Do I need Injection Moulding?

Injection moulding is the preferred manufacturing process when you want thousands or millions of the same plastic part.

The process involves heating up small plastic beads, usually to a liquid or near liquid state, and squirting it under pressure into the cavity of a metal mould.

After you have finalised the design of the plastic part you want to make, the first step in getting the part injection moulded is to build the mould.

The mould is normally made of steel, although softer metals such as aluminium is used for moulds for some applications.

The building of a mould requires great precision using specialist design software and metal working equipment. Moulds can be very expensive, the price depending on:

• the size of the mould
• the number of cavities in the mould
• the material the mould is made from
• the texture of the finish required on the moulded article
• the complexity of the part; among other factors

Mould Price Guide	Description
$1200	Small round flat 1" washer
$10 000	Plain shaped 10 oz drinking tumbler
$20 000	12-cavity mould to make tea spoons
$40 000	Front surround of your PC monitor.
$60 000	Beer jug (pitcher)
$300 000	Milk bottle crate
Please note that these are estimates only.

OK, maybe I don't need injection moulding

For production quantities of less than several thousand parts, there may be other manufacturing processes more cost affective than injection moulding.

Model makers such as Cumberland Patterns Pty. Ltd in Sydney NSW (Telephone 02 9602 6648) are able to fabricate small quantities of plastic parts.

You could also try Plastic Fabricators or Fibreglass Fabricators; several of which are listed in the Yellow Pages.

Yes, I need injection-moulding, how do I proceed?

You may need specialised advice at various stages in bringing your plasticware to market. For more information on how Pennicook Davison can help with your project please take a minute to complete our on-line quote form. Our target response time for genuine inquiries is within 5 working days.

As can be seen, the initial set-up cost (the design and manufacture of the mould) to make an injection-moulded part is quite high. That is why the injection-moulding process is the preferred method when you want thousands or millions of the same part, not normally when you want a few or even a few hundred. A well designed and built mould should make several hundred thousand parts before needing any major refurbishment.

Moulds are built by specialist companies called toolmakers in Australia (or moldmakers in North America). Many injection-moulding companies have toolmaking/mouldmaking facilities in-house and are able to build you the mould as well as mould your parts. Pennicook Davison Pty Ltd is one such company.

Having had your mould built, you then need to get a custom moulding company to mould the parts for you. The custom moulding company will generally charge you a price per part or per thousand parts for very small parts.

The price you pay

The price you will pay per moulded part will depend of course on:

• How heavy the part is - injection moulded parts can be as small as watch springs and larger than car bumper bars
• What material the part is to be made from - there are dozens of different types of plastics and dozens of grades within each type
• How thick the moulded part is
• How accurate the part has to be
• The number of cavities making the same part in the mould
• The quantity of your order - there is normally a set up charge with each moulding production run.

As a very rough guide, in a single cavity mould, the cost of the material may be between 30% and 50% of the selling price of the injection-moulded part. This will vary according to the cost of the material and the weight of the article. The balance of the price that the custom moulder charges you for the part is for machine processing time, labour, overheads and a profit margin.

If the article being moulded is heavy or made of expensive material, then the material proportion of the final price of the article is likely to be higher. On the other hand if the article being moulded is light or made of inexpensive material, then the material proportion of the final price of the article is likely to be lower.

The cost of plastic material varies greatly according to the type of properties needed for the application; to a lesser extent the quantity of material needed for the job; and the part of the world in which you will be buying the material. For example, the material used to make plastic buckets (pails) may cost $2-3 per kg; the material for clear drinking tumblers may be up to $5-6 per kg; the material that is used in the protective shields in taxi cabs and banks may be around $8-9 per kg; and you would pay over $50 per kg for high heat and chemical resistant material for technical and scientific applications.

An illustration of why it is not cost affective to injection mould for small quantities

Supposing you decide to injection mould a quantity of 50 parts, the mould maker charged you $20,000 for the mould and the moulder quotes you $1.00 each to injection mould the parts. The average cost per part is determined as follows:

Cost of mould $20,000
Cost of parts 50 x $1.00 = $50
Total cost for 50 parts = $20,050

Average cost per part ($20,050/50) = $401

If on the other hand you decide to injection mould 50,000 parts, the mould still costs you $20,000 and the moulded parts cost is $1.00, (and in reality it may be less than that because you are likely to get a cheaper moulding price for ordering large quantities), the average cost per part is calculated as follows:

Cost of mould $20,000
Cost of parts 50,000 x $1.00 = $50,000
Total cost for 50,000 parts = $70,000

Average cost per part ($70,000/50,000) = $1.40

So you can see that the more parts you make out of a mould, the cheaper each one gets. For production quantities of less than several thousand parts, there may be other manufacturing processes more cost effective than injection moulding. But of course the importance of the cost effectiveness of the process also depends on how much you can sell your moulded part for.

Any prices and costs quoted in this article are in Australian dollars and are very broad estimates presented as guides only.