In piercing, a smooth shearing surface can be obtained by reducing the clearance between the punch and the die. However, continuous piercing in a small clearance is difficult during mass production, since adhesion may easily occur.A Press Working punch(PW punch)is a punch for piercing a steel plate developed on the basis of cold backward extrusion technology. However, the dimensions of the PW punch were not evaluated accurately. In this study, we evaluated the adhesion resistance of the PW punch when used for the fine piercing of a steel plate. Experiments on continuous piercing using a PW punch with a 10 mm diameter and 0.5 % clearance are performed on a hot-rolled steel plate having a thickness of 4.5 mm. Experiments using a conventional right angle punch are also performed for comparison. A mirrorlike shearing surface was obtained using a ceramic-coated PW punch without causing adhesion in 600 continuous piercings. As a result, the PW punch was found to be highly advantageous for the piercing of steel plates.
The primary objective of this study is to clarify the basic characteristics of piercing high-tensile steel plates. The secondary objective is to propose an appropriate piercing condition for obtaining high-quality holes on surfaces. An experiment on piercing a mild steel plate and two types of high-tensile steel plate is carried out using a ceramic-coated Press Working punch (PW punch) and a ceramic-coated conventional right angle punch, with a range of clearance from 0.5 to 10%t. Here, the PW punch is used for piercing the steel plates and has been developed using cold backward extrusion technology. The main results of this study are given below: 1) If the clearance is small regardless of the shape of the punch, a high rate of shearing surface could be obtained. 2) However, in the case of piercing in a minute clearance by right angle punch, the squeeze force of steel plates to the punch flank increased sharply as the strength of the steel plates increased. 3) On the other hand, in the case of piercing in a minute clearance by the PW punch, no squeeze force after penetrating the steel plate was detected. 4) Thus, the PW punch was found to be an excellent punch for piercing high-tensile steel plates.
Recently, to meet the demands of emerging industries, such as magnetic storage devices and micro electro mechanical systems (MEMS), diamond-like carbon (DLC} coatings have been required to be ultra-thin and sufficiently durable. The present study employed frictional force microscopy (FFM) to measure the coefficient of friction (COF) of ultra-thin DLC films, and thus, characterize their mechanical durability. FFM revealed that the COF of DLC films prepared by filtered cathodic vacuum arc (FCV A) increased with decreasing thickness. To explain the above tribological behavior, several mechanisms were discussed. The indications are that an increase in contact area plays an important role in the increase ofCOF of ultra-thin DLC films.
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