Experimental observation and analysis of burr formation mechanisms in face milling of aluminum alloys

The purpose of this paper is to study the burr formation mechanisms in face milling process, and to investigate the influence of cutting conditions on burr formation in face milling of aluminum alloys. The fly milling cutter is used to carry out single-tooth face milling tests. Three aluminum alloys were tested: Al 1100 (cold drawn), Al 2024-T4 and Al 6061-T6. It is found that the burr geometry is strongly dependent upon the in-plane exit angle. Five types of burrs were observed in the experiments: knife-type, wave-type burr, curl-type, edge breakout and secondary burr. Formation mechanisms of each type of these burrs are discussed in details. The relationship between their existence and the machining condition is indicated. The machining guideline in face milling is given at the end of the paper to reduce burr size effectively through the formation of secondary burr.     

An experimental investigation of rotary ultrasonic face milling

Reliable and cost-effective machining of advanced ceramics is crucially important for them to be widely used in a number of critical engineering applications. The potential of Rotary Ultrasonic Machining (RUM) process has been recognized as one of the reliable and cost-effective machining methods for advanced ceramics and commercial machinery is available for the process. One limitation of the commercial RUM machines is that only circular holes can be efficiently machined. An approach to extend the RUM process to face milling of ceramics was proposed and the development of the experimental apparatus as well as the preliminary experimental results were published earlier in this journal. As a follow-up, this paper will present the results of an experimental investigation of the newly-developed Rotary Ultrasonic Face Milling (RUFM) process. In this investigation, a five-variable two-level fractional factorial design is used to conduct the experiments. The purpose of these experiments is to reveal the main effects as well as the interaction effects of the process parameters on the process outputs such as Material Removal Rate (MRR), cutting force, material removal mode and surface roughness.     

Minimization of exit burr in face milling of medium carbon steel by exit edge beveling

Elimination, or reduction, of burrs formed during machining is drawing focus of manufacturers and researchers since long or suppressing a burr regarding its formation or removal of it through a suitable deburring process. Deburring is an extra process often required to undertake, and it involves additional time and cost. Presence of burr may cause several problems, such as difficulty in assembly, dimensional inaccuracy, injury to the operator, etc. Like other industries, avoidance of burr on milled component surfaces in railways is of concern. In the present investigation, formation of burr in face milling is tried to reduce by beveling the exit edge of blocks of medium carbon steel (45C8) which is widely used in railways for manufacture of different components. Cutting conditions are also varied to observe the effect on burr formation. It is observed that at an exit edge bevel angle of 15°, negligible burr is formed at most of the cutting conditions undertaken, and hence, recommended.     

An experimental technique for the measurement of temperature on CBN tool face in end milling

An infrared radiation pyrometer with two optical fibers connected by a fiber coupler was developed and applied to the measurement of tool–chip interface temperature in end milling with a binderless CBN tool. The infrared rays radiated from the tool–chip interface and transmitted through the binderless CBN are accepted by the optical fiber inserted in the tool and are then sent to the pyrometer. A combination of the two fibers and the fiber coupler makes it possible to transmit the accepted rays to the pyrometer, which is set up outside of the machine tool. This method is very practical in end milling for measuring the temperature history at tool–chip interface during chip formation. The maximum tool–chip interface temperature in up milling of a 0.55% carbon steel is 480 °C when the cutting speed is 2.2 m/s and 560 °C at 4.4 m/s, and in the down milling, 500 °C at 2.2 m/s and 600 °C at 4.4 m/s.     

A study of high efficiency face milling tools

A new predictive force model for a single-tooth face milling cutter with a chamfered main cutting edge has been derived. Machining tests has been conducted for fly cutting with a chamfered main cutting edge tools on plane surfaces. An S45C medium carbon plate has been used as the workpiece matrial. Force data from these tests were used to estimate the empirical constants of the mechanical model and to verify its prediction capabilities. The results show a good agreement between the predicted and measured forces.Since tool manufacturers does not provide tools with selected combinations of chamfered main cutting edge, radial angle, axial angle and inclination angles, tool holders manufactured in-house were used in the tests. The tips were prepared to the required geometry using a tool grinder.     

An experimental and numerical study on the face milling of Ti-6Al-4V alloy: Tool performance and surface integrity

This paper is concerned with the experimental and numerical study of face milling of Ti-6Al-4 V titanium alloy. Machining is carried out by uncoated carbide cutters in the presence of an abundant supply of coolant. Experimental analysis is conducted by focusing on the measurement of specific cutting energy, surface integrity and tool performance. The experimental analysis is supplemented by simulations from a 3D finite element model (FEM) of face milling simulation where needed. A tool wear model parameterized from FEM predictions of the tool-chip interface temperature, contact stress and chip velocity is presented. Tool wear patterns are described in terms of various cutting conditions and the influence of tool wear on surface integrity is investigated. Tool wear predictions based on the 3D FEM simulation show good agreement with experimental tool wear measurements. The highest cutting speed realized for the cutting tool material is 182.9 m/min (600 sfpm). Good surface integrity in terms of favorable residual stress and surface finish is achieved under the machining conditions used with limited tool wear. Residual stresses imparted to the machined surface are shown to be compressive.     

A study on instantaneous cutting force coefficients in face milling

In this paper, the characteristics of instantaneous cutting force coefficients in face milling are studied. In order to estimate instantaneous cutting force coefficients in face milling, the relationships between instantaneous cutting force coefficients and measured cutting force signals are derived. A series of experiments are then conducted to study the natures of instantaneous cutting force coefficients. The relationships between instantaneous cutting force coefficients and other cutting parameters are also established. It is found that the normal force coefficient is mainly affected by chip thickness and cutting speed; the vertical force coefficient is mainly affected by chip thickness, cutting edge length and cutting speed; and that the horizontal force coefficient is not only affected by chip thickness, cutting speed and length of cut, but also the variation rate of chip thickness.     

Investigations on reducing burr formation in drilling

This paper reports the experimental investigations on reducing burr formation while drilling through-holes in metals. Experiments have been planned based on response surface methodology (RSM) technique. Mathematical models correlating response parameters (burr sizes) to the process parameters, e.g. feed, hole size and workpiece hardness have been obtained. Optimal process conditions to minimize the sizes of burr at the entry and exit of holes have been identified. In addition an attachment has been designed and developed to provide continuous modification of feed during drilling. It is reported that the optimal process conditions and the use of attachment can cause significant reductions in the sizes of burr.     

Predicting cutting forces in face milling

It is shown how orthogonal machining theory can be applied to predict the cutting forces in face milling from a knowledge of the work material properties and cutting conditions. Predicted and experimental results are compared.     

Micro electric discharge milling process performance: An experimental investigation

Micro electric discharge milling (μED-milling) process is gaining lot of interest in the area of microfabrication specifically for hard to machine materials. Any complex shape can be generated with a controlled motion of cylindrical tool in a predefined path similar to conventional micromilling. In this method the material removal mechanism in tool and workpiece is complex and requires a detail study of the process parameters. Parameters such as tool rotation speed, feed rate and aspect ratio (AR) can play a vital role in μED-milling process along with the fundamental parameter such as energy. This research work aims to provide exhaustive study of parameters on material removal rate (MRR) and tool wear rate (TWR) by conducting general factorial experiments. A new method is proposed to measure the volume of material eroded from workpiece and tool with an aid of design software. The experimental result shows that the parameters have individual and combined effect on MRR and TWR. Among the parameters, tool rotation speed has a significant function in flushing away the debris to ensure stable discharge. Detailed surface morphology of the machined features has also been analyzed using scanning electron microscope (SEM). A regression analysis was carried out to establish models for MRR and TWR as a function of process parameters.     

Modelling and experimental study of machined depth in AFM-based milling of nanochannels

A nanochannel depth prediction model for an atomic force microscopy (AFM)-based nano-milling fabrication technique was developed and the relationship between the normal load, tip feed, and nanochannel depth was systematically investigated. Machining experiments were performed to fabricate nanochannels on a 2A12 aluminum alloy surface, the depth of which was compared with that calculated with the model. The model predicted the depth of the nanochannels accurately when a feed in the range of 40–90 nm was used during machining. The cutting mechanism played an important role in determining the consistency of the experimental and theoretical results. In addition, the effects of normal load and feed on the surface quality of the machined nanochannel were studied. A nanochannel with a 3D structure at the bottom is presented by the nano-milling method. To machine a nanochannel with a desired depth, the appropriate normal force and feed to guarantee the surface quality can be selected simply and easily using this model.     

Partitioning of primary shear zone heat in face milling

The outcome of this paper allows calculating the fraction of heat generated in the primary shear zone that is transferred to the workpiece in face milling. The proposed approach is based on a sequentially coupled analysis of the heat partitioning in the cutting edge normal plane and in the reference plane. The latter, for the first time, allows to systematically take into account the removal of heated workpiece material by subsequent cutting tool engagements. The generated heat is related to the uncut chip thickness. Utilizing Weiner's approach, the heat flux density distribution is determined which serves as input for a three-dimensional thermal finite element simulation that is validated experimentally by temperature measurements.     

Experimental studies of cutting force variation in face milling

The purpose of this paper is to present a developed cutting force model for multi-toothed cutting processes, including a complete set of parameters influencing the cutting force variation that has been shown to occur in face milling, and to analyse to what extent these parameters influence the total cutting force variation for a selected tool geometry. The scope is to model and analyse the cutting forces for each individual tooth on the tool, to be able to draw conclusions about how the cutting action for an individual tooth is affected by its neighbours.A previously developed cutting force model for multi-toothed cutting processes is supplemented with three new parameters; eccentricity of the spindle, continuous cutting edge deterioration and load inflicted tool deflection influencing the cutting force variation. A previously developed milling force sensor is used to experimentally analyse the cutting force variation, and to give input to the cutting force simulation performed with the developed cutting force model.The experimental results from the case studied in this paper show that there are mainly three factors influencing the cutting force variation for a tool with new inserts. Radial and axial cutting edge position causes approximately 50% of the force variation for the case studied in this paper. Approximately 40% arises from eccentricity and the remaining 10% is the result of spindle deflection during machining. The experimental results presented in this paper show a new type of cutting force diagrams where the force variation for each individual tooth when two cutting edges are engaged in the workpiece at the same time. The wear studies performed shows a redistribution of the individual main cutting forces dependent on the wear propagation for each tooth.     

Rotary ultrasonic machining for face milling of ceramics

Among the various material removal processes applicable to ceramic materials, rotary ultrasonic machining has the potential for high material removal rate while maintaining low machining pressure and resulting in less surface damage. The limitation of rotary ultrasonic machining is that only circular holes or cavities can be machined due to the rotary motion of the tool. Attempts have been made by other researchers to extend rotary ultrasonic machining process to machining flat surfaces or milling slots. However, these extensions either changed the material removal mechanisms or had some severe drawbacks. One of the reasons for this might be an insufficient understanding of the material removal mechanisms involved. In this paper, a new approach to extend rotary ultrasonic machining to face milling of ceramics is proposed, which keeps all the material removal mechanisms of rotary ultrasonic machining. The development of the experimental apparatus and the design of the cutting tool are described. Preliminary experimental results are presented and discussed.     

Micro milling of titanium alloy Ti-6Al-4V: 3-D finite element modeling for prediction of chip flow and burr formation

Cutting process of titanium alloy Ti-6Al-4V is considered difficult due to chemical affinity between tool and work material, adhesion, built-up edge and burr formation, and tool wear resulting in loss of productivity. Three dimensional (3-D) chip flow together with local field variables such as temperature, elastic/plastic strain, strain-rate and velocity in the shear zones during micro milling process can be predicted using continuum-mechanics based 3-D Finite Element (FE) modelling and simulation of elastic/viscoplastic work material deformations. This paper provides much needed process insight for chip flow, built-up edge and burr formation by using modeling work with experimental validation. Scanning electron microscopic (SEM) observation of the 3-D chip morphology and burrs demonstrate ductile fractured surfaces together with localized instability and failure behaviors. FE simulations are utilized to investigate the effects of micro milling operation i.e. up and down milling and tool edge radius on 3-D chip flow, built-up edge, and 3-D burr formation. Simulated results are compared with measurements of chip morphology, shape, and dimensions together with tool edge condition of built-up edge and chip adhesion yielding to good agreements.     

Improvement of workpiece quality in face milling of aluminum alloys

The compliance with the quality requirements of components is essential for the functionality of the whole product. With respect to parts with face-milled faces, the surface quality and the shape of the workpiece edges are of great interest. Frequently, these faces take over the function of seal faces where high demands on the surface integrity and burr formation exist. To ensure the workpiece quality that is required, nowadays additional processes for deburring are often necessary. To avoid deburring, the modification of machining processes is a promising approach. In this study, the influence of process cooling on workpiece quality is investigated. Using this approach, two effects are expected. The cooling is used to minimize a reduction of flow stress generated from the process heat, which than leads to a lower formability. The second effect relates to the kinetic energy of the snow blast for deburring by deformation and breakage of the burrs. Using a process cooling with carbon dioxide, the surface quality is enhanced and the burr formation is minimized.     

Chip formation in grinding: an experimental study

Due to high cutting speeds and low single grain chip thicknesses no reliable approach to interrupt the cut in grinding was realized so far. This paper presents a new method to experimentally obtain and analyze chip roots during up-grinding. By means of high resolution SEM-micrographs several chip roots are analyzed, classified and discussed with regard to the fundamental chip formation and material removal mechanisms. Furthermore, there are conclusions drawn about the distribution and number of the active grains, which are in a good correlation with the Abbott-curve of the grinding wheel layer and the process parameters.     

Optimization and control of drilling burr formation of AISI 304L and AISI 4118 based on drilling burr control charts

Control charts for drilling burr formation for stainless, AISI 304L, and low alloy steel, AISI 4118, were developed. Split point twist drills are used for the experiments of this work. A Drilling Burr Control Chart, based on experimental data, is a tool for prediction and control of drilling burrs. Burr classification was carried out based on the geometric characteristics, burr formation mechanisms and sizes of the burrs. New parameters consisting of cutting condition variables and drill diameter were developed, and used to show unique distributions of the burr types. Burr types and the resultant burr size showed great dependence on the new parameters regardless of the drill diameters. Through the chart, burr type can be predicted with given cutting conditions. Also cutting conditions that are believed to create preferred burr types can be selected.     

An experimental study of tool wear and cutting force variation in the end milling of Inconel 718 with coated carbide inserts

Inconel 718 is a difficult-to-cut nickel-based superalloy commonly used in aerospace industry. This paper presents an experimental study of the tool wear propagation and cutting force variations in the end milling of Inconel 718 with coated carbide inserts. The experimental results showed that significant flank wear was the predominant failure mode affecting the tool life. The tool flank wear propagation in the up milling operations was more rapid than that in the down milling operations. The cutting force variation along with the tool wear propagation was also analysed. While the thermal effects could be a significant cause for the peak force variation within a single cutting pass, the tool wear propagation was believed to be responsible for the gradual increase of the mean peak force in successive cutting passes.