High-pressure Coolant Supply Research Articles

Experimental Investigation on Effect of High Pressure Coolant with Various Cutting Speed and Feed on Surface Roughness in Cylindrical Turning of AISI 1060 Steel Using Carbide Insert

Providing sufficient provisions to transfer heat from the work-tool interface is a key to improve tool life and surface integrity. With the conventional flood cooling system where the coolant is directed towards the work-tool interface at very low pressure, there are possibilities for the coolant to get heated up and produce vapors which in turn insulates the cutting zone from the coolant. This reduces the purpose of coolant. Supplying coolant at very high pressure and very high velocity may provide the best control to reduce cutting temperature and tool wear and correspondingly increases tool life. This paper deals with an experimental investigation on the effect of high pressure coolant on surface finish in cylindrical turning of AISI 1060 Steel using tungsten carbide turning insert. Surface Roughness values are captured with different cutting speed and feed rates with high pressure and low pressure coolant supply. It is observed that there was a considerable improvement in surface finish with the use of high-pressure coolant (HPC) under various cutting speed and feed rate.

Machinability Enhancement of Lead-free Brass Alloys

This paper deals with fundamental investigations on the machinability of lead-free brass alloys. The effect of microstructure and silicon as alloying element on chip formation, cutting forces, tool temperatures and tool wear is analyzed during external turning. Based on that, various approaches for machinability enhancement were investigated in order to enable high performance cutting operations. The paper focuses on the influence of various tool coatings such as TiB2, DLC and diamond on abrasive and adhesive tool wear. Besides a significant decrease of tool wear, dry turning of lead-free brass alloys was realized by adapted tool coating. Moreover, investigations on the performance of PCD tools as well as high-pressure coolant supply strategy were carried out.

Influence of the lubricoolant strategy on thermo-mechanical tool load

This paper deals with the influence of the cooling strategy on thermo-mechanical tool load during turning of different hard-to-cut materials. The aim is to describe how to control the complex of loads acting on the cutting edge to achieve suitable conditions for different combinations of cutting tool material and workpiece material. As an introduction, measurements and analysis of tool temperature, cutting forces and wear behaviour during turning of TiAl6V4 and Inconel 718 with cemented carbide and high-pressure lubricoolant supply are presented. Based on these results the tool wear behaviour of whisker reinforced cutting ceramics during turning of Inconel 718 with high-pressure lubricoolant supply and conventional flood cooling is evaluated. Additionally this paper presents results of tool temperature, cutting forces and wear behaviour during turning of TiAl6V4 with cemented carbide under cryogenic conditions (LN2 and CO2-snow). The results of the tests under cryogenic conditions will be brought in line with the results of the high-pressure coolant supply. Thereby it is possible to qualify the amount of different wear mechanisms onto the total tool wear under different cooling conditions and to show how they can be influenced specifically.

Tool life and wear mechanisms in high speed machining of Ti–6Al–4V alloy with PCD tools under various coolant pressures

Usage of titanium alloys has increased since the past 50 years despite difficulties encountered during machining. Many studies involving different tool materials, cutting parameters, tool geometry and cutting fluids when machining this important aerospace material have been published. However, there are relatively few literatures available on the application of ultra hard tools in the machining of titanium-alloys. The primary objective of this study is to investigate the behaviour of Polycrystalline Diamond (PCD) tools when machining Ti–6Al–4V alloy at high speed conditions using high pressure coolant supplies. Tool performance under different tribological conditions and the dominant wear mechanisms were investigated. Increase in coolant pressure tends to improve tool life and reduce the adhesion tendency, accelerated by the susceptibility of titanium alloy to gall during machining. Adhesion and attrition are the dominant wear mechanisms when machining at the cutting conditions investigated.

3257 Environmentally Conscious Deep Hole Drilling using Oil Mist Carried by Mixed Gas

The productivity of deep hole drilling is greatly improved in recent years, where the long twist drill with the high pressure coolant supply has been used. The problems of this system are revealed such as the excess consumption of electric power, and the dispose of the large quantities of waste coolant. To solve these problems, MQL drilling becomes practical and now widely used in many Japanese automobile factories. In this research, the process improvement technology for MQL drilling is proposed. Excellent tool life was achieved by using mixed gases as the mist carrier instead of the conventional compressed air. The results of drilling experiment shows the increasing drill-life and the increasing thrust force during drilling. The cutting force and chip thickness analysis suggest the novel tribological conditions derive from atmosphere.

High Productivity Rough Turning of Ti-6Al-4V Alloy, with Flood and High-Pressure Cooling

The performance of uncoated carbide tools when rough turning Ti-6Al-4V alloy were investigated under flood cooling and with 7 MPa coolant supply pressure. Up to twofold increase in tool life was achieved when machining at a speed of 80 m/min with a high-pressure coolant supply of 7 MPa relative to a conventional overhead coolant flow. The dominant tool failure mode(s) were maximum flank and nose wear. Higher tool wear rates were observed when machining with flood cooling due to excessive temperature generation at the cutting interfaces, which accelerated tool wear. There was evidence of plastic deformation on the machined surface after machining with both flood cooling and 7 MPa coolant supply at the higher speed conditions of 120 m/min. There was no evidence of surface hardening of the machined surfaces after machining in both coolant environments were investigated. This might be due to lower deformation forces that are unable to induce strain hardening of the machined surfaces.

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.

Surface integrity of finished turned Ti–6Al–4V alloy with PCD tools using conventional and high pressure coolant supplies

Surfaces generated when machining Ti–6Al–4V alloy with PCD tools using conventional and high pressure coolant supplies was investigated. Longer tool life was recorded when machining Ti–6Al–4V with high-pressure coolant supplies and the recorded surface roughness R a values were well below the tool rejection criterion (1.6 μm) for all cutting conditions investigated. The micro-structure of the machined surfaces were examined on a scanning electron microscope. Micrographs of the machined surfaces show that micro-pits and re-deposited work material were the main damages to the surfaces. Micro-hardness analysis showed hardening of the top machined surfaces when machining with conventional coolant while softening of the subsurface layer was observed when machining under high-pressure coolant supplies. The later is probably due to lower heat generated, with the consequent tempering action when machining with PCD tools with high-pressure coolant supplies. The microstructure below the machined surfaces had minimal or no plastic deformation when machining with conventional and high-pressure coolant supplies.

Machining of nickel-base, Inconel 718, alloy with ceramic tools under finishing conditions with various coolant supply pressures

Machining of Inconel 718 with whisker reinforced ceramic tool gave better performance in terms of tool life under high-pressure coolant supplies up to 15 MPa compared to conventional coolant supplies. The use of 15 MPa coolant supply pressure tend to suppress notching during machining thus improving tool life, while the use of higher coolant supply pressure of 20.3 MPa did not show improvement in tool life due probably to accelerated notch wear caused by water jet impingement erosion. Cutting forces decreased with increasing coolant supply pressure due to improved cooling and lubrication at the cutting interface as well as effective chip segmentation ensured by the momentum of the coolant jet. Surface roughness generated were well below the rejection criteria. This can be attributed to the round shape of the insert which tend to encourage smearing of the machined surface with minimum damage. Microstructure analysis of the machined surfaces show evidence of plastic deformation and hardening of the top layer up to 0.15 mm beneath the machined surface as a result of increase in dislocation density.

Evaluation of the performance of CBN tools when turning Ti–6Al–4V alloy with high pressure coolant supplies

Cubic Nitride Boron (CBN) tools are generally used for machining harder alloys such as hardened high Cr steels, titanium and nickel alloys. The tools are expected to withstand the heat and pressure developed when machining at higher cutting conditions because of their high hardness and melting point. This paper evaluates the performance of different CBN tool grades in finish turning Ti–6Al–4V (IMI 318) alloy at high cutting conditions, up to 250 m min −1, with various coolant supplies. Tool wear, failure modes, cutting and feed forces and surface roughness of machined surfaces were monitored and used to access the performance of the cutting tools. Comparative trials were carried out with uncoated carbide tools when machining at a speed of 150 m min −1. Test results show that the performance of CBN tools, in terms of tool life, at the cutting conditions investigated is poor relative to uncoated carbide tools, as expected and often, reported due probably to rapid notching and excessive chipping of the cutting edge associated with a relatively high diffusion wear rate that tends to weaken the bond strength of the tool substrate. An increase in the CBN content of the cutting tool also led to a reduction in tool life when machining at the cutting conditions investigated.

Finish Machining of Nickel-Base Inconel 718 Alloy with Coated Carbide Tool under Conventional and High-Pressure Coolant Supplies

Single-point turning of Inconel 718 alloy with commercially available Physical Vapour Deposition (PVD)-coated carbide tools under conventional and high-pressure coolant supplies up to 20.3 MPa was carried out. Tool life, surface roughness (Ra), tool wear, and component forces were recorded and analyzed. The test results show that acceptable surface finish and improved tool life can be achieved when machining Inconel 718 with high coolant pressures. The highest improvement in tool life (349%) was achieved when machining with 11 MPa coolant supply pressure at higher speed conditions of 60 m · min−1. Machining with coolant pressures in excess of 11 MPa at cutting speeds up to 40 m · min−1 lowered tool life more than when machining under conventional coolant flow at a feed rate of 0.1 mm · rev−1. This suggests that there is a critical coolant pressure under which the cutting tools performed better under high-pressure coolant supplies. Cutting forces increased with increasing cutting speed due probably to reactive forces introduced by the high-pressure coolant jet. Tool wear/wear rate increased gradually with prolonged machining with high coolant pressures due to improved coolant access to the cutting interface, hence lowering cutting temperature. Nose wear was the dominant tool failure mode when machining with coated carbide tools due probably to a reduction in the chip-tool and tool-workpiece contact length/area.

Effect of high-pressure coolant supply when machining nickel-base, Inconel 718, alloy with coated carbide tools

Inconel 718 was machined with a triple PVD coated (TiCN/Al2O3/TiN) carbide tool at speeds up to 50mmin−1 using conventional and various high coolant pressures, up to 203bar. Tool life, surface roughness (Ra), tool wear and component forces were recorded. The test results show that acceptable surface finish and improved tool life can be achieved when machining Inconel 718 with high coolant pressures. Compared to conventional coolant supplies, tool life improved as much as 740%, when machining at 203bar coolant pressure at a speed of 50mmin−1. Tool life generally increased with increasing coolant supply pressure. This can be attributed to the ability of the high-pressure coolant to lift the chip and gain access closer to the cutting interface. This action leads to a reduction of the seizure region, thus, lowering the friction coefficient which in turn results in reduction in cutting temperature and component forces. Chip breakability during machining is dependent on the depth of cut, feed rate and cutting speed employed as well as on the coolant pressure employed. Machining Inconel 718 with lower coolant pressures did not produce chip segmentation. Tool wear increased gradually with prolong machining with high coolant pressures. Nose wear was the dominating tool failure mode due probably to a reduction in the tool–chip and tool–workpiece contact length/area.

High speed machining of aero-engine alloys

Materials used in the manufacture of aero-engine components generally comprise of nickel and titanium base alloys. Advanced materials such as aero-engine alloys, structural ceramic and hardened steels provide serious challenges for cutting tool materials during machining due to their unique combinations of properties such as high temperature strength, hardness and chemical wear resistance. These materials are referred to as difficult-to-cut since they pose a greater challenge to manufacturing engineers due to the high temperatures and stresses generated during machining. The poor thermal conductivity of these alloys result in the concentration of high temperatures at the tool-workpiece and tool-chip interfaces, consequently accelerating tool wear and increasing manufacturing cost. The past decade has witnessed a radical approach to product manufacture, particularly in the developed economy, in order to remain competitive. Modern manufacturing philosophies, principles and techniques geared primarily towards reducing non value added activities and achieving step increase in product manufacture have been widely adopted. Recent advances in the machining of aero-engine alloys include dry machining at high speed conditions, the use of high pressure and/or ultra high pressure coolant supplies, minimum quantity lubrication, cryogenic machining and rotary (self-propelled) machining technique. Tool materials with improved hardness like cemented carbides (including coated carbides), ceramics, polycrystalline diamond and polycrystalline cubic boron nitride are the most frequently used for high speed machining of aero-engine alloys. These developments have resulted to significant improvement in the machining of aero-engine alloys without compromising the integrity of the machined surfaces. This paper will provide an overview on these recent developments and their application in the aerospace industry.

333 Surface Alteration when Machining Inconel 718 with Ceramic and Coated Carbide Tools under High Pressure Coolant Supply

The effect of cutting speed, feed rate and tool wear on the surfaces generated when machining nickel base, Inconel 718,alloy with conventional and high pressure coolant supplies was investigated. Tool life, failure modes, surface roughness (Ra) values and component forces were recorded. Machined surfaces were examined with the SEM and optical microscopes. Microhardness analysis show evidence of hardening of the top machined surfaces. In most cases the microhardness reading tend to approach the hardness of the base material at 0.3mm below the machined surface. This is due to the austenitic structure of Inconel 718 which promote work hardening when machining as a result of the high temperature and stresses generated at the cutting interface. The hardening effect decreased with increasing coolant pressures up to 203 bar as the coolant gain access closer to the cutting interface, thus minimising the cutting interface temperature. Analysis of machined surfaces shows that severe plastic deformation occurred when machining with conventional coolant supply than with high pressure coolant supplies. Surface damage or phase transformation was not observed when machining Inconel 718 under high pressure coolant supplies. Increasing the feed rate from 0.15 mm/rev to 0.25mm/rev when machining with ceramic tools at a cutting speed of 250m/min decreased the hardness of the machined surface. An increase in feed rate from 0.25mm/rev to 0.3mm/rev increased hardness of the machined surface when machining with coated carbide tools at a speed of 30m/min due to increased shearing forces encountered and consequent strain hardening of the machined surface.

Effect of High-Pressure Coolant Supplies when Machining Nickel-Base, Inconel 718, Alloy with Ceramic Tools

Chip breakability is significantly improved with the use of high pressure coolant supply. This is a result of the reduction in the tool-chip contact length during machining as the coolant under high pressure lifts the chip up after passing the deformation zone. Increasing the coolant pressure results in shorter ceramic tool life when machining Inconel 718 suggesting that the high pressure coolant supply reduces temperature at the cutting zone below a critical level where ceramic tools can perform satisfactorily. The inadequate fracture toughness of ceramic tools makes them more susceptible to failure by mechanical action such as notching at the depth of cut line and premature fracture. The notch wear rate increases with higher coolant supply pressure due to significant erosion of the tool material by the high pressure coolant jet. This mechanically related failure mode occurs on a random basis leading to inconsistency in tool performance, accelerated by fluctuations in thermal and mechanical properties when machining under high pressure coolant supplies. Presented at the 58th Annual Meeting in New York City April 28–May 1, 2003

The machinability of nickel-based alloys: a review

This paper presents a detailed review of the various types of nickel-based alloys available on a commercial basis and their development including alloying additions as well as processing techniques employed to achieve specific mechanical and/or chemical properties. Problems associated with the machining of nickel-based alloys as well as tool wear and the mechanisms responsible for tool failure are identified and discussed. The integrity of the machined surfaces and tool life are the most important considerations during machining. These and other factors governing the machinability of nickel-based alloys are mainly affected by notching of the cutting tool, primarily at the depth of cut region, as well as by flank wear and insert chipping/fracture; and by failure modes caused singly or jointly by diffusion, attrition, and abrasion wear mechanisms in addition to mechanical and thermal fatigue loading of the cutting tools. Most of the failure modes can be minimised when machining in the presence of coolants and in an oxygen-rich environment. The use of a high pressure coolant supply, despite improved chip segmentation and machining in the presence of argon and nitrogen-rich environments, tend to accelerate tool wear rate leading to lower tool life. Improvements in tool performance can be achieved with an increase in the included angle and/or the nose angle of cutting tools due to the increased edge strength and tool–chip contact area plus a reduction in the approach angle. Recently developed cutting tool materials such as mixed oxide, SiC whisker reinforced alumina ceramics, sialon and multi-layer coated cemented carbide cutting tool material have all exhibited the capability to machine nickel-based alloys at higher speed conditions than those achieved with conventional cemented carbide tools.

TOOL PERFORMANCE AND CHIP CONTROL WHEN MACHINING Ti6A14V AND INCONEL 901 USING HIGH PRESSURE COOLANT SUPPLY

Single point continuous turning tests were carried out on Ti6A14V and Inconel 901 using various geometries of straight grade (K20) cemented carbide inserts using a high pressure coolant jet directed at the tip of the tool where the chip is formed. Trials were also carried out using a conventional coolant supply for comparison. The test results show that improved tool life can be achieved when machining the titanium-base alloy under the high pressure coolant jet while shorter tool life was obtained when machining the nickel-base alloy. The use of high pressure coolant supply during machining generally maintains constant cutting forces and reduces the chip-tool contact length, thus increasing stresses at the tool edge. This behavior tends to accelerate notching that is predominant when machining the Inconel 901 alloy, resulting in shorter tool life. This effect is not obvious when machining Ti6Ai4V where the tools failed mainly due to excessive flank wear. Effective chip control was achieved when machining both materials because of the cyclic fragmentation mechanism of the newly generated chip.