Polymer Welding Research Articles

Ultrasonic Welding of Additively Manufactured PEEK and Carbon-Fiber-Reinforced PEEK with Integrated Energy Directors

The thermoplastic polymer polyether ether ketone (PEEK) offers thermal and mechanical properties comparable to thermosetting polymers, while also being thermally re-processable and recyclable as well as compatible with fused filament fabrication (FFF). In this study, the feasibility of joining additively manufactured PEEK in pure and short carbon-fiber-reinforced form (CF-PEEK) is investigated. Coupon-level samples for both materials were fabricated using FFF with tailored integrated welding surfaces in the form of two different energy director (ED) shapes and joined through ultrasonic polymer welding. Using an energy-driven joining process, the two materials were systematically investigated with different welding parameters, such as welding force, oscillation amplitude and welding power, against the resulting weld quality. The strengths of the welded bonds were characterized using lap-shear tests and benchmarked against the monotonic properties of single 3D-printed samples, yielding ultimate lap-shear forces of 2.17kN and 1.97kN and tensile strengths of 3.24MPa and 3.79MPa for PEEK and CF-PEEK, respectively. The weld surfaces were microscopically imaged to characterize the failure behaviors of joints welded using different welding parameters. Samples welded with optimized welding parameters exhibited failures outside the welded region, indicating a higher weld-strength compared to that of the bulk. This study lays the foundation for using ultrasonic welding as a glue-free method to join 3D-printed high-performance thermoplastics to manufacture large load-bearing, as well as non-load-bearing, structures, while minimizing the time and cost limitations of FFF as a fabrication process.

Self-healing and polymer welding of soft and stiff epoxy thermosets via silanolates

Incorporating dynamic bonds into polymers enables static thermosets to be transformed into active materials, possessing the reprocessability of thermoplastics while maintaining the bulk properties of fully crosslinked networks. This new class of materials, termed covalent adaptable networks (CANs), has helped bridge the gap between traditional thermosets and thermoplastics. Here, epoxy-based adaptable networks were synthesized by combining a diepoxide monomer with an oligosiloxane prepolymer containing aminopropyl groups, which crosslink irreversibly, and silanolate end-groups, which participate in dynamic bonding. Two separate diepoxide crosslinkers were used to give a range of soft to stiff materials with a Young’s modulus varying from 12 MPa to 2.2 GPa. This study documents how the thermal and mechanical properties (e.g., glass transition temperature and modulus) are affected by compositional changes in these silanolate networks. Dynamic bonding also results in self-healing properties, offering the ability to repair structural polymers and composites. When combined with tunable mechanical properties, self-healing capabilities make these materials well-suited to be sustainable alternatives for many traditional thermosets. For example, we demonstrated the ability to weld a stiff epoxy thermoset to a dissimilar soft material, a feature traditional epoxies do not permit.Graphical abstract

Influence of Tool Thread Pitch During Friction Stir Welding of High-Density Polyethylene Plate

AbstractThis study utilizes a face-centered central composite response surface design of experiments to determine the effects of thread pitch when friction stir welding high-density polyethylene. The tool pin thread pitch, along with rotation and traversing speed, was varied so that models of the maximum tensile strength, tool temperature, and tool forces could be analyzed. Coarser thread pitches facilitated higher tensile strength than finer threads due to greater material velocity and overlap between the stir zone and base material. In the tested range, the thread pitch provided a 6% linear contribution to ultimate tensile strength, whereas welds with coarse threads had on average a 2.83 MPa increase in tensile strength over the fine thread tool. The greater circumferential pin surface area of fine threads caused a greater increase in tool temperature, though this did not correlate to stronger welds. Ultimately, the most interdiffusion across the polymer joint occurred with the coarser thread pitch and slow traverse speed due to prolonged joint exposure to the molten polymer weld pool.

An approach to weld dissimilar polycarbonate and high-density polyethylene by friction stir spot welding

The friction stir spot welding of polymeric materials has been examined extensively; conversely, only a few researchers have addressed the friction stir spot welding of dissimilar polymers. In this study, the possibility of friction stir spot welding of dissimilar polycarbonate to high-density polyethylene is examined, which has not been previously investigated. The influence of welding parameters, namely, tool rotational speed and dwell time, was investigated experimentally, whereas the plunging depth, plunging rate, and tool geometry were kept constant during all tests. The induced temperature and the weld lap shear force were recorded and analyzed. Both materials are welded successfully by friction stir spot welding. At 2300 rpm and 40 s dwell time when the polycarbonate sheet was on the top, the maximum lap shear force of 0.37 kN was obtained. The findings demonstrated that an effective weld might be attained at a moderate frictional heating temperature slightly below the melting temperature Tm and glass transition temperature Tg of both welded materials. At very low temperatures, poor weld quality was obtained. When temperatures extensively increased, the results deteriorated to exhibit weak joint lap shear values because of the presence of cavities and pores in the weld junction.

Photoinduced 3D Printing through a Combination of Cationic and Radical RAFT Polymerization

Photopolymerization-based three-dimensional (3D) printing techniques have been widely utilized to fabricate polymeric materials with complex architectures. The application of reversible deactivation radical polymerization (RDRP) in 3D printing is emerging as a powerful tool to introduce various postprinting abilities but is still at an early stage. Here, a photoinduced free radical-promoted cationic reversible addition–fragmentation chain transfer (RAFT) polymerization method was developed, utilizing the direct photolysis of the RAFT agent as a radical source, which was further combined with photo-iniferter RAFT polymerization to prepare polymer networks. The polymerization mechanism was studied by model polymerization using monofunctional monomers. The effects of each component on the properties of the final materials and polymerization behavior of the cross-linking systems were studied in detail. This method was successfully applied in a digital light processing (DLP) technique-based commercial 3D printer. Finally, polymer welding of the printed objects through both cationic and radical RAFT chain extension was realized, expanding avenues of postprinting and future applications in various fields.

A stationary shoulder with fluid temperature control for friction stir welding of polymers: development and investigation

There is a growing interest in the application of thermoplastics and thermoplastic composites for lightweight structures, thus also in friction stir welding (FSW) as a suitable joining technology. With the transformation of FSW from metals to polymers, several new tooling concepts were developed; mainly various heating setups to add external thermal energy to the process were designed. However, current temperature control approaches do not consider the cooling of the process at high rotational speeds and the asymmetry of the process in thermomechanical conditions. In this paper, we present a stationary shoulder with fluid temperature control, which is also capable of cooling the process. Additionally, asymmetric temperature control conditions can be examined by applying different flow directions. For investigation, butt welds of PMMA sheets were welded and assessed using the weld morphology and tensile strengths. Different fluid temperatures, feed rates, and both flow directions were applied and led to different tensile strengths. It could be shown that the optimal control temperature is different for the advancing side (AS) and the retreating side (RS). By using a transverse flow, a heat transport from the warmer AS to the colder RS could be established, which improved the strength. Moreover, the tensile strength could be increased by cooling the process at a feed rate of 100 mm/min. To improve the effectiveness of the temperature control, a new shoulder with independent temperature-controlled areas is proposed.

Effect of Tool Design on the Mechanical Properties of Bobbin Friction Stir Welded High-Density Polyethylene Sheets: Experimental Study

Welding polymers by the friction stir welding (FSW) technique is one assembly process among several known assembly techniques which consists in welding two materials without filler material. The FSW process is based on the generation of heat due to friction and material deformation under an axial force. Among the main aspects affecting material flow, the choice of welding tool geometry has become of great interest to improve the welds quality. The main objective of this work is the welding of polymers using the FSW technique. A new method of welding HDPE (high density polyethylene) plates, called BT-FSW (bobbin tool friction stir welding) was developed. Standard rectangular shape intended for the distribution of natural gas has been successfully welded by BT-FSW. Tensile tests and hardness measurements were carried out on samples cut from the welded sheets and the results were analyzed to compare the mechanical characteristics of the plates welded by the BT-FSW and conventional FSW (C-FSW) processes. The results of the comparative studies on the micro-hardness characteristics and mechanical properties of the two welding processes indicate that welding using the bobbin tool can significantly reduce hardness and improve both weld formation and mechanical properties of joints. This study showed that the design of the welding tool has a big impact on the weld strength. An improvement in the mechanical properties of the specimens welded by BT-FSW was observed to give a better welding quality for the polymers studied.

Molecular Dynamics Simulations of Polymer Nanocomposites Welding: Interfacial Structure, Dynamics and Strength.

Polymer welding has received numerous scientific attention, however, the welding of polymer nanocomposites (PNCs) has not been studied yet. In this work, via coarse-grained molecular dynamics simulation, the attention on investigating the welding interfacial structure, dynamics, and strength by constructing the upper and lower layers of PNCs, by varying the polymer-nanoparticle (NP) interaction strength εNP-p is focused. Remarkably, at low εNP-p , the NPs gradually migrate into the top and bottom surface layer perpendicular to the z direction during the adhesion process, while they are distributed in the middle region at high εNP-p . Meanwhile, the dimension of polymer chains is found to exhibit a remarkable anisotropy evidenced by the root-mean-square radius of gyration in the xy- (Rg,xy ) and z- (Rg,z ) component. The welding interdiffusion depth increases the fastest at low εNP-p , attributed to the high mobility of polymer chains and NPs. Lastly, although the mechanical properties of PNCs at high εNP-p is the strongest because of the presence of the NPs in the bulk region, the welding efficiency is the greatest at low εNP-p . Generally, this work provides a fundamental understanding of the interfacial welding of PNCs, in hopes of guiding to design and fabricate excellent self-healable PNCs.

Numerical study of thermo-mechanical responses in laser transmission welding of polymers using a 3-D thermo-elasto-viscoplastic FE model

Numerical study of thermo-mechanical responses in laser transmission welding of polymers using a 3-D thermo-elasto-viscoplastic FE model

Recent advances in laser welding for joining polymeric components

Laser welding of polymers is a very popular industrial joining process, creating joints with good mechanical performance. However, the implementation of optimized laser welding processes is still quite limited since most industrial applications adopt an empirical approach to adjust the process parameters. The current work provides a summary of new findings on the subject of laser joining of polymers, describing the key operation modes of this joining method, its process parameters and how they affect the joint characteristics. The response of polymers to temperatures generated during laser welding is also discussed, as well as the effect of additives on the weldability of polymers.

A comparative analysis on friction stir welding of similar and dissimilar polymers: acrylonitrile butadiene styrene and polycarbonate plates

A comparative analysis on friction stir welding of similar and dissimilar polymers: acrylonitrile butadiene styrene and polycarbonate plates

Effect of tool rotational speed on friction stir welding of polymer using self-heated tool

Effect of tool rotational speed on friction stir welding of polymer using self-heated tool

Xanthate-Based Photoiniferter RAFT Polymerization toward Oxygen-Tolerant and Rapid Living 3D Printing

Three-dimensional (3D) printing based on photoinduced reversible addition–fragmentation chain transfer (RAFT) polymerization is emerging as a versatile and powerful method to prepare “living” 3D objects, which can be postmodified with various functionalities. However, an additional photoinitiator or photocatalyst is necessary in these systems, which is toxic and will cause negative effects on the properties of the prepared materials. Here, we report oxygen-tolerant and rapid living 3D printing based on photoiniferter RAFT polymerization, which does not need additional photoinitiators or photocatalysts. A xanthate, O-ethyl-S-2-ethyl propionate, was chosen as both the photoinitiator and RAFT agent in this process. Various monomers and RAFT agents were screened in this system. Materials with different properties were prepared utilizing the postfunctionalization of the printed living objects. Furthermore, a polymer welding method was proposed by painting fresh monomers between two living objects for post-photocuring. This photoiniferter RAFT polymerization-based living 3D printing method was also successfully applied to a commercial digital light processing technique-based 3D printer, offering a facile method to fabricate living 3D materials with different shapes.

Welding of polymers by infrared laser radiation

A number of polymeric materials are translucent for infrared radiation. The use of low-power infrared lasers makes it possible to weld polymer sheets due to the penetration of radiation into the material depth. The possibilities of transmission welding of polybutene sheets, as well as several layers of polyethylene film are investigated. Epilog Fiber Mark 20 installation equipped with 20-W fiber infrared laser with 1.062 μm radiation wavelength is used. According to the investigation results, the maximum penetration depth of polybutene sheets at thea given radiation power is determined. The ability of welding up to eight layers of colored polyethylene film of PVD-108 and PVD-158 grade is shown.

Laser polymer welding process: Fundamentals and advancements

Laser polymer welding provides a feasible alternative where traditional polymer joining processes have reached their limits. The flexibility of this process is unparalleled, and the weld quality is superior to that of most traditional polymer joining processes. A variety of laser irradiation techniques are devised and effectively utilized in laser welding of polymers. The polymer compositions, as well as optical and thermal characteristics, are significant factors influencing the laser polymer welding process. For a wide variety of polymers, laser polymer welding produces weld strength equivalent to the strength of the substrate material. Lasers are utilized for more than only polymer welding; they are also used to weld hybrid structures consisting of polymer-metal, polymer-ceramics, polymer-glass, polymer-wood composites, etc. This paper presents an overview of the process fundamentals and advancements in laser polymer welding process.

Laser Hybrid Welding of Electronic Copper Foil and Liquid Crystal Polymer

Laser Hybrid Welding of Electronic Copper Foil and Liquid Crystal Polymer

Laser beam positioning in quasi-simultaneous laser transmission welding of polymers

Laser beam positioning in quasi-simultaneous laser transmission welding of polymers

Parametric Study and Optimization for Welding Processes Using Machine Learning

Optimization facilitates in attainment of maximum strength, efficiency, reliability, productivity and longevity. In this work, data from three material joining processes - Ultrasonic welding of polymers, arc welding as Metal Inert Gas and Tungsten Inert Gas are analysed for establishing quantitative relationship between the process parameters and for prediction of weld features using Multivariate Linear Regression algorithm. The various dependency coefficients and characteristics generated with the ML algorithms are in agreement with the inherent dependency as obtained from experimental data and simulation results. This investigation is a preliminary attempt with a limited set of data to manifest the suitability of machine learning techniques; nevertheless, the results are far from conclusive owing to small data set and hence may be extended to precisely model joining processes with higher number of process parameters, degree of freedom and responses.

A nanoconcrete welding strategy for constructing high-performance wound dressing

Engineering biomaterials to meet specific biomedical applications raises high requirements of mechanical performances, and simultaneous strengthening and toughening of polymer are frequently necessary but very challenging in many cases. In this work, we propose a new concept of nanoconcrete welding polymer chains, where mesoporous CaCO3 (mCaCO3) nanoconcretes which are composed of amorphous and nanocrystalline phases are developed to powerfully weld polymer chains through siphoning-induced occlusion, hydration-driven crystallization and dehydration-driven compression of nanoconcretes. The mCaCO3 nanoconcrete welding technology is verified to be able to remarkably augment strength, toughness and anti-fatigue performances of a model polymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-based porous membrane. Mechanistically, we have revealed polymer-occluded nanocrystal structure and welding-derived microstress which is much stronger than interfacial Van der Waals force, thus efficiently preventing the generation of microcracks and repairing initial microcracks by microcracks-induced hydration, crystallization and polymer welding of mCaCO3 nanoconcretes. Constructed porous membrane is used as wound dressing, exhibiting a special nanoplates-constructed surface topography as well as a porous structure with plentiful oriented, aligned and opened pore channels, improved hydrophilicity, water vapor permeability, anti-bacterial and cell adherence, in support of wound healing and skin structural/functional repairing. The proposed nanoconcrete-welding-polymer strategy breaks a new pathway for improving the mechanical performances of polymers.

Modeling of thermal processes in laser welding of polymers

The Paton Welding Journal, 2021, №11. International Scientific-Technical and Production Journal «The Paton Welding Journal» «The Paton Welding Journal» has been published monthly since 2000 in English, ISSN 0957-798X. «The Paton Welding Journal» is a cover-to-cover English translation of the «Avtomaticheskaya Svarka» (Automatic Welding) journal. The «Avtomaticheskaya Svarka» journal has been published monthly since 1948 in Russian, ISSN 005-111X.