The emergency services were called to the premises of Macalloy Ltd on Caxton Way in Dinnington at around 3.12pm on Friday afternoon.
It is believed that a 47-year-old man, who is from the Rawmarsh area Rotherham, was fatally injured when he became trapped in machinery.
The man is yet to be identified by police.
A post mortem examination, carried out on Tuesday at Sheffield’s Medico Legal Centre, revealed that the man had died from multiple internal injuries and that death had been instantaneous.
An inquest into his death is due to be opened by the coroner in the next few days.
A South Yorkshire Police spokesman said: “Meanwhile, police are continuing to conduct interviews with members of staff at the premises and are liaising with the Health and Safety Executive.”
A joint investigation between South Yorkshire Police and the Health and Safety Executive (HSE) began on Friday.
The premises was closed at the weekend while investigations continued.
A spokesman for the HSE confirmed it was supporting the ‘police led’ investigation into the incident, but was unable to comment further until all inquiries had been completed.
The company has declined to make any comment on the incident.
Macaolloy Ltd, which was formed in 1948, supplies threaded bar and cable systems for use on wind turbines and high rise buildings across the globe.
November 2006 saw the company relocate to its new headquarters office and factory complex at Dinnington.
The purpose built factory enabled the company to carry on supplying its products worldwide, and to enter new markets throughout the world.
A year later in November 2007 Macalloy celebrated 60 years of providing its post tensioning system into the civil engineering system.
The company were awarded the Queen’s Awards for Enterprise 2010 for international trade as the company’s export earnings increased by 124 per cent in the previous six years.