Special Issue "Product/Process Fingerprint in Micro Manufacturing"

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "D:Materials and Processing".

Deadline for manuscript submissions: closed (28 February 2019)

Special Issue Editor

Guest Editor
Prof. Dr. Guido Tosello

Department of Mechanical Engineering, Technical University of Denmark, Produktionstorvet Building 427A, 2800, Kgs. Lyngby, Denmark
Website | E-Mail
Interests: precision polymer processing; statistical process control; precision additive manufacturing; metrology

Special Issue Information

Dear Colleagues,

The continuous miniaturization of products, and the growing complexity of their embedded multi-functionalities, call for incessant research and development of micro components and related micro-manufacturing technologies.

Highly-miniaturized systems, manufactured on a wide variety of materials, find applications in key technological fields, such as health-care devices, micro implants, mobility, communications, optics, and micro electromechanical systems.

Innovations required for high precision manufacturing of micro components can specifically be achieved through optimizations using post-process (i.e., off-line) and in-process (i.e., on-line) metrology of both process input and output parameters, as well as geometrical features of the produced micro parts. However, it is of critical importance to reduce the metrology and optimization efforts, since process and product quality control can take up a significant portion of the total production time in micro-manufacturing.

To solve this fundamental challenge, research efforts are undertaken in order to define, investigate, implement and validate the so-called “Product/Process Manufacturing Fingerprint” concept.

The “Product Manufacturing Fingerprint” concept refers to those unique dimensional outcomes (e.g., surface topography, form error, critical dimensions, etc.) on the produced component that, if kept under control and within specifications, it ensures that the entire micro component complies to its specifications.

The “Process Manufacturing Fingerprint” is a specific process parameter or feature to be monitored and controlled in order to maintain the manufacture of products within the specified tolerances.

By integrating both Product and Process Manufacturing Fingerprint concepts, the metrology and optimization efforts are highly reduced. Therefore, the quality of the micro products increases, with obvious improvement on the production yield.

Accordingly, this Special Issue seeks to showcase research papers, short communications, and review articles that focus on novel methodological developments and applications in micro and sub-micro scale manufacturing, process monitoring and control, as well as micro and sub-micro product quality assurance. Focus will be on micro manufacturing process chains and their micro product/process fingerprint, towards full process optimization and zero-defect micro manufacturing.

We look forward to receiving your submissions.

Prof. Dr. Guido Tosello
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • micro and nano manufacturing
  • process chains
  • micro and nano metrology
  • process monitoring
  • process control
  • micro production quality assurance

Published Papers (17 papers)

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Editorial

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Open AccessEditorial
Product/Process Fingerprint in Micro Manufacturing
Micromachines 2019, 10(5), 340; https://doi.org/10.3390/mi10050340
Received: 16 May 2019 / Accepted: 21 May 2019 / Published: 22 May 2019
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Abstract
The continuous trend towards miniaturization and multi-functionality embedded in products and processes calls for an ever-increasing research and innovation effort in the development of micro components and related micro manufacturing technologies [...] Full article
(This article belongs to the Special Issue Product/Process Fingerprint in Micro Manufacturing)

Research

Jump to: Editorial

Open AccessArticle
Analysis of the Downscaling Effect and Definition of the Process Fingerprints in Micro Injection of Spiral Geometries
Micromachines 2019, 10(5), 335; https://doi.org/10.3390/mi10050335
Received: 4 April 2019 / Revised: 16 May 2019 / Accepted: 16 May 2019 / Published: 22 May 2019
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Abstract
Microinjection moulding has been developed to fulfil the needs of mass production of micro components in different fields. A challenge of this technology lies in the downscaling of micro components, which leads to faster solidification of the polymeric material and a narrower process [...] Read more.
Microinjection moulding has been developed to fulfil the needs of mass production of micro components in different fields. A challenge of this technology lies in the downscaling of micro components, which leads to faster solidification of the polymeric material and a narrower process window. Moreover, the small cavity dimensions represent a limit for process monitoring due to the inability to install in-cavity sensors. Therefore, new solutions must be found. In this study, the downscaling effect was investigated by means of three spiral geometries with different cross sections, considering the achievable flow length as a response variable. Process indicators, called “process fingerprints”, were defined to monitor the process in-line. In the first stage, a relationship between the achievable flow length and the process parameters, as well as between the process fingerprints and the process parameters, was established. Subsequently, a correlation analysis was carried out to find the process indicators that are mostly related to the achievable flow length. Full article
(This article belongs to the Special Issue Product/Process Fingerprint in Micro Manufacturing)
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Open AccessArticle
Structuring of Bioceramics by Micro-Grinding for Dental Implant Applications
Micromachines 2019, 10(5), 312; https://doi.org/10.3390/mi10050312
Received: 13 April 2019 / Revised: 30 April 2019 / Accepted: 1 May 2019 / Published: 9 May 2019
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Abstract
Metallic implants were the only option for both medical and dental applications for decades. However, it has been reported that patients with metal implants can show allergic reactions. Consequently, technical ceramics have become an accessible material alternative due to their combination of biocompatibility [...] Read more.
Metallic implants were the only option for both medical and dental applications for decades. However, it has been reported that patients with metal implants can show allergic reactions. Consequently, technical ceramics have become an accessible material alternative due to their combination of biocompatibility and mechanical properties. Despite the recent developments in ductile mode machining, the micro-grinding of bioceramics can cause insufficient surface and subsurface integrity due to the inherent hardness and brittleness of these materials. This work aims to determine the influence on the surface and subsurface damage (SSD) of zirconia-based ceramics ground with diamond wheels of 10 mm diameter with a diamond grain size (dg) of 75 μm within eight grinding operations using a variation of the machining parameters, i.e., peripheral speed (vc), feed speed (vf), and depth of cut (ae). In this regard, dental thread structures were machined on fully sintered zirconia (ZrO2), alumina toughened zirconia (ATZ), and zirconia toughened alumina (ZTA) bioceramics. The ground workpieces were analysed through a scanning electron microscope (SEM), X-ray diffraction (XRD), and white light interferometry (WLI) to evaluate the microstructure, residual stresses, and surface roughness, respectively. Moreover, the grinding processes were monitored through forces measurement. Based on the machining parameters tested, the results showed that low peripheral speed (vc) and low depth of cut (ae) were the main conditions investigated to achieve the optimum surface integrity and the desired low grinding forces. Finally, the methodology proposed to investigate the surface integrity of the ground workpieces was helpful to understand the zirconia-based ceramics response under micro-grinding processes, as well as to set further machining parameters for dental implant threads. Full article
(This article belongs to the Special Issue Product/Process Fingerprint in Micro Manufacturing)
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Open AccessArticle
2-Step Drop Impact Analysis of a Miniature Mobile Haptic Actuator Considering High Strain Rate and Damping Effects
Micromachines 2019, 10(4), 272; https://doi.org/10.3390/mi10040272
Received: 11 March 2019 / Revised: 28 March 2019 / Accepted: 7 April 2019 / Published: 23 April 2019
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Abstract
In recent times, the haptic actuators have been providing users with tactile feedback via vibration for a realistic experience. The vibration spring must be designed thin and small to use a haptic actuator in a smart device. Therefore, considerable interests have been exhibited [...] Read more.
In recent times, the haptic actuators have been providing users with tactile feedback via vibration for a realistic experience. The vibration spring must be designed thin and small to use a haptic actuator in a smart device. Therefore, considerable interests have been exhibited with respect to the impact characteristics of these springs. However, these springs have been difficult to analyze due to their small size. In this study, drop impact experiments and analyses were performed to examine the damages of the mechanical spring in a miniature haptic actuator. Finally, an analytical model with high strain rate and damping effects was constructed to analyze the impact characteristics. Full article
(This article belongs to the Special Issue Product/Process Fingerprint in Micro Manufacturing)
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Open AccessArticle
Process Control in Jet Electrochemical Machining of Stainless Steel through Inline Metrology of Current Density
Micromachines 2019, 10(4), 261; https://doi.org/10.3390/mi10040261
Received: 28 February 2019 / Revised: 8 April 2019 / Accepted: 15 April 2019 / Published: 18 April 2019
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Abstract
Jet electrochemical machining (Jet-ECM) is a flexible method for machining complex microstructures in high-strength and hard-to-machine materials. Contrary to mechanical machining, in Jet-ECM there is no mechanical contact between tool and workpiece. This enables Jet-ECM, like other electrochemical machining processes, to realize surface [...] Read more.
Jet electrochemical machining (Jet-ECM) is a flexible method for machining complex microstructures in high-strength and hard-to-machine materials. Contrary to mechanical machining, in Jet-ECM there is no mechanical contact between tool and workpiece. This enables Jet-ECM, like other electrochemical machining processes, to realize surface layers free of mechanical residual stresses, cracks, and thermal distortions. Besides, it causes no burrs and offers long tool life. This paper presents selected features of Jet-ECM, with special focus on the analysis of the current density during the machining of single grooves in stainless steel EN 1.4301. Especially, the development of the current density resulting from machining grooves intersecting previous machining steps was monitored in order to derive systematic influences. The resulting removal geometry is analyzed by measuring the depth and the roughness of the machined grooves. The correlation between the measured product features and the monitored current density is investigated. This correlation shows that grooves with the desired depth and surface roughness can be machined by controlling current density through the adjustment of process parameters. On the other hand, current density is sensitive to the changes of working gap. As a consequence of the changes of workpiece form and size for the grooves intersecting premachined grooves as well as the grooves with a lateral gap, working gap, and current density change. By analyzing monitoring data and removal geometry results, the suitability of current density inline monitoring to enable process control is shown, especially with regards to manufacture products that should comply with tight predefined specifications. Full article
(This article belongs to the Special Issue Product/Process Fingerprint in Micro Manufacturing)
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Open AccessArticle
Process Fingerprint in Micro-EDM Drilling
Micromachines 2019, 10(4), 240; https://doi.org/10.3390/mi10040240
Received: 7 March 2019 / Revised: 28 March 2019 / Accepted: 8 April 2019 / Published: 11 April 2019
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Abstract
The micro electrical discharge machining (micro-EDM) process is extensively used in aerospace, automotive, and biomedical industries for drilling small holes in difficult-to-machine materials. However, due to the complexity of the electrical discharge phenomena, optimization of the processing parameters and quality control are time-consuming [...] Read more.
The micro electrical discharge machining (micro-EDM) process is extensively used in aerospace, automotive, and biomedical industries for drilling small holes in difficult-to-machine materials. However, due to the complexity of the electrical discharge phenomena, optimization of the processing parameters and quality control are time-consuming operations. In order to shorten these operations, this study investigates the applicability of a process fingerprint approach in micro-EDM drilling. This approach is based on the monitoring of a few selected physical quantities, which can be controlled in-line to maximize the drilling speed and meet the manufacturing tolerance. A Design of Experiments (DoE) is used to investigate the sensitivity of four selected physical quantities to variations in the processing parameters. Pearson’s correlation is used to evaluate the correlation of these quantities to some main performance and hole quality characteristics. Based on the experimental results, the potential of the process fingerprint approach in micro-EDM drilling is discussed. The results of this research provide a foundation for future in-line process optimization and quality control techniques based on machine learning. Full article
(This article belongs to the Special Issue Product/Process Fingerprint in Micro Manufacturing)
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Open AccessArticle
On the Process and Product Fingerprints for Electro Sinter Forging (ESF)
Micromachines 2019, 10(4), 218; https://doi.org/10.3390/mi10040218
Received: 25 February 2019 / Revised: 20 March 2019 / Accepted: 25 March 2019 / Published: 27 March 2019
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Abstract
Electro sinter forging (ESF) represents an innovative manufacturing process dealing with high electrical currents. Classified in the category of electrical current assisted sintering (ECAS) processes, the main principle is that Joule heating is generated inside the compacted powder, while the electrical current is [...] Read more.
Electro sinter forging (ESF) represents an innovative manufacturing process dealing with high electrical currents. Classified in the category of electrical current assisted sintering (ECAS) processes, the main principle is that Joule heating is generated inside the compacted powder, while the electrical current is flowing. The process is optimized through the analysis of the main process parameters, namely the electrical current density, sintering time, and compaction pressure, which are also evaluated as process fingerprints. The analysis was conducted on commercially pure titanium powder. Small discs and rings were manufactured for testing. The influence of the process parameters was analysed in terms of the final material properties. The relative density, microstructures, hardness, and tensile and compressive strengths were analysed concerning their validity as product fingerprints. Microstructural analyses revealed whether the samples were sintered or if melting had occurred. Mechanical properties were correlated to the process parameters depending on the material. The different sample shapes showed similar trends in terms of the density and microstructures as a function of the process parameters. Full article
(This article belongs to the Special Issue Product/Process Fingerprint in Micro Manufacturing)
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Open AccessArticle
Process Understanding of Plasma Electrolytic Polishing through Multiphysics Simulation and Inline Metrology
Micromachines 2019, 10(3), 214; https://doi.org/10.3390/mi10030214
Received: 27 February 2019 / Revised: 21 March 2019 / Accepted: 22 March 2019 / Published: 26 March 2019
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Abstract
Currently, the demand for surface treatment methods like plasma electrolytic polishing (PeP)—a special case of electrochemical machining—is increasing. This paper provides a literature review on the fundamental mechanisms of the plasma electrolytic polishing process and discusses simulated and experimental results. The simulation shows [...] Read more.
Currently, the demand for surface treatment methods like plasma electrolytic polishing (PeP)—a special case of electrochemical machining—is increasing. This paper provides a literature review on the fundamental mechanisms of the plasma electrolytic polishing process and discusses simulated and experimental results. The simulation shows and describes a modelling approach of the polishing effect during the PeP process. Based on the simulation results, it can be assumed that PeP can be simulated as an electrochemical machining process and that the simulation can be used for roughness and processing time predictions. The simulation results exhibit correlations with the experimentally-achieved approximation for roughness decrease. The experimental part demonstrates the results of the PeP processing for different times. The results for different types of roughness show that roughness decreases exponentially. Additionally, a current efficiency calculation was made. Based on the experimental results, it can be assumed that PeP is a special electrochemical machining process with low passivation. Full article
(This article belongs to the Special Issue Product/Process Fingerprint in Micro Manufacturing)
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Open AccessArticle
Design and Fabrication of an Artificial Compound Eye for Multi-Spectral Imaging
Micromachines 2019, 10(3), 208; https://doi.org/10.3390/mi10030208
Received: 28 February 2019 / Revised: 17 March 2019 / Accepted: 22 March 2019 / Published: 25 March 2019
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Abstract
The artificial compound eye (ACE) structure is a new type of miniaturized, lightweight and intelligent imaging system. This paper has proposed to design a multi-spectral ACE structure to enable the structure to achieve multi-spectral information on the basis of imaging. The sub-eyes in [...] Read more.
The artificial compound eye (ACE) structure is a new type of miniaturized, lightweight and intelligent imaging system. This paper has proposed to design a multi-spectral ACE structure to enable the structure to achieve multi-spectral information on the basis of imaging. The sub-eyes in the compound eye structure have been designed as diffractive beam splitting lenses with the same focal length of 20 mm, but with the different designed center wavelengths of 650 nm, 532 nm, and 445 nm, respectively. The proximity exposure lithography and reactive ion etching process were used to prepare the designed multi-spectral ACE structure, and the spectral splitting and multi-spectral imaging experiments were carried out to verify the multi-spectral imaging function of the structure without axial movement. Furthermore, the structure can be designed according to actual requirements, which can be applied to covert reconnaissance, camouflage identification, gas leakage or other fields. Full article
(This article belongs to the Special Issue Product/Process Fingerprint in Micro Manufacturing)
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Open AccessArticle
Product and Process Fingerprint for Nanosecond Pulsed Laser Ablated Superhydrophobic Surface
Micromachines 2019, 10(3), 177; https://doi.org/10.3390/mi10030177
Received: 7 February 2019 / Revised: 25 February 2019 / Accepted: 4 March 2019 / Published: 7 March 2019
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Abstract
Superhydrophobic surfaces have attracted extensive attention over the last few decades. It is mainly due to their capabilities of providing several interesting functions, such as self-cleaning, corrosion resistance, anti-icing and drag reduction. Nanosecond pulsed laser ablation is considered as a promising technique to [...] Read more.
Superhydrophobic surfaces have attracted extensive attention over the last few decades. It is mainly due to their capabilities of providing several interesting functions, such as self-cleaning, corrosion resistance, anti-icing and drag reduction. Nanosecond pulsed laser ablation is considered as a promising technique to fabricate superhydrophobic structures. Many pieces of research have proved that machined surface morphology has a significant effect on the hydrophobicity of a specimen. However, few quantitative investigations were conducted to identify effective process parameters and surface characterization parameters for laser-ablated microstructures which are sensitive to the hydrophobicity of the microstructured surface. This paper proposed and reveals for the first time, the concepts of process and product fingerprints for laser ablated superhydrophobic surface through experimental investigation and statistical analysis. The results of correlation analysis showed that a newly proposed dimensionless functional parameter in this paper, Rhy, i.e., the average ratio of Rz to Rsm is the most sensitive surface characterization parameter to the water contact angle of the specimen, which can be regarded as the product fingerprint. It also proposes another new process parameter, average laser pulse energy per unit area of the specimen (Is), as the best process fingerprint which can be used to control the product fingerprint Rhy. The threshold value of Rhy and Is are 0.41 and 536 J/mm2 respectively, which help to ensure the superhydrophobicity (contact angle larger than 150°) of the specimen in the laser ablation process. Therefore, the process and product fingerprints overcome the research challenge of the so-called inverse problem in manufacturing as they can be used to determine the required process parameters and surface topography according to the specification of superhydrophobicity. Full article
(This article belongs to the Special Issue Product/Process Fingerprint in Micro Manufacturing)
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Open AccessArticle
Charged Satellite Drop Avoidance in Electrohydrodynamic Dripping
Micromachines 2019, 10(3), 172; https://doi.org/10.3390/mi10030172
Received: 16 January 2019 / Revised: 7 February 2019 / Accepted: 25 February 2019 / Published: 1 March 2019
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Abstract
The quality of electrohydrodynamic jet (e-jet) printing is crucially influenced by the satellite drop formed when the primary drop detaches from the meniscus. If the satellite drop falls onto the substrate, the patterns on the substrate will be contaminated. The electric charge carried [...] Read more.
The quality of electrohydrodynamic jet (e-jet) printing is crucially influenced by the satellite drop formed when the primary drop detaches from the meniscus. If the satellite drop falls onto the substrate, the patterns on the substrate will be contaminated. The electric charge carried by the satellite drop leads to more complex satellite/meniscus interaction than that in traditional inkjet printing. Here, we numerically study the formation and flight behavior of the charged satellite drop. This paper discovered that the charge relaxation time (CRT) of the liquid determines the electric repulsion force between the satellite drop and meniscus. The satellite drop will merge with the meniscus at long CRT, and fail to merge and deteriorate the printing quality at short CRT. The simulations are adopted to discover the mechanism of generation and flight behavior of charged satellite drops. The results show that the critical CRT decreases with the dielectric constant of the liquid and the supplied flow rate. Namely, for small dielectric constant and fixed CRT, the satellite drop is less likely to merge with the meniscus, and for high flow rate, the satellite drop is prone to merge with the meniscus due to the delay of necking thread breakup. These results will help to choose appropriate parameters to avoid the satellite drop from falling onto the substrate. Full article
(This article belongs to the Special Issue Product/Process Fingerprint in Micro Manufacturing)
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Open AccessArticle
Multi-Response Optimization of Electrical Discharge Machining Using the Desirability Function
Micromachines 2019, 10(1), 72; https://doi.org/10.3390/mi10010072
Received: 16 November 2018 / Revised: 9 January 2019 / Accepted: 14 January 2019 / Published: 20 January 2019
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Abstract
Electrical discharge machining (EDM) is a modern technology that is widely used in the production of difficult to cut conductive materials. The basic problem of EDM is the stochastic nature of electrical discharges. The optimal selection of machining parameters to achieve micron surface [...] Read more.
Electrical discharge machining (EDM) is a modern technology that is widely used in the production of difficult to cut conductive materials. The basic problem of EDM is the stochastic nature of electrical discharges. The optimal selection of machining parameters to achieve micron surface roughness and the recast layer with the maximal possible value of the material removal rate (MRR) is quite challenging. In this paper, we performed an analytical and experimental investigation of the influence of the EDM parameters: Surface integrity and MRR. Response surface methodology (RSM) was used to build empirical models on the influence of the discharge current I, pulse time ton, and the time interval toff, on the surface roughness (Sa), the thickness of the white layer (WL), and the MRR, during the machining of tool steel 55NiCrMoV7. The surface and subsurface integrity were evaluated using an optical microscope and a scanning profilometer. Analysis of variance (ANOVA) was used to establish the statistical significance parameters. The calculated contribution indicated that the discharge current had the most influence (over the 50%) on the Sa, WL, and MRR, followed by the discharge time. The multi-response optimization was carried out using the desirability function for the three cases of EDM: Finishing, semi-finishing, and roughing. The confirmation test showed that maximal errors between the predicted and the obtained values did not exceed 6%. Full article
(This article belongs to the Special Issue Product/Process Fingerprint in Micro Manufacturing)
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Open AccessArticle
Investigation of Product and Process Fingerprints for Fast Quality Assurance in Injection Molding of Micro-Structured Components
Micromachines 2018, 9(12), 661; https://doi.org/10.3390/mi9120661
Received: 30 October 2018 / Revised: 12 December 2018 / Accepted: 13 December 2018 / Published: 15 December 2018
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Abstract
Injection molding is increasingly gaining favor in the manufacturing of polymer components since it can ensure a cost-efficient production with short cycle times. To ensure the quality of the finished parts and the stability of the process, it is essential to perform frequent [...] Read more.
Injection molding is increasingly gaining favor in the manufacturing of polymer components since it can ensure a cost-efficient production with short cycle times. To ensure the quality of the finished parts and the stability of the process, it is essential to perform frequent metrological inspections. In contrast to the short cycle time of injection molding itself, a metrological quality control can require a significant amount of time and the late detection of a problem may then result in increased wastage. This paper presents an alternative approach to process monitoring and the quality control of injection molded parts with the concept of “Product and Process Fingerprints” that use direct and indirect quality indicators extracted from part quality data in-mold and machine processed data. The proposed approach is based on the concept of product and process fingerprints in the form of calculated indices that are correlated to the quality of the molded parts. A statistically designed set of experiments was undertaken to map the experimental space and quantify the replication of micro-features depending on their position and on combinations of processing parameters with their main effects to discover to what extent the effects of process variation were dependent on feature shape, size, and position. The results show that a number of product and process fingerprints correlate well with the quality of the micro features of the manufactured part depending on their geometry and location and can be used as indirect indicators of part quality. The concept can, thus, support the creation of a rapid quality monitoring system that has the potential to decrease the use of off-line, time-consuming, and detailed metrology for part approval and can thus act as an early warning system during manufacturing. Full article
(This article belongs to the Special Issue Product/Process Fingerprint in Micro Manufacturing)
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Open AccessArticle
Manufacturing Signatures of Injection Molding and Injection Compression Molding for Micro-Structured Polymer Fresnel Lens Production
Micromachines 2018, 9(12), 653; https://doi.org/10.3390/mi9120653
Received: 18 September 2018 / Revised: 2 December 2018 / Accepted: 7 December 2018 / Published: 10 December 2018
Cited by 1 | PDF Full-text (14529 KB) | HTML Full-text | XML Full-text
Abstract
Injection compression molding (ICM) provides enhanced optical performances of molded polymer optics in terms of birefringence and transmission of light compared to Injection molding (IM). Nevertheless, ICM requires case-dedicated process optimization to ensure that the required high accuracy geometrical replication is achieved, particularly [...] Read more.
Injection compression molding (ICM) provides enhanced optical performances of molded polymer optics in terms of birefringence and transmission of light compared to Injection molding (IM). Nevertheless, ICM requires case-dedicated process optimization to ensure that the required high accuracy geometrical replication is achieved, particularly especially in the case of surface micro-features. In this study, two factorial designs of experiments (DOE) were carried out to investigate the replication capability of IM and ICM on a micro structured Fresnel lens. A laser scanning confocal microscope was employed for the quality control of the optical components. Thus, a detailed uncertainty budget was established for the dimensional measurements of the replicated Fresnel lenses, considering specifically peak-to-valley (PV) step height and the pitch of the grooves. Additional monitoring of injection pressure allowed for the definition of a manufacturing signature, namely, the process fingerprint for the evaluation of the replication fidelity under different process conditions. Moreover, considerations on the warpage of parts were related to a manufacturing signature of the molding processes. At last, the global part mass average and standard deviation were measured to correlate local geometrical replication performances with global part quality trends. Full article
(This article belongs to the Special Issue Product/Process Fingerprint in Micro Manufacturing)
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Open AccessArticle
Generation of Color Images by Utilizing a Single Composite Diffractive Optical Element
Micromachines 2018, 9(10), 508; https://doi.org/10.3390/mi9100508
Received: 30 August 2018 / Revised: 4 October 2018 / Accepted: 4 October 2018 / Published: 9 October 2018
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Abstract
This paper presents an approach that is capable of producing a color image using a single composite diffractive optical element (CDOE). In this approach, the imaging function of a DOE and the spectral deflection characteristics of a grating were combined together to obtain [...] Read more.
This paper presents an approach that is capable of producing a color image using a single composite diffractive optical element (CDOE). In this approach, the imaging function of a DOE and the spectral deflection characteristics of a grating were combined together to obtain a color image at a certain position. The DOE was designed specially to image the red, green, and blue lights at the same distance along an optical axis, and the grating was designed to overlay the images to an off-axis position. We report the details of the design process of the DOE and the grating, and the relationship between the various parameters of the CDOE. Following the design and numerical simulations, a CDOE was fabricated, and imaging experiments were carried out. Both the numerical simulations and the experimental verifications demonstrated a successful operation of this new approach. As a platform based on coaxial illumination and off-axis imaging, this system is featured with simple structures and no cross-talk of the light fields, which has huge potentials in applications such as holographic imaging. Full article
(This article belongs to the Special Issue Product/Process Fingerprint in Micro Manufacturing)
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Open AccessArticle
One-Dimensional Control System for a Linear Motor of a Two-Dimensional Nanopositioning Stage Using Commercial Control Hardware
Micromachines 2018, 9(9), 421; https://doi.org/10.3390/mi9090421
Received: 16 July 2018 / Revised: 14 August 2018 / Accepted: 21 August 2018 / Published: 22 August 2018
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Abstract
A two-dimensional (2D) nanopositioning platform stage (NanoPla) is in development at the University of Zaragoza. To provide a long travel range, the actuators of the NanoPla are four Halbach linear motors. These motors present many advantages in precision engineering, and they are custom [...] Read more.
A two-dimensional (2D) nanopositioning platform stage (NanoPla) is in development at the University of Zaragoza. To provide a long travel range, the actuators of the NanoPla are four Halbach linear motors. These motors present many advantages in precision engineering, and they are custom made for this application. In this work, a one-dimensional (1D) control strategy for positioning a Halbach linear motor has been developed, implemented, and experimentally validated. The chosen control hardware is a commercial Digital Motor Control (DMC) Kit from Texas Instruments that has been designed to control the torque or the rotational speed of rotative motors. Using a commercial control hardware facilitates the applicability of the developed control system. Nevertheless, it constrains the design, which needs to be adapted to the hardware and optimized. Firstly, a dynamic characterization of the linear motor has been performed. By leveraging the dynamic properties of the motor, a sensorless controller is proposed. Then, a closed-loop control strategy is developed. Finally, this control strategy is implemented in the control hardware. It was verified that the control system achieves the working requirements of the NanoPla. It is able to work in a range of 50 mm and perform a minimum incremental motion of 1 μm. Full article
(This article belongs to the Special Issue Product/Process Fingerprint in Micro Manufacturing)
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Open AccessArticle
Micro-Injection Moulding In-Line Quality Assurance Based on Product and Process Fingerprints
Micromachines 2018, 9(6), 293; https://doi.org/10.3390/mi9060293
Received: 15 May 2018 / Revised: 31 May 2018 / Accepted: 4 June 2018 / Published: 11 June 2018
Cited by 1 | PDF Full-text (7921 KB) | HTML Full-text | XML Full-text
Abstract
Micro-injection moulding (μIM) is a replication-based process enabling the cost-effective production of complex and net-shaped miniaturized plastic components. The micro-scaled size of such parts poses great challenges in assessing their dimensional quality and often leads to time-consuming and unprofitable off-line measurement procedures. In [...] Read more.
Micro-injection moulding (μIM) is a replication-based process enabling the cost-effective production of complex and net-shaped miniaturized plastic components. The micro-scaled size of such parts poses great challenges in assessing their dimensional quality and often leads to time-consuming and unprofitable off-line measurement procedures. In this work, the authors proposed a novel method to verify the quality of a three-dimensional micro moulded component (nominal volume equal to 0.07 mm3) based on the combination of optical micro metrology and injection moulding process monitoring. The most significant dimensional features of the micro part were measured using a focus variation microscope. Their dependency on the variation of µIM process parameters was studied with a Design of Experiments (DoE) statistical approach. A correlation study allowed the identification of the product fingerprint, i.e., the dimensional characteristic that was most linked to the overall part quality and critical for product functionality. Injection pressure and velocity curves were recorded during each moulding cycle to identify the process fingerprint, i.e., the most sensitive and quality-related process indicator. The results of the study showed that the dimensional quality of the micro component could be effectively controlled in-line by combining the two fingerprints, thus opening the door for future µIM in-line process optimization and quality assessment. Full article
(This article belongs to the Special Issue Product/Process Fingerprint in Micro Manufacturing)
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Micromachines EISSN 2072-666X Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
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