Papers by Author: Chung Chen Tsao

Abstract: This paper presents an experimental investigation on the turning of Inconel 718 using tungsten carbide and cermet insert tools with ultrasonic-assisted. The Taguchi method as well as an L18 orthogonal array, signal-to-noise (S/N) ratio and analysis of variance (ANOVA) are employed to examine the performance characteristics of the turning operations. The effect of the machining parameters (cutting tool, depth of cut, cutting speed, feed rate, working temperature and ultrasonic power) on roundness and flank wear in the turning operations are studied. For roundness, depth of cut (σ = 38.40 %) and feed rate (σ = 22.59 %) were recognized to make significant contributions. For flank wear, the significant contribution order was cutting tools (σ = 51.16 %) for different materials, follow working temperature (σ=22.37 %), depth of cut (σ = 13.59 %), and ultrasonic power (σ = 5.79 %). Cutting with ultrasonic-assisted improves roundness by 17.78 % to 45.73 %, and improves flank wear by 26.52 % to 46.26 7%. Finally, turning experiments with 5-20 nm nano-particles cutting fluid were investigated. The experimental results indicated the cutter-workpiece friction force is noticeably reduced and cutter service life is prolonged.

Abstract: The effect of passive backup force in drilling composite materials was investigated in this study. The passive backup force formation is due to material reacting and bending. The theoretical analysis indicated that the passive backup force has a significant effect on prevention of delamination damage in drilling composite materials. When the is large enough, the effects of the passive backup force and material behavior will be attenuated.

Abstract: In this paper, an approach is developed on Taguchi method to optimize the drilling parameters in drilling carbon fiber-reinforced plastic (CFRP) by the candlestick drill bits. The experimental results indicate that the feed rate (f) and the drill diameter (d) are the most important factors and the spindle speed (S) is insignificant in drilling CFRP laminates. The optimal drilling performance for the thrust force was obtained at 0.01 mm/rev feed rate, 800 rpm speed spindle and 6 mm drill diameter settings. The best combination to attain smaller delamination factor was 0.01 mm/rev feed rate, 800 rpm speed spindle and 10 mm drill diameter.

Abstract: Composites have become valuable construction materials in the aerospace, defense, automobile, and civil industries due to their superior mechanical properties. However, there are significant differences between the machining of metals and alloys and that of composites, because composites are anisotropic and inhomogeneous. Drilling with a conventional twist drill is characterized by a relatively large thrust force due to a negative rake and negligibly small cutting speed at the chisel edge. Such a large thrust force causes defects and damages the composites, leading to poor hole quality, and reduced in-service life under fatigue loads. Although significant efforts have been made to realize the thrust force of twist drill, there are few papers reporting the effect of peripheral drilling moment (torque) on delamination in drilling composite materials. In this paper, an attempt is made to develop the critical thrust of the twist drill with peripheral drilling moment using linear elastic fracture mechanics (LEFM) and energy conservation. The theoretical results agree well with the practical experience in industries.

Abstract: Drilling is the most economic and convenient operation of secondary machining for hole making of fiber-reinforced materials owing to the need for structure joining. Delamination is commonly recognized as a major defect after drilling composite materials. In general, the delamination is an irregular shape and size, containing long and fine breaks and cracks at the exit of the drilled hole, especially in the drilling of carbon fiber-reinforced plastic (CFRP). The conventional delamination factor ( ) is not appropriated to characterize the damage area because the shape of the delamination after drilled CFRP is not a regular representation of the damage magnitude. In this paper, a novel approach of the equivalent delamination factor ( ) is proposed and compared with the adjusted delamination factor ( ) and the conventional delamination factor ( ). The experimental results show the obtained is considered suitable for characterizing delamination at the exit of a hole after drilling composite materials.

Abstract: End milling is considered to be one of the most commonly applied for both roughing and finishing operations to make flat surfaces, slots and pockets in precision molds and dies. Predictive models were developed for cutting force, flank wear and surface roughness in end milling aluminum alloy by regression analysis. The correlation coefficients for cutting force, flank wear and surface roughness equations were 91.6 %, 89.8 % and 79.6 %, respectively. The goal of these predictive equations is to become a good assistant to the researcher in understanding the machining process. Through the analysis of variance (ANOVA), however, it can be found that the cutter diameter, the helix angle and the feed rate are the important milling process parameters to obtain the machined quality on cutting force, flank wear and surface roughness. The investigations show that cutting force, flank wear and surface roughness can be improved in end milling aluminum alloy by using the lower cutter diameter, medium helix angle and lower feed rate.

Abstract: Increasing the productivity and the quality of the machined parts are the main challenges of manufacturing industry, in particular for difficult-to-machine materials, such as Inconel 718, employed in aeronautic and aerospace applications. A L18 (2×37) orthogonal array (OA) and signal-to-noise (S/N) were employed to analyze the effect of mill parameters when milling Inconel 718. Experimental results indicated that the cutting tool, depth of cut, cutting speed, feed rate, frequency and coolant have statistical and physical significance on the flank wear, surface roughness and cutting force obtained, respectively.

Abstract: Unlike ductile metals cutting mechanism, the interfaces between fiber and matrix as a transitional layer experience mismatched deformation in machining process. In general, the most frequent operation performed on composite materials is drilling with a twist drill to generate a hole owing to their versatility and low production cost. However, delamination is one of the most common defects in drilling laminated fiber-reinforced composites and can cause a significant reduction in the load-carrying capacity of a structure. At the periphery, using such special drills as saw drill, candlestick drill and core drill, reducible to causing delamination damage than the twist drill. Experimental results indicated that the diameter ratio and feed rate have statistical and physical significance on the thrust force obtained with a core-candlestick drill.

Abstract: Twist drill is widely used in hole-making process in industries, due their low production cost and ease of regrinding after wear. However, drilling of fiber reinforced plastics with twist drill often results in defects and damages, such as delamination, debonding, spalling and fiber pullout. The chisel edge of twist drill is the mainly influence for the thrust force and the hole quality in drilling carbon fiber reinforced plastic (CFRP) laminates. Pre-drilled pilot hole or reduce chisel edge can eliminate the threat for twist drill in drilling induced-delamination. Drilling-induced thrust force was selected as quality character factors to optimize the drilling parameters (drill type, feed rate and spindle speed) to get the smaller the better machining characteristics by Taguchi method. The results show that the feed rate and drill type are the most significant factor affecting the induced-thrust in drilling CFRP laminates.

Abstract: Delamination is one of the most concern defects in drilling of composite material. Delamination depends on the factors such as feed rate, tool geometry and wear. The mechanics of drilling composite materials has been examined along with the quality of the hole and the effect of tool design parameters. The capacity of computerized tomography (CT) showing sample cross-section in a nondestructive way made it successful in measuring the drilling-induced delamination. In the experiment, the correlation between thrust force and the measured delamination extent in use of twist drill and core drill is illustrated and compared with the known ultrasonic C-scan. It is compared with the ultrasonic technique and is demonstrated a feasible and an effective tool for the evaluation of drilling-induced delamination.