High-precision Manufacturing Research Articles

Development of an adaptive, self-learning control concept for an additive manufacturing process

Error avoidance in high-precision manufacturing processes becomes more important for numerous state-of-the-art technologies. Selective laser melting is one of these technologies offering large potentials in the production of complex and flexible metal products. As the technology is relatively new, it is vulnerable for errors, given that the process parameters are not measured yet. A novel multilevel control concept, incorporating several sensors, has the potential to reduce errors significantly. For inner cascade control, the laser power will be adjusted by measurements with an intensity sensor for wavelengths in the visible range. This sensor is integrated into the optical path of the laser beam. An adapted self-learning strategy supports the stability of the process by updating the parameters of the used multidimensional model in order to attenuate environmental influences or shifts within the process. This work presents the concept of the control approach, first measurement results and the required relations between measurement, process and control parameters.

A Study of the Outer Reversed Taper Tooth Machining Based on the Generation Principle of Curtate Epicycloid

A machining method of the outer reversed taper tooth is presented to meet the processing requirements with high precision and high efficiency. The structure characteristic of the reversed taper tooth is analyzed. The curtate epicycloid rotational indexing machining principle for the outer reversed taper tooth is presented. Taking a driving gear machining in the gearbox as an example, the outer reversed taper tooth is machined by the above method, its span of measuring balls, error of the tooth direction and error of the tooth profile are 89.020 mm, 0.009 mm and 0.018 mm respectively. This result meets the accuracy requirements that the span of measuring balls should be in range of 89-89.06 mm, and the error of the tooth direction and error of the tooth profile should be less than 0.01 mm and 0.02 mm respectively. This machining example shows that the proposed machining method is valid. This paper provides a technical support for the high precision and high efficiency manufacture of the outer reversed taper tooth.

Tail Flare vs Fins in the Design of a Subcaliber Projectile

A typical aerodynamic configuration of a subcaliber projectile is composed of a slender body with a small cross-sectional area and fins at the rear part of the projectile. Projectile fins require high-precision manufacturing because their shape and size are designed to achieve high normal-force coefficients and a satisfactory static-stability margin. The influence of aerodynamic asymmetry to the projectile flight is minimized by the projectile rotation. An alternative aerodynamic configuration can be obtained by replacing fins with a tail flare. In this paper, the criteria for designing a tail flare replacing the fins were the maximum effective range and the maximum height of the trajectory. Computational fluid dynamics was used for calculating the aerodynamic coefficients of both a finned projectile and a projectile with a tail flare, with and without holes. The computation accuracy was verified by comparing the calculated aerodynamic coefficients with wind-tunnel measurements. The justification of the replacement of fins with a tail flare was verified through an analysis of trajectories for two characteristic firing elevation angles: the elevation angle required for the maximum effective range and the elevation angle defined for accidental firing.

Modular and reconfigurable desktop microfactory for high precision manufacturing

Sub-millimeter scale devices are developing rapidly taking smaller, smarter, and more precise forms. This is achieved thanks to advancements in micro-manufacturing tools and techniques. For micro-production, a miniaturization of the machinery is a prominent idea that has numerous benefits in terms of material usage, precision, transportation, modularity, and reconfigurability. In this paper, a modular and reconfigurable desktop microfactory for high precision machining and assembly of sub-millimeter scale mechanical parts is presented and experimentally validated. The proposed system is built based on important functional and performance requirements, including miniaturization, high precision operation, modular and reconfigurable design, parallel processing capability, ease of installation, and transportation. The miniature factory consists of five mini processing units; two parallel kinematic robots for manipulation, the laser micro-machining system, the camera system for detection and inspection, and the rotational conveyor system for micro-part delivery. Different configurations of the system layout are proposed taking advantage of their modular design. Experiments are conducted to evaluate the system performance within a single process, like pick-place of a metallic ball with 3 mm diameter, laser machining of a half-millimeter size contour on the surface of the ball, and inspection and verification of the machined contour by means of microscopic camera. The results presented in this work demonstrate micrometer precision operation of the microfactory, showing high potential for manufacturing electro-mechanical devices with ease of readjustment of the microfactory layout.

Optimization of high-precision cylinder manufacturing

Optimization of high-precision cylinder manufacturing

A Foil-Based Additive Manufacturing Technology for Metal Parts

In this paper, the method, system setup, and procedure of a new additive manufacturing (AM) technology for manufacturing three-dimensional (3D) metal parts are introduced. Instead of using metal powders as in most commercial AM technologies, the new method uses metal foils as feed stock. The procedure consists of two alternating processes: foil-welding by a high-power continuous-wave (CW) laser and foil-cutting by a Q-switched ultraviolet (UV) laser. The foil-welding process involves two subprocesses: laser spot welding and laser raster-scan welding. The reason for using two lasers is to achieve simultaneously the high-speed and high-precision manufacturing. The results on laser foil-welding and foil-cutting show that complete and strong welding bonds can be achieved with determined parameters, and that clean and no-burr/distortion cut of foil can be obtained. Several 3D AISI 1010 steel parts fabricated by the proposed AM technology are presented, and the microhardness and tensile strength of the as-fabricated parts are both significantly greater than those of the original foil.

An approach to realize the networked closed-loop manufacturing of spiral bevel gears

Digital closed-loop manufacturing technique, as a significant component of spiral bevel gear manufacturing system, has provided significant guarantee for improving the quantity and efficiency of spiral bevel gear tooth surfaces. The continuous fusion of digital closed-loop manufacturing and network technologies open a new route for the high-efficiency and high-precision manufacturing of spiral bevel gears. In order to realize the integrated operation and the information management in closed-loop manufacturing process of spiral bevel gears, this paper presents a universal networked closed-loop manufacturing model for spiral bevel gears by combining gear digital closed-loop manufacturing technologies and network technologies, which offers better support for the integrated design and machining of spiral bevel gear tooth surfaces. In this paper, the typical digital closed-loop manufacturing process of spiral bevel gears is deeply analyzed, and the framework of networked closed-loop manufacturing model is proposed. Furthermore, the integrated operation mechanism of networked closed-loop manufacturing model is established. On this basis, the key implementation mechanism of networked closed-loop manufacturing model such as the communication network construction, manufacturing information integration mechanism, and networked closed-loop manufacturing integration system development is elaborated respectively. Finally, an actual application experiment of spiral bevel gear pair networked closed-loop manufacturing is provided to demonstrate the feasibility and practicability of the proposed model.

Lithography-based additive manufacture of ceramic biodevices with design-controlled surface topographies

The possibility of manufacturing textured materials and devices, with surface properties controlled from the design stage, instead of being the result of machining processes or chemical attacks, is a key factor for the incorporation of advanced functionalities to a wide set of micro- and nano-systems. High-precision additive manufacturing (AM) technologies based on photopolymerization, together with the use of fractal models linked to computer-aided design tools, allow for a precise definition of final surface properties. However, the polymeric master parts obtained with most commercial systems are usually inadequate for biomedical purposes and their limited strength and size prevents many potential applications. On the other hand, additive manufacturing technologies aimed at the production of final parts, normally based on layer-by-layer melting or sintering ceramic or metallic powders, do not always provide the required precision for obtaining controlled micro-structured surfaces with high-aspect-ratio details. Towards the desired degree of precision and performance, lithography-based ceramic manufacture is a remarkable option, as we discuss in the present study, which presents the development of two different micro-textured biodevices for cell culture. Results show a remarkable control of the surface topography of ceramic parts and the possibility of obtaining design-controlled micro-structured surfaces with high-aspect-ratio micro-metric details.

Stress relaxation ageing behaviour and constitutive modelling of a 2219 aluminium alloy under the effect of an electric pulse

In creep age forming (CAF), stress relaxation and the creep process occur during the ageing heat treatment. However, there is a remarkable difference between the deformation and phase transformation activation energies in aluminium alloys. To achieve high-performance and high-precision collaborative manufacturing of large-scale complex panels with high levels of reinforcement, the difference in the energy barriers between the stress relaxation process and the ageing precipitation process needs to be coordinated. An electric pulsed current (EPC) was first introduced into the CAF process for 2219 aluminium. It was found that the EPC can effectively regulate the stress relaxation behaviour during the initial ageing stage. That is, the application of EPC during the first 1 h of the ageing treatment process decreases the stress gradients for different initial stress levels, which makes it possible to reduce the deformation and phase transformation inhomogeneities resulting from stress differences inside a component under a bending load. Meanwhile, the apparent deformation activation energy decreases with the EPC, which decreases the energy barrier difference between the stress relaxation and ageing precipitation from 47 kJ/mol to 18 kJ/mol. Furthermore, the action mechanism for EPC on the stress relaxation process is discussed, and a constitutive model for stress relaxation age forming considering the effect of the EPC is established.

Trajectory Planning for Reconfigurable Industrial Robots Designed to Operate in a High Precision Manufacturing Industry

This paper presents an algorithm for an automated planning of time-jerk optimal trajectories on a reconfigurable robot with an anthropomorphic structure. The trajectory planning algorithm is designed to provide reachable input set-points for the reconfigurable control system to accommodate not only changes in task objectives but also various reconfigurations of the robot kinematic structure and motion behavior adaptation in response to operational constraints. Firstly, appropriate reference frames are defined on the robotic modules and the position and orientation of the end effector in the Cartesian space is dynamically generated through a reconfigurable forward kinematics module. Secondly, through an iterative inverse kinematic method, the robot configuration space for the start and goal destinations and the geometric path for every motion tasks are generated. Finally, the joint space trajectories with coordinated motion profiles are generated by incorporating the motion laws and joint kinematic parameter values. The general outcome of the algorithm is a trajectory plan of the robot joints expressed as a time history of the robot motion. The trajectories are dynamically generated to satisfy widely varying tasks, constraints and objectives aiming towards a fully reconfigurable control without any hardware or software adjustment.

Topography Measurement for Monitoring Manufacturing Processes in Harsh Conditions

High precision manufacturing, e.g. milling and grinding, which have manufacturing tolerances in the range of <10 μm require microscopic measurement techniques for the inspection of the manufactured components. These measurement techniques are very sensitive to cooling liquids and lubricants which are essential for many manufacturing processes. Therefore, the measurement of the components is usually conducted in separate and clean laboratories and not directly in the manufacturing machine. This approach has some major drawbacks, e.g. high time consumption and no possibility for online process monitoring. In this article, a novel concept for the integration of high precision optical topography measurement systems into the manufacturing machine is introduced and compared to other concepts. The introduced concept uses a reservoir with cooling liquid in which the measurement object is immersed during the measurement. Thereby, measurement disturbance by splashing cooling liquids and lubricants can effectively be avoided.

Effect of large deflection angle on the laser intensity profile produced by acousto-optic deflector scanners in high precision manufacturing

Laser beam scanners have found wide applications in a variety of laser-assisted advanced microprocessing technologies such as printing, patterning, and doping. Traditional galvo-scanners affect the accuracy of beam positioning and repeatability in high precision manufacturing due to mechanical motion of the mirrors and backlash errors. The purpose of this study is to analyze an acousto-optic deflector (AOD) to achieve high diffraction efficiency and high deflection angle. Conventional AODs are operated with one-dimensional refractive index variation induced by modulating only the acoustic wave frequency. The effect of two-dimensional refractive index variations, which can be achieved by modulating both the phase and frequency of the acoustic waves, is analyzed. This study, therefore, advances the current AOD technology from just acoustic wave frequency modulation to a new class of AODs involving both phase and frequency modulations. This new type of AOD is designed by developing an analytic model based on the propagation of a laser beam through the AOD in which the refractive index varies in two dimensions. The model predicts a specific index modulation strength to achieve 100% diffraction efficiency. Also a fairly large diffraction efficiency can be obtained over a large angle of incidence, which is not possible in conventional AODs where the maximum diffraction efficiency occurs only at Bragg angle of incidence.

Nonconventional Sources of Movement Used to Obtain High Level Precision Manufacturing

Since the beginning of industrial era it was clear that the goal of perfect machine is far away. Things become more complicated as the tool machinery branch developed in quite a fast way so things as using full production capacity of a machine or working with adaptive control become normal and frequent. Reaching a good precision in manufacturing was realized by strengthening the structure , with related weight growth and use of more material both generating supplementary costs. Probably the best idea was to create a structure not so rigid , that means lighter ,a structure predictable in the way it works that means predictable deformation and their direction. The big advantage of the idea is that knowing the deformation we can take corrective actions so that the final precision at the edge of the cutting tool becomes very high. The corrective action consists in a very fine and very fast movement that composed with the structure deformations makes a great precision. The solution it self-generated a new challenge consisting in the need for almost instant movement , the source of which was not conventional. The authors are proposing a “magnetostrictive” engine as a new way of generating precise correction movements.

Genetic search for optimally-constrained multiple-line fitting of discrete data points

Advanced sensing technologies have produced a significant amount of discrete point data in the past decade. Measurement uncertainty frequently occurs at the geometric discontinuity of mechanical parts. In this paper, a genetic search algorithm is developed for optimally-constrained multiple-line fitting of discrete data points. It contains two important technical components: (a) constrained least-squares fitting of multiple lines, and (b) genetic search for optimal corner/edge points. The algorithm is designed for both two-dimensional and three-dimensional cases. Numerical experiments demonstrate the effectiveness of the proposed approach, compared to the conventional least-squares fitting method as well as exhaustive search method. A comparative study with a particle swarm method indicates that both the genetic search and particle swarm search produce similar results in terms of minimum fitting errors. It can be used for the effective determination of sharp edges or corners based on discrete data points measured for high-precision industrial inspection and manufacturing.

Evolution of High Precision Manufacturing of Contact Lenses

Today’s contact lens professionals must familiarise themselves with the various contact lens manufacturing methodologies that are capable of producing high accuracy optical products for their patients. Contact lens manufacturing dates back to the 19thcentury with the development of glass contact lenses and later evolved to various types of optical polymeric materials. The recent advances in the manufacturing of contact lenses can be attributed to the development of advanced polymeric materials and high precision processing technologies. Two basic techniques are identified for contact lens manufacturing. They are moulding method and ultra-high precision machining. Ultra-high precision machining is employed for direct shaping of contact lenses or for making mould inserts that will be used further in lens injection. Mould inserts can be made from high hardness steel, nickel plated steel, aluminium or other nonferrous alloys. Advanced light metal optical aluminium alloys provide a high integrity mould with fine microstructures for optical lens production. This review paper provides a chronological view of the evolution of contact lens manufacturing and identifies the importance of a recently developed aluminium alloy in the production of mould inserts for high quality contact lenses.

The Study on the Selectivity Ratio of SiC/Epoxy Resin Based on ICP Etching

SiC molds have excellent performance for high-temperature molding optical lenses. The stable physical and chemical properties of SiC results in the difficulty of manufacture high precision SiC molds. Using etching method can manufacture SiC molds apace and accurately, which is used for Micro-embossing needs to study the suitable selectivity ratio of SiC and the anti-etch layer-epoxy resin. The etching gas is SF6 and O2. Under different ICP power, bias voltage, the gas mixing ratio and other parameters, it has studied the influence of various factors on the etching ratio, the etching rate and the etching quality. Experiments show that under the parameters of SF6 flow of 80sccm, O2 flow of 5sccm, ICP power of 1200w, bias power of 70w, temperature of 30 °C, and pressure of 30mTorr, the SiC etching rate is 246.44nm/min, and the epoxy etching rate is 616nm/min. The SiC/epoxy resin etching ratio is stable at 1:2.5. The roughness of SiC is 1.2nm (Sa= 1.2nm). The anisotropic of etching is good.

High-Efficiency W-Band Electroforming Slot Array Antenna

A W-band $8 \times 8$ slot array antenna is proposed and fabricated by electroforming for high-precision manufacturing. The external mutual coupling between radiating shunt slots is compensated for input impedance matching and a uniform field distribution. The overall antenna aperture area is $473.1\,\rm{mm}^2$ with slot spacings of 2.8 and 2.64 mm in the transverse and longitudinal direction, respectively. The measured maximum gain is 26.8 dBi and the corresponding antenna efficiency is 81.9% at 94 GHz. The measured impedance bandwidth when the VSWR is less than 2.0 ( $- 10 \;\rm{dB}$ ) is 8.3%, with a range from 89.9 to 97.6 GHz.

Progressive measurement and monitoring for multi-resolution data in surface manufacturing considering spatial and cross correlations

Controlling variations in part surface shapes is critical to high-precision manufacturing. To estimate the surface variations, a manufacturing plant usually employs a number of multi-resolution metrology systems to measure surface flatness and roughness with limited information about surface shape. Conventional research establishes surface models by considering spatial correlation; however, the prediction accuracy is restricted by the measurement range, speed, and resolution of metrology systems. In addition, existing monitoring approaches do not locate abnormal variations and lead to high rates of false alarms or misdetections. This article proposes a new methodology for efficiently measuring and monitoring surface variations by fusing in-plant multi-resolution measurements and process information. The fusion is achieved by considering cross-correlations among the measured data and manufacturing process variables along with spatial correlations. Such cross-correlations are induced by cutting force dynamics and can be used to reduce the amount of measurements or improve prediction precision. Under a Bayesian framework, the prediction model is combined with measurements on incoming parts to progressively make inferences on surface shapes. Based on the inference, a new monitoring scheme is proposed for jointly detecting and locating defective areas without significantly increasing false alarms. A case study demonstrates the effectiveness of the method.

Design Concept of Hybrid Instrument for Laparoscopic Surgery and Its Verification Using Scale Model Test

This paper proposes a new design concept of hybrid instrument for single-port laparoscopic surgery (SPLS) and a new method of verification using a scaled-up prototype based on the principle of elastic similarity. The proposed concept is a hand-held instrument that uses a tendon-gear mechanism for dexterous movement of its end-effector and servomotors with flexible tendon-sheath transmission to maintain the dexterity by compensating the loss of output angle from tendon elongation during the manual operation. The kinematic relationship of the tendon-gear mechanism was derived mathematically, and the ratio of external moment to resistive flexural stiffness of the articulating joint was matched between the real-sized model and the large-scale prototype. Our scale model tests have shown good agreement between their input–output relationships under the equivalent loading conditions, and thus verified the validity of similarity analysis. Also, the proof-of-concept experiments have demonstrated the functionality of output loss compensation of the hybrid instrument. Our methodology can be used to simplify and speed up the prototype development process for SPLS by avoiding miniaturization challenges such as high precision manufacturing, which is costly and time-consuming.

Parameter Identification for Finite Element Based Models in Dry Machining Applications

Dry machining is a challenging topic in industrial manufacturing: The absence of coolants results in ecological and economical benefits, but also in a significant increase of the occurring thermal stress. This leads to geometrical deviations of the machined workpiece impairing the functional performance of the final part. The increased thermal stress is especially important in high-precision manufacturing and requires careful process planning. To determine process parameters in order to minimize geometrical errors, optimal control is an appropriate tool. A precise partial differential equation model representing the material behavior is required. The partial differential equation contains unknown physical quantities, such as heat fluxes, which cannot be measured directly. One common method to derive these quantities is solving an inverse problem by parameter identification, i.e. determining the model parameters, such that the model matches the measurements best. We will present a simultaneous analysis and design approach which states a numerical finite element discretization of the model as constraints of the resulting nonlinear optimization problem (NLP). The proposed method takes advantage of both, direct consideration of state constraints, like temperature boundaries, and lower computational costs compared to the nested analysis and design approach. The additional implementation costs can be significantly reduced by using an external finite element library for assembling the optimization constraints and its derivatives. This approach for determining physical parameters of milling experiments is user-independent and works fully automated. It is the first step for an optimal control of dry machining processes. We will give a description of this method as well as numerical identification results of real heat flux densities by the sparse NLP solver WORHP.