How windshields are made

A windshield is two sheets of glass bent together on one mold, with a plastic layer baked between them.

stations: 8
things upstream: 62
raw sources: 20
steps from the ground: 8

The short version

A windshield is two curved sheets of glass bonded around a thin plastic layer. Flat glass is cut into outlines and the edges are ground. Both sheets are heated and sagged together over a mold so they share a curve. The sandwich is pressed and baked under pressure in an autoclave, so the layers cannot separate.

Cut glass to outline

Flat sheets of float glass are scored and snapped into the rough outline of a windshield. Two matching blanks are cut for each one.

Goes in
Window glass
Grind the edges smooth

Abrasive wheels round the cut edges so the blanks will not chip and can sit exactly together.
Print the black border

A ceramic-based black band is printed around the edge. It hides the glue line and shields the adhesive from sunlight, and it fades into the clear glass in a pattern of dots to ease thermal stress.

Goes in
Ink
Sag two sheets together

The two blanks lie stacked on a curved frame as they pass through a furnace. They soften and slump together into the same curve, so they fit each other exactly.
Sandwich in the plastic layer

The sheets are separated, a thin film of polyvinyl butyral plastic is laid between them, and they are put back together. The film, which is clear and tough, holds the glass together if it breaks.

Goes in
Polyvinyl butyral
Roll out the air

Rollers or vacuum bags squeeze air pockets out of the sandwich. The assembly is heated lightly so that the film starts to bond.
Bake it in an autoclave

Heat and high pressure in an autoclave finish the bond. The glass and film then behave as one piece.
Glue it into the opening

At the car plant a bead of urethane adhesive is laid around the frame and the glass is pressed in. A bonded windshield adds rigidity to the body.

Goes in
Adhesive

End of the lineWindshield Next it goes into car, electric car.

Worth repeating

The plastic layer in laminated glass can absorb nearly all of the sun's UV-B light, and most UV-A as well.
A car's laminated glass panel is around 6.5 mm thick, and airplane glass is about three times thicker.
A broken windshield cracks in a spider-web pattern instead of dropping sharp shards.