Molybdenum rods: The core material of precision optical glass molding molds. Why are they crucial for the production of aspherical lenses?
In the field of manufacturing high-end optical lenses, especially in smartphones, vehicle cameras, medical endoscopes, and top camera lenses, aspherical lenses have become the core component for enhancing image quality, simplifying lens structures, and reducing size. And the cutting-edge manufacturing process for these highly precise aspherical lenses - the Precision Glass Molding (PGM) technology - its success or failure largely depends on the performance of a key material: molybdenum rods.
Molybdenum rods can be used to manufacture or repair the core molds in the glass molding production line. These molds directly determine the shape accuracy and surface quality of the lenses.
The stringent requirements for mold materials in glass molding process
The precision glass molding process takes place in an oxygen-free environment. The glass preform is heated above its transformation temperature to make it soft, and then a super-precise mold is used to apply pressure, forming the desired optical component in one step. After that, it is cooled and demolded. The entire process imposes almost cruel requirements on the mold materials:
The extremely high temperature resistance and hardness of the molybdenum rods: The molds must withstand tremendous pressure at temperatures ranging from 500°C to 800°C, while maintaining their shape and the mirror-like smoothness, and preventing plastic deformation or collapse.
The extremely low thermal expansion coefficient (CTE) of molybdenum rods: From high-temperature molding to cooling and demolding, the thermal expansion coefficients of the mold and the glass must be highly matched. If the thermal expansion and contraction range of the mold is too large, it will cause stress, cracking or mold adhesion in the formed lenses, resulting in defective products. The thermal expansion coefficient of molybdenum rods is very close to that of many optical glasses, which is the key reason why it is irreplaceable.
The excellent high-temperature oxidation resistance and chemical inertness of the molybdenum rods: At high temperatures, the molybdenum molds do not undergo any chemical reactions with the glass materials, nor can they be wetted or adhered by the glass, thus ensuring perfect demolding and extremely high surface quality of the lenses (without the need for secondary polishing).
The high melting point (2623°C) and creep resistance of the molybdenum rods: Ensure that the mold does not soften or develop fatigue cracks during long-term repeated thermal cycles, guaranteeing the stability of production and the lifespan of the mold.
From "molybdenum rods" to "precision molds": The transformation of cutting-edge processing
Powder metallurgy and forging: Usually, molybdenum powder is used to form the billet through powder metallurgy (PM), or through forging to refine the grains, eliminate internal defects, ensure the uniformity and isotropy of the material, which is the basis for high-precision shaping.
Ultra-precision machining: Using a diamond lathe, the molybdenum material is subjected to ultra-precise cutting, resulting in the machining of the mold surface to a shape accuracy of nanometer level and a surface roughness of sub-nanometer level (Ra < 1 nm). The mold surface directly becomes the "negative shape" of the future lens surface.
Surface coating treatment: To enhance wear resistance, oxidation resistance and to completely prevent mold adhesion, a layer of precious metal coating (such as iridium Ir, platinum Pt or tantalum nitride TaN, etc.) is typically deposited on the surface of the molybdenum molds. This coating also requires extremely high machining accuracy.
How does the molybdenum rod mold directly achieve outstanding optical performance?
Realizing complex aspheric designs: The ultra-precise molds made of molybdenum rods can be used to directly shape complex aspheric, free-form surfaces, even micro-structure arrays in a single process. This is because traditional grinding and polishing techniques are inefficient and costly.
Ensure extremely high surface shape accuracy and consistency: The high-temperature stability and low thermal expansion characteristics of the molybdenum molds ensure that after millions of injection molding cycles, every lens produced has exactly the same optical performance, and the batch production yield is extremely high.
Eliminating the polishing process and reducing production costs: The surface of the molded lenses has reached the optical level, eliminating the need for subsequent grinding and polishing. This significantly lowers the manufacturing costs of complex-shaped lenses, enabling the large-scale application of aspherical lenses.
Mosten Alloy can produce molybdenum rod, molybdenum target, molybdenum sheet, molybdenum tube, molybdenum foil, molybdenum wire, molybdenum processing workpiece according to customer demand.
