Michael D. Whitfield

Machining Cancellous Bone Prior to Prosthetic Implantation

The structure of cancellous bone can be described as heterogeneous, and as such, is difficult to shape by cutting tools during clinical surgical practices. The structure of bone can have a devastating effect on the performance of the cutting tool unless it is coated with a hard-wearing, thin solid film. Here, the use of diamond-coated cutting tools to prepare bone for biomedical implants are investigated. This paper describes developments in the use of coated cutting tools for machining of cancellous bone and to prepare a nanostructured surface.

Fundamentals of Machining

During chip formation there is a substantial increase in the specific energy as chip size is reduced during machining. It is believed this is due to the fact that all metals contain defects such as grain boundaries, missing and impurity atoms, and when the size of the material removed decreases the probability of encountering a stress-reducing defect decreases. Since the shear stress and strain in metal cutting is unusually high, discontinuous microcracks usually form on the primary shear plane. If the material is very brittle, or the compressive stress on the shear plane is relatively low, microcracks will grow into larger cracks giving rise to discontinuous chip formation. When discontinuous microcracks form on the shear plane they will weld and reform as strain proceeds, thus joining the transport of dislocations in accounting for the total slip of the shear plane. This chapter focuses on machining at the micro- and nanoscale and attempts to explain the dominant features of machining as the size effect becomes significant.

Computational analysis of the intimate contact between an inclined wedge and low carbon steel during metal cutting

The initial stages of intimate contact between an inclined wedge and low carbon steel creates significant opportunities for manufacturers of machined products to understand how dry machining and minimum quantity lubrication affect the economics of manufacturing, especially when one considers how important frictional interactions between chip and tool are on the final structure of the workpiece materials in terms of structural phase transformations. The present work not only compares various computational approaches to the solution of shear plane and tool face temperatures, but also explains why there is a large discrepancy when calculating temperature generated during machining when using Loewen and Shaws method for calculating shear plane and tool face temperatures.

Commercialisation of nanotechnologies: technology transfer from university research laboratories

This paper presents information on the commercialisation of nanotechnologies from research laboratories based in the USA. The paper discusses the early implementation of the National Nanotechnology Initiative and provides an analysis of how commercialisation of nanotechnologies is undertaken from university research laboratories.

Burr formation and elimination in micromilling processes

Machining at any scale usually produces burrs on surfaces; burrs are unwanted and add cost to the part. In general machining parameters are optimised to prevent burr formation, the cutting tool is assumed to be worn and is changed when burrs appear. When burrs appear on the part they must be deburred. At the micro scale deburring has been shown to be impractical because excessive dimensional errors and high tensile residual stresses are induced into the part. This study examines three methods of preventing burr formation: using coated tools to prevent tool wear; selecting a workpiece with a low amount of dislocations to prevent plastic deformation; and using machinable vice jaws to manipulate the flow stress. All these methods succeeded in suppressing burr formation.

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.

Micromachining from a Materials Perspective

Mechanical micromachining is a technique that has the potential to become a successful small-scale manufacturing process. If the abilities of macromachining can be scaled down to the microscale, then a versatile manufacturing technique will be created that is capable of processing a wide variety of materials. However, simply scaling down machines is not the solution, reducing the scale from macro to micro presents unique problems that must be overcome that include eliminating tool wear, machining heterogeneous workpiece materials in a uniform manner, and advances in machine tool design. Therefore, a review of the aspects of machining is presented that focuses on the machining process from a materials perspective.

Manufacture and Development of Nanostructured Diamond Tools

Chemical vapor deposited diamond films have many industrial applications but are assuming increasing importance in the area of microfabrication, most notably in the development of diamond-coated micro-tools. For these applications the control of structure and morphology is of critical importance. The crystallite size, orientation, surface roughness, and the degree of sp3 character have a profound effect on the machining properties of the films deposited. In this chapter, experimental results are presented on the effects of nitrogen doping on the surface morphology, crystallite size, and wear of micro-tools. The sp3 character optimizes at 200 ppm of nitrogen and above this value the surface becomes much smoother and crystal sizes decrease considerably.

Burr formation during dry microdrilling operations

Burr formation is a problem in that it interferes with the proper functioning of micro components. A multi-response optimisation method using a Taguchi approach is used for simultaneous minimisation of burr size, namely, burr height and burr thickness when drilling AISI 1018 steel. Taguchis L25 orthogonal array for each experiment was performed under different conditions of cutting speed, cutting feed, point angle, and lip clearance angle for a 600 µm drill diameter. In the utility concept for multi-response optimisation, the signal-to-noise ratio for each experiment in the orthogonal array was determined by employing weighting factors for burr height and burr thickness. Detailed analysis of ANOVA with the different combinations of weighting factors to determine the contributions of various micro drilling parameters in controlling the burr height and thickness is presented in this paper.

Two approaches to effective ventilation system design for the biomedical device and pharmaceutical industries

This paper provides two alternative solutions to the difficult task of providing adequate ventilation to operations found in the biomedical device and pharmaceutical manufacturing industries. The first approach involves a two-tier strategy that includes an isolation chamber and an appropriately designed local exhaust hood. The second approach involves the design of modular, walk-in hood. Mechanical and electrical design and development criteria for each option are delineated, and advantages and limitations are elucidated for both systems. Future efforts will target the testing of these two approaches under laboratory conditions to assess the merits of each.