F. Veniali

Cutting mechanisms in drilling of aramid composites

Abstract The results of an experimental research on the drilling of aramid fibre reinforced plastics are reported. A drilling machine has been instrumented in order to detect the thrust force and the torque as a function of the depth of the hole. The signals of the transducers were acquired by an analog to digital converter card inserted in a personal computer. The apparatus enabled analysis of the cutting mechanism of commercially available twist drills intended for the drilling of aramid fibre reinforced plastics. Relationships have been evidenced between the trends of the thrust force and the torque with regard to the tool bit geometry and the composite structure, for different feed rates and for different composite constructions. The thrust force shows irregular courses which are discussed in terms of non-uniform distribution of the thrust force along the tool cutting edges and of poor interlaminar strength of composites. A continuous decrease of the thrust force mean value has also been found which has been attributed to the heat build-up at the cutting front. The torque is strongly influenced by friction at the lands of the twist drill.

An Experimental Study of the Drilling of Aramid Composites

Major drilling characteristics of Aramid fiber-reinforced plastics are experimentally investigated. The chip appears highly deformed and tends to smear on the tool. Forces and, mainly torque are more influenced by the tool diameter than by the feed rate and cutting speed. On the contrary, the specific cutting energy strongly depends upon the feed rate due to size effects of the tool tip. The damage in the work, i.e., delamination at entry and exit side, can be controlled by taking into account the relationships between machining parameters and forces and torque. Generally, the tool fails by gross brittle failure at the periphery rather than by generalized land wear.

MACHINING PARAMETERS AND CUT QUALITY IN LASER CUTTING OF ARAMID FIBRE REINFORCED PLASTICS

ABSTRACT This paper deals with the quality evaluation in laser cutting of Aramid Fibre Reinforced Plastics. The typical features of cuts are described and the influence of the process parameters on cutting result is discussed. A new methodology based on a digital image processing technique for the evaluation of cut quality is presented.

An experimental study on grinding of silicon carbide reinforced aluminium alloys

This paper presents the results of an experimental research on the grinding of metal matrix composites. The aim of the investigation is to enhance the knowledge about the machinability of some aluminium alloys reinforced with SiC of different shape (powder or whiskers) and content. Investigations on chip morphology, ground surfaces and trend of forces acquired during the grinding process were carried out. The results show that the presence of the reinforcement enhances the machinability in terms of both surface roughness and lower tendency to clog the grinding wheel, when compared to a non-reinforced Al alloy. Particle-reinforced composites exhibit a linear relationship between the roughness of the ground surface and the average hardness of the material. Whisker-reinforced composites show higher roughness values than particulate composites. Data of grinding forces obtained under different machining conditions are reported which permit the evaluation of the specific cutting energy.

Corner Shaping by Barrel Finishing

Corner shaping is a necessary operation in manufacturing of most mechanical components. Edge radiusing is the principal way to reduce stress concentration in components like gear, crank shaft, ball bearing, to permit assembly and disassembly of parts, to avoid local damage and to reduce the possibility of hurting the operators. Often precise values of corner radius are specified in component design. Deterministic operations such as chipping, plastic deformation and non traditional ones such as electro discharge machining, abrasive jet deburring are well established technology. Yet, sometimes, it results not economic or even impossible to perform these operations due to the complicated part geometry, difficulty in part clamping and tool path, large number of parts to be produced. Barrel finishing is technique able to improve the roughness of parts of complicated shape by means of a soft mechanical action over the surface performed by abrasive media. The main features of this technology is that the parts do not need to be fixed. Radiusing is, in turn, a potential application area for barrel finishing which has been investigated in this paper. Experimental tests were conducted on finished specimens with sharp corners in order to achieve information about corner radius evolution as a function of the time for different set parameters. The radius values have been assessed by analyzing the acquired profiles with a proprietary fitting procedure. It has been found a square root relation between radius and working time and, by assessing the influence of single parameter, a radiusing model has been proposed.Copyright

Particle Tracking in Horizontal Ball Milling

Ball milling is a material processing method that allows near room temperature process of elements in powder and permits to synthesize materials with peculiar properties otherwise difficult or impossible to obtain. Due to the repeated fractures and cold welding of the reactants particles, solid solutions, amorphous alloys and equilibrium nanostructured materials can be obtained. Products coming from mechanosynthesis process can be advantageously applied as high performance structural and functional materials. Different milling devices can be utilized for the powder processing: planetary mill, attritor, horizontal ball mill, 1D and 3D vibrating machines. The wide differentiation in configuration of the mills obstacles the development of a unified model on powder transformation kinetics in the milling process and then most of processing procedures are still developed by using a trial and error method. The focus of this paper is on a horizontal fixed vial ball mill; in this configuration a high speed rotor launches several tumbling against the vial wall. During hits, a quantity of energy is released to the trapped powder and the solid state reactions are promoted. To characterize the powder transformation process, knowledge of the kinematics of the balls system must be inferred. For this purpose an experimental setup based on digital image acquisition was constructed and the movement of balls inside the vial was filmed. Particle trace analysis methodology permitted to obtain balls trajectories, velocity vector field and total hit frequency. The kinetic energy of the impacting balls inside the vial was quantified, so that the energy released to the powder in a milling experiment can be estimated.© 2006 ASME

Laser Machining of Composite Materials

In this chapter the fundamental technological aspects of the laser machining of composite materials are reviewed, including: laser material interaction; laser cutting performances; maximum cutting speed evaluations; cut quality parameters; and, evaluation of damage.

A study of the diffusion and trapping of hydrogen in Fe-3cr and Fe-5Cr alloys

Abstract Comparative hydrogen diffusivity measurements made in 0.1 M NaOH for Armco iron and two Fe-Cr alloys have shown a significant superiority of an alternating current (AC) technique over the direct current (DC) one. Based on the phase difference between the input and the output current recorded for 0.1 cm thick membranes at frequencies ranging from 10 to 40 mHz, the lattice diffusivities of hydrogen could be determined in all the three materials. The hydrogen diffusivity values measured at room temperature were 6.2x10−5, 5.5x10−5 and 2.8x10−5 cm 2 /s for annealed Armco iron, Fe-3Cr and Fe-5Cr alloy respectively. From the latter two values the Gibbs free energy of binding H atoms to Cr atoms was calculated. Depending upon the calculation method, the AG values ranged from −9.3 to −14.4 kJ/mol. At frequencies lower than 10 mHz and in experiments carried out with 0.03cm thick membranes, inaccurate, namely too low diffusivity values were obtained. This was mainly caused by surface impediments on the entry side of membranes. In contrast with AC tests, all DC measurements were affected by spurious effects which could not be eliminated by coating the entry side of membranes with a thin layer of palladium. The effect of surface barriers on diffusivity measurements is discussed.