Good Process Stability Research Articles

Improved Multibit Storage Reliability by Design of Ferroelectric Modulated Antiferroelectric Memory

In this article, we presented a new concept of ferroelectric (FE) modulated antiferroelectric (AFE) memory with independent two-step state switching and large polarization as a promising option for multibit storage in advanced technology nodes. Based on the Landau–Ginzburg–Devonshire (LGD) theory, four nonvolatile states of AFE with the built-in field can be obtained, and the step-by-step switching among four states was successfully simulated through pulse engineering; then, stable nonvolatile 2-bit storage was experimentally demonstrated in FE/AFE/FE capacitor device, and 0.97-MV/cm bipolar built-in field introduced by FE polarization switching was extracted. The FE + AFE device showed double-peak coercive electric field ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{c}$ </tex-math></inline-formula> ) distribution and large remanent polarization ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}_{r}$ </tex-math></inline-formula> ) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$16.9 ~\mu \text{C}$ </tex-math></inline-formula> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> with good process stability. Finally, benefitting from the independently step-by-step switching and large density of effective FE domain, the improved multibit storage reliability was verified by kinetic Monte Carlo (KMC) modeling compared to conventional multibit technology.

Rate-based model for predicting and evaluating H2S absorption in the haloalkaliphilic biological desulfurization process

The highly efficient performance of H2S absorption is the crucial indicator for haloalkaliphilic biological desulfurization (HBDS) because it immediately concerns the H2S removal efficiency and pH change of alkaline solutions. Therefore, we investigated the effect of operating parameters on the H2S absorption's performance under haloalkaline conditions. The gas–liquid ratio and packing height significantly improve H2S removal efficiency, from 80% to 90% and 66% to 99%, respectively. The absorption temperature had a trivial impact on the H2S removal efficiency, and the maximum value appeared at 45 °C. Additionally, all operating parameters caused pH changes that varied in the acceptable range (0.1 to 0.5) during the absorption process. A rate-based model was successfully developed to predict the haloalkaliphilic H2S absorption process accurately. Moreover, this model could be implemented to effectively evaluate the HBDS system's stability and provide reliable theoretical guidance for the industrial HBDS process to ensure good process stability.

Effect of mixture ratio and organic loading rate during anaerobic co-digestion of olive mill wastewater and agro-industrial wastes

Environmental pollution is a serious concern within the Mediterranean area, this situation results mainly from olive mill wastewaters (OMW), the liquid effluents generated during olive oil extraction. Anaerobic digestion of olive mill wastewaters is negatively affected by nitrogen deficiency, low pH, and the presence of phenolic compounds. This study examines the feasibility of OMW co-digestion with rich nitrogen substrates in batch and continuous mode under mesophilic conditions. Four substrates were tested at different ratios (substrate/OMW) in batch mode. Optimal ratio (substrate/OMW) was 80:20 for poultry manure (PM), 20:80 for both cheese whey (CW) and grass, and 50:50 for slaughterhouse wastewater (SWW). Furthermore, the effect of organic loading rate was assessed in continuous mode, using an anaerobic sequencing batch reactor for the mix (SWW/OMW) at 50:50. The reactor was able to degrade 10 g COD/L/day, as the maximal limit for biogas production and process stability. The results proved that co-digestion of SWW with OMW at 50:50 produced the higher biogas volume in batch mode and ensure good process stability, expressed by high alkalinity (2150 eq mg CaCo3/L) and low rate of volatile fatty acids (VFA) (150 eq mg acetic acid/L). Co-digestion of OMW with SWW is an efficient solution, to solve environmental pollution and recover renewable energy from these two organic wastes.

Production of vitex ( Vitex agnus ‐ castus L.) extract in powder form using spray‐drying: Potential for the production of functional foods

Vitex (Vitex agnus-castus L.) have bioactive compounds with potential to reduce the symptoms of menopause and premenstrual syndrome, as proved by several studies. However, such compounds may have low stability, and the spicy sensation caused by vitex fruits is a challenge for application in foods. Thus, the aim of this study was to produce microparticles by spray-drying loaded with vitex extract, and evaluate the physical and chemical properties of the powders for further application in new functional foods. The powders presented good process yield (ca. 63.4%) and retention (ca. 77.7%), volume weighted mean diameter of approximately 20.3 µm, and high stability of the bioactive compounds during the storage. Moreover, they showed good storage stability in different relative humidity, and they were classified as very low hygroscopic powders. Overall, these results are very promising and they may promote the production of a potential functional ingredient for new functional foods. Practical applications Considering the good process yield, retention and stability of the bioactive compounds during the storage, and the powder produced and characterized in the present study represents a potential functional ingredient with good technological properties. Moreover, it may be an alternative to increase the consumers’ ingestion of vitex bioactive compounds by application of the spray-dried powder in new functional foods such as chocolate and cereal bars.

False-twist draw-texturing with water-jet twister/cooler and superheated steam heater: effect of steam temperature on textured yarn properties

The objective of this research work was to investigate the effect of steam temperature on the properties of false-twist draw-textured yarns produced at speeds of 1000 m/min, 1200 m/min, and 1500 m/min using false-twist draw-texturing system with waterjet twister/cooler and superheated steam heater. This method replaces the contact heater of a standard false-twist texturing machine with a ‘super-heated steam heater’ and the normal false-twisting device and cooler replaced with a ‘water-jet twister/cooler’, combined into one unit, so as to reduce the thread-line length and to increase the production speed significantly. The new heating, twisting and cooling unit is only one meter in length. The reduced thread path has significant advantages when the surging speed is considered. The shorter thread path reduces thread instability and so higher texturing speeds can be achieved. Since the water-jet twisting is virtually friction-free, and has no mechanical moving parts, the production speed can be increased, avoiding filament breaks. Polyester POY used in this study was textured at up to 1500 m/min, significantly higher texturing speeds than the standard commercial texturing speeds, while maintaining 40% bulk levels with good process stability. Achieving texturing speed up to 1500 m/min is a significant breakthrough in the false-twist draw-texturing. Therefore, outcome of this study will have a significant impact on false-twist draw-texturing research, particularly application of water-jet twisting as a non-friction medium of false-twisting to achieve higher production speeds.

Ultra-Short Pulse HiPIMS: A Strategy to Suppress Arcing during Reactive Deposition of SiO2 Thin Films with Enhanced Mechanical and Optical Properties

In this contribution, based on the detailed understanding of the processes’ characteristics during reactive high-power impulse magnetron sputtering (HiPIMS), we demonstrated the deposition of silicon oxide (SiO2) thin films with improved optical and mechanical performances. A strategy for stabilizing the arc-free HiPIMS of Si target in the presence of oxygen was investigated. Arcing was suppressed by suitable pulse configurations, ensuring good process stability without using any feedback control system. It was found that arcing can be significantly alleviated when ultra-short HiPIMS pulses are applied on the target. The optical and mechanical properties of SiO2 coatings deposited at various pulsing configurations were analyzed. The coatings prepared by ultra-short pulse HiPIMS exhibited better optical and mechanical performance compared to the coatings prepared by long pulse HiPIMS. The optimized SiO2 coatings on quartz substrates exhibited an average transmittance of 98.5% in the 190–1100-nm wavelength range, hardness of 9.27 GPa, hardness/Young’s modulus ratio of 0.138, and critical adhesion load of 14.8 N. The optical and mechanical properties are correlated with the film morphology, which is inherently related to energetic conditions and process stability during film growth.

False-twist texturing with water-jet twister/cooler: effect of water pressure on textured yarn properties

The objective of this research work was to investigate the effect of water pressure on the properties of false-twist textured yarn produced using an innovative false-twist texturing system with waterjet twister/cooler and superheated steam heater. Commercial texturing speed of 800 m/min was selected for this paper so as to establish that this innovative method can be used for false twist texturing successfully. This method replaces the contact heater of a standard false-twist machine with a ‘super-heated steam heater’ and ‘the normal false-twisting device and cooler’ replaced with a ‘water-jet twister/cooler’ combined into one unit, so as to reduce the thread-line length and to increase the production speed significantly. The new heating, twisting and cooling unit is only one metre in length. The reduced thread path has significant advantages when the surging speed is considered. The shorter thread path reduces thread instability and so higher texturing speeds can be achieved. Since the water-jet twisting is virtually friction-free, and has no mechanical moving parts, the production speed can be increased avoiding filament breaks. Results show that this innovative method of false twist texturing can achieve high bulk levels above 40% with good process stability at 800 m/min. Water pressure has a significant positive correlation with twist level and bulk percentage and significant negative correlations with textured yarn tenacity and elongation. When the water pressure is increased, the level of twist imparted to the yarn and the bulk level increase to a maximum. Overall, the results show that the new method of false-twist texturing is capable to produce false-twist textured yarn with success.

Pulsed laser machining of high-performance engineering and biomedical alloys

The exceptional mechanical and thermal properties of high-performance engineering and biomedical alloys lead to difficulties in machining with conventional processes. This work explores nanosecond pulsed laser machining as a flexible alternative to overcome manufacturing-related limitations associated with Ni Hastelloy, Ti-6Al-4V titanium alloy and Stellite 6K. An extensive experimental campaign was performed with a 1064 nm nanosecond pulsed fibre laser, quantifying the ablation threshold, penetration depth and material removal rate as functions of average laser power (2 to 20 W), repetition rate (20 to 80 kHz), scanning velocity (100 to 2,000 mm/s) and number of laser passes (1 to 20). Optimum conditions for machining were achieved for all alloys with 20 W average power, 20 kHz repetition rate and 1,000 mm/s scanning velocity due to strong ejection of the liquid phase with high pulse fluence (71 J/cm2), good process stability and material removal rates in the range 0.08 to 0.17 mm3/s.

Enhancing the co-digestion efficiency of sewage sludge and cheese whey using brewery spent grain as an additional substrate

This study examined the influence of the application of brewery spent grain (BSG) on biogas production efficiency as well as its kinetics in the co-digestion of acid cheese whey (ACW) and sewage sludge (SS). The experiment was conducted in semi-flow anaerobic reactors under mesophilic conditions (35 °C) with different hydraulic retention times (HRT) of 16.7 d, 18 d and 20 d. The results indicate that the addition of BSG significantly enhanced the biogas yields, ensuring good process stability. The highest value of 0.54 m3 kg−1 VSadded was obtained at HRT of 16.7 d, while for ACW and SS it was only 0.50 m3 kg−1 VSadded at HRT 18 d. However, the decrease in the rate constant k occurred (0.07 h−1) as compared to the two-component system (0.096 h−1). The highest energy profit of 160% was enhanced for the three-substrate co-digestion, indicating it as a cost-effective solution.

A setup for arc-free reactive DC sputter deposition of Al-O-N

Aluminum oxynitride (Al-O-N) is a material suitable for hard, transparent thin films. Its physical properties and structure can be adjusted through the O-to-N ratio.Reactive Direct Current Magnetron Sputtering (R-DCMS) is a practical, widespread technique for the deposition of coatings. However, it proves to be challenging in the case of Al-O-N. The reason for this is the high reactivity of O2. Poisoning of Al targets by O2 causes formation of insulating oxide islands and consequently leads to target destruction and a failure of the deposition process.Here, we show that with two separate gas inlets for the two reactive gases, a good process stability can be achieved over the entire range of O-to-N ratios.

Crystallizing amino acids as bulking agents in freeze-drying

Bulking agents as mannitol (Man) and glycine (Gly) require high bulking agent to stabilizer ratios to ensure their crystallization during the freeze-drying process. The aim of this study was to investigate several amino acids (AA) as potential alternative bulking agents in low AA to sucrose (Suc) ratios. A fast freeze-drying process was performed above the collapse temperature (Tc) of the amorphous phase challenging the crystalline AA scaffold. Lyophilizates and liquid formulations were characterized by differential scanning calorimetry. Karl-Fischer titration and X-ray powder diffraction as well as macroscopic cake appearance and reconstitution times were evaluated. Stability of a monoclonal antibody was investigated by UV–Vis spectroscopy, light obscuration and size exclusion chromatography. Phenylalanine (Phe), leucine (Leu) and isoleucine (Ile) crystallized upon freeze-drying at 5/45 and 10/40 AA/Suc ratios. 2.5/47.5 AA/Suc ratio showed less pronounced crystallization. Crystallization peaks were not suppressed by 2 or 50 mg/mL antibody in Leu and Ile lyophilizates. Reconstitution times could be improved by addition of surfactant. No signs of protein aggregation were detected after freeze-drying. Man and Gly yielded inacceptable cake appearance when dried with the fast freeze-drying cycle in such low bulking agent to Suc ratios. Leu, Ile and Phe can be used as alternate bulking agents at lower bulking agent to Suc ratios compared to Man or Gly. The selected AAs provided promising cake characteristics and good protein process stability.

Determination of optimal geometrical parameters of peripheral mills to achieve good process stability

This paper focuses on optimization of the geometrical parameters of peripheral milling tools by taking into account the dynamic effect. A substructure synthesis technique is used to calculate the frequency response function of the tool point, which is adopted to determine the stability lobe diagram. Based on the Taguchi design method, simulations are first conducted for varying combinations of tool overhang length, helix angle, and teeth number. The optimal geometrical parameters of the tool are determined through an orthogonal analysis of the maximum axial depth of cut, which is obtained from the predicted stability lobe diagram. It was found that the sequence of every factor used to determine the optimal tool geometrical parameters is the tool overhang length, teeth number, and helix angle. Finally, a series of experiments were carried out as a parameter study to determine the influence of the tool overhang length, helix angle, and teeth number on the cutting stability of a mill. The same conclusion as that obtained through the simulation was observed.

Impact of fast and conservative freeze-drying on product quality of protein-mannitol-sucrose-glycerol lyophilizates

PurposeMannitol/sucrose formulations are employed to generate lyophilizates for biopharmaceuticals with an elegant cake appearance. The aim of this study was to dry protein/mannitol/sucrose formulations as fast as possible without loss of cake appearance and protein stability. Glycerol was included as potential additional protein stabilizer. Three proteins (lysozyme and two monoclonal antibodies) at low and high concentration were analyzed comparing fast with conservative freeze-drying. MethodsFreeze-drying cycle development was carried out with mannitol/sucrose formulations. A product temperature (Tp) close to the Te of mannitol and clearly above the Tg’ of sucrose was targeted. Protein formulations were exposed to the final fast lyophilisation process and to a conservative freeze-drying cycle. Lyophilizates were characterized by differential scanning calorimetry, Karl-Fischer titration and X-ray diffractometry. Additionally, macroscopic cake appearance and reconstitution times were evaluated. Protein stability was characterized by UV/Vis spectroscopy, light obscuration and size exclusion chromatography. ResultsThe fast freeze-drying cycle resulted in a primary drying time of 7 h (Tp: −10 °C) and a secondary drying time of 2 h in contrast to 47 h (Tp: −39 °C) and 12 h for the conservative cycle. Lyophilizates showed Tg values above 60 °C, a residual moisture level of 1%, reconstitution times of less than 35 s, δ-mannitol and elegant cake appearance. Mannitol/sucrose ratios below 4/1 did not lead to complete mannitol crystallization and were therefore not suitable for the selected process conditions. Characterisation of protein stability rendered low aggregation and particle levels for both, fast and conservative freeze-drying conditions. ConclusionsIt was shown that fast freeze-drying of mannitol/sucrose formulations above Tg’ at a Tp of −10 °C resulted in good protein process stability and appropriate cake characteristics at maximum time reduction.

Spray Characteristics and Tribo-Mechanical Properties of High-Velocity Arc-Sprayed WC-W2C Iron-Based Coatings

In terms of arc-sprayed coatings, the lamellar coating microstructure is mainly affected by the atomization behavior of the molten electrode tips. When using compressed air, oxide formations occur during atomization, across the particle-laden spray plume and when the molten droplets splash onto the substrate. Within the scope of this study, the potential of a high-velocity arc-spraying process due to elevated atomization gas pressures and its effect on the spray and coating characteristics was analyzed using a cast tungsten carbide (CTC)-reinforced FeCMnSi cored wire. Since the atomization behavior corresponds with the electrode phenomena, the power spectrum and the droplet formation were observed during spraying. The tribo-mechanical properties of CTC-FeCMnSi coatings were examined in dry sliding experiments and indentation tests. In addition, adhesion tests and metallographic investigations were carried out to analyze the bonding strength, cohesive behavior, and lamellar microstructure. The occurrence of oxide phases was evaluated by x-ray diffraction and electron microscopy. Moreover, the oxygen content was determined by using glow discharge optical emission spectroscopy as well as energy-dispersive x-ray spectroscopy. With respect to elevated atomization gas pressures, a dense microstructure with improved adhesion to the substrate and reduced surface roughness was observed. Dry sliding experiments revealed an advanced wear behavior of specimens, when using above average increased atomization gas pressures. Analytic methods verified the existence of oxide phases, which were generated during spraying. A significant change of the extent and type of oxides, when applying an increased flow rate of the atomization gas, cannot be observed. Besides an enhanced coating quality, the use of increased atomization gas pressure exhibited good process stability.

Functional and antioxidant properties of whey protein hydrolysate/pectin complexes in emulsions and spray-dried microcapsules

The aim of the present study was to investigate the potential of partially hydrolysed whey proteins to microencapsulate fish oil by spray-drying bilayer feed emulsions containing pectin, an oppositely charged biopolymer. Microcapsules were composed of fish oil, β-lactoglobulin (β-LG) or hydrolysates thereof produced by trypsin (DH6) and glucose syrup (DE38) as the matrix component. Pectin was attached to protein single-layer emulsions via electrostatic interactions using the layer-by-layer technique at pH 4.0. All emulsions exhibited good process stability during atomisation and drying as indicated by oil droplet size distribution and accordingly the microencapsulation efficiency was high (≥ 95.2 %) for all samples. The hydroperoxide formation in fish oil microcapsules prepared from single-layer feed emulsions was reduced in the presence of DH6 due to increased accessibility of antioxidant amino acids. The attachment of pectin to protein- or peptide-stabilised single-layer emulsions yielded bilayer microcapsules with increased stability (lower hydroperoxide content during storage). Increased thickness of the interfacial layer and the immobilisation of prooxidative ions by pectin may add to the antioxidative effect of the hydrolysate.

Reactive HiPIMS deposition of SiO2/Ta2O5 optical interference filters

In this contribution, based on the detailed understanding of the processes at the target during reactive high power impulse magnetron sputtering (HiPIMS), we demonstrate the deposition of both low- and high-index films and their implementation in optical interference filters with enhanced performance. We first investigate strategies for stabilizing the arc-free HiPIMS discharges above Si and Ta targets in the presence of oxygen. We show that hysteresis can be suppressed for these two target materials by suitable pulse-management strategies, ensuring good process stability without having to rely on any feedback control. Afterwards, we discuss the room temperature deposition of optically transparent SiO2 and Ta2O5 single layers as well as the fabrication of SiO2/Ta2O5 stacks such as 7 layer Bragg reflectors and 11 layer Fabry-Perot interference filters. We also analyze the optical and mechanical characteristics of these various coatings and compare them with their counterparts obtained by radio-frequency magnetron sputtering (RFMS). Among other findings, we observe that the coatings prepared by HiPIMS present higher refractive index and lower surface roughness values, suggesting a denser microstructure. In addition, the HiPIMS-deposited optical filters exhibit a better optical performance than their counterparts fabricated by RFMS, but it is especially with respect to the mechanical properties such as scratch resistance and low residual stress, that the coatings prepared by HiPIMS present the most dramatic improvements (up to 42% and 72% enhancement, respectively). Finally, we show that the stress values obtained for the HiPIMS-deposited SiO2 and Ta2O5 coatings are lower than for other deposition techniques commonly used in the fabrication of optical interference filters.

Production of methane by co-digestion of cassava pulp with various concentrations of pig manure

Cassava pulp is a major by-product produced in a cassava starch factory, containing 50–60% of starch (dry basis). Therefore, in this study we are considering its potential as a raw material substrate for the production of methane. To ensure sufficient amounts of nutrients for the anaerobic digestion process, the potential of co-digestion of cassava pulp (CP) with pig manure (PM) was further examined. The effect of the co-substrate mixture ratio was carried out in a semi-continuously fed stirred tank reactor (CSTR) operated under mesophilic condition (37 °C) and at a constant OLR of 3.5 kg VS m −3 d −1 and a HRT of 15 days. The results showed that co-digestion resulted in higher methane production and reduction of volatile solids (VS) but lower buffering capacity. Compared to the digestion of PM alone, the specific methane yield increased 41% higher when co-digested with CP in concentrations up to 60% of the incoming VS. This was probably due to an increase in available easily degradable carbohydrates as the CP ratio in feedstock increased. The highest methane yield and VS removal of 306 mL g −1 VS added and 61%, respectively, were achieved with good process stability (VFA:Alkalinity ratio < 0.1) when CP accounted for 60% of the feedstock VS. A further increase of CP of the feedstock led to a decrease in methane yield and solid reductions. This appeared to be caused by an extremely high C:N ratio of the feedstock resulting in a deficiency of ammonium nitrogen for microbial growth and buffering capacity.

Fast Pyrolysis of Biomass in a Fluidized Bed Reactor: In Situ Filtering of the Vapors

A system to remove in situ char/ash from hot pyrolysis vapors has been developed and tested at the University of Twente. The system consists of a continuous fluidized bed reactor (0.7 kg/h) with immersed filters (wire mesh, pore size 5 μm) for extracting pyrolysis vapors. Integration of the filter system in the fluidized bed should overcome operational problems related to the increase in pressure drop across the filter in time and a decrease in oil yield as typically observed in downstream pyrolysis vapor filtration and lead to process intensification. In this study the effect of in situ hot pyrolysis vapor filtration has been studied with respect to process stability, product yields, and product quality. Oil obtained via a more conventional cyclone system placed in parallel to the filter system served as reference for the quality and yields of the filtered oil. Good process stability concerning temperature and pressure drop across the hot gas vapor filter was achieved during a 2 h run, even when using a reused filter. Particles (char/sand) were retained inside the filter pores located at the outside surface of the filter, while the inside of the filter remained clean apart from some deposits formed on the metal wire and small 1 μm particles which slipped through the filter. Mass balance closures higher than 94 wt % were obtained. Comparable yields (cyclone + filtered oil) were obtained as in the experiments carried out with only the cyclones. The filtered oil contained significantly less solids, alkali metals, and ash compared to cyclone oil. For the alkali metals, only a considerable amount of potassium (K) was still present in filtered pyrolysis oil, which most likely entered the filtered oil via the vapor phase. There were no significant differences in the elemental composition of the oil produced via the filter line and cyclone line. The molecular weight of the filtered oil obtained with nondried feed was always marginally lower compared to the cyclone oil. Results of the aging tests show that the reactivity of pyrolysis oil can already originate from the highly reactive components in pyrolysis oil itself and does not need the presence of char/ash. To show the intrinsically high reactivity of solids-free pyrolysis oil vapors, an external filter section (1 μm pore size) was placed additionally and in series with the filter inside the fluidized bed. The results show that char is formed from the reactive pyrolysis vapors.

Welding of thin sheet of Al alloy (6082) by using Vario wire DC P-GMAW

This paper describes an investigation on the micro-structure, weld bead geometry, dilution rate and mechanical properties of the butt and overlap weld joints of 1-mm-thick 6082 aluminium alloy sheet. Weld joints were produced with the help of a variant of gas metal arc welding (GMAW) process, i.e. direct current-pulsed GMAW (DC P-GMAW), using a Vario wire. The capability of the new process has been assessed in terms of dilution, weld bead geometry, mechanical properties and porosity. The welding results with this new process showed good process stability in the welding of thin sheets of aluminium, while weld mismatch was found to increase with an increase in heat input. Weld bead geometry parameters such as weld size, throat and weld convexity increases with the increase in heat input. The dilution in case of lap joints (10–25%) was less than that of butt joints (60–80%). The increase in factor Φ (summarizing the effect of pulse parameters) increases the form factor and lowers the toe angle. Mechanical properties of the welds are poor as the tensile strength of 6082 alloy welds was around 150 MPa, and the percent elongation was about 1.3%, and it was primarily due to high porosity. Porosity (%) in weld joints was found in the range of 0.33–11.59%. The porosity is a major issue with DC P-GMAW welds.

Novel technique for laser lap welding of zinc coated sheet steels

When zinc coated steels are laser welded, zinc adjacent to the weld bead is vaporized and will cause serious weld pool disruption in lap welding unless special measures are applied such as provision of a joint gap for vapor venting. A novel alternative technique has been developed to stabilize laser lap welding: this involves addition of a small amount of aluminum to the faying surface region, so that a liquid Al–Zn alloy of high boiling point is formed, thus lowering the Zn vapor pressure. Lap welds have been made with good process stability using Nd: yttrium–aluminum–garnet and direct diode lasers, and with added Al in the form of inserted foil or previously applied cold sprayed coatings. The development is described in U.S. Patent Application No. 11/226,834. Process optimization is currently under way to define optimum aluminum addition rates that will reliably suppress defects while minimizing Al uptake into the steel weld pool.