Papers by Keyword: Cemented Carbide

Abstract: Recently, high-combustion-efficiency jet engines have become essential in the aircraft industry. High burning temperatures are necessary to maximize the combustion efficiency of jet engines. Inconel 718, which has excellent mechanical and chemical properties, has been selected for use in many jet engine parts. However, it is difficult to cut because of its low thermal conductivity. Consequently, wet cutting is typically used to reduce the heat generated in cutting Inconel 718. In this study, we conducted experiments to examine the relationships between the cutting characteristics and tool fracture in wet cutting.

Abstract: Machining efficiency of titanium alloys is crucial to the aerospace industry especially in the manufacture of bladed discs (blisks) where over 80% of titanium alloy material is roughed out to generate the complex shapes and contours of components. The choice of the right tool materials for machining titanium alloys contributes enormously to reducing the overall machining time by significantly lowering the cycle time and indexing of the cutting edges. These improvements lead to a reduction of the manufacturing cost by up to 30%. Uncoated and coated carbide tools have demonstrated encouraging performances when turning Ti-6Al-4V alloy, especially under roughing operations complemented by high pressure cooling technology, at high cutting speed and depth of cut conditions that increase the metal removal rate. Under such cutting conditions there is no significant difference in performance between coated or uncoated carbide tools when turning Ti-6Al-4V alloy. Super abrasives like ceramics and cubic boron nitride (CBN) tools are not suitable for machining titanium alloys as low tool life with no economic benefit is achieved because of severe chipping and fracture of the cutting edge. Machined surfaces produced with ceramic tools have very low surface integrity status because of loss of form as a result of accelerated tool wear and the consequent chipping and fracture encountered during machining. Polycrystalline diamond (PCD) tools are suitable for finish turning Ti-6Al-4V alloy at cutting speeds up to 250 m/min.

Abstract: Recently, high-combustion-efficiency jet engines have become required in the aircraft industry. High burning temperatures are necessary to maximize the combustion efficiency of jet engines. Inconel 718, which has excellent mechanical and chemical properties, has been selected for use in many jet engine parts. However, Inconel 718 is a difficult material to cut because of its low thermal conductivity. Consequently, wet cutting is typically used to reduce the heat generated in cutting Inconel 718. Wet cutting, which uses a large amount of cutting fluid, is costly and requires considerable energy for maintenance and disposal of the cutting fluid, making this cutting method environmentally unfriendly. To reduce the associated cost and environmental load, the near-dry cutting method, which uses a very small amount of cutting fluid, may be preferable for cylindrical cutting of Inconel 718. However, this method has some drawbacks, such as the cutting stock removal rate and the wear on cemented carbide tools. For example, the cutting stock removal rate is lower than with wet cutting because cutting edge fracture occurs easily in near-dry cutting. In this study, we conducted experiments to examine the relationships between the tool materials, cutting speed and tool fracture in near-dry cutting and wet cutting, and we compared the results obtained using the two cutting methods. We found that an S05-type cemented carbide coating can reduce tool wear. We also found that in the early stages of cutting, between cutting speeds of V = 50 and 90 m/min, the tool wear can be comparatively reduced.

Abstract: It is well known that a series of cracks running perpendicular to the cutting edge are sometimes formed on the rake face of brittle cutting tools during intermittent cutting. The cutting tool is exposed to elevated temperatures during the periods of cutting and is cooled quickly during noncutting times. It has been suggested that repeated thermal shocks to the tool during intermittent cutting generate thermal fatigue and result in the observed thermal cracks. Recently, a high speed machining technique has attracted attention. The tool temperature during the period of cutting corresponds to the cutting speed. In addition, the cooling and lubricating conditions affect the tool temperature during noncutting times. The thermal shock applied to the tool increases with increasing cutting speed and cooling conditions. Therefore, to achieve high-speed cutting, the evaluation of the thermal shock and thermal crack resistance of the cutting tool is important. In this study, as a basis for improving the thermal shock resistance of brittle cutting tools during high-speed intermittent cutting from the viewpoint of cutting conditions, we focused on the cooling conditions of the cutting operation. An experimental study was conducted to examine the effects of noncutting time on thermal crack initiation. Thermal crack initiation was found to be restrained by reducing the noncutting time. In the turning experiments, when the noncutting time was less than 10 ms, thermal crack initiation was remarkably decreased even for a cutting speed of 500 m/min. In the milling operation, the number of cutting cycles before thermal crack initiation decreased with increasing cutting speed under conditions where the cutting speed was less than 500 m/min. However, when the cutting speed was greater than 600 m/min, thermal crack initiation was restrained. We applied the minimal quantity lubrication (MQL) coolant supply to the intermittent cutting operation. The experimental results showed that the MQL diminished tool wear compared with that under the dry cutting condition and inhibited thermal crack initiation compared with that under the wet cutting condition.

Abstract:

Cemented carbides belong among materials with high hardness and wear resistance even at temperatures around 700 °C. These properties are due to carbide composite structure which is formed mainly of tungsten carbide (WC) in combination with a metal matrix (usually cobalt). A synergistic effect that has a positive impact on the final properties is obtained by the combination of hard carbides and a soft matrix. The high hardness of the cemented carbides is associated with a decrease in fracture toughness which in the case of cutting tools is an important property. It is therefore necessary to measure the value of fracture toughness and thus monitor the state of the material. In practice, the fracture toughness of cemented carbides is usually tested by indentation methods of metallographic samples. Therefore, this work focuses on the comparison and optimization of computational models for determining fracture toughness using indentation methods. Eight types of cemented carbides used for the manufacture of cutting tools were tested. Fracture toughness of selected cemented carbides was measured after heat loading.

Abstract: WC–5TiC–10Co cemented carbides inserts were prepared and used for the cutting tool for HT250 gray cast iron. The objective was to investigate the wear mechanism when machining HT250 gray cast iron with WC–5TiC–10Co cemented carbides inserts. WC–10Co cemented carbides with the same sintering technology and grain size were prepared for comparison. wear mechanism was examined at the same cutting parameters. The cutting tests were performed at a speed of 120 m/min with feed rate of 0.2 mm/rev and a constant depth of cut of 0.2 mm under dry conditions. Tool wear mechanism is analyzed by SEM and EDS. Adhesive and built-up-edge were found to be the predominant tool wear for WC–5TiC–10Co cemented carbides inserts. However, Attrition was the main wear mechanisms observed in WC–10Co cutting tools. The results obtained indicated that WC–5TiC–10Co cutting tools performed better than WC–10Co cutting tools, in terms of tool wear with current parameters.

Abstract: This paper describes on the experimental results of diamond wheel wear in groove grinding of cemented carbide. The speed ratio of grinding was widely changed. Square grooves and 90 degree V-grooves were ground. The square grooves were ground by using a resin-bonded diamond wheel and the V-grooves were by a vitrified diamond wheel. At first, a water-based coolant was used, but afterward, to investigate a possibility of nitrogen to suppress the wear of wheel, nitrogen gas was dissolved into the water-based coolant. The main results obtained are as follows, (1) The wheel wear increases as the speed ratio decreases, (2) The average grinding forces is almost independent from the grinding conditions but those at the lowest speed ratio are fairly large, (3) The influence of nitrogen gas dissolved coolant is small, but in a case of V-shape grinding at a middle speed ratio there found a considerable decrease of wheel wear.

Abstract: In order to establish a high performance grinding method of cemented carbide, the grinding force distribution on the working surface of the cup type electroplated diamond grinding wheel is experimentally analyzed with the grinding force variation of face grinding, which is carried out on the narrow workpiece. The grinding force distribution is obtained by the successive difference of the grinding force variation. The grinding state becomes steady as soon as beginning of the interference of grinding wheel in workpiece, because the edge profile of workpiece is formed as same as the envelope of the grinding wheel. Main conclusions obtained in this study are as follows. In the region of the front edge of the grinding wheel, relatively large grinding force occurs, then in the region of the rear edge of the grinding wheel, the grinding force becomes smaller. In the left right-side end of the wheel, the grinding forces are larger than the center of the wheel. It is made clear that the grinding force distribution shows the peak value near the outer part of the wheel, and the peak value is larger in the center part of the wheel, on the contrary, the peak width become broad in both the left and right-side end of the wheel.

Abstract: The effect of cryogenic treatment on the mechanical and magnetic properties of WC–6% Co Ultrafine cemented carbides has been investigated in this paper. The results show that after the cryogenic treatment, the hardness slightly increases from 1750 to 1830, however, the transverse rupture strength decreases from 2510 MPa to 2480MPa. ,the magnetization decreased from 5.82% to 5.72%, decreasing 1.71%for 24 h, but the coercive force slightly increases and reaches the maximum of 24 kA/m for 2h.

Abstract: Three hypotheses for the grain growth inhibiting mechanism of carbide grain were described in this paper: the dissolution hypothesis, the adsorption hypothesis and the segregation hypothesis. The weakness of these three existing hypotheses has been pointed out. On the basis of analyzing the existing research results of other researchers, this paper proposed a new grain growth inhibiting mechanism: segregation - dissolution hypothesis.