Constant Material Removal Research Articles

Evaluation of the Surface Topography and Deformation of Vertical Thin-Wall Milled Samples from the Nickel Alloy Inconel 625.

During the production of components, manufacturers of structures are obliged to meet certain requirements and ensure appropriate quality characteristics. It is especially important during the manufacturing of thin-walled structures, which are subject to many errors during machining due to the reduced rigidity of the products, including the deformation of thin walls, which may be the result of the vibration of the system. The appearance of vibrations reduces the quality of the machined surface affecting the increase in the values of surface topography parameters-waviness and roughness. Thin-wall structures-titanium or nickel alloy, among others-play a key role in the aerospace industry, which constantly strives to reduce the weight of the entire structure while meeting requirements. The present work focuses on the evaluation of the parameters of surface topography, dimensional and shape accuracy during the milling of nickel alloy Inconel 625 samples containing a thin wall in a vertical orientation. The experiment was conducted under controlled cutting conditions using a constant material removal rate. As part of the surface topography section, the distribution of waviness, Wa and Wz, and roughness, Ra and Rz, was determined in selected measurement areas in the direction parallel to the direction of the feed motion. Dimensional deviations, measured with a 3D optical scanner, were determined in selected cross sections in the direction perpendicular and parallel to the bottom of the sample presenting the deflection of the thin-walled structure. The results provide information that the used parameter sets affect the measured quantities to varying degrees.

Evaluation of the Vibration Signal during Milling Vertical Thin-Walled Structures from Aerospace Materials.

The main functions of thin-walled structures-widely used in several industries-are to reduce the weight of the finished product and to increase the rigidity of the structure. A popular method for machining such components, often with complex shapes, is using milling. However, milling involves undesirable phenomena. One of them is the occurrence of vibrations caused by the operation of moving parts. Vibrations strongly affect surface quality and also have a significant impact on tool wear. Cutting parameters, machining strategies and tools used in milling constitute some of the factors that influence the occurrence of vibrations. An additional difficulty in milling thin-walled structures is the reduced rigidity of the workpiece-which also affects vibration during machining. We have compared the vibration signal for different approaches to machining thin-walled components with vertical walls made of Ti6Al4V titanium alloy and Inconel 625 nickel alloy. A general-purpose cutting tool for machining any type of material was used along with tools for high-performance machining and high-speed machining adapted for titanium and nickel alloys. A comparison of results was made for a constant material removal rate. The Short-Time Fourier Transform (STFT) method provided the acceleration vibration spectrograms for individual samples.

Robotic Belt Finishing with Process Control for Accurate Surfaces

The aerospace industry still relies on manual processes for finish applications, which can be a tedious task. In recent years, robotic automation has gained interest due to its flexibility and adaptability to provide solutions to this issue. However, these processes are difficult to automate, as the material removal rate can vary due to changes in the process variables. This work proposes an approach for automatically modeling the material removal process based on experimental data in a robotic belt grinding application. The methodology concerns the measurement of the removed mass of a test part during a finishing process using an automatic precision measurement system. Then, experimental models are used to develop a control algorithm for continuous material removal that maintains a uniform finishing process by regulating the robot’s feed rate. Next, the results for various experimental material removal models under different process conditions are presented, showing the process parameter’s influence on the removal capacity. Finally, the proposed control algorithm is validated, achieving a constant material removal rate.

Grinding Path Planning of Abrasive Cloth Wheel Based on Modified Preston Equation

As for the efficient and high-precision grinding of blades, it was studied that a flexible grinding path planning method of the abrasive cloth wheel of the blades. In the paper, based on modified Preston equation, the radial material removal depth model is supplemented, which provides theoretical support for the establishment of the flexible grinding path of the abrasive cloth wheel. After obtaining the abrasive cloth wheel envelope surface by the double parameter sphere family method, the deformation amount of the abrasive cloth wheel is used as the directed distance from the point of the designed surface to the envelope. The sequential linear optimization algorithm is used to optimize the directed distance. Then, the flexible grinding path for constant material removal is obtained. The results of the simulation show that the profile error of the blade processing is improved under the requirements of surface roughness.

Investigation of Selected Surface Topography Parameters and Deformation during Milling of Vertical Thin-Walled Structures from Titanium Alloy Ti6Al4V.

Thin-walled elements are widely used in the aerospace industry, where the aim is to reduce the process time and the weight of the structure while ensuring the sufficient quality of the finished product. Quality is determined by geometric structure parameters and dimensional and shape accuracy. The main problem encountered during the milling of thin-walled elements is the deformation of the product. Despite the various methods available for measuring deformation, more are still being developed. This paper presents selected surface topography parameters and deformation of vertical thin-walled elements during an experiment under controlled cutting conditions for samples from titanium alloy Ti6Al4V. Constant parameters of feed (f), cutting speed (Vc,) and tool diameter (D) were used. Samples were milled using a tool for general-purpose and a tool for high-performance machining, as well as two different machining approaches: with greater involvement of face milling, and cylindrical milling with a constant material removal rate (MRR). For samples with vertical thin walls, the parameters of waviness (Wa, Wz,) and roughness (Ra, Rz) were measured using a contact profilometer in the selected areas on both processed sides. Deformations were determined in selected cross-sections perpendicular and parallel to the bottom of the sample using GOM measurement (GOM-Global Optical Measurement). The experiment showed the possibility of measuring deformations and deflection arrows of thin-walled elements proceeded from titanium alloy using GOM measurement. Differences in selected surface topography parameters and deformations were observed for the machining methods used with an increased cross-section of the cut layer. A sample with a deviation of 0.08 mm from the assumed shape was obtained.

An experimental study on the creep feed grinding of laser macro-structured alumina considering constant material removal volume

Engineering ceramics such as alumina have found special applications in aerospace, electronics, and automotive industries due to their superior mechanical and thermal properties. Among these properties, chemical stability at high temperatures, high strength to weight ratio, hardness, strength, wear, and corrosion resistance are of prime importance. Due to these superior properties, processing of these ceramics encounters some difficulties and requires special machining processes such as diamond grinding; in addition to high manufacturing costs, this technique suffers from noticeable challenges such as high grinding forces and temperatures which may lead to serious surface damages. To overcome these challenges, in recent years, laser-assisted grinding has been introduced; in this process, laser source is used to preheat or structuring the workpiece surface in order to reduce grinding forces and temperatures. In this research, first four different patterns were created on alumina using a pulsed laser. Then, these weakened structures were machined using creep feed grinding. In order to provide a better understanding from the effect of each pattern, the volume of the material that can be removed was kept constant in all four patterns. Finally, the effect of created patterns on grinding forces and surface roughness has been studied. Besides, scanning electron microscopy has been used to investigate possible surface damages. The results showed that the normal and tangential forces in the non-structured case were 2 and 2.7 times higher than the forces recorded in the best patterned samples. However, no significant effect of the created patterns on the surface roughness was observed. Furthermore, serious heat damage and cracks were not observed in the structured workpieces, but non-structured workpieces were crushed during operation. Among the created patterns, pattern with perpendicular grooves to the grinding direction was introduced as the best.

Višekriterijumska optimizacija zasnovana na verovatnoći kao osnova za primenu novog robustnog dizajna na parametre mašinske obrade

Introduction/purpose: New robust design by means of probability-based multi-objective optimization takes the arithmetic mean value of the performance indicator and its deviation as twin independent responses of the performance indicator. The aim of this article is to check the applicability of new robust design in optimizing machining process parameters. To conduct the examination in detail, the robust design for optimal cutting parameters to minimize energy consumption during the turning of AISI 1018 steel at a constant material removal rate is applied as well as the concurrent optimization of the machining process parameters and the tolerance allocation of a spheroidal graphite cast iron piston. Methods: In the spirit of the probability-based method for multi-objective optimization, the arithmetic mean value of the performance indicator and its deviation are taken as two independent responses of the performance indicator to implement robust design. Each of the above twin responses contributes one part of the partial preferable probabilities to the performance indicator of the alternatives in the treatment. The arithmetic mean value of the performance indicator should be assessed as a representative of the performance indicator according to the function or the preference of the performance indicator, and the deviation is the other index of the performance indicator, which has the characteristic of the 99 smaller-the-better in general. Furthermore, the square root of the product of the above two parts of the partial preferable probability forms the actual preferable probability of the performance indicator. Moreover, the product of partial preferable probabilities gives the total preferable probability of each alternative, which is the overall and unique index of each alternative in the robust optimum. Results: The paper gives the rational optimum cutting parameters for minimizing energy consumption during the turning of AISI 1018 steel at a constant material removal rate and the concurrent optimization of the machining process parameters and the tolerance allocation of a spheroidal graphite cast iron piston. Conclusion: The application study indicates its rationality and convenience of new robust optimization in the optimization of machining process parameters.

A novel approach to model the energy consumption of machine tools for machining cylindrical parts

Machine tools plays a significant role in manufacturing industries and are unfortunately responsible for huge energy consumption and associated greenhouse gas emissions. In industry, the length and diameter are reduced to obtain the final dimensions of a cylindrical part. Typically, external turning operation is used to reduce the diameter of the part i.e. Constant-Material Removal Rate (CMRR) machining process and facing is conducted to reduce the length of the part i.e. Variable-Material Removal Rate (VMRR) machining process. In the past, energy evaluation models for machine tools are developed based on CMRR machining processes only, while the machining of a cylindrical part requires both CMRR and VMRR machining processes to manufacture the final product. In the present study, the energy consumption of a machine tool is divided into different energy modules: start-up, standby, spindle acceleration, idle, rapid positioning, air-cutting, CMRR machining process and VMRR machining process. Energy consumption models for each module are developed and integrated to establish the total energy consumption model for a machine tool. Experiments are conducted on a LMW-Smarturn CNC lathe machine tool in the dry and wet environment to obtain the fitting coefficients of the developed models for different energy modules. The validation test results show that the developed model's accuracy is more than 97 %. The developed model can be applied in the industry by the process planners to identify the most energy-efficient process plan before the actual machining of a cylindrical part.

Modeling the superposition of residual stresses induced by cutting force and heat during the milling of thin-walled parts

Previous studies on machining-induced residual stress mainly concentrated on qualitative analyses of mechanical load and thermal load. Nevertheless, it remains a major challenge to quantify the influence of cutting force and heat on residual stress generation due to the lack of superposition mechanism. A newly empirical model of milling residual stress superposition was constructed to distinguish the effect of milling force from the effect of milling heat. The influence proportions of milling force and heat on the residual stress generation have been determined. Firstly, the residual stresses induced by the milling force, heat and force-heat coupling load were simulated independently, and the simulation models were verified by experiments. The simulation results presented that the milling force caused both residual compressive stress and residual tensile stress on the machined surface, while milling heat induced mainly residual tensile stress. Then, a mathematical model was put forward to quantify the superposition relationship between the force-induced residual stress and the heat-induced residual stress presented in the simulations. It has been found that the influence of milling force accounts for 53% to 78% in the generation of the surface residual stress when the force-to-heat ratio (RFT) varies from 0.09 to 0.39. Finally, with a constant material removal rate, the conclusion can be drawn that the parameter combination with a higher force-to-heat ratio is more beneficial for the generation of residual compressive stresses on the machined surface, which has been confirmed by the case experiments. Therefore, quantitative analysis of residual stress generation and superposition turns to be possible by using the proposed modeling.

A study on energy-saving optimization strategy for the stone processing industry—an improved method for modeling cutting power and energy consumption: A case study of block sawing process

Energy consumption has become one of the main costs of the stone processing industry and results in substantial stress on the environment. Consequently, the energy-saving issue has drawn increasing attention in the stone processing industry. Cutting power modeling is the crucial technology of energy prediction of stone machining process, being the foundation of energy-saving optimization in this sector. The cutting power changes dynamically during the variable material removal rate process (V-MRR process). Therefore, the power characteristic of the V-MRR process is more complicated than that of the constant material removal rate process (C-MRR process). In the stone processing industry, various machining processes belong to the V-MRR process, such as block sawing, slab chamfering, curved surface milling and grinding. In this paper, a modeling methodology of cutting energy consumption for variable-MRR process is proposed. The dynamic power characteristic can be reflected in this methodology, and the influences of cutting parameters on stone-cutting energy consumption are also fully considered. Based on the specially designed test system, experimental studies were conducted to obtain the fitting coefficients of the proposed energy consumption model. Then, energy calculations of four stone blocks sawing processes were performed. The results show that the predictive accuracy of all tested stone block sawing cases is above 90%. Finally, a case application is elaborated to demonstrate that the proposed method can help stone manufacturers determine the energy-optimal process plan. The detailed results of energy-saving & benefits-improving with using the proposed method are also proved in the case study.

Suppression of Chatter in High Speed Milling Machine Using Spindle Speed Variation Method with Acoustic Feedback PID Controller

High speed milling (HSM) process limited by tool failure and dynamic instabilities due to the influence of relative vibration between tool and workpiece, so called chatter. Chatter vibration literally responsible for lower productivity and poor surface quality. In this project, chatter occurrence during machining was suppressed using spindle speed variation (SSV) method via microphone online detection techniques. The initial experiment begins with constant material removal rate (MRR) where varies depth of cut, feedrate and spindle speed were analyzed using time and frequency domain. Then, based on the result, microcontroller based PID algorithm was tested again in active mode. The result shows magnificient differences in frequnecy.This proves that chatter occurrence during machining can be suppressed using spindle speed variation method with microphone feedback PID controller. This also offers high speed milling usage industries with extra benefits of high productivity and can conserve time and money. Moreover, this method could enable providing high efficiency, accuracy, quality of final workpieces and eliminates semi- finishing process.

Effect of tool design parameters study in micro rotary ultrasonic machining process

Selection of tooling to perform specific operations like drilling and milling on ceramic materials using rotary ultrasonic machining process is an important aspect to meet stringent dimensions on workpiece as well as intended performance of tool. This phenomenon is more critical for micro rotary ultrasonic machining. In the present study, an effort was made to do micro drilling operation of O0.3 mm tool with varying geometry, having different wall thicknesses and abrasive grain sizes using design of experiments. The effect of tool-based parameters like grain size and wall thickness has been studied on axial cutting force, radial cutting force, tool wear, edge chipping area and taper. After examining axial and radial cutting forces, it has been concluded that lower wall thickness (80 μm) tool is good for drilling operation; and higher wall thickness (100 μm) tool is good for milling operation under same material removal rate conditions. It has been also investigated that lower wall thickness (80 μm) tool has less edge chipping area and less taper and can impart high drilling depth as compared to higher wall thickness (100 and 150 μm) tool. It is also concluded that lesser grain size (15 μm) tools are advantageous in terms of edge chipping area and cutting force for drilling and milling operations as compared to higher grain size (30, 35 and 45 μm) tool at constant material removal rate. Higher grain size tools have been broken at 1.13 mm3/h material removal rate conditions due to bad profile accuracy. But higher grain size tools have worked fairly well at less material removal rate condition. Higher grain size tools produced less wear. Tool wear was found minimum in higher wall thickness (100 μm) tool having higher abrasive grain size (30 μm). Using inferred results, O0.3 mm drilling experiments have been carried out on six aerospace ceramic materials. Also, groove of 0.5 mm size using O0.3 mm optimised tool has been successfully carried out in sintered SiC.

Increased tool performance with niobium carbide based cutting materials in dry cylindrical turning

Niobium carbide (NbC) shows promising results as an alternative cutting tool material to tungsten carbide (WC) for turning of iron-based materials. Due to its hot hardness and low solubility of binderless NbC in solid chrome, nickel, cobalt, or iron, it presents excellent properties for cutting tool applications. These advantages result in a reduced tendency to adhesive and diffusion wear, which affects cutting tool lifetime and process stability. In order to investigate a possible substitution of the conventional substrate material tungsten carbide, the BAM Federal Institute for Materials Research and Testing and the Institute for Machine Tools and Factory Management (IWF) of the Technische Universität Berlin analyze the suitability of NbC for the use as a cutting tool in turning processes. Two different straight NbC materials are included in the machining trials prepared by Katholieke Universiteit Leuven, Belgium each differing in chemical composition and mechanical properties. A cobalt (Co) bonded niobium carbide defined as NbC0.88-12Co, a nickel (Ni) bonded NbC with the specification (NbC1.0-10TiC)-6Ni7.5VC and a commercially available cermet with a niobium content of wt.-%NbC = 25 % are selected and compared to submicron grain WC-6Co tool material. Carbon steel C45E and gear steel 42CrMo4+QT are chosen as workpiece materials of different representative technological applications for dry external cylindrical turning tests. A variation of cutting speed is carried out to show the impact of higher thermomechanical load during machining. The results evaluate the cutting performance of NbC compared to WC regarding material removal VW and crater wear KT. In contrast to WC tools NbC cutting tools show constant material removal VW at increased cutting speed vc combined with a higher process reliability.

Analysis of tool wear in face milling of alloy cast iron under constant material removal volume condition

Due to some special properties, alloy cast iron HTCuCrSn-250 is widely used to manufacture the cylinder block of the diesel engines. However, the additional alloying elements aggravated tool wear which is significantly affected by cutting parameters during machining process. In this paper, tool wear in face milling of alloy cast iron under constant material removal volume (MRV) condition was investigated. First, the relationship between tool flank wear (VB) and MRV was determined. Secondly, the wear morphology and mechanism were analyzed and a predicted model between cutting parameters and tool wear was proposed. Finally, the optimization was taken, and three groups of optimal parameters were obtained. This research illustrated that different combinations of cutting parameters result in different wear morphology and the main wear mechanisms are diffusion and oxidation. This research also indicated the two parameters, axial depth of cut and the radial depth of cut, which have significant impact on the tool wear. Meanwhile, a model between VB and the cutting parameters under the constant MRV condition during milling HTCuCrSn-250 was proposed.

Cutting forces, tool wear and surface finish in high speed diamond machining

We have investigated the cutting forces, the tool wear and the surface finish obtained in high speed diamond turning and milling of OFHC copper, brass CuZn39Pb3, aluminum AlMg5, and electroless nickel. In face turning experiments with constant material removal rate the cutting forces were recorded as a function of cutting speed between vc=150m/min and 4500m/min revealing a transition to adiabatic shearing which is supported by FEM simulations of the cutting process. Fly-cutting experiments carried out at low (vc=380m/min) and at high cutting speed (vc=3800m/min) showed that the rate of abrasive wear of the cutting edge is significantly higher at ordinary cutting speed than at high cutting speed in contrast to the experience made in conventional machining. Furthermore, it was found that the rate of chemically induced tool wear in diamond milling of steel is decreasing with decreasing tool engagement time per revolution. High speed diamond machining may also yield an improved surface roughness which was confirmed by comparing the step heights at grain boundaries obtained in diamond milling of OFHC copper and brass CuZn39Pb3 at low (vc=100m/min) and high cutting speed (vc=2000m/min). Thus, high speed diamond machining offers several advantages, let alone a major reduction of machining time.

A theoretical and experimental investigation of material removal characteristics and surface generation in bonnet polishing

This paper presents a theoretical and experimental investigation which attempts to provide a better scientific understanding of the material removal characteristics and surface generation in bonnet polishing. The experimental results reveal that the material removal is shared by the polishing pad and the abrasives trapped in the pad-workpiece interface, and the abrasive wear is dominated significantly by plastic removal mode of abrasive particles, while the material removal caused by the polishing pad should be mitigated in order to obtain super mirror finished surfaces. The surface generation is found to be a linearly cumulative effect of dwell time together with the constant material removal rate under the identical polishing condition. Hence, a multi-scale material removal model and a surface generation model have been built based on the contact mechanics, kinematics theory, abrasive wear mechanism, as well as the relative and cumulative removal process of surface generation in bonnet polishing. The models are verified through a series of spot and pattern polishing experiments. Based on the results of spot polishing experiments, the multi-scale material removal model is found to predict well for the material removal characteristics under various polishing conditions. The simulated patterns by the surface generation model are found to agree well with the measured patterns in the pattern polishing experiments which substantiate that the relative and cumulative removal process is a key surface generation mechanism in bonnet polishing.

Optimization of cutting parameters to minimize energy consumption during turning of AISI 1018 steel at constant material removal rate using robust design

Machine tools have an impact on the environment due to their energy consumption. New strategies with focus on the reduction of the energy consumed by manufacturing processes have received significant attention owing to the rise of the electricity costs. This paper presents an experimental study related to the optimization of cutting parameters in turning of AISI 1018 steel. The aim of the study was to minimize the quantity of electrical energy required by the machine tool in order to perform the cutting operation. The material removal rate was set to a constant value in all the experimental trials so as to analyze the effect that the cutting parameters have on the energy consumed. Robust Design was used to determine the effects of the depth of cut, feed rate, and cutting speed on the energy required by the machine tool, considering two sources of noise in the experimental trials. The results of this work show that the techniques covered by the concept of Robust Design can be used to minimize the energy consumed and variation of the machining process.

Correlation of the Volumetric Tool Wear Rate of Carbide Milling Inserts With the Material Removal Rate of Ti–6Al–4V

The objective of this paper is to assess the correlation of volumetric tool wear (VTW) and wear rate of carbide tools on the material removal rate (MRR) of titanium alloys. A previously developed methodology for assessing the worn tool material volume is utilized for quantifying the VTW of carbide tools when machining Ti–6Al–4V. To capture the tool response, controlled milling experiments are conducted at suitable corner points of the recommended feed-speed design space, for constant stock material removal volumes. For each case, the tool material volume worn away, as well as the corresponding volumetric wear profile evolution in terms of a set of geometric coefficients, is quantified—these are then related to the MRR. Further, the volumetric wear rate and the M-ratio (volume of stock removed to VTW) which is a measure of the cutting tool efficiency, are related to the MRR—these provide a tool-life based optimal MRR for profitability. This work not only elevates tool wear from a 1D to 3D concept, but helps in assessing machining economics from a stock material-removal-efficiency perspective as well.

Tool wear modelling for constant removal rate in two-bodies automated polishing

Complex shapes such as medical implants or injection moulds require the use of super-finishing operations to minimise geometrical defects, down to mirror effect finish. These pre-polishing and polishing operations are still regularly performed manually by skilled workers. In spite of advantages in terms of repeatability, productivity and geometrical quality, automatic polishing methods are not widely used because they require systematic and significant developments. One of the main issues is the modification of the abrasive tool efficiency during the process. It evolves over time due to abrasive grains tearing and transfers onto the abrasive tool surface of workpiece microchips. Thus a model of tool wear is proposed and compensation strategies are elaborated to ensure a constant material removal rate on the surface. Compensations are performed by optimising the spindle speed and/or the feedrate along the tool path and are validated through experimental investigations.

Feedrate scheduling for multi-axis plunge milling of open blisks

Multi-axis plunge milling has an increasing application in the manufacturing industry to rough machine open blisks. Its objective is to remove mass stock material with high efficiency and machining stability. In multi-axis plunge milling, cutting parameters are usually determined conservatively as constants to prevent excessive cutting forces and unexpected tool breakage. This is an obstacle to improve the cutting efficiency of rough machining. To address this issue, this article proposes an original approach to schedule the feedrate in multi-axis plunge milling of open blisks based on material removal rate. The material removal rate in plunge milling is directly proportional to the area of the cross section on the removed stock material. According to different types of the cross section, one feeding phase in plunge milling of open blisks is divided into three feeding stages. The cross section in each feeding stage is then identified with a mathematic and geometric method. Its area is then calculated by its constituting elements, such as a polygon, circular arches, and elliptical arches. After that, the feedrate is regulated to guarantee a constant material removal rate in the entire feeding phase. Experimental tests are conducted to verify the proposed feedrate scheduling method. This approach can reduce the cutting time and smooth the variances of cutting forces and torque in multi-axis plunge milling of open blisks.