Mechanical and interfacial characterization of laser welded Co-Cr alloy with different joint configurations

PURPOSE: The mechanical and interfacial characterization of laser welded Co-Cr alloy with two different joint designs. MATERIALS AND METHODS: Dumbbell cast specimens (n=30) were divided into 3 groups (R, I, K, n=10). Group R consisted of intact specimens, group I of specimens sectioned with a straight cut, and group K of specimens with a 45degrees bevel made at the one welding edge. The microstructure and the elemental distributions of alloy and welding regions were examined by an SEM/EDX analysis and then specimens were loaded in tension up to fracture. The tensile strength (TS) and elongation (epsilon) were determined and statistically compared among groups employing 1-way ANOVA, SNK multiple comparison test (alpha=.05) and Weibull analysis where Weibull modulus m and characteristic strength sigmaomicron were identified. Fractured surfaces were imaged by a SEM. RESULTS: SEM/EDX analysis showed that cast alloy consists of two phases with differences in mean atomic number contrast, while no mean atomic number was identified for welded regions. EDX analysis revealed an increased Cr and Mo content at the alloy-joint interface. All mechanical properties of group I (TS, epsilon, m and sigmaomicron) were found inferior to R while group K showed intermediated values without significant differences to R and I, apart from elongation with group R. The fractured surfaces of all groups showed extensive dendritic pattern although with a finer structure in the case of welded groups. CONCLUSION: The K shape joint configuration should be preferred over the I, as it demonstrates improved mechanical strength and survival probability.

Three-dimensional accuracy of different correction methods for cast implant bars

PURPOSE: The aim of the present study was to evaluate the accuracy of three techniques for correction of cast implant bars. MATERIALS AND METHODS: Thirty cast implant bars were fabricated on a metal master model. All cast implant bars were sectioned at 5 mm from the left gold cylinder using a disk of 0.3 mm thickness, and then each group of ten specimens was corrected by gas-air torch soldering, laser welding, and additional casting technique. Three dimensional evaluation including horizontal, vertical, and twisting measurements was based on measurement and comparison of (1) gap distances of the right abutment replica-gold cylinder interface at buccal, distal, lingual side, (2) changes of bar length, and (3) axis angle changes of the right gold cylinders at the step of the post-correction measurements on the three groups with a contact and non-contact coordinate measuring machine. One-way analysis of variance (ANOVA) and paired t-test were performed at the significance level of 5%. RESULTS: Gap distances of the cast implant bars after correction procedure showed no statistically significant difference among groups. Changes in bar length between pre-casting and post-correction measurement were statistically significance among groups. Axis angle changes of the right gold cylinders were not statistically significance among groups. CONCLUSION: There was no statistical significance among three techniques in horizontal, vertical and axial errors. But, gas-air torch soldering technique showed the most consistent and accurate trend in the correction of implant bar error. However, Laser welding technique, showed a large mean and standard deviation in vertical and twisting measurement and might be technique-sensitive method.

Avaliação da resistência flexural entre diferentes métodos de soldagem / Evaluation of flexural strength among different welding methods

A técnica de soldagem, muito utilizada em prótese parcial fixa, permite a união das partes metálicas, favorecendo a adaptação da prótese e a distribuição das forças mastigatórias, minimizando falhas no tratamento reabilitador. O objetivo deste trabalho foi avaliar a resistência flexural dos métodos de soldagem com chama direta, laser e TIG, utilizando uma liga de NiCr. Um grupo controle (M) foi confeccionado fundindo os corpos de prova em monobloco. Foram confeccionados três grupos: chama direta (C), laser (L) e TIG (T), onde os corpos de prova foram seccionados transversalmente. Em razão das características das soldagens laser e TIG que ocorrem apenas perifericamente, foram realizados outros dois grupos: laser (L1) e TIG (T1), em que os corpos de prova foram seccionados em chanfro de 45º. Os corpos de prova tiveram suas extremidades unidas com resina duralay e cada grupo passou pelo seu respectivo processo de soldagem, torneamento, simulação de cocção da porcelana e, finalmente, submetidos aos testes de flexão. Os valores numéricos registrados foram de 1,79 GPa (M), 1,37 GPa (C), 0,99 GPa (T), 1,26 GPa (T1), 1,03 GPa (L) e 1,09 GPa (L1). Os dados obtidos foram submetidos à análise estatística (Anova – p < 0,5). Concluiu-se que todos os grupos laser e TIG apresentaram resultados semelhantes entre si; os grupos laser e TIG com preenchimento foram semelhantes ao grupo chama e todos os grupos soldados foram diferentes estatisticamente do grupo controle.

Soldering methods used to join fixed partial dentures favor prosthesis fit and distribution of masticatory forces, minimizing failures in the oral rehabilitation process. The aim of this work was to evaluate the flexural strength of different soldering methods as brazing, TIG, and laser welding using a Ni-Cr alloy. A control group (M) was made using one-piece castings. Also, other three groups were made by brazing (C), TIG (T), and laser (L) being sectioned in a transversal direction. Another two groups were ssectioned in a 45-degree chanfer configuration. The specimens were joined with acrylic resin and submitted to flexural tests. The numerical values were 1,79 GPa (M), 1,37 GPa (C), 0,99 GPa (T), 1,26 GPa (T1), 1,03 GPa (L) e 1,09 GPa (L1). The Anova test (p=0.05) was performed to identify possible significant differences among groups. The conclusions were: all Laser and TIG groups were statistically similar with the brazing group and all the experimental groups were statistically different from the control group.

A study on fatigue strength of laser welding of titanium and titanium alloy / 实用口腔医学杂志

Objective:To investigate the corrosion fatigue strength of laser-welded specimens fabricated from commercially pure titanium (TA2) and titanium alloy(TC4). Methods:TA2 and TC4 were mechanically processed into a certain size and joined by laser welding. A fatigue testing machine was used to test tensile load and fatigue strength after soaked in synthetic saliva. The fatigue fracture surface was examined by scanning electron microscopy (SEM). Results: The fatigue strengths of the laser-welded test specimens showed no significant differences compared to specimens in air. SEM examination showed that there were no defects such as corrosion pits. Conclusion: There are no significant differences between either laser-welded metal in the corrosion fatigue strength for dry specimens and specimens in synthetic saliva.

Effect of laser welding on the titanium composite tensile bond strength

The aim of this study was to analyze the shear bond strength between commercially pure titanium, with and without laser welding, after airbone-particle abrasion (Al2O3) and 2 indirect composites. Sixty-four specimens were cast and divided into 2 groups with and without laser welding. Each group was divided in 4 subgroups, related to Al2O3 grain size: A - 250 µm; B - 180 µm; C- 110 µm; and D - 50 µm. Composite rings were formed around the rods and light polymerized using UniXS unit. Specimens were invested and their shear bond strength at failure was measured with a universal testing machine at a crosshead speed of 2.0 mm/min. Statistical analysis was carried out with ANOVA and Tukey's test (á=0.05). The highest bond strength means were recorded in 250 µm group without laser welding. The lowest shear bond strength means were recorded in 50 µm group with laser welding. Statistically significant differences (p<0.05) were found between all groups. In conclusion, airborne particle abrasion yielded significantly lower bond strength as the Al2O3 particle size decreased. Shear bond strength decreased in the laser welded specimens.

O objetivo deste estudo foi analisar a força de união entre o titânio comercialmente puro com solda e sem solda modificado por partículas de óxido de alumínio (Al2O3) e duas resinas indiretas. Um total de 64 espécimes foram fundidas e divididas em dois grupos sem solda e com solda a laser. Cada grupo foi novamente divididos em 4 subgrupos, de acordo com o tamanho de partículas de óxido de alumínio utilizado: A - Al2O3 (250 µm); B - Al2O3 (180 µm); C- Al2O3 (110 µm); D - Al2O3 (50 µm). Anéis de resina foram polimerizados ao redor das hastes de titânio no equipamento UniXS. Os espécimes foram embutidos em gesso e a força de união foi mensurada com auxílio da máquina de ensaios universais. ANOVA e teste de Tukey (p<0,05) foram utilizados para análise estatística. Os maiores valores de força de união foram registrados no grupo de 250 µm sem solda a laser. Os menores valores foram registrados para o grupo de 50 µm com solda a laser. Alterações estatisticamente significantes foram observadas entre todos os grupos (p<0,05). As forças de união diminuíram significantemente com a diminuição dos tamanhos das partículas de óxido de alumínio. A força de união diminuiu nas amostras que receberam a solda a laser.

Fracture strength of different soldered and welded orthodontic joining configurations with and without filling material

The aim of this study was to compare the mechanical strength of different joints made by conventional brazing, TIG and laser welding with and without filling material. Five standardized joining configurations of orthodontic wire in spring hard quality were used: round, cross, 3 mm length, 9 mm length and 7 mm to orthodontic band. The joints were made by five different methods: brazing, tungsten inert gas (TIG) and laser welding with and without filling material. For the original orthodontic wire and for each kind of joint configuration or connecting method 10 specimens were carefully produced, totalizing 240. The fracture strengths were measured with a universal testing machine (Zwick 005). Data were analyzed by ANOVA (p=0.05) and Bonferroni post hoc test (p=0.05). In all cases, brazing joints were ruptured on a low level of fracture strength (186-407 N). Significant differences between brazing and TIG or laser welding (p<0.05, Bonferroni post hoc test) were found in each joint configuration. The highest fracture strength means were observed for laser welding with filling material and 3 mm joint length (998 N). Using filling materials, there was a clear tendency to higher mean values of fracture strength in TIG and laser welding. However, statistically significant differences were found only in the 9-mm long joints (p<0.05, Bonferroni post hoc test). In conclusion, the fracture strength of welded joints was positively influenced by the additional use of filling material. TIG welding was comparable to laser welding except for the impossibility of joining orthodontic wire with orthodontic band.

Mechanical properties of laser-welded cast titanium and titanium alloy / 대한치과보철학회지

PURPOSE: The purpose of this study was to investigate the effect of the output energy(voltage) of laser welding on the strength and properties of joint of cast titanium(CP Gr II) and titanium alloy(Ti-6Al-4V). MATERIAL AND METHOD: Cast titanium and its alloy rods(ISO6871) were prepared and perpendicularly cut at the center of the rod. After the cut halves were fixed in a jig, and the joints welded with a laser-welding machine at several levels of output voltage of 200V.280V. Uncut specimens served as the non-welded control specimens. The pulse duration and pulse spot size employed in this study were 10ms and 1.0mm respectively. Tensile testing was conducted at a crosshead speed of 0.5mm/min. The ultimate tensile strength(MPa) was recorded, and the data(n=6) were statistically analyzed by one-way analysis of variance(ANOVA) and Scheffe's test at alpha=0.05. The fracture surface of specimens investigated by scanning electron microscope(SEM). Vickers microhardness was measured under 500g load of 15seconds with the optimal condition of output voltage 280V. RESULTS: The results of this study were obtained as follows, 1. When the pulse duration and spot size were fixed at 10ms and 1.0mm respectively, increasing the output energy(voltage) increased UTS values and penetration depth of laser welded to titanium and titanium alloy. 2. For the commercial titanium grade II, ultimate tensile strength(665.3MPa) of the specimens laser-welded at voltage of 280V were not statistically(p>0.05) different from the non-welded control specimens(680.2MPa). 3. For the titanium alloy(Ti-6Al-4V), ultimate tensile strength(988.3MPa) of the specimens laser-welded at voltage of 280V were statistically(p<0.05) different from the nonwelded control specimens(665.0MPa). 4. The commercial titanium grade II and titanium alloy(Ti-6Al-4V) were Vickers microhardness values were increased in the fusion zone and there were no significant differences in base metal, heat-affected zone.

Mechanical properties of laser welded Co-Cr alloy / 대한치과보철학회지

STATEMENT OF PROBLEM: The joints of removable partial denture alloys have failed frequently after routine usage. PURPOSE: The purpose of this study was to evaluate the mechanical properties of the laser welded Co-Cr alloys. MATERIAL AND METHOD: For this study, 20 Co-Cr specimens were casted and 10 of them were seperated on the middle area and laser welded with Alpha laser welding machine(Siro Lasertec, Pforzheim, Germany). Rest of them which were as cast, were used as a control group. For the section of the experimental specimens, wire cutting machine was used to make a even gap of the all specimens. Laser welding was done with manufacturer's instrunction and tested each specimen by Instron Machine. Tensile strength, 0.2% yield strength and % elongations were recorded. Fractured surfaces were investigated with SEM. RESULTS: The results were as follows : 1. The tensile strength of the laser welded group(617.7MPa) was about 75% of the as cast group(820.4MPa). It had stastically singnificant diffrences(p<0.05). 2. The % elongation of the experimental group was 6.6 which was lower than the control group(14.3). 3. Fracture of the experimental group occured in the welded surface and showed many voids. In contrast, the fracture surface of the control group was showed rough surfaces without any voids. CONCLUSION: The tensile strengths of the as-cast joints were higher than those for the laserwelded joints, and the % elongation of the experimental group was lower than the control group. Porosity was found in laser-welded joints.

Fit of Implant Frameworks Fabricated by One-Piece Casting, Laser Welding, Soldering, and Electric Discharge Machining / 대한치과보철학회지

The purpose of this study was to measure and compare the strains produced by screw-tightening implant frameworks fabricated by five different fabrication methods;(1)one-piece cast using plastic sleeve,(2)one-piece cast using gold cylinder,(3)laser welding,(4)soldering,and (5)electrical discharge machining,and also to measure and compare the strains produced when the order of screw tightening was changed. A research model incorporating eighteen strain gages was made to measure the fit of implant frameworks in three dimensions.Three implants aligned in an arc were fixed on the top ends of the L-shape aluminum bars of the research model,and standard abutments were joined to the implants with abutment screws.Five types of implant framework were placed on the abutments and screwed by a torque wrench using 10 Ncm. Under the conditions of this study,the following conclusions were drawn: 1.The electrical discharge machining group showed the smallest magnitude of strain,followed by the soldering group,the laser welding group,the one-piece cast group using gold cylinder,and the one-piece cast group using plastic sleeve.However,among the magnitude of strain for the remaining groups except the electrical discharge machining group,there were not significant differences. 2.When the order of screw tightening was changed,there were not significant differences in the magnitude of strain. 3.In comparison with the electrical discharge machining group,the laser welding group and the one-piece cast groups showed greater horizontal distortion and the soldering group showed greater horizontal and vertical distortion.

Experimental Study of Laser Welding in Urological Tubular Anastomosis / 대한비뇨기과학회지

Tissue welding is a potentially expectable surgical application in the field of medical laser technology. We investigated to establish the technology of laser welding and its efficacy with auxiliary stent and solder in the anastomosis of urological tubular organs including ureter and urethra of rabbits and vas of human using CO2, laser(Shaplan 1100 System). The objects consist of four groups including control group of the conventional microsuture anastomosis and three experimental groups that included group I of laser welding only, group II of laser welding with stent and group III of laser welding with solder. The overall success rate in control group was 90.7 % and in experimental groups were lower with 58.3% and 73.3% in group I and II , respectively, but higher with 95.5% group III. According to each tubular organ in experimental groups, the overall success rates in ureter, urethra and vas were 83.3%, 75.0% and 76.9% respectively, so that the thinner in the wall thickness of tubular organ revealed the higher success rate. Also, time of procedures was significantly shorter in laser groups than control group. Histological findings of laser welding showed the only localized adventitial reactions with intact subserosal layer. In conclusion, laser welding in the urological tubular organ anastomosis with auxiliary solder is not only a more simple and fast technique but also has higher success rate than conventional microsuture anastomosis.