A model-based sustainable productivity concept for the best decision-making in rough milling operations

[EN]There is a need in manufacturing as in machining of being more productive. However, at the same time, workshops are also urged for lesser energy waste in cutting operations. Specially, rough milling of impellers and bladed integrated disks of aircraft engines need an efficient use of energy due to the long cycle times. Indeed, to avoid dramatic tool failures and idle times, cutting conditions and operations tend to be very conservative. This is a multivariable problem, where process engineers need to handle several aspects such as milling operation type, toolpath strategies, cutting conditions, or clamping systems. There is no criterion embracing productivity and power consumption. In this sense, this work proposes a methodology that meets productivity and sustainability by using a specific cutting energy or sustainable productivity gain (SPG) factor. Three rough milling operations-slot, plunge nad trochoidal milling-were modelled and verified. A bottom-up approach based on data from developed mechanistic force models evaluated and compared different alternatives for making a slot, which is a common operation in that king of workpieces. Experimental data confirmed that serrated end milling with the highest SPG value of 1 is the best milling operation in terms of power consumption and mass removal rate (MRR). In the case of plunge milling technique achieve an SPG < 0.51 while trochoidal milling produces a very low SPG value.The authors acknowledge the support from the Spanish Government (JANO, CIEN Project, 2019.0760) and Basque Government (ELKARTEK19/46, KK-2019/00004). This research was funded by Tecnologico de Monterrey through the Research Group of Nanotechnology for Devices Design, and by the Consejo Nacional de Ciencia y Tecnologia de Mexico (Conacyt), Project Number 296176, and National Lab in Additive Manufacturing, 3D Digitizing and Computed Tomography (MADiT) LN299129. The authors also acknowledge the support from Garikoitz Goikoetxea and fruitful discussions with Mr. Jon Mendez (Guhring (c)) and Endika Monge (Hoffmann Group (c))

On the effects of cutting-edge angle on high-feed turning of Inconel 718© superalloy

Machining processes on heat-resistant superalloys—i.e., turbine cases, rings, or shafts—are challenging tasks. The high-added value of such parts makes cycle times be longer than expected. Recently, high-feed turning technique has attracted the attention of practitioners due to its high material removal rate capability. PrimeTurning™ tool unifies the concepts of high-feed and multidirectional turning using multiple active cutting edges. It should be capable of reducing machine downtimes in that kind of parts. However, to avoid early tool replacement and rejects on high added value parts, a deeper knowledge on the high-feed turning process is necessary. Here, inserts specifically designed for high-feed turning in heat resistant Inconel 718© alloy were tested using three cutting-edge angles. The results showed that when chip thickness is more relevant, a cutting-edge angle of 30° reduces the likelihood of notches. Even if force components are high, surface roughness is improved and the risk of fractures is minimized, together with a high evacuation volume. On the other hand, increasing the cutting-edge angle (45° and 60°) without compensating the feed rate, tends to produce tool fractures due to chip overload. Besides, experimental tests showed that long tool-to-workpiece contact times, tend to shorten tool life, due to excessive heat accumulation and poor chip control.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. Funding MCIN/AEI/https://doi.org/10.13039/501100011033 and "FSE invierte en tu futuro", from the Ministry of Science and Innovation of the Government of Spain, in the IB-RELIABLE project (DPI2016-74845-R). UPV/EHU for the financial aid for the pre-doctoral grants PIF 19/96

Analytical and experimental investigation of orthogonal turn-milling processes

Machining of hard-to-cut materials is challenging due to their high strength resulting in reduced productivity and high manufacturing cost. Conventional machining processes are commonly used for production of these parts where cutting speed, and thus the material removal rate, is limited due to high tool wear rate. Because of the increasing market demands for higher quality, reduced lead times and cost, alternative techniques are required in order to increase productivity in machining of these materials. An increase in potential production capacity was observed in the recent years due to advancements in machine tools that offer high precision, increased flexibility and spindle speed. Multi-axis machining, which can be a remedy for these demands, have been continuing to spread rapidly in many industries particularly in aerospace and defense. These processes are generally performed on multi-tasking machines through simultaneous cutting operations on the same part or machining of more than one part simultaneously. Turn-milling, which is a promising multi-axis cutting process combining two conventional machining operations; turning and milling, can offer high productivity for difficult-to-cut materials such as Ti and Ni alloys as well as parts with large diameters which cannot be rotated at high speeds on conventional lathes. However, the work done on analysis and modeling of turn-milling operations is very limited. On the other hand, due to the high flexibility and capability of turn-milling operations, there are numerous process parameters which need to be selected properly to utilize the full potential offered by these processes. In order to achieve this, process models which consider all cutting parameters are required. In this thesis, analytical models for turn-milling process geometry, chip formation and cutting force including eccentricity effects are presented. Furthermore, circularity, cusp height and surface roughness are modeled and simulated. Model predictions are verified by experiments carried out on a multi-tasking machine tool under different process conditions. Tool wear tests for hard-to-machine materials are also performed on the same machine where effects of turn-milling process conditions on tool life are shown. Simulation and experimental results show that substantial increase in productivity can be achieved using turn-milling in machining of difficult-to-cut materials when process conditions are selected properly

The difficulties of the assessment of tool life in CNC milling

In the manufacturing process, tool life is an important parameter in milling operations. The main objective of this paper is to explain how difficult is it to assess how much work a tool has undertaken before it must be changed. A number of ways of expressing tool life are currently used, including the conventional method based upon one of several configurations of the Taylor Tool Life Equation. These usually express tool life in terms of known material properties together with primary machining variables like speed, feed and depth of cut. Other approaches are based upon the extrapolation of a tool wear curve and considerations of the volume of metal removed. This initial investigation adopts an approach that is based upon a series of experiments, which produce data indicating the changes in machined feature form and dimension. For this study, a new test piece was designed in order to allow the indirect assessment of the tool flank wear by utilising a Coordinate Measuring Machine to accurately measure the workpieces. This work is intended to indicate how difficult it is to actually apply the existing methods to manage tool wear. The aim is to engineer a better way and to establish a methodology of measuring what the tool is actually doing in real time using the machine controller

Plunge milling time optimization via mixed-integer nonlinear programming

International audiencePlunge milling is a recent and efficient production mean for machining deep workpieces, notably in aeronautics. This paper focuses on the minimization of the machining time by optimizing the values of the cutting parameters. Currently, neither Computer-Aided Manufacturing (CAM) software nor standard approaches take into account the tool path geometry and the control laws driving the tool displacements to propose optimal cutting parameter values, despite their significant impact. This paper contributes to plunge milling optimization through a Mixed-Integer NonLinear Programming (MINLP) approach, which enables us to determine optimal cutting parameter values that evolve along the tool path. It involves both continuous (cutting speed, feed per tooth) and, in contrast with standard approaches, integer (number of plunges) optimization variables, as well as nonlinear constraints. These constraints are related to the Computer Numerical Control (CNC) machine tool and to the cutting tool, taking into account the control laws. Computational results, validated on CNC machines and on representative test cases of engine housing, show that our methodology outperforms standard industrial engineering know-how approaches by up to 55% in terms of machining time

THE INVESTIGATION OF END MILL FEEDS ON CNC ROUTER MACHINE USING VIBRATION METHOD

Vibration on End Mill Feeds will occur due to friction between the workpiece and end mill. The friction which occurs will cause tool wear in the insert blade. At this point, the tool wear experienced by the end mill can be seen from the imperfect feed of the workpiece that is resulted. Therefore, it is necessary to find out a method that can quickly and accurately detect tool wear at the end mill. The one that was experimented in this study was the vibration method. The vibration response was measured at their x, y, and z axes with rotation speeds of 2500 rpm, 3500 rpm, and 4500 rpm. At the broken end mill, it was shown that frequencies resulted did not affect the rotation while in the standard end mill. The initial frequency was highly influenced by spindle rotations treated on it

Assessing uneven milling cutting tool wear using component measurement

Tool wear is a complex phenomenon inherent in any cutting process. Cutting tool wear monitoring is therefore deployed in CNC milling to support machining operations in order to plan tool changes and avoid economic losses. The application of tool life management strategies can lead to premature removal of healthy tool or the continued use of a dangerously worn tool. This has led to the investigation of more appropriate strategies. Depending upon the nature of the sensor technology deployed tool wear monitoring methods are categorized as being either direct or indirect. The benefits and challenges to machine tool users of both approaches are subject to a body of ongoing research. In this study, a series of milling machining tests were performed in order to allow the confirmation of the presence of uneven tool flank wear. This was enabled by the indirect assessment of the tool condition by utilising a Coordinate Measurement Machine (CMM) to accurately measure the workpieces. Using a defined machining process with set cutting parameters each workpiece was machined to produce eight off 40 mm cylindrical holes; in this manner using four workpieces a series of 32 holes were machined. Each cylinder was machined using four separate cuts, at increasing depths, producing four identifiable sections. Each section was measured and the form of the geometry produced was established. After assessing the diameters of all the sections for each cylinder, the presence of uneven flank wear was confirmed and the levels obtained. This is related directly to the differing amount of metal removed by the cutter during the established cutting cycle. The same processes was undertaken using three different sets of cutting parameters. The analysis showed the CMM to be a reliable basis for the measurement of uneven tool wear based upon the geometry of the component

Influence of Advanced Coated Tools on Machinability Characteristics of Incoloy 825

With vast application of nickel-based super alloys in strategic fields, it has become increasingly necessary to evaluate the performance of advanced cutting tools for machining such alloys. In order to have elementary knowledge on machinability characteris tics of Incoloy 825 which was so far unknown, in the initial stage of experiment, tool wear and its mechanism, chip characteristics and surface integrity during dry machining were first studied using uncoated and chemical vapour deposition (CVD) multilayer TiN/TiCN/Al2O3/ZrCN coated tool with different cutting speeds. The coated tool could not improve surface finish, but outperformed its uncoated counterpart in terms of other aspects. In the second stage of the study, the primary objective was to recommend suitable cutting tool for machining Incoloy 825. Detailed study was undertaken using commercially available uncoated, CVD and physical vapour deposition (PVD) coated carbide tools, the performance of which was comparatively evaluated in terms of surface roughness, cutting temperature, cutting force, coefficient of friction, tool wear and its mechanism during dry machining. Effect of cutting speed (VC) and feed (f) was also studied. Although, CVD coated tool was not useful in decreasing surface roughness and temperature compared to uncoated one, significant decrease in cutting force and tool wear could be achieved with the same coated tool even under high cutting parameters (Vc=124 m/min and f=0.2 mm/rev). On the other hand, PVD coated tool consisting of alternate layers of TiAlN/TiN outperformed the other tools in terms of all machinability characteristics that have been studied. This might be attributed to excellent anti-friction and anti-sticking property of TiN and good toughness which is a salient feature of PVD technique as well as multilayer configuration, in combination with thermally resistant TiAlN phase. In the final stage of the research work, the feasibility of best performing PVD coated tool was evaluated under environment-friendly dry machining condition in comparison with uncoated tool under conventional flood cooling and minimum quantity lubrication (MQL). Although temperature obtained with PVD coated tool under dry machining has always been significantly more than wet environment, the same coated tool remarkably brought down cutting force, surface roughness and tool wear under dry environment. The results achieved under both rough and finish modes of machining clearly established the use of PVD coated tool under dry environment as a sustainable strategy for achieving green machining of nickel-based super alloys

Effects of machining parameters on cutting forces,shear angle and friction in orthogonal turning of titanium alloys

“Paper 1 presents the results of the investigations on the effects of machining parameters on cutting forces, shear angle and friction in orthogonal turning of titanium alloy tube. Uncoated fine-grained cemented tungsten carbide (WC/Co) and Physical Vapour Deposition (PVD) TiAlN coated grade turning tool inserts, with 5⁰ and 15⁰ rake angles were used under low and high cutting speeds of 120 and 240m/min, at three different feedrates (0.05, 0.075 and 0.1 mm/rev). The experiments were conducted under flooded coolant to reflect what is practically obtainable in manufacturing industries. The experimental results show that cutting forces at two selected cutting speeds of 120 and 240 m/min and the three selected feedrates increased with increase in feedrates for both uncoated and coated cutting tools. Paper 2 presents the results of the effects of machining parameters on cutting forces, shear angle and friction in orthogonal turning of titanium alloy using ribbed solid bar. Uncoated WC/Co and PVD TiAlN coated grade turning tool inserts, with 5⁰ and 16⁰ rake angles were used under low and high cutting speeds of 120 and 240m/min, at three different feedrates (0.05, 0.075 and 0.1 mm/rev). The experiments were conducted under flooded coolant to reflect what is practically obtainable in manufacturing industries. The experimental results show that cutting forces at the two selected cutting speeds of 120 and 240 m/min and three selected feedrates increased with increase in feedrates for both the uncoated and coated cutting tools”--Abstract, page iv