The migration of cells is caused by the interaction of cells and the local microenvironment around them, such as changes in stiffness, chemical gradients etc. The local topography of substrates in contact with cells is a key factor that regulates the migration of cells. The interaction between the topography of the substrate and cells is crucial for the understanding of tissue development and regeneration. In this paper, the fabrication of a graded micropillar substrate for studying topography-based cell migration is described in detail. The fabrication protocol comprises of the utilization of dynamic maskless lithography system, capillary molding, and corona arc surface treatment. The fabricated micropillar substrate has been shown and the cells have been successfully seeded on the substrate. Guided cell migration on the substrate with graded microtopography has been demonstrated to occur from the sparser zone to the denser zone. Moreover, some examples of potential applications are provided.

Metal additive manufacturing (AM) technologies, commonly referred to as 3D printing, provide a good prospect for medical applications because complex geometries and customized parts can be fabricated to meet individual patient needs. Orthopedic implants are a group of medical parts with high relevance for AM. This paper discusses relevant AM technologies, several orthopedic applications, materials and material properties, mechanical surface finishing techniques, and measurement techniques from the literature. Today, most metal 3D printed implants are manufactured through metal powder bed fusion technology which includes direct metal laser sintering (DMLS), selective laser melting (SLM), and electron beam melting (EBM). Common materials include titanium alloys, cobalt chromium (CoCr) and stainless steel, chosen because of their biocompatibility and mechanical properties. Surface finishing is most often required for 3D printed implants due to the relatively poor surface quality to meet the desired surface texture for the application. Typically, postprocessing is done mechanically, including manual and automated grinding, sandblasting, polishing, or chemically, including electrochemical polishing. This review also covers an overview of surface quality characterization of AM metal implants which includes surface texture and topography. The surface parameters used to characterize the surface of the implants: surface roughness (Ra), differences between the peak and valley (Rz), waviness, and micro-finish.

Brushes consist of a body with fixed highly flexible filaments and can be used for deburring and surface finishing operations. During the brushing process, axial and tangential deflections of the highly flexible filaments lead to an adaptation to the shape of the workpiece and interaction between the filaments. The described complex contact behavior has been insufficiently investigated so far. For a better understanding of the contact between a brush and the workpiece surface, this paper presents a model based on physical principles. The model describes the dynamic behavior of a brush in contact with different workpiece geometries and consists of separate physical descriptions for the filaments of the brush, the workpiece surface and the occurring contacts. A description of a single filament is given by a multi-body system of rigid links. The rigid links are connected by joints which approximate the material behavior of the filaments. To approximate different geometries, the workpiece surface is specified by a polynomial. Contact can occur between the filaments and the workpiece surface as well as between the filaments. For the description of the occurring contacts, Hertz’s theory of elastic contact and Coulomb’s law of friction are used. The aforementioned physical descriptions are included in the Lagrange’s equations to obtain a system of equations of motion that calculates the deflection of the filaments of the brush and the acting forces during the contact with the workpiece surface. A numerical solution to the system of equations of motion was calculated by using experimentally determined material and contact properties of the filament. A comparison of the calculated forces with experimentally determined values shows good correlations for different workpiece surfaces and process parameters. In this context, the developed model calculates the progression and the maximum value of the acting contact forces. The results show a shorter contact length of the filament l c for a circular surface compared to a plane surface, and a rise of the maximum normal force F n with the depth of cut a e . Furthermore, consideration of the filament interactions leads to a more accurate approximation of the brush-workpiece contact. Based on the findings, the developed model can be used to calculate predictions for different brushing processes which reduce the number of time-consuming preliminary tests for the process design.

An efficient strategy for robotic surface finishing of curved surfaces that includes real-time identification of the surface profile, control, and implementation is presented in this paper. Real-time identification of the surface profile in the robot base frame is accomplished by employing a proximity laser sensor mounted on the robot end-effector. This surface profile description allows us to generate trajectories for both motion and force control as it provides the surface normal at each point of the surface. Using the surface profile, a trajectory is generated that would orient the surface finishing tool to the local normal of the surface. An algorithm for simultaneous position and force control is developed for surface finishing of curved surfaces. The integrated robotic surface finishing system consists of a UR5 robot and a custom end-effector that includes a force/torque sensor, an electromechanical sander, and the proximity laser sensor. Robot Operating System (ROS) is utilized for real-time implementation, which would enable easy migration of the developed tools if other industrial robots are used. The effectiveness of the strategy is evaluated by conducting a number of experiments for flat and curved surfaces. A representative sample of results on force regulation and surface finishing are presented and discussed.

Surface finishing is an important manufacturing process. Many parts with complex geometries require finishing of internal regions before they can be used. In small and medium volume productions most of the finishing tasks are non-repetitive in nature, and have to be performed manually. These finishing operations for parts with complex geometries can be quite labor intensive, and may pose risk to humans. We have developed a collaborative finishing system where human operators work on high level decision making, and the robot assistants carry out the labor intensive low level finishing tasks. The human operator guides the robotic system by transferring operator knowledge through a user interface. Our system generates instructions for the robots based on the user inputs and task requirements. We have also developed a planning algorithm that automatically computes the paths for the robots by using the CAD model of the part. This significantly reduces the robot programming time and improves the efficiency of the finishing system. If needed, the system seeks help from the human operator by generating notifications.

Laser shock peening (LSP) is an advanced surface treatment technique that can extend fatigue life in metallic components by inducing near-surface compressive residual stresses. In this study, LSP was implemented to induce compressive residual stresses and modify material properties of selective laser melted (SLM) aluminum A357 specimens. An initial hypothesis on the effect of LSP during tension testing was formulated and tested using finite element simulation. The hypothesis was that, due to the LSP-induced tensile residual stress field in the middle of the specimen cross sections, yielding was expected to initiate in this region. True stress-strain curves of two as-built (AB) and two laser shock peened samples were obtained through transverse tensile tests. The single explicit analysis using time dependent damping (SEATD) technique was used to simulate LSP process utilizing Johnson-Cook (J-C) constitutive parameters. J-C parameters for the cast A357 alloy were used for preliminary study. This was followed by the simulation of the transverse tensile test. J-C parameters for SLM A357 alloy were then empirically estimated, and simulations were repeated accordingly. It was found that the specific LSP pattern induced tensile residual stresses along the edges as well as the middle of the test specimen’s cross-section. Axial residual stress and yield strength profiles along three different paths on specimen’s cross-section were compared and yield regions were investigated. This supported the initial hypothesis, but also provided for a more detailed understanding of actual tensile test failure in the specific SLM A357 specimens for the given LSP treatment. In addition, the same LSP treatment on SLM A357 alloy resulted in lower magnitude of compressive residual stress than for cast A357 aluminum alloy.

Laser polishing is a highly effective surface treatment process mainly used on metals and optical components, but it can also be used on plastic parts. It requires no manual labor, can be applied on parts of any size, and produces no hazardous or polluting substances on many plastic parts. Fused deposition modeling (FDM) is an additive manufacturing process in which parts are built by extruding thin layers of hot material through a nozzle. It has the advantage of producing complicated part geometries, and the possibility to change a design with no additional cost. This study investigates the use of laser polishing as an auxiliary post-process on Polylactic Acid (PLA) parts produced with FDM to improve the surface quality of final products. Although YAG lasers are commonly used in assisting metal machining processes, a CO 2 laser was utilized in this study to post-process 3D-printed parts in order to reduce the staircase appearance. The main purpose of this study is to demonstrate that instead of reducing step size in 3D printing processes, it is possible to use bigger step sizes and laser treat the surface quickly afterwards to decrease the total process time while not compromising from surface quality. Laser speeds of 43–180 mm/s and laser powers of 0.75–3.75 W were tested on blocks of 3D-printed PLA with a parallelogram prism shape at 0.3 mm layer height. By varying laser speed and power, roughness reductions of up to 97% were achieved resulting in a uniform average surface roughness of 2.02 μm. This presents a fast, automatable, and inexpensive auxiliary post-process to FDM.

An innovative surface treatment method, ultrasonic nanocrystal surface deformation (UNSM), was used to process a magnesium (Mg) AZ31B alloy in this study. In the UNSM process, ultrasonic impacts induce plastic deformation on material surface that lead to grain refinement and surface morphology changes. The hardness, tensile strength, surface morphology and weight loss from immersion testing of the materials before and after UNSM were studied systematically. Compared with the unprocessed samples, the UNSM-processed samples show significant improvements in hardness (64%) and yield stress (43%). Surface topography results reveal that UNSM generates a smooth surface with an average roughness of 93 nm. In addition, the immersion results in cell medium demonstrate that the UNSM-processed group showed lower weight loss, especially during the early immersion period. It can thus be concluded that UNSM can significantly improve the hardness and yield strength of Mg alloys and reduce the corrosion rate, indicating that UNSM is a promising new method to enhance the mechanical properties of the degradable Mg alloys.

A hybrid surface treatment method is presented on S7 tool steel by alloying the surface layer with boron and following with pulsed laser micro polishing (PLuP). The objective of the hybrid approach is twofold: First, surface alloying changes the properties of the surface layer that are relevant to the PLuP process (e.g. liquid metal density, viscosity, and surface tension). This allows more control over the laser polishing phenomena for better smoothing. Second, surface alloying and laser melting/quenching is proposed as a novel method of creating amorphous surface coatings. In this work, boron was introduced into the surface of an S7 tool steel sample using pack cementation. This sample was then ground on a bias to create a flat surface with a gradient in chemical composition and this surface was laser melted. The effect of this variation in alloy chemistry on the surface features created by pulsed laser melting is presented.

Laser hardening is a very flexible and useful process for surface treatment of medium carbon steels, capable of processing varied and complex geometries. In order to enlarge the range of industrial applications to which this process can be applied, a suitable model is necessary in order to reduce the setup time requested for the optimization of new components. The process model presented is based on the Arrhenius-like equation for estimation of the thermally induced process reaction time for microstructural transformations. By means of experiments, all unknown parameters in the equations have been determined, highlighting the accuracy and low computation time of the simulator.

A process for surface finishing of medical device and implant alloys is described. Unlike conventional electrochemical surface finishing processes, Faraday’s pulse reverse process does not require low conductivity/high viscosity electrolytes and does not require the addition of aggressive chemicals such as hydrofluoric acid to remove the passive film associated with electropolishing of passive and strongly passive materials. This paper focuses on pulse/pulse reverse electropolishing of Nitinol and other metals and alloys containing titanium, molybdenum and niobium.

This study investigates the potentiality of using atmospheric-pressure Direct Current (DC) plasma arc discharge as a surface treatment method of aluminum alloys in adhesively bonded joints in order to enhance adhesion. The surface morphology exposed to the arc for the current of 40 A (low intensity) and the plasma torch scanning speeds between 20 and 120 mm/s, exhibits a micro-scale surface roughness appropriate for adhesive bonding. The arc textured surfaces are characterized by using an optical profilometer. Additionally, the effect of modified surface on the stress distribution throughout the single-lap adhesively bonded joint in tension is explored by 2D FEM. The geometrical model for FE analysis of adhesively bonded structure is generated by including the surface texture coordinates obtained from the optical profilometer.

Microvia formation technology using lasers has become the dominant method for drilling microvia called blind via-holes (BVHs) in printed wiring boards (PWBs). Laser direct drilling (LDD), drilling directly outer copper foil by laser, has attracted attention as a novel method. In particular, when copper and resin with different processing thresholds are drilled at the same time, an overhang defect occurs on the drilled hole. However, the overhang generation mechanism has not been clarified. Therefore, we investigated it by detailed observation of the drilled-hole section. Moreover, the overhang length was estimated using the finite element method (FEM). Influences of surface treatment of outer copper foil and thermal properties of the build-up layer were evaluated experimentally and analytically. Consequently, an experiment with a prototype PWB with silica filler added in the build-up layer was carried out. Using the prototype PWBs, the overhang was reduced as shown in FEM analysis results.

Laser shock peening is a surface treatment technique similar to conventional shot peening. The laser induced plasma causes plastic deformations and compressive residual stresses in materials which are useful for developing improved properties in the fields of fatigue, wear or stress corrosion cracking. Finite element method is an efficient tool to predict the mechanical effects and the deformations caused due to laser shock peening, which otherwise are difficult to calculate due to the severe pressure imparted in a very short period of time. This paper presents the calculations performed using ABAQUS, for the simulation of multiple laser shock processing in order to evaluate the residual stress and the deformation of the material. A study of the effect of multiple laser shocks and their extent of overlap on the affected depths and the tensile and compressive residual stresses has been discussed. FEM calculations of residual stress fields and extent of surface deformation in annealed AISI 1053 steel has been investigated along with a study of the distribution of tensile and compressive residual stresses due to the difference in the extent of overlap of the multiple shocks.

Laser surface hardening is nowadays an industrial emerging technique, which is gradually substituting induction and flame surface hardening thanks to its advantages related to power saving and process versatility. This manufacturing technology is a challenging process especially when it has to be applied on surfaces larger than the beam spot. In this case several adjacent passes must be performed in order to scan the whole surface to be treated. This strategy involves inevitably an intrinsic tempering effect due to the re-heating of the previously hardened material. The extent of the softening occurring depends on several parameters. First of all, it depends on the material and its initial state, then on process parameters related to the laser source, such as type, optical path and spot dimension and further on the adopted surface scan strategy of the beam. This last set of process parameters is represented by: laser beam speed, number of tracks, pass overlapping degree and tracks sequence. The hardness uniformity of the heat treated layer and the consequent effectiveness of the process depend strictly on the tempering degree occurring in the material. According to this it is important to find a practical method devoted to quickly characterize the result of a laser surface treatment in terms of tempered zones extension and distribution. This article proposes, then, the definition of a “Covering Uniformity” index (CU) which represents an engineering approach to this problem and it allows to easily determine the effectiveness of a particular laser hardening treatment. The CU index is based upon hardness measurements and it is related to the ratio between the extension of the tempered zone and the total extension of the treated area. In order to underline and demonstrate the intrinsic value of this parameter a set of experimental trials was carried out on AISI 1070 carbon steel, AISI 1040 carbon steel and AISI 420B martensitic stainless steel.

Wafers made of materials such as silicon, III-V and II-VI compounds, and optoelectronic materials, require high-degree of surface quality in order to increase the yield in micro-electronics fabrication to produce IC chips and devices. Measures of properties of surface quality of wafers include: nanotopography, surface morphology, global planarization, total thickness variation (TTV) and warp. Due to the reduction of feature size in micro-electronics fabrication, the requirements of such properties become more and more stringent. To meet such requirements, the wafer manufacturing processes of brittle semiconductor materials, such as slicing, lapping, grinding, and polishing have been continually improved. In this paper, the lapping process of wafer surface treatment is studied with experimental results of surface roughness and material removal rate. In order to improve the performance of lapping process, effects of mixed abrasive grits in the slurry of the free abrasive machining (FAM) processes are studied using a single-sided wafer-lapping machine. Under the same slurry density, experiments employing different mixing ratios of large and small abrasive grits, and various normal loadings on the wafer surface applied through a jig are conducted for parameter study. With various mixing ratios and loadings, observations and measurements such as the total amount of material removed, material removal rate, surface roughness, and relative angular velocity are presented and discussed in this paper. The experiments show that the half-half mixing ratio of abrasives removes more material than other mixing ratios under the same conditions, but with a higher surface roughness. The results of this study can provide a good reference to the FAM processes that practitioners use today by exploiting different mixing ratios and loadings of abrasive slurry in the manufacturing processes.

This work considers the influences of various types of die surface treatment, lubricants and temperature on friction for hot forging process of brass. Well-known ring compression test were carried out to evaluate friction coefficient for various conditions. Tool material was hot work tool steel H13 and workpiece material was brass C3771. Tool surface condition selected were normal hardening, treated by hard chrome, plasma nitriding and vacuum nitriding. Tests were conducted with and without lubricants at elevated temperature between 400–600°C. The results of experiments without lubricant show that friction coefficient is reduced when using die with treated surface regardless of working temperature. The influences of surface treated on die are not significant when forming under lubricated condition. In other word, lubricant has minor effect to reduce friction when the treated tools are employed. However, graphite in water was found to be almost compatible lubricant to graphite in oil when forming by tool which is treated by vacuum nitriding. The hardness and roughness of tool surfaces are found no relevance to friction coefficient in this work.

Final polishing operation for die and mould manufacturing represents up to 30% of the total manufacturing cost and it is a high added value operation carried out manually by qualified personnel. The work presented in this paper proposes an automated solution for this task by the process known as Laser Polishing . This process is based on the application of a laser beam melting a microscopic layer of material, which lately solidifies filling the gaps, and smoothing the overall topography. Several Laser Polishing tests have been done with CO 2 and High Power Diode Lasers (HPDL) on two different materials commonly used in die and mould industry: a DIN 1,2379 Tool Steel tempered up to 62HRC, used for injection moulds inserts, and a spheroidal graphite Cast Iron DIN GGG70L used typically on large stamping dies manufacturing. By means of the tests and Design of Experiments (DoE) technique, the operation parameters for the Laser Polishing process as well as its degree of influence in the melted surface have been defined. Starting off from an initial surface obtained by means of High Speed Milling operation, it has been possible to obtain satisfactory results with final roughness reductions higher than 80% with respect to the initial values, and mean roughness values below 0.8μm Ra.

Laser shock peening (LSP) is an innovative surface treatment developed to improve surface integrity. This study explores the feasibility using LSP to direct-write surface micro dents for lubricant retention. Since LSP is a highly transient process with a pulse duration of 10 – 100 ns, a real time in-situ measurement of laser/material interaction such as transient stresses/strains is challenging. Therefore, a 3D finite element simulation of micro-scale laser shock peening was developed to determine the effect of laser pulse duration and peak pressure on the transient material behaviors of titanium Ti-6Al-4V. The simulated dent geometry is similar to the measured dent geometry in terms of morphology. The results suggested there is an optimal peening time that produces the deepest dent. The maximum transient stress in peening direction occurred at a certain laser pulse time. However, the stress along the depth and radius were drastically affected by the peak pressures.

Micro scale laser shock peening (μLSP) is a process in which compressive residual stresses are induced in a material surface to improve fatigue life and wear resistance under cyclic loading. Since the diameter of the laser spot used during the process is the same order of magnitude as grain size, the effects of anisotropy and heterogeneity have to be explicitly taken into account. In this study experimental and analytic work have been done in order to investigate the bicrystal aluminum response under Gaussian loading. Effects of heterogeneity under μLSP are studied through applying laser shocks onto the grain boundary of the aluminum bicrystal. μLSP on reference single crystals have also been performed for the purpose of comparison. The orientations of the crystals in the bicrystal as well as the reference single crystals have been chosen such that an approximate plane strain condition is achieved. A finite element model has also been developed based on single crystal micromechanics and a cohesive zone interface model. Simulation results are compared with experimental findings. The potential benefit of μLSP as a surface treatment for improvement of fatigue life is also discussed.