Helical Milling Research Articles

Study of the Influence of Helical Milling Parameters on the Quality of Holes in the UNS R56400 Alloy

Helical milling has been positioned as an alternative to conventional drilling, where the advantages it offers make it very attractive for use on difficult-to-machine alloys such as the titanium alloy UNS R56400. However, the correlation between the indicator of hole quality and the kinematic parameters has rarely been studied. The kinematics are what bring most advantages and that is why it is necessary to know their influence. In this aspect, there are different focuses of problems associated with the complexity of the process kinematics, which makes it necessary to undertake a deeper analysis of the process and to carry out a preliminary study. To address this problem, a DOE (Design of Experiments) is proposed to identify the sensitivity and the main trends of the properties that define the quality holes with respect to the kinematic parameters. At the same time, a nomenclature is proposed to unify and avoid misinterpretations. This study has allowed us to obtain conclusive results that offer very relevant information for future research

Comparative analysis of wobble milling, helical milling and conventional drilling of CFRPs

Due to its excellent specific mechanical properties, carbon fibre-reinforced polymer (CFRP) composite is a widely used structural material in the aerospace industry. However, this material is difficult to cut, mainly due to its inhomogeneity and anisotropic features and because of the strong wear effects of its carbon fibres. In the scope of aerospace industrial uses of this material, thousands of holes have to be machined for purposes of assembly. Nevertheless, conventional drilling technology – even if special drilling tools are used – is only moderately able to manufacture good quality holes. Wobble milling is a novel advanced hole-making technology, which has been developed to minimize machining-induced geometrical defects like delamination or uncut fibres. The main objective of the present paper is to compare wobble milling, helical milling and conventional drilling technologies concerning unidirectional CFRPs. In addition, the kinematics of wobble milling technology is discussed in detail. In the scope of this paper, numerous machining experiments were conducted in unidirectional CFRPs: herein the impact of the type of cutting tool and of process parameters on the quality of machined holes are analysed and discussed (diameter of holes, circularity error and characteristics of uncut fibres). During these investigations, experimental data were evaluated with the help of digital image processing (DIP) and with the help of analysis of variance (ANOVA) techniques. Experimental results show that the amount of uncut fibres can significantly be minimized through the application of wobble milling technology.

Evaluation of conventional drilling and helical milling for processing of holes in titanium alloy Ti6Al4V

Use of conventional drilling process have been utilized by academia and industry alike for making holes in difficult to machine materials like titanium alloys. However nowadays helical hole milling process has been adopted due to the advantages it brings in. This work therefore aims to evaluate the traditional drilling process against the newer helical milling process for hole making in titanium alloy. The evaluation was carried out considering the thrust force, surface roughness, hole diameter and machining temperature. The morphology of chips generated and the burr formation were also investigated. The comparison of thrust force and machining temperature were found to be lower for the holes processed using helical milling process. The finish of the machined hole surfaces was better when helical milling process was used. Additionally, helical milling of holes resulted in relatively diametrically accurate and burr free holes. The preliminary results obtained show that helical milling process can be a promising alternative to traditional drilling process for machining difficult-to-machine material like titanium alloy provided the productivity of the process can be improved.

Research trends in high speed milling of metal alloys: A short review

Milling is considered to be the basic machining process among the various cutting operation. This paper performs an overview of cutting characteristics of high speed and Computerised Numerically Controlled (CNC) milling with potentials and applicability for high-performance material. The recent development with various hardened and aerospace materials related to the milling process was briefly highlighted so as to indicate the future developments in this innovative area. First of all, the significance of hard milling has been pointed out. The concept of end milling and helical milling with turn-mill has been briefly elaborated. The various types of cutting tools with its characteristics and applications provide its suitable applicability in the milling cutting condition. The research trends for predictor variables have been discussed. Moreover, this review provides further research work both experimentally and theoretically in the milling machining sector considering the controllable parameters. The findings of this review will provide future possibilities with a good research path for machinist and researchers working in the milling research areas. In short, this summary provides some fundamental learning of the various milling process trends on the machining scenario and presents a backdrop of future analysis.

Identification and analysis of cutting force coefficients in the helical milling process

Identification and analysis of cutting force coefficients in the helical milling process

Mechanics and dynamics study of helical milling process for nickel-based superalloy

Helical milling is a new high-quality hole-making process which offers many advantages such as better chip transportation and lower cutting forces and cutting temperature than conventional drilling. This paper presents the mechanics and dynamics of helical milling process for nickel-based superalloy. Firstly, according to the kinematics and undeformed chip geometry of helical milling, a cutting force model which considers the variation of the axial depth of cut, the rounded corner effect, and the helix angle of the cutter is established. Next, on the basis of proposed cutting force model, the dynamic cutting forces of helical milling are calculated, and the stability of the operation is simulated with full-discretization method. Finally the cutting force and chatter stability models are validated by verification tests on a nickel-based superalloy GH4169 workpiece. The results show that the simulated cutting forces and chatter stability lobes agree with the measured data well and it is feasible to replace the conventional drilling with helical milling when machining the nickel-based superalloy.

Analysis of Characteristics of Surface Roughness of Machined CFRP Composites

Measuring and characterizing of surface roughness of machined surfaces of carbon fiber reinforced polymer (CFRP) composites are difficult due to the occurrence of special surface damages (delamination, uncut fibers, fiber pull-outs or micro-cracks, etc.). The main objective of the present study is to analyze the characteristics of surface roughness of machined unidirectional CFRP in detail. Numerous conventional drilling, helical milling, and edge trimming experiments were carried out with different cutting tools in order to analyze the influence of them on the average surface roughness (Ra), on the roughness depth (Rz) and on the Rz /Ra parameter. The surface roughness was measured by a Mitutoyo SJ-400 contact profilometer and an Alicona Infinite Focus confocal microscope. The usability of the contact profilometer was experimentally tested and compared its results with the results of the confocal microscope. Experimental results show that the contact profilometer is suitable for measuring surface roughness of CFRP, furthermore, values of Rz /Ra of drilled and edge trimmed surfaces of unidirectional CFRP are changing in a wide interval: from 5 to 14 μm/μm due to the special surface damages. Based on this research, the machinability analysis of CFRP is suggested to be extended to the analysis of the Rz /Ra parameter.

Geometrical texture and surface integrity in helical milling and ultrasonic vibration helical milling of Ti-6Al-4V alloy

Abstract Surface integrity of hole-making for Ti-6Al-4 V alloy is very important due to its application in aviation industry. Geometrical and mechanical behaviors of machined holes by helical milling (HM) and ultrasonic vibration helical milling (UVHM) were investigated. The textures of machined holes by the two processes were analyzed and the distances of adjacent textures were calculated according to the movement of peripheral edges. Due to the different surface geometrical textures, the hole-diameter error and surface roughness in UVHM are smaller than those of HM. A plastic deformation layer with thickness of 4–6 μm was observed by the distorted β phase in the cross-section of hole-surface in UVHM by SEM results. Compared with HM process, UVHM generates larger hardness at the subsurface of machined holes (20–200 μm) due to the material deformation caused by ultrasonic vibration. Compared with HM, the compressive residual stress of hole surface was increased larger than 63.5% by UVHM. The compressive stresses in UVHM are larger than 150 MPa at the depth less than 10 μm, which is consistent with the microstructure evolution caused by mechanical deformation.

Finite element prediction of fatigue lifetime for different hole making strategies

Residual stresses and surface roughness are known to be the surface integrity parameters most affecting the fatigue life in machining processes. It has always been tried to obtain a correct correlation between these parameters and fatigue life. In this study, an FE model based on damage mechanics was developed to estimate the fatigue life of specimens made by drilling, drilling+predrill, and helical milling processes. First, hole making strategies were simulated to obtain the induced residual stresses. The specimens were then exerted under cyclic uniaxial loading, while damage mechanic was applied in the model. Experimental models were also used to modify the predicted fatigue life based on surface roughness. Validation tests showed capability of the proposed model to predict the fatigue life of holed samples with the maximum difference of 13.1 ^. In addition, the predicted crack initiation site was consistent with the fractography analysis.

Helical milling response of glass fiber-reinforced polymer composite with carbon nanotube buckypaper interlayer

Fiber-reinforced polymer composites are increasingly utilized in applications where both the weight and the strength of the components are critical as in the aerospace industry. However, the full utilization of these materials could be hindered by the weak out-of-plane properties which precipitate delamination. Carbon nanotubes (CNTs) have recently gained massive interests due to its superior mechanical properties, which are excellent for improving the fiber/matrix interface. The current study considered two specimens of glass fiber-reinforced polymer composites (with and without CNT buckypaper) and subjected them to two tests, namely interlaminar shear strength and helical milling tests. Results show that the CNTs increase the interlaminar strength of the laminates by about 25% and the images of the machined parts reveal a separation of layers (delamination) on the specimens without CNT while on the other hand uncovering a relatively good quality surface and a good fiber/matrix/CNT interface for the specimens with CNT.

Multivariate GR&R through factor analysis

Several measurement tasks present multivariate nature. In the cases with quality characteristics highly correlated within groups, but with a relatively small correlation between groups, the available multivariate GR&R methods are not suitable to provide a correct interpretation of the results. The present work presents a new multivariate GR&R approach through factor analysis. Factor analysis is a multivariate statistical method which focuses on the explanation of the covariance structure of the data. Through orthogonal rotation of the factors a suitable structure can be achieved with loadings easy to relate the variables to the factors. The proposed multivariate GR&R method through factor analysis is described and applied in the quality evaluation of holes obtained through helical milling process of AISI H13 hardened steel. The method succeeded in achieving a simple structure, with one factor related to the roughness outcomes and other related to the roundness ones, simplifying the gage capability evaluation.

Vibration analysis of milling process with helix-angle cutter based on Euler method

The chatter vibration is the major limiting factor in increasing the metal removal rates of the machine tools. In this paper, a program for dynamic analysis of thin-walled milling process with helical milling cutter is developed, based on Euler iteration. The program can take into account the characteristics of thin-walled workpiece, the contact separation between workpiece and cutter, the helical angle of cutter teeth and other actual cutting process characteristics. Based on the stability lobe diagram obtained by semi-discrete method, the stability simulation in different cutting parameters around the stable island was carried out. The unstable form of the cutting process was determined by spectrum analysis and Poincare mapping method. The results show that the method is in good agreement with the results of stability Lobe diagram and can capture the stability island in small radial cutting process. This method can well grasp the cutting force and vibration evolution process in cutting process, and provide an effective means for stability analysis of cutting process.

FEA investigation of process parameters effect on machining characteristics in helical milling

Abstract The manufacturability of products depend on geometrical features and machining characteristics involved in operation like cutting forces, power consumption etc. The aim of proposed FEA study is estimating the cutting forces, power consumption and torque while helical milling AISI 4340 alloy steel, a hole making process and a unique alternate for drilling. The process parameters involved in study are spindle speed, feed and orbital speed. Simulations are performed based on L8 Taguchi DOE. The simulation outcomes are validated with artificial neural network predictions of the responses and the results found to be agreeable.

Modelling the unidirectional fibre composite milling force oscillations through capturing the influence of the stochastic fibre distributions

Although high frequency variation of cutting forces is an inherent characteristic when milling composites, studies and models on the explanation and time-domain simulation of such processing forces seem to be missing in the literature. This paper first claims that the variation of the composite milling forces comes from three aspects: i) the variation of chip thickness caused by the cycloid trajectories of the cutting edge; ii) the random fibre placements within the composite and iii) the continuous variation of the cutting direction relative to the fibre orientation due to the rotational motion of the milling cutter. Moreover, the cutter’s helix angle leads to each section of the cutting edge engaging different fibre orientations simultaneously, adding additional challenges in understanding and predicting the resultant forces. Thus, this paper develops an analytical approach which can be utilised to accurately simulate the milling forces in time domain for unidirectional fibre composites. The approach calculates the chip thickness, estimates the stochastic fibre placements and defines variable cutting coefficients for different fibre orientations to integrate their effects on the force variability. Besides, the helical cutter is discretized into several slices to simulate the force acting on each engaged part at its relevant fibre cutting angle, resulting in a procedure of simulating the composite cutting force with helical milling cutter. Both straight and helical milling cutters are taken into account to validate the model, the effects from the concluded three aspects are separately investigated to provide an in-depth understanding of the force variation and support the developed model. It is observed that the variation of milling forces follows a Gaussian distribution when the cutting direction of the fibre is fixed. Furthermore, the simulated milling forces show a satisfactory agreement with the experimental results, especially their oscillations illustrate a high degree of consistency.

A comparative study of hole making performance by coated and uncoated WC/Co cutters in helical milling of Ti/CFRP stacks

A comparative study of hole making performance by coated and uncoated WC/Co cutters in helical milling of Ti/CFRP stacks

A tilted orbital grinding technique for hole-making of CFRP composite laminates

Carbon fiber reinforced polymer (CFRP) laminates have been widely employed in the manufacturing of airplane. Usually, hole-making is the final machining process to join CFRP laminates with other components. However, CFRP laminates are considered as hard-to-machine materials, which results in some serious failures during hole-making process such as fiber pull-out, fiber break, and matrix delamination. To improve the hole-making quality, a tilted orbital grinding (TOG) method was proposed in this study. In the proposed TOG method, a grinding wheel was used as the machining tool and its axis was set as tilted against the axis of the hole with a small angle. Through replacing the revolving motion of the tool in conventional helical milling with conical pendulum motion of the grinding wheel, a hole could be made by a grinding process. The thrust forces, cutting temperatures, and the quality of the holes in the proposed TOG process were investigated by experimental methods. The results show that the thrust forces and cutting temperatures in TOG process are greatly less than those in the conventional orbital milling process. Scanning electron microscope (SEM) images of the hole that made by TOG method show that there is no crack generated in the entrance side of the hole, and the pull-out delamination in the exit side of the hole is significantly reduced. The experimental results indicate that the proposed TOG method has a potential application in the hole-making of CFRP laminates.

Kinematic view of cutting mechanism in hole-making process of longitude-torsional ultrasonic assisted helical milling

Compared with conventional hole-making process, rotary ultrasonic machining (RUM) is commonly believed to improve the cutting performance, such as low cutting force, good hole quality, long tool life, and high material removal rate. However, this work proposes an interesting observation on hole-making process using longitude-torsional ultrasonic assisted helical milling (LT UAHM). Due to the special kinematic motion in LT UAHM, the trajectory of the cutting tool has complex characteristics which may generate a negative effect on machining performance. In this study, a comparative experiment between LT UAHM and conventional helical milling (HM) was carried out. The results showed that the axial cutting force is not always reduced, the machined hole quality is also not improved consistently in LT UAHM. To comprehend the cutting mechanism of LT UAHM incisively, a kinematic trajectory model was proposed. By the theoretical kinematic trajectory model, LT UAHM can generate the ultrasonic elliptical cutting in the process, and the phase shift is a critical factor that can affect the elliptical trajectory shape even the vibration cutting direction of the tool’s cutting edge. The equivalent cutting angle and direction of friction between the rake face and chip in processing change accordingly. As a result, the magnitude of cutting force and machined hole quality in terms of burr height in this process will be significantly affected.

Enhancing dimensional accuracy and surface integrity by helical milling of carbon fiber reinforced polymers

Geometrical defects are one of the main problems in machining of carbon fiber reinforced polymer (CFRP) laminates Helical milling is a brand new machining process and a kind of manufacturing method that helical tool movement is added and results in better hole quality with one-time machining. In recent years, helical milling is attracting increasing attention of numerous researchers. In our study, an experimental investigation is carried out on CFRP laminates by using tungsten carbide tool. For the first time, effects of process parameters like cutting velocity and feed rate on the hole quality aspects such as hole diameter, circularity, cylindricity and surface roughness are experimentally and statistically discussed. Besides, surface morphology of the hole wall is examined. Analysis of variance (ANOVA) is carried out on hole quality parameters and their contribution rates are determined. Increasing cutting velocity improved hole diameter, circularity and cylindricity and had no significant influence on surface roughness. In addition, reduction in feed rate is suggested to have a high-quality hole in helical milling of CFRP. By statistical evaluation, results show that cutting velocity in all cases, is more effective than feed rate. Moreover, machining force is reduced in helical milling compared to conventional drilling.

Monitoring of orbital drilling process in CFRP based on digital image processing of characteristics of uncut fibres

Orbital drilling (helical milling) process with fixed and optimised technological parameters is suitable to produce good-quality holes in carbon fibre reinforced polymer (CFRP) composites, however, after the tool wear increases, the monitoring of drilling process is often required in order to keep the machined holes good-quality. The main objective of the present research was to develop an algorithm for the monitoring and diagnostics of orbital drilling process using digital image processing of characteristics of uncut fibres. Drilling depth and screw pitch of the helical tool path have chosen as independent process parameters. The acceptance criterion was defined as the ratio of drilled hole area to that of a nominal hole. Numerous orbital drilling experiments were carried out in order to validate the goodness and reliability of the developed method. Results show that holes machined by the application of the monitoring algorithm have less uncut fibres than the holes drilled with fixed technological parameters.

Deformation analysis and hole diameter error compensation for hybrid robot based helical milling

Deformation analysis and hole diameter error compensation for hybrid robot based helical milling