For a manufacturing process that has a history going back at least 4,000 years to ancient Egypt, it’s taken rotational moulding a long time to pick up speed.
While the pharaohs may not have worked out that polymers were a good substitute for slipware pottery, the modern process is very similar to its ancient forebear.
So perhaps it’s not surprising that rotational moulding is the poor cousin in terms of research and development, playing second fiddle to blow moulding, injection moulding and extrusion.
After all, from the moment mass produced plastic products hit the streets in the middle of the 20th century, our consumer appetites have scarcely dwindled, which means making a LOT of products.
Rotational moulding is often deemed suitable for low volume production runs olny and even being low-tech and ‘industrial’. In fact neither are true, but the process is simply not as common as other methods so has always been playing catch up.
In reality, rotational moulding offers some very considerable benefits and is perhaps finally beginning to get an improved profile.
There are the very obvious benefits that have always existed with the process:
• Low cost to entry thanks to much less expensive tooling so lower volumes can be manufactured without the capital outlay required for other methods and that lower budget projects are financially viable
• No pressure is applied during the process reducing potential for stress fractures and breakage
• Wall thickness can be changed without modifying the mould
In process benefits
But less well known is that rotational moulding offers the ability to manufacture products or components by overlayering or using laminated materials. For example, the hull of a boat or canoe can be moulded with a hard inner shell to provide the rigidity required for the shape of the item and to allow any additional post process fitments to be added. But it might be appropriate for the hull to have a softer outer skin to absorb bumps and knocks without risking the more brittle, rigid inner shell.
With rotational moulding, this can be readily achieved by adding in different types of polymer at different stages in the moulding process. It is also possible to mould in foam using the same technique providing additional buoyancy and making considerable savings on post production processes.
Equally the world of tooling is moving on apace. The most significant advance is the principle of the heating and cooling being an integral part of the mould. The bi-axial motion of existing machines is still used to rotate and distribute the polymer, but electrically heated elements built into the tool provide the heat and specially designed cooling channels allow air (either natural or compressed) to circulate efficiently and aid rapid cooling.
The benefits of this approach are incredible reductions in energy consumption, greater control over the process window leading to fewer rejects and a reduction in raw materials thanks to the ability to apply more heat where wall thickness is an issue.
Of course this comes at a price. A tool with this capability might be three to four times more expensive so it’s not for every application but the advance is nonetheless very exciting.
Another area tooling can look to is 3D printing. On the surface, 3D printing is a competitor to rotational moulding but with advances in Metal Additive Manufacturing, it is now possible to print steel tools to incredible levels of detail and tolerances.
This opens up huge opportunities to manufacture smaller products than might previously have been uneconomical to produce. The obvious next stage would be to print tools with built in heating capabilities…
What the future holds
Traditionally rotational moulding was seen as being good for hollow products, big products and industrial products. But with the advances in process production and tooling, this method produces components for commercial aeroplanes just as readily as for a water tank or a tractor.
What is certain is that while it may have taken 4,000 years, rotational moulding now offers some serious advantages over other methods and by being more creative and innovative in our industry’s approach, we can aim to make sure that rotational moulding is never the poor cousin again.