Effect of high-pressure cooling on the residual stress in Ti-alloys during machining

Titanium alloys are widely used in aerospace industry but also in other industry sectors. Details for compressors used for generation and petrochemical plants and medical devices can be mentioned as a few examples. Plastic deformation during forming of the metals introduces residual stresses. Fatigue, creep and corrosion are typical failure mechanisms that are stopped or accelerated in the presence of tensile residual stress. Metal cutting as a manufacturing method generates residual stresses in the surface layer. The stress state in the near-surface zone of components is of special interest as the surface often suffers loads and consequently the cracks initiate and begin to grow at that location. The scope of this thesis is to investigate the properties of the machined surface with regards to measurement of residual stresses. The results achieved by X-ray diffractometry were compared with the results using a simulating method with the same cutting data for checking the accuracy of these two methods. This review highlighted the residual stress character and how they can be measured by X-ray diffractometry in two different directions, the transversal, the cutting direction, and longitudinal, the feed direction. For measurement of residual stress under the surface, the material was removed by an electro-chemical polishing method for not introducing more stress. The same procedure was checked using Finite Element simulations. The results obtained from the investigation clarified that: The residual stress measurement by X-rays was quite accurate in comparison with finite element simulation on the surface generated by turning on titanium alloy. There were compressive residual stresses in the cutting and feed directions of the cut. Residual stress is beneficial for delay of crack propagation. High-pressure cooling produced and increased compressional residual stresses.Godkänd; 2005; 20061218 (haneit

Effect of high-pressure cooling on the residual stress in Ti-alloys during machining

Titanium alloys are widely used in aerospace industry but also in other industry sectors. Details for compressors used for generation and petrochemical plants and medical devices can be mentioned as a few examples. Plastic deformation during forming of the metals introduces residual stresses. Fatigue, creep and corrosion are typical failure mechanisms that are stopped or accelerated in the presence of tensile residual stress. Metal cutting as a manufacturing method generates residual stresses in the surface layer. The stress state in the near-surface zone of components is of special interest as the surface often suffers loads and consequently the cracks initiate and begin to grow at that location. The scope of this thesis is to investigate the properties of the machined surface with regards to measurement of residual stresses. The results achieved by X-ray diffractometry were compared with the results using a simulating method with the same cutting data for checking the accuracy of these two methods. This review highlighted the residual stress character and how they can be measured by X-ray diffractometry in two different directions, the transversal, the cutting direction, and longitudinal, the feed direction. For measurement of residual stress under the surface, the material was removed by an electro-chemical polishing method for not introducing more stress. The same procedure was checked using Finite Element simulations. The results obtained from the investigation clarified that: The residual stress measurement by X-rays was quite accurate in comparison with finite element simulation on the surface generated by turning on titanium alloy. There were compressive residual stresses in the cutting and feed directions of the cut. Residual stress is beneficial for delay of crack propagation. High-pressure cooling produced and increased compressional residual stresses.Godkänd; 2005; 20061218 (haneit

Depth profile of titanium alloy (Ti-6Al-4V) and residual stress measured by using X-ray diffraction after metal cutting assisted by high-pressured jet cooling evaluation of etching methods

Titanium alloys are used in aerospace industry owing to their high strength to weight ratio. These alloys are considered to be difficult to machine due to their rigidity and poor thermal conductivity. High-pressure jet-assisted machining of titanium alloys is beneficial. It not only increases production efficiency, by increasing the cutting speed and lowering temperature both in cutting zone and the cutting tool, but also improves chip control, and increases tool life. It also produces better surface integrity and compress residual stress, which improves the properties of work metals such as fatigue. In order to compare the effect of high-pressure jet-assisted machining on the work pieces of Ti-6Al-4V alloy, the depth profile of residual stress was measured using xray diffraction. As comparison, the depth profile of residual stress was also measured for the conventional machined work pieces. It was found that the residual stress was a function of machining parameters, such as cutting speed, feeding force and depth of cut and particularly the high-pressure jet increases the amount of residual compressional stresses in both cutting and feed direction. In the present paper, Ti6A14V rod was machined by turning in two different manners, finishing and roughing. Tests were conducted on a lathe using different cooling systems, high pressure and conventional. To illustrate the effect of high-pressure jet assisted machining on the properties of the work piece of Ti-6-Al-4V and the depth profile of its residual stress, X -ray defractometer was used. The maximal amplitude of residual stress, at both the longitude (feeding direction) and transversal (cutting) directions, the depth of compress residual stress and the depth of the total residual stress will be present as the function of the machining parameters.Validerad; 2005; 20070913 (ysko)ISBN:878499695</p

A method for identification of geometrical tool changes during machining of titanium alloy Ti6Al4V

There exists an increasing demand for cost and time efficient cutting tests for describing the performance of different combinations of cutting tools and workpiece materials in the cutting process both in industry and academia. Cutting tools are expected to withstand the heat and the pressure developed during the machining of difficult to machine materials such as Ti6Al4V. This article introduces a new test method which may be used in order to analyze both the machinability of a workpiece material as well as the cutting tool behavior. The experiments were performed by using a predefined sequence of feeds, a so called Stepwise Increased Feed Test (SIFT). A gradually increased load on the cutting edge was thus applied up to the point where plastic deformation of the cutting edge was obtained. The limit for the initial change in tool geometry was identified through analysis of measured cutting forces