. Through the single diamond grit wear simulation, D3 steel was chosen as the conditioning tool. The worn diamond abrasive morphology and Raman spectroscopy analysis revealed the conditioning mechanism. Under different conditioning stages, the BK7 glasses were correspondingly ground exhibiting different surface integrity and grinding forces. The experimental results indicated that the wheel’s run-out error could be rapidly reduced to 5.8 µm because of the blend graphitization, passivation, diffusion and microcrushing of the diamond abrasives. The precision ground BK7 glasses could achieve a surface roughness of Ra &lt; 20 nm and a subsurface crack depth around 2 µm, illustrating that the electroplated coarse-grained diamond wheel could be an alternative for precision grinding large-sized optical elements in terms of high accuracy, cost-effectiveness and high efficiency.

Grinding damage of BK7 using copper-resin bond coarse-grained diamond wheel

Coarse-grained wheels can realize high efficient grinding of optical glass. However, the serious surface and subsurface damage will be inevitably introduced by the coarse-grained wheels. In this paper, the grinding damage of a copper-resin bond coarse-grained diamond wheel with grain size of 150μm was investigated on optical glass BK7. The wheel was first properly trued with a metal bond diamond wheel, then pre-dressing for the wheel and grinding experiments are carried out on a precision grinder assisted with electrolytic in process dressing (ELID) method. The surface roughness (Ra) of ground surface was measured using an atomic force microscope (AFM) and the surface topography were imaged by a white light interferometer (WLI) and the AFM. The subsurface damage level of ground surface was evaluated by means of both MRF spot method and taper polishing-etching method, in term of the biggest depth of subsurface damage, distribution of micro defects beneath the ground surface, the cluster depth of subsurface damage, relationship between subsurface damage (SSD) and PV surface roughness (SR), propagating distance and pattern of cracks beneath the ground surface. Experimental results indicate that a well conditioned copper-resin bond coarse-grained diamond wheel on a precision grinder can generate good surface quality of Ra less than 50nm and good subsurface integrity with SSD depth less than 3.5e for optical glass BK7.

ELID Assisted Precision Conditioning of Coarse-Grained Diamond Grinding Wheel

In order to realize ductile machining of optical glasses using mono-layer nickel electroplated coarse-grained diamond grinding wheel, a novel conditioning technique features using a copper bonded diamond grinding wheels of 15m grain size dressed by ELID (electrolytic inprocess dressing) to condition the 46m grain sized diamond wheel has been developed. During the conditioning process, a force transducer was used to monitor the conditioning force, a coaxial optical distance measurement system was used to in-situ monitor the modified wheel surface status. White-light interferometry (WLI), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the conditioned wheel surface status as well as the ground optical glass surface topography correspondingly. The experimental result indicates that a minimized wheel radial run-out error of less than 2μm as well as the top-flattened diamond grains of constant wheel peripheral envelop profile were generated on a 5-axis ultra-precision machine tool. The grinding experiment proved that the well conditioned 46μm coarse-grained diamond wheel can be used in realizing the ductile grinding of optical glass BK7, which indicates that the newly developed conditioning technique is feasible and applicable to introduce the coarse-grained diamond wheels into precision machining of brittle and hard-to-machine materials.

Surface and Sub-Surface Integrity of Ultra- Machined BK7 Using Fine and Coarse Grained Diamond Wheels

This paper aims to evaluate the surface and sub-surface integrity of optical glasses which were correspondingly machined by coarse and fine-grained diamond grinding wheels on Tetraform ‘C’ and Nanotech 500FG. The experimental results show that coarse-grained diamond grinding wheels are capable of ductile grinding of optical glasses with high surface and sub-surface integrity. The surface roughness values are all in nanometer scale and the sub-surface damages are around several micros in depth, which is comparative to those machined by fine-grained diamond wheels.

ULTRA-PRECISION GRINDING OF BK7 OPTICAL GLASS USING COARSE-GRAINED ELECTROPLATED DIAMOND WHEEL

A novel conditioning technique is developed to precisely and effectively condition the 151μm grain-sized nickel electroplated monolayer coarse- grained diamond grinding wheel in aiming to realize ductile grinding of brittle materials. During the conditioning process, a copper bonded diamond grinding wheel (91μm grain size) dressed by ELID (electrolytic in-process dressing) is applied as a conditioner, a force transducer was used to monitor the conditioning force, and a coaxial optical distance measurement system are used to in-situ monitor the modified wheel surface status. Ultimately the coarse-grained diamond wheel is conditioned to achieve an ideal state in terms of less than 2μm run-out error, top-flattened diamond grains and constant wheel envelop profile. Then the well- conditioned 151μm wheel is applied to conduct taper grinding and contour grinding tests, the ground surface and sub-surface integrity are measured by WLI (white light interferometer), AFM (atomic force microscope) and SEM (scanning electrical microscope) respectively. The experimental results indicate that the well-conditioned 151μm grain-sized diamond wheel is able to realize ductile grinding of BK7 with nano-scale surface roughness, as well as the almost damage free sub-surface integrity. The results also show the promising prospect of the conditioning technique and coarse-grained diamond wheels to be applied in machining the hard-machine-materials and the other brittle materials such as ceramic and silicon carbide, etc.