Luigi Nele

Effect of tool wear on cutting forces in the orthogonal cutting of unidirectional glass fibre-reinforced plastics

Abstract Orthogonal cutting tests were carried out on unidirectional glass fibre-reinforced plastic composites, holding the cutting direction parallel to the fibre direction. The tools were made of high speed steel, with rake angle α = 0°; two relief angles γ, namely 7° and 15°, were adopted. A very low cutting speed was utilized, in order to avoid thermal effects on both the tool and the work material. The experimental results show that, under the selected operating conditions, the tool wear essentially consists of a very rapid rounding of the tool nose (nose wear). The face wear evolution is practically independent of the relief angle, whereas the latter affects the flank wear rate, which is slightly lower for the higher γ value. Both the horizontal and the vertical cutting forces exhibit notable increases with tool wear. The force data are interpreted in the light of a previously presented model, aiming to predict cutting forces as a function of the cutting parameters. It is shown that the observed increase in the horizontal force can be simply attributed to the increase in the vertical force at the tool flank, whereas the chip-tool interaction forces occuring at the tool face seem to be unaffected by wear phenomena. Finally, a strict correlation is found between the flank wear and the recorded vertical force variations.

Experimental Characterization of an Innovative Glare® Fiber Reinforced Metal Laminate in Pin Bearing

An experimental investigation is performed on an innovative Glare® Fiber Reinforced Metal Laminate (FRML), which is produced at the Alenia Aerospazio (Italy), with the aim to characterize its strength and behaviour in the case of mechanical joints. Several specimens are fabricated by varying width and hole-to-edge distance and tested in pin-bearing way without lateral restraints, which is the most critical testing procedure in the simulation of mechanical joints. Specimens, after bearing stress, are analysed in both non-destructive and destructive ways. Non-destructive evaluation is performed by means of lock-in thermography; for a validation of this technique, phase images are compared to photomicrographs. Results prove that a remote infrared imaging system may be a valuable tool to monitor the material behaviour either during the manufacturing processes, or in service.

Pin-bearing strength of glass mat reinforced plastics

An experimental investigation was carried out, in order to find simple analytical methods for the prediction of pin-bearing strength of glass mat reinforced plastics fabricated by hand lay-up. The specimens tested exhibited different failure modes, consisting of net-tension, cleavage, and bearing, depending on the geometry adopted. The parameters affecting the bearing strength were the ratio of the specimen width to the hole diameter D, and the ratio of the edge distance to D. The maximum bearing strength was attained when a pure bearing failure happened. The latter was the only safe failure mode: after its occurrence, the joint was still able to support about 70% of its virgin strength. The experimental data obtained were used to assess a simple procedure for the calculation of the joint load carrying capacity, previously proposed. Since a large scatter was found in the bearing strength of the material, the data were analysed statistically, assuming a probability of failure varying according to a two-parameter Weibull distribution. An excellent agreement was found between the experimental results and the theoretical model. Similar conclusions were drawn applying the previous approach to the residual strength after bearing failure. A limited amount of tests was performed to verify the influence of possible damage induced during hole drilling on the bearing behaviour. It was found that a 20% decrease in bearing strength occurs when delamination is induced by inaccurate drilling. However, the residual bearing strength was substantially unaffected by the drilling damage.

Infrared thermography in the quality assurance of manufacturing systems

The present work will focus its attention on the aid provided by infrared thermography (IR) in the evolution of manufacturing towards the achievement of highest quality at the lowest price; which is to say: improve manufacturing processes and avoid waste of time. IR can be fruitfully exploited to monitor temperature variations in-process in temperature-dependent manufacturing processes. It is possible to control efficiency of cooling systems in-processes involving material shaping like extrusion and injection moulding. It is also possible to control the temperature rises which can affect the integrity of components and life of tools in material removal processes involving cut, mill, drill. IR is also attractive for non-destructive inspection of end products to assure quality. Experimental tests are carried out to control temperature rises during mill finish, to visualize material inhomogeneities linked to extrusion or injection moulding processes, inclusions of spurious materials during welding or bonding processes and to determine variations of adhesive thickness in metallic joints and composites. Results, presented and discussed here, prove the possibility of using IR as a tool of quality assurance of manufacturing systems.

Drilling Polymeric Matrix Composites

This chapter presents the basics of drilling of polymeric matrix composites (PMCs). PMCs are becoming widely used in the manufacturing of products where a high mechanical strength must be accompanied by a low weight. However, the machining of PMCs implies coping with problems that are not encountered when machining other materials. Drilling is a particularly critical operation for PMCs laminates because the large concentrated forces generated can lead to widespread damage. This damage causes aesthetic problems but, more importantly, may compromise the mechanical properties of the finished part.

Chemical and Irradiation Cross-Linking of Polyethylene. Technological Performance over Costs

Abstract The present article is concerned with the production of cross-linked low-density polyethylene. The aim is to gain information about costs/benefits of two cross-linking methods, which are the chemical through silane grafting and the electron-beam irradiation. These two methods were used at the Megarad firm (Italy) for cross-linking of low-density polyethylene, which was mainly used for electric cable insulation. The two cross-linking processes were examined by evaluating the performance of the end product and the production costs. The performance of the final product was assessed through experimental tests, which consisted in the evaluation of some peculiar properties of the material such as gel fraction, thermal modifications under heat fluxes, modulus of elasticity at 150°C, elongation parameters. Costs were analyzed by considering both direct and indirect costs. It seems that, notwithstanding the elevated costs of installation, the electron-beam irradiation method is preferable because it allows for a product of superior characteristics with the lowest production costs.

A new cost-saving vacuum infusion process for fiber-reinforced composites: Pulsed infusion

A new innovative infusion technology, pulsed infusion, has been developed for the manufacturing of fiber-reinforced thermoset-based composites. Pulsed infusion is a double-bag vacuum infusion process that is based on the use of a proper designed reusable pressure distributor and able to better control the vacuum pressure in pulsed way. Thus, the transverse resin flow through the dry fiber reinforcement is promoted and a better adhesion between the resin and the fibers is achieved. The new process allows to obtain laminates with the same fiber volume fraction and tensile properties of those produced by conventional infusion technologies. An average increase up to 9% for the flexural modulus and up to 24% for flexural strength has been assessed for pulse-manufactured composites compared to traditional vacuum infusion ones. Furthermore, due to a minor consumption of resin and the absence of the distribution net, pulse infusion provides a material cost-saving advantage around 19% and a significant waste reduction.

Mechanical Characteristics of Welded Joints of Aluminum Alloy 6061 T6 Formed by Arc and Friction Stir Welding

Butt welds formed by arc welding in inert gas with nonconsumable electrode (tungsten inert gas (TIG) welding) and by friction stir welding (FSW) from aluminum alloy AA6061 T6 are studied. Comparative analysis of the structures and mechanical properties of the welded joints is performed using the results of optical and electron microscopy, tensile tests, tests for residual bending ductility, and measurements of microhardness. The changes in the microstructure in different zones and the degrees of degradation of the mechanical properties after the welding are determined. It is shown that the size of the tool for the friction stir welding affects the properties of the welds. Quantitative results showing the relation between the microscopic behavior of the alloy and the welding-induced changes in the microstructure are obtained. Friction stir welding is shown to provide higher properties of the welds.

Characterization of a New Dry Drill-Milling Process of Carbon Fibre Reinforced Polymer Laminates

Carbon Fibre Reinforced Polymer (CFRP) composites are widely used in aerospace applications that require severe quality parameters. To simplify the assembly operations and reduce the associated costs, the current trend in industry is to optimize the drilling processes. However, the machining of CFRP composites is very challenging compared with metals, and several defect types can be generated by drilling. The emerging process of orbital drilling can greatly reduce the defects associated with the traditional drilling of CFRP, but it is a more complex process requiring careful process parameters selection and it does not allow for the complete elimination of the thrust force responsible for delamination damage. As an alternative to traditional and orbital drilling, this work presents a new hole making process, where the hole is realized by a combination of drilling and peripheral milling performed using the same cutting tool following a novel tool path strategy. An original tool design principle is proposed to realize a new drill-milling tool, made of a first drilling and a subsequent milling portion. Two different tool configurations are experimentally tested to evaluate the performance of the newly-conceived combined drill-milling process. This process is quick and easy, and the experimental results show an improvement in the drilled hole quality.

Comparison of drilled hole quality evaluation in CFRP/CFRP stacks using optical and ultrasonic non-destructive inspection

Abstract In aeronautical industry, stringent requirements relate to the quality of drilled holes in carbon fiber reinforced plastic (CFRP) composite laminates as low hole quality determines poor assembly tolerance, structural properties reduction, and risk for long-term part performance. Non-destructive quality control techniques were applied to drilled CFRP laminate stacks for aeronautical applications to characterize the material damage induced by drilling in order to assess the hole quality for product acceptability. Experimental metrology procedures, including optical measurements and ultrasonic non-destructive evaluation, were employed to appraise both external and internal induced material damage in holes machined under diverse drilling conditions. The optical inspection procedure, comparable to the visual inspection method regularly utilized in industry, provided delaminated area evaluations that are underestimated in the case of severe drilling conditions by up to 7% for hole exit and up to 5% for hole entry. In the case of less severe drilling conditions, the underestimation was limited to <2.5% for both hole exit and hole entry, which can be considered a practically negligible disparity.