ULTRASONIC ASSISTED TURNING OF HARDENED STEEL WITH MONOCRYSTALLINE DIAMOND
INTRODUCTION The demand for ultra-precise steel parts with optical surface qualities and complex shaped geometries is increasing and could be applied for plastic injection molding or precision glass molding processes. Nowadays optical molds for injection molding are coated with a nickel layer, in order to be able to machine the surface with diamond tools. Directly machined steel parts would decrease manufacturing time, making the coating process step unnecessary. Additionally, the life time of the mold is increased dramatically. Uncoated steel tools have a higher scratch resistance and no risk of delamination. Therefore the potential of directly machining steel with monocrystalline diamond is exceptionally high.
Experimental Investigation and Finite Difference Modeling of Cutting Tool Temperature Distribution During Ultrasonically Assisted Turning
ABSTRACT: This paper summarizes the experimental and numerical simulations of 2D temperature fields on the chip and cutting tool during ultrasonic assisted turning of AISI 4140 hardened steel using carbide inserts. To achieve this goal, the finite difference method is used to develop a numerical model in order to predict cutting tool’s temperature during ultrasonic assisted turning. First, finite difference method is used to develop a predictive model of cutting tool’s temperature in case of conventional turning and then the analysis results are used in combination with the model developed for ultrasonic assisted turning to predict cutting temperature profiles during this process. Finally, finite differencebased simulation results are validated with experimental measurements of temperatures from ultrasonic assisted turning tests using thermocouple technique. Using the analysis results, the effect of machining and vibrational parameters (cutting speed, feed rate, and vibration amplitude) can be easily studied on ultrasonic assisted turning cutting temperatures. The results show that ultrasonic assisted turning is able to lower the maximum cutting temperature in the cutting tool, about 37%, in low feed rates (≈0.11 mm/ rev), with a vibration amplitude of (≈10 μm) and work velocity of (≈30 m/min). Review History:
Cross talk between redox signalling and metabolic activity of osteoblasts and fibroblasts in the presence of hydroxyapatite-based biomaterials influences bone regeneration
Regeneration of bone tissue defects that result from metabolic disorders, including periodontal diseases, can be supported by biomaterials based on hydroxyapatite. Despite of good biocompatibility of biomaterials they can cause oxidative stress and inflammatory processes as a result of mechanical interaction with surrounding tissues. Because osteoblasts are responsible for bone regeneration process in which gingival fibroblasts may also participate, the aim of the work was to investigate the influence of hydroxyapatite-based biomaterials (allogeneic and xenogeneic) and biomaterials combined with enamel matrix derivative (Emdogain) on osteoblast and fibroblast redox balance in the context of osteoblast proliferation and differentiation.
The results showed that examined substitutes were not cytotoxic in vitro, but affected redox balance of osteoblasts and fibroblasts (ROS level increase and GSH level decrease) which led to oxidative stress (MDA and protein carbonyl groups level increase) resulting in an increase of the Nrf2 and NFκB expression. The consequence of these changes was partial inhibition of proliferation and osteoblast differentiation. Emdogain alone and combined with biomaterials decreased ROS generation and increased GSH level in both osteoblasts and fibroblasts leading to reduction of transcription factors expression especially proinflammatory NFκB, which promoted osteoblast differentiation and mineralization process.