Engineered Structural Foam Moulding

Normally used for medium to high volume production, engineered structural foam mouldings (ESF) are produced on injection moulding machines where a foaming agent is added to produce mouldings with a hard outer surface and cellular inner core.

These mouldings are tough and unlike injection moulding, thick internal wall sections will not normally produce external sink marks.

The incredible strength and versatility of Engineering Structural Foam moulding allowed us to create a lower cost product with superior design features.
Peter North, Senior Design Engineer – Brandon Medical Limited

Important features of engineered structural foam moulding:

  • Allows great design and processing flexibility.
  • Fast cycle times coupled with high definition parts.
  • A high strength to weight ratio with excellent torsional stiffness.
  • High impact strength and dimensional stability.
  • Reduction in secondary finishing operations.
  • Aluminium tooling is generally suitable and can be coupled with the innovative use of multi cavity tools.
  • Possibility to integrate details to simplify assembly.
  • Components can be manufactured with a general 4mm wall thickness.
  • Most thermoplastics can be formed. Noryl, ABS, Polystyrene and Polycarbonate are popular and foamed versions have similar shrink rates.
  • Mouldings can be manufactured to meet UL94V0 flame retardency.
  • Recycled materials can be utilised.
  • Parts normally require painting and can be RFI shielded.
  • Rimplas moulding machines range from 60 tonnes to 800 tonnes.

FAQ's for Structural Foam Moulding

What is Engineering Structural Foam Moulding?

The ESF process is a low pressure, thermoplastic, injection moulding process, where an inert gas is introduced into the melted polymer via a blowing agent for the purpose of reducing the density hence the weight of the finished component.
ESF mouldings have a cellular core surrounded by rigid integral skins. This combination results in a moulding of a high stiffness ratio compared with non ESF (compact) mouldings.

What are the typical polymers used in Engineering Structural Foam Moulding?

The majority of thermoplastics can be foamed; however, some can be more challenging to process. The most common polymers to foam are: High Density Polyethylene (HDPE), Polypropylene (PP), High Impact Polystyrene (HIPS), Acrylonitrile Butadiene Styrene (ABS), Polycarbonate (PC), Polyphenylene Oxides (PPO), Polyphenylene Ether & PPE (Noryl)

What are Typical Mouldings Produced and Their Industries?

Examples of moulded parts and their market are: Operating Theatre Surgical Lamp Casing, Patient Transfer Boards, Medical and scientific enclosures, ATM Facias and POS terminal Cover, CAB Interiors, Dashboard chassis, Kiosk & POS Structures,
Pallets & Transit Cases, Rugged Casings for PCB Boards, Audio Speakers, Filter Frames for Oil Exploration. These are just a few examples.

Mould Tools, are they different to Standard injection mould tools?

Yes – With the low cavity fill pressures, the mould tools can be made in lighter grade materials, Aluminium. The costs are up to 30% cheaper than with normal injection moulding. When Structural Foam mouldings are made invariably the mouldings are for engineering applications. The foaming action within the material demands that the material is fed into the mould tools quickly and as such large feed gates are utilized and high injection speeds are necessary.

Can ESF replace metal component?

Yes – However; It is not a good idea to just copy the metal part straight into polymer. Consideration needs to be given to the environment in which it is situated, maximum and minimum service temperatures, chemicals it will likely encounter. The forces it will experience, both static and dynamic force including shock loads. Also ask the question, could the design incorporate other features that will reduce part count.
The part will need to be designed for the polymer selected. We, of course, will offer impartial advice on any project, including the most suitable process and what polymer is the best for your application.

What are the advantages and disadvantages of Engineering Structural Foam Moulding?

ESF offers design flexibility where complex curves, bosses and product specific features can be introduced, reducing component inventory and cost. Weight saving due to the cellular internal feature. Weight saving can be between 10% and 20% compare to standard injection mouldings. If replacing metal, parts a saving of 30% is not unusual. The components will be rigid but also have a better impact resistance. Because of the low mould pressures and the foaming process residual internal stress is reduced and so reducing any distortion on large flat components. This means a big reduction in sink marks on “A” surfaces – even with substantial ribs and bosses on the “B” surface. Wall sections can vary on a single moulding. Thicknesses of 5mm to 40mm can be achieved on the same part without distortion. Large parts can be moulded on a relative low clamping force press. The limiting factor on component size is Press Platen size and barrel capacity. Components up to 12 kgs have been achieved with ESF.
There are only 2 disadvantages – witness marks on the moulding surfaces known as swirl marks. These do not give a cosmetic surface. As the foaming process needs to be completed the moulding cycle times are longer than standard injection moulding.

Case Study

Engineering Structural Foam for Brandon Medical

A recent development project has showcased the exceptional versatility of Engineering Structural Foam (ESF) within the medical industry with Brandon Medical.
The incredible strength and versatility of Engineering Structural Foam moulding allowed us to create a lower cost product with superior design features.