Mark J. Jackson

Microscale wear of vitrified abrasive materials

The study of bonding hard materials such as aluminium oxide and cubic boron nitride (cBN) and the nature of interfacial cohesion between these materials and glass is very important from the perspective of high precision grinding. Vitrified grinding wheels are typically used to remove large volumes of metal and to produce components with very high tolerances. It is expected that the same grinding wheel be used for both rough and finish machining operations. Therefore, the grinding wheel, and in particular its bonding system, is expected to react differently to a variety of machining operations. In order to maintain the integrity of the grinding wheel, the bonding system that is used to hold abrasive grains in place will react differently to forces that are placed on individual bonding bridges. This paper examines the role of vitrification heat treatment on the development of strength between abrasive grains and bonding bridges, and the nature of fracture and wear in vitrified grinding wheels that are used for precision grinding applications.

Stress distribution in diamond films grown on cemented WC–Co dental burs using modified hot-filament CVD

Abstract A modified hot-filament chemical vapour deposition system has been used to deposit diamond films onto dental burs. The as-grown films were found to be polycrystalline and displayed good coverage. Micro-Raman spectra were taken at different positions of the coating to characterise stress distribution in the deposited film. The Raman diamond peak positions were used to calculate the stress along and across the diamond coating. It was found that the stress across the coating remained constant. However, the stresses along the coating displayed some interesting results. The stress at the base, in the middle and at the tip of the bur was calculated to be −1.7, −2.3 and −3.4 GPa in compression, respectively. The temperature of the bur during deposition was found to be different at different positions on the bur. At the base of the cutting area; at the middle of the bur; and at the tip of the bur the temperature was found to be 842, 908 and 952 °C, respectively. The stress in the films increased as the temperature of the bur increased. Scanning electron microscopy analysis was used to characterise the as-grown films for morphology and crystallinity.

Chemical vapour deposition diamond coating on tungsten carbide dental cutting tools

Diamond coatings on Co cemented tungsten carbide (WC-Co) hard metal tools are widely used for cutting non-ferrous metals. It is difficult to deposit diamond onto cutting tools, which generally have a complex geometry, using a single step growth process. This paper focuses on the deposition of polycrystalline diamond films onto dental tools, which possess 3D complex or cylindrical shape, employing a novel single step chemical vapour deposition (CVD) growth process. The diamond deposition is carried out in a hot filament chemical vapour deposition (HFCVD) reactor with a modified filament arrangement. The filament is mounted vertically with the drill held concentrically in between the filament coils, as opposed to the commonly used horizontal arrangement. This is a simple and inexpensive filament arrangement. In addition, the problems associated with adhesion of diamond films on WC-Co substrates are amplified in dental tools due to the very sharp edges and unpredictable cutting forces. The presence of Co, used as a binder in hard metals, generally causes poor adhesion. The amount of metallic Co on the surface can be reduced using a two step pre-treatment employing Murakami etching followed by an acid treatment. Diamond films are examined in terms of their growth rate, morphology, adhesion and cutting efficiency. We found that in the diamond coated dental tool the wear rate was reduced by a factor of three as compared to the uncoated tool.

Chemical vapour deposition of microdrill cutting edges for micro- and nanotechnology applications

Conventional cemented tungsten carbide-cobalt (WC-Co) microdrills generally have a low cutting efficiency and short lifetime mainly because they operate at very high cutting speeds. Since it is relatively expensive to make microtools it is highly desirable to improve their lifetime and in-service performance. Microtools used to make microelectronic and mechanical systems (M.E.M.S) devices with sharp cutting edges, such as milling or drilling tools need protective coating in order to extend life and improve performance. One method of achieving this objective is to use a suitable surface engineering technology to deposit a hard wear resistant coating, such as diamond. Diamond has excellent mechanical properties, such as ultra-high hardness and a low friction coefficient. One of the most promising surface treatment technologies for depositing diamond onto complex shaped components is chemical vapour deposition (CVD). However, CVD of diamond coatings onto the cemented WC-Co tool has proved to be problematic. Binder materials such as cobalt can suppress diamond nucleation resulting in poor adhesion between the coating and substrate. In this paper the effects of pre-treated substrate material on the coating structure are reported. The morphology and the crystallinity of the as-grown films was characterised by using scanning electron microscopy (SEM). Raman spectroscopy was used to assess the carbon-phase purity and give an indication of the stress levels in the as-grown polycrystalline diamond films. The diamond coated tools have potential applications in micro- and nanomachining of micro- and nano-sized components used in M.E.MS.

Diamond-coated cutting tools for biomedical applications

Diamond coatings are attractive for cutting processes due to their high-hardness, low-friction coefficient; excellent wear resistance, and chemical inertness. The application of diamond coatings on cemented, tungsten carbide (WC-Co) burs has been the subject of much attention in recent years as a method to improve cutting performance and tool life. WC-Co burs containing 6% Co and 94% WC substrate, with an average grain size of 1–3 µm, were used in this study. To improve the adhesion between diamond and WC substrates, it is necessary to etch away the surface Co and prepare the surface for subsequent diamond growth. Hot filament chemical vapor deposition (HFCVD), with a modified vertical filament arrangement, has been used for the deposition of diamond films. Diamond film quality and purity has been characterized using scanning electron microscopy (SEM) and micro-Raman spectroscopy. The performance of diamond-coated WC-Co burs, uncoated WC-Co burs, and diamond-embedded (sintered) burs have been compared by drilling a series of holes into various materials such as human teeth, borosilicate glass, and acrylic teeth. Flank wear has been used to assess the wear rates of the burs when machining biomedical materials such as those just described.

Laser micromachining of chromium-rich die steels under controlled atmospheres

Abstract Diode-pumped, solid-state (DPSS) lasers with multiwavelength capability have become an industrial reality in recent years. Multiwavelength capability allows DPSS lasers to perform operations such as micromachining in a variety of engineering materials such as ceramics, metals and polymers. A series of experiments was performed to investigate how shielding gas environments and gas pressure affect the ability to cut and machine chromium-rich die steels. Results from this study reveal that traditional plasma-controlling gases have a detrimental effect on the surface morphology of micromachined components.

Nanogrinding with Abrasives

The coating of piezoelectric materials with diamond particles, or fashioning an abrasive material coated to a piezoelectric material using a laser, has enabled the production of truly flat substrates so that features can be created on materials using a manufacturing process known as “nanogrinding with abrasives.” The principle of the process relies on applying an electric current to the abrasive-coated piezoelectric material that causes the material to strain in various directions. When the piezoelectric material is touching the substrate material, the abrasive particles remove small pieces of the substrate. The magnitude of the applied current controls the material removal rate. The process can be used to process many materials especially in the production of nanoscale channels that are used in micro- and nanofluidic devices. To achieve the generation of flat surfaces, the process must be executed within a specially constructed vibration dampening machine tool. This chapter describes recent developments in the field of nanogrinding with abrasives.

Diamonds synthesis, properties and applications

The depostition of diamond films using VFCVD onto tungsten carbide dental burs has been described. To enchance nucleation, growth and adhesion of the diamond substrate was pre-treated using a Murakami etch.The structure and morphology of the diamond coated bursa and uncoated burs have been compared.Diamond is an ideal material for numerous applications such as dental burs and drills due to its unique combination of chemical, mechanical and thermal properties. The most widely used method of growth diamond is chemical vapor deposition (CVD) namely hot filament and microxad wave plasma processes. The use of vertical filament chemical vapor deposition (VFCVD) process has been developed to uniformly coat complex shaped tools and is described in detail. The growth characteristics and film properties are described for use on dental burs and drills.

Diamond deposition of tungstencarbide bursing VFCVD

The depostition of diamond films using VFCVD onto tungsten carbide dental burs has been described. To enchance nucleation, growth and adhesion of the diamond substrate was pre-treated using a Murakami etch.The structure and morphology of the diamond coated bursa and uncoated burs have been compared.Diamond is an ideal material for numerous applications such as dental burs and drills due to its unique combination of chemical, mechanical and thermal properties. The most widely used method of growth diamond is chemical vapor deposition (CVD) namely hot filament and microxad wave plasma processes. The use of vertical filament chemical vapor deposition (VFCVD) process has been developed to uniformly coat complex shaped tools and is described in detail. The growth characteristics and film properties are described for use on dental burs and drills.

Primary Chip Formation During an Extremely High Speed Micromachining Process

The advent of nanotechnology has created a demand for precision-machined substrates so that ‘bottom-up’ nanomanufacturing processes can be used to produce functional products at the nanoscale. However, machining processes must be scaled down by an order of magnitude that requires very stable desktop machine tools to produce precision-machined substrates using cutting tools that are rotated at speeds in excess of one million revolutions per minute. Therefore, the mechanics of chip formation at this scale are critical when one considers the effect of chip formation on the generation of surface roughness on the substrate. The tight curl of a machined chip in orthogonal machining appears to be part of the primary shear process. It is also known that transient tight curl occurs before a secondary shear zone develops ahead of the removal of the chip from the cutting zone. However, continuum models predict that curled chips incorporate stresses due to the establishment of a secondary shear zone. A model is presented in terms of the heterogeneous aspects of continuous chip formation, which shows very good agreement with experimental data.Copyright