Our injection mould quotes are far apart: is the cheapest tool also the cheapest over the life of our product?

The cheapest injection mould is not automatically the cheapest over the life of the product. A tool that costs far less up front can cost more over the programme through a longer cycle, higher scrap and a replacement halfway through, and at series volumes those running costs can outweigh the gap between the quotes. The reverse also holds: at low or uncertain volumes the cheaper tool is often the right buy. Compare cost per good part over the volume you will realistically make, not the price of the steel.

Why are the quotes so far apart?

Because each toolmaker is quoting a different tool. Hand the same CAD to two shops and each fills in its own assumptions about tool life, cycle time and how much gets solved in the steel, and those assumptions rarely make it onto the quote.

Six specification choices account for most of the gap:

• Cavitation. Two cavities halve the shot count against one, in a bigger and more expensive tool.
• Steel and hardness. Prehardened P20 machines faster and costs less. Hardened H13 lasts far longer and costs more to build and to modify later. Aluminium is the cheapest and quickest of all.
• Runner system. A cold runner is cheaper to build but leaves a runner on every shot that is scrapped or reground. A hot runner costs more and saves material, often cycle time as well.
• Cooling layout. Research on injection moulding puts cooling at 60 to 80% of the total cycle. Saving on cooling channels means paying for it on every shot the tool will ever make.
• Side actions. An undercut one shop solves with a slide, another solves with a manual operation at the press, or with a design change you have not seen yet.
• What is included. Number of trials, T1 samples, a dimensional report, tool freight and documentation.

Tool life is the line that varies most and says least. Many quotes reference an SPI mold class. In the common reading, Class 101 is built for more than a million cycles with cavity and core hardness of at least 48 HRC, Class 102 for up to a million, Class 103 for under 500,000, Class 104 for under 100,000, and Class 105 for prototypes only. Published descriptions do not agree on those boundaries, though: for Class 104 you will find tool lives quoted anywhere from about 10,000 to 300,000 cycles. A class on a quote is a label. What you can hold a toolmaker to is a guaranteed shot count for your resin, in writing.

How do you work out the cost per good part over the programme?

Add up the tool, any replacement or refurbishment, the machine time and the scrap, then divide by the number of good parts over the programme. Leave material out as long as it is the same in both quotes. Machine time is shots multiplied by cycle time in seconds, divided by 3,600, multiplied by the machine hour rate.

Most of those inputs are not on the quote, but you can ask for them or back them out. Cycle time and guaranteed shots come from the toolmaker. The hour rate is hidden in the piece price: subtract material, divide what is left by the cycle time per part in hours, and you can see roughly what rate was used. Scrap is the hardest. Ask what rate the piece price assumes, and who carries the cost when actual scrap runs higher.

A worked example on invented figures, to show the arithmetic rather than any real tool price. Assumptions: 60,000 parts a year over four years, two cavities in both tools, so 120,000 shots. A machine rate of 45 euros an hour, and each scrapped part costing 50 cents in material and machine time.

| Worked example, 240,000 parts over four years | Tool A | Tool B | | --- | --- | --- | | Tool price | €22,000 | €36,000 | | Guaranteed life | 100,000 shots | 500,000 shots | | Cycle time | 34 seconds | 28 seconds | | Scrap rate | 3% | 1% | | Refurbishment at 100,000 shots | €8,000 | none | | Machine time for 120,000 shots | €51,000 | €42,000 | | Extra scrap, 2% of 240,000 parts | €2,400 | none | | Total over the programme | €83,400 | €78,000 | | Cost per good part | €0.348 | €0.325 |

In this example Tool A is 14,000 euros cheaper to buy and 5,400 euros more expensive to own. That margin is thin enough to flip on a single assumption. Halve the programme to 120,000 parts and Tool A never reaches its refurbishment, finishing 8,300 euros ahead. The turning point here is 200,000 parts, the moment Tool A runs out of guaranteed shots. Each second of cycle time is worth about 1,500 euros over this programme.

So the deciding variable is not the toolmaker. It is your volume, and that is the one number only you can supply. Use a realistic forecast, not the launch plan.

A cheaper tool is not automatically a slower one, either. Aluminium conducts heat four to five times better than P20, so an aluminium tool can run a shorter cycle. Where the difference often hides is in the number and placement of cooling lines, and in how the part leaves the tool; our piece on optimising your ejection strategy covers that last point. Ask every toolmaker for an expected cycle time. A quote without one cannot be costed.

When is the cheaper tool the right call?

When your total volume over the programme sits well below the guaranteed life of the lighter tool, or when you do not yet know what you will sell. Saving on tooling is then a deliberate decision rather than a gamble. Five situations where it holds:

• Low lifetime volume. A short-lived product, a seasonal variant or a part for a small series will never use the life of a production-class tool. You would be paying for steel you never run.
• A bridge tool. A simple tool to test the market, or to keep supplying while the production tool is built. You pay twice, but you launch earlier and learn from real parts before committing the expensive steel. That was the route for HEARS: prototype tooling first, then scaled up to mass production tooling.
• A family mould. Several different parts in one tool, such as a lid and a base. Cheaper than two tools, but every part shares one material and colour, filling is harder to balance, and if one part is off, the whole tool stops. It suits sets that are always ordered together, at modest volumes.
• Lower cavitation while demand is uncertain. Start with one or two cavities and accept a higher piece price. If demand grows, a second tool follows, which also gives you a backup if one goes down.
• A design that is still moving. Modifying hardened steel is slower and more expensive than modifying P20 or aluminium. Hardened steel on a design that is about to change gets paid for twice.

The honest downside of every one of these: while you run on the lighter tool the piece price is higher, and switching to a production tool means another round of sampling. Schedule that switch while you hold stock, not when the tool wears out.

How do you level the quotes before you choose?

Line them up against the same specification and chase every line that is missing. A quote that is silent on any of these points is not cheaper, it is incomplete.

| What to line up across both quotes | Why it explains the price | | --- | --- | | Cavitation and runner system | Sets the shot count and material loss per part | | Steel grade and hardness of cavity and core | Sets tool life and the cost of later changes | | Guaranteed shot count for your resin | The only tool life you can hold the toolmaker to | | Expected cycle time | Drives the machine time in every piece price | | Piece price at that cycle time | Without it the tool price cannot be judged | | Trials and samples included | Every extra round costs time and often money | | Who pays for corrections after T1 | Avoids a dispute just as you want to launch | | Maintenance and refurbishment | Decides whether the guaranteed life is reached | | Tool ownership, storage and documentation | Decides whether you can move the tool later |

Always ask for the tool price and the piece price together; apart, neither tells you anything. A low tool price can come back in every piece price, and a low piece price can assume a tool you did not order.

Then pin down how the trials will run. In our process, the first set of samples is followed by a tool correction and a second set, and a signed mould property contract is in place before production starts. Whatever you agree, put it in writing before the first trial shot, because after that you are negotiating over a tool that already exists.

Production Heroes takes products from design to series production, from feasibility and cost price to sourcing and supply chain, and supplies moulds and tooling to manufacturers across Europe, from the Netherlands and its own presence in China.

Sources: the share of cooling in the cycle (60 to 80%) comes from RWTH Aachen research on cooling time in injection moulding. SPI class descriptions, the 48 HRC requirement for Class 101, aluminium and steel tool life and the thermal conductivity of aluminium against P20 come from publicly available technical material by toolmakers and moulders; those sources disagree with each other, which is the point. The worked example and the figures in the FAQ use invented assumptions and are not a quotation.