Wire Arc Additive Manufacturing (WAAM) is attracting significant attention in industry and academia due to its ability to capture the benefits of additive manufacturing for production of large components of medium geometric complexity. Uniquely, WAAM combines the use of wire and electric arc as a fusion source to build components in a layer-by-layer approach, both of which can offer significant cost savings compared to powder and alternative fusion sources, such as laser and electron beam, respectively. Meanwhile, a high deposition rate, key for producing such components, is provided, whilst also allowing significant material savings compared to conventional manufacturing processes. However, high quality production in a wide range of materials is limited by the elevated levels of heat input which causes a number of materials processing challenges in WAAM. The materials processing challenges are fully identified in this paper to include the development of high residual stresses, undesirable microstructures, and solute segregation and phase transformations at solidification. The thermal profile during the build poses another challenge leading to heterogeneous and anisotropic material properties. This paper outlines how the materials processing challenges may be addressed in WAAM by implementation of quality improving ancillary processes. The primary WAAM process selections and ancillary processes are classified by the authors and a comprehensive review of their application conducted. Strategies by which the ancillary processes can enhance the quality of WAAM parts are presented. The efficacy and suitability of these strategies for versatile and cost effective WAAM production are discussed and a future vision of WAAM process developments provided.

https://purehost.bath.ac.uk/ws/files/183236429/StrategiesAndProcessesForHighQualityWireArcAdditiveManufacturing_Manuscript.pdf

Invited review article: Strategies and processes for high quality wire arc additive manufacturing

Manufacturing of hydrogel biomaterials with controlled mechanical properties for tissue engineering applications.

The effect of the local and global weld geometry as well as material defects on crack initiation and fatigue strength

A high power direct diode laser, emitting in the range of near infrared radiation at wavelength 808–940 nm, was applied to produce a titanium matrix composite on a surface layer of titanium alloy Ti6Al4V by laser surface gas nitriding. The nitrided surface layers were produced as single stringer beads at different heat inputs, different scanning speeds, and different powers of laser beam. The influence of laser nitriding parameters on the quality, shape, and morphology of the surface layers was investigated. It was found that the nitrided surface layers consist of titanium nitride precipitations mainly in the form of dendrites embedded in the titanium alloy matrix. The titanium nitrides are produced as a result of the reaction between molten Ti and gaseous nitrogen. Solidification and subsequent growth of the TiN dendrites takes place to a large extent at the interface of the molten Ti and the nitrogen gas atmosphere. The direction of TiN dendrites growth is perpendicular to the surface of molten Ti. The roughness of the surface layers depends strongly on the heat input of laser nitriding and can be precisely controlled. In spite of high microhardness up to 2400 HV0.2, the surface layers are crack free.

Titanium Matrix Composite Ti/TiN Produced by Diode Laser Gas Nitriding

Around the world are continued attempts to use the vibroacoustic phenomena for purposes of diagnosis of machine condition. Particularly important becomes non-invasive methods including methods based on vibration and acoustic signals. Vibroacoustic phenomena, which relates to the working of technical objects, includes all necessary information connected with the technical condition. The biggest difficulty is the transformation of registered vibroacoustic signals and creation on their basic measures, which will be non-sensitive to any type of interference occurring during the operation of objects and recording signals. To the group of technical objects, for which are already conducted numerous studies all over the world, connected with use of vibroacoustic phenomena for diagnostic purposes which relates to the automotive drive systems, including combustion engines. Combustion engines during its working generate a whole range of vibroacoustic phenomena bringing information on the proper operation of the engine, as well as on condition of each of its elements. In a combustion engine, there are many sources of vibroacoustic phenomena, which contributes to the disruption of diagnostic information. The development of appropriate methods for vibroacoustic signal processing and complete diagnostic systems may allow future extension of the on-board diagnostics OBD system – currently in used cars. The most interesting would be the development of complex system for diagnosing the condition of the individual elements of the car engine operating by basing on information from vibroacoustic signals. In this article are shown results of research, which aim is to diagnose damages of mechanical elements of car combustion engine using vibration signals and artificial neural networks.

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Application of the discrete wavelet transform and probabilistic neural networks in IC engine fault diagnostics

The goal of this research is to choose the proper method of car body welding. Properties of weld metal deposits depend on many conditions. First of all, this paper attempts to study the role of oxide inclusion sites on the transformation of austenite to acicular ferrite in steel weld metal deposits and their toughness. Safety and exploitation conditions of welded steel structure depend on many factors. The most significant of those factors are connected with materials, welding technology, state of stress and temperature. Because of that a good selection of steel and welding method is crucial to obtain proper steel structure. Car body elements of higher durability are made of low carbon and low alloy steel, very often with small amount of carbon and the amount of alloy elements such as Ni, Mn, Mo, Cr and V in low alloy steel and their welds. In the terms of the kind of steel it is used a proper welding method and adequate filler materials. In the present paper the influence of Mn, Ni, Mo, in WMD on the behaviour of steel structure for low temperature service was tested.

Oxide Inclusions in Steel Welds of Car Body

In analogy to the classification of metal weld deposits and arc welding processes of low-carbon and low-alloy steel in terms of the amount of hydrogen in metal weld deposits, a similar classification was given in terms of the amount of oxygen. Different methods of arc welding processes were chosen, such as welding with coated electrodes (basic, rutile, acid, oxide electrodes), shielded arc welding process MIG/MAG, submerged arc welding process (various wires, fluxes, shielded gases). The amount of oxygen and the percentage of acicular ferrite of metal weld deposits were mainly analysed and the impact toughness of it. Metallographical structures and fractography tests of metal weld deposit with varied amount of acicular ferrite were presented by putting attention to non-metallic inclusions and their morphology presented in metal weld deposit. Additional inclusions observation and measurements were done using a scanning electron microscope equipped with an energy-dispersive X-ray spectrometer. The studies were also made on the classification of metal weld deposits and arc welding processes of low carbon and low alloy steel in terms of the amount of oxygen in metal weld deposits on the following processes: low-oxygen processes, medium-oxygen processes, high-oxygen processes.

The classification of metal weld deposits in terms of the amount of oxygen

Low Alloy Steel Welding with Micro-Jet Cooling

Structure, safety and exploitation conditions of welding steel in car body depend on many factors. The main role of that conditions is connected with car body material, welding technology, state of stress and temperature. Because of that, a good selection of steel and welding method is very important for proper steel structure. Low alloy steel is used for car body structure, very often with small amount of carbon and the amount of alloy elements such as Ni, Mn, Mo, Cr and V in car body and welded joints. Depending on the kind of steel which is used, a proper welding method and adequate filler materials should be applied. The present paper describes the influence of Mn, Ni, Mo, Cr, V in WMD (Weld Metal Deposit) on the behaviour of steel structure especially for low temperature service.

Significant Alloy Elements in Welded Steel Structures of Car Body

In the steel structure the best mechanical properties of weld correspond with low-oxygen processes (approx. 400 ppm) that have strong influence on metallographic structure. Especially an maximal amount of acicular ferrite (AF), the most beneficial phase is translated by role of oxygen in metal weld deposit (MWD) [1-6]. AF in weld is connected with size, density and lattices parameters of oxide inclusion in weld. Having the most optimal inclusions in weld it is only possible to get even 65% of AF in weld, but no more [6-9]. High amount of AF in MWD has influence on impact toghness of welds. It was necessary to develop completely new welding technology to maximize of ferrite AF content. Micro-jet technology gives chance to obtain artificially high amount of AF in weld that corresponds with better mechanical properties of weld [10-14]. The micro-jet technology was tested for steel welding with various gases.

Tomasz Węgrzyn

Papers

Oxide Inclusions in Steel Welds of Car Body

The classification of metal weld deposits in terms of the amount of oxygen

Low Alloy Steel Welding with Micro-Jet Cooling

Significant Alloy Elements in Welded Steel Structures of Car Body

Main Micro-Jet Cooling Gases for Steel Welding