How many annealing cycles does an automotive headlight lens require?

In automotive headlight manufacturing, only the lens (the polycarbonate/PC light-distributing cover) undergoes a single annealing process;
other components (such as the reflector and housing) do not require this treatment.
During injection molding, the polycarbonate (PC) lens develops residual internal stress due to uneven cooling, making it prone to cracking or warping under temperature fluctuations or impact. Annealing is crucial for stress relief: immediately after molding, the lens enters a tunnel oven for hot-air circulation at 105–120°C for 10–120 minutes (1–2 hours for precision lenses; 25–60 minutes for standard lenses), followed by slow cooling to below 60°C to ensure optical uniformity and durability.
Repair scenarios (addressing yellowing or scratches) do not require annealing: after sanding and polishing, a UV coating is applied and cured via heating (at 60–80°C, which is a curing process, not annealing); a second annealing cycle would damage the original UV-resistant coating and accelerate aging.
A single annealing cycle is performed during original manufacturing (specific to the lens); this process does not need to be repeated during routine use or repairs.