Francesco Veniali

3D roughness profile model in fused deposition modelling

Purpose – The paper aims to predict the surface roughness of fused deposition modelling prototypes. Since average roughness is not comprehensive, this study aims to extend the characterization to all the roughness parameters obtainable by a profilometric analysis.Design/methodology/approach – A theoretical model of the 3D profile is supplied as a function of process parameters and part shape. A suitable geometry was designed and prototyped for validation. Data were measured by a profilometer and complemented by microscopic analysis. A methodology based on the proposed model was applied to optimise prototype fabrication in two practical cases.Findings – The proposed profile is effective in describing the micro‐geometrical surface of fused deposition modelling prototypes. The third dimension enables the calculation of amplitude, spatial and hybrid roughness parameters.Research limitations/implications – Because of mathematical assumptions and technological aspects, the validity of the model presents limitat...

Deburring of Sheet Metal by Barrel Finishing

In sheet metal processes the burrs cannot be completely eliminated during the process but can be minimized by optimization of the process parameters. Hence the deburring often becomes an essential secondary operation. Most of the deburring operations are hand-made and therefore several manufacturers tend to eliminate these tedious and labor-intensive operations due to time and cost issues. Moreover, clamping problems can arise which, together with the deburring forces, can induce dimension alterations and local deformations, particularly for thin sheets. Barrel finishing is an old technique commonly used to improve the surface roughness of complicated parts, but can find interesting applications also in the deburring. Aim of this work is to present an experimental investigation on the deburring of sheet metal performed by barreling. A technological model has been developed in order to assess the height of the burr as a function of the initial burr and of the working time.

Workpiece and media tracking in barrel finishing

The 2D kinetics of the workpiece during barrel finishing operation is studied. A particle image tracking technique was applied to a transparent thin barrel in order to acquire the position of the part within granular flow in rolling regime. The use of industrial near shape media leads to an intrinsic difficulty to trace the part position. The achieved trajectories permit to calculate the active working time, part density distribution, the media velocity gradient and the workpiece to media velocity gradient. These information are useful to calculate the total sliding and to get information about strain stress over part in order to investigate operation efficiency.

Radial Segregation of Workpiece in Barrel Finishing

Barrel finishing is a mass operation which is not yet completely known in its base mechanisms, even thought it is widely and effectively employed in the industry. As other operations which involve granular material movements, it is particularly complicated to be modeled. A laboratory apparatus has been contructed to experimentally analyze this operation. By using a technique based on digital image analysis it has been possible continuously catch the workpiece position within the barrel. So, it can be demonstrated that the entire finishing operation takes place in the so-called active layer. Yet, within this layer, the workpiece would be differently machined, due to the different relative working conditions at different radial position. In this work it is shown how the workpiece mean position within the active layer is influenced by workpiece density and media density.

The mechanisms of material removal in the fluidized bed machining of polyvinyl chloride substrates

In this paper, the mechanisms of material removal during the fluidized bed machining (FBM) of polymeric substrates are analyzed. Cylindrical components composed of polyvinyl chloride (PVC) were exposed to the impact of abrasives while rotating at high speed within a fluidization column. The interaction between the Al2O3 abrasive media and the PVC surfaces was studied to identify the effect of the main process parameters, such as the machining time, the abrasive mesh size, and the rotational speed. The change in the surface morphology as a function of the process parameters was evaluated using field emission gun—scanning electron microscopy (FEG-SEM) and contact gauge profilometry. An improvement in the finishing of the processed surfaces was achieved, and the related mechanisms were identified. The roles of the impact speed and the contact conditions between the abrading particles and the substrate were also investigated.

Hole Damage in Drilling of Reactive Powder Concrete

This study deals with the analysis of hole damage in the drilling of reactive powder concrete (RPC). Attention was first focused on the definition of an original approach on the basis of digital image processing (DIP) to quantify the extent of the damage. Then, an experimental approach, on the basis of the design of experiments (DoE), was performed to evaluate the influence of drilling operational parameters (namely, cutting speed, feed, and hole diameter) on the thrust force, torque, and RPC hole accuracy. The extent of hole damage was found to be influenced by the settings of feed and hole diameter, with cutting speed playing a minor role. Tool vibrations and troublesome centering procedures of the tools during drilling further complicated the interpretation of the hole damage.

Advances in laser processing of Metal Matrix Composites (MMCS)

The present work deals with the application of a High Power Diode Laser (HPDL) to improve the mechanical properties of Al2O3 particle-reinforced Aluminum Matrix Composites (AMCs). An experimental plan in which laser power and interaction time were individually varied was carried out to evaluate the influence of both process parameters on the surface performance of the AMCs. In this respect, the evolution of their surface morphology was assessed by contact-gauge profilometry. Further samples were, then, analyzed by FIMEC micro-indentation test, depth-sensing load controlled scratch and wear test. Experimental findings show that mechanical and tribological proprieties of the laser treated substrates can be considerably improved, although in an operating range of process parameters rather narrow. Finally, an analytical model was proposed to correlate the wear performance of the AMCs investigated to their morphological and mechanical properties.The present work deals with the application of a High Power Diode Laser (HPDL) to improve the mechanical properties of Al2O3 particle-reinforced Aluminum Matrix Composites (AMCs). An experimental plan in which laser power and interaction time were individually varied was carried out to evaluate the influence of both process parameters on the surface performance of the AMCs. In this respect, the evolution of their surface morphology was assessed by contact-gauge profilometry. Further samples were, then, analyzed by FIMEC micro-indentation test, depth-sensing load controlled scratch and wear test. Experimental findings show that mechanical and tribological proprieties of the laser treated substrates can be considerably improved, although in an operating range of process parameters rather narrow. Finally, an analytical model was proposed to correlate the wear performance of the AMCs investigated to their morphological and mechanical properties.

Estimation of Material Removal by Profilometer Measurements in Mass Finishing

This paper presents a new procedure to estimate the material removal (MR) in such conditions or operations where small amount of material or wear occur. The monitoring of material removal is essential to understand the machining mechanisms of several processes such as super finishing ones. For example the study of some mass finishing (MF) operations, i. e. the barrel finishing (BF) and the spindle finishing (SF), have been always limited by the difficulty to measure the local surface modification. Thus there is no knowledge about the relationship between process parameters and obtainable surface quality. The procedure is based on profilometer measurements typically used to characterized local surface morphology. An algorithm automatically finds the most representative peak of the profile. The comparison between the Abbot-Firestone curves, related to peaks achieved in different condition, permits to measure the volume of material removed by the operation. This method overcomes the well-known problem to repositioning the instrument in the same place when the part is moved from machining process to measurement one. In the case of BF, experimental demonstrated the reliability of this methodology to provide the evolution of material removed as a function of working time. Moreover the graphical plot of the representative peak at different times gave important information about machining mechanism. In particular it allowed to verify assumptions regarding the plastic deformation and the peak cutting which takes place.

Mass finishing of parts produced by direct metal laser sintering

This paper presents some practical considerations on finishing of parts made by direct metal laser sintering (DMLS). The main process capabilities limitations of this promising rapid tooling technique are in fact in the surface roughness of the produced parts. This fact hinders the introduction of DMLS as a widely employed industrial process, especially for what concerns the production of moulds and inserts and allows their use only as preseries tools in injection moulding of plastics, since the requirements for preseries tools are worse than those needed during the process. Barrel finishing, in turn, is a well established technique to improve the roughness of parts of complicated shape by means of a soft mechanical action over the surface. The results herewith presented show that it is possible to achieve roughness of the order of 1 μm Ra even when starting from initial roughness of the order of 15 μm Ra , i.e. those typically attained by DMLS.Copyright

Wear of HFACVD diamond coated tools in turning of MMC

HFACVD (Hot Filament Assisted Chemical Vapour Deposition) is a typical technology which permits the coating of soft materials with hard or super hard layers which lead to ultra wear resistant tools. Typical tools obtained with this technology are based on a diamond layer. Unfortunately, these tools are not suitable for machining of ferrous alloys due to chemical issues, yet their use is very promising in the machining of composites based on aluminium matrix and reinforced with alumina or silicon carbide. In this paper HFACVD diamond coated, WC and PCD tools are used in turning of Al2 O3 /Al composites until they are completely worn out. The results show that the diamond tools can be competitive with both the WC and PCD ones in the industrial applications.Copyright