Non-Traditional Manufacturing Processes and Applications PDF

Non-Traditional Manufacturing Processes and Applications Non-Traditional Manufacturing Processes and Applications Reading Materials Focus of this Class 1. Teaching notes from & PPT slides from Yi Qin ✓ Chemical Machining & Photo-Chemical-Machining ✓ Electrical-Discharge Machining ✓ Laser Beam Machin...

Non-Traditional Manufacturing Processes and Applications Non-Traditional Manufacturing Processes and Applications Reading Materials Focus of this Class 1. Teaching notes from & PPT slides from Yi Qin ✓ Chemical Machining & Photo-Chemical-Machining ✓ Electrical-Discharge Machining ✓ Laser Beam Machining & Surface Texturing 2. Serope Kalpakjian and Steven R. Schmid, "Manufacturing Engineering and Technology", 7th Edition, Addison-Wesley Publishing Company, New York. 3. Yi Qin, "Micro-Manufacturing Engineering and Technology", 2nd edition, Elsevier, Oxford, 2015. Dr. Jie Zhao Email: [email protected] Drivers for Non-traditional Manufacturing Drivers for Non-traditional Manufacturing Machining of Dies/Moulds Jet engine cross-section Bearing Manufacturing Difficulties relating to the machining with hard metals, metal composites, ceramics…… Difficulties relating to the machining with the structures with low structural strengths and stiffnesses …… 1 Drivers for Non-traditional Manufacturing Drivers for Non-traditional Manufacturing Micro-Components/Products in our life Large-scale Products Manufacture & Products with significant differences in sizes Aerospace Railway MEMS Electrical Medical Mechanical Chemical PRODUCTS Electronic Mechatronic Automotive Optical Difficulties relating to the manufacturing of small-scale/thin components: small size, low stiffness, shape complexity, heat sensitive……need to be no distortion and residual stress free …… Drivers for Non-traditional Manufacturing Multi-Materials Products Manufacture Continuous fibres Composite Sailboard Cross-section Difficulties for the machining with multi-materials products due to significant differences in properties …… MOEMS Consuminggoods Difficulties for the manufacture of large-scale products due to sizes and operational complexity …… Traditional manufacturing technologies often are unable to meet the challenges due to various difficulties concerning: ▪ Material properties ▪ Structural strength and stiffness ▪ Difficulties for using tools/jigs/fixtures ▪ Shape limits due to machine capability ▪ Size limit to the manufacturing machines ▪ Thermal stress and distortion ▪ Residual stress induced …… Therefore, new manufacturing techniques are needed …… 2 Look at how raw materials could be converted into products Energy types could be used for material conversion: ✓ Mechanical (e.g. cutting, forming, etc.) ✓ Chemical (Chemical etching, Coating, etc.) ✓ Electrochemical (Electron-forming, ECM, etc.) ✓ Electrical (Electro-discharge machining, etc.) Therefore, a series of modern manufacturing techniques were invented, based on different types of energy that could be used to convert raw materials into products …… ✓ Laser (Laser machining, drilling, joining, surface-texturing,etc.) ✓ Electron-Beam & Focused Ion Beam ✓ Pressurisation (Water-jet machining, hydroforming, hot air forming, etc. ) Chemical Machining Chemical etching, also called chemical machining, is one of most popularly used techniques for the fabrication of thin sheet-metal parts and shallow geometries over large or small areas. Chemical etching over the large areas …… Those two components are difficult to be machined due to the large sizes and thin sections. Chemical etching to remove thin layers of the materials is currently still an optimal solution, although the process might be slow. The process does not involve a cutting or deforming force, making the process simple without need for dedicated fixtures and large machine tools. 3 Chemical Machining Tecan Limited is a leading industrial company in production of thin, small metal components by chemical etching and plating, using photo-lithography techniques. The images shown here are the components made by this company, from optical filters, micro gears, to surgical tools, like micro-spanner and surgical knife …… Those components are in a range of dimensions from several millimetres to tens millimetres while the features may be blow tens micromillimeters. Chemical Machining Principle Material is removed from a surface by chemical dissolution, using chemical reagents Chemical Machining Applications: Shadow Masks; Leadframes; Encoder Discs; MEMS; Micro-tools; Micro-Fluidics; Optical masks; etc. The images shown above are the components made by this company, from audio equipment components, pressure measurement gauges, to optical filters …… Those components may be in a range of dimensions from several millimetres to tens millimetres while the features may be blow a couple of micromillimeters. Maskant is a material not sensitive to the etchant, with through patterns on it. For large features Main types of chemical machining Chemical milling (produce shallow geometry); Chemical blanking (produce through geometry); Photochemical machining (use photo-tool to produce micro features). These can be combined with electroplating, it is also called Photo-electro-forming (produce thickness or wall) Process slow ! Cleaning important ! 4 To create through geometry (a) Schematic illustration of the chemical-machining process. Note that no forces or machine tools are involved in this process. (b) Stages in producing a profiled cavity by chemical machining; note the undercut. Photolithography For micro-fabrication, it is difficult to produce micro-features on the maskant, therefore, photolithography technique was invented …… Pattern transfer by photolithography. Note that the mask in Step 3 can be a positive or negative image of the pattern. 5 Photo-resist thin film for maskant (Summary) ✓ A material which is sensitive to the light. ✓Under the UV light: exposed area becomes hard; unexposed area becomes soft (soluable). ✓ The soft part can be “developed away” to produce the patterns (mask with images). ✓ The mask determines the geometry to be produced on the metal/substrate Photolithography is traditionally used for microelectronics product manufacturing, and now similar technique is widely used in the metal-part fabrications for thin sheet metal components….. ✓ For different materials, the same mask design can be used and no need to change the photo-tool. Photo-Chemical-Machining (A case study on Micro-Fabrication) PCM on Metals – Mass-Production Process Clean, thin sheet of metal (typically 400mm x 300mm x 0.25mm) Photo Chemical Machining (PCM) of Metal Parts 6 PCM on Metals – Mass-Production Process PCM on Metals – Mass-Production Process Photographic film work produced UV sensitive polymer (or resist) film applied PCM on Metals – Mass-Production Process PCM on Metals – Mass-Production Process Resist exposed to UV light, cross links and hardens …and placed in contact with the resist UV UV 7 PCM on Metals – Mass-Production Process PCM on Metals – Mass-Production Process Sprayed with acid solution to etch the bare metal Unexposed resist ‘developed away’ In summary, Photochemical Machining involves PCM on Metals – Mass-Production Process Resist is stripped away to leave finished part Profile view Plan view 1. 2. 3. 4. 5. 6. 7. 8. 9. Photo-tool preparation Material selection & preparation Photoresist coating or placement UV exposure Development (by the solvent called developer) Chemical etching Photoresist stripping Cleaning Inspection 8 Flexible process for various sizes/features in a high-volume production scale Applications of chemical machining MATERIAL THICKNESSES Metal with thicknesses ranging from 0.01mm to 1.50mm are mostly suitable for micro chemical etching processes. METALS Virtually all metals are suitable. However, these metals are typical: Stainless Steel (301, 302, 304, 316, 430, etc.) and other stainless steel alloys (e.g. Kovar and Invar) Cu and Cu-alloys (e.g. Bronze, Brass) Ni and Ni-alloys (ideal for micro-plating) Merits of Chemical/Photo-chemical Machining ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ Subtractive process Burr and stress free Low tooling cost Fast turnaround High or low manufacturing volume Different metals can be processed with the same tooling Low cost tooling modifications Magnetic and other material properties unaffected Complex designs are easy to tool Increasing component complexity not reflected in part cost Parts may be supplied independently or tagged to sheets Tutorial Questions 1). What are the main challenges to traditional machining techniques ? 2). Which types of the energy have been used for the development of the Nonetraditional Machining Techniques ? 3). Name typical non-traditional machining techniques & their main applications ? 4). How do you define the working principle of Chemical Machining? 5). Which two types of chemical machining processes are widely used in industries and what are the procedures used for implementing those processes? 6). How do you describe the general procedure of Photolithography, and why it is useful in Photochemical machining for producing fine geometries? 7). What is a typical procedure of Photochemical machining (PCM) ? 8). How does a photo-resist work under the UV light ? 9). What are the major applications of the PCM (e.g. material types and geometries) ? 10). What are the merits of Chemical Machining / Photochemical Machining ? 9 Needs of tools …… Railway MEMS Electrical Aerospace Medical Mechanical Electronic One of the most popularly used technologies for tool-making and micro-fabrications …… Chemical PRODUCTS Mechatronic Automotive Optical MOEMS Consuminggoods Forging/forming/injection moulding/machining processes need tools Manufacture of Dies/Moulds Product types for forging/forming and needs of tools to work under extreme conditions: Manufacture of Dies/Moulds & Micro-Tools Complexity involving the tool-making…… Extrusion die/tool for extrusion of metal parts… Moulds for injection moulding of plastic parts … 1 Tools Materials Often Used ✓ Tool Steels - H13, TZM, HSS, Boron-Nitride ✓ Tungsten Carbide ✓ Nickel-based alloys ✓ Cermets ✓ Ceramics ✓ Diamonds …… Micro-Components with Hard-to-Cut and Hard-to-Deform Materials ✓ In general, micro-parts used in several environment ✓ MEMS, Sensors and actuators ✓ Medical implants and surgical tools ✓ Dies/moulds, cutting tools ✓ Micro-bearings ✓ Micro-engines, motors and robots ✓ Watch components …… Types of Materials ✓ ✓ ✓ ✓ ✓ ✓ High-strength Metals and Alloys Ceramics Cemented carbides Shape memory alloys Piezoceramic materials Magnetic materials Electro-Discharge Machining (EDM) to meet the manufacturing requirements and challenges …… Working Principle Metal removal is based on metal erosion by spark discharges; EDM World Spark discharges through the dielectric fliud when electrical potential reaches critical value; Dielectric concentrates the energy to very high level; Maintaining the gap is critical (0.005 to 1.0 mm). 2 EDM Machines for manufacturing at different scales Die-sink EDM & Machine Tool servo mechanism tool electrode controlling unit work piece dielectric fluid.. pulse generator. work tank x- and y- table. Micro-machine dielectric reservoir dielectric pump and filter Conventional machine Miniature machine Functionalities of Dielectric Fluid in EDM ▪ Insulator until the electrical potential is sufficiently high; ▪ Carrying away the derbies in the cutting area; ▪ Working as cooling medium; ▪ Mineral oil or water is normally used as a dielectric fluid Tools (electrodes) for Die-sink EDM ▪ The cavity shapes are determined by the tool-shape and tool motion (e.g. through machine control) ▪ The tool manufactured by other manufacturing processes, e.g. powder sintering and/or machining ▪ Electrode material selection: considering melting points of the tool material, electrical conductivity, and thermal wear-resistance, since spark erosion could also damage the electrode. It also depends on the power level to be used. But not necessarily high mechanical strength. ▪ Electrode materials: Copper/Copper Tungsten, Brass, Graphite. Graphite highest thermal wear-resistance ▪ Remember die-sink EDM always starts with making electrodes, similar to preparation of cutting tools ! 3 Process and parameters Process and parameters ▪ Any material which is electrically conductive can be cut; ▪ Melting point of the material is an important parameter but not strength or hardiness, which makes the process unique; ▪ The removal rate is determined by controlled parameters: ▪ Frequency of discharge (e.g. spark intervals from 0.01 microsecond to 10s microseconds) ▪ Current density (e.g. from 5 to 500 amps/mm2) ▪ Voltage (e.g. 50 to 300 volts) ▪ High-rate EDM cutting means: - high energy input requirements; - high temperature at the working zone; - large heat-affected zone; - high cooling rate (and hence, high thermal stress and residual stress); - large volume removed per spark – rough surface produced. ▪ High rate means poor surface integrity - why? 50 µm 20 µm 5 µm Single discharge crater (a), surface topography (b), and removed particles (c) a b c Wire EDM Process and parameters High surface finish means: - high frequency of discharge to be used; - but low energy input (low voltage, low current density) needed; - resulting in low production rate but better surface roughness and integrity; - expensive machining due to lower efficiency; - particularly needed for micro-components & micro-tools …… 50 µm 20 µm Dielectric fluid 5 µm Single discharge crater (a), surface topography (b), and removed particles (c) a b c 4 EDM Wire Cutting Merits of Wire EDM, comparing to Die-sink EDM ✓ usually the wire is 0.25 mm in diameter; ✓ made of brass, copper or Zinc- or brass-coated; ✓ sufficient tensile strength and fracture toughness are necessary; ✓ high electrical conductivity is necessary; ✓ the wire is generally used once; ✓ travels with speed range of 0.15-9 m/min; ✓ removal rate is measured using cross-sectional area cut per unit time. ✓ No bulk electrodes are needed – saving machining and material cost; ✓ Finer geometry can be achieved, e.g. wire diameter down to 0.01mm is available; ✓ For thin plate and straight outer surface fabrication, Wire-EDM is more flexible and efficient; ✓ Combining Wire-EDM with controlled motion of the workpiece, some complex grooves and surface profiles are achievable; ✓ Wire-EDM can be used for drilling micro-size holes, polishing fragile tool/component, suitable for micro-fabrication. General Engineering Applications of EDM EDM Process Variants a b c d e f Process variants of EDM: Die-Sinking (a), WEDM (b), ED-Drilling (c), ED-Milling (d), EDG (e), and WEDG (f) ✓ Any material - an electrical conductor, can be cut; ✓ Especially for hard metals such as tool-steels and Tungsten carbide; ✓ Largely used for die/mould-making and micro-fabrications; ✓ Various shapes possible, mostly cavity, slots and holes; but deep slots and narrow openings should be avoided; ✓ Bulk-material removal may be done by conventional processes such milling, followed by EDM; ✓ Tool-making may be followed by grinding to improve surface roughness and remove brittle surface; ✓ Cannot cut non-electrical-conductive materials like polymers, silicon, etc. 5 Applications of EDM Micro/Nano-EDM Surface quality and Post-processing 200 µm Rough cutting – high production rate Polishing / Grinding Micro-EDM (EDM for Micro-Manufacturing and Tooling) Tool Electrode 500 µm 500 µm (a). Micro structured referential workpiece, (b). Mould insert for hot embossing of micro opto-electronic connecting plugs, and (c). Microgear of a micro planetary drive (provided by IPK of Germany) Applications of EDM to Moulds-making, including that for micro-injection moulding Moulds are widely used in manufacturing parts/components (polymers, composites materials, etc.), like Mobile phone covers, TV frames/covers, Car panels, Functional components of miniature/microdevices, etc.) Electrodes after machining. 6 Applications of EDM to Moulds-making, including that for micro-injection moulding Tutorial Questions 1). How does Die-sink Electro-discharge machining work (a sketch to show the set-up of the EDM)? 2). Which roles does a dielectric fluid play in EDM? Assembly & Testing 3). Why is maintaining the gap between the tool and the workpiece important in EDM? 4). How an electrode material should be selected for Die-sink EDM ? 5). Which three parameters have significant influences on the EDM process and product quality? In principle, how should the value of these parameters be set to achieve better surface quality of the component/part or high production rate? Product Design & Die/Mould Design …… Electrode Design & Machining 6). How does the wire EDM work (set-up and functions of the wire)? Why it is efficient and flexible, comparing to Die-sink EDM? EDM Process & Component Manufacturing 7). What considerations should be taken into account in selecting the wire and controlling the process in wire-EDM? 8). What are the applications of EDM (including material types and geometries, product types, etc.)? 9). What is a typical procedure of Tool/Mould-making, associated with the use of die-sink EDM? 7 Laser-Based Manufacturing Laser Beam Material-Processing - Machines ✓ Laser cutting ✓ Laser drilling ✓ Laser surface texturing (ablation) ✓ Laser joining (welding/soldering) ✓ Laser forming ✓ Laser deposition/melting ✓ Laser printing Laser polishing of metal surface Laser printing ✓ Laser alloying / surface treatment …… Laser ablation of glass Laser Machining Light Amplification by Stimulated Emission of Radiation (LASER) Multi-reflection to amplify energy to very high level. Laser Machining - Principle for cutting Molecules are excited to high energy level. Gain medium can be of any state: gas, liquid, solid, or plasma 1 A simplified heat balance equation (for selection of a laser system): Two Material Parameters Specific heat The energy required to raise the temperature of a unit mass of material by one degree (J/Kg. K). QL = Q R + Q M + Q C Thermal Conductivity QL - the required laser energy (the power level required); QR - the energy lost due to reflection; Melt Pool Laser Beam QM - the energy required to create a melt pool; QC - the energy lost due to thermal conduction Heat affected zone Workpiece Summary of Laser Machining Working principle Highly focused, high-density energy (Focussed laser beam can have power density in. excess of 1 MW/mm2) melts and evaporates portion of the workpiece in a controlled manner. Parameters Reflectivity of material surfaces Thermal conductivity of the work material Specific heat of the work material Combined with gas to increase temperature and prevent from oxidation. Indicates the ease with heat flows within and through the material (W/m. K) Example: C15 Al99.5 Specific heat 465 896 48 215 Thermal conductivity Applications & Types of Lasers Cutting Metals Plastics Ceramics Drilling Metals Plastics Marking/Engraving Metals Plastics Ceramics TYPE of LASER PCO2, CWCO2, Nd:YAG, ruby CWCO2 PCO2 Surface treatment, metals CWCO2 Welding, metals PCO2, Nd:YAG, Nd:glass, ruby PCO2, Nd: YAG, Nd:glass, ruby Excimer PCO2, Nd:YAG Excimer Excimer Note: P = pulsed, CW = continuous wave; Nd:YAG is a crystal that is used as a lasing medium for solid-state lasers; Ruby laser: a solid-state laser that uses a synthetic ruby crystal as its gain medium; Excimer, originally short for excited dimer (a molecule or molecular complex) - a form of ultraviolet laser, commonly used in the production of microelectronic devices 2 Flexibility of the system setup 3D Laser Machining with Two Beams Concept Tool Two-beam concept to remove a volume of material - emulates the Help to positioning the laser actions of a mechanical tool, such as that used in grinding and turning. Detect the temperature B2 B1  Combining monitoring, measurement and machining Laser-assisted Machining Combining localised heating by laser beam and mechanical cutting, for difficult machined materials such as metal matrix composites Application Aspects of Laser Machining ▪ Various materials can be cut, except that heat-sensitive; ▪ Thin sheets/tubes are mostly suitable ▪ Manufacturing is clean; ▪ Small holes/ grooves (0.005mm, L/D=50) not large holes; ▪ Cut at difficult angles or locations; ▪ Rough surface produced (heat-effected zone); ▪ Fixture simple (no force involved); ▪ Safe protection necessary…… 3 Laser-machining: Examples Design considerations for Laser Machining MICRO-CUTTING OF SILICON ▪ Reflectivity of the workpiece surface / Dull and unpolished surfaces APPLICATIONS prefer-able; Microelectronics ▪ Designs with sharp corners should be avoided; PARAMETERS ▪ Deep cut should be avoided (produce tapers); Thickness 625 m ▪ Adverse effects on the material properties, caused by high local Slot width 150 m Slot distance 100 m temperature and the heat-affected zone, should be considered. Working time 15 s per slot Entrance (up) and exit (down) Laser-machining: Examples Laser-machining: Examples MICRO-DRILLING OF CERAMIC MATERIALS APPLICATIONS APPLICATIONS Microelectronics Microfluidics MICRO-DRILLING OF SILICON CARBIDE Microelectronics PARAMETERS PARAMETERS Material alumina Material SiC Thickness 1 mm Thickness 400 m Hole number 604 Hole number 164 Hole diameter 40 m Hole diameter 40 m Hole pitch 100 m Hole pitch 100 m Working time 2 s per hole Working time 500 ms per hole 4 Laser-machining: Examples Laser-ablation for Micro-Structuring Surfaces for special functionalities Recent developments in solar cell manufacturing, display manufacturing, micro-tooling, medical implants, microfluidic devices have involved laser surface texturing significantly …… Nano-features to trap the light Image of animal skin & tree leaves Laser cutting of Stents – most successful manufacturing technology available so far …… Micro-Tooling Laser-Surface-Texturing With a combination of ultra short pulses and high resolution interference methods, structures with dimensions of less than 300 nm can be generated, either in polymer parts directly, or in steel replication tools. Microstructured replication tool for self cleaning surfaces Super hydrophobic surface Laser-Surface-Texturing: Applications Recent developments in solar cell manufacturing, display manufacturing, micro-tooling, medical implants, microfluidic devices have involved laser surface texturing significantly …… Laser manufactured micro injection moulding tool insert Anti-microbial surfaces for home uses and hospital Silver Coating or Surface Texturing Microfluidic channels ablated with excimer laser radiation 5 Laser-ablation for Micro-Structuring Surfaces for special functionalities Micro structuring with laser radiation adopts one of the following techniques: ✓ Mask-based technique ✓ Scribing technique The mask-based technique, for example, combined with lithography, to generate micro-fluidic systems and nano scaled optical devices. The scribing technique is adopted for full-3D structuring and is comparable to mechanical milling. Mask-based Technique Laser-ablation for Micro-Structuring Surfaces for special functionalities Ultra-short Pulsed Lasers popularly used …… Using ultra short pulsed lasers with pulse durations of 10 ps (picosecond = 1/1000 nanosecond) in pulse bursts of several pulses with a time spacing of 20 ns each; The surface quality of metal micro ablation have been increased significantly and allows for the production of tools and parts with roughness values of less than 0.5 µm. Scribing Technique For mask-based laser ablation the laser radiation is formed and homogenized by a telescope and projected onto a mask representing the desired intensity distribution. The mask is imaged by an objective lens to the final intensity distribution. Laser Surface Structuring for Functionalised Surfaces …… 6 Comparison of three non-traditional manufacturing techniques on Materials Capability Wire-EDM (Electrical-Discharge- Summary on non-traditional manufacturing techniques…… Holes in Silicon plates Machining) Thermal sensitive Nialloys (Invar) thin foils Laser cutting / Drilling Preliminary fabrication on tool-steels Photo-chemical-machining Consideration also on the geometry capability ? Surface Roughness and Tolerances in Machining Tutorial Questions on Laser Machining 1). What is the working principle of Laser Machining, and how is the metal removed by the laser heating (three stages)? 2). Which three surface/material parameters have significant influences on a Laser machining process and why ? 3). Why could 3D laser cutting be more efficient (two beam concept), compared to single beam laser cutting? 4). What are the main issues, in relation to the applications of laser machining (characteristics and capabilities in materials and geometry) ? 5). What are the major design considerations for laser-machining? 6). Compared to Chemical etching and EDM, what advantages Laser machining holds, in terms of material processing capabilities? 7). Compared to Chemical etching, what negative effect does laser machining have? 8). What are the possible industrial applications of laser machining ? 7