Papers by Keyword: Drilling

Abstract: The drilling of microholes in hard and brittle materials by ultrasonic grinding was carried out using polycrystalline diamond (PCD) micropins fabricated by electrical discharge machining. They can be employed as micro-grinding tools because the convex parts of discharge craters formed on the tool surface can serve as cutting edges of abrasive grains in grinding wheels. In the drilling of crown glass, the increase in the grinding force and the generation of cracks and chippings at hole edges were suppressed owing to the high wear resistance of PCD. Under suitable conditions, drilling was also successfully performed in silicon, which is apt to exhibit cracks and chippings at hole edges.

Abstract: Conventional cutting fluids are known for being expensive, polluting and a non-sustainable part of modern manufacturing processes. Global industrial trends are leaning towards environmental and health friendly technologies. CO2 cooling is an innovative and sustainable method, capable of replacing conventional oil-based cutting fluids under various conditions. The current study intends to cover the indexable insert drilling of aluminium-silicon carbide (Al-SiC) metal matrix composite (MMC) using different diamond coated carbide inserts. Al-SiC composite containing 20% wt. of SiC was used as workpiece material under different cooling strategies. Response Surface Methodology (RSM) and SEM analysis were incorporated to evaluate the tool performance and to understand the wear development in drilling of MMC. Performance tests were carried out at various cutting data and cooling strategies (external CO2, external emulsion, internal CO2 and internal emulsion) in order to study the output in terms of tool life, surface finish and diameter difference of the holes. The results revealed an advantage in the favour of CO2 cooling concerning tool life, precision and surface finish. Drilling with internal supply of CO2 significantly improves the tool life. The internal supply of CO2 generated the best precision and surface finish compared to the other cooling strategies. The test results clearly indicate that the tool failure for internal CO2 is governed by the flaking of the diamond coating in contrast to a combination of flank wear and flaking for emulsion. The results from the external cooling strategy show that there is no significant difference between emulsion and CO2 while the internal cooling strategy shows that CO2 provides the best results. Since the shape and the surface of the hole are generated by the cutting edge of the periphery insert, the wear development on the periphery insert is the main factor which governs the tool life, surface finish and the diameter difference. This can be explained by the internal CO2 strategy that protects the periphery insert.

Abstract: It is well understood that the fabrication process for glass fibre reinforced polymer (GFRP) composite is a near net-shape process. Nevertheless, drilling is often performed in the final stage in product component manufacture. Drilling of GFRP composites usually produces delamination damage that deteriorates the long-term performance of the composite materials. Hence, this project aims to obtain desired drilling parameters for minimum delamination damage under high-speed conditions. Taguchi L₂₇ orthogonal array has been employed for the experimentation and the controlled variables include spindle speed, feed rate, and drill bit. The results of Taguchi analyses showed that feed rate and drill geometry have major influence towards delamination damage.

Abstract: Drilling is a widely used machining process for various components pertaining to industries such as aerospace, automobile etc. Ti6Al4V is very often used for high stressed components like aircraft structure because of its excellent strength to weight ratio. Tool geometry plays a vital role in effective drilling. It is very difficult to develop a modified geometry in order to achieve better hole quality and improved tool life and validating its outcome experimentally is very expensive. The current paper presents the concept of drilling simulation process using commercial finite element software, Abaqus/Explicit. Five major drill bit geometry such as point angle, helix angle, clearance diameter, and web thickness were varied The proposed simulation model for drilling process was based on Eulierian formulation with explicit interaction. The results of simulation were compared with that of experimental drilling. The simulated result has a good correlation with the experimental result. The change in reference point to chisel tip in the simulation yielded better results as compared to when the reference point is taken at top surface of the tool.

Abstract: The carbon fibre reinforced composites are one such class of materials finding widespread application owing to their superior mechanical and chemical properties. The addition of fillers has further increased their application spectrum. The present paper focuses on the multiple performances analysis in machining characteristics of drilling carbon fibre reinforced Composites produced through compression moulding route. Experiments are conducted on a radial drilling machine using L₁₆orthogonal array. Drilling test is carried out using coated HSS drill of 6 and 10 mm diameter. The effect of drill diameter, wt % of fly ash,spindle speed and the feed rate has been investigated on the thrust force and delamination. After conducting experiment, mathematical models have been developed to fit the output responses using Response surface methodology and drilling parameters have been optimized using Desirability based approach. This methodology deals with the development of modelling equations for each response.The relative significance of the various parameters has been found using ANOVA.

Abstract: The knowledge about machinability indices for distinct machining processes allows finding the most appropriate values of the relevant factors for definite machining operations. Several criteria can be used to characterize machinability, such as the tool wear, the magnitude of the cutting forces, the roughness of the machined surfaces, or the shape of the chips that are formed during the machining process. One of the methods for studying the machinability is based on the analysis of drilling operations that are made under constant feed force. A drill press is probably the most readily available device to implement an experimental setup for drilling machinability tests. In normal operation, however, the chip accumulation at the dead end of the machined hole has a detrimental impact on the results of machinability tests, so that an improved setup was designed. A two-level, full factorial experiment with three independent factors (the drilling tool diameter, the rotational speed of the spindle and the feed force) has proven the suitability of the new experimental setup. Using it, we could find a power-type empirical model that explains the impact of the input factors in the depth of a hole that is machined in a pre-defined time interval.

Abstract: In this paper are presented and analyzed a series of problems that are appearing during the CFRP machining. Due to their properties, the composite materials began to replace traditional materials (ferrous and non-ferrous) in a lot of industries leading out the development of new methods of machining or adaptation of the classic. Unlike traditional material, drilling in CFRP is more difficult due to inhomogeneity of the material, its high hardness but also due to lack of knowledge relating to how these materials behave. This paper investigates different types of tool wears as corner wear, welding, crater wear that are appearing in drilling operation due to the highly abrasive nature of the carbon fibers. Also, here is presented an evaluation that refers to the machined hole quality and describe defects as delamination, pull outs, fibers projections, pyrolysis and shape errors. The main goal of this paper is to verify the current status of technique in CFRP drilling in order to develop and produce a new drill geometry in a cooperation between the Technical University of Cluj-Napoca and the cutting tool company Gühring KG.

Abstract: The research in the last decade regarding their cutting machinability have highlighted the insufficiency of the data for establishing of the optimum cutting processing conditions and the optimum cutting regime. The purpose of this article is the optimization of the tool life and the cutting speed at the drilling of the stainless steels in terms of the maximum productivity. A nonlinear programming mathematical model to maximize the productivity at the drilling of a stainless steel is developed in this paper. The optimum cutting tool life and the associated cutting tool speed are obtained by solving the proposed mathematical model. The use of this productivity model allows greater accuracy in the prediction of the productivity for the drilling of a certain stainless steel and getting the optimum tool life and the optimum cutting speed for the maximum productivity. The obtained results can be used in production activity, in order to increase the productivity of the stainless steels machining. Finally the paper suggests new research directions for the specialists interested in this field.

Abstract: In the specialized literature the cost of the machining process has been analyzed using a number of approaches and varying degrees of simplification to determine the optimum tool life and the tool speed. The accuracy of prediction is dependent on the degree of sophistication of the model. The purpose of this paper is the optimization of the cutting tool life and the cutting speed at the drilling of the stainless steels in terms of the minimum machining cost. A more comprehensive nonlinear programming model to minimize the total cost at the drilling of a stainless steel is developed in this paper. The optimum tool life and the associated tool speed are obtained by solving this model. The results can be taken into consideration in the educational studies and in the theoretical technical research. They can be implemented in the manufacturing activity.

Abstract: This article studies the cutting moment at drilling of the stainless steel X5CrNiMo17-12-2. The structure of the cutting moment relation was modified with respect to the relation available in the technical literature for common steels. The tool speed was included in the calculus relation. The experimental data and their subsequent processing represent the original contributions of the authors to the estimation of polytropic exponents and to the assessment in terms of structure of the calculus relation of the cutting moment. The paper also contains graphs with the cutting moment variation depending on the parameters of the cutting technology. The graphs are drawn based on the analytic relationship of the cutting moment, obtained in the article, using the mathematical software Maple. The results presented in this study can be taken into consideration in the educational studies and in the theoretical technical research. Also, they can be readily implemented in the manufacturing activity. Our further studies aim these problems for other classes of steels and cutting machining processes.