Bending as a key factor in windshield manufacturing

Juha Karisola - Windshield bending technologies have developed since the first commercial pieces of glass were bent at the end of the 1940s.

The simple one-directional bending method didn’t require much from technology.  Yet the first double curves introduced in the late 1950s started an evolution that continues today. Although there are many sub-processes involved, the key technique for optical quality and shape accuracy is the bending process. Without perfect bending, the whole process fails. There are three bending processes that are in use today: gravity bending, press bending and press-assisted bending.

Gravity bending

Gravity bending is a cost-effective process to create any shapes, even deeper sags, wrap-around corners and also when a wider variety of coating options are needed. Gravity bending is best used for short series because many different types of molds can be used simultaneously in the process. This makes it the best bending process for automotive replacement glass manufacturers (AGRs) as only one mold is required for short runs.

Earlier, shaping was difficult because heat came only from above. Now with the latest technology, focused overall heating with power regulation and double-actuated molds with triggering devices allow much more precise shape control resulting in better end quality.

Press bending

From a process point of view, press-based bending systems are simple and don’t require focused heating or complicated molds. There are only two phases in the process: heating the glass in a furnace and using molds to press it into the desired shape. This bending process gives very high output, good repeatability and tight tolerances.

The construction is relative complicated and requires expensive shape-specific tooling.  Due to its high initial investment and tooling cost, it is applicable only for OEMs who need very high-volume production.

Press-assisted bending

The press-assisted system gives high output, good repeatability and tight tolerances, which makes it suitable for long-series OEM production. This bending process combines the benefits of both gravity bending and press bending. When combined with a gravity-based system, the furnace can be used either as a gravity bender or press bender. This makes it the perfect tool for medium-scale operations requiring operational flexibility and long-series OEM windshield production.

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