Burr Control Research Articles

A review on metallic drilling burrs: geometry, formation and effect on the mechanical strength of metallic assemblies

Abstract Machining processes produce unwanted remainders of material on the free edges which are called burrs. In particular, the drilling process generates an entry burr, and a typically larger exit burr. When drilling stacks of several workpieces, exit and entry burrs are produced simultaneously at the interfaces. The presence of burrs can degrade the static and fatigue strength of the parts and assemblies containing them. An example concerns the burrs formed at the interface during the drilling of multi-stacks in One-Way-Assembly processes, where deburring is not systematically applied. The effect on fatigue can be significant. Reductions of up to 70 % in fatigue life have been reported, even though the explanatory rationale is not clear. This paper reviews existing works on burrs, focusing on drilling burrs. A description of the morphology of different types of burrs and of measurement technologies is given. Burr formation mechanisms and its modelling are reviewed. Burr control strategies and the main deburring technologies are examined. The limited literature on the effects of burrs on the static and fatigue strength of mechanical assemblies is also explored.

Special Issue on Advanced Metal Cutting Technologies

Cutting technologies are utilized in many industrial sectors, such as automobile, aircraft, and medical-device manufacturing as well as dies and molds. Thus, the requirements for higher geometric accuracy, better surface integrity, and longer component service lifetimes have substantially increased. In addition, maintaining high machining efficiency while simultaneously reducing power consumption and CO2 emissions during machining is important for sustainable development. This special issue features 11 papers on the most recent advances in cutting technologies for metals and composite materials. - Reverse finishing characteristics of drilling surfaces - Machining error simulation for end milling - Visualization of cutting phenomena using a single-crystal diamond tool - Milling of TiB2 particle-reinforced high-modulus steel - Electrodischarge-assisted turning of carbon fiber-reinforced polymers - Suppression of chatter vibration during double-insert turning - Prediction of surface roughness components during turning - Microtome blades for high-precision tissue sectioning - Boiling of coolant near the cutting edge in high-speed machining - Residual stress during drilling of aluminum alloy - Effect of strain hardening on burr control during drilling This issue provides an understanding of recent developments in cutting technologies, aiming to inspire further research in this field. We deeply appreciate the careful work of all the authors and thank the reviewers for their diligent efforts.

Effect of Strain Hardening on Burr Control in Drilling of Austenitic Stainless Steel

Austenitic stainless steel has been widely used in various industries, such as aerospace, medical, and hydrogen energy, due to its high strength over a wide range of temperatures, corrosion resistance, and biocompatibility. However, stainless steel is a difficult-to-cut metal because its ductility and low thermal conductivity induce a strain hardening with significant plastic deformation at high temperatures. Burr formed at the back side of a plate is a critical issue which deteriorates the surface quality, especially in drilling. Burr removal operation, therefore, should be done in the machine shop. This study discusses the effect of strain hardening of austenitic stainless steel, SUS 316L, on burr formation. Hardness and cutting tests were conducted to compare the strain hardening effect for three types of workpieces: as-received, pre-machined, and tensile treated specimens. In the employed specimens, the tensile treated specimen is harder than the as-received specimen. Those specimens have uniform hardness in the depth direction from surfaces. Pre-machined specimen, in which the back side of the plate was finished by face milling, has a distribution of hardness in the depth direction from a surface. The highest hardness appears in the subsurface of the pre-machined specimen. The cutting forces in the steady processes, in which the entire edges remove material, were nearly the same as the tested specimens each other. However, remarkable differences were confirmed in the chip thickness and burr formation. The higher strain hardening of the tensile treated specimen is effective to suppress burr formation. The cutting characteristics are then identified to associate burr control with the shear plane model of orthogonal cutting using an energy-based force model. The shear stresses, shear angles, and friction angles of the tensile treated and as-received specimens are compared to discuss the effect of strain hardening on reduction of burr formation.

Modelling and experimental validation of burr control in micro milling of metals

Classical deformation theories are limited to predicting microscopic deformation when the machining parameters are comparable to the dimension of a single grain. Micro-cutting is one such process where the physical phenomenon is significantly influenced by the microstructure characteristics and initial state of stress. The micro-features such as burrs caused owing to these cutting processes, are undesired and affect the quality of the product. In this study, an analytical methodology is proposed, supported by FEM pre-processing, to determine the burr morphology during the micro-milling process for Ti-6Al-4V, Al-6061 and OFHC-Cu. At first, the flow stress is calculated with the help of strain gradient and dynamic recrystallization methods; contact pressure on the cutting edge and minimum chip thickness are introduced through an FE simulation, this assists to find out the axial and radial plastic strain which eventually yields the dimensions of individual burrs. Peening of the material surface prior to micro-milling provided 67 % less formation of top burr. The average burr width and height are measured and validated with predicted results. The grain structure and dynamic recrystallization of the micro-milled surface are revealed by electron backscatter diffraction. Further, the burr distribution from FE modelling is verified with an SEM image.

Prediction of Burr Types in Drilling of Al-7075 Using Acoustic Emission and Convolution Neural Networks

The formation of exit burrs during the drilling of ductile metals such as aluminum is critical in precision manufacturing and manufacturing automation. Because drilling burrs are difficult to remove, methods to predict various burr types and/or implement burr minimization schemes that consider the various attributes of burrs must be devised. In this study, not only drilling process conditions, including feed, cutting speed, and drill diameter, but also an artificial neural network is implemented to predict the formation of burrs during the drilling of aluminum-7075, which is widely used in the aerospace and automobile industries. Based on the drilling conditions, the main exit burr characteristics, such as burr size and type, were classified experimentally. Three different types of exit burrs (uniform burrs, uniform burrs with caps, and transient burrs) were observed from the aluminum 7075 workpieces. The classification results were further analyzed using burr control charts and an empirical equation, which enables the understanding of the overall influence of the drilling conditions over the burr types. Moreover, acoustic emission (AE) sensor monitoring scheme was utilized to sample the sensitive time-series signals during drilling burr formation. Subsequently, burr types were predicted using artificial intelligence techniques, namely machining learning and deep learning. First, backpropagation (BP) neural networks were constructed using the drilling conditions and AE signals as input vectors. For a comparative prediction, a convolution neural network (CNN) was implemented to obtain spectrogram image inputs from the sampled AE data. The proposed scheme is useful in predicting drilling burr types by employing a sensitive sensor monitoring setup and advanced artificial intelligence techniques, where both prediction results are well matched with experimental results. In addition, the CNN model shows effectiveness for a commonly practiced manufacturing process as it predicts the burr types with better accuracy than the BP network model (0.9375 over 0.8571).

Investigation on the Exit Burr Formation in Micro Milling.

The burr on micro part has harmful effect on the dimensional accuracy and service performance. The original control of exit burr formation during micro milling is desirable and advisable. In this paper, the formation mechanism of exit burr was studied based on the varying cutting direction during micro milling. Three exit burr control strategies were concluded, the material properties embrittlement, the support stiffness increasing and machining parameter optimizing operations. Then, micro milling experiments were carried out to investigate the exit burr morphology and size. It was found that the exit burr formation was attributed to the change of material flowing path at the exit surface, which was caused by the negative shear deformation zone that was induced by the discontinuous shape features. Different exit burr morphologies were classified; the triangle exit burr type was caused by the varying exit burr growing direction along the exit surface. The optimal machining parameters in micro milling to obtain a small exit burr were suggested.

Research on the burr-free interrupted cutting model of metals

In the interrupted cutting of metal parts, burrs are generally produced at the edge of the exit surface, which will seriously affect the use and assembly performance. Adding deburring process is a way to solve the problem of burr, but it will increase the cost of economy and time, and hinder the automation of production line. This study focused on the active burr control technology, which can prevent burr formation during the cutting process. A new burr-free theoretical model was established based on the analysis of burr formation, and it indicated that changing the exit surface angle of the workpiece was the key to realize burr-free interrupted cutting. The finite element method (FEM) was applied to simulate the cutting burr. In the simulation, ten gradients from 30° to 90° were set for the exit surface angle, both the stress plot and the final burr shape were presented in good agreement with the theoretical model. A cutting experiment of aluminum alloy 7075-T651 was carried out and the burr-free interrupted cutting was realized under the guidance of the derived theoretical model. The critical exit surface angle of burr-free state was also verified by the experiment, which was predicted from the theoretical model. This study provided a theoretical and practical basis for solving burr problem in interrupted cutting.

Experimental study of micromilling burrs of 304 stainless steel

Stainless steel is a well-known difficult-to-machine material with high toughness, low thermal conductivity, and high work hardening characteristics. Burrs generated in micromilling of the stainless steel seriously affect the performances of the fabricated high-accuracy miniaturized geometrical features. Aiming at reasonable control of burrs in micromilling of the 304 austenitic stainless steel, single-factor analyses, multi-factor optimization, and further post processing procedures are introduced in the paper. First, the axial depth of cut ap, feed per tooth fz, spindle speed n, and radial depth of cut ae are investigated by single-factor micromilling experiments. It shows that burrs generated in up milling are smaller than that in down milling. The minimum burr widths of 171.93 μm can be achieved, and the overall trend of micromilling force is in accordance with the burr widths. Then, multi-factor orthogonal experiments have been carried out to optimize micromilling parameters based on the Taguchi method. It shows that the significance sequence of key parameters for burr widths from large to small is ap, n, ae, and fz. The optimized minimum burr width is 83.69 μm with micromilling parameters ap of 45 μm, fz of 1.0 μm/z, n of 48,000 min−1, and ae of 200 μm. To further reduce the burrs, ap of 0 is set for post processing experiments. It shows that the radial depth of cut affects burr sizes greatly. The optimized radial depth of cut is 500 μm, and burr widths have been finally reduced to 14.3 μm. The study provides an effective method to reduce burr sizes in micromilling of very ductile materials.

The Explosive Nature of Tab Burrs in Li-Ion Batteries

Lithium-ion battery fires and explosions in various battery-operated products have raised safety concerns. While external abuse of batteries can cause fires and explosions, most of the reported problems arose from internal battery defects, which are often difficult to detect. One particular and significant defect pertains to burrs on the tab used to connect the anode and cathode layers to the external terminals of the battery. This paper investigates burr-related issues, presents a case wherein a burr most likely caused thermal runaway in a battery and overviews the standard associated with burr control and the application of computed tomography scanning to assess the risks.

Classification and prediction of burr formation in micro drilling of ductile metals

In the micro drilling of precision miniature holes, the formation of exit burrs is a topic of interest, especially for ductile materials. Because such burrs are difficult to remove, it is important to be able to predict various burr types and to employ burr minimisation schemes that consider burrs’ micro-scale characteristics. In the present work, an artificial neural network (ANN) was used to predict the formation of burrs in the micro drilling of copper and brass, along with burr formation/optimisation analysis specialised for micro drills. The influence of cutting conditions, including cutting speed, feed and drill diameter, upon exit micro burr characteristics such as burr size and type was observed, analysed and classified. Based on the results, an empirical equation to predict micro burr height is proposed herein. The classification results were compared with conventional burr cases using burr control charts. Then, micro burr types were predicted by means of an ANN, using the influential parameters as input vectors. The usefulness of the proposed scheme was demonstrated by comparing the experimental and prediction/analysis results.

Research on burr formation mechanism in metal cutting with a backup material

In order to investigate the mechanism of burr formation and burr minimization, experiment and finite element simulation were performed using identical backup material. The influences of backup material height and thickness on burr sizes and burr profiles were characterized. The experimental results and simulated analyses indicated that effective burr control can be achieved using appropriate selection of backup material parameters. Furthermore, the cutting forces at steady state were found to be the same with different backup material heights and thicknesses. Therefore, the proposed technique will have a wide range of application prospects saving time and cost of deburring. This may bring remarkable economical and societal benefits.

Investigation of chip formation and burr control in PCB fixture hole

Purpose – This paper aims to analyze their generation mechanism and factors influencing burr generation. The final goal is to use appropriate drill design and drilling process to control the generation of burrs. Design/methodology/approach – The mechanism of burr generation was studied through finite element method (FEM) simulation and drilling experiments. High-speed photography technology and scanning electron microscope (SEM) were used in this study. Findings – High-speed drilling burr is a printed circuit board (PCB) copper foil burr. Within a certain range, the feed speed and burr height is in positive correlation, and decrease in the feeding speed will favor the exit burr. Drill angle influences burr and chisel edge affect significantly, followed by the point angle, and helical angle has little effect. From the perspective of reducing the burr, a smaller chisel edge and smaller point angle should be chosen. Grinding chisel edge is another choice to decrease the burr but also ensures the blade strength. Originality/value – This paper investigates the mechanism of burr generation of PCB fixture hole drilling. The process of burr generation was captured by high-speed camera. The controlling methods of burr generation were illustrated at the end.

Burr Control for Removal of Metal Coating from Plastics Substrate by Micro-Milling

Manufacturing of miniaturized circuits on the surface of plastic substrate plays an important role for the industrial application. Many of these kinds of parts cannot be fabricated by conventional processing methods due to the manufacturing requirements are improved continuously and the plastic substrate presents 3D structure. Since the superior advantages of the micro-milling, graphically removal of metal coating from plastic substrate by micro-milling has led the way in manufacturing of high-accuracy circuits. In order to improve the edge quality of the circuits, the effect of processing parameters on burr sizes is quantitatively analyzed and a control model of burr formation is established based on the experiments. Furthermore, aiming at the problem that surface of the polyimide (PI) substrate often shows free-form state due to the machining error, the technology that removal of constant material from free-form substrate surface is proposed. With the optimized parameters and compensation technology of milling depth, a typical antenna circuit is machined via micro-milling at last. The experimental results indicate that the edge of the pattern is smooth, and there are almost no burrs. The achievements in this study could be applicable to industrial production.

Prediction of Cutting-Direction Burr Height in Micro-Milling

Due to the high precision and strong molding capacity, micro-milling plays an important role in the field of micro-machining. The components machined in micro-machining is smaller than conventional components, and sometimes the generated burrs are as large as the feature size of components, so the study of micro burr control is very important. In the reseach, cutting-direction burrs are based on the traditional milling characteristics, also combined with the characteristics of micro-milling. The experimental data verify the correctness of the model well, so it provides theoretical guidance for the burrs control in micro-milling.

Experimental Study of Micro Milling Burr Control Based on Process Parameters Optimization

With the development of the times, micro and small products are needed increasingly. The machining accuracy and surface quality are especially important to micro machining. However, in the micro milling, the size of the burr compared with that of the part is much greater than that of conventional milling. Moreover, it is difficult to remove micro milling burr by conventional deburring methods due to the small part size. The existence of burr will not only affect the match of parts, but also reduce the dimensional accuracy and surface quality of the work piece. Therefore, it is important to control and reduce micro-milling burr. Micro-milling experiments are carried out on the material of copper with micro-milling cutter diameter 0.5 mm. Micro grooves are milled with different cutting process parameters. The burrs generated under different conditions are analyzed using orthogonal test method. When the spindle speed and feed rate are constant, burrs increase with the increasing of cutting depth. Keeping the spindle speed and the depth of cut constant, burrs are generated increasingly with the increase of feed rate. And the decreasing of the spindle speed leads to the increase of burrs if the other parameters are constant. The experimental research provides reference for the burr control of micro-milling based on the optimization cutting process parameters.

Active Control Methods of Cutting Burr in Precision and Ultra-Precision Machining

The burr formation and control is one key technology of achieving precision and ultra-precision machining and automatic machining. Based on the theory of system engineering, the metal cutting burr formation, control and removal technology system are constructed in the paper. Then, the basic principles of burr control are presented. Combined with precision and ultra-precision machining and automatic machining, the active control methods and technologies of burr are presented. They are the modified design of parts structure, the option of tool geometry parameters, the adjustment of cutting data and processing technologies optimization etc. So, these methods lay a solid foundation on achieving minimum burrs.

Mechanical microdrilling of negative-tapered laser-predrilled holes: a new approach for burr minimization

Despite considerable research effort being concentrated on improving hole quality, minimisation of burrs still remains a key challenge in mechanical microdrilling of ductile materials. Recently, a sequential laser-mechanical microdrilling technique, which was developed by the authors, has proved effective in improving tool life and reducing burr size. The improvement in burr size was achieved by means of laser predrilling a pilot hole before utilising a twist drill to finish the hole. This paper presents further development of the sequential laser-mechanical microdrilling process based on negative-tapered laser-drilled pilot holes. In the sequential laser-mechanical microdrilling process, although a large predrilled hole reduces the burr size, it has a negative effect on roundness and cylindricity of the hole. The results of further studies highlight that a smaller entry hole size supports the drill and suppresses tool wander which, in turn, improves hole cylindricity. Furthermore, a larger exit hole size significantly reduces burr size. Compared to pure mechanical drilling without any pilot hole, the reduction in burr size for the mechanical microdrilling of near zero tapper and negatively tapered laser-predrilled holes was observed to be 2.5 and 6 times, respectively. Moreover, the mechanical finishing of these holes does not compromise tool life and/or surface integrity. Thus, the use of a negative taper laser-predrilled hole presents a significant improvement in burr control in microdrilling of nickel-based super alloys in addition to providing a step change increase in tool life.

Burrs—Analysis, control and removal

Increasing demands on function and performance call for burr-free workpiece edges after machining. Since deburring is a costly and non-value-added operation, the understanding and control of burr formation is a research topic with high relevance to industrial applications. Following a review of burr classifications along with the corresponding measurement technologies, burr formation mechanisms in machining are described. Deburring and burr control are two possible ways to deal with burrs. For both, an insight into current research results are presented. Finally, a number of case studies on burr formation, control and deburring along with their economic implications are presented.

Formation and control of burrs in precision machining

The existence of the metal cutting burr not only reduces the dimension and shape accuracy of the workpiece, but also increases the manufacturing cost. Currently, the burr has been the most troublesome obstruction to high productivity and automation of machining processes. In this paper, the hazard of the burrs is systematically discussed in the precision or ultra-precision machining firstly and then, the formation principle and morphology of burrs in precision turning, planing, drilling and milling are studied. Finally many new technologies and methods of restraining or decreasing burrs have been developed by the cutting experiments.

Burr control in meso-punching process

The shearing process for the sheet metal is normally used in the precision elements such as semi-conductor components. In these precision elements, the burr formation brings a bad effect on the system assembly and demands the additional de-burring process, so this imposes high cost on manufacturing. In this paper, we have developed the in-situ auto-aligning precision meso-punching system to investigate the burr formation mechanism and ultimately minimize burr. Firstly, we introduced the punch-die contact sensing method to align the punch and the die at initial state prior to the punching process. Secondly, by using the low-price semi-con- ductor laser, burr formed on the edges is measured intermittently during the punching process. We could, finally, make burr on the sheet metal uniformized and minimized by controlling of the precision X-Y table, 1㎛ resolution, and measuring burr height by semiconductor laser. Experimental results show the validity of our system for pursuing the burr-free punched elements.