Avraham Benatar

Fabrication of diffractive optics by use of slow tool servo diamond turning process

In recent years, it has become possible to fabricate complicated optical surfaces using multi-axis ultraprecision machines. Two diffractive optical designs were fabricated using an ultraprecision diamond turning machine equipped with four independent axes. Unlike the conventional clean-room-based micromachining process, this research demonstrates the development of two innovative diamond tool trajectories that allow the entire diffractive pattern to be machined in a single operation directly, without going through multiple steps, as commonly used in conventional lithography processes. The machined diffractive optical elements were measured for curve geometry and surface roughness. In addition, the optical performance was also evaluated. Finally, a simple welding test setup was utilized to test the 256-level diffractive optical elements (DOEs). Compared to conventional approaches where feature indexing is difficult and unreliable, the slow tool servo (STS) process can be utilized to produce DOEs with accurate geometry and optical surface finish; therefore, the process may be called non-clean-room or maskless micromachining. Unlike its predecessors, this micromachining process which is based on ultraprecision diamond machining can be used to produce true three-dimensional (3D) features in a single operation, thus making it a promising technology for micro-optical, electromechanical component fabrication. Moreover, the 3D micro features can be readily applied to a freeform substrate, making this process a unique approach for fabrication of complicated micro-optical devices.

A high volume precision compression molding process of glass diffractive optics by use of a micromachined fused silica wafer mold and low Tg optical glass

Recent advances in compression molding of glass optical elements for mass production offer the potential of extending this technology to elements with micro and nano scale features. In this research, glass diffractive optical elements (DOEs) with lateral features in the order of 10 µm and vertical height of 330 nm were fabricated using a fused silica glass mold and a special low Tg (glass transition temperature) glass material K-PG325. Molded DOEs were studied using an atomic force microscope (AFM) and scanning electron microscope (SEM) to evaluate the glass molding process capability. Optical testing of the molded DOEs was a further demonstration of the effectiveness of the molding process for high volume micro and diffractive optical component fabrication. The combination of two high-precision, high-volume processes, i.e., semiconductor batch process for optical mold making and glass molding for DOE replication, is an effective alternative manufacturing method for high-quality, low-cost optical components. The reported experiment is a detailed illustration of the glass molding process capability. With further process optimization a robust manufacturing process can be developed for mass production of diffractive and micro glass optical elements.

Diffractive optics as beam-shaping elements for plastics laser welding

This work reviews the use of diffractive optics for beam-shaping of high-power lasers (50–100 W) for welding and microwelding of plastics. While the use of lasers to weld plastics is well known, the use of diffractive optics to reshape lasers for welding of plastics has not been previously reported. By using inverse Fourier transformations diffractive lenses were designed and fabricated. An 80 W fiber laser with a wavelength of 1084 nm was coupled in air to the diffractive optical element (DOE) to shape the beam into predetermined patterns. These patterns were then reduced with standard optics to a desired size. Weld quality was assessed in terms of fidelity and replication of the original bitmap image that was used to design the DOE. Good results were obtained for both image fidelity and replication. In many cases the weld image retained the individual bitmap elements of the original artwork used to encode the DOE. It was also found that the overall efficiencies of the system were as high as 59% and weld times were less than 1 s. Weld joints were also determined to be relatively strong and weld circles as small as a few hundreds of µm in diameter could be formed.

Welding and Disassembly of Microwave Welded HDPE Bars

Microwave welding of polymers is performed by placing an electromagnetic absorbent material (polyaniline) at the interface. The absorbent polyaniline converts electromagnetic energy into heat which is conducted into the bulk materials forming molten layers. Pressure, which is applied after the heating stage squeezes the molten layers to form the welded joint. However, if sufficient conductive polymer is retained at the interface, then the welded samples can be placed in the microwave, reheated, and disassembly for recycling and reuse purposes can be performed. Controlling the amount of remaining conductive polymer at the joint interface is the key for achieving disassembly of a microwave welded joint. For this purpose the total displacement was used to characterize both the welding and the disassembly processes. The effect of displacement on joint strength was analyzed. It was found that if the total displacement exceeded 2.7 mm, regardless of the polyaniline concentration (30, 40, 50, 60%) and welding parameters employed, a joint strength of at least 90% the bulk strength is obtained. Disassembly of butt welded joints was then performed. It was found that ajoint with a tensile strength of approximately 60% of the bulk strength can be disassembled with a relatively low force of 27 N. However, a long reheating time of 120 seconds and a high power level of 2000 W is required for disassembly to occur. In order to increase the disassembly capability a tuned single-mode microwave system was used. Thus, while the reheating time and power level decreased to 30 seconds, and 1000 W respectively, the maximum joint strength which can be disassembled increased to 80% of the bulk strength. The maximum displacement which can be disassembled was found to be 1 mm regardless of the concentration of PANI used. After disassembly the 60% PANI samples were welded once more with the same parameters as the original welds. The rewelded samples exhibited a maximum loss of 15% in tensile strength.

Metallurgical characterisations of CMSX-4 vacuum-brazed with BNi-2 and BNi-9

High temperature brazing of nickel-based superalloys often produces joints containing hard, brittle micro-constituents that can be detrimental to mechanical properties and challenging to characterise consistently. In this study, techniques including low angle micro-sectioning, image analysis with ImageJ and electron probe micro-analysis were used to determine the composition, hardness and dispersion parameters of phases in single crystal superalloy CMSX-4, vacuum furnace brazed with BNi-2 and BNi-9 filler metals (FMs). Both FMs produced similar joints with hard centreline eutectic phases, a soft isothermally solidified zone and boron diffusion-affected zone in the CMSX-4. The volume fraction, particle size distribution and inter-particle spacing data generated will provide a framework for future metallurgical characterisations and assist in the development of microstructure–mechanical property relationships.

Thermodynamic and kinetic simulations of high temperature brazing: microstructure evolution in CMSX-4 joints

ABSTRACT In this study, thermodynamic and kinetic simulations with Thermo-Calc and DICTRA software were utilised to predict the microstructural evolution observed in brazing of high-strength nickel base single crystal superalloy, CMSX-4, with two commonly used filler metals (FMs), AWS BNi-2 (AMS 4777) and AWS BNi-9. DICTRA diffusion models of the Ni-B binary system were used to calculate base materials dissolution, the amount of centreline eutectic constituents and time required for complete isothermal solidification at various joint gaps. Thermo-Calc simulations using the CALPHAD technique predicted transformation temperatures and equilibrium phases of the joints based on the chemical compositions of the two FMs. Experimental brazing and characterisations of joint microstructure at various brazing temperatures, hold times and joint gaps were used to validate the simulation modelling results. Good correlation with both Thermo-Calc and DICTRA simulations and empirical data demonstrated the benefits of using this modelling approach for braze joint development and applications.

Numerical Simulation of Laser/IR Assisted Micro‐embossing

The use of hot embossing for fabrication of polymeric microfluidic devices is gaining a great deal of attention in recent years because it is a relatively simple and low‐cost process. Conventional microembossing is a relatively slow process that requires both the mold and the polymer substrate to be heated during embossing and cooled before de‐embossing. In order to shorten the cycle time, a laser/IR‐assisted microembossing (LIME) process was evaluated in this study. Since laser/IR heats the substrate rapidly and locally, the heating and cooling time can be substantially reduced. Experimental results have shown that both shorter cycle time and good replication accuracy can be achieved. In order to better understand this process, a commercially available FEM code DEFORM® was used for process simulation. Because the temperature distribution inside the polymer substrate is affected by the penetration of radiation energy flux from laser/IR heating, the relationship between penetration energy flux and temperat...

Fractal Analysis and Radiographic Inspection of Microwave Welded HDPE Bars

Publisher Summary Microwave welding uses microwave energy to generate heat in a conductive polymer gasket which is placed at the joint interface. The conductive polymer used throughout this work is polyaniline (PANI) doped with HCl. In order to assure structural compatibility at the interface, PANI and HDPE powder are initially mixed and a gasket is compression molded. The conductivity of the gasket placed at the interface controls the amount of heat produced. The welding parameters, which mostly affect the joint strength are heating time, power level, welding pressure, and percentage of conductive polymer in the gasket. The strength of a microwave welded joint depends on the amount of gasket remaining at the interface. As the amount of gasket remaining at the interface increases the joint strength decreases, while the disassembly capacity increases. The joint interface pattern is studied employing fractal geometry. The fractal dimension is calculated for a set of samples whose welding parameters are widely varied. The welding parameters chosen for analysis are percentage of conductive polymer (polyaniline), heating time, and power level. The box counting method is used to calculate the fractal dimension. As the fractal dimension approaches unity, maximum joint strength is obtained. Due to its electronic nature the conductive polymer is more X-ray absorbent than the surrounding HDPE. Therefore, X-ray radiography is performed on the welded joints. A pass/no pass test method can be set-up to control the joint quality depending on the relationship between the amount of squeeze out and joint strength.

Polystyrene/multi-wall carbon nanotube composite and its foam assisted by ultrasound vibration:

Polystyrene/multi-wall carbon nanotube composite with an interconnected honeycomb-like structure was prepared by firstly coating the surface of the polystyrene pellets with multi-wall carbon nanotube, and sequentially welded through an ultrasound vibration technique. The mechanical and morphological properties of as-prepared composite were investigated in various measurements. It was found that an aggregative and honeycomb-like morphology of multi-wall carbon nanotube existed in the polystyrene/multi-wall carbon nanotube composite according to the polarized optical microscopic and scanning electron microscopic results; the ultrasound vibration could benefit to the performance of flexural strength. Furthermore, different composite foams were studied in this work, employing supercritical carbon dioxide as a blowing agent. Compared to other foams prepared by the conventional methods, the compressive strength of the foams derived from as-described novel method, was significantly improved. Also, being ascribed to this interconnected structure by coating carbon nanotube on polystyrene pellets, good electrical conductivity of 0.05–0.11 S/m was achieved in the novel composite foams.

Laser Microwelding of Polystyrene and and Polycarbonate

Thermoplastics offer significant advantages in the fields of biomedical engineering, communications, and in particular applications related to Micro Electro Mechanical Systems (MEMS). For example, the low manufacturing costs of polymers may allow industry to fabricate disposable MEMS. Rapid, consistent, and inexpensive assembly or packaging is critical to the commercialization of polymer based MEMS. One method of laser welding that offers great promise of success is Through Transmission Infrared (TTIr) welding. TTIr works by passing a laser through one of the components to be joined and focusing it on the second which has an absorbing material (such as carbon black) added to it. In the following studies, the radiation from a 1 W laser diode (850 nm) was fiber coupled to a lens that focused the beam to a spot size of either 25 or 50 µm. Polycarbonate and polystyrene samples were welded by scanning the beam across the samples at rates from 8 to 60 mm/s. It was possible to generate welds below 15 µm in width. Some of the other key findings included: 1. Tensile testing of micro-welds is difficult because of problems with peeling 2. When rectangular samples were sealed (welded) the welds were hermetic and able to sustain burst pressures as high as 0.50 MPa 3. A distributed heat source model can accurately predict temperature fields in plastic laser welds 4. Distributed heat model predicts weld widths more accurately than point heat source models 5. For micro-welding of plastics, when the dimensionless distribution parameter is less than two, a point heat source model predicts similar widths to those predicted by a distributed heat source model 6. At relatively high travel speeds (>100 mm/s), the distributed model predicts a location within the plastic that experiences two peak temperatures 7. At relatively low power levels, (∼50 mW) it is possible to heat PC so that visible, temporary deformation occurs. Additional findings included the confirmation that the following observations made in traditional laser welding were also seen in micro-welding of plastics:At relatively higher heat input ablation can occur which reduces weld strength independent of weld width.Thermoplastics offer significant advantages in the fields of biomedical engineering, communications, and in particular applications related to Micro Electro Mechanical Systems (MEMS). For example, the low manufacturing costs of polymers may allow industry to fabricate disposable MEMS. Rapid, consistent, and inexpensive assembly or packaging is critical to the commercialization of polymer based MEMS. One method of laser welding that offers great promise of success is Through Transmission Infrared (TTIr) welding. TTIr works by passing a laser through one of the components to be joined and focusing it on the second which has an absorbing material (such as carbon black) added to it. In the following studies, the radiation from a 1 W laser diode (850 nm) was fiber coupled to a lens that focused the beam to a spot size of either 25 or 50 µm. Polycarbonate and polystyrene samples were welded by scanning the beam across the samples at rates from 8 to 60 mm/s. It was possible to generate welds below 15 µm in width...