Prediction and optimization of residual stresses, weld-bead profile and mechanical properties of laser welded components

Recently, laser welding has become a leading industrial joining process. Mainly because it has become highly automated using sophisticated robotic systems. However, to make effective use of automated laser welding it is essential to have a high degree of confidence in predicting the welding outcome. To achieve a desired weld quality, the weldments are normally examined and related to the weld input parameters. This input-output relationship can be in the form of mathematical models that can be programmed and fed to the robotic control system. This work aims to introduce experimentally based mathematical models developed by applying Response Surface Methodology (RSM) using Design-Expert software V7 to relate the residual stress distribution, weld bead parameters, mechanical properties and operating cost to the laser welding input parameters, namely: laser power, welding speed and focal point position. Also, the desirability approach was used in conjunction with RSM to find out the optimal combination of the welding parameters to achieve the required weld quality. In addition to this, microstructural investigation of the welded joints was carried out to study the effect of varying the welding conditions on the microstructure of the Weld zone (WZ) and Heat affected zone (HAZ). Common materials were investigated in this work (i.e.AISI1016, AISI1045 and AISI304) with different thicknesses and joint configurations using a 1.5 kW CW C02 Rofin laser as a welding source and two focusing lenses with focal lengths of 127 and 190 mm. Many models were developed to predict the responses of interest for similar and dissimilar welding. Also, the main effects and the interaction effects of the process parameters on the responses were discussed and presented graphically for all materials and joint configurations. Moreover, by using the developed models the welding process was optimized by determining the optimal combination of the process input parameters at which the desired weld quality can be achieved for each material. Finally, the size and orientation of the solidified structures were related to the welding conditions. It was observed that when the heat input increases the weldbead geometry and the microstructures become bigger and coarser respectively

Optimising the laser-welded butt-joints of medium carbon steel using RSM

The optimization capabilities in design-expert software were used to optimise the keyhole parameters (i.e. maximize penetration (P) and minimise the heat input, width of welded zone, (W) and width of heat affected zone (WHAZ)) in CW CO2 laser butt-welding of medium carbon steel. The previous developed mathematical models to predict the keyhole parameters in terms of the process factors namely; laser power (LP), welding speed (S) and focused position (F) were used to optimize the welding process. The goal was to set the process factors at optimum values to reach the desirable weld bead quality and to increase the production rate. Numerical and graphical optimization techniques were used. In fact, two optimization criteria were taken into account. In this investigation optimal solutions were found that would improve the weld quality, increase the productivity and minimize the total operation cost. In addition to that, superimposing the contours for the various response surfaces produced overlay plots

Multi-response optimization of CO2 laser welding process of austenitic stainless steel

Recently, laser welding of austenitic stainless steel has received great attention in industry, due to its wide spread application in petroleum refinement stations, power plant, pharmaceutical industry and households. Therefore, mechanical properties should be controlled to obtain good welded joints. The welding process should be optimized by the proper mathematical models. In this research, the tensile strength and impact strength along with the joint operating cost of laser welded butt joints made of AISI304 was investigated. Design-expert software was used to establish the design matrix and to analyze the experimental data. The relationships between the laser welding parameters (laser power, welding speed and focal point position) and the three responses (tensile strength, impact strength and joint operating cost) were established. Also, the optimization capabilities in design-expert software were used to optimise the welding process. The developed mathematical models were tested for adequacy using analysis of variance and other adequacy measures. In this investigation the optimal welding conditions were identified in order to increase the productivity and minimize the total operating cost. Overlay graphs were plotted by superimposing the contours for the various response surfaces. The process parameters effect was determined and the optimal welding combinations were tabulated

Application of response surface methodology in the design of functionally graded plasma sprayed hydroxyapatite coatings

The highly complex process-property-structure relationship poses a major challenge in the optimization of plasma sprayed hydroxyapatite coatings. In addition, contradictions in relation to the ideal coating properties exist; a dense, highly crystalline coating is required for long term coating stability, whereas coatings with lower crystallinity dissolve more rapidly but have an improved osteogenic response in vivo. In this study, response surface methodology (RSM) is utilized to investigate the influences and interaction effects of current, gas flow rate, powder feed rate, spray distance and carrier gas flow rate on the roughness, crystallinity, purity, porosity and thickness of plasma sprayed HA coatings. Roughness related to the particle velocity and particle melting, and was highest at low gas flow rates and, due to the quadratic effect of current, at the central current value. High crystallinity resulted at high current and low spray distance due to the presence of bulk crystalline material and recrystallization of amorphous material. Purity was highest at low carrier gas flow rate and high gas flow rate, where particle temperature was reduced. Porosity was dependent on the degree of particle melting and was highest at low gas flow rate and powder feed rate and at high current and spray distance. Coating thickness was determined by the number of particles and the degree of flattening on impact, and was highest at high current, low gas flow rate, high powder feed rate and low spray distance. From this in-depth analysis, predictive process equations were developed and optimized to produce two distinct coatings; a stable coating and a bioactive coating, designed to form the base and surface layers of a functionally graded coating respectively, to provide enhanced osteogenesis, while maintaining long-term stability. Culture of osteoblast-like cells on the coatings demonstrated an increased osteogenic response on the bioactive coating compared to the other groups. Overall, this study identifies parameter effects and interactions leading to the development of optimized coatings with the potential to enhance the functional life of HA coated implants in vivo

Energy diversity through renewable energy source (RES) – a case study of biomass

Biomass has played a dominant role in the energy need of the continued world growing population. Its conversion from biomass to biogas in its production, have been a very promising means of producing an energy carrier from renewable resources and of achieving environmental benefits in multiples. As the population continue to grow coupled with the devastating effects of climate, efforts are being made by all and sundry at all level such as; scientists, researchers and policy makers in finding a lasting solution to the current predicament of climate change. As it is known fact now that the present demand for oil for biofuel production greatly exceeds the supply, this as a result has led to alternative sources of biomass being required. In achieving this, various biomasses have been considered for energy production, such as microalgae, yeast, grass and other renewable biomass substrates. Apart from the contribution biomass have made to sustainable development, it will also provide energy security for the growing population which currently stands at 7 billion. The resources availability and easily conversion process into the secondary energy carriers without much capital intensive makes this study a high profile research. Through this, it also aid in the reduction of greenhouse gas emissions by offsetting fossil fuel greenhouse gas (GHG) emissions when produced and used in a sustainable way Biomass as a renewable energy source is being discussed therein. Though there are large variations in biogas yields and composition of the gas among the raw materials considered. This is due to the variation in their compositions, digestion technologies and their digestion conditions that are applicable. Energy diversity through (RES) is herein therefore considered using biomass as a case study with particular emphasis on biogas/biofuel production

Underlying factors to consider in improving energy yield from biomass source through yeast use on high-pressure homogenizer (HPH)

Pioneering the works of Brookman (1975), Middelberg et al. (1992a, 1992b) and Kleinig and Middelberg (1996), on cell disruption of yeast through high pressure homogenizer (HPH), the underlying factors in improving energy yield from biomass source has to be considered. This has become a global issue for scientists, researchers and policy makers as the energy demand has grown over the years due to the growing population. As cleaner energy has become highly needed for save environment and protection of the climate hence shifting away from the utilization of fossil fuels will be of higher priority. In this paper, these factors will be highlighted and discussed herein as well as other parameters that influence the energy production efficiency from the high-pressure homogenizer (HPH) through using yeast as a biomass source. The HPH for consideration in this study is the GYB40-10S; this has a pressure of up to 100 MPa with two stage homogenizing valves pressure. This is adjustable so as to produce superfine, homogenous, stable liquid-liquid or solid-liquid under multiple actions of cavitation effect and high speed impact. And also shear through the adjustable homogenizing pressure valve in the conditions of high pressure and thereby making the material compatible after homogenization

Yeast: a potential biomass substrate for the production of cleaner energy (Biogas)

Yeast cell wall and its entire contents disruption treatments are required in the enhancement of protein and the overall biodegradability of the cell wall materials during homogenization process. Yeast as a cheap, good resource and easily available source of energy from biomass into biogas, it was used as a substrate for the cleaner energy production due to its richly and high level content of protein contained in it. An initial study on the effects of high-pressure homogenizer mechanical pretreatment has been conducted in sequence as generated by the design matrix of the design of experiment (DOE) focusing on protein yields from bakers’ yeast also known as Saccharomyces cerevisiae and in order to achieve the maximum yield of protein which in other words aid biogas production, the following optimum process parameters were set in. The yeast block was refrigerated at between 0 – 4 °C with fermentation at (0 – 24 h), a pH value of (5.3) maximum was used in the preparation of the buffer solution C. This was obtained through diluting solution B into A until the pH was attained (details as shown in the materials and methods section). Number of cycles (passes) of the soluble yeast were undergone to enable the yeast cell walls be broken down for the release of more protein and at temperature range (15 – 25 °C). The pressure for the compressed state during homogenization was set between (30 – 90 MPa). The results presented therefore showed the rates of protein released from the disruption through using the Design Expert Software V.8 in identifying the ideal conditions as set in the parameters