Two-Station Embossing Process for Rapid Fabrication of Polymer Microstructures

2005 ◽  
Author(s):  
Donggang Yao ◽  
Allen Y. Yi ◽  
Lei Li ◽  
Pratapkumar Nagarajan
Keyword(s):  
Thermal Cycling ◽  
Elevated Temperatures ◽  
Polymeric Materials ◽  
Large Mass ◽  
Hot Embossing ◽  
Electrical Heating ◽  
Thermal Mass ◽  
Mold Surface ◽  
Cycle Times ◽  
Rapid Thermal Cycling

The hot embossing technique is becoming an increasingly important alternative to silicon-and glass-based microfabrication technologies. The advantage of hot embossing can be mainly attributed to the versatile properties and mass production capability of polymeric materials. However, because of the use of a large mass in thermal cycling, hot embossing is subject to substantially longer cycle times than those in traditional thermoplastic molding processes.1 The longer dwell time at elevated temperatures could further result in degradation of the embossing polymer, especially for thermally sensitive polymers. The problem exacerbates when thick polymer substrates are used. To address this problem, rapid thermal cycling of the tool is needed. One method for rapid thermal cycling is to employ a low-thermal-mass multilayer mold with electrical heating elements installed right beneath the mold surface.2 This method, however, is complex in nature and may be prone to problems caused by mismatching of thermal and mechanical properties between different layers.

Development and Testing of a Low-Cost Rapid-Cycle Hot Embossing System for Manufacturing Microscale Parts

2009 ◽  
Author(s):  
Melinda Hale ◽  
David E. Hardt
Keyword(s):  
Large Scale ◽  
Low Cost ◽  
Polymeric Materials ◽  
Hot Embossing ◽  
Capital Cost ◽  
Electrical Heating ◽  
Cycle Times ◽  
Capital Costs ◽  
Heating And Cooling ◽  
Order Of Magnitude

Hot embossing is an effective technology for replicating micro-scale features in polymeric materials, but large-scale adoption of this method is hindered by high capital costs and longer cycle times relative to other technologies. This paper details a hot embossing machine design strategy motivated by maximum production speed with minimal capital cost. Innovative design aspects include the choice of new ceramic substrate heaters for electrical heating, design of a moveable heat sink to minimize heat load during the heating cycle, and the careful design of the thermal elements to minimize the heating and cooling cycle times. The hot embossing equipment fabricated from this design has a capital cost estimated to be an order of magnitude less than currently available options. The minimum cycle time is two minutes, and microstructures are replicated within a maximum area of 25mm by 75mm. The hot embossing machine has been tested to characterize the process variability. Runs of polymethylmethacrylate (PMMA) parts manufactured using this equipment are measured to have submicron variation under a variety of processing conditions.

A Strategy for Rapid Thermal Cycling of Molds in Thermoplastic Processing

2006 ◽  
Vol 128 (4) ◽  
pp. 837-843 ◽  
Author(s):  
Donggang Yao ◽  
Pratapkumar Nagarajan ◽  
Lei Li ◽  
Allen Y. Yi
Keyword(s):  
Thermal Cycling ◽  
Rapid Heating ◽  
Thermal Contact ◽  
Experimental Studies ◽  
Thermal Response ◽  
Large Mass ◽  
Design Parameters ◽  
Thermal Mass ◽  
Mold Surface ◽  
Shell Mold

Thermal cycling of molds is frequently desired in thermoplastic processing. Thermal cycling of the entire mold with a large mass, however, requires an exceedingly long cycle time. A processing strategy for mold rapid heating and cooling, involving a thin-shell mold and two thermal stations (one hot and one cold), was investigated. Because of its low thermal mass, the shell mold can be rapidly heated and cooled through heat conduction by selectively contacting with the two stations. Numerical simulations were performed to study the effect of different design parameters, including thermal contact resistance, shell material, and shell thickness, on the thermal response at the mold surface. Experimental studies showed aluminum shell molds with a thickness of 1.4mm can be rapidly heated from room temperature to 200°C in about 3s using a hot station at 250°C. The method was used for thermal cycling of embossing tools. Surface microfeatures can be rapidly transferred from thin metallic stamps to polymer substrates with cycle times less than 10s.

scholarly journals Development of a Low-Cost, Rapid-Cycle Hot Embossing System for Microscale Parts

2008 ◽  
Author(s):  
Melinda Hale ◽  
David E. Hardt
Keyword(s):  
Cycle Time ◽  
Large Scale ◽  
Low Cost ◽  
Polymeric Materials ◽  
Hot Embossing ◽  
Capital Cost ◽  
Machine Design ◽  
Electrical Heating ◽  
Design System ◽  
Wide Range

Hot embossing is an effective technology for reproducing micro-scale features in polymeric materials, especially micron scale patterning. The equipment used for hot embossing to date is often research oriented, (intended to be flexible and provide a wide range of processing conditions), and a dedicated equipment industry has yet to develop. This paper details a hot embossing machine design strategy suitable for large-scale manufacturing. The design is motivated by capital cost reduction, right-size machine design, system simplicity, and production flexibility and scalability. Toward this end, a minimal number of components were used, commercially available off-the-shelf components were chosen where possible, system layout was designed to be modular, and system size was scaled for the intended products (in this case microfluidic devices). Innovative design aspects include the use of new ceramic substrate heaters for electrical heating, choice of a moveable heat sink to minimize heat load during the heating cycle, and the careful design of the thermal elements to minimize cycle time. The capital cost and the cost per part produced with this machine are estimated to be an order of magnitude less than currently available options. This design has a minimum cycle time of two minutes, and replicates microstructures within a 25mm by 75mm area.

Thermal shock resistance of Ti3SiC2 ceramic under extremely rapid thermal cycling

2021 ◽  
Vol 866 ◽  
pp. 158985
Author(s):  
Xiaojia Su ◽  
Yiwang Bao ◽  
Detian Wan ◽  
Haibin Zhang ◽  
Ludi Xu ◽  
...  
Keyword(s):  
Thermal Cycling ◽  
Thermal Shock ◽  
Thermal Shock Resistance ◽  
Shock Resistance ◽  
Rapid Thermal Cycling

Oxidation of Some Titanium Alloys in Air at Elevated Temperatures

2008 ◽  
Vol 595-598 ◽  
pp. 967-974 ◽  
Author(s):  
E. Godlewska ◽  
M. Mitoraj ◽  
B. Jajko
Keyword(s):  
Thermal Cycling ◽  
Titanium Alloys ◽  
Constant Temperature ◽  
Cross Sections ◽  
Elevated Temperatures ◽  
Mixed Oxides ◽  
Oxidation Mechanism ◽  
Testing Procedure ◽  
Oxidation Products ◽  
Outward Diffusion

This paper presents comparative studies on the performance of two titanium alloys (Ti- 6Al-1Mn, Ti-45.9Al-8Nb) in an oxidizing atmosphere at 700 oC and 800 oC. Testing procedure comprised thermogravimetric measurements at a constant temperature and in thermal cycling conditions (1-h and 20-h cycles at constant temperature followed by rapid cooling). The overall duration of the cyclic oxidation tests was up to 1000 hours. The oxidized specimens were analyzed in terms of chemical composition, phase composition, and morphology (SEM/EDS, TEM/EDS, XRD). The extent and forms of alloy degradation were evaluated on the basis of microscopic observation of specimen fractures and cross-sections. Selected specimens were examined by means of XPS, SIMS and GDS. Oxidation mechanism of Ti-46Al-8Nb was assessed a two-stage oxidation method using oxygen-18 and oxygen-16. Apparently, the oxidation of this alloy proceeded in several stages. According to XPS, already after quite short reaction time, the specimens were covered with a very thin oxide film, mainly composed of aluminum oxide (corundum). A thicker layer of titanium dioxide (rutile) developed underneath. These two layers were typical of the oxidation products formed on this alloy, even when tested in thermal cycling conditions. In general, the scale had a complex multilayer structure but it was thin and adherent. Under the continuous layer of titania, there was a fine-grained zone composed of mixed oxides. The alloy/scale interface was marked with niobium-rich precipitates embedded in a titanium-rich matrix. There were some indications of secondary processes occurring under the initial continuous oxide layers (e.g. characteristic layout of pores or voids). Thickness of inner scale layers clearly increased according to parabolic kinetics, while that of the outer compact layer (mainly TiO2) changed only slightly. The distribution of oxygen isotopes across the scale/alloy interface indicated two-way diffusion of the reacting species – oxygen inward and metals outward diffusion. Silicon deposited on Ti-6Al-1Mn alloy positively affected scale adhesion and remarkably reduced alloy degradation rate.

Modifiable Silicones for Harsh Environments

2011 ◽  
Vol 2011 (1) ◽  
pp. 000090-000098 ◽  
Author(s):  
Michelle Velderrain ◽  
Matthew Lindberg
Keyword(s):  
Elevated Temperatures ◽  
Electronic Devices ◽  
Polymeric Materials ◽  
Harsh Environments ◽  
Electrically Conductive ◽  
Polymeric Systems ◽  
Low Modulus ◽  
Conductive Fillers ◽  
Processing Techniques

Silicones have been used for decades in aerospace and other harsh environments where temperature extremes are common. As the level of sophistication increases for electronic devices to serve these industries where failure is not an option, the material supplier has to also be able to meet these needs. Silicones are polymeric materials composed primarily of repeating silicon and oxygen bonds, known as siloxanes, which can be optimized for various chemical and physical properties by incorporating different organic groups onto the silicon atom. Employing advanced processing techniques to the siloxane system can also greatly reduce mobile siloxane molecules to reduce contamination that can cause electronic failures during assembly or operation. Siloxane based polymeric systems are also unique polymers compared to standard organic based materials in that they have a large free volume that imparts a low modulus which absorbs stresses during thermal cycling as well as not degrading at continuous operating temperatures up to 250 C. They are also slightly polar which allows the incorporation of fillers to impart a variety of unique properties. Filler technology is also a rapidly growing enterprise where fillers with various particle sizes and shapes can be added to silicones to impart key properties such as maintaining electric conductivity at elevated temperatures. This paper will explain fundamentals of silicone chemistry and processing related to getting the optimal performance in harsh environments. A case study comparing two different electrically conductive fillers and how they can influence the electrical conductivity at elevated temperatures will be presented.

scholarly journals Thermal Contact Conductance-Based Thermal Behavior Analytical Model for a Hybrid Floor at Elevated Temperatures

Materials ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 4257 ◽  
Author(s):  
Min Jae Park ◽  
Jeong Ki Min ◽  
Jaehoon Bae ◽  
Young K. Ju
Keyword(s):  
Thermal Behavior ◽  
Elevated Temperatures ◽  
Heated Surface ◽  
Thermal Contact ◽  
Polymeric Materials ◽  
Steel Plates ◽  
Thermal Contact Conductance ◽  
Small Scale ◽  
Element Analysis ◽  
Contact Conductance

Hybrid floors infilled with polymeric materials between two steel plates were developed as a prefabricated floor system in the construction industry. However, the floor’s fire resistance performance has not been investigated. To evaluate this, fire tests suggested by the Korean Standards should be performed. As these tests are costly and time consuming, the number of variables were limited. However, many variables can be investigated in other ways such as furnace tests and finite element analysis (FEA) with less cost and time. In this study, furnace tests on heated surface areas smaller than 1 m2 were conducted to investigate the thermal behavior of the hybrid floor at elevated temperatures. To obtain the reliability of the proposed thermal behavior analytical (TBA) model, verifications were conducted by FEAs. Thermal contact conductance including interfacial thermal properties between two materials was adopted in the TBA model, and the values at elevated temperatures were suggested based on thermo-gravimetric analyses results and verified by FEA. Errors between the tests and TBA model indicated that the model was adequate in predicting the temperature distribution in small-scale hybrids. Furthermore, larger furnace tests and analysis results were compared to verify the TBA model’s application to different sized hybrid floors.

Solution Precipitation of CdSe Quantum Dots

1992 ◽  
Vol 283 ◽  
Author(s):  
Cherie R. Kagan ◽  
Michael J. Cima
Keyword(s):  
Quantum Dots ◽  
Elevated Temperatures ◽  
Heat Treating ◽  
Solution Temperature ◽  
Supersaturated Solution ◽  
Thermal Mass ◽  
Cdse Quantum Dots ◽  
Glass Film ◽  
Optical Absorbance ◽  
Fluorescence Measurements

ABSTRACTSynthesis of CdSe quantum dots with a high degree of monodispersity is achieved by nucleation from a supersaturated solution followed by growth to the desired particle size. The effects of temperature on the kinetic mechanisms of nucleation and growth were observed. A reaction vessel equipped with a low thermal mass internal heating element enabled controlled ramping of the solution temperature during the reaction. Nanocrystallite diameter is determined by the reaction time and the solution temperature during particle growth.A method was developed to fabricate ∼1μm thick glass films containing ∼3 vol% CdSe quantum dots. A sol was prepared by mixing a silica organosol with a nanocrystallite dispersion of CdSe and was applied to amorphous quartz substrates by spin-coating. The sols were dried at elevated temperatures in a nitrogen atmosphere. Optical absorbance and fluorescence measurements of the glass film were used to characterize the optical properties of the embedded nanocrystallites. Comparison of the excitonic absorbance of the quantum dot dispersion and the doped glass film shows that particle monodispersity is maintained upon incorporation into the dielectric matrix. Stokes shifts in the band-to-band fluorescence relative to the film absorbance were measured. Shifts in the wavelength of the excitonic absorbance and fluorescence were observed upon incorporation of the quantum dots into the glass film and upon heat treating the glass film to elevated temperatures.

Constant-Temperature Embossing of Amorphous Poly(Ethylene Terephthalate) Films

2007 ◽  
Author(s):  
Donggang Yao ◽  
Pratapkumar Nagarajan ◽  
K. R. T. Ramasubramani
Keyword(s):  
Thermal Cycling ◽  
Amorphous Phase ◽  
Constant Temperature ◽  
Ethylene Terephthalate ◽  
Mold Temperature ◽  
Cycle Times ◽  
Poly Ethylene Terephthalate ◽  
Micro Features ◽  
Poly Ethylene ◽  
Pet Film

In the standard hot embossing process for thermoplastic polymers, thermal cycling is needed in order to soften and subsequently cool and solidify the polymer. This thermal cycling, however, not only results in long cycle times but also deteriorates the quality of embossed features. A new embossing method based on slowly crystallizing polymers was investigated to eliminate thermal cycling. Poly(ethylene terephthalate) was used as a model system for demonstration. Due to its slow crystallization, amorphous PET film can be made by casting a PET melt onto a chill roll. The amorphous PET film was embossed at a constant temperature of 180°C for a period of time comparable to or longer than PET’s half-time of crystallization. During constant-temperature embossing, the film first liquefies, caused by rubber softening of the amorphous phase, and then solidifies, resulting from the crystallization of the amorphous phase. Since the embossed film is hardened under the constant mold temperature, no cooling is needed. Selected micro features, including circular microchannels and high aspect ratio rectangular microchannels, were successfully embossed using a total cycle time about 40 s.

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