Rough Machining Research Articles

Evaluation of machined surface quality of Si3N4 ceramics based on neural network and grey-level co-occurrence matrix

Cutting and extruding processing technology for ceramics based on the edge-chipping effect is a non-traditional rough machining method for engineering ceramics. A set of new methods for evaluating unconventional rough surfaces of such ceramics was developed by using grey-level co-occurrence matrix (GLCM) and a neural network (NN). The influences of three parameters including step size, greyscale quantisation and direction on the GLCM were investigated to measure the morphology of the machined surface of Si3N4 ceramic by using a GLCM with suitable such parameters. Based on a generalised regression network, a prediction model for the textural features of sintered Si3N4 ceramic surfaces was established with multiple processing parameters. Moreover, a competitive layer network was used to sort the roughness grades of the machined surface. The division and cooperation of the generalised regression network and competitive network are able to preferably identify and predict the roughness of the machined surface without contact.

Comparative investigation on using cryogenic machining in CNC milling of Ti-6Al-4V titanium alloy

ABSTRACTTi-6Al-4V titanium alloy is one of the most important materials in industry, 80% of which is used in aerospace industry. Titanium alloys are also notoriously difficult-to-machine materials owing to their unique material properties imposing a major bottleneck in manufacturing systems. Cryogenic cooling has been acknowledged as an alternative technique in machining to improve the machinability of different materials. Although milling is considered to be the major machining operation for the manufacture of titanium components in aerospace industries, studies in cryogenic machining of titanium alloys are predominantly concentrated on turning operations. To address this gap, this article provides an investigation on the viability of cryogenic cooling in CNC end-milling of aerospace-grade Ti-6Al-4V alloy using liquid nitrogen in comparison with traditional machining environments. A series of machining experiments were conducted and surface roughness, tool life, power consumption, and specific machining energy were investigated for cryogenic milling as opposed to conventional dry and flood cooling. Analysis revealed that cryogenic machining using liquid nitrogen has the potential to significantly improve the machinability of Ti-6Al-4V alloy in CNC end-milling using solid carbide cutting tools and result in a paradigm shift in machining of titanium products. The analysis demonstrated that cryogenic cooling has resulted in almost three times increased tool life and the surface roughness was reduced by 40% in comparison with flood cooling.

Mechanistic Modeling of Five-Axis Machining With a Flat End Mill Considering Bottom Edge Cutting Effect

In five-axis milling, the bottom edge of a flat end mill is probably involved in cutting when the lead angle of tool axis changes to negative. The mechanistic model will lose accuracy if the bottom edge cutting effect is neglected. In this paper, an improved mechanistic model of five-axis machining with a flat end mill is presented to accurately predict cutting forces by combining the cutting effects of both side and bottom edges. Based on the kinematic analysis of the radial line located at the tool bottom part, the feasible contact radial line (FCRL) is analytically extracted. Then, boundaries of the bottom cutter-workpiece engagements (CWEs) are obtained by intersecting the FCRL with workpiece surfaces and identifying the inclusion relation of its endpoints with the workpiece volume. Next, an analytical method is proposed to calculate the cutting width and the chip area by considering five-axis motions of the tool. Finally, the method of calibrating bottom-cutting force coefficients by conducting a series of plunge milling tests at various feedrates is proposed, and the improved mechanistic model is then applied to predict cutting forces. The five-axis milling with a negative lead angle and the rough machining of an aircraft engine blisk are carried out to test the effectiveness and practicability of the proposed model. The results indicate that it is essential to take into account the bottom edge cutting effect for accurate prediction of cutting forces at tool path zones where the tool bottom part engages with the workpiece.

Numerical Solution of Mixed Thermal Elastohydrodynamic Lubrication in Point Contacts With Three-Dimensional Surface Roughness

Elastohydrodynamic lubrication (EHL) is a common mode of fluid-film lubrication in which many machine elements operate. Its thermal behavior is an important concern especially for components working under extreme conditions such as high speeds, heavy loads, and surfaces with significant roughness. Previous thermal EHL (TEHL) studies focused only on the cases with smooth surfaces under the full-film lubrication condition. The present study intends to develop a more realistic unified TEHL model for point contact problems that is capable of simulating the entire transition of lubrication status from the full-film and mixed lubrication all the way down to boundary lubrication with real machined roughness. The model consists of the generalized Reynolds equation, elasticity equation, film thickness equation, and those for lubricant rheology in combination with the energy equation for the lubricant film and the surface temperature equations. The solution algorithms based on the improved semi-system approach have demonstrated a good ability to achieve stable solutions with fast convergence under severe operating conditions. Lubricant film thickness variation and temperature rises in the lubricant film and on the surfaces during the entire transition have been investigated. It appears that this model can be used to predict mixed TEHL characteristics in a wide range of operating conditions with or without three-dimensional (3D) surface roughness involved. Therefore, it can be employed as a useful tool in engineering analyses.

Passive and active gravity compensation of horizontally-mounted 3-RPS parallel kinematic machine

Taking a horizontally-mounted 3-RPS parallel kinematic machine (PKM) as an example, this paper investigates passive and active gravity compensation strategies for improving PKM precision. Herein, R, P and S denote revolute, actuated prismatic and spherical joint, respectively. Based on inverse position kinematic and force analysis, passive gravity compensation is firstly implemented by three extension springs. Geometric parameters of these springs are optimized by minimizing potential energy fluctuation within a prescribed workspace. Then deformation caused by gravity is adopted to evaluate compensation strategies. The deviations of an end reference point demonstrate that passive gravity compensation is capable of substantially balancing gravity. In order to further eliminate the effect of gravity, active gravity compensation is proposed to adjust spring displacements by several one degree-of-freedom (DoF) translational mechanisms. Deformation of the 3-RPS PKM is directly regarded as the objective function for determining the active translations. Overall, both passive and active gravity compensations are able to improve mechanism precision due to the partial and complete gravity balancing capability, respectively, which makes the 3-RPS PKM suitable for the application of rough and fine machining.

Application of RS-SVM in Coal Mine Fire Warning System

In order to reduce the false alarm rate in coal mine fire warning system, we apply information fusion technology to the system and propose a fire forecast algorithm based on Rough Set Support Vector Machine ( RS-SVM ). Firstly, we map the feature description of coal mine fires to the knowledge representation system described by rough set; Secondly, we discrete the continuous attributes and eliminate the redundant information for attribute reduction to form a rule set of this knowledge representation system; At last, we use the above rule set as the training sample to optimize the parameters for the fire warning support vector machine. The experimental results show that the accuracy of the algorithm is very high. It can make timely and accurate prediction of coal mine fire.

Research on Semi-Finishing of NC Milling

Usually, bigger diameter milling tools were firstly applied in rough machining of NC Milling for improving efficiency and reducing cost before semi-finishing. In order to make the surface of parts more smooth and get accurate dimension parameters and proper shape, it is necessary to select appropriate tools to carry out the finishing of NC Milling. Moreover, higher precision dimension or shapes of parts can be achieve by the method of the semi-finishing, which it can be carried out after rough machining of high efficiency. Currently, the main methods of semi-finishing include semi-finishing of using IPW and semi-finishing of using reference tool.

The Influence of Abrasive Instrument and Cutting Modes in Fine Grinding of Wear Resistance Composite Parts on the Parameters of Surface Roughness Friction of Printing Machines

Background. Study on the technological process of thin abrasive grinding of wear resistance composite parts, synthesized on the base of utilized and regenerated industrial wastes of nickel alloys XH55BMTKЮ, XH50BTФKЮ, ЭП975 with additions of hard lubricant CaF2 has been carried out.Objective. The purpose of the work is the experimental research of processes of thin abrasive grinding of friction parts made of new composite materials based on nickel and identification of influence on the parameters of part surface roughness of the abrasive instrument type, its granularity and cutting modes.Methods. Surface treatment of printing machines wear-resistant parts based on nickel by thin grinding on the plain-grinding, round-external-finishing and internal-grinding machines with grinding instruments made of chromium electrocorundum (33A) with granularity 14–28 µm on the glyphtal bond and application of thin cutting modes.Results. It was show, that granularity, the abrasive instrument bond material and parameters of thin abrasive grinding essentially influence the parameters of surface roughness machining Ra. The best performance Ra parameters satisfy the grinding chromium electrocorundum 33A discs with granularity 14–28 µm on the glyphtal bond and thin cutting modes that meet the high requirements at work surfaces of friction parts for printing machines. Advantage of the surface machining with grinding chromium electrocorundum discs was shown.Conclusions. Also it was demonstrated, that the formation of high quality parameters of details surface, made of new composite materials based on nickel essentially depends on the type of the abrasive instrument, cutting modes of composites and bond material. The recommendations on the production were developed.

Tool wear characteristics of cutting and extrusion processing technology based on the edge-chipping effect

Purpose – The cutting and extruding processing technology for ceramics based on the edge-chipping effect is a new contact removal machining method for hard, brittle materials such as engineering ceramics. This paper aims to provide an important reference to understand the tool wear mechanism and the wear law of this new processing technology. Design/methodology/approach – The real-time temperature monitoring and the observation of micro-morphology are used to analyse the wear characteristics of the tool face. In addition, the research focuses on the influence of three processing parameters (axial feed rate, thickness of flange and depth of groove) on characteristics including tool wear. Findings – The temperature variation shows that the new processing technology improves the tool temperatures condition. The tool is worn mainly by mechanical friction including abrasive wear, and the flank face also suffers the sustained scratching of residual materials on the rough machining surface. With increased feed rate, the wear of the rear face of the major flank initially decreased and then increased. As the depth of the retained flange increases, the wear became worse. The wear initially decreased and then increased with increasing depth of groove. Research limitations/implications – Study on the new processing technology is still in its early stages. Therefore, researchers are encouraged to test the proposed propositions further. Practical implications – The machining process itself destroys materials, albeit a controllable manner: based on this principle, the authors proposed a new machining technology based on cracks driven by edge chipping. In this way, the surface of such ceramics is removed. Therefore, the research provides a new method for reducing processing costs and promoting the extensive application of engineering ceramic materials. Originality/value – The cutting and extruding processing technology based on cracks driven by edge-chipping effect makes full use of the stress concentration effect caused by prefabricated defects, and the edge-chipping effect which occurs during machining-induced crack propagation. The wear mechanism and law of its tool is unique than other machining ways. This paper provides an important reference to understand the tool wear mechanism and the machining mechanism of this new processing technology. With the application of this study, the ceramics could be removed with less energy consumption and the tools with the hardness of lower than its own one. Therefore, it could not only reduce the processing costs but also promote the extensive applications of engineering ceramic materials.

Effects of microstructure and strength on wear performance in rough milling of austempered ductile iron

The machinability of various grades of austempered ductile iron (ADI) has been investigated for rough milling operations. ADI 900, ADI 1050 and ADI 1200 grades were commercially produced, commercially heat treated and machined under controlled conditions using coated carbide inserts with coolant in the laboratory. The milling performance of the various grades was compared to that of AISI/SAE 4340 with similar hardness. In this study, machinability characteristics relative to wear rate (ISO 8688-2) and machining forces were measured and related to initial microstructure and properties. These preliminary results have been used to establish initial rough milling machining guidelines for machining ADI with coated carbide milling inserts.

Spherical Approximation of Free-Form Surface Closed to a Sphere in Semi-Finishing

The free-form surface closed to a sphere of brittle material has been used widely, but it is difficult for machining and the efficiency of processing is insufficient. In order to get a product, several processes are needed, such as rough machining, semi-finishing and finishing. Axisymmetric curved surface can take place of the free-form surface in roughing or semi-finishing for wiping off the mass allowance efficiently. Therefore, a spherical approximation algorithm of free-form surface closed to sphere is presented in which free-form surface optical lens will be replaced by a spherical surface in semi-finishing and get the approximate sphere of the free-form surface. It can be certified in the test that this method is simple and reliable. The efficiency and precision in machining is excellent and the distribution of allowance for finishing is uniform in the whole surface, which has great practical significance in machining of optical free-form surface of brittle materials.

The Statistical Analysis of Granulometric Composition and Microgeometrical Indicators of Abrasive Grains of Grinding Wheels for Rough Machining

The analysis of geometry of abrasive grains on macrogeometrical and microgeometrical indicators is carried out; charts of distribution of these indicators are submitted. The research technique based on application of photometry for obtaining digital images of abrasive grains is described. On the basis of this method we have established that abrasive grains can be devided into following form types: isometric, beam-type, and laminar. Grains sharpening and peaks rounding radii R in samples scanning plane were investigated in order to analyse abrasive grains microgeometry. Statistic analysis provided following results: average grain sharpening angle is within limits of 85° ≤ β ≤ 90°; average grain peak rounding radius is equal to 0.2 ≤ R ≤ 0.4 mm.

Precision Sculptured Surface CNC Machining Using Cutter Location Data

Industrial parts with sculptured surfaces are typically, manufactured with the use of CNC machining technology and CAM software to generate surface tool paths. To assess tool paths computed for 3-and 5-axis machining, the machining error is evaluated in advance referring to the parameter controlling the linearization of high-order curves, as well as the scallop yielded as a function of radial cutting engagement parameter. The two parameters responsible for the machining error are modeled and corresponding cutter location data for tool paths are utilized to compare actual trajectories with theoretical curves on a sculptured surface assessing thus the deviation when virtual tools are employed to maintain low cost; whilst ensuring high precision cutting. This operation is supported by applying a flexible automation code capable of computing the tool path; extracting its CL data; importing them to the CAD part and finally projecting them onto the part’s surface. For a given tolerance, heights from projected instances are computed for tool paths created by changing the parameters under a cutting strategy, towards the identification of the optimum tool path. To represent a global solution rough machining is also discussed prior to finish machining where the new proposals are mainly applied.

Determining the Optimum Parting Direction in Plastic Injection Molds Based on Minimizing Rough Machining Time during Mold Manufacturing

ABSTRACTThe versatility of plastic materials allows engineering components of very complex geometries and functionalities to be injection molded from them. Because the manufacturing cost of a mold increases with the complexity of the cavity, it is important to optimize the design of component and mold concurrently. In this study, a methodology for determining the optimum parting direction (PD) considering mold‐manufacturing factors such as tool accessibility and the amount of material to be removed is presented. The methodology starts with an accessibility analysis in which a three‐dimensional part is discretized, and candidate PDs are selected based on maximizing the accessible area, that is, the area that can be machined with a single workpiece orientation or setup. Then, the rough machining process is considered, and an optimum PD that minimizes the rough machining time for both the cavity and core plates is selected. The methodology is applied to four different automotive components: a mirror cover, an interior panel, a pillar, and a fender splash shield.

Failure Analysis of a Striking Bar

This paper describes the failure investigation of a tubular shaft that is part of a hammer drill assembly. The failure investigation was particularly challenging as the fracture surfaces were completely damaged during service subsequent to the failure process. However, careful examination of the component and its assembly revealed many clues that pointed to the root causes of failure. The basic failure mode was identified as torsional fatigue failure in combination with high bending stresses. The failure was determined to be originated on the inside diameter of the tubular shaft. The root causes were determined to be operational overload in the presence of rough machining marks on the bore surface and higher than necessary operating torque required to overcome the dry adhesive friction in the system. The preventative measures recommended were manyfold including improving surface finish on the bore diameter, reducing dry sliding friction, decreasing the overall level of dynamic loads by appropriate design changes, and adding a surface strengthening heat treatment.

Investigating surface metrology of curved wall surface during milling of SS304 with different tool path strategies

Curved mating surfaces that exist in complex engine parts such as turbine blades play a critical role in part fitting and assembly and, thus, system performance. Control of precise surface metrology (e.g., form error, surface roughness) during machining of such surfaces is highly challenging, especially when processing super alloys like hardened steels. This work aims to experimentally investigate surface metrology of a 12.70-mm-thick curved plate platform (with S-shaped sidewall) of AISI SS304 material during milling on a vertical three-axis milling machine with three different tool path strategies: ramp, contour, and peripheral. Experiments are performed to study surface location error (SLE) and roughness during upward and downward feeding of tool on both concave and convex sidewall surfaces at different spindle speed and feed combinations. SLE values that are estimated as undercut or overcut with respect to the desired surface are found to be minimum with ramp (15.05 μm), followed by contour (18.63 μm), and maximum with peripheral (24.12 μm) milling paths. However, peripheral milling may be preferable in terms of surface roughness (improved about 40 %) and overall machining time (six times faster than ramp milling). The findings are analyzed based on the associated cutting mechanics and cutting forces.

An Evaluation Method Based on Grey Relational Grade for Cutting Tool Performance in the Milling of Titanium Aircraft Components

Cutting tools play an important role in the cutting process of titanium aircraft components, but it is difficult to comprehensively evaluate the cutting tool performance, so the selection of appropriate cutting tool becomes extremely important. In this paper, an evaluation method using grey relational analysis for cutting tool performance was proposed. Meanwhile, in this method, a test benchmark with some typical difficult-to-machined features extracted from titanium aircraft components was designed, and the processing route was developed. Grey comprehensive evaluation models of cutting tool performance were established for the rough and finish machining respectively. Finally, the grey comprehensive evaluation models were used to evaluate the cutting tool performance in the milling experiments of the benchmarks. The results show that the grey relational comprehensive evaluation method is convenient and effective to evaluate milling tools performance for titanium aircraft components.

Study on Influence of Electrode Material on Hole Drilling in Micro-EDM

Micro-EDM technology is widely used in micro hole machining for its small force and high precision. However, the slow machining rate and large tool wear are the two major problems. In this research, machining with different electrode materials has been characterized under rough, semi-finish and finish machining conditions. Since the tool material has an influence on the tool feed, the relationship between the electrode feed and the machining time has been investigated to show the detailed information of electrode feed. As significant indicators for machining accuracy, the relationship between side gap-width and machining feed, as well as the relationship between electrode wear ratio and machining feed were also investigated. In addition, the influence of electrode material on tool wear is also discussed.

High-efficient Dry Hybrid Machining of EDM and Arc Machining

EDM milling experiments on AISI 304 stainless steel (AISI 304 SS) using high-efficient hybrid machining with a high-speed air dielectric were conducted in this study. The novel and efficient hybrid machining is the arc machining and electrical discharge machining (EDM) working in parallel. AISI 304 SS can be quickly melted by significantly high machining energy and fast expelled by high-speed air flow and high-speed electrode rotation. The maximum material removal rate (MRR) of 5534 mm3/min was obtained, which was hundred times compared with that of conventional dry EDM. Comparative experiments on AISI 304 SS using high-efficient dry hybrid machining, dry arc machining, and dry EDM were conducted. The influences of air flow rate, peak current of arc machining, peak voltage of EDM, and electrode rotation speed on MRR, relative electrode wear rate and surface roughness were also studied. Moreover, the cross section and surface morphology were investigated. This study demonstrates that high-efficient dry hybrid machining is an efficient rough machining method in the processing fields that require removing vast materials.

Development of a Pulse Generator for Rough Cutting of Oil-based Micro Wire-EDM

This paper aims to develop a specific pulse generator for rough cutting of oil-based micro wire electrical discharge machining (wire-EDM). A two-stage current-limiting resistance power supply was presented to suppress thermal damage on the machined surface of polycrystalline diamond (PCD) while achieving stable machining by supplying high open voltage and low discharge current pulse waveforms. Tests revealed that the two-stage resistance power supply could achieve lower thermal damaged layer, better surface quality and surface finish than a conventional pulsed power supply since the former could provide smaller peak current and shorter discharge duration than the later. Experimental results demonstrate that boron-doped polycrystalline composite diamond (BD-PCD) is superior to polycrystalline diamond in the smoothness of cutting edge, surface quality and surface roughness since the former has lower specific resistance and thermal conductivity than the later. This study has indicated that the proposed power supply could enable a prototype micro wire-EDM machine to achieve a surface finish as low as 0.45μm Ra and a thermal damaged layer as small as 6μm on the machined surface of BD-PCD after one rough machining operation.