Investigating the Machinability of AISI 420 Stainless Steel Using Factorial Design

This work aims at studying the machining characteristics of high-strength materials using carbide cutting tool inserts at different cutting conditions. This is an essential step in building up an accurate machining information system. The tested material is high-strength stainless steel of the AISI 420 type. Machining tests were carried out using orthogonal cutting conducted to investigate the machining characteristics for high-strength stainless steel AISI 420 at different cutting conditions and tool rake angles. This assessment is achieved by investigating the effect of cutting parameters (cutting speed, feed, depth of cut, and tool geometry) on cutting forces, specific cutting energy, shear angle, coefficient of friction, shear stress, shear strain, and shear strain rate. Empirical equations and a correlation for the behavior of each of the output responses were investigated as a function of the independent variables. Main effect and interaction plot were presented for the most influential factors affecting the main cutting force and the power consumed.     

Performance of alumina-based ceramic inserts in high-speed machining of nimonic 80A

The study of machining forces and cutting tool wear during the machining is important for designing and selection of machining system and improving the productivity. This study reports the machinability of Nimonic 80A superalloy with alumina-based ceramic inserts. The objective is to analyze the reason for higher cutting forces generated during machining and tool wear mechanism on machining parameters. The cutting forces and tool wear are found to be mainly influenced by the cutting speed. The main causes of tool failure while machining Nimonic 80A are adhesion and abrasion. The role of tool wear is more dominant on the surface finish at lower cutting speed. Also, with an increase in cutting speed, thermally activated wear quietly increases at tool surfaces. The mechanistic approach is used to model the main cutting force. Developed cutting force model agrees well with experimental cutting force values.     

Design, development and testing of a turning dynamometer for cutting force measurement

In this study, a turning dynamometer that can measure static and dynamic cutting forces by using strain gauge and piezo-electric accelerometer, respectively, has been designed and developed. The orientation of octagonal rings and strain gauge locations has been determined to maximize sensitivity and to minimize cross-sensitivity. The developed dynamometer is connected to a data acquisition system. Cutting force signals were captured and transformed into numerical form and processed using a data acquisition system consisting of necessary hardware and software running on MS-Windows based personal computer. The obtained results of machining tests performed at different cutting parameters showed that the dynamometer could be used reliably to measure cutting forces. Although the dynamometer was developed primarily for turning operations, it can be used to measure cutting forces during nearly all machining operations (milling, drilling, etc.).     

Prediction of cutting force based on machining parameters on AL7075-T6 aluminum alloy by response surface methodology in end milling

Cutting forces modeling is the basic to understand the cutting process, which should be kept in minimum to reduce tool deflection, vibration, tool wear and optimize the process parameters in order to obtain a high quality product within minimum machining time. In this paper a statistical model has been developed to predict cutting force in terms of geometrical parameters such as rake angle, nose radius of cutting tool and machining parameters such as cutting speed, cutting feed and axial depth of cut. Response surface methodology experimental design was employed for conducting experiments. The work piece material is Aluminum (Al 7075-T6) and the tool used is high speed steel end mill cutter with different tool geometry. The cutting forces are measured using three axis milling tool dynamometer. The second order mathematical model in terms of machining parameters is developed for predicting cutting forces. The adequacy of the model is checked by employing ANOVA. The direct effect of the process parameter with cutting forces are analyzed, which helps to select process parameter in order to keep cutting forces minimum, which ensures the stability of end milling process. The study observed that feed rate has the highest statistical and physical influence on cutting force.     

Machining fixture verification for linear fixture systems

This paper presents a fixture configuration verification methodology that takes into account dynamic machining conditions--including the effect of dynamic gravitational forces--in the verification process. The fixture verification system is modelled as a linear optimization problem with respect to minimum clamping forces. The method provides a simple and effective means for (a) verifying whether a particular fixturing configuration is valid with respect to locating stability, deterministic workpiece location, clamping stability and total restraint; (b) identifying which locator loses contact with the part for an invalid fixture configuration; (c) identifying which clamp needs to be replaced; and (d) determining the minimum clamping forces to restrain the piece during the entire machining process. Since a fixture configuration design is validated not only under a given cutting direction, but also under an inverse cutting direction, this allows designers to understand thoroughly whether the fixture configuration is valid and what the sufficient dynamic clamping forces are for the fixture system to withstand unpredicted machining forces over the entire machining time. Hence, it makes the verification system more robust and reliable. Two case studies are included to demonstrate the effectiveness and the capabilities of the methodology.     

Simultaneous measurement of forces and machine tool position for diagnostic of machining tests

A diagnostic system of the milling process through the cutting forces and cutting tool position (coordinates X, Y, and Z) simultaneously collected is detailed in this paper. After the milling test, the cutting forces generated during the machining and the machine position where they occurred can be correlated. After collecting and recording of both the force and position signals, a graphic representation of force components can be applied. In this way, the machine user is able to check those events that happened during the milling; thus, a more useful diagnosis of machining problems is possible. The collecting system is composed by a dynamometric plate for the measurement of the three components of the cutting force, as well as an acquisition device connected to the analog output of the position control loops. After machining, the file containing position and force data is post-processed and chromatic and vector maps are generated. The analysis tool shows its capabilities being applied to three examples, referring to three research projects.     

Performance Improvement of End Milling Using Graphite as a Solid Lubricant

In any machining operation, the use of coolants is essential to dissipate heat generated during machining and hence to improve productivity, machinability, etc. However, the use of cutting fluids in machining operations may seriously degrade the quality of environment. New cutting techniques are to be investigated to alleviate the problems associated with wet machining. To overcome some of the problems, an attempt has been made to use graphite as a solid lubricant. This paper deals with an investigation on using graphite as a solid lubricant to reduce the heat generated at the milling zone. An experimental setup has been developed to direct graphite powder continuously onto the workpiece and tool interface at the required flow rate. Experimental studies have been conducted to see the effect of tool geometry (radial rake angle and nose radius) and cutting conditions (cutting speed and feed rate) on the machining responses such as cutting forces, specific energy, and surface finish in solid lubricant assisted machining using four fluted solid coated carbide end mill cutters. Results indicate that there is a considerable improvement in the performance of milling AISI 1045 steel using graphite as a solid lubricant when compared with machining using cutting fluids in terms of specific energy requirements, cutting force, and surface finish.     

An analytical tim6 domain evaluation of the cutting forces in BTA deep hole machining using the thin shear plane model

This paper presents an analytical approach to describe the cutting forces in 1ST A deep hole machining processes in the time domain. The method takes into account the effect of different machining conditions. Since the cutting velocities employed in BTA deep hole machining process are relatively high, and since small chips are produced due to the presence of tool chip breakers, the analysis is developed on the basis of the thin shear plane model.

The cutting velocity is a linear function of radius and the rake angle. Cutting is different in the two regions of the cutting tool, so the total cutting force acting on the cutting tool is determined by integrating the force on a small incremental thickness of the cutting tool. This approach, to predict the value of the cutting forces without resorting to any empirical techniques, clearly illustrates the effect of various system parameters on the machining process.

The resultant force system on a new BTA cutting tool consists of an axial force and torque. But with the increase in the number of holes bored, not only does the cutting profile deteriorate, but the wear pads do too. The resultant force system will then consist of three force components and a torque, due to the fact that the forces are not balanced at the wear pads. Under such conditions, the cutting force equations derived in the latter half of the paper, coupled with the properties of the randomly varying component, can be used as the forcing function on the machine tool to evaluate not only the response but also the regions of stability and instability during the machining.     

一种龙门式加工中心横梁的动力学仿真研究

对一种国产龙门式加工中心的横梁关键部件,采用机械系统多刚体动力学仿真软件ADAMS和有限元分析软件ANSYS进行了静动态特性分析;在考虑重力和切削力作用下,由ADAMS计算出导轨与滑块间的作用力,从而计算出横梁部件的静态变形;通过动态测试和参数辨识方法获得导轨结合面特性参数并将其应用到横梁滑箱系统整体有限元模型中,经过模态分析得到系统固有频率和各阶振型图,并进一步分析了结合面参数变化对横梁滑箱系统整体动态特性的影响.     

Chemical vapour deposition (CVD) diamond coated tools performance in machining of PEEK composites

This paper presents a study about the chemical vapour deposition (CVD) diamond coated tool performance in machining unreinforced PEEK and composite PEEK CF30 (reinforced with 30% of carbon fibres).

The experimental procedure consisted of turning operations, during which cutting forces and surface roughness obtained in composite workpieces were measured.

The obtained results showed a best cutting performance for CVD diamond coated tool in machining PEEK composites, particularly in terms of cutting forces and power consumption, when compared with polycrystalline diamond (PCD) and cemented carbide (K10) cutting tools. This fact is very important due to the minor production costs of CVD diamond coated tools in comparison with PCD tools.     

Dynamic management of cutting tools for flexible and quality machining

Traditional economic tool-life models assume a homogeneous cutting environment, where a tool's continued service is irrespective of its condition. It is wellknown that the quality of a machining process is significantly impacted by a tool's wear-and-tear. To ensure good machining quality, tool assignment should consider the wear level of the tool as well as the type of machining job to be performed. This paper presents a dynamic management model for cutting tools that emphasizes the cost of machining quality. The model describes a heterogeneous environment typical of computerized manufacturing systems, where a tool carries out variable machining assignments during its life. The formulation is a stochastic dynamic programme, which determines optimal preventive actions based on a periodic evaluation of the tool's operating conditions. Tool deterioration is described as movement to different operating states (increasing levels of tool wear) and job assignment of tools is state-dependent. A tool's optimal economic life is also determined within the context of variable machining. The cost of quality-deviation is assessed using Taguchi's quality-loss function.     

Micro-mechanical modeling of machining of FRP composites – Cutting force analysis

Orthogonal machining of unidirectional carbon fiber reinforced polymer (UD-CFRP) and glass fiber reinforced polymer (UD-GFRP) composites is simulated using finite element method (FEM). A two-phase micro-mechanical model with fiber assumed elastic and the matrix elasto-plastic is used to estimate the cutting forces during machining. A cohesive zone simulated the interface debonding between the fiber and matrix. Fiber failure was based on maximum principal stresses reaching the tensile strength. The matrix elastic modulus was degraded to include damage once yield strength was reached. The model assumes plane strain and quasi-static condition. The cutting forces during orthogonal machining were studied both experimentally and numerically for a range of fiber orientations (θ), depths of cut (t) and tool rake angles (γ). The contact forces developed between the tool and the fiber provided a good estimate of the cutting (F_h) and thrust (F_v) forces during the orthogonal cutting process. The failure of fiber is found to be a combination of crushing and bending, with the bending effect becoming more significant as the fiber orientation changes from 90° to 15°.     

Turning of Microgrooves Both With and Without Aid of Ultrasonic Elliptical Vibration

Microgroove, as a form of surface texturing, has a wide array of industrial applications. However, the use of conventional methods to machine microgrooves leads to a number of problems including large burrs, high cutting forces, and poor machining quality. In this paper, ultrasonic elliptical vibration cutting is used to assist microgrooves turning on cylindrical workpiece surfaces. The elliptical locus in the cutting process is generated by a newly designed 2D resonant ultrasonic vibrator. A series of microgrooves cutting experiments without and with the ultrasonic elliptical vibration-assistance is performed to verify the effects of the ultrasonic elliptical vibrations as compared to the ordinary cutting method. The generated cutting forces, burr suppression action, and microgroove surface quality are compared for the two classes of processes. Comparison results show the effectiveness of elliptical vibration-assisted microgroove cutting in reducing cutting forces and improving microgrooves machining quality for difficult-to-cut materials. The results also show that ultrasonic elliptical vibration-assisted cutting improves the microgroove turning process with respect to cutting forces, microgroove surface roughness, and burr formation for difficult-to-cut materials.     

A dynamometer design and its construction for milling operation

In this study, a strain gauge based dynamometer capable of measuring three-force components during metal cutting has been designed and constructed. In order to read and save the cutting force data automatically on a computer during metal cutting, a data acquisition system with the necessary hardware and software was also devised and connected to the developed dynamometer. Cutting force signals were captured and processed using a personal computer through operational amplifiers and analog-to-digital converter. Although the dynamometer was developed primarily for milling operations, it can be used to measure cutting forces during nearly all machining operations (turning, grinding, drilling, etc.). Machining tests were performed at different cutting parameters and the results showed that the dynamometer could be used reliably to measure cutting forces.     

Influence of cryogenic coolant on turning performance characteristics: A comparison with wet machining

Machining of 17-4 Precipitation Hardenable Stainless Steel (PH SS) is one of the difficult tasks because of its high cutting temperatures. Conventional cutting fluids are used to overcome the high cutting temperatures, but these are not acceptable from the health and environmental sustainable points of view. Cryogenic cooling is one of the potential techniques to overcome such problems. In the current work, comparison is made of cryogenic turning results, such as tool flank wear, cutting forces (feed force, main cutting force), cutting temperature, chip morphology and surface integrity characteristics with wet machining during machining of heat-treated 17-4 PH SS. The result showed that in cryogenic machining, a maximum of 53%, 78%, 35% and 16% reductions was observed in tool flank wear, cutting temperature, surface roughness and cutting force, respectively, when compared with wet machining. It was also evident from the experimental results that cryogenic machining significantly improved the machining performance and product quality even at high feed rates.     

Near-Cryogenic Machining of Polymethyl Methacrylate for Micromilling Tool Development

Micromilling tools with a diameter of 22 micrometers were developed to machine polymethyl methacrylate (PMMA) for micro systems applications. Due to the small diameter of the tool, and therefore its slow cutting speed, the specific cutting energy of PMMA in the near-brittle state was needed so the micromilling feed could be estimated. To determine the specific cutting energy in the near-brittle state, PMMA was cooled with liquid nitrogen and machined with diamond tools under normal machining conditions. Cutting forces and surface finish were measured from room temperature down to -53°C. It was found that as the temperature of the PMMA was reduced, the specific cutting energy increased linearly to approximately that of oxygen-free high conductivity copper. It was also found that the surface finish became rougher as the temperature decreased. Using these results, micromilling tools were fabricated using focused ion beam machining. The tools were used to micromachine PMMA electroforming molds with high precision, small features, and excellent surface finish. Using the feed indicated from the cryogenic machining and other tests, the micromilling tools did not break after extended periods of machining.     

Broaching Performance of Superalloy GH4169 Based on FEM

The nickel-based superalloy GH4169 is an important material for high temperature applications in the aerospace industry. However, due to its poor machinability, GH4169 is hard to be cut and generates saw-tooth chips during high speed machining, which could significantly affect the dynamic cutting force, cutting temperature fluctuation, tool life, and the surface integrity of the parts. In this paper, the saw-tooth chip formation mechanism of superalloy GH4169 was investigated by the elasto-viscoplastic finite element method (FEM). Using the finite element software of ABAQUS/Explicit, the deformation of the part during high speed machining was simulated. The effective plastic strain, the temperature field, the stress distribution, and the cutting force were analyzed to determine the influence of the cutting parameters on the saw-tooth chip formation. The study on broaching performance has great effect on selecting suitable machining parameters and improving tool life.     

Developing a virtual machining model to generate MTConnect machine-monitoring data from STEP-NC

The ability to predict performance of manufacturing equipment during early stages of process planning is vital for improving efficiency of manufacturing processes. In the metal cutting industry, measurement of machining performance is usually carried out by collecting machine-monitoring data that record the machine tool’s actions (e.g. coordinates of axis location and power consumption). Understanding the impacts of process planning decisions is central to the enhancement of the machining performance. However, current methodologies lack the necessary models and tools to predict impacts of process planning decisions on the machining performance. This paper presents the development of a virtual machining model (called STEP2M model) that generates machine-monitoring data from process planning data. The STEP2M model builds upon a physical model-based analysis for the sources of energy on a machine tool, and adopts STEP-NC and MTConnect standardised interfaces to represent process planning and machine-monitoring data. We have developed a prototype system for 2-axis turning operation and validated the system by conducting an experiment using a Computer Numerical Control lathe. The virtual machining model presented in this paper enables process planners to analyse machining performance through virtual measurement and to perform interoperable data communication through standardised interfaces.     

Experimental investigations on cryogenic cooling by liquid nitrogen in the end milling of hardened steel

Milling of hardened steel generates excessive heat during the chip formation process, which increases the temperature of cutting tool and accelerates tool wear. Application of conventional cutting fluid in milling process may not effectively control the heat generation also it has inherent health and environmental problems. To minimize health hazard and environmental problems caused by using conventional cutting fluid, a cryogenic cooling set up is developed to cool tool–chip interface using liquid nitrogen (LN₂). This paper presents results on the effect of LN₂ as a coolant on machinability of hardened AISI H13 tool steel for varying cutting speed in the range of 75–125 m/min during end milling with PVD TiAlN coated carbide inserts at a constant feed rate. The results show that machining with LN₂ lowers cutting temperature, tool flank wear, surface roughness and cutting forces as compared with dry and wet machining. With LN₂ cooling, it has been found that the cutting temperature was reduced by 57–60% and 37–42%; the tool flank wear was reduced by 29–34% and 10–12%; the surface roughness was decreased by 33–40% and 25–29% compared to dry and wet machining. The cutting forces also decreased moderately compared to dry and wet machining. This can be attributed to the fact that LN₂ machining provides better cooling and lubrication through substantial reduction in the cutting zone temperature.     

Flank milling model for tool path programming of turbine blisks and compressors

In this paper, a methodology for complex surface machining based on cutting forces prediction is presented. The work is focused on blade finishing operations. The cutting forces model developed can be applied to three axis and five axis milling cases. For three-axis cases, the chip thickness is calculated according to traditional analytical methods. On the contrary, for five-axis cases the chip thickness is obtained from a geometric method developed in the paper. The cutting forces values can be calculated for the complete toolpath, but the presented model can also provide the programmer information about the cutting forces in a single point of the toolpath. The cutting force model is integrated in the CAM software in order to provide an extra tool that helps the programmer to decide which the optimal milling strategy is, based on the minimum cutting forces. In the last section, results of a case study based on impeller and blisk blades flank milling are discussed. Model predicted forces and real measured forces of flank milling operations are compared for model validation. Applying this methodology, cutting forces can be taken into account as a decisive criterion for optimal tool path selection.