Enhanced redundancy packages have been agreed for 296 workers at the Alcoa aluminium plant in Swansea, say unions.
The Alcoa plant opened in 1968 and once employed more than 1,400
The US firm announced at the end of November that the plant would close as part of its Europe-wide restructuring.
Attempts to identify new business and come up with a rescue plan were unable to find a viable proposal.
Workers on Friday hold a farewell drinks event at a local rugby club to share nearly 40 years of memories of the plant, which closes on 6 April.
There is a phased shutdown of the plant, which was bought in 1968 and which produces aluminium for the drinks container industry.
Workers organised Friday's farewell event at Waunarlwydd Rugby Club, as a final opportunity when all would be together before the closure.
Paul Howard, chairman of the site's Transport and General Workers Union branch, has worked at the plant for 23 years.
He said: "It's been a great industry for Waunarlwydd, it was the last heavy industry in area.
The plant produces aluminium for the drinks container industry
"The T&G, with Amicus, have ironed out the best possible package achieveable for our members, making sure they can get used to the outside world.
"We're having a good get-together and hopefully all the lads will realise it's time to start all over again.
"It's part of your life when you are working somewehere for 20-odds years."
Alcoa has blamed rising energy, labour and materials costs for the "tough decision" to close the plant.
The Welsh Assembly Government has said the £2.5m given to Alcoa will have to be paid back if the factory closes.