Development of a micro-drilling burr-control chart for PCB drilling

A drilling burr-control chart (DBCC), based on experimental results, is a tool for the prediction and control of drilling burrs for a large range of drilling parameters. A micro-drilling burr-control chart (M-DBCC) was developed for a standard double-sided copper-clad laminated (CCL) printed circuit board (PCB) with laminated fiber-reinforced plastic (FRP) substrate. This chart will assist in the selection of favorable drilling parameters for predicting and achieving preferred types of burrs. Burr classification was carried out according to the burr geometric characteristics, burr formation mechanisms, burr height, and drill bit breakage while drilling. The design of experiment (DOE) technique based on the Taguchi method was used to find the most significant drilling parameter affecting burr height. The results show that the drill diameter makes a statistically significant contribution to burr-height variation.     

Characterization and modeling of burr formation in micro-end milling

Mechanical micromachining is increasingly finding applications in fabrication of components in various fields, such as, biomedical devices, optics, electronics, medicine, communications and avionics. In order to ensure adequate functionality, there are stringent requirements for form and finish in case of biomedical devices like cochlear implants and metallic optics. This necessitates that the post machined surface must be burr free. To address these issues in micromachining, this paper presents results of an experimental study to investigate the influence of main process parameters i.e. speed, feed rate, depth of cut, tool diameter and number of flutes on the formation of the various types of burrs i.e. exit burrs and top burrs produced during micro-end milling operation. The experiments performed using Taguchi method shows that three types of burr formation mechanisms prevail during micro-end milling operations; these are: lateral deformation of material, bending and tearing of the chip. Also, three types of burrs were observed include: Poisson burr, rollover burr in down milling and tear burr in up milling. Further, it is observed that the depth of cut and the tool diameter are the main parameters, which influence the burr height and thickness significantly. However, the speed and the feed rate have small to negligible effect on the burr thickness and height. Besides the experimental analysis, the paper presents an analytical model to predict the burr height for exit burr. The model is built on the geometry of burr formation and the principle of continuity of work at the transition from chip formation to burr formation. Note that prediction of burr height in micro-end milling is extremely challenging due to the complex geometry of material removal and microstructural effects encountered during cutting at that length scales. The model fares well and the prediction errors range between 0.65 and 25%.     

轴向振动钻削工艺效果试验

利用自制的压电式振动台,驱动工件正弦振动,进行了硬铝和不锈钢的轴向振动钻削试验,对轴向振动钻削的断屑效果、尺寸精度以及孔出口毛刺进行了试验研究和理论分析。与普通钻削相比,由于轴向振动钻削具有良好的断屑排屑条件、较高的入钻定位精度和切削液作用效果,因此它能够有效地改善断屑效果、提高尺寸精度、减小孔出口毛刺。     

工作台振动钻削的初步试验研究

与常见的刀具振动钻削不同,介绍了一个实现轴向振动的工作台。轴向振动工作台可以带动工件实现轴向振动,在钻削过程中,通过改变振动频率,进行了振动钻削硬铝试验。试验现象显示：振动钻削的工件断屑效果有明显的改善,进出口的毛刺尺寸有所变化,孔的表面粗糙度Ra值可达到5.9μm。     

Finite element simulation for burr formation near the exit of orthogonal cutting

A coupled thermo-mechanical model of plane-strain orthogonal metal cutting including burr formation is presented using the commercial finite element code. A simulation procedure based on Normalized Cockroft–Latham damage criterion is proposed for the purpose of better understanding the burr formation mechanism and obtaining a quantitative analysis of burrs near the exit of orthogonal cutting. The cutting process is simulated from the transient initial chip formation state to the steady state of cutting, and then to tool exit transient chip flow by incrementally advancing the cutting tool. The predicted burr profile is compared with experimental data and found to be in reasonable agreement. The effect of the tool conditions and cutting conditions on the burr formation process was also investigated.     

Modeling of burr thickness in milling of ductile materials

Accuracy and surface finish play an important role in modern industry. The presence of undesired projections of materials, known as burrs, negatively affect the part quality and assembly process. To remove burrs, a secondary operation known as deburring is required for the post-processing and edge finishing of machined parts. The thickness of the burr is of interest as it describes the time and method necessary for deburring of the machined part. Burr thickness (B _t) measurements are costly and non-value-added operations that in most cases require the use of a scanning electron microscope for accurate burr characterization. Therefore, to avoid such expenses, the implementation of alternative methods for predicting the burr thickness is strongly recommended. In this research work, an analytical model for predicting the burr thickness in end milling of ductile materials is presented. The model is built on the geometry of burr formation and the principle of continuity of work at the transition from chip formation to burr formation that also takes into account the cutting force influence on burr formation. A very good correlation was found between the modeled and experimental B _t values. The model has shown a great sensitivity to material properties such as yield strength and specific cutting force coefficient (K _c). In addition, the sensitivity of the proposed model to the feed per tooth (f _t) and depth of cut (a _p) was considerably high. The proposed model allows the prediction of the thickness of the exit up milling side burr, without the need for experimental measurement and/or approximation of shear angle (Φ), friction angle (λ), and the tool chip contact length (L), unlike existing analytical burr size prediction models. Besides analytical modeling, statistical analysis is performed on experimental results in order to distinguish dominant process parameters on B _t. It is observed that the depth of cut and feed per tooth are the main parameters which significantly affect the B _t, while the speed has only a negligible effect on it.     

PROBABILISTIC PREDICTION OF BURR PATTERNS OF 1045 CARBON STEEL IN FACE MILLING

Face milling burrs in ductile materials such as 1045 carbon steel exhibit three distinct burr patterns: uniform, wavy, and secondary burrs. It is found that the three burr patterns are dependent on the in-plane exit angle, undeformed chip ratio, and undeformed chip area at the exit stage of cut. Empirical equations, representing the burr transition curves from the uniform to wavy burr and wavy to secondary burr, are found. Based on the empirical relationships, a probabilistic model, in which the operational Bayesian modeling approach is adopted to include the empirical equations, is derived for burr prediction.     

Burr formation in milling cross-connected microchannels with a thin slotting cutter

This paper studies the burr formation mechanism in milling cross-connected microchannels, and investigates the influences of radial depth of cut a_e, cutting speed v, feed speed vf and mesh size on the burr formation. A thin slotting cutter is carried out to fabricate cross-connected microchannels in a metal plate of thickness H. Two kinds of large burrs are produced in the meshes formed by two sets of perpendicular and cross-connected microchannels: flake-like burr and curl-like burr. Results indicate that when a_e is equal to or slightly larger than H/2, flake-like burrs are formed. When a_e is much larger than H/2, curl-like burrs are produced. Furthermore, curl-like burrs formed at low v are relatively longer than those formed at high v. High vf is unfavorable for the occurrence of long curl-like burrs. In addition, larger mesh is in favor of longer burrs due to its larger capacity.     

A simple pneumatic device for plunge-freezing cells grown on electron microscopy grids

A detailed design for a simple and inexpensive variable-speed (1.0–5.8 m s^?1) pneumatic plunge-freezing device is presented. Cultured cells, grown on Formvar-coated 75-mesh gold finder grids, are pneumatically driven into a stirring mixture of propane/isopentane (3:1) cooled by liquid nitrogen (LN₂). Premature freezing of the sample in the cryogenic vapors above the cryogen is prevented by plunging through an entry tube into an insulating box, to which a partial vacuum is applied. The cryogenic vapors are drafted into the box at the level of the liquid cryogen by the vacuum, thereby preventing a layer of cold gas from collecting above the cryogen. To prevent the sample from thawing during transfer from the cryogen to the substitution medium, the box top is removed and compressed air is forced through a corrugated tube running the length of the box. The resulting boiling LN₂ creates an atmosphere below ?120°C in which the transfer can be accomplished.     

Effects of cutting edge radius and fiber cutting angle on the cutting-induced surface damage in machining of unidirectional CFRP composite laminates

Carbon fiber reinforced polymer composite laminates are anisotropic, inhomogeneous, and mostly prepared in laminate form before undergoing the finishing operations. The edge trimming process is considered as one of the most common finishing operations in the industrial applications. However, the laminate surface is especially prone to damage in the chip formation process, and the most common damage mode is burrs. Burrs may increase cost and production time because of additional machining; they can also damage the surface integrity. Many studies have been done to address this problem, and techniques for reducing burr size in material removal process has been the focus of the research. Nonetheless, the combined effects of the cutting edge radius and the fiber cutting angle on the burr formation have seldom been conducted, which in turn restricts to find out the mechanism of burr formation. The purpose of the present paper is to study the particular mechanism that leads to burr formation in edge trimming of CFRP laminates and investigate the effects of fiber cutting angle and cutting edge radius on burr formation. The results indicate that the burrs are prone to form in the fiber cutting angle range of 0° < χ < 90° when a large cutting edge radius of the tool is used for both milling and drilling of CFRP composites.     

A FINITE ELEMENT ANALYSIS OF BURR FORMATION IN FACE MILLING OF A CAST ALUMINUM ALLOY

The research discussed in this article focuses on the effects of tool geometry (i.e., rake angle and cutting edge radius) and flank wear upon burr formation in face milling of a cast aluminum alloy. As to tool edge preparation, the use of a tool with variable cutting edge radius was investigated using FEM, and compared for its cutting performance (i.e., burr reduction and tool life) with a conventional tool with uniform cutting edge radius. In order to evaluate 3D face milling through 2D orthogonal cutting simulations, the cross-sections that consist in the cutting speed direction and chip flow direction were selected at different locations along the tool rounded corner. At these cross-sections, the local value of cutting edge radius and their associated tool rake angles as well as the effective uncut chip thickness were determined for 2D cutting simulations. In addition, 3D face milling simulations were conducted to investigate more realistic chip flow and burr generation. Comparisons were made for burrs produced from 3D simulations with a sharp tool, 3D simulations with a worn tool and face milling experiments. Finally, recommendations for cutting tool design are made to reduce burr formation in face milling.     

Micro-drilling of Ti–6Al–4V alloy: The effects of cooling/lubricating

This paper presents a series of experimental investigations of the effects of various machining conditions [dry, flooded, minimum quantity lubrication (MQL), and cryogenic] and cutting parameters (cutting speed and feed rate) on thrust force, torque, tool wear, burr formation, and surface roughness in micro-drilling of Ti–6Al–4V alloy. A set of uncoated carbide twist drills with a diameter of 700 μm were used for making holes in the workpiece material. Both machining conditions and cutting parameters were found to influence the thrust force and torque. The thrust force and torque are higher in cryogenic cooling. It was found that the MQL condition produced the highest engagement torque amplitude in comparison to the other coolant–lubrication conditions. The maximum average torque value was obtained in the dry drilling process. There was no substantial effect of various coolant–lubrication conditions on burr height. However, it was observed that the burr height was at a minimum level in cryogenic drilling. Increasing feed rate and decreasing spindle speed increased the entry and exit burr height. The minimum surface roughness values were obtained in the flood cooling condition. In the dry drilling process, increased cutting speed resulted in reduced hardness on the subsurface of the drilled hole. This indicates that the surface and subsurface of the drilled hole were subject to softening in the dry micro-drilling process. The softening at the subsurface of drilled holes under different cooling and lubrication conditions is much smaller compared to the dry micro-drilling process.     

Prevention of exit burr in microdrilling of metal foils by using a cyanoacrylate adhesive

In the microdrilling of metal, an exit burr forms due to plastic deformation of the remnant material when the drill approaches the bottom of the hole. In this work, a cyanoacrylate adhesive was applied at the exit surface to prevent the exit burr. The copy papers smeared with cyanoacrylate were layered at the exit surface in a uniform coat. The cyanoacrylate can be easily removed by immersion in acetone. The cyanoacrylate layer was effective in preventing exit burr in the drilling of low-hardness materials, such as aluminum or copper. In the case of harder materials, however, such as 304 stainless steel, the cyanoacrylate layer failed. In this case, backup foil adhered with cyanoacrylate was shown to be effective in burr prevention.     

Comparative evaluations of machining performance during turning of 17-4 PH stainless steel under cryogenic and wet machining conditions

Productivity in machining of 17-4 PH stainless steel is adversely affected by the premature failure of tool and poor surface finish as a consequence of high cutting temperatures. Conventional cutting fluids not only create environmental and health problems but also fail to overcome the high cutting temperatures during machining. Cryogenic cooling is an environmentally clean cooling technology for attractive management of machining zone temperatures. The present study investigates the effect of cryogenic liquid nitrogen (LN₂ at ?196°C) on cutting temperatures, cutting forces (main cutting force, feed force), surface roughness, tool flank wear and chip morphology in turning of 17-4 PH stainless steel with AlTiN PVD-coated tungsten-coated carbide inserts and results were compared to wet machining. In overall, cryogenic machining reduces the cutting temperature, cutting forces, surface roughness and tool flank wear to a maximum of 73.4, 17.62, 44.29 and 55.55%, respectively. Improved chip breakability was found in cryogenic machining.     

Investigation of surface integrity in end milling of 55NiCrMoV7 die steel under the cryogenic environments

Abstract

Cryogenic assisted machining is experiencing growing popularity and acceptance as a toxic-free, eco-friendly, hazardless process producing improved structural components. This article deals with the analysis of 3D and 2D roughness profiles, surface morphology, residual stress and microhardness of 55NiCrMoV7 die steel after end milling operation under dry, wet, cryogenic CO₂ and LN₂ cooling environments. Among different cooling methods, the cryogenic CO₂ was seen enhancing the surface topography and morphology due to the presence of minimal wear track. The result indicates the production of an insignificant amount of residual stress in the machined surface by the cooling environments at a spindle speed of 1989?rpm and feed rate of 0.02?mm/rev. The surface microhardness values were higher under cryogenic conditions compared to dry and wet conditions. Cryogenic LN₂ provided the highest microhardness value among the four cooling methods.     

Defining the effects of cutting parameters on burr formation and minimization in ultra-precision grooving of amorphous alloy

Amorphous nickel phosphorus (Ni-P) alloy is a suitable mold material for fabricating micropatterns on optical elements for enhancing their performances. Ultra-precision cutting is preferred to be used to machine the mold material for high precision in a large workpiece. However, burrs and chippings always form and are detrimental especially when fabricating micropatterns. The formation mechanisms of burrs and chippings have not yet been revealed precisely in the cutting processes of amorphous alloys, because their cutting behavior is more complex and less discussed in existing researches than that of crystalline metals. In the present study, the burr formation process of amorphous Ni-P is defined and a three-dimensional cutting model using energy method is proposed to predict and minimize burrs and chippings. Microgrooving experiments were conducted with different undeformed chip geometries using three types of cutting tools to observe burr formation processes. Large burrs and chippings were formed when cutting with a tapered square tool and a tilted triangle tool. These large burrs and chippings were found to be induced by large slippages that are unique to amorphous alloys. It was revealed that burrs and chippings appear when the angle between the chip flow direction and the groove edge is less than a critical value. Energy method was used to predict the chip flow directions and the calculated results agree with the experimental ones, which proved that the energy method is valid for designing an appropriate undeformed chip geometry to reduce burrs and chippings in ultra-precision grooving.     

干式冷风车削不锈钢的高速钢刀具磨损试验研究

采用低温冷风射流技术,对高速钢刀具加工不锈钢工件的磨损情况进行了试验研究。加工时采用低温冷风射流空气代替传统的切削液,不仅起到有效的冷却和润滑作用,而且能够避免环境污染。通过干式常温切削和干式冷风切削1Cr18Ni9Ti的不锈钢的对比实验,探讨了干式低温冷风切削对高速钢刀具寿命的影响,并且发现了在冷风切削作用下积屑瘤生成的新特点。     

FE modeling of burr size in high- speed micro-milling of Ti6Al4V

This article is focused on the finite element modeling of burr formation in high speed micromilling of Ti6Al4V. Studies show that the burr produced at the up milling side at the exit of the micromilling tool is the biggest among burrs at other locations. Therefore, side exit burr at the up milling side has been modeled through finite element modeling. Johnson cook material constitutive model has been implemented in the formulation of burr formation. Experimental work has been performed to validate the developed model. It is found that the burr height and width obtained from the simulation has been validated experimentally with a maximum error of 15%. It was found from the literature review that the cutting speed is the factor, which influences the burr formation. Therefore, the model has been further extended to study the effect of cutting speed on the burr size. A maximum tool rotation of 200,000 rpm was considered with a tool diameter of 500 μm. It is predicted from the simulation that, the burr size was reduced by 96% (both height and width) if cutting tool speed was increased from 10,000 to 200,000 rpm. Therefore, it is concluded that the cutting speed is the major factor to reduce the burr size in micromilling of Ti6Al4 V. This study shows that the high speed micromachining center can be helpful in producing the micro parts with less or no burrs. It is expected that further extension of the burr formation model can minimize the burr size to zero/near zero size.     

Cutting performance of nano-crystalline diamond (NCD) coating in micro-milling of Ti6Al4V alloy

Hard coatings are an important factor affecting the cutting performance of tools. In particular, they directly affect tool life, cutting forces, surface quality and burr formation in the micro-milling process. In this study, the performance of nano-crystalline diamond (NCD) coated tools was evaluated by comparing it with TiN-coated, AlCrN-coated and uncoated carbide tools in micro-milling of Ti₆Al₄V alloy. A series of micro-milling tests was carried out to determine the effects of coating type and machining conditions on tool wear, cutting force, surface roughness and burr size. Flat end-mill tools with two flutes and a diameter of 0.5 mm were used in the micro-milling process. The minimum chip thickness depending on both the cutting force and the surface roughness were determined. The results showed that the minimum chip thickness is about 0.3 times that of the cutter corner radius for Ti₆Al₄V alloy and changes very little with coating type. It was observed from wear tests that the dominant wear mechanism was abrasion. Maximum wear occurred on NCD-coated and uncoated tools. In addition, maximum burr size was obtained in the cutting process with the uncoated tool.     

Evaluation of micro-drilling technologies for metal-injection-molded 420 stainless steel

Metal-injection-molded (MIM) 420 stainless steel is a commonly used material for high-value products such as fuel injector nozzles. However, the trade-offs involved in using different micro-drilling processes on this material are not well-documented in literature. This article presents a micro-drilling study of MIM 420 stainless steel using four candidate processes: micro-electrical discharge drilling (micro-EDD), ultrasonically assisted micro-EDD, micro-mechanical drilling (micro-MD), and ultrasonically assisted micro-MD. The micro-EDD results shows that the use of ultrasonic vibrations significantly improves the overall process time, spark erosion efficiency, and material removal rate of the process. However, this improvement comes at the expense of increased tool wear and surface roughness, especially while machining under high-discharge-energy conditions. The micro-MD results show that the use of ultrasonic vibrations is beneficial in lowering the thrust force, drilling torque, and tool wear at chipload values greater than the minimum chip thickness of the material. However, the ultrasonic vibrations do not have a notable effect on the surface roughness or on the size of the exit burrs. The results obtained from this study have been used to develop a Likert-type comparison scale to enable application-specific selection of micro-drilling processes for MIM 420 stainless steel.