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An investigation of high speed machining of selected titanium alloys : process and thermal aspects

  • Authors: Kruger, Pieter
  • Date: 2013-11-21
  • Subjects: Titanium alloys , High-speed machining , Titanium alloys - Heat treatment
  • Type: Thesis
  • Identifier: uj:7784 , http://hdl.handle.net/10210/8679
  • Description: M.Ing. (Mechanical Engineering) , High strength alloys such as titanium are widely used within applications that require specific material properties. These include high strength, high temperature as well as low weight applications. Thus a need arises to investigate the fundamental to understand the mechanics of how these materials are machined. Titanium alloys are known for the difficulties that arise during the machining thereof. Complexities arise due to its inherent material properties, the most important property being the retention of strength at high temperatures. In addition to maintaining its strength, it becomes highly chemically reactive with other materials at increased temperatures. All these factors contribute to extreme temperatures at the tool chip interface contributing to increased tool wear and shortened tool life. The aim of the research is to investigate the effect of machining on various cutting process parameters including cutting force, temperature, tool wear and surface finish for grade 2 and grade 5 titanium alloys during high speed turning. Grade 2 titanium is a commercially grade with lower mechanical properties, while Grade 5 is titanium alloy with substantially higher mechanical properties and is the most widely used titanium alloy. In addition an experimental setup was developed and verified to conduct fundamental research on the high speed machining of titanium alloys. A literature review was concluded with focus on the machining of titanium alloys. This was followed by the development of the experimental setup, measurement and compilation of data. The data was compiled into graphs and compared with the current research available. The research found that for the cuts performed, that cutting forces are independent of cooling applied and that no substantial variation was noted between the two grades. When temperatures were evaluated, dramatic drops in temperature were noted when coolant was applied. As temperatures increased, specifically during un-cooled cutting, the inserts deteriorated having an effect on the quality of the surfaces obtained. When coolant was applied, substantial temperature drops were achieved, improving tool life and directly improving surface finishes. The best surface finish was achieved for higher cutting speeds as and lower feed rates. This phenomenon was found for both grades of titanium evaluated. The largest amount of tool wear was noted for the highest cutting speeds, with increased values noted for Grade 5 in comparison with Grade 2. This phenomenon is noted for crater as well as flank wear.
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An investigation of machining induced residual stresses on Grade 4 and 5 titanium alloys

  • Authors: Edkins, Kyle Douglas
  • Date: 2013-07-18
  • Subjects: Residual stresses , Titanium alloys - Mechanical properties , High-speed machining
  • Type: Thesis
  • Identifier: uj:7645 , http://hdl.handle.net/10210/8515
  • Description: M.Ing. (Mechanical Engineering) , Titanium and its alloys have the potential to serve as a strategic economic driver of the South African economy. The manufacture and use of high strength, lightweight materials such as titanium alloys have become of great importance in the aerospace and biomedical industries over the past few decades. The manufacturing costs of titanium alloy components however, are considered high due to the poor machinability of the material. Furthermore, as with all metals during machining, surface residual stresses are induced into the material. These are of particular interest in the aerospace industry as they can be either detrimental or beneficial to the performance and fatigue life of materials. The aim of this investigation is therefore to examine the effect that machining parameters have on the magnitude, sign and distribution of residual stresses induced in Grade 4 and 5 titanium alloys during high performance machining (turning). The effect of these machining parameters is investigated by residual stress measurements conducted with X-ray diffraction and grain structure analysis of the machined surfaces by optical microscopy. Results show that cutting speed and depth of cut have a significant effect on the residual stresses. At low cutting speeds, the surface residual stresses are largely compressive, becoming more tensile with an increase in cutting speed. An increase in depth of cut also introduces more compressive residual stresses into the material. The microstructural analysis of the alloys shows that grain deformation decreases with an increase in cutting speed and cutting depth.
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An investigation on the effect of high speed machining on the osseointegration performance of grade 4 titanium alloy

  • Authors: Reddy, Andrish
  • Date: 2015-02-12
  • Subjects: Titanium alloys , Titanium alloys - Testing , High-speed machining
  • Type: Thesis
  • Identifier: uj:13323 , http://hdl.handle.net/10210/13339
  • Description: M.Eng. (Mechanical Engineering) , High speed machining (HSM) has the potential to greatly increase productivity and to lower manufacturing costs if workpiece surface integrity can be controlled. The surface fmish of a biomaterial is vitally important for proper implant functioning, and is the focus of this study. Grade 4 titanium was turned on a lathe with cutting speeds increasing from the conventional to the high speed range. The surface finish was assessed using profilometry, atomic force microscopy, and contact angle measurement. The ability of the material to bond directly with bone was predicted by cell adhesion studies. Results indicate that there is a general relationship between cutting speed, surface roughness, contact angle, and cell adhesion. Turning grade 4 titanium at cutting speeds between 150m/min and 200m/min may provide an optimal surface for osseointegration.
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An investigation on the effects of high speed machining on the surface integrity of grade 4 titanium alloy

  • Authors: Mawanga, Philip
  • Date: 2012-08-01
  • Subjects: Titanium alloys , High-speed machining , Titanium alloys - Testing
  • Type: Thesis
  • Identifier: uj:8924 , http://hdl.handle.net/10210/5394
  • Description: M.Ing. , Grade 4 titanium is a commercially pure grade titanium alloy extensively used in various industries including the chemical industry and more recently in the biomedical industry. Grade 4 has found a niche as a biomedical material for production of components such as orthopaedic and dental implants. Its physical properties such as high corrosion resistance, low thermal conductivity and high strength make it suitable for these applications. These properties also make it hard-to-machine similar to the other grades of titanium alloys and other metals such as nickel based alloys. During machining of titanium, elevated temperatures are generated at the tool-workpiece interface due to its low thermal conductivity. Its high strength is also maintained at these high temperatures. These tend to impair the cutting tool affecting its machinability. Various investigations on other grades of titanium and other hard-to-machine materials have shown that machining at high cutting speeds may improve certain aspects of their machinability. High speed machining (HSM) is used to improve productivity in the machining process and to therefore lower manufacturing costs. HSM may, however, change the surface integrity of the machined material. Surface integrity refers to the properties of the surface and sub-surface of a machined component which may be quite different from the substrate. The properties of the surface and sub-surface of a component may have a marked effect on the functional behaviour of a machined component. Fatigue life and wear are examples of properties that may be significantly influenced by a change in the surface integrity. Surface integrity may include the topography, the metallurgy and various other mechanical properties. It is evaluated by examination of surface integrity indicators. In this investigation the three main surface integrity indicators are examined. These are surface roughness, sub-surface hardness and residual stress. White layer thickness and chip morphology were also observed as results of the machining process used. The effect of HSM on the surface integrity of grade 4 is largely unknown. This investigation therefore aims to address this limitation by conducting an experimental investigation on the effect of HSM on selected surface integrity indicators for grade 4. Two forged bars of grade 4 alloy were machined using a CNC lathe at two depths of cut, 0.2mm and 1mm. Each bar was machined at varying cutting speeds ranging from 70m/min to 290m/min at intervals of approximately 20m/min. Machined samples were prepared from these cutting speeds and depths of cut. The three surface integrity indicators were then evaluated with respect to the cutting speed and depth of cut (DoC). iv Results show that a combination of intermediate cutting speeds and low DoC may have desirable effects on the surface integrity of grade 4. Highest compressive stresses were obtained when machining with these conditions. High compressive stresses are favourable in cases where the fatigue life of a material is an important factor in the functionality of a component. Subsurface hardening was noticed at 0.2mm DoC, with no subsurface softening at all cutting speeds. Surface hardness higher than the bulk hardness tends to improve the wear resistance of the machined material. Though surface roughness values for all depths of cut were below the standard fine finish of 1.6μm, roughness values of samples machined at 0.2mm DoC continued to decrease with increase in cutting speed. Low surface roughness values may also influence the improvement of fatigue life of the machined components. These machining conditions, (intermediate cutting speeds and low DoC), seem to have promoted mechanically dominated deformation during machining rather than thermal dominated deformation. Thermal dominated deformation was prominent on titanium machined at DoC of 1mm.
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Design and performance evaluation of a high speed synchronous machine

Enhancing the integrity of machined titanium alloy

  • Authors: Mathoho, Ipfi
  • Date: 2017
  • Subjects: Titanium alloys , Mechanical alloying , Milling (Metal-work) , High-speed machining , Surfaces (Technology)
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/269763 , uj:28661
  • Description: M.Phil. (Mechanical Engineering) , Abstract: Titanium alloys have proved to be the working horse in industries, such as aerospace, chemical and biomedical; and especially Ti-6Al-4V alloy owing to their excellent weight-to-strength ratio, corrosion resistance and biocompatibility. Such properties define a material that is required for engineering purposes; and therefore, this justifies the use of titanium alloys extensively nowadays. However, titanium alloys are known to be hard to machine materials, due to their low thermal conductivity, poor modulus of elasticity, chemical reactivity and strain hardening. Milling is a machining process, which is known to be a flexible process – with the ability to generate different three-dimensional shapes; and it makes use of a multi-point cutting tool that rotates during milling. It is known that milling parameters (feed rate, cutting speed/spindle speed and depth of cut) and machining conditions play a critical role in determining the operational efficiency of the workpiece. The current research project successfully milled Ti-6Al-4V 100x100x7 mm plates, using a vertical-milling machine; while varying the spindle speed (120, 150, and 180 rev/min), depth of cut (1, 1.5, and 2 mm) and keeping the feed rate constant at 4.6 mm/min. Milling was conducted by making use of a tungsten carbide cutting tool; and for each parameter, a new cutting tool was inserted to elude the effect of tool wear; since there are limited research studies on the milling of Ti-6Al-4V, which does not elude the effect of tool wear on the outcome of the milling operation. Furthermore, milling was conducted under dry conditions and flood conditions – using a synthetic soluble cutting fluid...
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On high speed machining of titanium alloys : analysis and validation

  • Authors: Sonnekus, Reino
  • Date: 2010-08-30T06:55:07Z
  • Subjects: Titanium alloys , High-speed machining
  • Type: Thesis
  • Identifier: uj:6906 , http://hdl.handle.net/10210/3418
  • Description: M.Ing. , This report documents the steps taken to gain insight into the phenomena of high speed machining (HSM) of titanium alloys. This was done by firstly studying titanium alloys and the problems associated with machining titanium alloys. An experimental set-up and procedure was developed for measuring and recording both the machining temperature and component forces. A sufficient set of experimental data was collected through extensive experimentation. The cutting temperatures and component forces in HSM of Ti-6Al-4V were examined simultaneously. The cutting speed was found to be the most influential and limiting parameter on the machining temperature and component forces. A new approach for modeling the temperatures in HSM of titanium alloys was developed. Analytical predictions of the cutting temperatures were performed and used to evaluate the influence of a variation in the process parameters on the cutting temperature. The research provides insight for future work into the phenomena of HSM of titanium alloys . The results of the analytical model were found to be representative and comparable to the experimental data. It is however expected that the deviation between the predicted and measured result may be significantly reduced by changing the experimental approach. It is recommended that a complete set of experiments be done, using a new tool insert for every cut, thus removing the effect of possible tool wear on the experimental data obtained. In addition it is recommended that the iterative solution be improved through more in depth programming, considering the change in both the thermal and mechanical materials properties with a change in temperature. Ultimately the assumptions made in order to simplify the problem addressed in this report needs to be improved upon, in order to analyze data trends and even magnitudes to a greater degree of certainty.
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The effect of high speed machining on the fatigue performance of Ti6Al4V

  • Authors: Madyira, Daniel M.
  • Date: 2016
  • Subjects: High-speed machining , Titanium alloys - Mechanical properties , Metal-cutting , Titanium alloys
  • Language: English
  • Type: Doctoral (Thesis)
  • Identifier: http://hdl.handle.net/10210/225157 , uj:22734
  • Description: Abstract: Grade 5 titanium alloy (Ti6Al4V) is the workhorse titanium alloy used in many industrial applications including aerospace, automotive, chemical and biomedical. Its attractive mechanical properties such as high strength-to-weight ratio, low density and corrosion resistance make it eminently suitable for such applications. However, its use is limited to these specialized applications due to its high cost. This high cost is mainly due to the primary processing of the material using the Kroll process. Little can be done, currently, to reduce the primary processing cost due to the high reactivity of titanium with oxygen. However, cost reduction measures can be implemented during secondary processing to make this alloy more affordable for general engineering applications. Such measures may include powder metallurgy, laser additive manufacturing, high performance machining and high speed machining. High speed machining (HSM) has been used to improve productivity and reduce component manufacturing costs in aerospace applications such as wing sections. HSM involves machining at high cutting speeds. Such high speed cutting can be implemented under milling or turning conditions. In this investigation, high speed cutting using turning was investigated. However, high speed machining has an effect on the surface and sub-surface condition of a machined component. This may affect the service performance of a component, especially fatigue life. Surface integrity descriptors that may be influenced by machining, and which may affect component fatigue life include surface roughness, micro hardness, microstructure and residual stresses. The cumulative effect of HSM on the fatigue behavior and life of components is largely unknown. This work aims to redress this by conducting experimental investigations supported by numerical analysis, on the effect of HSM on the fatigue performance of turned components for finish cutting conditions of Ti6Al4V. Literature study showed that residual stresses induced during HSM have a significant influence on fatigue performance. The effect of HSM on residual stresses was therefore investigated on specimens machined on 75 mm diameter forged bar of Ti6Al4V. The specimens were... , D.Ing. (Mechanical Engineering)
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The effect of high speed machining on the surface integrity of certain titanium alloys

  • Authors: Van Trotsenburg, Samantha
  • Date: 2012-08-15
  • Subjects: Titanium alloys - Testing , High-speed machining
  • Type: Thesis
  • Identifier: uj:9396 , http://hdl.handle.net/10210/5832
  • Description: M.Ing. , This dissertation documents the stages involved in determining the parameters that define surface integrity. Chapter one gives a basic introduction to the project; the problem statement; scope of work and project obstacles. This chapter laid down the requirements for the literature study in Chapters two and three. The literature study discusses machining, high-speed machining, titanium alloys and high speed machining of titanium alloys. Information from the literature study was used to determine the experimental program presented in Chapter 4. Two materials were investigated in this study: grade 2 titanium (commercially pure) and grade 5 titanium (an alloy containing 6% Aluminium and 4% Vanadium). A fixed feed rate of 0.25mm/rev was selected. Two depths of cut were used: 0.2mm and 1mm. Cuts were performed both lubricated and un-lubricated. Different cutting speeds were used both inside and outside recommended ranges. Surface roughness tests, optical microscopy, scanning-electron microscopy, microhardness tests and x-ray diffraction were used in the experimental program. Results obtained presented trends seen in previous work on surface integrity. Efforts were made to reduce errors in obtaining and examining data. Conclusions were drawn with regards to each surface integrity parameter tested for. It was found that different cutting speeds affect each surface integrity parameter differently.
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