Milling Spindle Research Articles

Enhancing face-milling efficiency of wood–plastic composites through the application of genetic algorithm–back propagation neural network

ABSTRACT Wood–plastic composites (WPCs) have advanced physicochemical properties and are widely applied in various fields. How to achieve high-efficiency, high-quality machining of WPC is a pressing issue that WPC manufacturing enterprises need to address. To this end, this research focused primarily on improving the machinability of WPC with end milling experiments. In this work, a single-factor method was used to analyse the impact of axial milling depth, spindle speed, and tool rake angle on resultant forces and surface roughness. Main effects analysis was applied to explore the degree of influence of axial milling depth, spindle speed, and tool rake angle on cutting forces and surface roughness. Furthermore, three-dimensional characterisation techniques were utilised to analyse the surface morphology characteristics of WPC during end milling. Finally, a genetic algorithm–back propagation neural network was applied to develop prediction models for resultant force and surface roughness, and optimal milling conditions were identified as axial milling depth of 0.50 mm, spindle speed of 7841 r/min, and rake angle of 15°; these produced the lowest resultant force and surface roughness. The findings of this work are proposed as a guide for better cutting performance in the industrial production of WPC.

Improving Robotic Milling Performance through Active Damping of Low-Frequency Structural Modes

Industrial robots are increasingly prevalent due to their large workspace and cost-effectiveness. However, their limited static and dynamic stiffness can lead to issues like mode coupling chatter and regenerative chatter in robotic milling processes, even at shallow cutting depths. These problems significantly impact performance, product quality, tool longevity, and can damage robot components. An active inertial actuator was deployed at the milling spindle to enhance dynamic stiffness and suppress low-frequency vibrations effectively. It was identified that the characteristics of the actuator change with its mounting orientation, a common scenario in robotic machining processes. This variation has not been reported in the literature. Our study includes the identification of model parameters for the actuator in both horizontal and vertical mountings. Additionally, the novelty of the present work lies in the specific design and implementation of compensation filters tailored for the active inertial actuator in both horizontal and vertical configurations. These filters address the unique challenges posed by low-frequency vibrations in robotic milling, offering significant improvements in dynamic stiffness and vibration suppression. Traditional model-based compensators were effective for vertical mounting, while pole-zero placement techniques with minimum phase systems were optimal for horizontal mounting. These compensators significantly enhanced dynamic stiffness, reducing maximum low-frequency robot structural modes by approximately 100% in horizontal mounting and approximately 214% in the vertical configuration of the actuator. This advancement promises to enhance industrial robot capabilities across diverse machining applications.

Development of a Digital Model for Predicting the Variation in Bearing Preload and Dynamic Characteristics of a Milling Spindle under Thermal Effects

The spindle tool is an important module of the machine tool. Its dynamic characteristics directly affect the machining performance, but it could also be affected by thermal deformation and bearing preload. However, it is difficult to detect the change in the bearing preload through sensory instruments. Therefore, this study aimed to establish a digital thermal–mechanical model to investigate the thermal-induced effects on the spindle tool system. The technologies involved include the following: Run-in experiments of the milling spindle at different speeds, the establishment of the thermal–mechanical model, identification of the thermal parameters, and prediction of the thermal-induced preload of bearings in the spindle. The speed-dependent thermal parameters were identified from thermal analysis through comparisons with transient temperature history, which were further used to model the thermal effects on the bearing preload and dynamic compliance of the milling spindle under different operating speeds. Current results of thermal–mechanical analysis also indicate that the internal temperature of the bearing can reach 40 °C, and the thermal elongation of the spindle tool is about 27 µm. At the steady state temperature of 15,000 rpm, the bearing preload is reduced by 40%, which yields a decrease in the bearing rigidity by approximately 16%. This, in turn, increases the dynamic compliance of the spindle tool by 22%. Comparisons of the experimental measurements and modeling data show that the variation in bearing preload substantially affects the modal frequency and stiffness of the spindle. These findings demonstrated that the proposed digital spindle model accurately mirrors real spindle characteristics, offering a foundation for monitoring performance changes and refining design, especially in bearing configuration and cooling systems.

Quality enhancement of micro-milled channels with automated laser assistance

AbstractMicrochannels are utilised on material surfaces of a body, allowing coolant to pass through them and enabling heat dissipation by increased contact area. Fabrication of metal surface microchannels is primarily achieved by employing a micro-milling process, which has drawbacks such as excessive cutting forces, top burrs, tool wear, and lower tool life. Alternatively, it is also realised by using Laser micro milling, which has problems associated with lower quality of surface finish, un-desired taper, heat-affected zone, and spatters. The existing literature, after due review of the current state of the art, has brought out gaps needing attention. These gaps are limited capability to reduce surface roughness, unaddressed burr width, and irregular bottom surface morphology, which affect microchannel quality. These gaps motivate this research work to improve and sustain the microchannel quality. To achieve the goals, this research work performs the fabrication of microchannels by micro-milling with automated laser assistance being achieved in two ways (a) sequentially, (b) non-sequentially, termed as LASMM and LPCMM, which are novel for the scientific community. The effects of micro milling parameters, spindle speed and feed on the quality were analysed while machining commercially pure titanium (cp-Ti). Results show that laser assistance to micro-milling provides a lower generation of undesired forces and lesser top burrs compared to micro-milling alone. In sequential laser assistance, the channels have a mean down burr width ~ 58% lower and a maximum down burr width ~ 38% lower than the channels done non-sequentially. In the case of up-burr width, a mean value ~ 60% lower and a maximum value ~ 73% lower is achieved in channels done non-sequentially as compared to those done sequentially. In the case of surface roughness, channels done sequentially have a maximum Sa value of 1.508 µm, a maximum Sq value of 1.912 µm whereas non-sequentially, they show a maximum Sa value of 3.495 µm, maximum Sq value of 4.59 µm. Steady tool wear is observed sequentially, whereas in non-sequential, rapid tool wear occurs after 500 mm of cutting length.

Ensuring the stability of machining when using end mills

This paper reports a new approach to ensuring the stability of the end milling process, due to vibration-free cutting modes, which are determined from the stability lobes diagram of the dynamic machining system. An application program for automatic calculation of the stability lobes diagram in the coordinates «mill spindle speed – feed» has been developed, which is a tool for the technologist-programmer when designing control program for numerically controlled machines. The mathematical model underlying the application program represents a dynamic machining system as a single-mass system with two degrees of freedom, covered by negative feedback in the direction of two coordinates. The trailing machining is represented as positive feedback loops with a delay function in each. The mathematical model is given in the form of state variables, which allows applying numerical modeling methods to determine both transient and frequency responses. The software developed includes a separate module for automatic design of the stability lobes diagram whose algorithm uses the features of the location of the Nyquist diagram on the complex plane. Since the functioning of the developed program requires a priori information about the dynamic parameters of the machining system, a procedure for their experimental identification is presented. The stiffness of the machining system in two coordinates was determined with the help of a dynamometer, and the frequency responses were determined by the impulse response function, which was obtained with an impact hammer. The research results were confirmed experimentally both by computer simulation and milling on a machine tool and could be recommended for determining the cutting mode at end milling

Study of the dependence of the natural frequencies of a rotor system with a vertically positioned rotor on the preload

The article discusses the possibility of using a method for determining the preload force for trust and radial bearings of spindle assemblies for high-speed milling. Previously, a method was developed and tested for determining the preload force of bearing supports on high-speed grinding electrospindles with a horizontal spindle.
 The object of study is a support with angular contact bearings 7004 ACD_P4A SKF and a vertical rotor. An information-measuring system has been developed, which consists of PCB 352C34 vibration acceleration sensors, a Vishay 614 force sensor, an NI-cRIO-9056 controller, NI 9250, NI 9237 and NI 9481 modules, and software written in the National Instruments Labview language.
 The system of test actions has been improved due to its automation. Test effects began to be carried out using a solenoid with a core, which was controlled by an NI controller and developed software. Due to this, the same time delay was formed between the test action and the start of recording the vibration acceleration signal.
 Vibration acceleration signals are obtained for the entire preload range. To study the controllability of the unit, two vibration acceleration sensors were used: with a parallel and perpendicular arrangement of the axes of the direction of vibration and test action. For the first and second groups of vibration accelerations, spectral transformations were carried out, and the amplitude-frequency characteristics of the assembly were obtained for the entire range of preload values.
 As a result of the work, it was concluded that the presented methodology and criteria are applicable to high-speed milling spindle assemblies with a vertical rotor. It is also shown that this technique can be automated.

Optimization of cutting power and power efficiency during particleboard helical milling

AbstractWith the aim of providing scientific guidance for the application of spiral cutters in particleboard machining, this work studied the influence of milling parameters on milling power and power efficiency during helical milling of particleboard. And the response surface methodology was applied to optimize the milling parameters to reduce machining energy consumption and improve energy efficiency. The factors of milling depth, spindle speed and helical angle were selected as input parameters, and the mathematical models between the input parameters and the response parameters were established. Then, the significant influence of each factor and the interaction of two factors were determined by variance analysis, and the change trend of milling power and power efficiency was studied by response surface methodology. Results showed that the milling depth had the greatest impact on milling power and power efficiency, followed by the spindle speed and helical angle. An increase in the milling depth and spindle speed resulted in an increase in milling power and power efficiency, while the increased helical angle resulted in a decrease in milling power and power efficiency. The optimized values of helical angle, spindle speed and milling depth were 54°, 5650 min−1 and 1.3 mm, respectively.

Optimal number of thermal hotspots selection on motorized milling spindle to predict its thermal deformation

Two primary heat-generation sources in motorized machine tool spindles are (i) friction in spindle bearings, and (ii) losses in the motor components. The difference in heat generation and heat dissipation rate from the high-speed motorized milling machine tool spindle cause structural deformation, resulting in part inaccuracy. Several research groups used thermo-mechanical and data-based modelling of high-speed motorized spindles to predict and compensate thermal deformation and improve machining accuracy. In real-time thermal compensation, selection of optimal number of thermal hotspots to place the temperature sensors on the spindle is crucial. The present work proposes an approach to select the optimal number of temperature sensors that can be employed to predict the thermal deformation while maintaining required prediction accuracy. For this purpose, the experiments were conducted to evaluate the thermal heat flux across the spindles at different rotational speeds. Furthermore, a finite element analysis (FEA) was performed to simulate the thermal deformation at the tool center point (TCP). The input parameters considered for predicting the simulated deformation were different temperature sensor data on the motorized spindle and the ambient temperature. This work uses the thermal deformation results obtained from FEA to build an improved second-order polynomial regression model. The model reduces the requirement of temperature sensors from three to one to predict the TCP deflection. Results show that the proposed model accuracy was 86.72% with two temperature sensors and 85.99 % with one temperature sensor. It indicates that one temperature sensor is sufficient to predict the TCP deflection with a compromise of 0.73% prediction accuracy level.

Development of contactless dynamic spindle testing using an eddy current brake

It is important to determine the dynamic stiffness of machine tools in terms of chatter vibration. Although a hammering test is widely used to measure the dynamic stiffness, it is difficult to measure a moving object at high speed because the method requires direct contact. In particular, the dynamic stiffness of milling spindles that can rotate at high speed changes considerably between the resting and rotating states. Therefore, it is essential to develop a contactless dynamic spindle test (CDST) method. Although a few CDST methods have been proposed, a conclusive method has not yet been established because of the problem of convenience. The present study proposes a novel CDST method that uses the concept of an eddy current brake. The proposed method offers advantages in that it does not require a power supply or external control, although the excitation frequency depends on the rotation speed. The present paper first introduces the principle of the proposed method. Next, the measurement results obtained by a conventional hammering test and those obtained by the proposed method are compared in order to confirm the reliability and effectiveness for an actual milling spindle.

Elaboration of a lubrication system for universal spindle hinges of rolling mills

The experience of running drives of most of heavy-duty rolling mills shows that the designs of universal spindles with blade hinges under conditions of increased alternating loads are most acceptable comparing with other spindles types. Open friction surfaces are the drawbacks of these types of spindles, which complicate the matter of continuous supply of lubrication. Perfected effective system of forced lubrication of rolling mill spindles hinges proposed. The facility for their lubrication has a bearing support of balancing design, spindle, in radial holes of which spring-loaded plungers are installed in a diametrically opposite order. Besides, the facility has suction valves and force valves installed in the spindle axial holes, connecting with the radial ones. A methodology proposed to select the eccentricity of the internal cylindrical surface of the bearing support of the spindle hinge, the axis of which is located eccentrically relative the spindle rotation axis. A calculating scheme and a mathematical model of the process of lubrication supply into joints of rolling mill spindle hinge elaborated. A differential equation of lubrication motion in the conical slot of the hinge between a blade and insertions drawn up. Parameters of hydrodynamic motion of lubrication in the conical slot established. Modes of the lubrication motion in the conical slot between roller blade and hinge insertion determined. Based on experience of operation of friction couple bronze-steel, a lubrication for rolling mills universal spindles proposed. To improve the operation characteristics of hinges based on the friction couple bronze-steel, a thick lubrication having antifriction properties namely based on oils with additives ИП-10, КП-10 and ДФ-11 proposed. Dependence of pressure distribution along the length of the hinge conical slot presented for various lubrications of low viscosity (ИП-10 + ДФ-11) and high viscosity (КП-10 + ДФ-11). The quality effect of the speed of roller blade movable wall on distribution of speeds of lubrication layer motion over the height of the hinge conical slot for comparatively low and comparatively high boundary speeds demonstrated.

Surface roughness and chip morphology of wood-plastic composites manufactured via high-speed milling

Wood-plastic composites have attracted extensive attention throughout the world because of their advantages. However, the manufacturing mechanism of the wood-plastic composites, i.e., high-speed milling technology, is not perfect and needs further study. The effects of the cutting parameters, i.e., the spindle speed, feed rate, axial milling depth, and radial milling depth, on the surface roughness and chip morphology were studied; the surface roughness values, Ra and Rz of high-speed milling wood-plastic composites samples were measured via high precision surface roughness measuring instrument, and their regression equations were calculated. The chips produced via a high-speed milling process were collected and studied. The results showed that the surface roughness of the wood-plastic composites increases with an increase in the axial depth, feed rate, or radial depth, but decreases with an increase in the spindle speed. In addition, the axial milling depth, feed rate, and spindle speed had a significant effect on the morphology of the chips. However, the effect of the radial milling depth on the morphology of the chips was not obvious. The results can provide a scientific basis for the optimization of high-speed milling processing of wood-plastic composites.

Surface roughness of thermally treated wood cut with different parameters in CNC router machine

The effects of different machining parameters on surface roughness values of thermally treated pine, beech, and linden woods cut in a computer numerical control (CNC) router machine were examined. Wood specimens were thermally treated at 170, 190, and 210 °C for 2 h. Then, specimens were cut in the radial and tangential directions with three different spindle speeds (12000, 15000, and 18000 rpm) and three different feed rates (3000, 4000, and 6000 mm/min) using two different end mill tools (spiral and straight) on the CNC machine. The end mill type significantly affected the roughness values of the untreated and thermally treated specimens in both directions. Lower roughness values were found in the specimens (especially pine) machined with the straight end mill compared to those machined with the spiral end mill. Roughness generally decreased in the thermally treated specimens. However, thermal treatment temperature did not have a notable effect on roughness. As the spindle speed increased, the roughness values of all specimens decreased. In contrast, as the feed rate increased, the roughness values increased. Therefore, the end mill type, feed rate, and spindle speed were the most influential parameters on the roughness.

Design and verify a natural frequency using ANSYS software

In this paper we determine the natural frequency of highest speed milling spindle for length 335.4 mm and 16000 rpm speed based on modal analysis. This manuscript taking the high speed milling spindle of bar that is derived and presented by using finite element model in ANSYS software. This method takes into account bearing support contact interface that is recognized by spring damper element COMBIN 14 for giving cushioning effect to spindle. Furthermore, the modal analysis has completed by means of ANSYS commercial software. After that this result is compared with experimental result provided by FFT analyzer. The results show that the natural resonance region speed is far greater than the designed milling spindle.

A Study on the Influence of Milling Parameters on the Properties of TC18 Titanium Alloy

Based on the orthogonal experimental design, the effect mechanism of different processing parameters on the surface microhardness and metal microstructure of TC18 titanium is studied. Meanwhile, the variation law of milling force and surface roughness of TC18 titanium alloy during high-speed milling is obtained. The results show that the milling depth has the greatest influence on the milling force under down-milling. Meanwhile, the milling depth and spindle speed have the greatest influence on the milling force in up-milling, which with the increase of milling depth and with the increase of spindle speed and downward trend. The greatest influence of surface roughness is the milling depth, and the surface roughness decreases with the increasing of milling depth. After milling complete, the surface hardness of TC18 titanium alloy work piece decreases. With the surface depth increases to 0.01 mm, the hardness is slightly higher than the matrix hardness. The microstructure of TC18 matrix is mainly β phase by observing the metallographic structure. The equiaxed α phase grows after milling.

HydraX, a 3D printed robotic arm for Hybrid Manufacturing. Part II: Control, Calibration & Programming

This part of the study focuses on programming, control and calibration aspects of HydraX, a low cost 6-axis 3D printed robotic arm that performs both Additive and Subtractive Manufacturing. G-code was implemented as the programming language for HydraX, after proper process CAM modeling and code extraction. CAM software post-processor was developed as a Finite-State Machine (FSM), so that NC output files are automatically adjusted, when software input variable values change. Arduino Mega microcontroller has been connected in parallel to the motion controller board of HydraX for expansion of system functionality and enabling the hybrid manufacturing concept. Custom commands (M codes) have also been developed to establish the connection between CAM post-processor and Direct Numerical Control (DNC) software. With these additions, the automatic end effector changer controls the CNC milling spindle, hot end with temperature measurement, filament extrusion and cooling fan speed adjustment, thus leading to successful hybrid manufacturing processes.

Thermal condition monitoring of a motorized milling spindle

Growing power densities in the main spindle of machine tools caused by approaches to increase the productivity lead to deflections of the tool-center-point (TCP) and thus limit the achievable accuracy. In order to optimize the operating point of a spindle in the context of these contrary requirements, effective tools need to be developed. By modeling thermo-elastic effects using a FE approach, interactions of heat sources and sinks can be investigated deeply on the one hand and a model based correction of TCP deflections can be established on the other hand. For a practical use, short computing times as well as precise simulation results are core requirements. In the present paper, an online thermal simulation model is developed, parameterized and validated.

Inverse Analysis of Inconel 718 Laser-Assisted Milling to Achieve Machined Surface Roughness

This manuscript proposes an inverse analysis method for the machined surface roughness in laser-assisted milling on Inconel 718. The method solves the forward problem considering the tool profile and the elastic recovery of machined surface and applies the variance-based recursive method to guide the updating mechanism of process parameters to match the measurements. Subsequently, the inverse analysis identifies four process parameters of feed per tooth, tool tip radius, minimum cutting thickness, and tool tip angle, and finds the optimal solution for target performance, the surface roughness. The measurements are collected under the single beam coaxial laser-assisted milling spindle. The proposed modified Kalman filter algorithm introduces the gain coefficient G when updating the process parameters to improve robustness and accuracy. The inverse analysis is conducted on all measurements, and the average error of target performance is 0.460% when the laser is on and 0.394% when the laser is off. The average difference of process parameters is less than 5%, and the selection process is done in 50 loops within a minute. Therefore, the proposed inverse analysis model is robust, adaptive to different initial guesses and measurements, highly accurate, and saves computation time.

Design of eddy current dampers for vibration suppression in robotic milling

The milling robot normally has a low stiffness which may easily cause chatter during machining. This article presents a novel eddy current damper design for chatter suppression in the robotic milling process. The designed eddy current dampers are installed on the milling spindle to damp the tool tip vibrations. The structural design and the working principle of the eddy current dampers are explained. The magnetic flux density distribution and the magnetic force generation of the designed eddy current damper are analyzed with the finite element method. The tool tip dynamics without and with eddy current dampers are modeled, and the damping performance of the proposed eddy current dampers in the robotic milling process is verified through both simulations and experiments. The results show that the peaks of the tool tip frequency response function caused by the milling tool modes are damped significantly, and the stable depth of cut is improved greatly with eddy current dampers.

Robust Chatter Mitigation Control for Low Radial Immersion Machining Processes

Chatter is a typical kind of unstable dynamics often encountered in machining processes, which often results in overcut and rapid tool wear. Hence, chatter phenomenon worsens the surface quality and reduces productivity in milling systems as well. Recent years have witnessed a surging industrial demand of high quality and high efficiency machining. Specifically, for low radial immersion milling situation, large depth of cuts is inevitably needed so as to increase the machining efficiency. To fulfill such a task, this paper develops a robust active control method to mitigate the chatter dynamics of low radial immersion milling processes. The present approach increases the axial depth of cuts, and the improvement is inversely proportional to the radial immersion ratio. Finally, case studies are conducted to show the substantially enlarged stable region in the stability lobe diagram (SLD) spanned by spindle rotational speed and axial depth of cut. Thus, the method can be expected to improve the efficiency of milling processes. Note to Practitioners —This paper seeks to mitigate machining chatters that worsen the workpiece surface quality in high-speed machining processes. To overcome such unexpected effects, traditional passive schemes simply adjust the rotational speed and cutting depth, which do not seek assistance from external power sources. Hence, neither the damping nor stiffness of the system can be changed, and a high maximal material removal rate (MMRR) is arduous to obtain. By contrast, this paper develops a robust active control method to mitigate the chatter dynamics for low radial immersion milling. In the design stage of the milling spindle, two active magnetic bearings (AMBs) are embedded in the tool house as control actuators, which produce extra force to counteract the chatters. In real milling processes, the chatters are detected by the associated inductive displacement sensors around the AMBs, and an uncertainty model is accordingly established with low radial immersion. With the detected vibration displacements, robust active control signals are calculated online, and then fed into the power amplifiers to drive the two AMBs. By this means, a closed-loop active control system is thus established for milling processes, which substantially enlarges the stable region of the SLD spanned by rotational speed and cutting depth. As a result, the proposed active control scheme can be expected to increase the MMRR and, hence, to enhance the productivity of milling processes.

Hard Machining of Spur Gears with the InvoMillingTM Method

Recently, the 5-axis machining of gears has become increasingly important. This technology enables a flexible production of diverse gear types on a single universal machine with standard tools. In addition to the economic aspects, the focus is on the high quality standards that has to be achieved. This paper deals with hard machining for the finishing of spur gears with the 5-axis InvoMilling™ method developed by Sandvik Coromant. A comparison of the hard and soft machining of a module 5 gear is made. The achievable gear qualities in the profile and flank direction, the achievable surface roughness in the profile direction, the torque applied to the milling spindle during the machining process and the wear of different types of inserts are compared and evaluated. In addition, the hard machining with different insert materials/coatings is carried out.