Tooling is a confusing term in the manufacturing world because “tooling” can take so many different forms depending on what you’re doing. You can’t talk about Tooling in a vacuum. You have to talk about it in relation to a specific manufacturing process since depending on the process it can mean a jig or fixture for assembly, a gauge for inspection purposes, or a pattern for casting. Sometimes it can even mean all of those if you’re talking about tooling up a production line.
In this article, we are going to cover a specific type of tooling, the molds used in Plastic Injection Molding. If you’re unfamiliar with the process of plastic injection molding, we’ve covered the basics in including the parts of the mold itself. We’re going to build on those basics in this article, so we highly suggest reading that article first or having a good grasp of what plastic injection molding is before continuing.
Understanding Tooling Cost
In our article we discuss how the mold forms the part or component being manufactured but you can make a mold that accomplishes that goal in a lot of different ways. Ultimately, what we care about is “cost”. But “cost” has become a more and more nebulous as we start to try to account for all of the costs to different stakeholders in the production process. Cost isn’t just money we spend on the tool. Cost can also include things like:
Missed Sales Opportunity Cost
What we could have generated in sales if we were producing the product. However due to the time it takes to create tooling, we could not produce product, so we could not make sales to the market.
Future Maintenance Cost
Costs that will be incurred in maintenance since we made choices in our tooling to save time or money that resulted in our tooling needing to be repaired more frequently in the future.
Modification Cost
Cost we incur to modify tooling to better meet our customer’s requirements after starting to make the tool or after running the tool.
Export Cost
Costs incurred because of tariffs and exports if our tooling is made or operated overseas.
For the purpose of this article, we’re going to look at cost being both time it takes to make the injection mold and the dollar cost of purchasing or making the injection mold. When thinking of buying or making a mold you can generally draw an inverse relationship between the upfront cost of the mold and per piece cost of the product that you’re going to produce. The more time and money you invest upfront, the less each piece is going to cost coming off the machine.
Let’s look at the factors that make this relationship so strong:
Number of Cavities
Just like when you go to the Dentist, the more cavities you have, the more it’s going to cost. In this case, more cavities actually pays off with a lower piece price. If you build a large tool with a lot of cavities, you can make more pieces with each cycle of the machine. These numbers start to really add up over the course of an 8 hour shift.
To demonstrate this, let’s compare a small two-cavity mold and a larger eight-cavity mold below. In both instances it takes 30 seconds to completely cycle (from start to finish of the plastic injection molding process).
Two-Cavity Mold
60 seconds in a minute x 60 minutes in an hour = 3,600 seconds in an hour
3,600 seconds in an hour / 30 seconds per cycle = 120 cycles in an hour
120 cycles in an hour x 2 parts per cycle = 240 parts per hour
240 parts per hour x 8 hours in a shift = 1,920 parts per shift
1,920 parts per shift
Eight-Cavity Mold
60 seconds in a minute x 60 minutes in an hour = 3,600 seconds in an hour
3,600 seconds in an hour / 30 seconds per cycle = 120 cycles in an hour
120 cycles in an hour x 8 parts per cycle = 960 parts per hour
960 parts per hour x 8 hours in a shift = 7,680 parts per shift
7,680 parts per shift
7,690 parts is 4 times the amount of parts we got out of the two-cavity mold. Every day of the year. That makes the process 4 times more productive and so the labor associated with each piece 1/4th of what it would have if we had used the two-cavity mold. We can get more productivity out of one employee, and also get 4 times the potential capacity to be able to meet spikes in demand.
But, making more cavities in the mold takes more time, a larger piece of steel, more design work from the mold designer, and might even take a larger machine to run. This is not only going to stretch out how long it’s going to take to get the mold onto the production line, but it will also cost more to get the tooling.
Bottom Line
More cavities in a tool take longer to cut, but reduce the piece price substantially.
Mold Material
Not all steel (or aluminum) is made equal, and so not all injection molds are made equal. The hardness of the material used directly effects how many parts you can make before having to pull the mold too maintain it. So, you may be asking, why would we ever make tools out of softer steel or even aluminum?
The simple answer, it’s faster and the material costs less.
Generally speaking, every component that’s made using the process of plastic injection molding has a custom tool specifically built to make it. There are ways to shortcut this that we’ll talk about later in this article, but there is always going to be a custom-made part of every tool. The harder the material is that you use to make your tool, the harder it is to cut the cavity in that material, and the longer it takes. Which means that the Tool & Die maker is going to spend more time on the tool and probably wear out more of their tools in the process. It’s also just plain more expensive to buy the steel to make it.
Bottom Line
Harder tools cost more up front but have fewer issues over time resulting in lower maintenance costs.
One factor that also needs to be considered when reviewing the cost of a mold is the dimensions and/or features of the part. This exists outside of the inverse relationship discussed above.
Dimensions of the Part
This is pretty straightforward, the larger the part you’re making is, the larger the mold has to be to make it. Larger molds take more steel, and more time, so they cost more. What also needs to be considered is the complexity of the part. The more undercuts, and other features that a part has, the more complicated the mold has to be, and the more expensive it is.
Bottom Line
Injection Molds for bigger components and/or more complex components cost more.
Tooling Choices
Injection molders realize that you have to balance the cost of a tool with the benefits you gain. While each mold is a custom designed and made affair, we tend to lump them into a couple of different overarching categories. At Whitman, we like to think about them in coordination with the development of a component.
Basic Tooling Choices:
Rapid Soft Tooling
This is very cheap plastic injection mold normally made from a really soft tool steel or aluminum that is meant to help with the prototype phase of product development. At Whitman, we can complete tooling like this on most medium sized components in 15 days. The part can be run like any other injection molded component. This means that you can hold the same tolerances and use the same material that you will see in true production, which isn’t always possible with 3-D Printing. However, these pieces are going to have the highest piece price because they normally only have one cavity and possibly hand loaded inserts for complex parts.
Advantages:
Quick to Produce
Cheap
Provides production quality parts for initial product assemblies to validate product design and assembly line design
Disadvantages:
Highest per piece price
Wears out quickly
Can’t support very large volumes of production
Bridge Tooling
This is also a cheap, quick plastic injection mold made from a really soft tool steel or aluminum. It could be a slightly modified version of the soft tooling made during the product prototyping phase, or it may be an injection mold that was made to quickly get into production to fill a gap. Either way it’s not built to last for a long time. This tool will probably have very few cavities and none of the features that you would build into a high-volume dedicated mold. Its extremely unoriginal name comes from the fact that this tool is used to bridge the gap of time between the approval of prototypes and when a high-volume dedicated mold can be put into production. Normally when a new product is entering the market and needs production but may not have a large market share so our production line isn’t having to operate at full capacity.
Advantages:
Quick to Produce
Cheap
Provides some production for lower volume production requirements
Disadvantages:
Higher per piece price
Wears out quickly
Can’t support very large volumes of production
Dedicated Tooling
This is the most expensive option for tooling and is made from harder tool steels and designed to incorporate as many features as possible to decrease cycle times and increase automation. Dedicated tooling normally has the lowest piece price. However, it is going to have the highest initial cost. For large volume production or very difficult and complex components, this is the way to go.
Advantages:
Very low piece price
Supports complex and large components
Very little maintenance
Disadvantages:
Expensive tooling
Long production timeline
Other Tooling Choices:
Quick Change Tooling:
This is a specific kind of tooling that may or may not be offered based on the product dimensions. Quick Die Change Units allow you to pull the cavity from the injection mold and replace it without changing out the entire mold. It’s faster and cheaper to make then a complete tool and is normally made from a better steel then bridge or soft tooling. The only disadvantage is that the Quick Die Change Unit normally can’t support large or exceedingly complex molds.
Advantages:
Quick to produce
Cheaper than a dedicated mold
Lower piece price then softer tooling
Disadvantages:
Can’t support large or complex component production
Can’t support very large volumes of production
Family Tooling:
This is another specific kind of tooling that can be used when two different components are being made from the same material. Normally at a fixed ratio. For example, if you’re making two gears (one larger and one smaller) for an item that always needs one of each gear to assemble and they’re both being made from Nylon. That would be a good point to use a family mold.
Advantages:
One mold for two parts
Cheaper than a dedicated mold
Lower piece price then softer tooling
Disadvantages:
Can’t support large or complex component production
Can’t support components made out of different materials
Optimizing Tooling Choices
The categories discussed above are general categories to provide you with some context of the different kinds of injection molds that you may want to talk about with a Tool & Die Designer when they’re quoting the tooling to you. We highly suggest using a combination of tools to move from design into full scale production by starting with Rapid Tooling, and after design approval, either using a Dedicated Tool or a Quick Die Change Tool to meet full production volumes.
At Whitman, we span the entire life cycle of component delivery from tool design to part production. When we look at producing a component, we always lay out a path to production for our customers. We’re lucky that we can bring world-class Tool & Die Designers, Master Tool & Die Makers, Plastics Process Engineers, and Product Design Engineers to the table on every one of projects which allows us to optimize our value add to the customer and cut out costs wherever possible.
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