Chemical composition of commercially pure grade 2 titanium in % wt.
The microstructure and mechanical properties of laser and mechanically formed commercially pure grade 2 titanium plates are discussed in this chapter. The microstructure of the as received parent material is compared to that resulting from laser and mechanical forming processes. Residual stress results from the two forming processes are analysed and bring to light changes brought about by these processes to the titanium used. The effect of the two forming processes on the mechanical properties is discussed, and the effect of process parameters on these properties is also argued in detail.
- laser forming
- mechanical forming
- residual stress
- tensile testing
- hardness testing
The processing of engineering materials has become a specialist field, and this industry will continue to grow due to rising costs in raw materials which have forced many automotive and aviation industry suppliers to invest heavily in this field. In order to be relevant and competitive in today’s industrial world, companies around the world are now forced to dedicate billions of dollars in profits to research and development. Many research centres are looking at titanium as a solution to some of the engineering challenges facing both automotive and aviation industries. Titanium is now finding favour with companies in pursuit of savings in fuel consumption and related improvements to mechanical properties. Savings in fuel consumption is achieved by reducing weight on aircraft and automobiles yet still meeting acceptable industrial norms and standards like improved structural integrity on the finished product. Improvements in engine and turbine design have also helped in the pursuit of fuel efficiency in these industries. In-depth research into the behaviour of titanium alloys under varying loading conditions is therefore essential in the quest to find more industrial applications of this metal. The last century saw a major development in processing and fabricating techniques. These developments were largely in part as a result of great emphasis placed in research and a continued search for improved methods in metal forming. This contributed to the development in forming techniques, materials, processing and understanding of changes a metal goes through during forming. There has always been room for improvement in the forming of materials due to the widespread use of forming operations in the automotive, aviation and shipbuilding industries. An in-depth study into the effects of laser and mechanical forming processes on the mechanical properties of commercially pure grade 2 titanium plates was conducted. This was achieved by producing a radius of curvature of approximately 120 mm on the plates with the aid of the mechanical forming machine. The plate samples were then subjected to mechanical testing to evaluate changes in mechanical properties. A Nd:YAG laser was used to replicate what had been achieved using the mechanical forming machine to bend titanium to the same radius of curvature. It was anticipated that this would lead to an extension of applications of laser forming and the possibility of increasing strength of thin commercially pure (CP) grade 2 titanium plates due to the heat treatment characteristics induced by the process. The laser forming study used established parameter settings which greatly influence the microstructure and bend radii. The intention of the study was to use both mechanical and laser forming to bend titanium plates to a final radius of curvature of 120 mm.
2. Commercially pure grade 2 titanium
Table 1 shows the chemical composition of the titanium used in this study which is weldable and formable and has excellent corrosion resistance properties. The tensile and yield strength values go up with grade number for pure grades.
Titanium can be cold rolled at room temperature to above 90% reduction in thickness without serious cracking . Titanium undergoes allotropic transformation from the hexagonal close-packed (hcp) alpha phase to the body-centred cubic (bcc) beta phase at a temperature of 883°C. At room temperature, its properties are controlled by chemical composition and grain size. The presence of these elements determines the nature of the alloy and its chemical properties. The density of alpha titanium alloy falls between that of aluminium alloys (2.7
2.1 Laser forming
Laser forming (LF) evolved from more mature, but less sophisticated thermo-mechanical forming processes. Specifically, manual application of an oxyacetylene torch for forming steel plates for the ship building industry has been used for some time and is seen as the precursor to LF .
The laser forming process has become a choice to fabricators of metallic components and as a means of rapid prototyping and of adjusting and aligning . Laser forming is of importance to industries that previously relied on expensive stamping dies and presses for prototype evaluations. Industry sectors making use of this process include aerospace, automotive, shipbuilding and those in microelectronics. The laser forming process involves no mechanical contact, which is a requisite in mechanical forming and is considered a virtual manufacturing kind of method. The laser forming process can be used to produce predetermined shapes. The process results in minimal distortion on the formed components . The laser forming process can produce metallic, predetermined shapes with minimal unwanted distortion, and investigations are also ongoing in the removal of unwanted distortion resulting from the procedure.
A successful and significant research in the laser forming of materials needs a good understanding of thermal transfer concepts as they play a crucial role in the process. Concepts like conduction and thermal radiation need to be understood fully to balance all the process variables. Thermal radiation is the transfer of energy by electromagnetic waves, whereas thermal conductivity, on the other hand, is the property a material possesses indicating its ability to conduct heat. Thermal conductivity of titanium is lower than most competing metals like steel, magnesium and aluminium. This means that in order to cause changes in the microstructure, a higher intensity of heat would have to be emitted by the heat source and in this scenario by the laser. The ability of the plate material to absorb and transfer heat is the major underlying factor. This factor plays a major role in the forming of plates as the effect of conduction affects the microstructure, thereby influencing the mechanical properties. The heat flux (power density), which plays a considerable role in the laser forming process, is the amount of energy flowing through a particular surface area per unit of time and is represented by the following formula:
where q is the heat flux, Q is the laser beam power (W), r is the beam radius (m), and π is the constant.
According to Ion et al., a large number of variables influence the interaction between a laser beam and a material; over 140 variables can be identified for welding alone. In this instance, the power density will be considered when a beam is switched on. The heat flow becomes steady state, and the energy absorbed by the surface is balanced by that conducted heat into the plate, and the temperature field becomes constant. The principal process variables are the beam power, the beam radius and material properties. The power density can be increased four times by quadrupling the power or by reducing the beam radius to a half. When this variable group is identified, a smaller subset of experiments can be undertaken to establish that the power density determines the peak surface temperature attained. These factors determine the principal mechanism of thermal interaction—which could either be heating, melting or vaporisation . The laser powers used, the thermal conductivity, the line energy, scanning velocities, beam interaction time and also the heat flux (power density) generated during the laser forming process are all shown in Table 3.
|Grade||C||O2||N2 Max||Fe Max||H Max||Ti|
|Commercially pure titanium (as supplied)||0.005||0.155||0.009||0.04||0.003||Bal|
|Property||Linear expansion coefficient||Thermal conductivity||Specific heat capacity||Electrical resistivity||Alpha/beta transform temperature||Young’s modulus||Shear modulus||Poisson’s ratio||Density|
|Alpha titanium||8.36 × 10−6 K−1||14.99 W/m.K||523 J/kg.K||5.6 × 10−7 Ohm.m||882.5°C||115 GPa||44 GPa||0.33||4.51 g/cm3|
|Laser power (kW)||Thermal conductivity (W/m.K)||Line energy (kJ/m)||Scanning velocity (m/min)||Beam interaction time (sec)||Heat flux (×106 W/m2)||Thermal gradient (×103 K/m)||Beam diameter (mm)||Average radius of curvature (mm)|
Power and scanning velocities were adjusted during the preparation of plate specimens used in this study and the other given parameters resulted from these adjustments (beam interaction time, heat flux and thermal gradient). The heat flux formula was considered for analysis in order to understand the concepts involved in this process. The laser power ranged from 1.5 to 3.5 kW for the specimens evaluated, and an increase in power resulted in an increase to the heat flux and line energy generated. With the arrangement used, the samples are not clamped in any way, and the line heating application alternates in succession from each end incrementally moving towards the centre of the plate. The open mould method shown in Figure 1 was used in the laser forming of the CP grade 2 titanium plates.
The beam interaction time was an important factor in the analysis of the resulting microstructure and can be determined by the formula
The variables and represent the beam radius and the scanning velocity, respectively. The power density, beam radius and beam interaction time play a considerable role as they determine whether the material will be cut, welded, melted or hardened. The heat flow in laser processing can be complex, but for many processes it may be approximated to three fundamental conditions: steady state, transient or quasi-steady state. Fourier’s first law describes steady state conditions as
where F is the heat flux (
The line energy specified by Magee is a function of laser power and the scanning velocity. In determining the process parameters for the experimental exercise, four sets of power levels believed to result in the desired curvature were chosen and are listed in Table 3 and discussed here. The laser forming process produces large thermal gradients that could either bend or shorten the material. The bending or shortening of the material is a result of the line energy produced by the laser and is given by the formula
The prime pocket monitor shown in Figure 2 was used in this study to measure the laser power projected on the surface of titanium specimens. Readings were taken to fully understand the incident power hitting the titanium plate surface. As an example for a laser power setting of 3500 W, the pocket monitor reader would show 3250 W. This value indicates a 10% loss in power on the irradiated sample . This assisted in understanding and acknowledging the presence of losses in laser irradiation in material processing. For the purpose of this study, the losses were ignored and not taken into consideration in the analysis.
2.2 Mechanical forming
Metals are used extensively as engineering materials in part because of their ability to deform plastically. Various forming processes are used to form engineering materials to desired shapes and sizes. These forming operations generally occur after the metal is cast, so it is important to understand how forming operations interact with pre-existing casting defects. Most metal forming operations reduce the severity of casting defects, such as microporosity, and break up coarse particles, such as non-metallic inclusions, that form during solidification. The mating die method was used to bend titanium alloy plates to the desired radius of curvature. The mating die method of stretch-draw forming involves an upper and lower die block mounted in a hydraulic press bed. The workpiece is securely held in tension by movable grippers. Yield stress of the finished part may be increased as much as 10% by the stretching and cold working operations. Shown in Figure 3 is how the bending of titanium plates was achieved using the mechanical forming machine and also the resulting shape.
The objective of this study was to bend a flat plate of titanium to a radius of 120 mm, and this would help in understanding the principles behind the mechanical forming process. The study also aimed at comparing mechanical to laser forming with regard to the microstructure and mechanical properties of the material and any changes that happen thereafter as a result of both forming operations.
2.3 Tensile test
The mechanical properties of CP grade 2 titanium alloy vary with its grade as indicated in Table 4. CP grade 2 titanium plate specimens were evaluated according to the American Society for Testing and Materials (ASTM) E8/E8M test method. The tensile test was performed on the parent material (CP grade 2 titanium plates) in accordance with ASTM E8, using the Hounsfield machine.
|Alloy||E (GPa)||δ 0.2 (MPa)||UTS (MPa)||Elongation (%)|
The resulting data were made available using computer software of the machine. The table shows average values taken from both the transverse and longitudinal directions of the plate. The ultimate tensile strength (the maximum engineering stress in tension that may be sustained without fracture) is given as 452 MPa, the yield 338 MPa and a percentage elongation of 28%.
Figure 4 shows microstructures from the parent material specimens, and this material has equiaxed α-grains usually developed by annealing cold-worked alloy above recrystallization temperature. The microstructure has shown results from the manufacturing process of CP grade 2 titanium, which cannot be altered in the plates without the addition of heat or cold deformation processes.
The microstructure of mechanically formed plates contains the same equiaxed alpha grains found in the parent material. Mechanical forming produces no heat, and therefore the similarities in microstructure are to be expected. There were no major changes to the microstructure as a result of this process when compared to the as received material . The microstructure of a mechanically formed plate is shown in Figure 5.
Figure 6 shows the fine structure of titanium from the plates irradiated at a power of 1500 W using line energies of 35 and 47 kJ/m, respectively. There is a variation in the depth of the heat-affected zone (HAZ) for both line energies . The unaffected material in both cases has equiaxed α-grains similar to those in the parent material. Based on microstructural observations, it becomes clear that the temperature generated at
The resulting microstructure from a line energy of 35 kJ/m points to a higher scanning velocity. The thermal energy from the laser managed to effect changes to a quarter of the plate’s thickness . The cycle took around 18 minutes to irradiate all the 10 plates in each batch at this power and line energy setting. The laser forming process resulted in a semi-circular-shaped heat-affected zone in the lower line energies (
Figure 7 shows a major change in the microstructure of CP grade 2 titanium plates with enlarged primary α-grains and enlarged β-grains (
On the section of the plate closest to the source of laser irradiation and as thickness of the plate increases, the effect of thermal energy diminishes. The different microstructures shown are also an indication of different hardness values. The forming parameters at this power level led to plastic deformation on the laser-facing side. Before getting to plastic deformation, the grains were similar to those of the as received material (parent and mechanically formed plates). The scanning velocity used here happens to be the lowest in this study. The low scanning speed meant that the laser got more time to effect changes per unit area of the material resulting in the microstructure shown. The cooling of the plates also contributed to the microstructure. All the plates were naturally cooled. Thermal measurements have also shown the effect of the scanning velocity on the material. In multiple scan scenarios, each scan effects change on the microstructure. Differences in microstructure are brought about by the laser intensity power of
Figure 8 also shows the microstructure of a sample irradiated at
Figure 9 shows the microstructure layout as a result of laser forming at the highest power setting. The grains from this setting were the biggest in all the plates evaluated in this study. Twin bands can be seen throughout the microstructure of the plate. All sections of the plate had different grain sizes attesting to different cooling rates in the plate. The surface facing the laser did not cool down at the same time as the opposite side of the plate . Acicular alpha can also be seen on the side opposite the laser-irradiated surface. The complete laser irradiation for these samples took about 20 minutes, which explains the changes in the microstructure when compared to a power of 2.5 and 3 kW, respectively. Changing the power from 2500 to 3000 W resulted in a 40% increase in heat flux. The heat flux increased by 16% from a power of 3000–3500 W. This means that by changing the power values, there was a related increase in the heat transferred per unit area, per unit time. These changes contributed to changes in the accompanying microstructure and mechanical properties. The study on the microstructure and mechanical properties helped in understanding the behaviour of titanium in different forming scenarios. The information gathered also made it easier to analyse the hardness results.
The hardness number is a resistance for the local plastic deformation, and the hardness is closely related to residual stresses . The average Vickers hardness obtained for the parent material is 160 ± 5Hv0.3, and whilst the average hardness number for the parent material is higher than that obtained in mechanically formed samples, the laser formed specimens show higher values. The average hardness results of the mechanically and laser formed CP grade 2 titanium specimens are shown in Table 5.
|Material||Parent (as supplied)||Mechanically formed||1.5 kW (35 kJ/m)||1.5 kW (47 kJ/m)||2.5 kW (90 kJ/m)||3 kW (90 kJ/m)||3.5 kW (90 kJ/m)|
|Average Vickers hardness||160||130||176||171||410||349||311|
Mechanically formed plates did not behave like laser formed samples as there was a slight increase in hardness moving away from the top section resulting in an average hardness of 130 ± 5Hv0.3. This is a result of changes in the material structure caused by the die during mechanical forming. The microstructure of plates irradiated at
On examining the microstructure of specimen irradiated at
The reduction in hardness values at this power setting could be traced back to the grain structure found in samples irradiated. The microstructure contained acicular alpha and beta phases which have a significant effect on the mechanical properties of titanium. An average Vickers hardness value of 349Hv0.3 was obtained at this power setting, and it was the lowest on the samples evaluated. Plates irradiated at 3000 W had the hardness value of 349Hv0.3 in plates formed at a line energy of 90 kJ/m. The same plates showed a marked improvement in hardness at the middle section of the plates. The forming process effected physical changes on the surface of the plates. These changes translated to changes in the hardness of the material. The results show an improvement of more than 100% when compared with the as received material. These changes also made the material hard to polish during the preparation of residual stress samples .
A hardness value of 311Hv0.3 was obtained at a power setting of 3500 W. This is the third highest value in samples irradiating a line energy of 90 kJ/m. The size of grains and their structure were different when compared to other laser formed plates. Readings taken from the top section of the laser-irradiated side indicate a considerable increase in the average hardness of titanium. An average Vickers hardness value of 311Hv0.3 was obtained from the top section which indicates a 40% increase in the hardness of titanium. The Vickers hardness readings taken closer to the surface show increased hardness values which are much higher than those obtained from the parent plate by a bigger margin. The improvement in hardness as a result of the laser forming process could help in the preparation of titanium for other engineering applications in need of hardened titanium plates .
2.6 Residual stress
The graphs plotted from the analysed plates were a result of residual stress information gathered by the MTS3000 machine on each plate sample evaluated. Comparisons are made between the plates based on the graphs obtained. The relieved strain from the parent material differs to that obtained from other evaluated plates. Figure 10 shows relieved strain measured on the parent material, and all the micro-strain values (
The parent material shows minimum values in both residual stress and strain. Even when the drill depth increases, residual stress and strain remain constant. The graph obtained is totally different when compared to other plates evaluated in this study. With the other power levels in laser formed plates, there were changes in residual stress and strain with changes in drill depth . This figure also shows an even distribution of residual strains on the material, and, unlike the laser formed plates, it seems possible that the temperature gradient on the parent plates during fabrication was not steep. The residual strains are not modified in any way but result from the manufacturing procedure used to produce titanium. The other forming operations witnessed in the study show a marked change to the residual stress/strain distribution. Residual stress from as received parent material shows steep residual stress versus drill depth gradient. The gradient is typical of stress induced by the manufacturing process. Surface residual stress is of high importance to mechanical design engineers as they show areas of high residual stress. The high residual stress areas help contribute to fatigue failure of the material . All values obtained in the analysis of residual stress and strain of CP grade 2 titanium plates are shown in Table 6, and results obtained allude to the performance of these plates during fatigue testing.
|Samples||Minimum strain (μɛ)||Maximum strain (μɛ)||Minimum and maximum stress (MPa)|
|1500 W (35 kJ/m)||−81||−180||−284||5||0.7||3|
|1500 W (47 kJ/m)||−68||−245||−427||29||17||16|
The readings obtained from the parent material form the base for the analysis of residual stress, and strain results for the forming process utilised in this study. Results from the parent material show a difference between the maximum and minimum stresses of 12.9 MPa which is tensile. The stress values also give an indication as to why the parent material performed better than other plates during fatigue testing. The laser formed plates showed higher values of stress than both mechanically formed and the parent materials. The effect of these stresses is therefore evident in fatigue testing and is documented in the results obtained . The mechanical forming process resulted in minor changes to the relieved stress and strain, when compared to the parent material results. The mechanical forming process rearranges the residual stress and strain in the parent material. The term rearrange is applicable in this scenario as the material had residual stress within, prior to both forming processes. Some engineering applications encourage the presence of residual stresses within the material. The changes in residual stress are due to physical changes in the material as a result of laser and mechanical forming. Manufacturing processes introduce residual stress into mechanical parts, thereby influencing fatigue behaviour. The influence of all the forming operations is well documented in the analysis of fatigue results. The only difference between these processes is the intensity at which each forming process transpires. There are variations from process to process as witnessed in this study between mechanical and laser forming processes. After the attainment of maximum stress, there is a reduction in stress as the depth increases .
The mechanically formed plates had higher residual stress values than the parent material at 41 MPa. This is a 54% increase in stress when compared to the parent material. The difference in stress between maximum and minimum stresses was 38 MPa, a 66% improvement when compared to the parent material. These results had an influence on the fatigue results of the material. The graphs also show changes in residual stress with each forming process. There are similarities in residual stress between the parent material and the mechanically formed plates. The stress peaks at about 0.5 and 0.7 mm and then taper as maximum depth is approached. Based on results obtained from the parent material, forming moves the location of maximum and minimum principal stress closer to the surface. The low line energies had minimum effect on the residual stress distribution in the titanium plates  (Figure 11).
On the laser formed plates, there is a relative increase in the strain relaxation curve when compared to the parent and mechanically formed plates. In laser formed plates due to the physical changes in the material, there is a modification in the residual stress and strain due to phase transformation. The phase transformation is due to the intense heat from the laser and effects of the temperature gradient mechanism . As witnessed on other laser formed plates, there is an increase in relieved strain as the line energy increases. The effect of deformation compatibility, as a result of internal stresses, is evident on the laser formed plates, and unlike mechanical forming, the effects of heat energy are evident on the tested specimens. The laser forming process was carried out in such a way that there was an overlap on the scan tracks, meaning some portions of the laser-irradiated specimens did not get direct heat energy from the laser but were exposed to its effects. This resulted in large thermal gradients in the material contributing to an increased presence of internal stresses in the plates. The laser forming process has the ability to move the location of the maximum stress within the specimens as witnessed in all the laser formed specimens.
For the parent and mechanically formed specimens, the location of maximum principal stress was between 0.5 and 0.7 mm, respectively. With the laser formed plates, the location of maximum principal stress is between the depths of 1.5 and 2 mm. The changes in redistribution of residual stress are due to the thermo-mechanical properties of the laser forming process. For a power of 1500 W and a line energy of 35 kJ/m, the maximum stress attained was 116 MPa (T) and a minimum stress of 2.9 MPa(C). This maximum stress was the lowest in all laser formed plate samples. Maximum and minimum residual stress values do not decrease with changes in depth as witnessed with the parent plate. The changes in line energy change the location of maximum and minimum residual stress . The line energy generated managed to penetrate and force a change on the microstructure of CP grade 2 titanium. Based on the microstructural analysis, there is a noticeable difference in microstructure between the line energies developed at a power of 1.5 kW (
The change in line energy from 35 to 47 kJ/m can be seen on the residual stress and strain results. With the line energy of 47 kJ/m, the relieved strain starts positive and ends negative due to a surge in gauge 2 and 3. These changes are due to the effects of laser forming which greatly influence the distribution of residual stress and strain. Changes in residual stress are also dependent on the process parameters and the line energy and heat flux generated. The line energy and heat flux are responsible for the phase transformation in the physical properties of the material. Titanium changes phase at a temperature of 883°C, and it appears that temperatures exceeding this value were reached during the laser forming process. The thermal gradient is the same as that obtained at an energy of 35 kJ/m. The same goes with values in heat flux which remain constant. The only difference is brought about by changes in scanning speed and beam interaction time. Changes in line energy caused variations in minimum and maximum residual stress values .
The maximum and minimum stress was the highest in all the specimens evaluated at 1.5 kW and is shown in Figure 12 above. The increase in residual stress resulted in a reduction to fatigue life in laser formed specimens. There is a steady increase in both maximum and minimum principal residual stress and strain as line energy increase. These changes are influenced by changes in temperature which also affect the microstructure. Differences in residual stress are a result of different scanning speeds. The line energy of 47 kJ/m was obtained after adjusting the scanning velocity [from 2.6 to 1.9 m/min]. The change in speed meant there was an increase in beam interaction time causing more physical changes to the material. More time was therefore available per unit area per unit time to cause changes to the material. The power setting of 2500 W had a slower scanning velocity, a high heat flux, a higher line energy and minimal beam interaction time. These plates also experienced a higher thermal gradient which influenced changes in residual stress and strain .
Changes in microstructure also influenced the distribution of residual strains. The variations in thermal gradient between a power of 1500 and 3500 W caused major changes to the microstructure and led to a rise in non-uniform thermal strains, whose effect became hyperbolic when the material is elastically stiff and has a high-yield strength. The variations in temperature caused changes to the resulting mechanical properties. This means that the material properties are largely dependent on temperature. The higher the temperature, the greater will be the change in material properties .
The microstructure of the laser-irradiated specimens’ changes as the depth of the specimen increases moving away from the laser-irradiated surface. The change in line energy to
On plates irradiated at 2500 W, the maximum and minimum residual stress was 182 MPa (T) and 11 MPa©, respectively. The difference in stress was 170 MPa, and the maximum stress is obtained at a depth of 1 mm. High residual stress had a negative effect during fatigue testing, as the material had deformed plastically. There is an alteration in the thermal gradient at this power, and the scanning velocity is also the slowest in all the speeds used in this study. The slow scanning velocity led to variations in residual stress, when comparing plates irradiated at a power of 26,500 W. Changes in phases associated with the physical properties of the material are related to transformation strains. Strains can be viewed as modes of deformation with the special characteristics of being accompanied by a change in crystal structure . All these factors influence residual stress distribution in titanium. At this power level, there is a reduction in both maximum and minimum stress values, which is in contradiction with other laser powers used in the study. This power had the optimum parameters for a line energy of 90 kJ/m  (Figure 14).
The specimens processed at 3 kW had a maximum stress of 176 MPa and a minimum stress of 0.3 MPa (C). The residual stresses had a major effect in fatigue life as they changed the location of the fracture line. The maximum principal stress at a power of 3000 W is obtained at a depth of 2 mm. The changes in residual stress and strain are closer to the surface of the irradiated plate. The laser forming process increases the hardness of titanium. Residual stresses in this study are a result of interactions between time, temperature and the material. These factors played a major role in the resulting residual stress layout on all laser formed plates. The effect of the thermal gradient is evident when these plates are compared with plates not affected by thermal energy. The highest temperature gradient was obtained at a power of 3500 W. The thermal gradient became a deciding factor in microstructural layout. Even though the line energy was the same from a power of 2500 W up to a power of 3500 W, the effects on the microstructure were not uniform. This led to the conclusion that the thermal gradient is the most influential factor in laser forming  (Figure 15).
The maximum stress obtained at 3.5 kW was the second highest at 181.9 MPa (T) and a minimum stress of 1.4 MPa (T). The hardness of plates was equivalent to the parent material, but this is where similarities end. The difference in stress was 185 MPa on the laser-processed plates. This difference in stress is related to changes in hardness of titanium as a result of laser forming process. The differences in temperature between 3000 W and 3500 W played no role in influencing minimum and maximum residual stress. The optimum settings for a line energy of
The primary motivation of this study was to investigate, analyse, characterise and compare laser and mechanical forming processes. The study focussed on the main parameters that influence the bending of plates and their effect on the microstructure and mechanical properties. New theories and discoveries are discussed in the context of contribution to the subject and body of knowledge which is wide and immense in scope. Theories and conclusions are as follows:
Nelson Mandela University (NMMU) for financial assistance and laboratory facilities. Mr. Victor Ngea-Njoume for technical assistance.