Mark Stanford

Investigation into the Relationship between Tool-Wear and Cutting Environments when Turning En32 Steel

New environmental legislation is forcing companies to realign their use of metalworking fluids in favour of non‐polluting cutting environments that will return acceptable tool wear rates and reduced costs. Studies have been undertaken to determine the effectiveness of various environments on tool wear, in order to either reduce or even eliminate totally, the dependency on flood coolants. Industrially reproducible cutting tests were devised, where an EN32 case hardening steel material was turned in a range of different cutting environments and tool life measured. Low oxygen gaseous environments were compared with conventional cutting environments and a 55 per cent flank wear reduction has been recorded using uncoated tooling.

The potential application of a Cobalt Chrome Molybdenum femoral stem with functionally graded orthotropic structures manufactured using Laser Melting technologies.

The cementless fixation of porous coated femoral stems is a common technique employed for Total Hip Arthroplasty (THA). With the rate of revision surgery appearing to rise and younger more active patients requiring primary surgery it can be thought that alternative methods for increasing implant longevity need to be considered. The stress shielding of periprosthetic bone still remains a contributing factor to implant loosening, caused through a mismatch in stiffness between the implant and the bone. However, the ability to achieve stiffness matching characteristics is being realised through the use of Additive Layer Manufacturing (ALM) technologies and Functionally Graded Materials (FGM). This paper proposes an alternative design methodology for a monoblock Cobalt Chrome Molybdenum (CoCrMo) femoral stem. It hypothesises that a femoral stem suitable for cementless fixation can be manufactured using Laser Melting (LM) technology offering orthotropic functionally graded porous structures with similar mechanical properties to human bone. The structure and mechanical properties of the natural femur have been used as a basis for the design criteria which hypothesises that through a combination of numerical analysis and physical testing, an optimal design can be proposed to provide a lightweight, customised femoral stem that can reduce the risk of implant loosening through stress shielding whilst maintaining bone-implant interface stability.

A numerical investigation into the influence of the properties of cobalt chrome cellular structures on the load transfer to the periprosthetic femur following total hip arthroplasty

Stress shielding of the periprosthetic femur following total hip arthroplasty is a problem that can promote the premature loosening of femoral stems. In order to reduce the need for revision surgery it is thought that more flexible implant designs need to be considered. In this work, the mechanical properties of laser melted square pore cobalt chrome molybdenum cellular structures have been incorporated into the design of a traditional monoblock femoral stem. The influence of incorporating the properties of cellular structures on the load transfer to the periprosthetic femur was investigated using a three dimensional finite element model. Eleven different stiffness configurations were investigated by using fully porous and functionally graded approaches. This investigation confirms that the periprosthetic stress values depend on the stiffness configuration of the stem. The numerical results showed that stress shielding is reduced in the periprosthetic Gruen zones when the mechanical properties of cobalt chrome molybdenum cellular structures are used. This work identifies that monoblock femoral stems manufactured using a laser melting process, which are designed for reduced stiffness, have the potential to contribute towards reducing stress shielding.

The future role of metalworking fluids in metal cutting operations

As more stringent environmental legislation is enforced throughout Europe manufacturing businesses, employing metal cutting processes, can no longer ignore the growing importance of environmental aspects relating to cutting fluids. Businesses, through market forces, are being forced into offering a “clean solution” to the metal cutting processes which they operate. Cutting fluids despite playing an important role in metal cutting, have considerable environmental impact. There is a need therefore to understand the role of cutting fluids within the cutting process in order to evaluate possible environmentally friendly alternatives to the use of cutting fluids. In order to achieve this the operating environment in which the process is being carried out, and the consequences of removing the cutting fluid from the process altogether has to be assessed. This paper therefore, reflects on the role of cutting fluid and the implications of their use. Viable methods of reducing cutting fluid consumption are also reported, together with efficient methods of cutting fluid utilisation (e.g. minimum quantity delivery systems). Finally, the difficulties experienced in removing cutting fluids from the metal cutting process are highlighted through the consideration of dry cutting technologies.

Microstructure and Tensile Strength of Rapid Manufacturing Parts

The purpose of this work is to investigate the microstructure and tensile strength of Ti6Al4V pre-alloyed powders produced by a direct metal laser sintering technique. Traditionally, Ti6Al4V products for biomedical applications were produced through hot working or machining of wrought semi-finished products. A change in the production route for manufacturing Ti6Al4V products, from the more traditional methods to an additive manufacturing route, requires an investigation of microstructure and mechanical properties because these are strongly influenced by the production route. The microstructure obtained through rapid solidification during laser sintering shows a very fine α+β lamellar morphology. There is also evidence of martensite which was expected due to high solidification rate of the liquid pool from a temperature above the β-transus during the laser sintering process. Structurally, good mechanical properties which are comparable to the bulk material were obtained.

Tool wear investigation whilst turning BS970‐080A15 carbon steel using TiCN‐Al2O3 CVD coated carbide tooling in gaseous and liquid nitrogen environments

Purpose – The purpose of this work is to investigate the performance of non‐contaminating metal cutting environments and investigate the associated tool chip interface conditions. The work benchmarks flood coolant characteristics and considers gaseous cutting environments as possible alternatives.Design/methodology/approach – Cutting trials were undertaken for a range of cutting environments. Flood coolant was investigated as was dry cutting, compressed air, room temperature nitrogen and liquid nitrogen environments. A range of cutting variables was measured in order to document the effect of cutting environment.Findings – The gaseous component of the liquid nitrogen environment limited the adhesion on the tool face to a region along the flank edge of the tool, shifting rake face conditions from seizure to that of sliding. Tighter chip curl, shorter contact lengths, reduced adhesion and lower feed forces are evidence that liquid nitrogen is acting as a “liquid inert barrier” beneath the chip within the to...

Numerical and Experimental Studies on the Laser Melting of Steel Plate Surfaces

The direct impingement of laser on the surface of a platform occurs during additive layer manufacturing especially for the first layer of powder coating. As a result, thermal stresses develop due to high temperature gradients in a thin layer of the plate surface, which can result in undesired surface deformation of the steel platform used. This study investigates the residual stress profiles on a hot-rolled AISI 1015 steel plate produced by direct laser application. A three-dimensional finite element simulation model is developed which considers the laser heating process as a sequentially coupled thermal elasto-plastic problem. Experiments using optical laser scanning microscopy to obtain surface topography of the melted surface are also presented showing reasonable agreement with the simulation results. The influence of the plate thickness on the stress-depth distribution is presented.

Experimental and Numerical Analysis of Residual Stresses in Additive Layer Manufacturing by Laser Melting of Metal Powders

Determining the three-dimensional residual stress fields and the associated distortions using numerical simulations for multi-layered parts has proved to be a challenge in additive layer manufacturing. This paper presents an innovative three-dimensional thermal-elasto-plastic finite element model for predicting the deformation and residual stress fields in TiAl6V4 parts built on steel platforms. The developed model utilises temperature dependent material physical and mechanical properties as well as latent heat of melting. Experiments conducted using surface profilometry showed good agreement with the simulation results. The finite element model was used to investigate the overall effect of the melting powder on the platform deformation and residual stresses for multiple layers of deposited powder.

Construction of next-generation superplastic forming using additive manufacturing and numerical techniques:

The superplastic forming process is used in a wide range of high-value-added manufacturing sectors to make lightweight, complex-shaped components for high-performance applications. Currently, it is a high-cost process, for example, the superplastic forming of titanium alloys involves a high-temperature furnace, costly (mould) tooling and has a high utilization of resources such as argon gas and energy. The authors of this article propose a prototype for next-generation superplastic forming laboratory equipment. The aim is to develop improved methods, particularly for heat management in the superplastic forming process, to allow a more widespread application of the process to manufacture lower cost products. The next-generation superplastic forming tool comprises a tool in the form of a hemispherical shell, pressure chamber with incorporated water cooling system and an infrared heating system. The construction, usability and suitability of the next-generation superplastic forming equipment have been proven by a series of physical experiments, and numerical simulations are performed and the results are presented and discussed in this article.

Direct metal laser sintering of a Ti6Al4V mandible implant

The aim of this study is to investigate the direct manufacturing of a titanium mandible implant via a laser sintering process which involves the different areas of medicine, engineering and product design. The manufacturing and challenges for producing customised titanium implants are described in this work. Implant data and its functional requirements of loading and fixation are established based on CT scan data. The process of converting different types of data from CT scans to 3D design and then to readable machine data and its associated processing software are illustrated and explained. The mandible tray was designed with a predefined porous structure to reduce weight and stimulate better bio-factor delivery at the same time. The laser sintering process and its critical steps for producing a tailored structure and complex shape are reported. This includes titanium powder preparation, processing parameters, support structures, model inclination, post-processing works and associated costs. Results show that it is possible to fabricate a customised mandible implant with a complex structure and having sufficient detail through the laser sintering process. This technique provides a platform to respond quickly and build accurate parts with good surface finish.