Joining Of Polymers Research Articles

Ultrasonic Assisted Thermal Direct Joining of Thermoplastic Composites and Aluminum for Multi Material Design

The trend towards multi material design is strongly driven by improved functionality and decreased total weight of hybrid parts. Conventional joining techniques for metals and polymers usually require a complex process and are thus time consuming and expensive. A novel technique addressing these shortcomings is ultrasonic assisted thermal direct joining of metals and thermoplastic polymers. The metallic joining partner is laser pre-treated to generate a specific surface topology. The subsequent joining process is a combination of thermal direct joining and ultrasonic joining. This hybrid joining process results in short cycle times, and the maximum heat input is localized to the joining area. The joint performance was measured by lap shear tests, resulting in strength values exceeding 18 MPa, while the duration of the joining process was about 1.5 seconds. The relevant joining parameters were identified and a process window was obtained. The results indicate that there may be an optimum energy range for successful joining. An appropriate energy map may allow a deeper understanding of the process and enables prediction of process windows for various material combinations.

Atomically locked interfaces of metal (Aluminum) and polymer (Polypropylene) using mechanical friction

Joining different parts is one of the crucial components of designing/engineering of materials. Presently, the current energy efficient low weight automotive and aerospace components consist of a different class of materials, such as metals, polymers, ceramics, etc. Joining these components remains a challenge. Here, we demonstrate metal (aluminum) and polymer (Polypropylene, pp) joining using mechanical friction. The detailed characterization clearly demonstrates that atomically locked interfaces are formed in such joining and no chemical bonds are formed during the joining. Also, a waterproof and strong interface is formed in such a process. Fully atomistic molecular dynamics simulations were also carried out in order to further gain insights on the joining process.

Effects of molding conditions on injection molded direct joining under various surface fine-structuring

Injection molded direct joining (IMDJ), a metal–polymer joining technique, consists of two basic processes: surface fine-structuring and injection insert molding. During molding, melt polymer infiltrates the surface fine structure on a metal workpiece that is initially placed in a mold; subsequently, the metal workpiece is joined with an injection-molded polymer. This study investigates the effects of molding conditions on the joining strength of IMDJ using two different surface types of fine-structured metal workpieces. The primary difference in the fine structures is size; one has a nanometer scale and the other a micrometer scale. Using two types of metal workpieces, we perform injection molding experiments with six different injection speeds and two different flowing shapes of mold. The results of the joining strength evaluated by tensile shear tests show that the speed–strength correlation depends on the fine structure. To explain this dependency on fine structure size, we assume the infiltration of melt polymer differs between the nanometer scale fine structure and the micrometer scale fine structure. The results also show that the flowing shape affects the joining strength. To confirm the effect of the shape, we measure the time-course variations of the temperature and pressure in the mold, and observe the fiber distribution in the molded polymer parts using X-ray micro computed tomography.

Melt processing for enhancing compatibility of aluminum-reinforced acrylonitrile–butadiene–styrene and polyamide 6 for friction welding applications

Friction welding is one of the established solid-state welding techniques with wide aerospace, automobile and industrial applications. For thermoplastic components, it is extremely difficult to join the dissimilar material [e.g., acrylonitrile butadiene styrene (ABS) to polyamide (PA) 6] with friction welding process. For such joining/welding applications, there is a need of strong material compatibility/processing technique. This study highlights melt flow index (MFI) as one of the rheological/flow properties which can be used as controlling parameter for dissimilar thermoplastic friction welding. The twin screw extrusion and fused deposition modeling as melt processing techniques have been used for processing/fabrication of functional/non-functional surfaces/prototypes. The results of study suggest that ABS with 15% Al metal powder by weight (ABS-15Al) and PA6 with 50% Al metal powder by weight (PA6-50Al) have a similar range of MFI as 11.57 and 11.97 g/10 min, respectively (which confirmed the compatibility for joining of both polymers by friction welding). The results are supported by photo-micrographs and mechanical testing.

Atomistic Modeling of the Formation of a Thermoset/Thermoplastic Interphase during Co-Curing

Co-curing of a thermoset epoxy matrix in contact with thermoplastic foils is an essential step in damage-free joining of polymers or polymer-based composites. We present results of all-atom molecular dynamics simulations that shed light onto the resulting hybrid interface. Using poly(vinylidene difluoride) (PVDF) and a multicomponent epoxy resin as model systems, we have developed a computational co-curing protocol that ensures both adequate structural representation and mobility of the PVDF chains and a realistic cross-linking conversion and topology of the epoxy resin. As a result, we reveal that mutually entangled loops of thermoplastic chains and resin strands form across the interface within the extended interphase region separating the two polymers. In tensile stress simulations we find that these loops contribute to a surprisingly large interfacial strength. In the absence of extrinsic defects, failures nucleate at the PVDF side of the interphase and propagate via a chain-pullout mechanism characteristic of semi-interpenetrating polymer networks involving thermoplastic materials.

An artificial neural network model for predicting joint performance in ultrasonic welding of composites

Ultrasonic welding is a robust and cost-effective joining method. It can be applied to joining of metals, polymers and composites. Several approaches have been used in the identification of the relationships between input parameters of the ultrasonic welding (e.g., welding energy, time) and the joint strength, including experimental methods and finite element based prediction. Both these two methods are accurate but require long lead time for model development. The empirically identified relationships may be very complex and the accuracy of prediction is sensitive to the variations of welding conditions. Hence, a more robust and intelligent method is needed for predicting the joint strength. In this paper, an artificial neural network (ANN) method is proposed for predicting the joint strength in ultrasonic welding of polymer composites based on experiments. The input parameters are welding energy, plunging speed, trigger force, surface condition, and annealing temperature. The output parameter is the maximum loading force in a lap shear test. A supervised algorithm of training the network is applied because the equations governing the process are very complex and the conditions of the welding are continuously changing. The trained network is used for determining the quantitative relationship between significant inputs and output parameters as well as for predicting the performance for other inputs which are not experimentally tested or modeled, but fit in the range of training. The ultrasonic welding ANN is a dynamic model which can be continuously trained with new cases, serving as a flexible and cost-effective tool for designing welding procedure.

An experimental study on mechanical properties of a novel hybrid metal–polymer joining technology based on a reaction between isocyanate and hydroxyl groups

This study developed a novel joining technology to produce a hybrid polymer–metal material. The technology is based on a reaction between isocyanate groups (NCO) in a solution and hydroxyl groups (OH) on a metal surface. This technology has some advantages compared with other joining methods, such as lack of stress concentration and mechanical and thermal residual stress in the metal structure and very low cost. The effects of different process parameters including the NCO/OH ratio, mould temperature, and polymer melt temperature on the strength of adhesion were investigated employing single lap shear tests. Also, the mechanical behaviour of the hybrid under tensile load was investigated using uniaxial tensile tests. The results showed that increasing mould temperature or melt temperature reduces adhesion strength. Moreover, adhesion strength reaches a peak and then decreases by increasing the NCO/OH ratio. Most importantly, tensile test results showed that the new material postpones the necking phenomena of the stainless steel, and increases the deformation of stainless steel before fracturing by 16%. It is an important result in metal forming that stainless steel can withstand more deformation in its plastic regime.

Improving energy efficiency in friction assisted joining of metals and polymers

The influence of the clamping frame material in Friction Assisted Joining of polymer-metal sheets is investigated. An experimental campaign was conducted by varying the clamping frame material (steel and wood) and the heating time. The process was applied to join Al-Mg aluminum alloy and Polyvinyl Chloride sheets. Thermal analysis and energy measurements were conducted during the process. The morphology, fracture surface and strength of the joints were analyzed. The clamping frame made of wood enabled different advantages to be achieved, including reduction of the energy loss towards the clamping frame, faster heating of the materials being joined, and more uniform distribution of the temperature over the joining area, which resulted in increased mechanical strength. Under optimal conditions the joint efficiency approached 97%.

Uniqueness of weak solutions to a prion equation with polymer joining

Abstract We consider a model for prion proliferation that includes prion polymerization, polymer splitting, and polymer joining. The model consists of an ordinary differential equation for the prion monomers and a hyperbolic nonlinear differential equation with integral terms for the prion polymers and was shown to possess global weak solutions for unbounded reaction rates [11]. Here we prove the uniqueness of weak solutions.

Investigating the suitability of roughness parameters to assess the bond strength of polymer-metal hybrid structures with mechanical adhesion

Abstract The joining of distinct incompatible materials, like metals and polymers or fiber-reinforced polymers, is gaining in importance, especially for lightweight applications. Here, it is advantageous if the materials can be joined during the manufacturing of the hybrid component. Besides conventional technologies, like over-molding or the use of adhesive bonds, the use of micro structures is a promising approach for in-mold assembly. However, the characterization of these micro structures to assess the bond strength is difficult, especially for a load perpendicular to the joining surface. This paper deals with the assessment of the bond strength of polymer-metal hybrid structures with micro-structured metal inserts by the use of roughness parameters. The micro structures were produced by electrochemical treatments.

Radiation stable, hybrid, chemical vapor infiltration/preceramic polymer joining of silicon carbide components

This paper reports on a nuclear-grade joining material for bonding of silicon carbide-based components. The joint material is fabricated via a hybrid preceramic polymer, chemical vapor infiltration process. The joint is comprised entirely of β-SiC and results in excellent mechanical and permeability performance. The joint strength, composition, and microstructure have been characterized before and after irradiation to 4.5 dpa at 730 °C in the High Flux Isotope Reactor. The hybrid preceramic polymer-chemical vapor infiltrated joint exhibited complete retention of shear strength and no evidence of microstructural evolution or damage was detected following irradiation.

Lightweight joining of polymer and polymer-metal sheets by sheet-bulk forming

This paper presents an environmentally friendly joining process based on sheet-bulk plastic deformation to connect two polymer (or a polymer and a metal) sheets perpendicular to one another. The methodology draws from material characterization and finite element modelling, using an extension of the flow formulation to pressure-sensitive polymers, to experimentation in a laboratory tool setup and destructive testing of the produced joints.The results allow characterization of the joinability window as a function of the major operating parameters and demonstrate the feasibility of the process to produce polymer and hybrid joints (polymer-metal) at room temperature. A variant to the proposed process is disclosed to handle situations where the elastic recovery of the polymer sheets needs to be better controlled. The overall content of the paper is an extension of a previous work of the authors for fixing longitudinally in position two metal sheets perpendicular to one another, and seems promising for the manufacture of lightweight joints made from polymers or polymers and metals.

Ultrasonic dissimilar joining of aluminum alloy and polymer with the composite material of ABS polymer doping carbonized rice husk

The metal housing is typically jointed with plastic fittings by conventional gluing method or embedding injection molding to produce this type of devices. We propose to improve this new technique with more practical approach. In plastic-aluminum substrate dissimilar joining, the 5052 aluminum plate coarsening process was performed to increase the porosity of the permeable dissimilar phase. The ABS polymer plus carbonized rice husk powder was later induced or deposited on the microstructure to improve the bonding effect. The plastic -aluminum substrate dissimilar joining is completed by the final step of ultrasonic welding. The finished substrate will be tested on the properties of tensile strength to ensure its quality. According to the simulation analysis and measuring results, the maximum temperature between the interface of ABS polymer and 5052 aluminum alloy is about 400~450 °C during ultrasonic welding, which can make the surface of ABS polymer to be melted. Furthermore, after drilling micro-hole array and covering ABS plus carbonized rice husk powder, the 5052 aluminum alloy shows better joining effect with ABS polymer sheet by ultrasonic welding. This improved approach does not require mold or injection molding machinery to produce the high quality plastic -aluminum bonding parts.

Existence of global classical and weak solutions to a prion equation with polymer joining

We consider a nonlinear integro-differential equation for prion proliferation that includes prion polymerization, polymer splitting, and polymer joining. The equation can be written as a quasilinear Cauchy problem. For bounded reaction rates we prove global existence and uniqueness of classical solutions by means of evolution operator theory. We also prove global existence of weak solutions for unbounded reaction rates by a compactness argument.

Chemical Sculpturing of Al Micro-Particles for Polymer Composites and Universal Polymer-Polymer Joints

Composite materials attract more and more attention due to their unique properties in many fields. For certain applications metal particle-polymer composites are very attractive, where e.g. lightweight heat-conductive composites are needed. For particle-polymer composites the typical problem is the deterioration of the mechanical properties of the polymer matrix due to poor adhesion at the polymer-metal particle interface. Our approach solves this problem by generating a mechanical interlocking surface structure on the metal particle surface via wet chemical etching which we call sculpturing. In this work commercially available granular Al micro-particles with a typical size distribution between 200 - 800 µm and a purity of 99.7 % is used. These Al particles are structured in an optimized aqueous HCl based electrolyte. The key idea is to balance the passivation and dissolution of the metal surface in such a way that the desired interlocking structures form. Similar to HNO3-HF based Si etchants, the employed electrolyte makes use of in-situ formed reaction products controlling the structuring homogeneity and reaction speed. Figure 1a) provides a top view on Al particles sculptured in such way with a magnification view in Fig. 1b). The sculptured surface structure consists of a multitude of rectangular structures with flat faces in a step-like arrangement or as free-standing hooks. These rectangular structures vary in size and are tilted towards each other depending on the crystal orientation. The EDX analysis confirms that the surface of these Al micro-particles after sculpturing is covered only by a native oxide layer. By adjusting the chemical fabrication process the Al micro-particles could be fully or partially sculptured. Correspondingly, the Al micro-particles showed a change in their optical properties depending on the etching duration. Fully-sculptured Al micro-particles are dark gray in color, partially structured ones are light-gray, and the untreated ones are silver colored. With these sculptured Al micro-particles polymer composites can be formed as shown in Fig. 1c. Here, a densely packed polythiourethane (PTU)-sculptured Al particle composite is formed in the shape of a dog bone. Tensile test results show that the addition of sculptured particles results in a strongly increased Young’s modulus and reaching at least the maximum tensile strength of the pure polymer, unlike in case of the addition of untreated Al micro-particles. In case of polydimethylsiloxane (PDMS) which is well-known for its poor adhesion to metals, polymers and ceramics, the effect on the increase of Young’s modulus is even far more pronounced as well as a tremendous increase in the maximum tensile strength. The fracture surfaces of all sculptured Al micro-particle-polymer composites showed always cohesive failure where even the particles themselves are torn apart, which is the best reachable adhesion strength. Another very important application for sculptured Al micro-particles could be adhesive-free joining of immiscible polymers like ethylene-vinyl acetate (EVA) and polyoximethylen (POM) or other low surface energy polymers. Here, the sculptured micro-particles are partially imprinted into the thermally-softened POM surface and then joined with the softened EVA. Owing to the hook and step structures of the sculptured particles a robust connection between the Al micro-particles and any polymer matrix is obtained. No matter how the sculptured particles are partially imprinted in the polymer surface, they stick to it and hinder delamination. This is impressively shown via tensile testing, where only cohesive failure within the EVA component is found, while the direct joint without particles and via untreated particles fail adhesively directly at the POM-EVA interface. Fig. 1: SEM top view on chemically sculptured a) Al micro-particles, b) in high magnification of the structured Al micro-particle surface and c) Al micro-particle filled PTU composite in the shape of dog bone. Figure 1

Chemical Sculpturing of Al Micro-Particles for Polymer Composites and Universal Polymer-Polymer Joints

This paper presents a practical method to produce Al micro-particles via anisotropic wet chemical etching with a particle surface structure perfectly suited for mechanical interlocking with polymers. This particle surface structure consists of a multitude of cuboid features forming step-like structures with hooks forming tight connections to various polymers. These composites formed from these sculptured Al micro-particles and medical-grade PDMS show a drastically increased Young’s modulus as well as a 34% increased ultimate tensile strength compared to the pure PDMS. Additionally, the tight, adhesive-free joining of immiscible polymers via these sculptured Al micro-particles is presented exemplarily for POM/ EVA and POM/ LDPE.

Experimental investigations for mechanical and metallurgical properties of friction stir welded recycled dissimilar polymer materials with metal powder reinforcement

Abstract Friction stir welding (FSW) is one of the established processes for joining of polymers, metals and alloys. In the recent past many applications of this process have been explored. But hitherto very less has been reported on the friction stir welded joints with dissimilar polymer/plastic (DP) materials (with metal powder reinforcement). In the present work investigations have been made to perform FSW of two DP materials namely: low density polyethylene (LDPE) and high density polyethylene (HDPE). The present study of FSW for DP (LDPE and HDPE) has been performed on vertical milling machine. The effect of FSW process parameters on mechanical and metallurgical properties (such as: Shore D hardness, tensile strength and porosity of weld joint) has been investigated for structural engineering applications. The results are supported by photomicrographs.

Effect of Double Shoulder Tool Rotational Speed on Thermo-Physical Characteristics of Friction Stir Welded 16mm Thick Nylon6

Friction stir welding (FSW) of polymers is relatively a new concept among modern polymer joining techniques. This study demonstrates the applicability of FSW on 16mm thick nylon-6 plates at constant welding rate of 25mm/min and varying rotational speed between 300 to 1000RPM. A special designed tool was fabricated which has double shoulder and right-hand threaded pin profile. It has shown excellent results at relatively lower rotation speeds. Visual inspection and microstructural examination of cross sections showed that the cavities and tunnel defects appeared only at higher rotational speeds. A linear relationship was observed between temperature and rotation speed.

Shoulder design developments for FSW lap joints of dissimilar polymers

This paper describes the process of developing a stationary FSW tool for welding thin plates of dissimilar polymers. Previous FSW research seems to be still far from the type of systematic engineering approach that leads to consistent results, in particular for polymeric materials and especially for lap joining of polymers. This study is focused on the development of welding tools, aiming at sound and robust friction stir welding of dissimilar polymeric materials in lap joint configuration. Different materials and geometries have been tested in order to analyse quality of the welds and appearance. It has been verified that stationary shoulders made out of polymer materials give the best result. The welds produced with this tool improved the welds surface quality and strength significantly. The use of the proposed tool showed to improve the stability in the axial force magnitude during the welding procedure in comparison with a conventional FSW tool.

Relation of joint strength and polymer molecular structure in laser assisted metal and polymer joining

The study of laser assisted metal and polymer joining has been conducted to identify the mechanism of the hybrid joint. The bonding mechanism has been revealed to be due to the expansion pressure of pyrolysis fragments. Previous research has dealt with superficial factors without consideration of the polymer thermal decomposition phenomenon, which is the major factor of the joining strength. With experiments and simple chemical analysis for simple structured polymers this paper presents the quantitative relationship among the joint strength, the expansion pressure, the gas fragment composition, and the molecular structure. To verify the relation of the joint strength and the polymer molecular structure, the results were analysed and compared with the results of previous studies. Correlation of the quantified joint strength and the quantified expansion pressure and the monomer yield is also defined. The results confirm that the joint strength is correlated with the polymer structure.