Surface waviness is a broad, low-frequency distortion rather than a fine texture. It may be visible only in reflected light or may affect fit and panel flatness.
Uneven sheet temperature and sag can establish waves before forming. Gauge bands, early tool contact, inconsistent mold temperature, differential cooling, and low panel stiffness can preserve or amplify them. A smooth glossy surface makes small deviations especially visible.
Corrective action
The sheet should be observed during heating and immediately before forming. If the wave exists before tool contact, oven balance, sheet quality, and support are involved. If it develops during cooling, mold temperature and structural stiffness should be examined.
A stable thermal field and uniform thickness are the first requirements. Large appearance panels may also need intentional curvature or backing support because a nominally flat thin shell is highly sensitive to small stress differences.