Design Considerations for Glass

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Information about Design Considerations for Glass

Published on January 9, 2008

Author: Sibilla



IES ALC NOVEMBER 2007:  IES ALC NOVEMBER 2007 Design Considerations For Glass Lenses Used in Airfield and Obstruction Lighting Presented By: Christopher Michael Kopp Glass, Inc Objective:  Objective Provide practical tips to optimize lens design & economics Presentation Overview:  Presentation Overview Introduction Manufacturing Process Tooling Design Glass Lens Design Considerations Chromaticity/Color Lens Design Conclusion Introduction:  Introduction Presentation will be focused on molded glass lenses for the aerospace industry. Borosilicate glass is the predominate glass type used for aerospace applications. Characteristics of Borosilicate Glass:  Characteristics of Borosilicate Glass Mechanically Strong Thermal Shock Resistant (Low thermal expansion, 37x10-7 to 43x10-7 typical) Impact Resistant Scratch / Diffusion Resistant Corrosion & Chemical Resistant Stable Color Manufacturing Process:  Manufacturing Process Pot Melted Glass Fits Aviation Market Flexible batch process Low to moderate volume capability Flexibility for size & colors Custom compositions Manufacturing Process:  Manufacturing Process Mix batch  Load pot (batch & cullet)  Melt glass  Gather/mold  Anneal  Temper/finish (optional)  Inspection (quality, color, photometric) Ship Tooling Design:  Tooling design is a critical step in the manufacturing process Manufacturability Ability to meet tight tolerances Impacts economics (tooling cost & piece price) Minor tooling design adjustments are not uncommon after first article sample production Tooling Design Tooling Design:  Molds Block Hinged or Hub/shell Blow Multiple cavity Overflow Materials Cast iron, stainless, tool steel, other Tooling Design Glass Lens Design Considerations:  Chromaticity / Color Glass Lens Design Considerations Chromaticity/Color:  Chromaticity/Color Light Absorption, Reflection & Transmission Light Source Drives Color Selecting the Right Glass Filter (composition) Custom Compositions Chromaticity/Color:  Chromaticity/Color Transmission ~92% for clear glass Chromaticity/Color:  Chromaticity/Color Chromaticity/Color:  Chromaticity/Color Aviation Red Filter with Different Light Sources Chromaticity/Color :  Chromaticity/Color Incandescent LED White Y Value .3219 .3392 Transmission 24% 13% Meet Aviation Color Spec.? Yes No Aviation Red Filter with Different Light Sources Custom Composition Case Study:  Custom Composition Case Study Project Convert incandescent light source to LED Maintain aviation color and photometric specifications. Issues Blue outer lens is required for daylight recognition Existing filter (dome) did not meet minimum transmission requirements with new LED Solution Develop a custom composition that Shifted the peak transmission in line with the dominant wavelength of the LED Lighten the color of the glass to maximize transmission Case Study: Custom Glass Composition For LED Application:  Case Study: Custom Glass Composition For LED Application Peak transmission point of standard aviation blue filter does not line up with LED Custom Glass: shifted peak and lightened color resulting in greater than 80 percent transmission Lens Design:  Lens Design Size/Weight Shape Thickness Tolerances Anneal/Temper Aesthetics/Quality Selected Design Issues: Lens Design:  Lens Design Typical Min./Max. dimensions on molded parts Diameter 0.025” to 24” Height 15” (taller possible) Thickness 0.040” to 0.600” (thicker possible) Size may impact process flexibility and/or quality Multiple pots/gathers Dimensional tolerances Cosmetic / quality Size/Weight: Lens Design:  Lens Design It’s all about glass flow! Long-narrow & tall parts are difficult to mfg. Large lenses difficult to meet flatness, contour, and aesthetic requirements Difficult shapes can be manufactured, but the design drives up the cost for tooling & lens Shape: Lens Design:  Lens Design Typical thickness on an airfield lens is 0.200”-0.400” range depending on the size, shape, use Thicker or thinner lenses can be made Tooling design can impact thickness/economics Thickness: Lens Design:  Lens Design Economics can be impacted significantly by design Manufacturability can sometimes become an issue Slight design or tolerance changes can often reduce cost. Work with your glass supplier during the early design phase of your project to optimize design/economics Overview: Tolerances:  Tolerances Design tolerances are critical for Manufacturability Economics Tooling design is key for striking the optimal balance Meeting design tolerances Lowest possible economics Tolerances:  Tolerances Draft angle Thickness Flange Wall Dome Radii Diameter Flatness Contour Steps Anneal / Temper:  Anneal / Temper Annealed borosilicate is good for thermal shock in excess of 100oC (MIL Spec. 7989) Tempering provides a compression layer to the outside surfaces of the glass Tempering will improve thermal shock and impact resistance. Anneal / Temper:  Anneal / Temper Process can generate losses Common design challenges for annealing/tempering Too thick = tough to anneal Glass too thin = tough to temper (chemical temper may be an option) Large thickness variation Deep valleys (prismatic design) Anneal / Temper:  Anneal / Temper Quality / Aesthetics:  Quality / Aesthetics Cosmetic and other imperfections are inherent in pot melted / hand molded glass Requirements for aesthetics that exceed fitness for use criteria will drive up cost Educate your customer (refer to Mil-C-7989) Quality / Aesthetics:  Quality / Aesthetics Dimensional Defects Not meeting print dimensions Not filled / too heavy Thickness Press through, over, up Out of shape Structural Defects Check/cracks/crizzle Chips (size dependent) Heavy cords Fractured stones Other Cosmetic Defects Seed lines Wrinkles/settle wave Shear marks Pits Imbedded seeds / blisters Cords (light to medium) Laps Scale Haze & orange peel Conclusions:  Conclusions Right glass formulation Right lens design (for manufacturability & photometrics) Right tooling design Manufacturing expertise Involve your glass supplier in the early design phase of your projects Critical Factors for Success:

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