Abstract
The tool coating and cooling strategy are two key factors when machining difficult-to-cut materials such as titanium alloy. In this paper, diamond coating was deposited on a commercial carbide insert as an attempt to increase the machinability of TC11 alloy during the turning process. An uncoated carbide insert and a commercial Al2O3/TiAlN-coated tool were also tested as a comparison. Furthermore, MQL was applied to improve the cutting condition. Cutting performances were analyzed by cutting force, cutting temperate and surface roughness measurements. Tool wears and tool lives were evaluated to find a good matchup between the tool coating and cooling strategy. According to the results, using MQL can slightly reduce the cutting force. By applying MQL, cutting temperatures and tool wears were reduced by a great amount. Besides, MQL can affect the tool wear mechanism and tool failure modes. The tool life of an Al2O3/TiAlN-coated tool can be prolonged by 88.4% under the MQL condition. Diamond-coated tools can obtain a good surface finish when cutting parameters and lubrication strategies are properly chosen.
Highlights
TC11 (Ti-6.5Al-3.5Mo-1.5Zr-0.3Si) is a kind of α + β two-phase titanium alloy mostly used in turbine blades for its high temperature resistance and creep strength, which leads to its poor machinability
This paper evaluated the cutting performance of carbide, Al2 O3 /TiAiN-coated and diamond-coated tools in the turning of TC11 under dry and minimum quantity lubrication (MQL) conditions, with cutting force and temperature, tool wear and tool life, and surface integrity in terms of roughness being compared as tool selection criteria
The following conclusions can be drawn: Under the same cooling condition, the lowest forces were obtained with the Al2O3/TiAlN-coated tools and the highest with the diamond-coated tools, which might be explained by the differences in the friction coefficient of the coating material and the contact radius of the inserts
Summary
TC11 (Ti-6.5Al-3.5Mo-1.5Zr-0.3Si) is a kind of α + β two-phase titanium alloy mostly used in turbine blades for its high temperature resistance and creep strength, which leads to its poor machinability. Performed new-dry cutting with a specially designed internally cooled diamond-coated tool, resulted in a long tool life while maintaining high standards of the surface finish. Kamata et al [10] performed a finish turning process on Inconel 718 with different coating tools and attained a better tool life and surface finish than that in the wet and dry machining. When machining high-temperature alloys, other than cooling and lubrication effects, chip breaking is of great importance. This paper evaluated the cutting performance of carbide, Al2 O3 /TiAiN-coated and diamond-coated tools in the turning of TC11 under dry and MQL conditions, with cutting force and temperature, tool wear and tool life, and surface integrity in terms of roughness being compared as tool selection criteria
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