Rosemar Batista da Silva

Overview of the Machining of Titanium Alloys

Machining of titanium alloys has always attracted considerable great interest in the manufacturing sector as well as within the scientific research community worldwide. Titanium alloys are widely employed in aero-engine and for airframe manufacture because of their outstanding strength to density ratios relative to other materials. Due to the expensive cost of titanium alloys, relative to other metals, attributed mainly to the complexity of the extraction process, difficulty of melting and problems during fabrication and machining, integrated researches have been established globally to improve their machinability. Success in the machining of titanium alloys can be achieved by employing the correct selection of cutting tools, cutting environment, and appropriate cutting conditions for each machining operation. This article reviews the machining of titanium alloys, highlighting the main cutting tools, cutting parameters, and cooling environments that have been employed in last three decades. The purpose is to enhance the general understanding of practitioners and researchers on the principles of machining titanium alloys, the properties that impair their machinability, performance of different cutting tools, wear mechanisms, and dominant failure modes of cutting tools under different machining conditions, including various techniques that enhance the machining of titanium alloys. A good understanding of these parameters as well as processing time and functionality of the machined component will lead to efficient and economic machining of titanium-base superalloys.

Increasing productivity in high speed machining of Ti-6Al-4V alloy under high pressure coolant supply

Cemented carbide tools are the most common tool materials employed in the machining of titanium alloys. Polycrystalline Diamond (PCD) tools can substantially enhance the machining productivity. So, this study investigates the performance of PCD tools when machining Ti-6Al-4V alloy at cutting speeds up to 250 m min-1 with coolant delivered under pressures. The results show that longer tool life can be achieved when machining with high pressure coolant supplies up to 20.3 MPa compared with the conventional coolant flow. Up to three folds increase in cutting speed can be achieved when machining with uncoated cemented carbide tools relative to that currently used for manufacture in industry, while with PCD tools, up to five fold increase in cutting speed is achievable when machining with PCD tools.

Application of the auxiliary wheel cleaning jet in the plunge cylindrical grinding with Minimum Quantity Lubrication technique under various flow rates

Minimum Quantity Lubrication is an alternative technique to conventional techniques that are related to environmental sustainability and economic benefits. This technique promotes the substantial reduction of the amount of coolant employed in machining processes, representing a mitigation of risks to people’s health that are involved with the process. On the other hand, it has been reported in the literature that some problems of using the Minimum Quantity Lubrication technique can impair the grinding efficiency. One of these problems is associated with wheel clogging phenomenon, which is caused by inefficient chip removal from the cutting zone as well as from mixture of metal dust and oil accumulated on the wheel surface during grinding. If chips lodge inside the pores of the grinding wheel as machining progresses, they will adversely affect dimensional and geometric quality of final product. Also, this will require more frequent dressing. A solution for this problem can be an effective cleaning system of the abrasive wheel during grinding with the traditional Minimum Quantity Lubrication technique Assisted with Wheel Cleaning Jet. In this context and aiming to explore the various potential health, environmental and economic benefits that have been widely reported in the literature about the use of Minimum Quantity Lubrication technique in grinding, this study presents an application of the Minimum Quantity Lubrication technique at flow rates (30, 60 and 120 mL/h) and assisted with wheel cleaning jet (Minimum Quantity Lubrication + Assisted with Wheel Cleaning Jet) in plunge grinding of a hardened steel with an aluminum oxide wheel. Experiments were also carried out with traditional Minimum Quantity Lubrication (without wheel cleaning) and with the conventional coolant techniques for comparison. The output variables were geometrical errors (surface roughness and roundness) of the workpiece, diametric wheel wear, acoustic emission, vibration and tangential cutting force. Results showed that Minimum Quantity Lubrication + Assisted with Wheel Cleaning Jet (with wheel cleaning jet) not only outperformed the traditional Minimum Quantity Lubrication technique in all the parameters analyzed, but in some cases it proved to be compatible with the conventional coolant technique under the conditions investigated. Also, most of values of the output parameters tested decreased with increase in flow rate.

Application viability evaluation of the Minimum Quantity Lubrication coolant technique under different flow rates in Plunge Cylindrical Grinding of the ABNT 4340 steel with aluminum oxide wheel

The coolant delivery technique known as Minimal Quantity Lubrication (MQL) has been employed in machining since the end of the 20th Century and has gained considerable evidence in the last years as a viable alternative to the use of the conventional coolant technique (flood). Due to the low oil flow rate delivered by the MQL technique in grinding operations, that generally varies from 20 to 240 ml / h in relation to near 600,000 ml / h flow rate of the conventional coolant technique, the MQL technique provides a reduced risk for human health and environmental damage associated with the use, maintenance and disposal of cutting fluids. In this context, this study was carried out to evaluate the application viability of the minimum quantity lubrication coolant technique under different flow rates in the plunge cylindrical grinding of ABNT 4340 steel with an aluminum oxide wheel. Three flow rates were tested: 30, 60 and 120 ml/h. Grinding trials with the conventional coolant delivery method were also tested for comparative purposes. The output variables used to assess the efficiency of the MQL technique in this work are: roughness, roundness and hardness of the workpiece. Grinding wheel wear and power consumption were also monitored. The results showed that, despite the higher values of roughness and roundness of the workpiece, as well as the grinding wheel wear, the values of these same parameters obtained after machining with the MQL technique were close to those obtained after machining with the conventional technique. No thermal damages and cracks on the machined surface, or even below the machined surface, were observed after grinding ABNT 4340 steel irrespective of the coolant-lubrication condition investigated. The results showed that the MQL with 120 ml/h can be an alternative coolant technique due to cleaner environment and lower consumption of fluid in grinding under the conditions investigated in this work.

Retificação cilíndrica do aço VP50 utilizando o rebolo de carbeto de silício verde com a técnica de MQL

Grinding is a high heat generation process that requires large amount of coolant, therefore, its use in large-scale lead to research and development of new lubri-cooling techniques to attend technical requirements, environmental laws, to preserve the health of operator and, whenever possible, to reduce production costs. Into this context, it is important to find solutions that maintain the same quality standards, finishing and the same technological effects. An alternative that has been used since the end of 20th. century is the MQL (minimum quantity lubrication) technique, which uses a mixture of air with low oil flow with medium pressure. The steel to be used as a specimen was VP50, widely used in industry for injection mold of thermoplastic. The grinding wheel used was green silicon carbide with vitrified binder that possess good thermal properties, high chemical stability and is recommended for grinding of ferrous and nonferrous materials. The output variables employed in this work were the surface roughness, roundness errors and microhardness. The acoustic emission signal and diametrical wear were also monitored. Analyses of the machined surfaces to evaluate the occurrence of thermal damages were also carried out via optical microscope. Results show that machining with the MQL technique outperformed the traditional coolant delivery method in terms of roundness and diametrical wear. No evidence of microstructural changes in the machined surfaces was observed after grinding with both lubri-coolant techniques.

Turning of SAE 1050 Steel With Vegetable Base Cutting Fluid

The study of cutting fluid performance in turning is of great importance because its optimization characteristics has associated benefits such as improved tool life and overall quality of machined components as well as reduction in power consumption during machining. However, there are recent concerns with the use of cutting fluids from the environmental and health standpoints. Since environmental legislation has become more rigorous, the option for “green machining” attracts the interest of several manufacturing companies. It is important to consider the cost of machining which is associated with tool wear, depending on the cutting environment. The use of vegetable oil may be an interesting alternative to minimize the health and environmental problems associated with cutting fluids without compromising machining performance. This paper presents a comparative study of mineral and vegetable cutting fluids in terms of tool wear after turning SAE 1050 steel grade with cemented carbide cutting tools. Constant depth of cut of 2mm and variable cutting speed (200 and 350 m/min) and feed rate (0.20 and 0.32 mm/rev) were employed. Test results suggest that is possible to achieve improvement in machinability of the material and increase tool life by using vegetable cutting fluid during machining. Tool life increased by about 85% when machining with vegetable-based fluids compared to mineral-based fluids. Analysis of the worn tools, however, revealed a more uniform wear on the worn flank face when machining with mineral-based fluids.© 2012 ASME