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Thermally-assisted end milling of titanium alloy Ti-6Al-4V using induction heating

Titanium and its alloys are considered as difficult-to-cut materials due to their inherent properties, such as low thermal conductivity, high cutting temperature, high chemical reactivity and strong adhesion between cutting tool and work material. This paper presents the benefits of thermally assisted machining on machinability improvement in end-milling of titanium alloy by utilising induction coil heating. The effect of online induction heating on the machinability (cutting force, tool life, vibration, and metal removal rate) are widely investigated. End milling tests were conducted on a vertical machining centre. Titanium alloy Ti-6Al-4V bar was used as the workpiece. Machining was performed with a 20 mm diameter end-mill tool holder fitted with a polycrystalline diamond (PCD) inserts. Flank wear was considered as the criterion for tool life and the wear was measured using a Hisomet II toolmaker’s microscope. The tool life tests were conducted until the flank wear exceeded 0.30 mm. Cutting force measurements were conducted using Kistler rotating cutting forced dynamometer. Vibration during cutting was captured using an online vibration monitoring system. The results lead to conclusions that thermally assisted machining significantly increases the tool life, reduces the vibration and cutting force, and increase the metal removal rate.

A Review of Additive Mixed-Electric Discharge Machining: Current Status and Future Perspectives for Surface Modification of Biomedical Implants

Surface treatment remained a key solution to numerous problems of synthetic hard tissues. The basic methods of implant surface modification include various physical and chemical deposition techniques. However, most of these techniques have several drawbacks such as excessive cost and surface cracks and require very high sintering temperature. Additive mixed-electric discharge machining (AM-EDM) is an emerging technology which simultaneously acts as a machining and surface modification technique. Aside from the mere molds, dies, and tool fabrication, AM-EDM is materializing to finishing of automobiles and aerospace, nuclear, and biomedical components, through the concept of material migrations. The mechanism of material transfer by AM-EDM resembles electrophoretic deposition, whereby the additives in the AM-EDM dielectric fluids are melted and migrate to the machined surface, forming a mirror-like finishing characterized by extremely hard, nanostructured, and nanoporous layers. These layers promote the bone in-growth and strengthen the cell adhesion. Implant shaping and surface treatment through AM-EDM are becoming a key research focus in recent years. This paper reports and summarizes the current advancement of AM-EDM as a potential tool for orthopedic and dental implant fabrication. Towards the end of this paper, the current challenges and future research trends are highlighted.

Effect of Cryogenic Cooling on the Heat Transfer during Turning of AZ31C Magnesium Alloy

ABSTRACT A combined analytical and experimental study was carried out to analyze the effects of cryogenic cooling on temperature during turning of AZ31C magnesium alloy. Finite element method was employed to model and simulating the cryogenic and dry turning. Results obtained from the model were found to be in good agreement with the experimental observations. For the maximum temperature at the turned surface, the difference in the experimental and predicted value observed during dry and cryogenic turning was only 4 and 8% respectively. A significant reduction in the maximum temperature on the chip surface (around 35%) and tool surface (around 29%) was observed during the cryogenic turning compared to dry turning. This reduction in temperature was an attribute of liquid nitrogen, which produces intense cooling effect around the vicinity cutting zone where heat generation takes place hence enhancing the heat transfer. The isothermal region belonging to the highest temperature on the tool surface was also reduced by about 42%. The reduction in temperature during cryogenic conditions were found to be beneficial for the machining of magnesium alloys under safe conditions, reducing the risk of ignition and explosions, and also increases the sustainability of the process.

Optimization of bone drilling parameters using Taguchi method based on finite element analysis

Thermal necrosis results fracture problems and implant failure if temperature exceeds 47 °C for one minute during bone drilling. To solve this problem, this work studied a new thermal model by using three drilling parameters: drill diameter, feed rate and spindle speed. Effects of those parameters to heat generation were studied. The drill diameters were 4 mm, 6 mm and 6 mm; the feed rates were 80 mm/min, 100 mm/min and 120 mm/min whereas the spindle speeds were 400 rpm, 500 rpm and 600 rpm then an optimization was done by Taguchi method to which combination parameter can be used to prevent thermal necrosis during bone drilling. The results showed that all the combination of parameters produce confidence results which were below 47 °C and finite element analysis combined with Taguchi method can be used for predicting temperature generation and optimizing bone drilling parameters prior to clinical bone drilling. All of the combination parameters can be used for surgeon to achieve sustainable orthopaedic surgery.

Cutting Force and Temperature Variation in Bone Drilling - A Review

Orthopaedic surgery procedure widely utilizes bone drilling in the work for correcting bone fracture and attaching prosthetics. Clean and accurately positioned holes are desired during bone drilling without damaging the surrounding tissues. However, bone temperature rises during drilling. It is always required to keep the temperature during drilling below 47 °C to avoid thermal osteonecrosis (bone cell death), which might lead to a loose of bone-implant interface. Drill design, drill parameters, and coolant delivery were believed to contribute to heat generation. As complex anisotropic biological tissues, determining the bone temperature during drilling is another issue. Complex mechanical and thermological properties are also other problems to be investigated due to the sensitivity to testing and specimen preparation.

Hydroxyapatite mixed-electro discharge formation of bioceramic Lakargiite (CaZrO3) on Zr–Cu–Ni–Ti–Be for orthopedic application

ABSTRACT To suit a target application, the machining mechanism of electro discharge machining (EDM) process has been hybridized to powder mixed EDM (PM-EDM) by adding various substances in the form of additives into the dielectric fluid. In this study, the application of PM-EDM to fabricate Lakargiite (CaZrO3) coating on Zr–Cu–Ni–Ti–Be substrate surface for potential orthopedic application, using hydroxyapatite (HA) powder as dielectric additive was proposed. The effect of various HA powder concentrations on deposition of CaZrO3 on Zr–Cu–Ni–Ti–Be surface was investigated. Zr–Cu–Ni–Ti–Be bulk metallic glass (BMG) has exceptional mechanical and chemical properties compared to its crystalline counterpart. It is expected that, the formation of a nanoporous bioactive CaZrO3 coating on the BMG surface will enhance its bioactivity. The FESEM investigation presents the formation of various interconnected shallow craters, nanopores, and few nanocracks and the energy dispersive X-ray spectroscopy results depict the presence of about 50% Lakargiite phase on the HA-deposited BMG surface. The X-ray powder diffraction characterization identified the phases includes ZrC, ZrO, TiC, and CaTiO3 formed on the PM-EDMed surface. The Rockwell hardness testing revealed the rise of BMG surface hardness to about 42%. The roughness of EDMed surface reduced from 6.22 nm to 2.00 nm after HA powder suspended in the dielectric fluid.

Surface Morphology and Corrosion Behavior in Nano PMEDM

This research study was conducted to investigate the effect of nanoaluminum powder mixed electrical discharge machining (PMEDM) on surface morphology and corrosion rate of titanium alloy material. The development of devices such as implants in biomedical engineering application nowadays requires materials having good mechanical and physical properties. Conventional machining process of titanium as implant is a challenge resulting relative poor surface quality. Even using electrical discharge machining (EDM) which is non-conventional machining process there are limitations including machined surface alteration with relative poor machined surface quality, low corrosion resistance and. PMEDM is hypothesized to address the above mentioned problems. In this study, PMEDM on titanium alloy using nanoaluminum powder and copper-tungsten electrode was assessed to investigate the improvement for implant application. Process parameters used are peak-current, ON-time, gap voltage and powder concentration. Surface morphology and average corrosion arte are selected output responses. Results showed that Surface morphology of PMEDM machined surface is significantly improved. PMEDM marginally enhanced corrosion rate of biomedical grade titanium alloy.

Experimental Investigation and 3D Finite Element Prediction of Temperature Distribution during Travelling Heat Sourced from Oxyacetylene Flame

This paper presents a 3D transient finite element modelling of the workpiece temperature field produced during the travelling heat sourced from oxyacetylene flame. The proposed model was given in terms of preheat-only test applicable during thermally enhanced machining using the oxyacetylene flame as a heat source. The FEA model as well as the experimental test investigated the surface temperature distribution on 316L stainless steel at scanning speed of 100mm/min, 125mm/min 160mm/min, 200mm/min and 250mm/min. The parametric properties of the heat source maintained constant are; lead distance Ld =10mm, focus height Fh=7.5mm, oxygen gas pressure Poxy=15psi and acetylene gas pressure Pacty=25psi. An experimental validation of the temperature field induced on type 316L stainless steel reveal that temperature distribution increases when the travelling speed decreases.

Experimental Investigation to Improve Surface Integrity of Biomedical Devices by End-Milling AISI 316L Stainless Steel

This paper presents the influence of machining parameters namely cutting speed and feed rate on the machinability enhancement of AISI 316L stainless steel, in terms of surface integrity using end-milling with coated tungsten carbide tool (TiAlN). Optical microscopy, Scanning Electron Microscopy (SEM) and surface roughness measurement were used to analyze the surface integrity in terms surface topography and hardness test. A multi view approach is adopted to study the effect of different cutting parameters on the surface integrity of AISI 316L stainless steel. It was found that high cutting speed and low feed rate influence the surface roughness. Low surface roughness makes AISI 316L stainless steel more corrosion resistant which prevents wear of the implants.

Improved Surface Integrity during End Milling AISI 316L Stainless Steel Using Heat Assisted Machining

Different heat source had been investigated for thermally enhanced machining on various engineering materials. Even so, temperature control from the heat source remained a challenged to the process effectiveness.This study used oxyacetylene combustion flame as a heat source in heat assisted machining. The study focuses on the relationships between process conditions; maximum temperature distribution and the surface integrity of 316L stainless steel during preheat machining as compared to dry hard part machining. Two levels of cutting speed 1000rev/min, 630rev/min and feed rates 160mm/min and 100mm/min were investigated while the depth of cutting was maintained constant at 1mm. While preheat machining for 60seconds along the span of the work piece material at cutting speed 1000 rev/min and feedrate 100mm/rev, the average surface finish have improved by 94% over dry hard part machining. This corresponds to flank wear VB = 0.0644mm during heat assisted machining and 0.1425mm for dry hard part machining respectively. Such improvement was accompanied with longer tool life and secured surface integrity which improves the material’s life cycle.