When mold tooling is made in hard steel, it can typically be used to make hundreds of thousands of high-quality plastic parts. The downside, however, is that making adjustments to a plastic part’s design after the mold is made is neither fast nor cheap. It triggers mold tooling revisions: new machining work, leading to longer lead times and higher costs.
“Revisions” are a form of rework. And we are discussing the rework on molds that comes from a change in the geometry or finishing of the part made out of that mold. One wants to avoid rework as much as possible, yet it is quite common in this context.
Experienced product development teams know that such tooling revisions are common, and they plan accordingly. Inexperienced teams get caught by surprise when they realize tooling revisions are necessary. Our objective here is to help you avoid unpleasant surprises.
But let’s start by understanding what that rework includes.
What is usually done during mold tooling revisions?
Several of the following changes are typically done:
- Adding some metal
- Welding
- Addition of a mold insert
- Removing some metal:
- CNC machining
- EDM (i.e. spark erosion)
- Wire cutting
- Polishing
- Texturing
The more processing that is needed, and the larger the area to process, the more it will cost and the longer it will take.
3 real examples of tooling revisions we’ve made for customers
Now, let’s look at some examples* of mold tooling revisions from our own tooling workshop, Agilian Plastic & Molds, which will help you understand why they happen, what they typically involve, and how much they can cost.
*We will not identify the customer or products to maintain confidentiality.
Example 1: Water treatment device
A new type of compact water treatment device was developed. After a long period of research & development, once major chemistry challenges were solved, the company decided on a final product structure and wanted to move into production quickly.
Once samples came from the tooling trials, an issue with the closing mechanism (which was seen as being too loose) led to a redesign. The company saw various other ways to improve the product design and pushed for the corresponding adjustments. All in all, 7 parts had to undergo design changes and their molds had to go through revisions.
For example, the following changes were done on a part of the enclosure:
- Addition of the logo (embossed)
- Cancellation of 4 holes
- Changes in the height of screw posts, and other changes to reduce shrinkage
- An edge was made to protrude further to cover a gap
- The polished area was made wider, for aesthetic reasons
In total, for all 7 parts, the changes cost an extra 2,000 USD and, more importantly, took several weeks to complete (including re-trials).
Example 2: Innovative home product
Our customer developed an innovative home product. As the prototypes made from 3D printed parts seemed pretty close to working (except for a few leaking issues that were planned to be fixed by the higher accuracy of parts coming off tooling), the company decided to finalize the mechanical design and have tooling done.
Under high time pressure, the tooling team paid extra attention to the precision of machining, applied polishing & texture, and did the 1st trial (T0). The mechanical & electronic engineers put together prototypes, tested them, and sent them to the customer just in time for a trade show. Everybody agreed the quality of finishing on those T0 samples was extraordinary.
After some user testing and a lot of feedback gathered at the trade show, the customer came back with a list of changes needed. All in all, 11 parts’ designs had to be adjusted, which led to these changes on the corresponding molds:
- Various dimensional changes
- Addition of pillars
- Dimensional changes to some ribs
- Adding of support ribs
- Addition of an angle to a button
- Removal of parting line burrs
- Addition of ribs to affix the pipe more strongly
- Addition of a pin to the PCBA contact plate
Those changes triggered an extra charge of about 4,500 USD and added some weeks to the timeline.
Example 3: A new type of earbuds
An innovative type of earbuds was developed. Audio performance was good. With relatively high confidence in the product design, and an upcoming trade show, the product manager gave the green light to mold fabrication.
Hard steel was used. It was machined with high precision, for a nice finish. The cost of the molds was about 24,000 USD. Prototypes made with parts off tooling looked quite good.
A lot of feedback was gathered during the trade show. A lot of new ideas about the shape of the product emerged. The need for different ways to capture the surrounding sound appeared, as the team decided active noise cancelling was a must-have.
After months of redesign work, the team realized that the molds couldn’t be used. Actually, only the mold base could be re-used.
The new molds were made in relatively soft steel (grade 2738H) and the processing was simpler. The cost was 10,000 USD. The new mold will have a shorter lifetime and will necessitate more processing just before high-volume production.
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As you have seen in the examples, sometimes relatively small changes are required that do not add too much cost or time to a project, but, on the other hand, if the product requires wider changes, even a new set of tooling may be required, which is more costly. While mold tooling revisions are not necessarily a bad thing, they can increase costs, so we need to see how to minimize the chances of requiring them in the first place.
Conclusion
Tooling revisions can be seen as an unavoidable part of product development, but their impact can be minimized if some care is taken. It’s smart to try to anticipate potential design changes and work closely with experienced manufacturers. Fabricating lower-cost soft tooling with only 1 cavity may make sense for early iterations. By doing so, companies can avoid unnecessary costs and delays.
In the next post, “How to minimize the risk of needing tooling revisions?,” we will share some practical tips you can follow to reduce the risk of having to revise a mold.
