Learning objectives
On completion of the course, students should have attained knowledge and expertise relating to non-conventional manufacturing technologies, including laser materials processing, additive manufacturing, ultrasonic machining, water jet machining, abrasive water jet machining, electro-discharge machining and electro-chemical machining. Study of these processes will be undertaken with a systematic approach based on modelling, to allow interpretation and understanding of the laws and mechanisms on which they are based. The advantages and limitations of each process will be analysed both in comparison to traditional machining technologies as well as for production of specific components. Process modelling will be oriented towards the analysis and prediction of the influence of process parameters on the obtained results.
Prerequisites
Technical Design, Physics, Chemistry, Materials Science and Technology, Mathematical Analysis, Manufacturing Technology
Course unit content
Study of non-convectional manufacturing technology, including:
- Laser materials processing
- Additive manufacturing
- Ultrasonic machining
- Water jet machining
- Abrasive water jet machining
- Electro-discharge machining
- Electro-chemical machining
Full programme
Introduction to non-conventional manufacturing processes: definition, classification and examples.
Laser Materials Processing (LMP). The duality of light: electromagnetic wave (wavelength, wavenumber) and flow of photons. Blackbody radiation as a function of temperature. Fundamental quantum mechanics underlying laser function. Absorption, spontaneous emission and stimulated emission.
Population inversion. Three- and four-level laser systems. Optical resonance and light amplification in lasers. Longitudinal modes and optical cavity length. Laser beam properties: linewidth, coherence (spatial and temporal), divergence and radiance. Laser efficiency and comprising elements.
Transverse electromagnetic modes (TEM) and beam quality factor. Spatial profile of a laser beam and definition of diameter. Temporal profile of a laser beam: continuous-wave and pulsed regimes. Techniques for generation of laser pulses as a function of duration. Polarisation (linear, circular, random).
Architecture of the most common types of gas and solid-state industrial laser sources. Active media: carbon dioxide, neon, neodymium, thulium, p-n junction (semiconductor). Modern fibre lasers.
Snell’s law. The Fresnel equations and differences in absorption of “p” and “s” polarised waves. Laser-materials interactions: differences between metallic and non-metallic materials. Reflectivity and absorptivity and the dependence of these parameters on the wavelength, temperature, surface roughness, presence of oxide layers etc. Propagation and optical absorption within materials according to the Beer-Lambert law. Thermal effects on materials and changes of state in conditions of thermal equilibrium. Classification of the main processes as functions of process parameters.
Optical transport systems: mirrors and optical fibre. Function of an optical fibre and the concept of total internal reflection. Beam focalisation systems: minimum beam diameter depth of field and Rayleigh range. Focalisation from optical fibre. Beam movement systems: galvanometric heat, f-theta lens, linear axes and anthropomorphic robot.
Laser hardening: resolution of Fourier’s equation under transient conditions. Thermal cycle: surface melting, quenching and tempering. Process feasibility for different types of component and production volumes. Industrial applications and laser hardening machines.
Solutions for the linear heat flux equation for semi-infinite solids subject to laser heating. Start-up and switch-off of laser source and effects on the treated material. Laser hardening of large surfaces and axial-symmetric components. Numerical simulation of general cases.
Laser cutting: functioning principle of the assist gas (inert or reactive). Influence of process parameters (power, cutting velocity, focused beam diameter, type of assist gas and gas pressure) on the cut depth and quality. Modelling of the cutting process: moving circular source. Prediction of the cut front angle and maximum cutting thickness.
Laser welding in different geometric configurations (overlap, but welding etc.). The influence of process parameters on the transition from conduction to keyhole welding. Instability of the keyhole. Modelling of laser welding: moving linear and point heat sources. Pulsed laser welding of thin sections.
Pulsed laser process, including laser ablation and surface modification. Laser-material interactions as a function of the pulse duration and fluence. Relaxation time and thermal conduction following ultrashort laser pulses. Changes of state in non-equilibrium conditions: over heating, critical temperature, vaporisation, fragmentation, phase explosion. Numerical simulation of laser ablation with short and ultrashort pulses. Industrial applications and systems for short pulse laser processing.
Classification of Additive Manufacturing (AM) techniques. Methods of material deposition. Stereo lithography (SLA): process and device descriptions. The functioning principles of SLA: interaction between a UV laser and photopolymer. Selective Laser Sintering (SLS): functioning principles and industrial applications.
Selective Laser Melting (SLM). Functioning principles and the influence of process parameters (laser power, spot diameter, scanning velocity, hatch spacing, layer thickness) on the porosity and mechanical strength of components. Design for additive manufacturing: manufacturing and functional advantages compared to traditional manufacturing technologies. Case-study of SLM fabrication of innovative components.
Ultrasonic Machining (USM). Underlying physical principles: impact of abrasive on a surface, hammering, cavitation, erosion. Process parameters: power, frequency, amplitude, removed volume. Process types: cleaning, drilling, milling, cutting, welding. Industrial applications and USM machines.
Water Jet Machining (WJM). Underlying physical principles: pressure intensification, nozzle and catcher. Material removal mechanism. Calculation of the strike pressure as a function of the supplied pressure. Morphology of water jet: core, transition zone, extinction zone. Definition of the stand-off distance. Process parameters and their influence on the maximum cut thickness and cut quality. Industrial applications and WJM machines.
Abrasive Water Jet Machining (AWJM). Differences compared to WJM: type of abrasive employed, nozzles for water-abrasive mixing. Material removal mechanism: abrasion zone, transition zone and plastic-deformation zone. Process parameters. Calculation of the ideal mixing ratio for maximisation of the cut depth. Industrial applications and AWJM machines.
Electro-Discharge Machining (EDM). Process of material removal via electrical discharge between two electrodes separated by a dielectric liquid. Analysis of plasma channel and surface crater formation phases. Generators and relaxation, the Lazarenko circuit. Controlled pulsed generators. The dielectric: functions, cleaning, vacuum and injection. Effects of the dielectric on the tool. Industrial applications, EDM machines and tool feed systems with voltage feedback control.
Roughing and finishing operations with sinker EDM. Tool materials and dimensioning. Influence of process parameters, including discharge current, frequency and discharge time. Model for approximation of the feed velocity and surface roughness. Wire EDM: wire feed system. Cut progression, including front and side gaps. Actual cut edge profile and differences from theoretical profile. Correction of wire positioning compared to programmed profile.
Electro-Chemical Machining (ECM): Functioning principles of anodic dissolution and differences between ECM and galvanic coating. Faraday’s law. Energy necessary to perform ECM. The phenomenon of electrode passivation. Calculation of the equilibrium gap during processing and in correspondence with inclined surfaces. Theoretical considerations and real conditions. Function of the electrolyte and its operating conditions. Temperature profile calculation in the working zone. Limitations imposed by the current regime.
Industrial applications and machines for ECM. The structure of the generator, pumping power necessary for circulation of the electrolyte, treatment systems. Tool dimensions, analytical methods for determining the cathode form. Influence of process parameters on ECM: feed speed and its influence on the equilibrium gap, absorbed energy, surface roughness. The influence of the current intensity of the removal ratio and surface roughness.
Bibliography
S. Kalpakjian, S. Schmid, Manufacturing engineering and technology, 2013
M. Monno, B. Previtali, M. Strano, Tecnologia meccanica le lavorazioni non convenzionali, 2012
E. Capello, Le lavorazioni industriali mediante laser di potenza, 2009
Teaching methods
Lessons with comprise both theoretical treatment of various non-conventional manufacturing technologies, as well as analysis of specific cases where such technologies have been successfully introduced into manufacturing environments. Presentation slides used as supporting material during lessons will be uploaded to the Elly platform on a weekly basis. Course registration on line is necessary to download the slides. Practical exercises will be undertaken for select manufacturing technologies to provide a more thorough understanding of the physical phenomena addressed during lessons. The preparation of a project relating to a specific non-conventional technology will form a fundamental part of the learning process and will be discussed during the oral exam.
Assessment methods and criteria
Assessment of students will comprise the following two parts:
1) A report summarising the results of a project relating to a specific non-conventional manufacturing technology. The report will be assessed on a scale of 0-30 (weighted 50% of final course mark);
2) An oral exam consisting of questions relating to two different non-conventional manufacturing technologies covered in the course. The oral exam will be assessed on a scale of 0-30 (weighted 50% of final course mark).
Students should note that on line registration is obligatory for the oral exam. Exam results will be published on the Esse3 portal within one week of the exam date.
