This manuscript aims to study the effects of drilling factors on the thermal-mechanical properties and delamination experimentally during the drilling of glass fiber reinforced polymer (GFRP). Drilling studies were carried out using a CNC machine under dry cutting conditions by 6 mm diameter with different point angles of ∅ = 100°, 118°, and 140°. The drill spindle speed (400, 800, 1600 rpm), feed (0.025, 0.05, 0.1, 0.2 mm/r), and sample thickness (2.6, 5.3, and 7.7 mm) are considered in the analysis. Heat affected zone (HAZ) generated by drilling was measured using a thermal infrared camera and two K-thermocouples installed in the internal coolant holes of the drill. Therefore, two setups were used; the first is with a rotating drill and fixed specimen holder, and the second is with a rotating holder and fixed drill bit. To measure thrust force/torque through drilling, the Kistler dynamometer model 9272 was utilized. Pull-in and push-out delamination were evaluated based on the image analyzed by an AutoCAD technique. The regression models and multivariable regression analysis were developed to find relations between the drilling factors and responses. The results illustrate the significant relations between drilling factors and drilling responses such as thrust force, delamination, and heat affect zone. It was observed that the thrust force is more inspired by feed; however, the speed effect is more trivial and marginal on the thrust force. All machining parameters have a significant effect on the measured temperature, and the largest contribution is of the laminate thickness (33.14%), followed by speed and feed (29.00% and 15.10%, respectively), ended by the lowest contribution of the drill point angle (11.85%).

https://www.mdpi.com/2073-4360/13/11/1884/pdf

Thermo-Mechanical and Delamination Properties in Drilling GFRP Composites by Various Drill Angles.

Plastics materials are nowadays used in many structural applications for the substitution of metals with respect to weight reduction. In order to utilize the high freedom of design and the light-weight potential of plastics materials in crash-relevant structural parts, so-called hybrid composites which combine the high rigidity and strength of steel with the advantages of plastics materials are investigated in the outlined research. Thereby, the joining of both materials as well as the design by means of numerical methods such as the finite element analysis (FEA) are challenges which have to be met. A new approach in joining is based on the modified arc welding process where metal pin structures are formed in one working step and subsequently welded onto the surface. The pins are formed with ball-shaped, cylindrical or spiky ends and produced directly from the welding wire without requiring additional pre-fabricated components such as studs or similar. This allows the small-scale surface structuring of metal components that can be adapted optimally for a form fit on the respective plastics structure. Subsequently, injection molding is used for the application of the plastics material onto the pin-structured metal part in order to generate a positive fit between metal and plastics in an intrinsic joining process. An additional joining process, which is carried out after injection molding, is not required. Within the framework of the research presented, comprehensive mechanical tests are presented to illustrate the suitability of pin-structured metal-hybrid composites in crash applications. In comparison to structures which are in particular exposed to static loads and therefore designed to exhibit maximum component strength, crash applications are designed to fail in a continuous process to achieve maximum energy consumption. The outlined research illustrates the enhanced failure behavior of pin-structured plastics/metal-hybrid composites and the increased energy consumption under impact loading. Moreover, a comparison between pin structuring and laser structuring with regard to the obtainable mechanical properties under impact loading is given. Concluding, the current potential and weak points in the simulation of plastics/metal-hybrid structures using FEA is presented and discussed.

Analysis and specification of the crash behaviour of plastics/metal-hybrid composites by experimental and numerical methods

Fabrication processes of metal-fiber reinforced polymer hybrid components: a review

This article presents a comprehensive thermomechanical analysis and failure assessment in the drilling of glass fiber-reinforced polymer (GFRP) composites with different thicknesses using a CNC machine and cemented carbide drill with a diameter of 6 mm and point angles of ϕ = 118°. The temperature distribution through drilling was measured using two techniques. The first technique was based on contactless measurements using an IR Fluke camera. The second was based on contact measurements using two thermocouples inserted inside the drill bit. A Kistler dynamometer was used to measure the cutting forces. The delamination factors at the hole exit and hole entry were quantified by using the image processing technique. Multi-variable regression analysis and surface plots were performed to illustrate the significant coefficients and contribution of the machining variables (i.e., feed, speed, and laminate thickness) on machinability parameters (i.e., the thrust force, torque, temperatures, and delamination). It is concluded that the cutting time, as a function of machining variables, has significant control over the induced temperature and, thus, the force, torque, and delamination factor in drilling GFRP composites. The maximum temperature recorded by the IR camera is lower than that of the instrumented drill because the IR camera cannot directly measure the tool–work interaction zone during the drilling process. At the same cutting condition, it is observed that by increasing the thickness of the specimen, the temperature increased. Increasing the thickness from 2.6 to 7.7 had a significant effect on the heat distribution of the HAZ. At a smaller thickness, increasing the cutting speed from 400 to 1600 rpm decreased the maximum thrust force by 15%. The push-out delaminations of the GFRP laminate were accompanied by edge chipping, spalling, and uncut fibers, which were higher than those of the peel-up delaminations.

https://www.mdpi.com/2073-4360/13/14/2246/pdf

Heat-Affected Zone and Mechanical Analysis of GFRP Composites with Different Thicknesses in Drilling Processes.

This paper aims to optimize the machining parameters of the drilling process of woven-glass-fiber reinforced epoxy (WGFRE) composites. It will focus on modeling and optimizing drill spindle speed and feed with different laminate thicknesses, with respect to torque and delamination factor. The response surface analysis and artificial neural networks are utilized to model and evaluate the effect of control parameters and their interaction on the drilling process outcomes. The particle swarm optimization algorithm is used to improve the ANN training, to increase its performance in prediction. The optimization method of desirability, based on RSM, is applied to validate the optimal combination of control factors, in the space of the study. The influences of the control parameters on the drilling process outcomes are discussed in detail. The optimal machining parameters were 0.025 mm/r and 1600 rpm for feed and spindle speed, respectively, with a GFRE laminate of 5.4 mm thickness. The RSM and ANN–PSO models applied to predict the drilling-process parameters showed a very high agreement with the experimental data.

/pdf/drilling-process-of-gfrp-composites-modeling-and-3f1miuav.pdf

Drilling Process of GFRP Composites: Modeling and Optimization Using Hybrid ANN

Innovative joining technology for the production of hybrid components from FRP and metals

Fiber-reinforced plastics (FRP) are increasingly used in modern industry. They offer numerous advantages in comparison to traditional materials. However, they cannot meet all requirements, which is why it is necessary to join FRP to a metallic base structure in most cases. Existing joining techniques cannot fulfill the demands of a fiber-fair joining technique that does not damage the fibers and can transfer applied forces into underlying laminate layers on the one hand but also provides a ductile failure behavior that is detectable with an integrated sensor on the other hand. An innovative, modified arc welding process offers a way to create small-scale pin structures that work as micro shear connectors without damaging the fibers of the composite, but ensure a multi-step failure behavior. This particular failure behavior enables the use of an integrated sensor system, which monitors the joint.

„Smart Multi Material Joint" – Hybrid Joint of Steel and FRP

The invention relates to a method for producing a component (1, 2) consisting of a fibre-reinforced plastic and prepared for the welding of a metal component (4), which comprises at least one fibre element (2) impregnated with a plastic matrix, wherein at least some portions of at least one metal joining partner (1) are integrated into a fibre element, a first section of the joining partner (1) being surrounded by the fibres of the fibre element (2) such that it is in contact therewith, and a second section of the joining partner (1) projecting over a surface of the fibre element (2) or lying at least in the surface, the joining partner (1) being connected, by at least some portions, to the liquid and hardening plastic matrix, especially at least by the first section. The invention also relates to a metal joining partner for integrating into a component consisting of fibre-reinforced plastic in order to weld a metal component (4) thereto.

Method for producing a component consisting of a fibre-reinforced plastic and prepared for the welding of a metal component, and metal joining partner therefor

Fiber reinforced plastic (FRP) materials are often used in combination with other materials. Hence, it is necessary to join FRP with other, mostly metallic structures in a material-appropriate way. The joining technique is therefore a key technology for exploiting the lightweight potential of fiberreinforced plastics in multi-material structures. A new hybrid joining method allows the combination of adhesive bonding and form-fitting elements in order to join FRP and metallic components. The adhesive bond is achieved by the matrix resin itself, which is required to fabricate the FRP. The form-fit is realized by small scale pin structures which are welded upon the metallic base material and are afterwards embedded into the FRP. Combining the two principles of adhesive bonding and form-fitting elements causes a multi-step failure behavior, which allows sensor-based monitoring of the joining zone. The adhesive failure can be detected at an early stage in order to prevent critical component failure.

Sensor-Monitored Multi-Material Joint made ofFiber-Reinforced Plastic (FRP) and Metal-"Smart Multi-Material Joint"

Parts or Components made of fibre-reinforced plastics (FRP) are often connected to metallic components. However, joining FRP to metals is currently a particular challenge. As a rule, such connections are currently glued and/or mechanically joined. Recent research has focused on innovative hybrid connections, which are reinforced by small-scale 3D structures in the z-direction of the component axis. Although different approaches are being followed for the production of FRP/metal hybrids, there is still a great need for a joining process that meets the technical and economic challenges in this context.

Jens Lotte

Papers

Innovative joining technology for the production of hybrid components from FRP and metals

„Smart Multi Material Joint" – Hybrid Joint of Steel and FRP

Method for producing a component consisting of a fibre-reinforced plastic and prepared for the welding of a metal component, and metal joining partner therefor

Sensor-Monitored Multi-Material Joint made ofFiber-Reinforced Plastic (FRP) and Metal-"Smart Multi-Material Joint"

Resistance Welding of FRP to Steel Components in High-Volume-Production