Strong Weld Research Articles

Effect of gate dimension on micro injection molded weld line strength with polypropylene (PP) and high-density polyethylene (HDPE)

As a defect of micro injection molding parts, weld line is unfavorable since it will influence the surface quality and mechanical properties of micro parts. Therefore, the investigation on the developing process of weld line would be a significant issue for improving the quality of micro injection molded parts. In this study, one injection mold with four micro tensile sample cavities was designed and constructed. Every cavity responses to various gate dimensions, which is marked as Gate \( {\text{Nr}}.1\left( {1.5 \times 0.1 \times 0.{\text{5mm}},{\text{width}} \times {\text{depth}} \times {\text{length}}} \right) \), \( {\text{Nr}}.2\left( {1.0 \times 0.1 \times 0.{\text{5mm}},{\text{width}} \times {\text{depth}} \times {\text{length}}} \right) \), \( {\text{Nr}}.3\left( {1.0 \times 0.05 \times 0.{\text{5mm}},{\text{width}} \times {\text{depth}} \times {\text{length}}} \right) \), and \( {\text{Nr}}.4\left( {0.5 \times 0.1 \times 0.{\text{5mm}},{\text{width}} \times {\text{depth}} \times {\text{length}}} \right) \). The effects of gate dimension of the mold on mechanical properties of weld line have been studied by experiments in different processing parameters. The tensile test was used to characterize the micro injection molded weld line strength. The results for polypropylene show that with the changing of injection pressure and mold temperature, Gate Nr.3 is corresponding to the strongest weld strength; the next is Gate Nr.2; Gates Nr.4 and Nr.1 are in the end. The difference between them is not obvious. For high-density polyethylene, Gate Nr.1 is not able to be completely filled, which is due to the blocking of stick materials and dirt based on the simulation analysis. The investigation was only carried out for the other three gate sizes; results present that Gate Nr.3 always gives the best weld line strength whatever the processing parameters are, Gate Nr.4 is next and then Gate Nr.2. There are always middle optimal values for processing parameters leading to strongest weld line strength, when injection pressure is 80 MPa, injection speed is 90 cm3/s, melt temperature is 200°C, and mold temperature is 130°C. Higher and lower processing parameters result in reduced weld line strength.

Joining of titanium to 304L stainless steel by friction welding

The dissimilar metal joint of titanium (Ti) to 304L stainless steel (SS) is essential in the nuclear industry for the dissolution of spent fuel that is carried out in boiling nitric acid in the dissolver vessel (made of Ti) and the dissolved solution is transported through the 304L SS pipes to the other plant components made of 304L SS. Because of the radioactive environment, leak tightness and corrosion resistance of this dissimilar joint are important. In this work, friction welding process was attempted to join Ti to 304L SS. Direct friction welding of Ti to 304L SS results in a stronger weld in which failure occurs in the Ti base metal during tensile testing. However, the joints have almost zero bend ductility that has been attributed to the formation of intermetallics due to mechanical alloying, strain hardening of Ti near the joint interface and residual stresses. Post-weld heat treatment marginally increases the bend ductility to 5° because of relieving of the effects of strain hardening and of residual stresses at the joint interface. Corrosion test in boiling nitric acid as per ASTM A-262 Practice C shows that the average corrosion rate is 10 mpy with the joints remaining intact after the corrosion test. The details of mechanical tests, microstructure analysis using optical and scanning electron microscopy, are discussed.

Effect of micro tensile sample’s cross section shape on the strength of weld line in micro injection molding process

As a suitable mass and cost efficiency fabrication method, micro injection molding is doing a very good performance in micro plastic parts production. The mold design is an important part affecting micro parts properties. In this study, a micro injection mold with multi cavities of micro tensile bar is used. These micro cavities are fabricated by a micro milling process in different cross section shapes (semicircle R = 0.5 mm, equilateral triangle D = 0.3 mm, and trapezoid D = 0.336 mm t = 0.2 mm bottom angle = 95°). With an Arburg® 320C injection molding machine, micro tensile test sample are prepared in different processing parameters so that a correlation between the cross section shapes with micro weld line strength in different conditions could be investigated by tensile test. Final results show that when the cross section shape is different, their corresponding weld line strength is also different. Equilateral triangle cross section is leading to strongest weld line, and then followed by trapezoid, semi-circle is the last. By analysis of these tensile test results, the quantitative factor a is defined as the ratio of perimeter to area of cross section shape, and higher a value is corresponding stronger weld line. After weld line strength comparison in different processing conditions, the results show that higher injection pressure induced to lower weld line strength whatever the cross section shape is. By higher mold and melt temperature, equilateral triangle cross section gives improved weld line strength. But mold and melt temperature affect weld line strength negative for other cross section shapes.

Effect of laser welding parameters on fusion zone morphological, mechanical and microstructural characteristics of AISI 304 stainless steel

AbstractNowadays, the Nd:YAG laser has been a promising key tool for joining thin components. In this research, mechanical and microstructural properties of laser welded thin austenitic stainless steel sheets were investigated with experimental investigations, as a function of laser welding parameters. Butt welded joints were made using a Nd:YAG laser in the pulsed wave mode. The appropriate laser welding parameters were found in order to obtain quality and strong weld seam. The pulsed laser seam welding process is controlled by a variety of parameters. We focus on the effects of the several processing parameters on mechanical and microstructural characteristics of joint and weld quality. The aim of this research was to evaluate the influence of these processing parameters on joint strength and microstructure. And also we examined the weldability of stainless steels in butt joint configuration by a pulsed Nd:YAG laser beam.

Spatially resolved ultrasonic attenuation in resistance spot welds: Implications for nondestructive testing

Spatial variation of ultrasonic attenuation and velocity has been measured in plane parallel specimens extracted from resistance spot welds. In a strong weld, attenuation is larger in the nugget than in the parent material, and the region of increased attenuation is surrounded by a ring of decreased attenuation. In the center of a stick weld, attenuation is even larger than in a strong weld, and the low-attenuation ring is absent. These spatial variations are interpreted in terms of differences in grain size and martensite formation. Measured frequency dependences indicate the presence of an additional attenuation mechanism besides grain scattering. The observed attenuations do not vary as commonly presumed with weld quality, suggesting that the common practice of using ultrasonic attenuation to indicate weld quality is not a reliable methodology.

Three-dimensional reconstruction of specular surface for a gas tungsten arc weld pool

Observing the weld pool and measuring its geometrical parameters are key issues for developing the next generation intelligent welding machine and modeling the complex welding process. In the past few years, different techniques have been applied, but the dynamic specular weld pool surface and the strong weld arc complicate these approaches and make observation difficult. To resolve the problem, a new three-dimensional sensing system using structured light is proposed for a gas tungsten arc welding (GTAW) process. In the system, a dot-matrix laser pattern is projected on the specular weld pool surface, which can reflect light onto an imaging plane. The reflected images are captured by a high-speed camera and can successfully be processed by image processing algorithms developed. With the acquired information, a three-dimensional reconstruction scheme is proposed and discussed in this paper. A surface reconstruction method with several slope-based algorithms is first developed to rebuild the region of weld pool surface which reflects the laser pattern. Then a two-dimensional piecewise model is provided to calculate weld pool boundary by utilizing the edge condition. Finally the optimal estimate of the three-dimensional weld pool surface is synthesized. The acceptable accuracy of the results verified the effectiveness of the reconstruction scheme.

Fatigue crack growth towards the weld interface of alloy and maraging steels

A methodology to model the weld between the constituent bodies of a bimetallic configuration is presented for estimating the effect of strength gradient across the weld interface on crack growth characteristics under fatigue load. The constituent bodies and the interface weld have similar elastic and thermal expansion properties but different plastic properties. A Mode I crack is in parent soft alloy steel (ASTM 4340) which grows perpendicularly towards the ultra strong weld of maraging steel (MDN 250). A cyclic plastic or cohesive zone develops ahead of the crack tip under fatigue load. This zone penetrates into the weld, possibly crossing over into maraging steel, as the crack grows nearer to the weld which causes the drop in stress intensity parameter at the crack tip from the applied value. The cohesive zone split across the weld interface is modeled in linear elastic regime with the help of Kolosov–Muskhelishvili complex potentials leading to a computational model for assessing the effect of the weld on the advancing crack. Paris law based on cyclic crack tip stress intensity parameter is used to estimate the crack growth rate. Theoretical assessment is substantiated with the help of experiments. Bimetallic compact tension specimens, prepared by electron beam welding of the steels, are subjected to high cycle fatigue load to measure crack growth rates in them. Results of the bimetallic specimens are analyzed and compared with those of the plain alloy steel specimen. Influence of ultra high strength weld substantially reduces the growth rate of the approaching crack resulting in enhanced fatigue life of the bimetallic body. Experimental results are in good agreement with theoretical estimations.

Photochemical welding of silica optical components to silicone rubber by F2 laser

Photochemical welding of fused silica glass to silicone rubber has been demonstrated by 157-nm F2 laser-induced photochemical modification of the silicone surface in contact with the glass. Fused-silica coverslips (150 m thick), silica optical fibres (125 µm diameter), and 2.9- µm diameter microspheres were successfully welded onto 2-mm-thick silicone rubber by irradiating the silicone surface through the partially transparent glasses. Sufficient photochemical conversion for strong welding was provided by multiple exposures of tens to thousands of pulses in a narrow optimized fluence window near ∼6-mJ/cm2 per pulse.

The Effect of Anvil Geometry and Welding Energy on Microstructures in Ultrasonic Spot Welds of AA6111-T4

The formation of ultrasonic spot welds of AA6111-T4 has been investigated using a single-transducer unidirectional wedge-reed welder. The evolution of weld microstructures and weld strength due to anvil cap geometry and welding energy was studied. The variations in lap-shear failure load and weld microstructures as a function of welding energy were only slightly influenced by the changes in the anvil cap geometry. Weld failure in lap-shear tensile tests occurs by interface fracture for low energy welds and by button formation for high energy welds. Initially, microwelds or weld islands several microns in diameter are generated presumably at asperities of the two pieces being joined. As the welding energy increases, the weld interface can change from a planar to a wavy morphology and the weld strength increases. Deformation wakes and bifurcation are ubiquitous in strong welds. Microporosity is observed at the periphery of growing weld islands and along the flow lines associated with the wavy deformation microstructures. Grain growth occurs inside the weld zone after isothermal annealing. However, the porous microstructure at the weld interface is not affected by isothermal annealing. Ultrasonic spot welding of AA6111-T4 aluminum was found to be insensitive to variations in anvil cap size and the knurl patterns investigated in this research.

Improving the technology used to make welded carbon-steel tubes

Electric-welded tubes made of carbon steels are less expensive, have a better-quality surface, and have more accurate dimensions than equivalent seamless tubes. An efficient method has been proposed for making the distribution of the strains and residual stresses in such tubes more uniform about their perimeter (and reducing the stress level in general). The method employs cold reduction in the final passes of the forming mill, which has a closed pass. Similar reductions are also made in the welding and guide stands. The authors constructed a model to control the voltage on the induction coil, and they determined the dependence of temperature in the welding zone on the length of the edges in the welding gap. The introduction of new tube-production methods and equipment developed as part of this research has made it possible to master the industrial production of new types of special-use tubes, tubes with fewer or no internal burrs, and tubes with stronger welds, better mechanical characteristics, and other improved quality indices.

Influence of carbon, manganese and nickel on microstructure and properties of strong steel weld metals: Part 2 – Impact toughness gain resulting from manganese reductions

Two experimental high strength steel weld metals were produced with 7 wt-% nickel and either 2 or 0·5 wt-% manganese. Neural network predictions that it is advantageous to reduce the manganese concentration in high nickel alloys have been confirmed, with impact energy increasing from 32 to 113 J at −40°C. High resolution microstructural investigations showed that both weld metals contained mainly martensite at interdendritic regions and predominantly bainite at dendrite core regions, as a consequence of manganese and nickel segregation. In the high manganese weld metal significant amounts of coarse grained coalesced bainite formed whereas mainly upper bainite was seen with 0·5 wt-% manganese. Reducing manganese content increased the transformation temperature, promoting fine upper bainite at the expense of coarse coalesced bainite. Increased toughness was attributed to the finer grain size of bainite constituents and a more effectively tempered microstructure.

Influence of carbon, manganese and nickel on microstructure and properties of strong steel weld metals: Part 1 – Effect of nickel content

The effects of increasing the nickel content from 3 to 7 or 9 wt-% were investigated in high strength steel weld metals with 2 wt-% manganese. Nickel additions were beneficial to strength but detrimental to impact toughness. Significant segregation of nickel and manganese to interdendritic regions was observed at the two higher nickel contents. In these weld metals a mainly martensitic microstructure developed at interdendritic regions, whereas bainite was found at dendrite core regions. The microstructural inhomogeneity was due to segregation and the accompanying stabilisation of austenite in solute enriched regions to lower transformation temperatures. With 3 wt-% nickel the microstructure was found to be more homogeneous, with mainly bainite forming. The decrease in impact toughness with increasing nickel content was mainly attributed to the formation of coarse grained coalesced bainite.

Influence of carbon, manganese and nickel on microstructure and properties of strong steel weld metals: Part 3 – Increased strength resulting from carbon additions

Neural network predictions suggested that the strength of a high strength steel weld metal with 7 wt-% nickel and 0·5 wt-% manganese could be increased significantly at moderate expense to impact toughness by additions of carbon. Based on this, three experimental weld metals were produced with carbon contents between 0·03 and 0·11 wt-%. Mechanical test results were in agreement with predictions. At low carbon content the microstructure was largely bainitic in dendrite core regions whereas martensite was found at interdendritic regions. From microstructural studies and dilatometry experiments it was found that carbon stabilised austenite to lower transformation temperatures and that the microstructure became more martensitic in nature. Effects on strength and impact toughness were explainable in terms of a refinement of the microstructure and tempering behaviour.

Effects of Geometry on the Tensile Strength of Extrusion Blow Molding Pinch-Off Welds

The pinch-off weld is formed when the mold closes on the parison. A strong weld is dependant on the correctly designed pinch-off geometry of the mold. A pinch-off design relies mostly on past experience and trial and error. There are few equations available to properly design the pinch-off. Material suppliers have provided some guidelines on pinch-off geometry for their materials. The experiments performed in this study show the effect of pinch-off geometry on the tensile load of the weld in extrusion blow molding parts. When the mold closes on the parison and it is squeezed, the geometry affects how the material flows in the pinch-off region. Previous research on pinch-off load was done without an accurate measurement of the parison thickness. The geometry tested was the land length, first angle, second angle, distance to second angle, and flash pocket. The tensile load of the weld was examined in these experiments by the use of design of experiments.

Object oriented and distributed software applied to industrial robotic welding

Associating robot manipulators with industrial welding operations is common and maybe one of the most successful applications of industrial robots. Nevertheless, it is far from being a solved technological process, mainly because the welding process is not fully understood but also because robots are still at an early satge of development, being difficult to use and program by regular operators. This is also true for Human Machine Interfaces (HMI), which are not intuitive to use and are therefore unsatisfactory. In this paper we discuss these problems and present a system designed with the double objective of serving our R&D efforts on welding applications, but also our need to assist industrial partners working with welding setups. Frequently industrial partners are not happy with available commercial systems, requiring tailored solutions that could be adapted to several robots and robot controllers. The developed system is explained in some detail, and demonstrated using two test cases which reproduce two situations very common in industry: multi‐layer butt welding (used on big structures requiring very strong welds) and multi‐point fillet welding (used for example on structural pieces for the construction industry).

A new scheme of terrestrial paleoclimate evolution during the last 1.5 Ma in the western Black sea region: integration of soil studies and loess magmatism

A refined pedostratigraphic scheme in the western Black sea region is proposed on the basis of paleopedological reconstructions coupled with magnetic susceptibility, and other rock magnetic parameters, and Mössbauer spectroscopy. The new scheme matches well with oxygen isotope stages despite local variations in erosion/deposition, strong welding of paleosols and subtle discrepancies in the position of the Matuyama/Brunhes boundary. These limitations are reduced by optimizing resolution of magnetic cycles and paleosol identification. Two humid/warm maxima during the Quaternary are found in pedocomplex PK4 at about 0.5 Ma (corresponding to oxygen isotope stages 13 and 15), and in pedocomplex PK8 related to the Jaramillo subchron. Comparison with the oxygen isotope curve shows that the apparent major driving force of regional soil/loess cyclicity is the 100 ka eccentricity period.

Temperature controlled CO(2) laser welding of soft tissues: urinary bladder welding in different animal models (rats, rabbits, and cats).

Laser welding of tissues is a method of closure of surgical incisions that, in principle, may have advantages over conventional closure methods. It is a noncontact technique that introduces no foreign body, the closure is continuous and watertight, and the procedure is faster and requires less skill to master. However, in practice, there have been difficulties in obtaining strong and reliable welding. We assumed that the quality of the weld depends on the ability to monitor and control the surface temperature of the welded zone during the procedure. Our objective was to develop a "smart" fiberoptic laser system for controlled temperature welding. We have developed a welding system based on a CO(2) laser and on infrared transmitting AgClBr fibers. This fiberoptic system plays a double role: transmitting laser power for tissue heating and noncontact (radiometric) temperature monitoring and control. The "true" temperature of the heated tissue was determined by using an improved calibration method. We carried out long-studies of CO(2) laser welding of urinary bladders in various animal models. Cystotomies were performed on the animals, and complete closure of the bladder was obtained with a surface temperature of 55 +/- 5 degrees C at the welding site. In early experiments on 31 rats, the success rate was 73%. In later experiments with 10 rabbits and 3 cats, there was an 80% and a 100% success rate, respectively. The success rate in these preliminary experiments and the quality of the weld, as determined histologically, demonstrate that temperature controlled CO(2) laser welding can produce effective welding of tissues. The fiberoptic system can be adapted for endoscopic laser welding.

Effects of shallow basaltic intrusion into pyroclastic deposits, Grants Ridge, New Mexico, USA

A localized aureole up to 10 m wide developed around a 150-m-wide, 2.6 Ma basaltic plug at Grants Ridge, New Mexico. The plug intruded into nonwelded, pumice-rich compositionally homogenous tuff and volcaniclastic sediments of similar age (3.3 Ma). Color variation (pinkish to orange), strong local contact welding, brecciation, partial melting, and stoping characterize the host rock within the contact zone. Despite the high-temperature basaltic intrusion, there is no indication of extensive fluid-driven convective heat transfer and pervasive hydrothermal circulation and alteration of the country rock. The proportion of volcanic glass, loss on ignition (LOI), fluorine, iron, and some trace and rare earth element contents in the host rocks are somewhat depleted at the contact of the intrusion. Conversely, the degree of devitrification and the potassium content are higher along the contact. Vapor-phase expulsion of elemental species as complexes of fluoride, chloride, hydroxide, sulfide, and carbon dioxide may have been responsible for the minor depletion of the elements during the devitrification of silicic glass at near-solidus temperature related to the basaltic intrusion. The results of finite-difference numerical modeling of the intrusion as a dry, conduction-dominated system agree well with geochemical and mineralogical data. Contact welding of the host rocks apparently occurred at temperatures >700°C under a density-driven lateral load of approximately 1 MPa, corresponding to the observed depth below the former ground surface of ∼100 m. Other physical changes in the first 10 m of host rock, represented by partial devitrification and color changes, apparently occurred at temperatures of 500–600°C, which probably persisted for up to 55 years after the emplacement of the basaltic plug. Devitrification is generally enhanced by the presence of aqueous fluids; however, the abundance of volcanic glass within a short distance (∼10 m) from the plug is consistent with our inference that the plug intruded into a dry (unsaturated) environment.

Dye-Assisted Laser Skin Closure with Pulsed Radiation: An In Vitro Study of Weld Strength and Thermal Damage

Previous laser skin welding studies have used continuous wave delivery of radiation. However, heat diffusion during irradiation prevents strong welds from being achieved without creating large zones of thermal damage. Previously published results indicate that a thermal damage zone in skin greater than 200 μm may prevent normal wound healing. We propose that both strong welds and minimal thermal damage can be achieved by introducing a dye and delivering the radiation in a series of sufficiently short pulses. Two-cm-long incisions were made in guinea pig skin, in vitro. India ink and egg white (albumin) were applied to the wound edges to enhance radiation absorption and to close the wound, respectively. Continuous wave (cw), 1.06 μm, Nd:yttrium-aluminum-garnet laser radiation was scanned over the weld producing ∼100 ms pulses. The cooling time between scans and the number of scans was varied. The thermal damage zone at the weld edges was measured using a transmission polarizing light microscope. The tensile strength of the welds was measured using a tensiometer. For pulsed welding and long cooling times between pulses (8 s), weld strengths of 2.4±0.9 kg/cm2 were measured, and lateral thermal damage at the epidermis was limited to 500±150 μm. With cw welding, comparable weld strengths produced 2700±300 μm of lateral thermal damage. The cw weld strengths were only 0.6±0.3 kg/cm2 for thermal damage zones comparable to pulsed welding. © 1998 Society of Photo-Optical Instrumentation Engineers.

Experimental and Computational Laser Tissue Welding Using a Protein Patch

An in vitro study of laser tissue welding mediated with a dye-enhanced protein patch was conducted. Fresh sections of porcine aorta were used for the experiments. Arteriotomies were treated using an indocyanine green dye-enhanced collagen patch activated by an 805-nm continuous-wave fiber-delivered diode laser. Temperature histories of the surface of the weld site were obtained using a hollow glass optical fiber-based two-color infrared thermometer. The experimental effort was complemented by simulations with the LATIS (LAser-TISsue) computer code, which uses coupled Monte Carlo, thermal transport, and mass transport models. Comparison of simulated and experimental thermal data indicated that evaporative cooling clamped the surface temperature of the weld site below 100 °C. For fluences of approximately 200 J/cm2, peak surface temperatures averaged 74°C and acute burst strengths consistently exceeded 0.14×106 dyn/cm (hoop tension). The combination of experimental and simulation results showed that the inclusion of water transport and evaporative losses in the computer code has a significant impact on the thermal distributions and hydration levels throughout the tissue volume. The solid-matrix protein patch provided a means of controllable energy delivery and yielded consistently strong welds. © 1998 Society of Photo-Optical Instrumentation Engineers.