Injection Mold Cost - The Real Story

What is injection mold cost?

It is the price an injection molder will pay to purchase a mold. But that is not the full story.

If you are an injection molder then you might be interested in reading more so that you can save yourself a ton of money and avoid some serious headaches.

There is a second cost which I call residual cost. These are costs which start once a new mold is in production and occur over the life of a mold. Residual costs relate to any inefficiencies in a mold such as molding rejects or slow cycle time.

Residual costs will increase your cost per part.

The benefit of taking both costs into consideration is to get a realistic picture of your mold makers ability to improve your injection molding business.

Stage 1 - The Initial Purchase Price

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This is the quoted price of a mold plus any freight costs. If a molder buys from a local injection mold manufacturer then freight costs are negligible. If a mold is bought overseas and transported by ship then costs are still relatively low.

The initial purchase price is influenced by the following factors:

• Part size – large parts require a large mold so mold material cost is higher than with smaller parts.
• Part design - complicated part designs will require complicated mold designs so this will make the price high. Whereas, simple part designs require simple mold designs and lower prices (although this is not always the case).
• Part material - if the plastic material is corrosive such as PVC then stainless steels will be required and they are expensive.
• Part quality requirement – will require quality mold steels, quality machining techniques and quality injection mold design – the purchase price will be a premium. Molders with low part quality requirement often buy cheap molds but be careful about doing this as this can cost more in the end due to slow cycle times and the cost of producing large quantities of rejects.
• Annual quantity requirement - high volumes will require high cavitation and therefore a bigger mould. High volume requires a mold with good internal strength so high quality materials are required which increases the injection mold cost.
• Cycle time requirement – fast cycle times will require well designed and built molds which will be a premium cost.
• Molding machine size - mold should be big enough to support high tonnage machines. Mold should cover most of platen area to ensure quality parts are produced over the long term. Small molds in large machines will give quality problems because small molds damage the machine platens. Damaged machine platens will increase the reject rate in all molds.
• Country of manufacture – low cost countries will be a lot cheaper than western countries.

These costs are easy to see and understand. However, what is not so easy to see and understand are the costs associated with poor mould quality –called residual costs.

Stage 2 - Residual Costs

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Residual costs occur over a period of time and start from first mold trial.

A well designed and built injection mold will have a low residual cost because it will be easy and quick to setup, easy to start, have a low reject rate, have fast cycle time and the mold will consistently perform well beyond its required life expectancy.

Whereas, a poorly designed and built mold will have a high residual cost because it will have long setup times, be difficult to start, have high reject rates and a slow cycle time. And you can be sure that if a mold is delivered in this condition it will only get worse day by day.

These types of molds cannot be fixed.

These molds are usually cheap and if bought overseas there is the cost of travel – the molder must pay an airfare to meet the mold maker and sign a contract or to give final mold quality approval.

What’s more, there are other high residual costs and the effects, of which, are difficult to measure. These include the effect on employee morale (due to time pressures and unsafe work practices) and the cost of damage to molding machines (poorly made moulds will usually not be flat and this will slowly destroy tie bars, platens and toggle clamping systems).

And that’s not all, damaged molding machines will gradually damage all other moulds which will increase part reject rate day by day.

Additional Comments

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Injection mold cost is really about taking into consideration long term performance not just the initial purchase price. Having this information will give the best chance of making the right decision in future mold projects.

Remember, cheap molds make expensive parts and expensive molds make cheap parts.

Which one do you prefer?

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