Stress FAQ's
Here are few answers to commonly asked questions. Polyurethane foam is a relatively simple material to work with, but it is vital that we have all neccessary information before we go into production, so that we can provide you with the perfect product at the end of the day.

 
 

 
Guide to Polyurethane Foam Moulding.

PU foam is made by mixing two liquid components under shear and pouring or injecting them into a mould cavity. The chemical reaction kicks off within seconds and carbon dioxide gas is given off as bubbles. As the polymer is formed the bubbles are trapped in the matrix forming a foam.The constituents can be modified to form foam with many different densities and properties. We have been specialists in viscoelastic foam moulding since the early 1990's - the leaders in the UK. (Viscoelastic is the soft squeezy memory foam we make our stress products from).


 
 
Pigments or dyes can be added to one of the components, or injected at the mixing stage so you can have any colour you want - even fluorescents. Note: When considering colour, bear in mind that PU eventually goes yellow on exposure to UV light - so very light colours are unwise in products needing a long lifetime in daylightTypically a foam moulding can be demoulded within about 5 minsBecause of this long cycle time it is usual to produce multiple mould cavities to get a continuous production flow. Normally this would be between 20 and 50 cavities.
 
 
The good news is that PU tooling is a lot less expensive than plastic injection moulding because the pressures involved are much less. So even with multiple cavities a full set of PU moulds can cost a fraction of the price of a normal injection mould. Resin tooling is cheapest and quickest for relatively small mouldings - say anything less than 300x300mm in size. Above this it’s often cheaper to go down the machining route.There are many variants of this basic process, for example an in-mould coating can be applied to the inside surface of the mould before material is injected so that the moulding has a silky smooth surface, material such as fabric or leather can be laminated to the foam in the moulding process, inserts can be encapsulated into the foam – the possibilities are huge.
 
 

How do I get my product developed?

It depends on where you are starting from. The normal flow is as follows:-Produce your concept or design with sketches or CAD drawings (we can help with the drawing if necessary) If PU foam or elastomer is your material of choice then it is important to talk to us at this early stage. We can pick up on design problems that can make manufacturing difficult, and where possible they can be designed out here. We can also advise on materials in the context of the product application (eg does it need to be waterproof, does it need to be light etc etc) We could give estimates of cost for the project at this stage depending on the level of our involvement.A full 3D final CAD drawing will then be produced by you or us.Depending on size we would often then produce a Stereolithography (SLA) model for final physical approval.We would produce a test mould using that model to prove the moulding process and deliver some samples for final approval.We would then produce production tooling and make the bulk order.
 

 
How Long Will it Take?

We have been known to go from concept to bulk in 3 weeks – although to achieve this everything has to work right first time (it usually doesn’t).

To produce a CAD drawing can take a couple of hours or a couple of days depending on the complexity. If it’s more complicated than that it probably can’t be made out of foam.

 
 


To produce a Stereolithography (SLA) model from the CAD file takes 3-4 days.

To produce a resin master mould and a test moulding will take another 3-4 days.

To produce resin tooling for a bulk production run takes about a week.If the decision has been made to go down the metal milling route then this whole process can take longer.Usually it’s client approval and decision making that slows this timeline down.

If new materials are being used sometimes this whole process can take longer – it can take us a while to work out the processing parameters of a new chemical system.

 

 
How much will it cost?

In all of this you are mostly only paying for time. The raw material and tooling cost can be significant in big mouldings – but in small mouldings the time is usually the bigger element.
If you are using a standard material that is running on one of our moulding lines then test mouldings are cheap. If we have to shut down a line and fill it with new material this can take a day and so will cost more.
We are happy to give detailed advice for free of course but we think you will find our charges easy to live with. (We don’t have expensive lifestyles here.)