Essay On Titanium Alloys
explanatory Essay
1835 words
Tool wear is a problem in machining titanium alloy, so it is of great importance to find out the wear mechanism of cutting tools in order to improve the cutting tool life time. The mechanism controlling the wear of cemented carbide and influence of cutting parameters on different wear modes in machining Ti6Al4V has been investigated in this paper. Diffusion and chemical wear at high cutting speed and feed rate and attrition in low speed and feed rate is suggested to be the dominant wear mechanism in this case.
1. Introduction
Titanium shows a high strength-weight ratio and has exceptional corrosion resistance. Titanium alloys have received considerable interest recently due to their wide range of applications in the aerospace, automotive and medical industries. The most common titanium alloy is Ti6Al4V, which belongs to the α+ β alloy group. However titanium alloys are difficult to machine due to their low modules of elasticity. Titanium is a poor conductor of heat, its thermal conductivity is about 1/6 that of steel. Heat, generated by the cutting action, does not dissipate quickly; therefore, most of the heat is concentrated on the cutting edge and the tool face [1]. Titanium has a strong alloying tendency or chemical reactivity with materials in the cutting tools and also reacts with oxygen and nitrogen in air at tool operating temperatures. This causes galling, welding, and smearing along with rapid destruction of the cutting tool [1].
The element diffusion from the tool through the tool-chip interface leads to composition change of tool substrate, which may increase the possibility of mechanical damage of the cutting edge also the high strength of titanium at elevated temperature contributes to the high compressive stresses ...
... middle of paper ...
...ay crater and flank wear in combination with chipping and cracking along the cutting edge.
• At low cutting conditions attrition was found dominant wear mechanism of cemented carbide cutting tool.
• At severe cutting condition by increasing the temperature, mechanism of tool wear involve diffusion.
• The brittle failure is due to high contact stresses at the cutting edge due to a combination of critical cutting parameters. The weak cutting edge du to the crate also contributes to the brittle failure.
• Plastic deformation can also be a major contributor to wear mechanisms of cutting tool when machining titanium alloys
• High compressive stresses and the development of high temperature close to the cutting edge causes plastic deformation of cutting edge
• The tendency for chipping and micro fracture along the cutting edge increases with feed rate and cutting speed.
In this essay, the author
- Explains that tool wear is a problem in machining titanium alloy, so it is of great importance to find out the wear mechanism of cutting tools in order to improve the cutting tool life time.
- Explains that cemented carbide with a cobalt content of 6 wt% and wc grain size between 0.8 and 3 m has been used in these experiments.
- Explains that ti-6al-4v was used as work piece material in the turning test.
- Describes how orthogonal turning was performed in a cnc (computer numerical control) lathe, using sandvik coromant tool holder and cutting tool insert.
- Explains that after a certain machining time, the flank wear and crater wear of cutting tool were assessed.
- Describes the use of scanning electron microscopy to study the underlying wear mechanisms present in turning of titanium alloy.
- Explains that the cemented carbide cutting tools display crater and flank wear in combination with chipping and cracking along the cutting edge.
- Explains that at low cutting conditions attrition was found dominant wear mechanism of cemented carbide cutting tool.
- Explains that the brittle failure is due to high contact stresses at the cutting edge and weak cutting edges.
- Explains plastic deformation can be a major contributor to wear mechanisms of cutting tool when machining titanium alloys.
- Explains that high compressive stresses and the development of high temperature close to the cutting edge causes plastic deformation of cutting edges.
- Explains that the tendency for chipping and micro fracture along the cutting edge increases with feed rate and cutting speed.
- Explains that titanium alloys have received considerable interest due to their wide range of applications in the aerospace, automotive and medical industries.
- Illustrates a worn cemented carbide cutting tool which has turned ti6al4v for 30 seconds at 115 m/min before and after etching in hydrofluoric acid for 20 minutes.
- Explains that the depth of crater wear of cutting tools was measured using a wyko optical surface profilometer and is shown in figures 6 and 7.
- Explains the comparison of flank wear progression of cemented carbide cutting tools used for turning ti6al4v at 90 and 115 m/min turning speeds.
- Illustrates the rake faces of the cutting tool after 1 minute turning at 115 m/min and 0.2 mm/rev feed rate. chipping and catastrophic failure will be the probable wear modes.
- Explains that high plastic strain is probable where the temperature is high, because an elevated temperature over 800 c significantly decreases the yield stress of cobalt.
- Explains that attrition is a wear mechanism which consists basically in: (1) adhesion of workpiece material on the cutting tool surfaces; (2) breakaway of microscopic particles and (3) dragging of these particles.
- Explains that diffusion is a thermal activated process where the material removal and friction energy lead to the maximum temperature on the tool rake face.
- Explains that adhesion was dominant at lower feed rate, while diffusion wear dominated with increasing feed rates and speed.
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