Definition
The period after adhesive has been applied to the surfaces being bonded but before those surfaces are brought together and clamped. During this time the parts remain apart and exposed to the air, allowing solvents to evaporate or the adhesive to reach the correct tack before mating.
Plain English
The waiting time after you spread the glue but before you press the two parts together, while the glued surfaces are still out in the open.
Context Anchor
Seen in aircraft repair work that uses adhesives, especially when bonding panels, skins, or composite parts.
Derivation
Open' here means the glued surfaces are still open to the air — not yet closed against each other. 'Assembly' refers to putting the parts together. So 'open assembly time' is literally the time the assembly is still open.
Why Pilots Care
Adhesive bonds only reach full strength when the manufacturer's open and closed assembly times are respected. Mating parts too early traps solvents; waiting too long lets the adhesive skin over and fail to bond. Either error can cause a structural repair to come apart in service.
Analogy
It is like applying glue to two pieces of wood and waiting too long before pressing them together; after a certain point, the glue may no longer hold as intended.
Intuition Check
Open does not mean the repair can be left unfinished indefinitely. Here, open means the adhesive-coated surfaces are still separated and exposed, and the time limit is already running.
Example Sentence 1
The technician spread the adhesive on both surfaces and observed the open assembly time listed on the product data sheet before joining the parts.
Example Sentence 2
If the open assembly time is exceeded, the repair must be disassembled, cleaned, and started over to ensure a reliable bond.