Feed Direction Research Articles

An intelligent process parameters determination method based on multi-algorithm fusion: a case study in five-axis milling

• An intelligent parameters determination method is proposed based on multi-algorithm. • An improved GRNN with high accuracy is proposed for small batch of experiments. • An improved NSGA-II is proposed to generate the Pareto frontier with good uniformity. Process parameters have a significant effect on surface integrity, which determines the service performance of the parts. To improve surface integrity, the process parameters are determined: 1) by experienced engineers directly, 2) based on the Pareto frontier automatically constructed by swarm intelligence algorithms. However, as the Pareto frontier contains many non-dominated solutions, the final parameters are still determined by experienced engineers, which reduces the intelligence level. Therefore, an intelligent process parameters determination method based on multi-algorithm fusion is proposed towards minimal surface residual stress in feed or transverse direction ( Rs f , Rs t ) and surface roughness ( Ra ) in five-axis milling. Firstly, the Improved Generalized Regression Neural Network ( IGRNN ), which enhances the nonlinear mapping capability even in dealing with a small batch of experiments, is proposed to predict the Rs f , Rs t , and Ra with certain inputs (including lead angle, tilt angle, cutting depth, feed speed, and spindle speed). Then based on the proposed model, the Improved Non-dominated Sorted Genetic Algorithm-II ( INSGA-II ), which improves the uniformity of the Pareto frontier, is used to obtain a series of non-dominated process parameters. Finally, the optimal parameters are determined by the Principal Component Analysis ( PCA ) without manual weight assignment for Rs and Ra . By comparing with the second-best one, although the Rs f decreases by 0.33%, which is still able to obtain negative residual stress, the Rs t and Ra are greatly improved by 9.3% and 47.94%, respectively. The proposed method could improve the intelligent level of process parameters determination and the service performance of the parts. Furthermore, it lays a foundation for the realization of intelligent manufacturing.

Coupled thermo-mechanical modeling of drilling of multi-directional polymer matrix composite laminates

The influence of in-situ cutting temperature on machining induced damage and machining forces during drilling of multi-directional carbon fiber reinforced polymer (MD-CFRP) composites has been examined using a coupled thermo-mechanical finite element (FE) framework. The MD-CFRP laminate has been modeled ply-by-ply as an equivalent homogeneous anisotropic material (EHM) using temperature dependent laminate elastic and fracture properties. Stress-based criteria has been adopted for element deletion simulating the drilling process. The intralaminar damage model for simulating various composite machining induced damage modes was implemented in the FE framework via a user material subroutine. A new composite damage criterion is proposed that accounts for the out-of-plane drilling damage behavior along tool feed direction. Additionally, a fracture mechanics approach has been used to simulate interlaminar delamination onset using surface based cohesive elements at the drill exit plies. The current numerical model predictions show a good agreement with drilling experiments for thrust force, delamination damage, and in-situ cutting temperature.

Evaluation of the strength characteristics of Cunninghamia lanceolata timber using continuous mechanical stress rating equipment

Before timber is used for engineering and structural purposes, it is necessary to grade the strength of the timber. In order to obtain the static modulus of elasticity value of timber quickly and accurately, this study used ultrasonic waves and continuous mechanical stress rating equipment and two non-destructive test methods to analyze the correlation between the non-destructive test measured value and the static modulus of elasticity value. It also evaluated the influence of the feeding orientation of the boards, the forward and reverse feed directions, feeding speed, and break area ratio. The analysis results indicated that the modulus of elasticity value determined through continuous mechanical stress rating equipment had the highest correlation with the static modulus of elasticity value. Moreover, according to the results, the feeding orientation of the boards, the forward and reverse feed directions, and the feeding speed did not influence the prediction of the continuous mechanical stress rating equipment modulus of elasticity value. Meanwhile, to ensure the accuracy and uniformity of the continuous mechanical stress rating equipment modulus of elasticity detection value, it is necessary to avoid an excessively high break area ratio in Cunninghamia lanceolata timber during the preparation process.

Generalized modeling of milling dynamics for the 4DOF machining system with asymmetric flexibility

Asymmetric flexibility of the machining system exists widely in the practical milling process. In this paper, a generalized milling dynamics modeling method for an asymmetric flexible 4DOF cutter-workpiece system is proposed, which is further used to reveal how the asymmetric flexibility affects the milling dynamics characteristics. The regenerative milling force model is firstly established through the coupling coefficient matrix, in which the milling condition with non-parallel direction between the axis directions of coordinate system, the vibration directions of system DOF and the acting directions of milling force are well handled. Then, a generalized 4DOF milling dynamics model considering a new dimension, namely the cutter and workpiece feed direction angle combination ψ (ψc, ψw), is presented. The studies point out that the milling dynamics characteristics of the asymmetric flexible machining system, including the milling stability and surface location error (SLE), have a significant feed direction-dependent feature. Moreover, the generation mechanism of this kind of asymmetric milling dynamics has been successfully clarified. The proposed method has been experimentally validated by a series of milling tests in an asymmetric flexible machining system. Lastly, the influences of the asymmetry degree of the system flexibility, milling type and radial depth of cut on the milling dynamics are both analyzed by numerical simulation.

Effect of cutting parameters on chips and burrs formation with traditional micromilling and ultrasonic vibration assisted micromilling

In the traditional micromilling (TMM) of Inconel718 alloy, due to the influence of material plasticity and size effect, relatively large burr will be produced. In order to hinder the burr forming in micromilling, ultrasonic vibration in feed direction is applied to the workpiece to complete vibration cutting. Combined with trajectory simulation and cutting experiment, the burr formation mechanism of TMM and ultrasonic vibration assisted micromilling (UVAMM) was studied. The results show that when the ratio of amplitude (A) to feed per tooth (ƒz) is greater than 0.5, continuous cutting changes to intermittent cutting in the vibration cutting process. The fractured area with dimples on the burr increases with the increase of amplitude. Compared with TMM, UVAMM improves chip breaking ability, facilitates the propagation of burr crack, and effectively inhibits the formation of burr. When the chip breaking condition is reached, the burr shape is usually tearing or flocculent. Under the conditions of low speed (n), large ƒz, and large A, the burr suppression is more obvious.

Cutting characteristics of implant materials in milling

The demand of implant parts has recently been increasing with aging of the population progresses. In terms of biocompatibility and mechanical strength, stainless steels and cobalt chromium molybdenum (CoCrMo) alloy have been applied to implant parts. Laser sintering parts processed in additive processes have also been manufactured to adapt for each human body. However, the machinability of these materials is much lower than the conventional ones such as carbon steels. Residual stresses are also associated with the cutting forces for long lives of implant parts. This paper discusses the cutting processes of CoCrMo alloy, sintered stainless steel (SUS420J2), and wrought stainless (SUS304) in ball end milling with the cutter axis inclination. The cutting characteristics are compared in the cutting force, the surface finish and the residual stress. The cutting force of the sintered stainless steel includes large dynamic components due to non-uniformity of material with voids. Z component in the cutting force becomes large in milling of CoCrMo alloy. The surface finishes, then, are discussed in terms of the cutting force and the vibration. The surface finish also depends on the tool vibration associated with the dynamic response of tool and adhesion. The residual stresses measured in the feed direction of the tool and the width direction of the groove for some cutting parameters and the testing materials. In order to discuss the mechanical effect on the residual stress, the residual stresses are associated with the resultant cutting force in the feed and the width directions. The sensitivity of the residual stress to the cutting force is discussed for the testing materials. The residual stress in the width direction has large dependency on the cutting force, which may be controlled by the cutting parameters and the tool geometry. The residual stress of the feed direction depends on the material behavior controlled by the material properties.

Experimental investigations on the ultrasonic vibration-assisted hard turning of AISI 52100 steel using coated carbide tool

Ultrasonic vibration-assisted turning (UVAT) is a hybrid and eco-friendly machining technique. The UVAT is performed by superimposing high frequency and low amplitude sound waves on the cutting tool in conventional turning. In the present work, a comparative evaluation of the machining performance is presented during conventional turning (CT) and ultrasonically vibration-assisted turning (UVAT) of AISI 52100 hardened steel (62 HRC). Hard turning experiments were performed using a PVD coated TiAlSiN carbide tool considering the effect of process parameters such as cutting speed, feed, and depth of cut. The performance is measured in terms of cutting force and surface roughness. This study observed a better surface finish during of around 8.29% in UVAT when compared to conventional turning. Better surface finish achieved under UVAT could be attributed to better chip breaking and disentanglement of the chip around the tool during UVAT against long curly chips produced that further entangled on the tool while CT. These entangled long curly chips affected the surface finish. On the other hand, no significant difference is observed in cutting force while hard turning under CT and UVAT. This is mostly due to the fact that, although UVAT has less cutting force at slower cutting speeds, but it behaves very identically with CT when cutting speed approaches tangential velocity. This study finds further scope for machinability studies considering the effect of vibrations superimposed on a tool in feed, tangential, and radial directions.

Dynamic rotating-tool turning of micro lens arrays

Diamond micro milling of high-quality micro lens arrays suffers from low machining efficiency, due to the inevitable milling marks along tangential feed direction and the slow spiral tool path interpolated by multiple linear axes. In this article, an advanced cutting process is proposed, namely dynamic rotating-tool (DRT) turning, in which a U-axis attachment on a rotary stage is developed to enable synchronous cutter rotation and radial feed motions of a diamond turning tool. This method is experimentally verified and compared with milling, with significantly enhanced surface quality and machining efficiency, thus bringing a new perspective into ultra-precision machining.

Investigation of process window for AA7075 considering effects of different wire feed directions in lateral Laser Metal Deposition

This work addresses the influences of the feed direction of AA7075 high-strength aluminum alloy in wire-based lateral laser metal deposition (LMD). The additive manufacturing process is investigated for the deposition of thin-walled structures. The interaction between wire and laser beam as well as the evolution of the melt pool are in-situ monitored by a high-speed camera. The consequences of different feed directions are analyzed in terms of processability, surface morphology, geometry, and porosity. Besides, the appropriate process parameters for AA7075 in lateral wire LMD are also studied. A maximal relative density level of about 99.7 % can be reached. No macro-cracks on the specimen surface or inside the specimen are observed. Optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy are employed to characterize the microstructure and measure the chemical composition of specimen produced with the optimal process parameters. The plateau-like distribution of the hardness evolution and the uniform layer thickness in the middle of the thin-walled structure indicate that a stable LMD-process can be achieved.

Finite Element Study on Forming Helical Springs by Wire Bending with a Plate

Coil springs, widely used as mechanical elements, will enter another new production outlook due to the application of CNC wire bending machines and as the era of On-Demand Manufacturing is approaching. This article tries to follow the trend and use finite element analysis investigating parameters, such as the angle, shift distance, and wire diameter, applied in a CNC bending machine with a swivel plate as the die on the formed cylindrical helical coil springs. The results show that the angle of the swivel plate normal to the wire feeding direction and shift distance have a significant effect on the spring diameter, while the wire diameter has a significant effect on the spring pitch. The result will be used as a reference for the industry to develop On-Demand Manufacturing machinery applications in the future.

ANALYSIS OF THE CHANGE IN ROUGHNESS ON A FACE-MILLED SURFACE MEASURED EVERY 45° DIRECTION TO THE FEED

In this article, we analyze the difference (inhomogeneity) of the roughness values measured on a nonalloy carbon steel surface milled with a parallelogram-shaped (κr = 90°) insert as a function of the the tool movement direction and the relative position of the examining points on the workpiece surface. The characteristic distribution of roughness and the magnitude of the deviations were examined by measuring at selected points along several planes on a surface characterized by the movement conditions of the workpiece and the symmetrically arranged tool perpendicular to the machined surface, which formed double milling marks. The selected points mark the lines with specified inclinations with respect to the feed direction, and their measured values were compared. In these directions, the magnitude of the difference in roughness measures was obtained.

METHOD FOR CALCULATING CUTTING FORCES BY MODELING CAD WITH A SYSTEM OF GEOMETRIC CUTTING PARAMETERS WITH RADIAL MILLS

The accuracy of processing surfaces of a complex profile largely depends on the selected processing strategy, which will allow creating the same, within certain limits, power characteristics of the shaping process at the intervals of the programmed tool path. In this case, it becomes possible to include tuning modules in programs for CNC machines that form vector values of corrections in certain areas, as reactors for elastic deformations of the cutting process. Therefore, it is especially important to know the modulus and direction of the resulting cutting force vector, which does not necessarily coincide with the feed direction.
 The purpose of this work is to build a method for calculating cutting forces by modeling the geometric parameters of a cut with a CAD system, a cutter with a nonlinear generatrix. Solid modeling of the process is based on the Boolean operations of "intersection" and "subtraction" of 3D objects: the teeth of a radius cutter with a helical cutting edge and a workpiece "moving" at a feed rate. The tool for the implementation of this method is a software module created on the basis of API functions, the input data for which are: a 3D tool and a workpiece, the equation of the trajectory of its movement and the parameters of the infeed movement. Targeting API properties, the application makes it possible to simulate various trajectories, helical or trochoidal, when machining complex surfaces. In the future, it is possible to take into account the plastic deformation processes in the chip formation zone in the model by connecting external modules.
 In the course of the conducted research on milling with radial end mills with a helical cutting edge, when two or more teeth are within the arc of contact, it was determined by 3D modeling how much thickness and width the layer cuts off each of the teeth during the feed per revolution. Consequently, in the process of shaping, normal and tangential cutting forces, which are different in direction and modulus, are present as a function of the angle of rotation of the cutter. Therefore, the concept of "circumferential force on the cutter", accepted in the theory of cutting, as a certain constant component of the process, can introduce an error when considering the causes of the excitation mechanism of vibrations of different nature that arise in the processing zone.

Surface Topography Prediction Model in Milling of Thin-Walled Parts Considering Machining Deformation.

With the continuous improvement of the performance of modern aerospace aircraft, the overall strength and lightweight control of aircraft has become a significant feature of modern aerospace parts. With the wide application of thin-walled parts, the requirements for dimensional accuracy and surface quality of workpieces are increasing. In this paper, a numerical model for predicting surface topography of thin-walled parts after elastic deformation is proposed. In view of the geometric characteristics in the cutting process, the cutting force model of thin-walled parts is established, and the meshing relationship between the tool and the workpiece is studied. In addition, the influence of workpiece deformation is considered based on the beam deformation model. Cutting force is calculated based on deformed cutting thickness, and the next cutting–meshing relationship is predicted. The model combines the radial deflection of the workpiece in the feed direction and the changing meshing relationship of the tool–workpiece to determine the three-dimensional topography of the workpiece. The error range between the experimental and the simulation results of surface roughness is 7.45–13.09%, so the simulation three-dimensional morphology has good similarity. The surface topography prediction model provides a fast solution for surface quality control in the thin-walled parts’ milling process.

Feed Direction-Dependent Milling Dynamics of an Asymmetric Flexible Machining System

Abstract Asymmetric flexible machining system has been widely used in numerical control machining. In traditional milling dynamics model, the cutter feed direction is usually defined as parallel to its vibration DOF, while the nonparallel condition and its induced milling dynamics response are not deeply considered. This paper presents a general dynamics modeling method for asymmetric flexible machining systems. First, to the best of the author’s knowledge, a new dimension named feed direction is proposed, which is used to establish the generalized coupling relationship between the vibration displacement and the regenerative milling force, thus improve the applicability of the milling dynamics model and reduce the experimental workload compared with the traditional modeling. Second, through the theoretical and experimental research, it is shown that the asymmetric flexible machining system has a significant feed direction-dependent characteristics, and implied the existence of high performance machining region with higher stability and lower surface location error (SLE) by contrast with the symmetric milling system and the traditional models. Finally, by controlling the feed direction angle, the milling parameters in roughing and finishing operations are optimized, and the machining efficiency has been greatly improved on the premise of stable cutting and machining accuracy.

High-Precision Adjustment of Welding Depth during Laser Micro Welding of Copper Using Superpositioned Spatial and Temporal Power Modulation

For joining metallic materials for battery applications such as copper and stainless steel, laser beam micro welding with beam sources in the near-infrared range has become established in recent years. In laser beam micro welding, spatial power modulation describes the superposition of the linear feed motion with an oscillating motion. This modulation method serves to widen the cross-section of the weld seam as well as to increase the process stability. Temporal power modulation refers to the controlled modulation of the laser power over time during the welding process. In this paper, the superposition of both temporal and spatial power modulation methods is presented, which enables a variable control of the weld penetration depth. Three weld geometries transverse to the feed direction are part of this investigation: the compensation of the weld penetration depth due to the asymmetric path movement during spatial power modulation only, a W-shaped weld profile, and a V-shaped. The weld geometries are investigated by the bed on plate weld tests with CuSn6. Furthermore, the use of combined power modulation for welding tests in butt joint configuration between CuSn6 and stainless steel 1.4301 with different material properties is investigated. The study shows the possibility of precise control of the welding depth by this methodology. Depending on the material combination, the desired regions with maximum and minimum welding depth can be achieved by the control of local and temporal power modulation on the material surface.

Study on the Formation Mechanism of Surface Adhered Damage in Ball-End Milling Ti6Al4V.

Ball-end cutters are widely used for machining the parts of Ti-6Al-4V, which have the problem of poor machined surface quality due to the low cutting speed near the tool tip. In this paper, through the experiments of inclined surface machining in different feed directions, it is found that the surface adhered damages will form on the machined surface under certain tool postures. It is determined that the formation of surface adhered damage is related to the material adhesion near the cutting edge and the cutting-into/out position within the tool per-rotation cycle. In order to analyze the cutting-into/out process more clearly under different tool postures, the projection models of the cutting edge and the cutter workpiece engagement on the contact plane are established; thus, the complex geometry problem of space is transformed into that of plane. Combined with the case of cutting-into/out, chip morphology, and surface morphology, the formation mechanism of surface adhered damage is analyzed. The analysis results show that the adhered damage can increase the height parameters Sku, Sz, Sp, and Sv of surface topographies. Sz, Sp, and Sv of the normal machined surface without damage (Sku ≈ 3) are about 4–6, 2–3, and 2–3 μm, while Sz, Sp, and Sv with adhered damage (Sku > 3) can reach about 8–20, 4–14, and 3–6 μm in down-milling and 10–25, 7–18, and 3–7 μm in up-milling. The feed direction should be selected along the upper left (Q2: β ∈ [0°, 90°]) or lower left (Q3: β ∈ [90°, 180°]) to avoid surface adhered damage in the down-milling process. For up-milling, the feed direction should be selected along the upper right (Q1: β ∈ (−90°, 0°]) or upper left (Q2: β ∈ [0°, 90°)).

Optimization of Cryogenic Process Parameters for the Minimization of Surface Residual Stress in Pure Iron Using Taguchi Design

The plastic deformation produced in the machining process can cause residual stress. As an effective way to control the residual stresses, the cryogenic process is used in modern industries such as aerospace, automobile, and shipping industry. Focusing on the minimization of surface stress in the cryogenic process of pure iron, the Taguchi design is used in this paper. The effect of cryogenic temperature (77–193 K), holding time (8–24 H), cooling rate (2–6 K/min), and warming-up rate (0.5–1.5 K/min) on surface residual stress is discussed and the optimal combination of cryogenic parameters is obtained using signal-to-noise (S/N) ratios. To overcome the weakness of the Taguchi method that cannot calculate stresses, an exponential model to predict residual stresses considering cryogenic parameters is developed. The coefficients of this mathematical model are obtained using multilinear regressive analysis based on the database of the Taguchi experiment. After this, the optimization process is conducted with this model using the genetic algorithm (GA). The optimized results using both ways coincide with each other. The optimal cryogenic parameters are obtained, i.e., cryogenic temperature of 193 K, holding time of 24 h, cooling rate of 2 K/min, and warming-up rate of 0.5 K/min. When the optimum cryogenic parameters are used, the surface residual stress is reduced by 42.9% in the cutting direction and 46.2% in the feeding direction. The method can be applied to the actual machining engineering to realize the low-stress control on the cutting surface.

Investigation of the morphological and fractal behavior at nanoscale of patterning lines by scratching in an atomic force microscope.

In this work, the topographical effect of the scratching trajectory and the feed direction on the formation of lithographed lines on the (001) InP surface was investigated using an atomic force microscope (AFM) tip-based nanomachining approach. Nanoscratching tests were carried out using the sharp face of a diamond AFM tip in contact mode. From the topographic maps obtained by AFM, several morphological and fractal parameters were obtained and analyzed. Surface morphology presented a surface smoothing for surfaces with scratches produced in [011] and [001] directions. The height parameters confirmed this behavior because scratches in [001] direction exhibited lower roughness. Moreover, this scratch direction promoted the height distribution most symmetrical and platykurtic. The other morphological parameters revealed that this direction provided a more irregular surface (smaller Smc and Sxp ), peak distribution, denser and pointed, smaller portion of material in the core, less deep furrows, higher spatial frequency components, and high isotropy. Fractal parameters revealed that FRE90 has the highest spatial complexity, it is dominated by higher spatial frequencies, and has the lowest surface percolation. Furthermore, all samples exhibited high topographic uniformity.

Grindability study of hard to cut AISI D2 steel upon ultrasonic vibration-assisted dry grinding

Ultrasonic vibration-assisted dry grinding is a sustainable hybrid manufacturing technology that decreases the negative environmental impact of coolant, reduces manufacturing costs, and improves surface integrity. The present investigation analyses the mechanisms associated with ultrasonic vibration-assisted dry grinding of AISI D2 tool steel with an alumina grinding wheel. It also compares the influence of traditional dry grinding and traditional wet grinding modes with the ultrasonic vibration-assisted dry grinding mode at different ultrasonic vibration amplitudes. Ultrasonic vibration was applied to the sample in the longitudinal feed direction. Further, kinematics of the abrasive grit path during the traditional grinding and ultrasonic vibration-assisted dry grinding is presented schematically. In this research, the impacts of ultrasonic vibration amplitude as well as the depth of cut on the process yields such as ground surface topography, grinding force, specific grinding energy, force ratio, surface finish, microstructure, and hardness were investigated experimentally. Experimental results revealed that the highest decline in tangential and normal grinding forces in ultrasonic vibration-assisted dry grinding at ultrasonic vibration amplitude 10 µm and the reduction in surface roughness parameter ( Ra, Rq, and Rz) in ultrasonic vibration-assisted dry grinding was 43.23%, 42.59%, and 33.69%, respectively, in comparison to those in traditional dry grinding and 26.35%, 26.94%, and 27.48%, respectively, in comparison to those in traditional wet grinding. It was observed that ultrasonic vibration-assisted dry grinding is beneficial as the profile produced by ultrasonic vibration-assisted dry grinding has a comparatively flat tip, and profile points are shifted to the bottom of the mean line. This study is expected to assist ultrasonic vibration-assisted dry grinding of hard materials.

Velocity effect sensitivity analysis of ball-end milling Ti-6Al-4 V

Ball-end cutters are widely used in industries of dies, molds, and aerospace, which have the problem of poor machined surface quality due to the low cutting speed near the tool-tip. With the increase in the complexity of parts, it will become more and more difficult to avoid the tool-tip participating in the cutting. In this paper, the velocity effect sensitivity of the ball-end cutter is analyzed, and several key positions, including the intersection points of the CWE boundaries, are selected to describe the cutting speed in three dimensions. The relationships between the cutting speed of the critical points and important variables such as the machining inclination angle and the feed direction were investigated. The optimal range of feed direction is obtained when the tool-tip engages in the contact circle. The core aim of the feed direction selection is to make the tool engagement area in a high position by changing the feed direction, to avoid surface damage and improve the quality of the machined surface. Finally, an experimental study was carried out, and the results corroborate the effectiveness of the selection method. In the experiment, it was also found that cutting-out from the cutter contact position can improve the surface quality in the directions of non-optimal range, and the milling force and chips shape will vary with the change of the feed direction.