Difference between standard and compression moulding

Fibreglass construction of all types requires some type of mould. It could be a simple bowl or a complicated resin transfer mould. There are single use, disposable moulds that you can only make one item from or a full fibreglass mould that can produce 100’s of items.

But here we will discuss the difference between standard fibreglass moulds and compression moulds. The production time of an item from each type of mould is basically the same. One mould will produce one item from it over one day. If you require more than one item per day you will need more moulds.

There is a considerable difference between standard fibreglass moulding and compression moulding. Standard moulding is the simplest and most cost effective type of moulding and Compression moulding is considerably more involved, complicated and expensive to produce, but produces a far superior item.  

Standard fibreglass production generally only requires one mould to produce an item. The finished item will be gloss one side and raw fibreglass finish on the other side. 

The mould construction is relatively simple. It does not require matching pieces, additional fittings and lugs and generally no special jigs. Any mounting lugs, bolt standoffs or spacers have to be added after the time is already built.

Compression moulds are two sides of an item bolted together to create a 2 sided fully finished item. Both sides of the item have a moulded finish. They can have included mounting lugs, screw platforms, bolt stand-offs and spacers already moulded into the finished item. There is no need to add anything to the finished item. 

With a standard mould you require only one plug to make it from. You make the mould from this simple plug and the mould is finished.

But for compression moulds you have 2 sides of an item to mould. So you have to set-up and mould one side of the item, being careful there is no contortion or change to the moulded item shape and then you have to mould the other side of the item and then you have to make sure both sides of the mould bolt together perfectly. The mould has to bolt together perfectly to create the finished item. Because the mould is two sided and produces the finished item from compression a jig often has to be made. For a small item clamps will generally do the job. But for items that have a wider span a compression jig is often made. This is a metal frame the mould is placed in and then compressed to the required item thickness. The frame ensures there is consistent thickness of the item wall across the whole item. 

A standard fibreglass mould is the less expensive and less complicated way to mould and will do the job for a large percentage of fibreglass production.A compression mould a lot more expensive and far more complicated to build and more complicated to produce an item from but it will produce a double side item that looks far better and can be created for use in far more applications.