Analysis of Discontinuous Bead Formation by PTAW Process

This research investigates the effects of input parameters on discontinuities in bead formation during material deposition by the plasma transferred arc welding (PTAW) process. Experiments based on L27 orthogonal array have been carried out by deposition of stainless steel powder (SS304 L) on stainless steel plate (SS316). Three types of depositions have been observed, namely continuous, partially continuous and discontinuous deposition. A process map has been developed, based upon powder and energy deposition per length, where the above-mentioned three types of depositions are distributed. The discontinuities in the deposition can be overcome by increasing the energy deposition per length or by reducing the powder deposition per length.     

Optimization of the Quality Characteristics of Laser-Assisted Cold-Sprayed (LACS) Aluminum Coatings with Taguchi Design of Experiments (DOE)

This study employs Taguchi design of experiments to identify optimal process parameters (deposition temperature, transverse speed, powder feed rate, and operating pressure) associated with quality characteristics (porosity and hardness) of laser-assisted cold-sprayed (LACS) pure aluminum coatings. Optimal quality characteristics of the coatings were obtained by setting deposition temperature at 450°C, transverse speed at 5 mm/s, operating pressure at 30 bar, and powder feed rate at 25 rev/min. This study helps in improving the yield and stability of pure aluminum coatings produced via LACS process while it also reduces its variability which results in high rejection, rework, and warranty costs.     

Investigating effects of resistance wire heating on AISI 1023 weldment characteristics during ASAW

In this article, effects of advanced submerged arc welding process parameters on weld bead geometry have been investigated. A novel water-cooled torch has been developed which allow a use of higher preheat current values for a continuous advanced submerged arc welding (ASAW) operation. Weld beads have been deposited on AISI 1023 steel plates by varying open circuit voltage, wire feed rate, welding speed, nozzle to plate distance, and preheat current as per central composite design. The relationships between welding parameters and weldment characteristics namely bead width, penetration, reinforcement, and dilution have been developed using multiple linear regression. The effects of individual process parameters and their interactions on response parameters were examined. Finally, single and multiobjective optimization of process parameters were performed using desirability approach and Jaya algorithm. The results reveal that a smaller bead width and lower dilution can be achieved with the developed torch by allowing the use of higher preheat current values.     

Experimental investigation on the effects of process parameters of GMAW and transient thermal analysis of AISI321 steel

Gas metal arc welding (GMAW) develops an arc by controlling the metal from the wire rod and the input process parameters. The deposited metal forms a weld bead and themechanical properties depend upon the quality of the weld bead. Proper control of the process parameters which affect the bead geometry, the microstructures of the weldments and the mechanical properties like hardness, is necessary. This experimental study aims at developing mathematical models for bead height (HB), bead width (WB) and bead penetration (PB) and investigating the effects of four process parameters
viz: welding voltage, welding speed, wire feed rate and gas flow rate on bead geometry, hardness and microstructure of AISI321 steel with 10 mm thickness. The transient thermal analysis shows temperature and residual stress distributions at different conduction and convection conditions.     

Characterization and Performance of AlTiN,AlTiCrN, TiN/TiAlN PVD Coated Carbide Tools While Turning SS 304

This study presents the physical, mechanical properties and dry turning performance of AlTiN, AlTiCrN, and TiN/TiAlN coatings produced on K-grade tungsten carbide insert by advanced physical vapor deposition technique. Scanning electron microscopy, microhardness tester, and scratch tester were used to examine surface morphology, coating thickness, microstructure, microhardness, and adhesion of coating. The performance in terms of cutting force and temperature of AlTiN, AlTiCrN, and TiN/TiAlN coated inserts was evaluated while dry turning of SS 304 steel. SS 304 is considered as “difficult-to-cut” material due to its exotic properties. The experiments were conducted at cutting speed of 140, 200, 260, and 320 m/min. Feed and depth of cut were kept constant and their values were 0.20 mm/rev and 1 mm, respectively. Experimental observations depicts that AlTiCrN coated insert demonstrated better performance because of its good adhesion and high oxidation resistance followed by TiN/TiAlN coated insert. TiN/TiAlN coated insert exhibited higher cutting temperature than AlTiCrN and AlTiN coated inserts. The findings of the study should also provide economic machining solution in case of dry turning of SS 304 stainless steel.     

Effect of Welding Parameters on Dilution and Weld Bead Geometry in Cladding

The effect of pulsed gas metal arc welding （GMAW） variables on the dilution and weld bead geometry in cladding X65 pipeline steel with 316L stainless steel was studied. Using a full factorial method, a series of experiments were carried out to know the effect of wire feed rate, welding speed, distance between gas nozzle and plate, and the vertical angle of welding on dilution and weld bead geometry. The findings indicate that the dilution of weld metal and its dimension i.e. width, height and depth increase with the feed rate, but the contact angle of the bead decreases first and then increases. Meantime, welding speed has an opposite effect except for dilution. There is an interaction effect between welding parameters at the contact angle. The results also show forehand welding or decreasing electrode extension decrease the angle of contact. Finally, a mathematical model is contrived to highlight the relationship between welding variables with dilution and weld bead geometry.     

Powder Deposition in Three Parallel-Oriented Dies of Different Shapes

Uniformity of bulk density distribution during the die filling process is required to minimize quality problems, such as distortion and cracking, for powder compacts. Understanding the die filling process is necessary in ensuring a uniform powder deposition. The second-generation pressure deposition tester (PDT-II) was used to investigate the deposition process and final pressure distribution of powder filling in toroidal, cylindrical, and E-shaped dies. All tests were conducted using a spray-dried free-flowing granular powder. The results indicated that for toroidal dies: (1) the area around 0° orientation (the leeward end) had the highest pressure values (1186.7 to 2498.0 Pa), with the average pressure values of the remaining area 353.7–648.0 Pa; (2) the pressure distribution was symmetrical about the centerline parallel to the feed shoe movement direction; (3) the highest feed shoe speed (500 mm/s) led to the most nonuniform pressure distribution among the three speeds; (4) higher feed shoe speed did not always result in higher final pressure values; and (5) the right die tended to have higher final pressure values (215.0 to 2498.0 Pa) than the center die (95.4 to 2052.5 Pa). For E-shaped dies: (1) the final pressure values of the middle leg (308.9 to 760.7 Pa) were higher than those of the left and the right legs (148.9 to 530.3 Pa); (2) the area along the backside had the highest final pressure value (1054.6 to 1303.8 Pa); (3) the pressure distribution was symmetrical about the centerline parallel to the feed shoe movement direction; and (4) neither the center die nor the right die always had higher pressure values than the other one at all locations. Comparison between cylindrical and toroidal dies indicated that: (1) neither of the two die shapes (cylinder and toroid) led to consistently higher or lower final pressure values at all locations and (2) for all three feed shoe speeds, the toroidal die had higher average final pressure values in the 0° orientation.     

不同工艺参数对高硬度铁粉等离子弧增材熔覆的影响

目的优化马氏体不锈钢等离子弧增材熔覆工艺。方法利用等离子热源在300M表面对新型高硬度铁粉的增材熔覆工艺进行研究。基于三因素三水平熔覆工艺的正交试验,研究在大温度梯度熔覆环境下,等离子弧电流、焊枪移动速度及送粉速率对单道金属熔池的非平衡凝固组织的影响机制,综合考虑单道焊道宏观形貌、成形尺寸及稀释率,确定增材熔敷的电流、焊枪移动速度及送粉速率;在此基础上,基于多道单层及单道多层熔覆的宏观形貌及拉伸性能,确定多道多层增材熔覆的搭接率及熔覆工艺。结果在电流为140～180 A、移动速度为20～30 cm/min和送粉速率为20～30 r/min的工艺窗口内,电流对焊道的稀释率有较大影响,送粉速率次之;送粉速率对高宽比的影响最大,扫描速度次之。结论当电流大小为140 A,送粉速率为30 r/min,扫描速率为30 cm/min时,单道单层焊道的稀释率及宽高比最小,热影响区晶粒尺寸较小,叠加率为40%时,熔覆层表面平整度较高。     

Uniformity Differentiation Analysis of Powder Deposition Characteristics in Circular and Rectangular Shallow Dies Using Feed Shoe with Square Cross-Section

The inhomogeneity of the pressure distribution after completion of the filling process might create tablet and compact quality issues. Generating a uniform precompaction powder deposition into a die would minimize one source of tablet quality issues. This article determines the characteristics of the deposition process into a rectangular die and a circular shallow die, using a feed shoe with a square cross-section tube. A series of experiments were performed that determined the cumulative influence of particle size, die geometry, and feed shoe speed on uniformity of pressure distribution at the end of filling process. For uniformity comparison, the profiles of pressure distribution at the end of filling process were displayed as contour plots. Symmetry analysis, variance metrics, and uniformity analysis were implemented to quantify the deposition characteristics. Feed shoe speeds of 20 and 100 mm/s were used to fill the die. Due to their differing particle characteristics and importance, a pharmaceutical powder filler (microcrystalline cellulose-Avicel PH102) and a battery powder mixture (BPM) were used as test materials. The results showed that (1) contour plot was the most reliable method for evaluating uniformity deposition characteristics in dies; (2) based on contour plot analysis, BPM deposition at 100 mm/s feed shoe speed for circular shallow dies resulted in the most uniform pressure distribution among all, that is, 64% uniformity at ±20 dm (decimeter) resolution and 14.7% coefficient of variation (COV); (3) Avicel deposition at 20 mm/s feed shoe speed for circular dies had the least uniformity (46%); (4) rectangular dies generally had lower symmetry index (61%) in comparison with circular dies, which was attributed to sharp edges of rectangular die, that is, particles trapped in corners generated higher stresses inside the rectangular die versus circular die.     

The coalescence of combustion-sprayed ethylene–methacrylic acid copolymer

A design of experiments approach was employed to study the coalescence of combustion-sprayed ethylene-methacrylic acid copolymer (EMAA). The powder feed rate, stand-off distance, substrate temperature, propane flow rate, and compressed air flow rate were studied by using a 2^5-1 factorial design matrix. Empirical models were developed to predict coating surface roughness, coating temperature and splat elongation ratio. Such methods allow process optimization, estimation of interactions among parameters, and the determination of the factors which influence the coalescence of ethylene-methacrylic acid copolymer coatings. This revised version was published online in November 2006 with corrections to the Cover Date.     

Influence of Particle Size and Heating Rate on Decomposition of BC Dry Chemical Fire Extinguishing Powders

Pyrolysis of BC dry chemical fire extinguishing powders which are useful for Class “B” and Class “C” fires was conducted on a thermogravimetric analyzer with sample loading of 10–25 mg under dynamic air atmosphere. The effect of particle sizes (medium value 48.99, 27.24, 4.93 µm) and heating rates (10, 15, and 20°C min^?1) were examined. The pyrolysis kinetics of the samples was analyzed using a distribution activation energy model. It was found that the decomposition temperature decreased and the pyrolysis rate increased after the samples were milled. The agglomeration of particles during production did not have an appreciable influence on the pyrolysis process of the samples in our experimental conditions. The activation energy value was 77.13?219.78 kJ · mol^?1, 58.18?288.67 kJ · mol^?1, and 44.59?209.17 kJ · mol^?1 for the powder of particle size 48.99, 27.24, 4.93 µm. We should use micro powder in fire extinguishing.     

Application of integrated Taguchi and TOPSIS method for optimization of process parameters for dimensional accuracy in turning of EN25 steel

Abstract

The turning process is one of the fundamental machining operations wherein optimization of parameters leads to better machining performance. This study has applied integrated Taguchi and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) methods to determine the optimum process parameters in turning operation of EN25 steel using coated carbide tools. The process parameters considered are cutting speed, feed rate, and depth of cut. The objective is to minimize circularity and cylindricity simultaneously. An orthogonal array, Signal to Noise (S/N) ratio, and TOPSIS are employed to analyze the effects of input parameters on the output parameters. In this study, a decision matrix is formed using S/N ratios; then the TOPSIS method is used to transmogrify a multi-criteria optimization problem into a single-criterion problem. The result revealed that the proposed method is appropriate for solving multi-criteria optimization of process parameters. Results also showed that cutting speed of 215 m/min, feed rate of 0.07 mm/rev, and depth of cut of 1.5 mm are the optimum combination of process parameters.     

The influence of nozzle geometry on powder flow behaviors in directed energy deposition additive manufacturing

To show the relationship between the nozzles and the powder flows, computational fluid dynamics and discrete element methods were used to simulate the interactions between the powder particles and the gas flows. Experiment was carried out for the validations. Then, laser irradiation rate (LIR) and powder aggregation degree (PAD) were defined to evaluate the influences of the nozzle geometries on the powder flow behaviors in DED. Results indicate that the divergence angle of the powder stream can be obviously affected by the changes of nozzles. The divergence angle can be increased from 15° with three-jet nozzle to 17° with four-jet nozzle. But at the same work conditions, the divergence angle with annular nozzles is only 8°. The powder mass concentration (PMC), LIR and PAD can be further used for the determination of the stand-off distance in DED. The determined stand-off distance of the annular coaxial nozzle is larger than the three-jet and four-jet nozzles. The PMC is increased by 66.7% in DED with annular coaxial nozzle in comparison with the three-jet and four-jet nozzles. The defined parameters of PMC, LIR and PAD can be used for the systematic determination of stand-off distance for better controlling of DED.     

Uniformity Differentiation Analysis. Part 1: Powder Deposition Characteristics in Rectangular Shallow Die Using Feed Shoe with Circular Cross Section

The process of die filling is a significant unit operation in many industries. Inhomogeneity of distribution such as in mass, bulk density, and pressure might cause many tablet and compact quality issues, such as lamination, capping, and distortion. No systematic investigations have been done to evaluate pressure distribution characteristics in dies with small aspect ratios (ratio of fill height to characteristic cross section dimension <0.5). In order to evaluate pressure distribution during filling of shallow dies, a circular cross section feed shoe was used at two speeds. The deposition characteristics of two powders with differing particle characteristics were studied in this research. The second-generation pressure deposition tester (PDT-II) was used to measure the two powders' pressure distribution characteristics. A battery powder mixture (BPM) and microcrystalline cellulose (Avicel PH102) were used to fill a rectangular shallow die 32 × 30 mm in dimension and 6.5 mm deep. Feed shoe speeds of 20 and 100 mm/s were used to fill the die. Symmetry analysis, variance metrics, Gini coefficient, and uniformity analysis were used to quantify the deposition characteristics. The results showed that (1) the contour plot was the most reliable method for measuring powder deposition characteristics; (2) the leeward and forward pressure distrbution comparisons generated a larger symmetry index than the front and back pressure distribution; (3) based on contour plot analysis, BPM at 100 mm/s feed shoe speed resulted in the most uniform pressure distribution (64% uniformity at +/?20 dm (decimeter) resolution) among all; (4) feed shoe speed greatly influenced pressure distribution uniformity inside the die; and (5) the high stress zone was mostly observed in forward and back regions inside the die.     

Fe90合金激光熔覆工艺优化及性能研究

针对以18Cr2Ni4WA渗碳钢为材质的车辆典型零件磨损面激光再制造问题,采用Fe90合金粉末进行了失效零件的激光熔覆再制造工艺研究;以熔覆层为分析对象,通过SN比和方差分析获得影响熔覆层稀释率的显著因素为激光功率和送粉量,并给出了工艺参数与稀释率关系的定量袁征关系范围,综合组织、相组成分析了熔覆层具有较高硬度的原因....     

Uniformity of Powder Die Filling Using a Feed Shoe: A Review

The process of die filling for achieving a uniform fill is a critical unit operation that is far from being sufficiently understood. Factors influencing powder flow from a feed shoe and powder deposition into a die are reviewed in this article. The factors include feed shoe speed, feed shoe holding time over the die, particle shape and size, powder size distribution, die shape and size, die configuration, filling intensity, filling direction, and the height of powder in the feed shoe. Devices suitable for evaluating the quality of powder deposition in dies need to be more: (1) specific to simulate the filling process, (2) versatile to encompass different filling parameters, and (3) able to provide quantitative evaluation. Recommendations to improve die deposition and density uniformity are given with respect to powder characteristics and die and feed shoe properties. New devices using load cells, pressure sensors, or tactile sensors to investigate powder deposition are important for further the investigation of the deposition process and spatial density uniformity. These primary measurement devices have the potential to bridge the knowledge gap and enable the development of discrete and/or continuum-concept computational models for the dynamic die-fill process.     

Uniformity of Powder Die Filling Using a Feed Shoe: A Review

The process of die filling for achieving a uniform fill is a critical unit operation that is far from being sufficiently understood. Factors influencing powder flow from a feed shoe and powder deposition into a die are reviewed in this article. The factors include feed shoe speed, feed shoe holding time over the die, particle shape and size, powder size distribution, die shape and size, die configuration, filling intensity, filling direction, and the height of powder in the feed shoe. Devices suitable for evaluating the quality of powder deposition in dies need to be more: (1) specific to simulate the filling process, (2) versatile to encompass different filling parameters, and (3) able to provide quantitative evaluation. Recommendations to improve die deposition and density uniformity are given with respect to powder characteristics and die and feed shoe properties. New devices using load cells, pressure sensors, or tactile sensors to investigate powder deposition are important for further the investigation of the deposition process and spatial density uniformity. These primary measurement devices have the potential to bridge the knowledge gap and enable the development of discrete and/or continuum-concept computational models for the dynamic die-fill process.     

High-Speed Incremental Forming Process: A Trade-Off Between Formability and Time Efficiency

Making use of “optimal experimental design,” the paper attempts to investigate individual and interactive effects of predictor parameters, namely tool size, pitch size, feed rate, spindle rotational speed, and blank thickness, on sheet formability in single point incremental forming (SPIF) process. For the sake of precision, a novel sensor system was developed and employed to detect crack as it initiates on SPIF test specimens. A novel benchmark for formability in SPIF was established by addressing normal strain along sheet thickness, maximum attainable forming angle, and the rate of variation in forming angle. The process was finally optimized in terms of maximum achievable formability and minimum processing time. Accordingly, high-speed forming (with forming speed of at least 5000 mm/min) was realized to be perfectly viable, whereas the sheet formability remains quite satisfactory (over 90% of the maximum value). The key role of high spindle speed (up to 3000 rpm) was also highlighted in this regard.     

TC4零件激光快速修复加工参数带的选择

通过研究激光加工参数,包括激光功率、光束扫描速度以及送粉率对热输入效率η和熔覆层形状系数ζ的影响规律,并结合激光快速修复过程对热输入效率和熔覆层形状系数的要求,建立了TC4激光快速修复的加工参数带。采用文章所确定的加工参数带中的参数,有利于减小激光快速修复件的变形,得到的修复件无熔合不良缺陷。     

Gas phase deposition of aluminum on nickel alloys

A gas phase aluminum deposition process was developed for nickel base alloys. The substrate to be coated is out of contact with a powder mixture which generates the gaseous transport agent. Gas diffusion was shown to be the factor controlling the aluminum deposition rate in the process for both internal and external surfaces. The aluminum deposition rate increased with decreasing partial pressure of the transporting agent. Complex aluminum halides of an alkali or alkaline earth metal were demonstrated to have sufficient “throwing power” to deposit aluminum uniformly on internal surfaces.