S. Izman

Cutting force and surface roughness characterization in cryogenic high-speed end milling of Ti-6Al-4V ELI

This study investigates the cutting forces induced during high-speed end milling of titanium alloy (Ti–6Al-4V ELI) as well as the surface quality of the milled surfaces. The high-speed machining was performed using carbide tool of coated and uncoated types at three cutting speeds of 200, 250, and 300 mm/min and two feed rates of 0.03 and 0.06 mm/tooth. Surface integrity was characterized in terms of surface roughness (Ra) and morphology. Cutting speed was found to be inversely proportional to the resultant cutting force at any cutting conditions. Cutting force in the X direction displayed higher sensitivity against cutting conditions. The results showed that feed rate is proportional to cutting force in X and Y directions regardless of tool type. Under the fixed feed rate condition, cutting force decreased at higher cutting speed for both tools. It was also found that uncoated tool induces less cutting force compared to coated one. High-speed end milling using uncoated tool provided better surface finish than using a coated carbide tool, especially at lower cutting conditions. However when coated carbide tool was used, surface roughness improved significantly with the increase in cutting speed. In contrast, almost opposite phenomenon was observed when uncoated tool was used.

Surface Modification Techniques for Biomedical Grade of Titanium Alloys: Oxidation, Carburization and Ion Implantation Processes

Titanium and titanium alloys are widely used in a variety of engineering applications, where the combination of mechanical and chemical properties is of crucial importance. Aerospace, chemical and automotive industries as well as the medical device manufacturers also benefited from the outstanding properties of titanium alloys. The wide spread of its uses in biomedical implants is mainly due to their well-established corrosion resistance and biocompatibility. However, not all titanium and its alloys can meet all of the clinical requirements for biomedical implants. For instance, it is reported that bare titaniumvanadium alloy has traces of vanadium ion release after long period exposure with body fluid (Lopez et al., 2010). Excessive metal ions release into the body fluid and causes toxicity problems to the host body. A new group of titanium alloy such as Ti-Nb and Ti-Zr based are recently introduced in the market to overcome the toxicity of titanium-vanadium based alloy (Gutierrez et al., 2008). Although, these alloys have a high strength to weight ratio and good corrosion resistance and biocompatible, but it suffers from poor tribological properties which limits their usefulness to a certain extent especially when they are applied to joint movements. Wear debris generated from these articulation joints can induce inflammation problem and toxic effect to the human body. In biomedical point of view, post implantation is very crucial stage where the interaction between the implanted material surface and the biological environment in human body is critically evaluated. Either in the short or long run, the toxic effect becomes an issue to host body. Hence, the implant material surface has a strong role in the responses to the biological environment. In order to improve the biological and tribological properties of implant materials, surface modification is often required (Huang et al., 2006, Kumar et al., 2010b). This chapter embarks on the commonly used implant biomaterials, followed by general overview on the surface modification techniques for treating titanium alloy. The basic principles of oxidation, carburization and ion implantation methods and their developments are discussed in the following sections.

The application of surface response methodology to the pretreatment of WC substrates prior to diamond coating

High cobalt (Co) content greater than 10% in tungsten carbide is desirable because Co improves the toughness of the cutting tool. However, the additional Co poses a huge challenge in surface preparation given that the Co content must be reduced to less than 1% on the substrate surface prior to applying a diamond coating. The excessive presence of Co on the substrate surface during coating suppresses diamond nucleation and causes the deterioration of diamond film adhesion. Many attempts have been made to overcome this issue, including the use of chemical etching, mechanical blasting, and heat treatment, but the successful pretreatment of WC-12%Co is still very limited. In this paper, a single-step chemical pretreatment using a mixture of sulfuric acid and hydrogen peroxide solutions was carried out on WC-12%Co. Two independent variables, i.e., etching time and acid temperature, were varied in the experiments to reduce Co contents as well as to roughen the substrate surface. The experimental plan was based on a central composite design. Variance analysis was employed to verify the precision of the mathematical models and their relative parameters. The predicted models generated by the response surface methodology (RSM) were compared with the experimental results, and close agreement was observed. The models demonstrated the significance of both factors, namely, acid temperature and etching time, in reducing Co contents to less than 1% as well as a roughening of the substrate surface within the desirable range.

Machining parameters effect in dry turning of AISI 316L stainless steel using coated carbide tools

Austenitic stainless steel AISI 316L is used in many applications, including chemical industry, nuclear power plants, and medical devices, because of its high mechanical properties and corrosion resistance. Machinability study on the stainless steel is of interest. Toward sustainable manufacturing, this study also includes the power consumption during machining along with other machining responses of cutting force, surface roughness, and tool life. Turning on the stainless steel was performed using coated carbide tool without using cutting fluid. The turning was performed at various cutting speeds (90, 150, and 210 m/min) and feeds (0.10, 0.16, and 0.22 mm/rev). Response surface methodology was adopted in designing the experiments to quantify the effect of cutting speed and feed on the machining responses. It was found that cutting speed was proportional to power consumption and was inversely proportional to tool life, and showed no significant effect on the cutting force and the surface roughness. Feed was proportional to cutting force, power consumption, and surface roughness and was inversely proportional to tool life. Empirical equations developed from the results for all machining responses were shown to be useful in determining the optimum cutting parameters range.

The Effect of Cutting Parameters on Power Consumption during Turning Nickel Based Alloy

Machining process should also consider environmental aspect, with power consumption as one of the criteria. Cutting parameters can be optimized to minimize power consumption. This paper takes a study on turning of nickel-based hastelloy under dry condition (no cutting fluid) which varies cutting speed (150, 200, and 250 m/min) and depth of cut (0.5, 1.0, and 1.5 mm). Power consumption of particular machining process at various cutting parameters was derived and calculated. It was found that minimum power consumption was shown when the turning process was performed at the lowest cutting speed and depth of cut.

Effects of Adding Multiwalled Carbon Nanotube into Dielectric when EDMing Titanium Alloy

The low thermal conductivity and gummy-like characteristic of titanium based materials reduce the tool life of cutting tool significantly when machining using conventional processes. Non-contact machining like electrical discharge machining becomes one of the alternative methods to machine these titanium alloys especially when involving complex shapes and geometry. The use of powder-mixed dielectric (PMD) has been successfully applied in machining moulds and dies steel based materials but limited study has been reported on PMD-EDMing titanium alloys. In the present work, EDMing performance of Ti6Al4V using kerosene dielectric with and without adding multi-walled carbon nanotube is compared experimentally. The effects of three controlled parameters, i.e. Pulse ON Time, Interval Time and Peak Current were evaluated on the machined samples. It is found that addition of multi-walled carbon nanotubes in dielectric shows significant improvement in material removal rate (7%) and surface finish (9%) together with reduction in white layer thickness as compared to plain dielectric without powder.

In Vitro Evaluation of Bioactivity of Chemically Deposited Hydroxyapatite on Polyether Ether Ketone

Polyether ether ketone (PEEK) is considered the best alternative material for titanium for spinal fusion cage implants due to its low elasticity modulus and radiolucent property. The main problem of PEEK is its bioinert properties. Coating with hydroxyapatite (HA) showed very good improvement in bioactivity of the PEEK implants. However the existing methods for deposition of HA have some disadvantages and damage the PEEK substrate. In our previous study a new method for deposition of HA on PEEK was presented. In this study cell proliferation of mesenchymal stem cell and apatite formation in simulated body fluid (SBF) tests were conducted to probe the effect of this new method in improvement of the bioactivity of PEEK. The mesenchymal stem cell proliferation result showed better cells proliferation on the treated layer in comparison with untreated PEEK. The apatite formation results showed the growth of the HA on the treated PEEK but there was not any sight of the growth of HA on the untreated PEEK even after 2 weeks. The results showed the new method of the HA deposition improved the bioactivity of the treated PEEK in comparison with the bare PEEK.

Recent Developments on Computer Aided Fixture Design: Case Based Reasoning Approaches

Fixture design is an important issue in the process of manufacturing. As a critical design activity process, automation in fixture design plays an integral role in linking computer aided designs and computer aided manufacturing. This paper carries out a literature review of computer aided fixture design (CAFD) developments using intelligent methods that have been commonly utilized in automation in the last two decades. The first part of this review considers the steps of fixture design along with the significant researches and requirements of fixtures over time. After that, the paper presents important and relevant research carried out in the field of CAFD using intelligent approaches and the working principles surrounding this issue. The following section concentrates on the details of case based reasoning (CBR) approach, the most successful approach in CAFD. The examination of this approach is carried out based on applications, stages of CBR based systems fixture design, working principles, and pertinent proposed approaches. Lastly, the present drawbacks of the current methods and shortfalls in research are identified for future studies.

Influence of Heat Treatment Cooling Mediums on the Degradation Property of Biodegradable Zn-3Mg Alloy

Recently, Zn-based alloys were introduced as alternative biodegradable metals to the well-studied Mg and Fe based alloys for temporary implants. In this work, Zn-3Mg alloy was developed using a conventional casting method followed by heat treatment with different cooling media. As-cast samples were heat treated at 370 oC for 10 hours then cooled in open air, water bath and inside furnace environments. The microstructure of as-cast alloy was characterized under optical microscope and phase analysis was evaluated using X-ray diffraction (XRD) technique. Potentiodynamic polarization tests were carried out on the heat treated samples for evaluating the degradation rate. It was observed that as-cast Zn-3Mg alloy consists of star-like-shape of primary Zn-rich dendrites which are segregated in the eutectic mixture of Mg2Zn11 phase. The segregation of these dendrites has been significantly reduced under water bath cooled treatment as compared to open air and inside furnace cooling. It is also found that the microstructure of the water cooled samples is more homogenous with less porosity than the as-cast, air or furnace cooled samples. The water cooled sample exhibits better degradation resistance for at least 2 folds than other treatments.

Effect of thermal oxidation temperature on rutile structure formation of biomedical TiZrNb alloy

Wear debris and metal ion release generated during application of biomedical devices would cause adverse cellular response, inflammation and pain in the human body. Modifying of implant surface with rutile structure is one of the methods to reduce these problems. In the present study, an attempt was made to evaluate the effect of thermal oxidation temperature on surface morphology and structure of the Ti13Nb13Zr biomedical material. The substrates were heated at varied temperatures of 550°C, 700°C and 850°C for 9 hours and cooled inside muffle furnace at a constant rate of 5oC/min. Scanning electron microscopy and x-ray diffractive were employed to evaluate the surface morphology and analyze the structure of the oxidized substrates respectively. All thermally oxidized samples exhibit the presence of oxides without spallation regardless of the thermal oxidation temperatures. Surface morphology of oxidized substrates changes from smooth to nodular particles-like shape when the oxidation temperature increases from low to high. Rutile structure dominants the surface area when the substrate is thermally oxidized at 850 °C.