LIA NEWS
Tis results in a full metallurgical bond with a small heat affected zone and minimal dilution. It has been developed for surface wear and corrosion coatings, component repairs and remanufacturing, and generation of complete components from scratch. Two other variations of LMD – hot/cold wire
cladding and internal diameter cladding – have now evolved into successful industrial processes and are now widely used in the oil industry, agriculture, power generation and remanufacturing sectors. A recent key development by Fraunhofer IWS is a new coax laser deposition head Coaxwire which provides omni-directional welding
performance for the use of metallic wires as filler material, which is of particular use for 3D build up additive manufacturing of metallic components. One area of laser material processing that has
benefitted the most from technology improvements in both spatial and temporal properties of the laser is laser machining. In addition, the advent of lower cost and smaller footprint laser power sources has lead to much wider industrial adoption of laser technology. Te latest generation of pulsed lasers with pulse lengths from milliseconds all the way to femtoseconds has led to a rich pipeline of innovations impacting virtually every manufacturing industry. For example, laser cutting
of battery electrodes can produce excellent cut quality and achieve high cutting speeds for application in lithium-ion battery cells. Similarly lasers can be used for coating removal for electrical contacts on battery foils. Large area coating removal for paint stripping, deoxidisation, mould and die cleaning or removal of special coatings is conducted by applying high power lasers. Lasers are also used for high rate drilling processes for up to 15,000 holes per second.l
Rahul Patwa is project manager, and Craig Bratt executive director, at the US Fraunhofer Center for Laser Applications.
3D printing of conductive CNT-polymer composite By Ying Liu, Wei Xiong, Lijia Jiang, Yunshen Zhou and Yongfeng Lu
A
dvanced three-dimensional (3D) micro/ nanofabrication of functional devices represents a key research topic in modern nanoscience and nanotechnology, and is
critically important to numerous scientific and industrial applications. Among various existing 3D micro/nanofabrication methods, two-photon polymerisation (TPP) based on laser direct writing is regarded as one of the most promising methods thanks to its unique combination of true three dimensionality and high spatial resolution. Te TPP technique is based on the nonlinear
interaction of femtosecond laser pulses with photosensitive material, which induces a highly localised chemical reaction leading to polymerisation of the photoresist, with current resolutions down to 40 nm. Te capability of the TPP technique is significantly determined by the properties of photoresists employed, which are electronic insulating in general. To increase the functionality and expand the applications of TPP, we used carbon nanotubes (CNT) as filling materials in the host polymers.
CNTs continue to deliver a huge impact on
nanotechnology for their remarkable mechanical, electrical, thermal and optical properties. However, it is difficult to achieve both high CNT concentration and homogenous CNT dispersion because of the strong van der Waals interactions among individual CNTs. Moreover, the linear optical absorption of CNTs also limits the maximum doping level of CNTs in composite resins for nonlinear TPP lithography. Te relatively low CNT loading concentration leads to limited performance of the composite resins. To overcome these limitations, a TPP-compatible composite material based on multi-walled carbon nanotubes (MWNT), thiol and acrylic photoresist is presented here. Te schematic illustration of the composite preparation and 3D printing is shown in figure 1. Te TPP compatible composite polymer was prepared by directly mixing acrylic monomer, thiol,
functional 3D micro/ nanostructures using the composite resins have been successfully developed
Various
and photoinitiator with MWNT powder, with various weight percentages. Te resins prepared showed excellent dispersion of MWNTs through the composite resins and had a high stability, lasting for one week under ambient conditions without obvious MWNT aggregation. Using TPP lithography, a femtosecond laser beam was tightly focused into the composite resin to make 3D scans according to geometric user designs, resulting in solidified 3D micro/nanostructures with MWNTs simultaneously incorporated inside the polymer. Aſter the TPP lithography, the samples were developed with the
unsolidified resin rinsed away, leaving the 3D architectures of MWNT-based composite polymer on the substrates. A broad range of functional micro/nanostructures were fabricated, including micro-coil inductor, woodpile, spiral-like photonic crystal, micro-engine inlet fan, micro-car model and micro-gear, as shown in figure 2.
Figure 1: Experimental procedure in preparing CNT-polymer composite resins and the experimental setup of TPP fabrication
32 LASER SYSTEMS EUROPE ISSUE 37 • WINTER 2017
Figure 2: Functional micro/nanostructures fabricated using the MWNT-based composite resins by TPP lithography
Figure 3: Precise assembly of MWNTs by TPP lithography and direct pyrolysis
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