Joining Quality Research Articles

Bioactive glass coatings fabricated by laser cladding on ceramic acetabular cups: a proof-of-concept study

Deposition of bioceramic coatings on medical implants is a valuable strategy to impart key added values, such as bioactivity. While flat coatings can be easily produced by enameling and similar techniques, applying a bioactive glass layer on surfaces with curved geometry is a great challenge from a technological viewpoint. In this work, for the first time we demonstrated the feasibility of bioactive glass coatings produced by laser cladding on alumina/zirconia ceramic acetabular cups for hip joint prosthesis. Laser-cladded glass coatings can be fabricated in a dense (pore-free) or porous form. Morphological analyses by scanning electron microscopy and micro-computed tomography revealed the good quality of joining at the coating/substrate interface and the good interconnectivity of the pores (size within 200–400 µm) in the outer porous layer. Indentation tests at the interface confirmed the excellent joining between glass and ceramic substrate. These coatings also exhibited a good bioactive behavior in vitro, as demonstrated by the formation of a surface apatite layer upon immersion studies in simulated body fluid.

Joining TWIP-Steel Simulation Models

JoiningTWIP project aims to support the introduction of TWIP-steels for automotive applications (in cars, trucks and buses) by identifying possible applications and further developing mechanical and low-heat joining technologies to be able to implement multi-material design with TWIP-steels. To guarantee a full view of the project team members from steel industry, car manufacturers, joining technology suppliers and universities are working together.This work describes the simulation stage of the different technologies. During the project, the materials described in the scope of the project were tested in order to obtain material characterization. Also, the different multi-material joints were tested to describe the joining process and the joining quality. These results will be used to build complex simulation models and prototypes, which show the performance and the behavior of the joining processes of TWIP-steels. Five different technologies were analyzed in the scope of the project: clinching, high-speed bolt setting, resistance element welding (REW), friction element welding (FEW) and flow drill screwing (FDS). To guarantee the performance of the simulation models, the results were compared to the sampled joint and processes. An optimization process of the different technologies was applied to improve the quality and the performance of the different joints.

Effects of prefabricated hole structure on cold-pressing joining reliability between dissimilar sheets

The structural form of prefabricated holes is one of the important factors to determine the quality and reliability of cold-pressing joining between dissimilar sheets. Different numbers of holes with the same area will lead to different wall thickness distributions and joining strengths. This paper takes the cold-pressing joining between AA1100 pure aluminum sheet and SS304 stainless steel sheet as an example, the further study results show that the end of aluminum sheet has an increasing tendency along the directions of length and width in the process of cold-pressing joining. The wall thickness of joints shows a symmetrical distribution on both sides and the joining thickness decreases from the center to both sides sequentially. With the continuous increase of the punch loading pressure, the average thinning ratio of the joints becomes larger. By contrast, when the other parameters are all the same, the joining strength is the most ideal when the punch loading pressure is 250 kN. The loading pressure which is too small or large is easy to cause an insufficient joining strength or defects. This paper provides a scientific basis in this aspect for optimizing the cold-pressing joining plan and designing a reasonable joint structure. It can also promote the existing cold-pressing joining technologies to be mature, and enrich the existing solid-state joining technology.

Eigen-line in welded structures of thermoplastic polymers

Welding is widely used as a joining method for thermoplastics, and it is imperative to ensure the joining quality, particularly for critical applications. In a previous work by the authors, an Eigen-line was found in the electrofusion joint of polyethylene (PE) pipes based on ultrasonic tests and it could be used to detect and assess cold welding defects. However, the nature of the Eigen-line and reasons for the Eigen-line's existence in ultrasonic images have not yet been fully understood, which limited its applications. In this paper, Eigen-lines were observed in other thermoplastics including polypropylene (PP), polyamide 6 (PA 6), polyoxymethylene (POM) and polyethylene terephthalate (PET), suggesting that Eigen-lines have common existence. Microindentation tests were conducted on specimens cut from electrofusion joints and butt joints of PE pipes. It was found that a significant change of elastic modulus exists around the Eigen-line, which can partly explain the appearance of an Eigen-line in ultrasonic images. Scanning electron microscopy (SEM) and reflective optical microscopy were also employed to explore the nature of the Eigen-line. The results showed that an Eigen-line is a thin layer with polymer chain orientation between base material and welded zone.

Acoustic-Emission-Analysis of Dissimilar Laser-welds of Aluminium and Polyamide 6.6

A novel laser joining process for hybrid polymer-metal structures has proven a strong bond between polyamide and aluminium. This welding technique is strongly requested by the automobile producing industry for numerous applications within structure components. However, the joining quality exhibits a strong dependency on process-related variables, which highlights the need for an online inspection technique. The requirements for a chosen inspection technique are [1], [2]: 1. Showing the results on-line during the joining process; 2. Working non-destructive; 3. Working as an integral method; Being able to determine weld defects. In that case only the Acoustic Emission Analysis (AEA) as a Non-Destructive-Technique (NDT) can be used to guarantee reasonable results. During the first tests at the welding laboratory at the Laser Technology Competence Centre (LTCC) at the University of Luxembourg, AEA sensors are applied onto the surface of the test specimen which has to be welded. In this principle acoustic events, caused by welding defects, are recorded during the laser joining. The most important laser process parameters, like velocity, power and horizontal focal position of the laser spot, have been verified and evaluated by the AEA. It was observed that insufficient laser power can lead to the break of the melting bath, which is often not recognizable by non-destructive optical methods [2]. The AEA however was able to detect this lack of fusion. Using high laser power, the appearance of gas bubbles arising from the Polyamide 6.6 could be detected afterwards in a microscopic micrograph. The AEA signals related to this effect can be correlated clearly. Due to the high pressure of the gas bubbles, the aluminium weld is often interrupted, which can be traced back to the solidification of the aluminium molten mass. Due to the actual situation, the AEA is a well-working NDT online monitoring method and can be used for the correlation of acoustic events and welding defects within the mentioned joining method. Future tasks will develop some algorithms to separate the different defects by pattern recognition of the AEA signals and parameter

금속 3D 프린팅 소재와 폴리머 레이저접합에 관한 연구

A 3D printed metal part and thermal plastic polymer part were joined by direct laser irradiation. The 3D metal part was fabricated by using DED(Direct Energy Deposition) with STS316 material. The experiment was carried out through no patterned metal surface, 3D metal printed surface and micro laser patterned surface. The most secure joining quality was obtained at the laser micro patterned surface specimen and the counterparts of polymers were PLA and PE based thermo plastics. The applied laser power was 350Watt and the distance of patterns was maintained at 150μm. The laser line width was optimized at 450μm and the laser micro pattern depth was 180μm for the best joining quality. Based on the result analysis, the possibility of laser material joining for metal to polymer was proposed and multi-material joining will be possible in 3D laser direct material fabrication. Key words: Laser, Pattering, Design, DED(Direct Energy Deposition)

Novel full-ceramic monoblock acetabular cup with a bioactive trabecular coating: design, fabrication and characterization

Over the last 25 years, the philosophy behind an optimal fixation of orthopaedic implants to hard tissues progressively evolved towards “bone-conservative” solutions in order to minimize bone resection/loss and maximize tissue-implant integration. Hence, the researchers׳ attention moved from “traditional” fixation of the prosthesis to host bone by using screws or acrylic cement to new strategies based on physico-chemical bonding and surface modification of the implant. This research work explores the feasibility of a novel bioceramic monoblock acetabular cup for hip joint prosthesis that can be fixed to the patient׳s bone by means of a bone-like trabecular coating able to promote implant osteointegration. Sponge replica method was properly adapted and optimized to produce hemispherical foam-like bioactive glass-ceramic coatings that were joined to Al2O3/ZrO2 composite cups by the interposition of a glass-ceramic interlayer. Morphological analyses by scanning electron microscopy (SEM) and micro-computed tomography revealed the good quality of joining at the different interfaces. Preliminary investigation of the mechanical properties was carried out to evaluate the suitability of the device for biomedical use. In vitro bioactive behaviour was assessed by immersion studies in simulated body fluid and evaluating the apatite formation on the struts of the trabecular coating. The concepts and findings reported in the present work can have a significant impact in the field of implantable devices, suggesting a valuable alternative to currently-applied but often suboptimal techniques for bone-prosthesis fixation.

Tool Wear Monitoring for Ultrasonic Metal Welding of Lithium-Ion Batteries

This paper presents a tool wear monitoring framework for ultrasonic metal welding which has been used for lithium-ion battery manufacturing. Tool wear has a significant impact on joining quality. In addition, tool replacement, including horns and anvils, constitutes an important part of production costs. Therefore, a tool condition monitoring (TCM) system is highly desirable for ultrasonic metal welding. However, it is very challenging to develop a TCM system due to the complexity of tool surface geometry and a lack of thorough understanding on the wear mechanism. Here, we first characterize tool wear progression by comparing surface measurements obtained at different stages of tool wear, and then develop a monitoring algorithm using a quadratic classifier and features that are extracted from space and frequency domains of cross-sectional profiles on tool surfaces. The developed algorithm is validated using tool measurement data from a battery plant.

Vpliv različnih oblik vrtilnih konic na kvaliteto spoja pri tornem vrtilnem varjenju

Vpliv različnih oblik vrtilnih konic na kvaliteto spoja pri tornem vrtilnem varjenju

(Invited) Silver Sinter Joining and Stress Migration Bonding for WBG Die-Attach

High temperature lead-free solder has been under development though several candidates have been already proposed such as Bi alloys and pure Zn/Zn-Sn alloys as well as the conventional Au alloys. Transient liquid phase bonding is also examined for off-eutectic Au or Ag alloys. Nowadays, wide band gap power semiconductors (WBGs) such as SiC or GaN with their excellent performances have been expected to be used in harsh environments. Among various proposals for die-attach materials and processes, Ag sinter joining is a promising approach for power semiconductors as well as for power LED, providing excellent heat-resistant of stable joint structures beyond 200 °C. This paper summarizes the present status of the Ag sinter joining and of the new approach with Ag film bonding, both of which have developed by the authors’ group. Sinter joining with Ag nanoparticles under pressure is an attractive choice of die-attach [1, 2]. Nevertheless, the high pressure beyond 5 MPa required for the joining may become a critical issue for thin and brittle semiconductor dies. In contrast, sinter joining with micron-sized Ag hybrid particle pastes provide a stable bonding structure at 200 ºC without applied high pressure. The presence of oxygen plays a key role in cleaning the surface of Ag at around 200 ºC in air resulting in a successful low-temperature low-pressure Ag sintering joining. Ag can clean its surface around 200 °C in air atmosphere. The Ag hybrid paste lowers its resistivity even below 200 °C in contrast to the Ag nanoparticle paste. At 200 °C, Ag coating on substrates/dies provides high strength due to Ag sintering ability in air. Thus, Ag sintering joining can be benefitted from the presence of oxygen, which is a great advantage as compared with other sintering materials. Recently, the Ag thin film stress migration bonding method has been developed, providing a perfect bonding without any voids performed in ambient pressure at 250 ºC in air [3-5]. This joining has two key aspects. One is the reduction reaction of Ag oxides or of other Ag compounds on the surface of Ag at around 200 °C as mentioned above. The other is thermo-mechanical stress caused by thermal expansion mismatch between Ag plating layer and substrates, resulting in massive stress migration of Ag atoms from the bottom of the plating to the surface. This paper briefly describes the current status of Ag sinter joining and Ag film stress migration bonding at our laboratory. Ag has great advantages in both the surface reaction in air benefitting joining quality and the excellent electric/thermal properties. Ag sinter joining has already exhibited a great potential in the market as high temperature interconnection technology. A new synthesis of Ag particles could lead to further low temperature sintering capability based on the reaction between Ag and oxygen. Our Ag film stress-migration bonding is expected to provide an alternative route for low temperature bonding. Similar bonding methods using Cu or other metal materials instead of Ag would be explored as cost-effective interconnections in future.

Dissimilar joining of aluminum alloy and stainless steel thin sheets by thermally assisted plastic deformation

Aluminum alloy/steel hybrid components are widely used in different industrial areas because of their high performance. However, the high importance of reducing the thickness of components to realize lightweight products requires the dissimilar joining of Al alloy and steel thin sheets (less than 1mm in thickness), which is a major challenge using current joining technologies. In this paper, an alternative dissimilar joining process by thermally assisted plastic deformation is proposed for thin metallic sheets. The effects of various parameters on the joining performance were investigated. After exposure to an elevated temperature of 450°C for 22s, an optimized joint type was achieved by local plastic deformation using a punch-die pair. This joint type exhibited an average joint efficiency factor of 85.2%, and an average absorption energy of 1.69kNmm in tensile shear tests, as well as satisfactory joining performance in peel tests. In addition to mechanical anchoring and surface enlargement, atomic interdiffusion at the interface activated by the elevated forming temperature was found to be critical for obtaining high joining quality. The thickness of the Fe-Al interdiffusion layer at the interface was positively correlated with the heat input and the locally distributed plastic strain. This study shows that the proposed dissimilar joining process for Al alloy and steel thin sheets is a promising joining method for Al alloy/steel lightweight structures owing to the excellent joining performance, weight effectiveness, simple operation and long tool lifetime.

The New Knowledge of Environmentally Friendly Joints Made by Thermal Drilling

The contribution deals with possibilities of new progressive technologies in materials joining processes. By using of friction, physical factors as temperature and thermal conductivity in joining, we can increase the quality of material joining and can join of various types of material. There is also shortage the production time, provide automation in operations is possible, spare of economical expenses and also we can protect the environment. The product increasing of automobile industry, pipe industry, development of mechanical products, materials, design of joining in civil engineering force the producers to accelerate the production and to utilize new technologies.

Effects of process conditions on the matched cold-pressing joining quality between dissimilar sheets

The process condition is one of the major factors to the quality of the matched cold-pressing joining between dissimilar sheets. The material AA1100 pure aluminum sheets and 304 stainless steel sheets were taken for experimental studying in this article. It was reached systematically that the effects of process conditions such as the loading pressure, the thickness of the aluminum sheets, and the joint structure on joining process and quality. As results shown, there was shunt behavior on the joint area of the aluminum sheet. The thickness of the joining decreased from the center to the both sides sequentially. The thickness of the aluminum sheets was proportional to the joining strength, and the loading pressure was inversely proportional to the joining strength when the other parameters were all the same. The technical reserves for the development of cold-pressing joining deformation joining for dissimilar sheets were provided in this study.

Design of energy optimization for laser polymer joining process

Different laser heat inputs were applied on the gray-colored acrylonitrile butadiene styrene (ABS) plastic using fixed laser power and variable scanning speeds to join ABS- and polycarbonate (PC)-based polymers. Experiments with a laser power between 6 and 8 W and a scanning speed of 1,500, 3,000, and 4,500 mm/min were used for the joining. Heat-affected zone (HAZ) and melt zone measurements were performed to find the joining energy threshold, and the mechanical properties of welds were evaluated. At the low scanning speed, the total heat input at the given area resulted in carbonization damage on the surface. However, energy distributed laser beam joining process by galvanometers resulted in secure and sound weld joining quality. Damage threshold was calculated as 127 J/cm2 with relatively less sensitivity of scanning speed. However, the ablation threshold was measured to be 215, 281, and 424 J/cm2 for the scanning speed of 4,500, 3,000 and 1,500 mm/min, respectively.

Modeling and Optimization of Mask Assisted Laser Transmission Micro Joining Process

This article uses semiconductor laser for mask assisted laser transmission micro joining PET and PET with clear weld absorbents, the mask slit width is 0.3mm, using CCD to plan experimental design. The mathematical model of joining process parameters with joint strength and joint width was established using response surface methodology. Experimental verification was also done. The actual joint width was compared to mask slit width and the process parameters were optimized. The results show that the mathematical model can response the relationship between process parameters and joining quality, the mask can effectively control the joint width, reasonable process parameters can obtain high-precision, high-intensity joining quality.

Microstructural and mechanical integrity of Cu/Cu interconnects formed by self-propagating exothermic reaction methods

A rapid and flexible Cu/Cu soldering process has been developed through self-propagating exothermic reaction (SPER) using Al–Ni multilayer nano-film as heat source. The localized intensive heat generated by SPER has a short affecting time and thus a low thermal impact, which promises various potential benefits for electronics interconnects, including the reduction of stress caused by CTE (coefficient of thermal expansion) mismatch and the high temperature soldering by reflow process. In this study, the strong metallurgical Cu/Cu joining interfaces of hundreds nanometers IMCs (intermetallic compounds) layers were formed, which exhibit a shear strength greater than 32MPa. This work has also characterized the interfacial IMC morphology, thickness, porosity and the fracture behaviour of the joint to allow an analysis and evaluation of the feasibility and reliability of SPER interconnects. In addition, the formation mechanisms of defects and the influence of applied pressure, solder thickness and ambient temperature in SPER process have been investigated, which can further assist the optimization of process and the improvement of joining quality.

Research on Quality and Reliability of Cold-Pressing Joining Between Aluminum and Stainless Sheets

Lightweight forming was one of the main ways to achieve energy conservation and emission reduction in advanced manufacturing. However, the cold-pressing process was easier to realize dissimilar sheets joining and could reduce the weight of both the material and the structure; therefore, this process was widely used. Taking aluminum and stainless sheets joining as an example, this study designed three kinds of joining schemes based on the theory of materials mechanics. It was concluded that the increase of the load pressure made the joining parts of the two sheets fitted quickly, but it decreased the joining thickness through the research of different joining project results. In the joining process, defects such as overlap, warping, protrusions, pitting, and partial cracking led to decreasing surface quality and reliability of the joining part. It was demonstrated by the sheet specimen unidirectional tensile test that the “embedding” and the “interlocking” were the main mechanisms of cold-pressing joining.

English

A high quality joint between tool steel and stainless steel alloys is hard to achieve with the conventional welding process. In this study, a new process of joining semi-solid AISI D2 tool steel and AISI 304 stainless steel using a partial remelting method is proposed. Metallographic analysis and Vickers hardness tests were performed. The results obtained from investigating the basic geometries demonstrated a good joining quality that differs from the conventional process of welding or mechanical joining with screws or nails. Metallographic analyses along the joint interface between semi-solid AISI D2 and 304 stainless steel showed a smooth transition from one to the other, with neither oxides nor microcracking being observed. Local mechanical properties of different regions show three different readings according to the results of the hardness tests. The current work successfully confirmed that the avoidance of dendritic microstructure of the semi-solid joined zone and high bonding quality components can be achieved. From the present study, it can be said that the thixojoining process can be utilized safely for dissimilar metal pairs.

Manufacturing of Steel-Reinforced Aluminum Parts by Co-Extrusion and Subsequent Forging

The processes of manufacturing continuously and discontinuously steel-reinforced aluminum profiles by means of co-extrusion and subsequent forging were examined. In the co-extrusion and subsequent forging of discontinuously reinforced parts, influences of the reinforcing elements on forming behavior and material bonding for both processes were investigated. It was shown that forming temperature as well as ram speed have no influence on joining quality and forming behavior of the reinforcing elements in the co-extrusion of continuously reinforced profiles. The analyses of the joining zone between the composite partners revealed that a good connection of the two materials could be achieved.

A new current hybrid inertia friction welding for nickel-based superalloy K418–alloy steel 42CrMo dissimilar metals

The nickel-based superalloy K418 and alloy steel 42CrMo dissimilar metals friction welding joints lack strength and toughness due to high hardening and poor joining quality at the friction interface. To resolve this issue, a new current inertia friction welding (CIFW) method is carried out by hybrid an external additional electronic current in inertia friction welding (IFW) process. The characteristics of welding formation, the elements’ diffusion, and the mechanical properties of K418–42CrMo dissimilar metal joints are studied by scanning electron microscope, energy dispersive spectrometer, and X-ray diffractometer tools. The experimental results show that hybrid additional electronic current has a significant positive influence on interface characteristics of IFW joints. The required welding time for CIFW to complete a good qualified joint is shortened due to mixture actions of both friction heat and resistance heat. The width of the element diffusion zone increases in CIFW joints, and elements in 42CrMo side diffuse through the K418/42CrMo interface into the K418 side in CIFW joints. The width of the K418/42CrMo bonding interface increases in CIFW joints. The microhardness at the K418/42CrMo bonding interface is decreased in CIFW joints. The mechanical tensile property of CIFW joints is increased obviously. The interface bonding pattern becomes jagged and interlocking perfect formations. These above changes improve the joining quality of K418–42CrMo dissimilar metal friction welding joints. The heat treatment effect and resistance heat effect originated from hybrid external electronic currents are discussed by comparing CIFW with IFW. A new model is proposed to illustrate the interface’s evolution and development mechanism in K418–42CrMo dissimilar metal CIFW.