Nonisothermal glass molding for the cost-efficient production of precision freeform optics

Vu, Anh-Tuan; Kreilkamp, Holger; Dambon, Olaf; Klocke, Fritz

doi:10.1117/1.oe.55.7.071207

Cited by 29 publications

(28 citation statements)

References 11 publications

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“…Over last few years, glass molding has become a key replication‐based technology in the satisfaction of such ever‐increasing demands from today's photonics market. In fact, while precision glass molding (PGM) enables the fabrication of ultraprecision optics for high‐end applications at intermediate volumes, nonisothermal glass molding (NGM) recently promises a cost‐efficient and large volume production of complex‐shaped optics . Such advanced technologies, however, usually require elaborated process chains, ranging from optical and mold designs, simulation, and mold manufacturing down to the actual molding process as well as the assembly and qualification of the optical systems.…”

Section: Introductionmentioning

confidence: 99%

Experimental investigation of contact heat transfer coefficients in nonisothermal glass molding by infrared thermography

Liu

Grunwald

et al. 2018

J Am Ceram Soc

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Nonisothermal glass molding has recently become a promising technology solution for the cost‐efficient production of complex precision glass optical components. During the molding process, the glass temperature and its temperature distribution have crucial effects on the accuracy of molded optics. In nonisothermal molding, the glass temperature is greatly influenced by thermal contact conductance because there is a large temperature difference between the glass and mold parts. Though widely agreed to be varied during the molding process, the contact conductance was usually assumed as constant coefficients in most early works without sufficient experimental justifications. This paper presents an experiment approach to determine the thermal contact coefficient derived from transient temperature measurements by using infrared thermographic camera. The transient method demonstrates a beneficially short processing time and the adequate measurement at desirable molding temperature without glass sticking. Particularly, this method promises the avoidance of the overestimated contact coefficients derived from steady‐state approach due to the viscoelastic deformation of glass during the inevitably long period of holding force. Based on this method, the dependency of thermal contact conductance on mold surface roughness, contact pressure, and interfacial temperature ranging from slightly below‐to‐above glass transition temperature was investigated. The results reveal the dominance of interfacial temperature on the contact conductance while the linear pressure‐dependent conductance with an identical slope observed for all roughness and mold temperatures. The accurate determination of the contact heat transfer coefficients will eventually improve the predictions of the form accuracy, the optical properties, and possible defects such as chill ripples or glass breakage of molded lenses by the nonisothermal glass molding process.

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Section: Introductionmentioning

confidence: 99%

Experimental investigation of contact heat transfer coefficients in nonisothermal glass molding by infrared thermography

Liu

Grunwald

et al. 2018

J Am Ceram Soc

Self Cite

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“…As shown in Figure A, the temperature of the glass reaches about 576.5°C at t = 1 second, which is 6.5°C above its initial temperature. This temperature rise of the glass, as a direct representation of the ultrasonic thermal effect, will exert both real‐time and final impacts on the molding process, which has been demonstrated in the nonisothermal glass molding process (NGMP) . Meanwhile, it is noted from Figure B that the strain of the glass outside the mold V‐grooves is larger than the strain inside.…”

Section: Numerical Simulation Of Ugmpmentioning

confidence: 65%

Mechanism study on microformability of optical glass in ultrasonic‐assisted molding process

Luo

Nguyen

et al. 2018

Int J of Appl Glass Sci

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Ultrasonic‐assisted glass molding process (UGMP) has gained a promising start in microptics fabrication in recent years. To further understand the microforming process and comprehensively evaluate the microformability of the glass in UGMP, theoretical considerations and numerical simulations are performed in this study. A generalized dynamic viscoelastic model of glass in UGMP is first reformulated based on the ultrasonic thermo‐mechanical effects. Correspondingly, a multiphysics numerical model of UGMP is developed to dynamically observe the thermo‐mechanical rheological behaviors of the L‐BAL42 glass inside the microscale mold cavities. The stress distributions and deformation features of the formed micro‐V‐grooves in different molding processes are further employed to fully investigate the ultrasonic mechanical and thermal effects on glass molding. The results show that, as a product of the combined ultrasonic mechanical and thermal effects, the filling rate of the glass in UGMP is observably increased and homogenized, while its maximum forming stress is reduced by 57.6% compared with the conventional molding process (GMP). It is also found that, the ultrasonic thermal effect is dominant in lowering the forming stress of the glass, while the ultrasonic mechanical effect plays a leading role in homogenizing the filling rate of the glass. This study will provide both theoretical and technical supports for high‐efficiency and high‐precision fabrication of surface‐relief microptical elements.

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“…Two relatively rough surfaces manufactured with rough ( R a = 0.47 µm‐mold 1) and fine grinding ( R a = 0.16 µm ‐mold 2) are exhibited in Figure A,B, respectively. In addition, ultra‐precision mold surface finishes machined by ultrasonic‐assisted diamond turning, typically used for the mold manufacturing in nonisothermal glass molding, are provided in Figure C,D. Figure D exhibits the newly machined surface after the diamond turning ( R a = 6 nm‐mold 4).…”

Section: Methodsmentioning

confidence: 99%

“…To quantify pressure‐dependent thermal contact conductance, experiments are performed with applied loads ranging from 2 to 20 MPa. Such pressure range is equivalent to the pressing forces commonly utilized in glass‐forming processes . The glass pressing process contains two sequential steps‐the position control and force control.…”

Section: Methodsmentioning

confidence: 99%

Numerical and experimental determinations of contact heat transfer coefficients in nonisothermal glass molding

Helmig

et al. 2019

J Am Ceram Soc

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Heat transfer at the interfacial contact is a dominant factor in the thermal behavior of glass during nonisothermal glass molding process. Recent research is developing reliable numerical approaches to quantify contact heat transfer coefficients. In most previous studies, however, both theoretical and numerical models of thermal contact conductance in glass molding attempted to investigate this factor by either omitting surface topography or simplifying the nature of contact surfaces. In fact, the determination of the contact heat transfer coefficient demands a detailed characterization of the contact interface including the surface topography and the thermomechanical behavior of the contact pair. This paper introduces a numerical approach to quantify the contact heat transfer by means of a microscale simulation at the glass‐mold interface. The simulation successfully incorporates modeling of the thermomechanical behaviors and the three‐dimensional topographies from actual surface measurements of the contact pair. The presented numerical model enables the derivation of contact heat transfer coefficients from various contact pressures and surface finishes. Numerical predictions of these coefficients are validated by transient contact heat transfer experiments using infrared thermography to verify the model.

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Nonisothermal glass molding for the cost-efficient production of precision freeform optics

Cited by 29 publications

References 11 publications

Experimental investigation of contact heat transfer coefficients in nonisothermal glass molding by infrared thermography

Experimental investigation of contact heat transfer coefficients in nonisothermal glass molding by infrared thermography

Mechanism study on microformability of optical glass in ultrasonic‐assisted molding process

Numerical and experimental determinations of contact heat transfer coefficients in nonisothermal glass molding

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