Which manufacturing method uses a master mold for every combo of power, base curve, and diameter?

Which manufacturing method uses a master mold for every combo of power, base curve, and diameter?

• A. Spin Casting
• B. Cast Molding
• C. Injection Molding
• D. Extrusion

Answer: (B)

Cast molding works by forming the lens shape directly in a mold that defines both surface curvatures and edge size. To achieve a specific prescription—meaning a particular back curve (base curve), front surface power, and edge diameter—you need mold surfaces that match those exact geometries. A master mold is created for that exact combination, and it is used to produce the corresponding mold cavities used for casting the lenses. Because each unique set of power, base curve, and diameter requires precise surface shapes, a dedicated master mold is required for every combination. Other methods don’t rely on a separate master mold for each prescription. Spin casting shapes the lens during spinning, and the optical power is adjusted more by processing conditions than by swapping in a new master mold. Injection molding uses mold cavities to define geometry, but it’s not inherently organized around a master mold per power/base-curve/diameter combination in the same way cast molding is.

Cast molding works by forming the lens shape directly in a mold that defines both surface curvatures and edge size. To achieve a specific prescription—meaning a particular back curve (base curve), front surface power, and edge diameter—you need mold surfaces that match those exact geometries. A master mold is created for that exact combination, and it is used to produce the corresponding mold cavities used for casting the lenses. Because each unique set of power, base curve, and diameter requires precise surface shapes, a dedicated master mold is required for every combination.

Other methods don’t rely on a separate master mold for each prescription. Spin casting shapes the lens during spinning, and the optical power is adjusted more by processing conditions than by swapping in a new master mold. Injection molding uses mold cavities to define geometry, but it’s not inherently organized around a master mold per power/base-curve/diameter combination in the same way cast molding is.