Juan Carlos Campos Rubio

Delamination in High Speed Drilling of Carbon Fiber Reinforced Plastic (CFRP)

When holes are produced on carbon fiber reinforced plastic (CFRP) laminates, in particular for the aerospace and automotive industries, special attention should be focused on as the machining parameters influencing the damage. In this study special drill bits and high-speed cutting (HSC) are used and compared with conventional cutting conditions. The digital image of the damage was conducted in order to analyze the delamination when two composite boards were drilled simultaneously. The experimental results indicated that the use of HSC in drilling is suitable to reduce the damages produced in CFRP with material removal rate increasing considerably.

Statistical design of polymeric composites reinforced with banana fibres and silica microparticles

The study describes a design of experiment analysis performed on hybrid polymeric composites reinforced with unidirectional banana fibres and silica microparticles. Maleic anhydride was also evaluated as a chemical additive to improve the adhesion between phases. A full factorial design (2231) and the analyses of variance were performed to identify the significance of the microstructure constituents against different mechanical and physical properties in a total population of 120 biocomposites samples. The microstructure parameters considered were fibre volume fraction (30% and 50%), silica addition (0%, 20 wt% and 33 wt%) and maleic anhydride addition (0% and 2 wt%). The mechanical and physical properties of the composite considered as factorial and analyses of variance responses were the apparent density, apparent porosity, water absorption, modulus of elasticity and mechanical strength under tensile and flexural loading. The design of experiment analysis has shown that the volume fraction of the fibres significantly affects all responses, with the composite made from 30% of banana fibres exhibiting superior mechanical strength and modulus of elasticity. While the addition of silica has featured a statistically noticeable contribution to the porosity and the water absorption, the presence of the particles did not provide any significant enhancement to the composites mechanical strength. Maleic anhydride showed a significant contribution to the apparent density, water absorption and flexural modulus, not improving the adhesion between phases, with a consequent decrease of the Young’s modulus and increase of the water absorption within the composites.

Delamination assessment after drilling medium-density fibreboard (MDF) by digital image analysis

Abstract Medium-density fibreboard (MDF) is a wood-based composite made from lignocellulosic fibres bound together by synthetic resin. It has become one of the most important materials for furniture manufacture and the building industry. This work investigates the defects observed at the entrance and exit sides of drilled MDF plates and establishes a relationship between the damage features and machining parameters. A novel delamination factor is used to characterise defects in the drilled hole using digital image analysis. The results show that higher cutting speeds should be used to obtain the greater material removal rates associated with minimal delamination.

Micromechanical analysis of hybrid composites reinforced with unidirectional natural fibres, silica microparticles and maleic anhydride

The work describes the analytical and experimental characterisation of a class of polymeric composites made from epoxy matrix reinforced with unidirectional natural sisal and banana fibres with silica microparticles and maleic anhydride fabricated by manual moulding. The analytical models, ROM rule of mixtures and Halpin-Tsai approach, have been used in conjunction with a Design of Experiments (DOE) analysis from tensile tests carried out on 24 different composites architectures. The following experimental factors were analyzed in this work: type of fibres (sisal and banana fibres), volume fraction of fibres (30% and 50%) and modified matrix phase by adding silica microparticles (0%wt, 20%wt and 33%wt) and maleic anhydride (0%wt and 2%wt). The ROM approach has shown a general good agreement with the experimental data for composites manufactured with 30%vol of natural fibres, which can be attributed to the strong adhesion found between the phases. On the opposite, the semi empirical model proposed by Halpin and Tsai has shown greater fidelity with composites manufactured from 50%vol of natural fibres, which exhibit a weak interfacial bonding. The addition of microsilica and maleic anhydride in the system did not enhance the adhesion between the phases as expected.

Machining behaviour of three high-performance engineering plastics

Polymeric materials have been widely used to replace traditional metallic materials due to their high specific elastic properties. Even though polymeric materials can be produced as near net shapes, machining is still required to make the assembling of the final products. The selection of tool and cutting conditions is very important to machine plastics because of the high ductility and low melting point of the materials. In this study, the machining behaviour of high-performance engineering polymers, such as ultra-high-molecular-weight polyethylene, polyoxymethylene and polytetrafluoroethylene, has been investigated using a full-factorial design (design of experiment). The effect of the factors such as feed speed, spindle speed and drill point angle was identified for each of the response variables (circularity error, surface roughness (Ra) and thrust force (Ff)). The drilling mechanism was substantially affected by the physical and mechanical properties of the polymers. Different cutting set-up conditions were able to optimize the responses. The polytetrafluoroethylene exhibited better results, achieving lower circularity error, surface roughness and thrust force. In the opposite manner, the ultra-high-molecular-weight polyethylene exhibited a rough topography at low feed rate and spindle speed levels.

Experimental studies on hole quality and machinability characteristics in drilling of unreinforced and reinforced polyamides

In this study, experimental studies on hole quality and machinability in drilling of unreinforced polyamide (PA6) and reinforced polyamide with 30% of glass fibers (PA66-GF30) using cemented carbide (K20) tool have been carried out. The experiments have been planned as per full factorial design of experiments. The effects of spindle speed, feed rate, and point angle on hole quality such as hole diameter and circularity error; the machinability characteristics such as thrust force and specific cutting coefficient have been analyzed by developing response surface methodology based second-order mathematical models. The parametric analysis shows that the quality of holes can be improved by proper selection of cutting parameters. The analysis also indicates the influence of reinforced fiber on proposed machinability characteristics during drilling of polyamides.

Micropositioning device using solid state actuators for diamond turning machines: a preliminary experiment

Ultra-precision machining to sub-micrometer depths is shown to be a threshold area of work requiring a combination of the best of materials, sensors, positioning devices and control strategies. In ultra-precision design, it is extremely likely that there will be few design options for selection. In the case of ultra fine tool feed, the piezoelectric actuator is a potential choice. Currently, European and Japanese tool manufacturers are investigating magnetostrictive actuators for this purpose. Both piezoelectric and magnetostrictive materials suffer from hysteresis type non-linearity, so that the output of such systems depends upon the previous input, and absolute positioning is only achievable with the aid of feedback control. This work compares several modern control techniques for the positioning of a tool post for ultra- precision machining of brittle materials (in the nanometric range), e.g., lead-lag filter, PI+D, PID+feedforward, and fuzzy logic/neural network. The performance of the micropositioning device using both piezoelectric and magnetostrictive (solid-state) actuators are assessed by means of simulation techniques. The performance results are compared with results obtained by other authors.

Investigation on the Effect of Drill Geometry and Pilot Holes on Thrust Force and Burr Height When Drilling an Aluminium/PE Sandwich Material

Composite materials are widely employed in the naval, aerospace and transportation industries owing to the combination of being lightweight and having a high modulus of elasticity, strength and stiffness. Drilling is an operation generally used in composite materials to assemble the final product. Damages such as the burr at the drill entrance and exit, geometric deviations and delamination are typically found in composites subjected to drilling. Drills with special geometries and pilot holes are alternatives used to improve hole quality as well as to increase tool life. The present study is focused on the drilling of a sandwich composite material (two external aluminum plates bound to a polyethylene core). In order to minimize thrust force and burr height, the influence of drill geometry, the pilot hole and the cutting parameters was assessed. Thrust force and burr height values were collected and used to perform an analysis of variance. The results indicated that the tool and the cutting speed were the parameters with more weight on the thrust force and for burr height they were the tool and the interaction between tool and feed. The results indicated that drilling with a pilot hole of Ø4 mm exhibited the best performance with regard to thrust force but facilitated plastic deformation, thus leading to the elevation of burr height, while the lowest burr height was obtained using the Brad and Spur drill geometry.

Machinability Evaluation in Hard Milling of AISI D2 Steel

Milling of hardened steel components provides considerable benefits in terms of reduced manufacturing cost and time compared to traditional machining. Temperature variation in milling is an important factor affecting the wear of cutting tools. The poor selection of milling parameters may cause excessive tool wear and increased work surface roughness. Hence, there is a need to study the machinability aspects during milling of hardened steel components. In the present work, influence of cutting speed, feed rate and radial depth of cut on milling temperature, surface roughness and cutting force during milling of AISI D2 steel has been investigated using response surface methodology (RSM) based models. From the parametric analysis, it is revealed that temperature increases linearly, whereas surface roughness increases non-linearly with cutting speed. However, for higher values of feed rate, an increased cutting speed considerably reduces the cutting force for specified depth of cut range. The present work also reveals that the selection of best cutting conditions is useful at the CAPP stage in the milling process particularly with tight tolerances.

The effect of silica microparticles and maleic anhydride on the physic-mechanical properties of epoxy matrix phase

Abstract Thermoset polymers, especially epoxy resin, have been applied in several industrial applications in which high stiffness and adhesive strength are demanded. On the other hand, epoxy resin is rather brittle and has poor fracture toughness. For this reason, the addition of fibres/particles into thermoset polymer can be used to enhance strength and toughness for several structural applications. This work investigated the addition of silica microparticles and maleic anhydride (as a coupling agent between the phases) into epoxy resin, which will be used as the matrix phase of hybrid biocomposites. A full factorial design was conducted to evaluate the effect of silica microparticles and chemical additive into the epoxy matrix under compressive loadings. Apparent density was also evaluated. Experimental factors such as weight fraction of silica microparticles (0, 20, and 33.3 wt%) and weight fraction of maleic anhydride (0 and 2 wt%) were investigated. The statistical analysis revealed that the main factors ‘chemical additive’ and ‘silica addition’ significantly affected the compressive modulus of the composites.