Kinetostatic analysis, manufacturing, and experimental application of a press machine based on Stephenson II mechanism

Press machine tools are often used in important industrial establishments, such as automobiles, aerospace, and aviation; these machine tools must be produced with high precision. Therefore, studies related to improving press tools and enhancing their precision are being conducted. In this study, a press machine tool based on the Stephenson II mechanism is proposed. Compared to that of conventional crank presses, this mechanism increases the slider balance using a ternary link and unique connecting rods. Thus, the slider precision can be improved with a small addition to the mechanism, and load transmission can be ensured in a balanced manner. To test the contribution of the mechanism, dynamic analysis is performed using the kinetostatic method, and the dynamic data of the mechanism are obtained. Subsequently, a press machine prototype is designed and manufactured. The experimental results are verified against the theoretical results, confirming that the proposed press machine tool based on the Stephenson II mechanism has better characteristics than those of the conventional press machine owing to the favorable distribution of forces on the slide and lower reaction to the slide guides.

Easily Sinterable Low-Alloy Steel Powders for P/M Diamond Tools

The work presents the design and fabrication procedures used to manufacture inexpensive iron-base powders employed as a matrix in diamond-impregnated tool components. Three newly developed low alloy steel powders, containing from 94.4 to 99.4 wt.% Fe, have been formulated with the assistance of ThermoCalc software and produced by means of a proprietary process patented by AGH-UST. It has been shown that the powders are readily pressureless sintered to a closed porosity condition (>95% theoretical density) at a temperature range between 840 and 950 °C. All as-consolidated materials achieve the desired tool matrix hardness of more than 200 HV. One of the experimental powders has been designed to partly melt within the sintering window. This is particularly important in fabrication of wire saw beads by the conventional press and sinter route because sintering of a diamond-impregnated ring and its further brazing to a tubular steel holder can be combined into one operation.

Revisiting flangeability in hole-flanging by single-stage incremental forming and conventional process

Recently, hole-flanging by single-stage incremental forming (SPIF) has been proposed as a suitable process to perform hole flanges for small- and medium-sized batches with high flexibility in shape. However, this incremental forming has many differences compared with the conventional press working operation in terms of strain and thickness distributions, failure mechanisms and flangeability measures. In fact, regarding the evaluation of the formability of the flanges, the classical Forming Limit Ratio (LFR) should be used with care to quantify this property in hole-flanging by SPIF. Additionally, the FLC (Forming Limit Curve for necking) and FFL (Fracture Forming Limit) curves, powerful tools for analysing sheet failure in practice, may also yield erroneous prediction of necking in conventional press working or fracture in SPIF. The aim of this work is to present a comparison and analysis of the formability of hole flanges performed by SPIF and press working in AA7075-O sheets. Two complementary parameters to the LFR to compare the flangebility in both operations are discussed, along with the influence of bending induced by the forming tool and the stress triaxiality in the evolution of the principal strains during the forming process. The results point out the limitations in the current practice.

Evaluation of the Properties of an Electro-Sinter-Forged Bearing Steel

In this study one of the most innovative sintering techniques up to date was evaluated: Electro-Sinter-Forging (ESF). Despite it has been proved to be effective in densifying several different metallic materials and composites, bearing steels such as 100Cr6 have never been processed so far. Pre-alloyed Astaloy CrM powders have been ad-mixed with either graphite or graphene and then processed by ESF to produce a 100Cr6 equivalent composition. Porosity has been evaluated by optical microscopy and compared to that one of 100Cr6 commercial samples. Mechanical properties such as hardness and transverse rupture strength were tested on samples produced by employing different process parameters and then submitted to different treatments (machining, heat treatment). The experimental characterization highlighted that porosity is the factor mostly affecting mechanical resistance of the samples, correlating linearly to the transverse rupture strength. Hardness on the other side does not correlate to the mechanical resistance because process related cracking has a higher effect on the final properties. Promising results were obtained that give room to the sinterability by ESF of materials difficult to sinter by conventional press and sinter techniques.

Analysis of Flangeability by Single-Stage SPIF and Press-Working in AA7075-O Sheet

Recently, the research interest of hole-flanging has turned from conventional press-working to SPIF as a viable process for small- and medium-sized batches. Both technologies have been studied separately using different approaches and, therefore, most studies cannot be easily compared. Besides, some studies that measured the formability in SPIF using the classical Limiting Forming Ratio (LFR) showed conflicting results that still need to be clarified. Under these circumstances, the aim of this work is to provide a better understanding of the deformation process and the material formability in hole-flanging by critically comparing both forming processes. To this end, a series of experimental tests on AA7075-O sheet of 1.6-mm thickness by press-working and single-stage SPIF, using forming tools with different profile radii, are analysed. The material formability and flange geometry are compared and discussed in detail. The process limits are analysed by using both the Forming Limit Diagram (FLD) and the LFR. The failure modes by necking and fracture are clearly identified and assessed on both processes along with the influence of the bending induced by the tools during the flange forming. Results conclude that the LFR is not an adequate parameter to compare formability between processes other than press-working and, accordingly, two additional variables based on either the flange height or the average thickness reduction are proposed to successfully analyse flangeability.

Development of titanium metal matrix composites reinforced with coated powders

This paper evaluates the feasibility of using SiC and TiC as reinforcement particulates for titanium metal matrix composites (Ti-MMC). The SiC and TiC particles were coated with titanium using a chemical coating technology in order to achieve a homogeneous mixing when they were mixed with pristine Ti. The Ti-MMC with these specially prepared reinforcements were fabricated by a conventional press and sinter route. The effects of sintering temperature in Ti matrix were investigated with respect to phase constituents, microstructure and tribology properties. No in situ phases were observed during sintering and the reinforcement and matrix show sufficient bonding, which acts as a major parameter to enhance hardness and wear resistance compared to pure Ti. All the composite samples had a high sintered density. The hardness of the composites increased with an increase in the sintering temperature. It was also noticed that with the increase in the temperature ranging from [Formula: see text]C to [Formula: see text]C, improvement in the mechanical and tribological properties of the developed titanium matrix composites could be observed. The highest hardness value [Formula: see text] was recorded for Ti-2 wt.% Ti-coated SiC composite when sintered at [Formula: see text]C for 3 h.

Wie viel Streiten gibt es in Streitgesprächen? Eine textlinguistische und sprachorientierte Untersuchung am Beispiel von Streitgesprächen in der Presse

How much arguing is there in press disputes? A linguistic study by the example of press disputesThe interview as a journalistic text type has an established position in the mass media such as radio, press and television. The dispute as a special type of the interview plays an important role in these media. The paper deals with language and linguistic characteristics of the press disputes. Based on general concept of a conversation, the debate is presented from the perspective of linguistic and media studies. In addition, the paper points out the differences between dispute and conventional press interview. Special attention is given to the linguistic realisation of press disputes.

Effects of Open Atmosphere Solutionizing Treatment on the Microstructural and Mechanical Properties of Porous 60NiTi Parts

Titanium alloys have been widely used for medical implants due to their good biocompatibility and excellent corrosion resistance. 60NiTi, an intermetallic nickel-titanium alloy containing approximately 60 wt.% Ni and 40 wt.% Ti, is a promising material for medical components such as implants and prostheses. 60NiTi is hard with good biocompatibility, highly corrosion resistant and has relatively low stiffness. In this study, conventional press-and -sinter method was employed to produce porous 60NiTi parts suitable for general bone replacement applications such as spinal and cranial inserts. The effect of solution treatment in a non-protected furnace and water quenching on the mechanical and microstructural properties of 60NiTi were investigated. It was found that this procedure produces a hard integral ceramic layer, a complex mixture of nickel and titanium oxide compounds, on the surface and around the pores of 60NiTi parts. Results showed that this heat treatment procedure causes the embrittlement of the parts due to an increase in oxide content. However, the produced ceramic surface can also enhance the resistance to corrosion, which is beneficial from a biocompatibility point of view.