Hole Milling Research Articles

Experimental investigation into helical hole milling of fiber metal laminates

Drilling of multi-material fiber metal laminates (FMLs) is a challenging process. The challenges stem from serious issues like ply delamination, poor dimensional accuracy and surface quality, burr formation coupled with chip evacuation and serious tool wear observed during drilling of FMLs. Recently, helical hole milling process has gained popularity for making holes in metallic alloys due to several advantages it possesses over hole drilling process. Therefore, a comprehensive experimental investigation into the influence of process parameters viz. helical pitch, spindle speed and feed rate on the process responses viz. milling forces, surface finish, machining temperature and hole diameter during hole making in glass laminate aluminum reinforced epoxy (GLARE) FML is carried out. The process responses are analyzed and the findings based on the study are summarized.

Study on the Machinability of SMC Composites During Hole Milling: Influence of Tool Geometry and Machining Parameters

The machining of composite materials is generally performed to obtain the required geometry and dimensional tolerances. This paper applies the Taguchi method to investigate the effects of end-milling parameters on the machinability outputs of chopped glass fiber-reinforced polymer composites. The main aim is to investigate the machinability and defects generated by four different end-mill tool geometries when applying hole expansion on A-Class Sheet Mold Compound (SMC) composites. The resultant force, surface roughness, and peel-up delamination behavior were evaluated under different cutting conditions in milling operations, while the milling experiments were conducted under different parameters and levels according to the Taguchi method. The contribution ratio of parameters on machinability outputs was analyzed statistically via analysis of variance and regression analysis. The most suitable cutting conditions to achieve a high-quality hole in the least amount of machining time on an SMC composite include higher cutting speed, lower feed rate, higher number of teeth—as with six-fluted helix and eight-fluted burr-style end mills—and down-milling with CCW circular interpolation.

A sustainability comparison between drilling and milling for hole-enlargement in machining of hardened steels

Hole-making is one of the most important processes of metal shaping domain. Although, drilling is a commonly used approach to cut holes in metallic parts, the process cannot be completed with the cutting action of one drill bit if the work material is hard and diameter of the hole is large. Usually, a drill having diameter equal to the required diameter of the hole is utilized to enlarge a predrilled hole of a smaller diameter. In this work, we have investigated sustainability of using another method of enlarging a pre-drilled hole, namely side and end milling and compared it with the drilling-based approach. The work material used in the study is a high carbon steel, which is heat-treated to two distinct levels of surface hardness. Besides process type and work material hardness, the other two parameters tested in the investigation are cutting speed and depth of hole. A total of 16 experiments were performed to generate data regarding the sustainability measures, namely hole surface roughness, specific cutting energy and tool wear. Process choice (drilling or milling) for hole-enlargement was found to possess a significant effect on all the measured responses. Analyses carried out on the experimental data revealed that although the drilling-based option led to an immensely better surface finish, the milling-based option performed better with respect to the other measures of economic and environmental sustainability.

Multi-objective robust design of helical milling hole quality on AISI H13 hardened steel by normalized normal constraint coupled with robust parameter design

Helical milling is a hole-making process which has been applied in hardened materials. Due to the difficulties on achieving high-quality boreholes in these materials, the influence of noise factors, and multi-quality performance outcomes, this work aims the multi-objective robust design of hole quality on AISI H13 hardened steel. Experiments were carried out through a central composite design considering process and noise factors. The process factors were the axial and tangential feed per tooth of the helix, and the cutting velocity. The noise factors considered were the tool overhang length, the material hardness and the borehole height of measurement. Response models were obtained through response surface methodology for roughness and roundness outcomes. The models presented good explanation of data variability and good prediction capability. Mean and variance models were derived through robust parameter design for all responses. Similarity analysis through cluster analysis was performed, and average surface roughness and total roundness were selected to multi-objective optimization. Mean square error optimization was performed to achieve bias and variance minimization. Multi-objective optimization through normalized normal constraint was performed to achieve a robust Pareto set for the hole quality outcomes. The normalized normal constraint optimization results outperformed the results of other methods in terms of evenness of the Pareto solutions and number of Pareto optimal solutions. The most compromise solution was selected considering the lowest Euclidian distance to the utopia point in the normalized space. Individual and moving range control charts were used to confirm the robustness achievement with regard to noise factors in the most compromise Pareto optimal solution. The methodology applied for robust modelling and optimization of helical milling of AISI H13 hardened steel was confirmed and may be applied to other manufacturing processes.

Prediction of surface topography due to finite pixel spacing in focused ion beam milling of circular holes and trenches

Successful implementation of focused ion beam technologies in fabrication of practically important structures, including circular holes and trenches requires evaluating the ion dose delivered to the specimen by the beam and subsequently predicting the formed topography. In this article, the analytical expressions for the ion dose are obtained in polar coordinates using Bessel functions. These expressions can be transformed into relatively straightforward formulas useful in many applications. On the basis of the expressions derived, the surface shape of structures under consideration is analytically described if constant sputtering yield conditions are realized throughout the milling process. For practically relevant structure preparation, when the distance between neighboring beam stops is less than approximately two beam diameters, it was established that the mean depth and the peak-to-valley surface roughness can be evaluated by simple formulas. The outcomes of theoretical findings are confirmed by the comparison with the numerically obtained results and experimental data retrieved from the fabricated circular holes.

Study on micro helical milling of small holes with flat end mills

Helical milling as an eco-friendly hole-making process has various advantages comparing to conventional drilling process and has been widely studied. But micro helical milling for small holes was not investigated. This paper focuses on preliminary studies on micro helical milling of small holes with flat micro end mills. The cutting phenomena of the radial and axial cutting edges are considered and discussed separately. Based on the size effect existing in microcutting processes, the minimum undeformed chip thicknesses (hmin) for both radial and axial cutting edges are identified for work material copper C26000 by finite element method and micro helical milling experiments. Since burrs are noticed during experimental studies, burrs at the hole entrance are analyzed elementarily and it shows that the burr size has a relation with the critical conditions in micro helical milling. The study turns out that the ratio of hmin to cutting edge radius in micro helical milling is from 0.6 to 0.68 and is larger than that of conventional microcutting processes for various materials, which is usually in the range from 0.14 to 0.43. It is a good sign for micro helical milling of small holes with higher productivities since the ratio of hmin to tool cutting edge radius is larger than that of conventional microcutting processes.

Hole drilling and milling of magnetic alloys parts by shaped tube electrolytic machining

In this research shaped tube electrolytic machining of drilling and milling of magnetic alloys parts and difficult-to-cut metals, steels and alloys is presented. New research made in the field of space, aviation, automobile, medical, computer and electronics, and others has created the need for small and fine holes with high aspect ratio in these materials. The primary investigations of ECM with the tubular tool electrode are presented. Compared with mechanical machining, shaped tube electrolytic machining (STEM) exhibits an advantage in producing micro-holes with a high aspect ratio and in producing the curved holes. In order to realize the process of electrochemical machining, experimental assembly with the shaped tube tool electrode has been designed and manufactured. Completed researches indicate that this tool electrode has a high potential to machine difficult-to-cut and brittle metals economically and efficiently.

Hole geometry effect on stop-band characteristics of photonic crystal in Ti-diffused LiNbO3 waveguide

Effects of finite hole depth and non-cylindrical hole shape on stop-band characteristics of photonic crystal formed by air-hole square lattice in Ti-diffused LiNbO3 strip waveguide were studied theoretically. The study shows that hole depth determines the contrast of stop-band, and the hole radius and conical angle determine the bandgap and location. Cylindrical holes must be sufficiently deep so as to overlap most of waveguide mode and hence obtain a stop-band with high contrast, sharp edge and broad bandgap. Non-cylindrical holes seriously affect the stop-band features. Conical holes cause low contrast and narrow bandgap, and the stop-band shifts with the conical angle. For the cylindrical-conical hybrid holes, the cylindrical portion determines the desired features. Given the difficulty in fabricating high aspect-ratio cylindrical holes, we propose to fabricate the holes at the bottom of a shallow trench, which is introduced into waveguide surface prior to the hole milling.

Three-dimensional dynamic cutting forces prediction model during micro-milling nickel-based superalloy

Nowadays, there are urgent demands of micro structure/parts which have high strength in high-temperature environment in the fields such as aerospace, energy, power, biomedical, etc. Nickel-based superalloy with high strength and high hardness under high temperature is the suitable material for manufacturing this kind of micro parts. Aimed at the problem of the complicated cutting force variation rule when micro-end milling nickel-based superalloy, the cutting forces model during micro-end milling of nickel-based superalloy processing is studied. Firstly, micro-end milling hole experiments are carried out to establish the radical run-out prediction model of cutting edge, which lays the foundation for establishing the cutting thickness calculation model during micro-end milling. Then, based on the minimum cutting thickness value, micro-end milling of nickel-based superalloy process is divided into two different cutting processes: shear-dominant regime cutting process and ploughing-dominant regime cutting process. Moreover, cutting forces prediction model during shear-dominant regime cutting process is developed based on the cutting forces in proportion to cutting layer area, which takes the effect of ploughing into account. Meanwhile, cutting forces prediction model during ploughing-dominant regime cutting process is developed based on the cutting force in proportion to interference volume between the flank surface of cutting tool and the workpiece. The experiment results verify that the cutting forces prediction results and experiment results are well matched.

3D FEM simulation of helical milling hole process for titanium alloy Ti-6Al-4V

As an emerging hole-machining methodology, helical milling process has become increasingly popular in aeromaterials manufacturing research, especially in areas of aircraft structural parts, dies, and molds manufacturing. Helical milling process is highly demanding due to its complex tool geometry and the progressive material failure on the workpiece. This paper outlines the development of a 3D finite element model for helical milling hole of titanium alloy Ti-6Al-4V using commercial FE code ABAQUS/Explicit. The proposed model simulates the helical milling hole process by taking into account the damage initiation and evolution in the workpiece material. A contact model at the interface between end-mill bit and workpiece has been established and the process parameters specified. Furthermore, a simulation procedure is proposed to simulate different cutting processes with the same failure parameters. With this finite element model, a series of FEAs for machined titanium alloy have been carried out and results compared with laboratory experimental data. The effects of machining parameters on helical milling have been elucidated, and the capability and advantage of FE simulation on helical milling process have been well presented.

Hydraulic Workover Unit (HWU) Application in Down-hole Milling Operations in Niger Delta

The major challenge with down hole milling operations using HWU is employing a suitable fluid circulating system, which is very critical for effective well bore cleaning and transporting of cuttings from the well bore to the surface. A bell nipple with sufficient side outlet diameter to ensure efficient fluid circulating system was designed and installed above the top of the BOP stack. During the HWU rig up, the height of the unit was kept as low as possible to ensure unit stability during operation, without further increasing the height of the unit and reducing its stability. Furthermore, HWU being directly rigged up on top of BOP stack, did not require the bell nipple to be a load bearing spool to support the weight of the unit and the work string when fully rigged up and operational. This paper reviews the application of Hydraulic Work over Unit in down hole milling operation in Niger Delta highlighting the steps taken to ensure good circulating system without compromising the unit stability, and eliminating additional cost of load bearing bell nipple/spool.Key words: HWU; Milling; Cement retainers; Cement plug; Workover; Bell Nipple; Wellbore clean-up

Residual Stress Measurement with Laser-Optical and Mechanical Methods

A new approach in hole-drilling residual stress analysis is described, applying a laser for quasi non-destructive material removal by laser ablation and measuring simultaneously the residual deformation around the hole by means of high-resolution, digital holographic interferometry. To evaluate this technology, experiments measuring well-defined in-plane stresses in curved strip specimen, on experimental bending device based on the European Standard for four-point bending tests, were carried out with the conventional hole drilling and milling technique and the laser-optical technique described.

DEVELOPMENT OF A CUTTING TOOL FOR COMPOSITES WITH THERMOPLASTIC MATRIX

Fibre reinforced thermoplastic composites (FRTC) are becoming an increasingly important material for a wide range of applications. Thus, the demand for high performance tools for machining of this material is increasing. The main goal of the presented research results is to decrease cutting costs during trimming operations of thin plates and to increase the quality of machined composite materials by suitable shape, geometry and material of the cutting tool and by suitable cutting conditions. Statistical methods were used in order to obtain the control factors (cutting conditions) which are the most important for machining FRTC. Subsequently, an optimal adjustment of cutting conditions was identified. The paper is a brief summary of the cutting tool development. It includes important parts of tests and their results as well as some interesting findings implicit in experiments and measuring. There are many variants of fibres in these two main groups and other groups such as aramide, basalt and natural fibres. Two mostly used types of fibres are carbon fibres and glass fibres. Carbon fibres are tougher and conduct heat better than glass fibres. The type of reinforcement also influences the behaviour of the composite during milling. The fibres are very hard and abrasive. They cause rapid wear of the cutting tool. The content and orientation of fibres in composites influence tool life time and surface quality (delamination, burrs creation) as well [Sheikh Ahmad 2009]. There are three main types of reinforcement in the case of fabric: unidirectional, multidirectional and woven reinforcement [Ehrenstein 2009]. This paper focuses on the milling of FRTC materials. Milling of composite materials is a branch which is primarily focused on trimming of flat or curved panels as parts of planes, cars and industrial and energetic devices. Other milling operations are milling of internal shapes and holes and slotting. The trimming operation of flat panels was chosen in this paper because it is the most representative technology of the milling of FRTC materials. The main task was to improve the surface quality and productivity and decrease costs which are connected with this type of machining. Some papers have been focused on milling of composite materials. The results presented in these papers affected the design of our experiment. The up milling was identified as better than down milling for better surface roughness [Konig 1985] but the situation is different for the delamination of composite. Down milling was slightly better in Coligan and Ramulu paper [Colligan 1991]. This paper was also focused on the orientation of the fibres in the composite and various types of delamination. Cutting speed and feed rate was identified as relevant for testing on the basis of the Davim’s experiments. The feed rate was more significant than the cutting velocity but both were statistically significant. The delamination and cutting forces were smaller when the feed rate was smaller [Davim 2004]. The depth of cut could be also relevant for testing. The surface roughness is influenced by depth of cut [Sheikh Ahmad 2009]. The tests were divided into two stages. The first one was oriented to the test of standard commercially available tools which were recommended by producers for machining of polymeric composites. Six tools were chosen from the wide portfolio of cutting tools on the market as suitable representatives ( Fig. 1). The second stage focused on testing new cutting tools which were proposed on the basis of the test in the first stage.

Vector modeling of robotic helical milling hole movement and theoretical analysis on roughness of hole surface

To avoid the machine problems of excessive axial force, complex process flow and frequent tool changing during robotic drilling holes, a new hole-making technology (i.e., helical milling hole) was introduced for designing a new robotic helical milling hole system, which could further improve robotic hole-making ability in airplane digital assembly. After analysis on the characteristics of helical milling hole, advantages and limitations of two typical robotic helical milling hole systems were summarized. Then, vector model of helical milling hole movement was built on vector analysis method. Finally, surface roughness calculation formula was deduced according to the movement principle of helical milling hole, then the influence of main technological parameters on surface roughness was analyzed. Analysis shows that theoretical surface roughness of hole becomes poor with the increase of tool speed ratio and revolution radius. Meanwhile, the roughness decreases according to the increase of tool teeth number. The research contributes greatly to the construction of roughness prediction model in helical milling hole.

Novel Design of Porous Silicon Based Sensor for Reliable and Feasible Chemical Gas Vapor Detection

In this study, an innovative design for porous silicon (PSi) based sensors is proposed to eliminate some problems of conventional PSi sensors such as undesired reflections from imprecise positioning of the fiber optic cable and the PSi structure. Our design has three stages as hole milling for fiber socket, fabrication of filter structure, and integration of the fiber optic cable to the bulk Si. We have carried out reflectivity measurements of alcohols with close refractive index values by the proposed and conventional sensors. From the measurements, we note that both sensors have equal sensitivity in identifying alcohols, that repeatability of our proposed sensor is relatively higher, and that our sensor allows easy positioning and flexibility in sensing applications. Nonetheless, our proposed sensor necessitates a thorough fabrication process and a methodological preparation.

Orbital milling hole of aerospace Al-alloy with big pitch

To improve the processing efficiency and the quality of orbital milling hole of aerospace Al-alloy, the bigpitch influence on cutting force and hole quality was studied experimentally. First, a program based on horizontal lathe was proposed based on kinematics analysis of orbital milling. Then, the cutting force at different stages and the hole quality with different pitches were measured. Results show that the axial force and radial force increase with the pitch amplification during orbital milling. However, the axial force in the orbital milling hole is about 8–10 times smaller than that in the conventional drilling. The diameter error of milling hole is 48–93 μm, and the surface roughness of milling hole is 1.2–1.7 μm. Finally, an orbital milling device with big pitch was designed.

Gas Turbine Cylinder Nc Milling Tilt Hole Parametric Programming

In machining, it often encounters milling large inclined holes with spindle on unvertical space. On 3 axis coordinated NC boring-milling machine, universal Angular milling head for changing spindle direction is adopted to align hole axis with milling cutter axis, using geometrical space establishes mathematical model between each processing variables to realize NC program parameterization of space inclined hole milling. Results show that the work piece only need chucking once, give the relevant variable values, can be completed holes, processing high accuracy, saving labor and power, and it also can be extended to machine similar space bevel surface and tilt slot.

TEM foil preparation of sub‐micrometre sized individual grains by focused ion beam technique

Analysis of presolar silicate grains provides new knowledge on interstellar and circumstellar environments and can be used to test models of the Galactic chemical evolution. However, structural information of these grains is rare because sample preparation for transmission electron microscopy is very difficult due to the small dimensions of these grains (<0.5 mum). With the use of the focused ion beam technique thin foils from these grains for transmission electron microscopy analysis can be prepared. Nevertheless, reaching the required precision of some tens of nanometres for the preparation of the transmission electron microscopy foil in the place of interest is not trivial. Furthermore, in the current samples, the grain of interest can only be identified by its different isotopic composition; i.e. there is no contrast difference in scanning electron microscopy or transmission electron microscopy images which allow the identification of the grain. Therefore, the grain has to be marked in some way before preparing the transmission electron microscopy foil. In the present paper, a method for transmission electron microscopy foil preparation of grains about 200 to 400 nm in diameter is presented. The method utilizes marking of the grain by Pt deposition and milling of holes to aid in the exact orientation of the transmission electron microscopy foil with respect to the grain. The proposed method will be explained in detail by using an example grain.

Simulation of ion beam induced micro/nano fabrication

The shrinking critical dimensions of modern technology place heavy requirements on optimizing feature shapes at the micro and nano scale. Ion beams are increasingly used for technology development in the nano-scale world. In recent years, many approaches and research results have indicated that re-deposition of sputtered target atoms is the most serious problem in fabricating micro and nano devices. A simulation tool is essential to reduce unnecessary time and efforts spent in process development. In this paper, we present two-dimensional string-based simulation software for ion milling and focused ion beam direct fabrication, AMADEUS-2D (advanced modeling and design environment for sputter processes). We discuss the numerical model for considering sputtering and re-deposition fluxes. In addition, we investigate sputtering yield and sputtered atom distributions as obtained from several binary collision simulation codes. The newly developed simulation code is validated by comparison with experimental data on single-pixel hole milling, on the width and dose dependence of trench formation and on the effective sputtering yield as a function of scan speed.

FibDAC - Residual Stress Determination by Combination of Focused Ion Beam Technique and Digital Image Correlation

New challenges for design, manufacturing and packaging of MEMS/NEMS arise from the ongoing miniaturization process. Therefore there is a demand on detailed information on thermo-mechanical material properties of the applied materials. Because of size effects and the strong dependency of the thermo-mechanical behavior of active and passive components on process parameters often unsolved questions of residual stresses lead to system failure due to crack formation. With the fibDAC (Focused Ion Beam based Deformation Analysis by Correlation) method which is presented in this paper the classical hole drilling method for stress release measurement has been downscaled to the nanoscale. The ion beam of the FIB station is used as a milling tool which causes the stress release at silicon microstructures of MEMS devices. The analysis of the stress release is achieved by digital image correlation (DIC) applied to load state SEM images captured in a cross beam equipment (combination of SEM and FIB). The results of the DIC analysis are deformation fields which are transferred to stress solution by application of finite element analysis. In another step the resolution of the method has been improved by the application of trench milling instead of hole milling. Thereby deformation measurements in the nm range are established. The method is also a powerful tool for the analysis of sub-grain stresses of engineering materials.