The 41-year-old from Tibshelf, Derbyshire, who does not want to be named, lost the end of his little finger and his ring finger to his second joint, as well as suffering burns, following the incident at Sapa Profiles UK on 18 March 2014.
He was off work for eight months, after which he returned to the company in a different role.
Chesterfield Magistrates' Court heard that the man was working to unblock a machine that pushes out aluminium to produce a manufactured piece. Solid aluminium is fed into the machine and heated to around 450 degrees, to soften it, so it can be extruded into a die, which will create the final item.
An investigation by the Health and Safety Executive (HSE) found that the interlocks on the machine, did not fully isolate the power when opened.
Access inside the press was required by employees to remove blockages from two points in the machine where they commonly occurred. This was a two person job.
On the 18 March 2014, the injured person and another person entered the machine to remove one of these blockages. They accessed the machine through separate gates. The second person left the machine, closing his gate, leaving the injured person inside with his gate open. Unfortunately, having only the one gate open didn't fully isolate the machine.
So when the machine was restarted it allowed the loading clamps to operate whilst the injured person was inside the danger zone. His hand was trapped, resulting in contact burns and serious finger injuries.
The company had failed to carry out a risk assessment to the machine prior to making these crucial changes.
Sapa Profiles UK, of Mansfield Road, Tibshelf, pleaded guilty to breaching regulation 3(1) of the Management of Health and Safety at Work Regulations 1999 and regulation 11(1) of the Provision and Use of Work Equipment Regulations 1998.
HSE inspector Lindsay Bentley said: "Sapa Profiles UK Ltd allowed access to the dangerous parts of the press, including the loading arms and clamps that injured the worker.
"Furthermore, the company's risk assessment was not suitable and sufficient to ensure that the relevant dangerous parts of the Press would stop before a person entered the Press. Following the incident it took just 10 minutes for these interlocks to be reprogrammed.
"It should not have been possible to access a danger zone without the machine being safely isolated. It meant operators who had to frequently unblock the machine were routinely exposed to unnecessary risk. "