The world of composites can be a complex one. Having to navigate the materials, resins and then the production process options can be daunting. However, as we take delivery of our additional hot platen presses, and new CNC trimming equipment, we thought it would be a good idea to discuss some of the key facts around the pressing option and its benefits.
Given there are many aspects to consider, this is only a brief overview. However, don’t miss the opportunity to register for a more detailed explanation in the first session in our “HOW TO” series, which will be focused on “How to choose if pressing is the right option for your composite manufacturing”
So let’s kick off with the most common questions you should be considering:
- When to use pressing?
- Why consider pressing?
- What are the alternatives to pressing?
Ultimately – when these are considered, the most compelling and common thread in all of these questions and reasons is cost saving.
When to use pressing?
This is dependent on the timescale, volume and budget that you have. Pressing is the optimal process when there is a requirement, for example, for;
- Medium to High production volumes (it can still be used on low volumes for proof of process)
- Making multiple coupons for testing from single large sheets.
- Repeatability in the processes and quality
- Shaped or flat structural components
- High structural properties
Why you should consider pressing
In our humble opinion, if your project fits into the description above, pressing is going to be the most efficient approach by far. It all comes down to the cost, time and properties
Alternative options can quickly ramp up costs. Consider the consumables required such as vacuum bagging and the limited mould life. Given the lengthy curing time with autoclaving for example, there is also the need for multiple moulds to reach the quantities required in any volume production as well as multiple processes required, not to mention the labour intensive lay-up, de-bulking and bagging processes and the huge waste of energy (heat and pressure) given up on each autoclave cycle.
Structural properties can be significantly improved in press moulding, eg: compressive strength and inter-laminate sheer strength because of higher cavity pressure. Vacuum bagging for example can get 1 bar of pressure, with autoclaving you can get to 8 or 9 bars of pressure and whereas in press moulding in comparison we are often seeing 20-40 bar of cavity pressure. Quite simply more pressure, results in the plies being stuck together better and matched tooling gives a better surface so reduces the amount of work needed if you are adding a surface finish like paint.
What are the alternatives to pressing?
- In today’s composite industry, the most common alternatives include:
Vacuum bagging – where laminates are vacuumed down into a single sided mould with vac bag consumables layers to hold the vacuum.
- Infusion – dry cloth laid up into single sided tooling under vacuum bag with similar consumables, with resin pulled through to wet-out. Often used on larger structures where a longer period is needed to get reinforcements in place than resin systems might allow.
- Resin Transfer Moulding (RTM) – a closed tool and the resin is injected into the mould under pressure. Good surface finish, but high tooling cost.
- Autoclaving – pre-preg laid up in tooling with bagging materials and cured by heating the whole autoclave with extra air pressure to consolidate the laminate. Improved properties but increased cost of process.
*Cecence offer vacuum bagging, infusion and autoclave processing if required.
How pressing saves money
So when all of the above is considered and you decide to go with pressing – how are you going to save money and by what magnitude?
- Mould cost – a limited use autoclave mould could cost £600 for example, a multi-use press mould costs £1200 – on face value twice the cost.
- Mould units – to make 50 parts in an autoclave you would need 10 moulds @£600 = £6000 or £120 cost per part, in a press you require 1 mould @£1200 or £80 cost per part – saving of £4,800
- Time to cure – an autoclave process can take up to 7hrs to cure. Pressing with a Cecence snap cure material can be done in 7 mins or less – saving in labour cost, not to mention the associated energy and utility costs. There are no consumables (bagging films to set up) we have a water-based release agent we can spray on between mouldings to give us a continuous process.
- Equivalent cost comparison – not including labour etc – a direct cost comparison results in autoclave = £12,000 for 50 parts, while pressing = £5,200 for 50 parts.
While this is a crude and quick example of cost saving – there are so many additional advantages which we have proven time and time again – most significantly is time to production, which when looking at volume production is significant. Alternative methods just require too much labour and facility foot print to be really cost effective at scale.
To learn more about our learnings around press processing and snap cure, please register your interest for our “How to choose if pressing is the right option for your composite processing” info series and a chance to put your questions directly to our engineering experts.