On the Influence of the Radius Between Face and Flank on the Tool Life of Sintered Carbides

Experimental investigations carried out by the authors in interrupted cutting, show that if the cutting edge survives to few impacts, then fracture will take place to very high number of impacts. Early fractures can be explained by assuming the presence of microscopic defects on the tool edge; a longer life can be referred to an increase tool strengthness due to rounding of the edge as a consequence of the wear process. In order to study the effects of the rounding of the edge, experimental tests have been carried out on several inserts of sintered carbides with different values of the radius of the edge between face and flank obtained by a tumbling process. The results show that the greate…

A technical note on an experimental device to measure friction coefficient in sheet metal forming

Abstract In the paper the authors present the results of several experimental tests aimed to determine the Coulomb friction coefficient in sheet metal forming operations at the varying of the sheet metal material and for different operative conditions. In particular a few pressure and lubricating conditions have been investigated. In order to develop such experiments a dedicated fixture was designed and set-up starting from the one proposed by Wilson.

Metal Matrix Composites - Mmc - Turning: Comparison of Tool Materials

The main properties required to the modem cutting tools to be employed in production, are both high wear resistance and chemical stability. In this last years, in the machining of MMCs several kinds of coated tools have been developed; they are characterized by high hardness to resist to the relevant strength and abrasive action of the reinforce fibers or particles, arranged inside the matrix. In turning of MMC the employ of Tungsten Carbide tools coated with Polycrystalline Diamond (PCD) have shown to be very effective, whereas they are very expensive thus increasing the production costs.

Wear of Ceramic Tools When Working Nickel Based Alloys

In order to improve the toughness of alumina materials, various trials have recently been made. These include toughening by the addition of zirconia and of significant amounts of titanium carbide to ceramic oxide Al2O3 and the more recent use of nitride based ceramics, which have resulted in an increase of fracture toughness and in a significant improvement of ceramic tool performance. Another very recent way of improving ceramic materials consists in adding SiC whiskers to Al2O3 matrix. This composite material is also suitable for machining nickel based alloys. In order to evaluate and to qualify these materials some test cycles have been carried out in continuous cutting conditions, emplo…

Rubber Forming Processes of Thin Sheets

In the last decade flexible media have been increasingly utilized in sheet metal drawing processes in order to reduce the tooling cost and to improve the product quality. In the present paper an axisymmetric deep drawing process of thin steel sheets is taken into account: in particular a flexible pad is utilized in order to simplify the tooling set. The process mechanics is investigated through numerical simulations and experimental tests with the aim to find out a proper set of operative parameters allowing the stamping of sound components and to highlight the particular deformation path of the drawing cup. The comparison between the numerical predictions and the experimental verification …

WEAR PERFORMANCE OF CERAMIC CUTTING-TOOL MATERIALS WHEN CUTTING STEEL

Abstract Some test cycles have been carried out in continuous cutting conditions, employing cutting parameters (feed, depth of cut and cutting speed) chosen following experimental planes and suitable test fields. The wear tests have been carried out on AISI 1040 steel with cutting speeds from 5m/sec to 11m/sec. The silicon nitride, sintered carbide, cubic boron nitride and alumina reinforced with SiC whiskers inserts, have shown, at each assigned cutting parameter, poor wear resistance when cutting steel. Alumina and alumina in submicron grain, which has been toughened by ZrO2 phase transformation, and the oxide-based alumina, have been the better wear resistance. The mixed based alumina ha…

Wear rates and wear mechanisms of alumina-based tools cutting steel at a low cutting speed

Abstract Three ceramic insert materials, zirconia-toughened alumina (Al 2 O 3 –7vol%ZrO 2 ), mixed-based alumina (Al 2 O 3 –TiN–TiC–ZrO 2 ) and alumina reinforced with SiC whiskers (Al 2 O 3 –SiC w ), were used to cut AISI 1040 steel at 3.9 m s −1 . In addition, a traditional grade P10 insert (WC–TiC–Co) was tested. The lifetimes, according to KT/KM and VB B criteria, were determined using a profilometer and by image processing. The worn zones were observed with scanning electron microscopy techniques. Adhesion and plastic deformation were dominant wear mechanisms in zirconia-toughened alumina, mixed-based alumina and sintered carbide P10, both in the craters and in the cutting edges. As we…

Computer vision profilometer: equipment and evaluation of measurements

Abstract This paper describes a new equipment that measures roughness values by a computer vision (CV) technique. Measurements carried out by a CV profilometer are also evaluated. A laser source (power 2 mW), a cylindrical lens and a charge coupled device (CCD) TV-camera with a suitable optical system form an image of the profile of the sample under inspection. This image is then transformed into a binary image by thresholding and the line that divides the bright zone from the dark zone is the sample profile. From this line the characteristic roughness values can be calculated. The roughness measurements are carried out both by the CV profilometer and a stylus profilometer on eight specimen…

The performance of molybdenum toughened alumina cutting tools in turning a particulate metal matrix composite

In this paper, a study of the tool wear mechanism in turning aluminium alloy reinforced with alumina using molybdenum-toughened alumina tools is presented. Alumina tools with three different amounts (15, 20 and 25 vol.%) of molybdenum were prepared and tested. The wear type was identified and its evolution with cutting time was measured. The results show that the main mechanism of tool wear is abrasion and not heat. The best overall performance was achieved, as far as flank wear is concerned, using the tool with 20 vol.% of molybdenum added. This has been explained using some of the composites intrinsic properties. SEM examination revealed that molybdenum particles are easily torn from the …

Ceramic materials wear mechanisms when cutting nickel-based alloys

Abstract In this paper the performances of some commercial ceramic inserts when cutting AISI 310 steel are investigated and compared to those of a traditional carbide based tool. The most important wear mechanism in the ceramic inserts is related to the segmented edges of the chips that abrade a notch at the end of the cut zone. Alumina–zirconia inserts are very sensitive to this kind of wear, whereas tools made of Sialon and alumina with SiC whiskers exhibit slightly better performances despite the concomitant chemical wear mechanisms.

The influence of the tape-casting process parameters on the geometric characteristics of SiC tapes

Abstract The production process of the tape-casting technique applied to the production of porous ceramic membranes, suitable for the separation of different chemical species, has been explored, with emphasis on the influence of the operative parameters on the macrogeometric characteristics of the manufactured ceramic porous tapes. The effects of the slurry casting rate, the doctor blade height and the mean particle diameter have been studied and the results reported. The characterization analyses indicate the degree of reliability of this technique to produce planar SiC components and the importance of the particle size in enhancing the structural homogeneity. A study on the variance analy…

Prediction of Ductile Fractures Occurrence in Deep Drawing of Square Boxes

Abstract The authors propose a new approach for the prediction of tearing in the deep drawing process of square boxes. Such an approach is based on a damage mechanics formulation and in particular on the yield condition for damaging materials proposed by Tvergaard and Needleman and on a strain controlled nucleation model. The flow rule associated to the yield condition is introduced in a finite element explicit formulation founded on the solution of the dynamic equilibrium equation and on an explicit time integration scheme. By this way the developed model allows to calculate the void volume fraction value during the deep drawing process of square boxes and consequently to predict the insur…

Performances of Three Layered Ceramic Composites Inserts for Steel Cutting

Sandwich-structured three-layered ceramic inserts were made with the aim of obtaining ceramic cutting tools with an increased useful life.

Cutting Temperatures Evaluation in Ceramic Tools: Experimental Tests, Numerical Analysis and SEM Observations

The authors propose a multiple approach for the evaluation of cutting temperatures in ceramic tools. The first approach was the experimental evaluation of equitemperature lines, obtained in three-dimensional cutting by employing constant melting point powders scattered on planes parallel to rake face. In the second approach, a numerical finite element analysis was performed. At this step the determination of the percentage of total heat produced in the operation that flows into the tool was considered and, consequently, the temperature distribution within the whole volume of the insert. Finally, the examination of the crater zone with SEM microscopy confirmed the temperature levels as previ…

Machining of Steel with Advanced Ceramic Cutting-Tools

Cutting performance and indentation behaviour of diamond films on Co-cemented tungsten carbide

Abstract Diamond films were grown by Hot Filament Chemical Vapour Deposition (HFCVD) on differently pretreated ISO-grade K10 cemented carbide (WC-5.8 wt.%Co) cutting inserts. Etching with diluted HNO3 and surface roughening by Murakami's reagent were used as substrate pretreatments. The adhesion of the films was evaluated by indentation tests. In order to obtain a reliable estimation of the adhesion by the slope of the crack radius–indentation load curves, a careful SEM measurement of the crack lengths was performed. Bare and diamond-coated cutting inserts were used for turning tests of Al2O3-reinforced aluminum alloy. The adhesion levels obtained from the indentation curves correlated well…

WEAR MECHANISM OF CERAMIC TOOLS

Abstract Cutting tests were performed using ceramic cutting tools under continuous cutting conditions. The tests were carried out on AISI 1040 steel, with cutting speeds ranging from 5 to 11 m s −1 . The wear mechanism was investigated for both crater and flank. Alumina-toughened zirconia of submicron grain size showed the best wear resistance. Alumina with TiC, TiN and ZrO 2 inclusions exhibited a wear resistance a little lower than the above-mentioned materials. Low chemical stability seems to be the reason for the poor performances of the silicon carbide whiskers-reinforced alumina, silicon nitride and the tungsten carbide inserts.