Development of a real-time ultrasonic sensing system for automated and robotic welding

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The implementation of robotic technology into welding processes is made difficult by the inherent process variables of part location, fit up, orientation and repeatability. Considering these aspects, to ensure weld reproducibility consistency and quality, advanced adaptive control techniques are essential. These involve not only the development of adequate sensors for seam tracking and joint recognition but also developments of overall machines with a level of artificial intelligence sufficient for automated welding. The development of such a prototype system which utilizes a manipulator arm, ultrasonic sensors and a transistorised welding power source is outlined. This system incorporates three essential aspects. It locates and tracks the welding seam ensuring correct positioning of the welding head relatively to the joint preparation. Additionally, it monitors the joint profile of the molten weld pool and modifies the relevant heat input parameters ensuring consistent penetration, joint filling and acceptable weld bead shape. Finally, it makes use of both the above information to reconstruct three-dimensional images of the weld pool silhouettes providing in-process inspection capabilities of the welded joints. Welding process control strategies have been incorporated into the system based on quantitative relationships between input parameters and weld bead shape configuration allowing real-time decisions to be made during the process of welding, without the need for operation intervention.British Technology Group (BTG

Variable frequency microwave (VFM) processing facilities and application in processing thermoplastic matrix composites

Microwave processing of materials is a relatively new technology advancement alternative that provides new approaches for enhancing material properties as well as economic advantages through energy savings and accelerated product development. Factors that hinder the use of microwaves in materials processing are declining, so that prospect for the development of this technology seem to be very promising. The two mechanisms of orientation polarisation and interfacial space charge polarisation, together with dc conductivity, form the basis of high frequency heating. Clearly, advantages in utilising microwave technologies for processing materials include penetration radiation, controlled electric field distribution and selective and volumetric heating. However, the most commonly used facilities for microwave processing materials are of fixed frequency, e.g. 2.45 GHz. This paper presents a state-of-the-art review of microwave technologies, processing methods and industrial applications, using variable frequency microwave (VFM) facilities. This is a new alternative for microwave processing

Thermal analysis comparison between two random glass fibre reinforced thermoplastic matrix composites bonded by adhesives using microwaves: preliminary results

[Abstract]: This paper compares the thermal analysis of two types of random glass fibre reinforced thermoplastic matrix composites joined by adhesives using microwave energy. Fixed frequency, 2.45 GHz, microwave facility is used to join thirty three percent by weight random glass fibre reinforced polystyrene composite [PS/GF (33%)] and thirty three percent by weight random glass fibre reinforced low density polyethylene composite [LDPE/GF (33%)]. The facility used is shown in Figure 1. With a given power level, the composites were exposed to various exposure times to microwave irradiation. The primer or coupling agent used was 5-minute two-part adhesive. The heat distribution of the samples of the two types of composites was analysed and compared. The relationship between the heat distribution and the lap shear strength of the samples was also compared and discussed

Microwave heating, isothermal sintering, and mechanical properties of powder metallurgy titanium and titanium alloys

This article presents a detailed assessment of microwave (MW) heating, isothermal sintering, and the resulting tensile properties of commercially pure Ti (CP-Ti), Ti-6Al-4V, and Ti-10V-2Fe-3Al (wt pct), by comparison with those fabricated by conventional vacuum sintering. The potential of MW sintering for titanium fabrication is evaluated accordingly. Pure MW radiation is capable of heating titanium powder to ≥1573 K (1300 C), but the heating response is erratic and difficult to reproduce. In contrast, the use of SiC MW susceptors ensures rapid, consistent, and controllable MW heating of titanium powder. MW sintering can consolidate CP-Ti and Ti alloys compacted from -100 mesh hydride-dehydride (HDH) Ti powder to ~95.0 pct theoretical density (TD) at 1573 K (1300 C), but no accelerated isothermal sintering has been observed over conventional practice. Significant interstitial contamination occurred from the Al2O3-SiC insulation-susceptor package, despite the high vacuum used (≤4.0 × 10-3 Pa). This leads to erratic mechanical properties including poor tensile ductility. The use of Ti sponge as impurity (O, N, C, and Si) absorbers can effectively eliminate this problem and ensure good-to-excellent tensile properties for MW-sintered CP-Ti, Ti-10V-2Fe-3Al, and Ti-6Al-4V. The mechanisms behind various observations are discussed. The prime benefit of MW sintering of Ti powder is rapid heating. MW sintering of Ti powder is suitable for the fabrication of small titanium parts or titanium preforms for subsequent thermomechanical processing

Contrast joints of glass-fibre with carbon-fibre reinforced low density polyethylene composite bonded by microwave irradiation

This paper contrasts the loss tangent, durability of reinforcement and the lap shear strengths of 33 percent by weight random glass fibre reinforced low density polyethylene matrix composite [LDPE/GF (33%)] with 33 percent by weight random carbon fibre reinforced low density polyethylene matrix composite [LDPE/CF (33%)] bonded using microwave irradiation. Fixed (2.45 GHz) and variable (2-18 GHz) frequency microwave (VFM) facilities are used to bond the two composites. With a given power level, the composites were exposed to various exposure times to microwave irradiation. The primer or coupling agent used for joining the glass-fibre-reinforced composite was 5-minute two-part adhesive, Araldite. No filler was used in joining the carbon-fibre-reinforced composite

Contrasts on fracture toughness and flexural strength of varying percentages of SLG-reinforced phenolic composites

Many previous studies had reported the improvement in the mechanical properties of vinyl ester resin reinforced with SLG. Among these material properties, fracture toughness and flexural properties are important material characteristics. This paper investigates the relationship between these two set of material properties in enviroshperes (SLG) reinforced phenolic composites. The material properties of the phenolic resin composites containing different percentage by weight of SLG are experimentally measured using the short bar method and the tree-point test. The findings indicated that the PF/E-SHERES (30%) constitute the best compromise with respect to cost, fracture toughness and flexural strength. It is hoped that the discussion and results in this work would not only contribute towards the development of SLG reinforced phenolic composites with better material properties, but also useful for the investigations of fracture toughness and flexural strength in other composites

Applications of microwaves in non-destructive testing

This paper describes a new area of application of microwave energy in non-destructive testing (NDT), in which the quality of adhesively bonded products can be detected by the intrinsic spectrum signals generated by a variable frequency microwave (VFM) source. When microwave energy is launched into a metallic cavity, which is partially or fully loaded with a material, the electromagnetic energy reflects backward and forward between the cavity walls and travels through the material many times until a final standing wave condition is established. Materials property variables like internal or surface defects, dielectric properties, physical geometry and, physical and chemical properties can contribute to its unique signal output characteristics. The reflected and input signals form a ratio, percentage of reflectance, which can be monitored and plotted as a function of the frequency. The percent of reflectance against frequency curve is called the microwave reflective spectrum. The spectrum generated can be used as a signature curve for assessing bond quality during processing. By this way, the same material under the same processing parameters provides a common characteristic curve, which can be used as a tool to provide a rapid, on-line, non-intrusive, non-destructive and volumetric monitoring of adhesively bonded polymer materials