The Basics of Mould Making

There are numerous articles that can be made with the use of composites. Whatever you can think of, such as underground petrol tanks, garden ponds, boats, showers and vehicle repairs, to name a few, fibreglass can generally do the job. As you are limited only by your imagination, many large projects can be tackled with just a few simple tools.

Due to the vast number of fibreglass/composite products available on the market today and the fact that they are made from a variety of methods, your number one consideration must be the ability to remove your final product from the mould.

Steps for making a light weight mould....

Step 1: Make a Plug:
A plug is an exact replica of your particular project. This can be constructed from whatever material is cost effective, such as high density foams, ply, customwood or bog. Since you want your product to emerge from the mould in a specific way, you must finish the plug to the quality you want your finished product to be. It is important to sand out blemishes and defects on the plug as everything on the plug is reproduced exactly and will appear on the product.

Step 2: Make a Mould:
The mould is a mirror image of the plug, taken right off the plug. The fibreglass laminate will stick to the plug, so you have to prepare the plug with a releasing agent to prevent it. How you construct the mould will depend on the number of units you are making with it, a one-off can be very light, whereas a mould designed for high production must be very solid and well supported.

Step 3: Make the Article:
The article is your finished product constructed on the basis of final use and the quality you used in the preparation of the previous two steps. The cost is no greater using an superior finish than in using a terrible finish. The extra cost is realised in steps 1 and 2.

Determining the final article cost...

Plug and mould costs are mulitples of the final article cost. A moderately complex article requiring a one piece mould for approximately 50 units could be figured as follows:

Mould: 2-4 times the article cost.
Plug: 2-4 times the mould cost.

Points to consider for ensuring a cost effective price and a quality product....

1. Properties - Using composites in conventional applications against conventional materials is not cost effective unless you are exploiting its advantages. Get the most out of it if you are going to use it. Basic composite laminates are not stiff, although they are strong. It is important not to confuse the 2 properties. Although a 4mm thick strip of fibreglass may bend more that a 4mm thick strip of ply, it could conceivably take 4 times the load to break the fibreglass. (Figures are indicative only.)

2. Corners - Corners need to be radiused a minimum of 6mm in most cases. The more, the better! Four millimeters or less can be possible, but the decrease in radius dramatically increases the chances of chipping on either the mould or article.

3. Shape - Shape is the virtually limitless advantage of using composites!