Table Of Contents
This article is a member of our series on different manufacturing processes for custom gaskets. It follows the same structure, and includes similar introductory text, to ensure that whether you read a single article in the series or multiple, you’ll have all the information you need.
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Choosing a Process
Choosing the right manufacturing process for producing your custom gasket is as much of an art as it is a science. The right manufacturing partner should be able to review your design, understand your needs for volume, and help you decide the appropriate method for production.
As much as we all wish it was an incredibly simple decision to determine the right manufacturing process fit for your needs, there are a ton of considerations that go into the decision. Any manufacturing partner worth working with long-term should have a very thorough Design for Manufacturing (DFM) process to help work through this with you.
Choosing the right manufacturing process is about balancing all of the following factors:
- Lead time
- Volume of parts
- Quality and/or tolerance levels
- Material selection
Often making a decision that improves one factor can have an affect on the other factors, so understanding which process to choose ultimately comes down to prioritization. Deeply understanding how to achieve the requirements of your design as well as understanding what matters to you outside of the design itself leads to the right choice. And that is what the DFM process is all about.
This article breaks down some of the considerations that would lead to choosing CNC or digital cutting as the correct manufacturing process. It is meant to provide some general guidelines, but is by no means exhaustive, nor is it a replacement for undergoing the DFM process on a specific design.
How it Works
Computer Numerically Controlled (CNC) cutting, also called digital cutting uses a very precise knife to cut the material. With this method, the design file is uploaded into a computer that is controlling the digital cutter. Referencing the digital file, the machine runs and produces as many parts as you have programmed it to cut.
Typically, there are two cutting implements that can be used: a drag knife and a pneumatic oscillating knife.
A drag knife works in the way you’d expect from a typical knife where it is inserted into the material and dragged across the cutting path to produce the part.
The pneumatic oscillating knife, by contrast, works by moving up and down to cut through the material. Essentially the knife is pressed down through the material, lifted, then shifted forward and pressed through again.
When is CNC or Digital Cutting a Fit?
Digital cutting is often used when materials are not compatible with Steel Rule Die Cutting or for low volumes of quick turn parts such as prototypes.
However, depending upon the number of parts being produced, the material being used, the complexity of your design, and the speed at which you need the parts delivered, digital cutting is useful across a variety of situations.
In general CNC cutting may be a good choice for the following situations:
- Rapid prototyping: No hard tooling means small volumes can be produced quickly and less expensively than methods that require hard tooling.
- Material waste: Designs that nest well can provide less material waste than die cutting and may help reduce your material cost.
- Handles small or large parts well: Great for parts that aren’t a fit for die cutting because they are too small or narrow, or are too large for the die press.
- Short lead times: If you need your parts faster than hard tooling solutions can turn them around, CNC cutting may be the right fit.
Take a deeper look at some of these considerations in the sections below.
One of the most important aspects of the DFM process is an understanding of the material you are looking to make your gasket with.
In general there is a misconception that tolerances for a specific design are determined primarily by the machines cutting or producing the gaskets. In reality, the ability for a manufacturer to meet tolerances on a specific gasket design depends far more heavily on the material itself than on the manufacturing process.
The interplay between the material itself and the method of gasket production is a very large part of the DFM process. Getting the right match between the two is a big part of the battle.
Density and thickness of the material being cut is often a large part of the determination of if die cutting will work to achieve the desired result. And unfortunately, it isn’t as simple as just looking at the material properties themselves; it is actually more a factor of how the design of the gasket and the material properties will affect each other.
CNC cutting is a great fit for the cases where the interplay between material and design make die cutting impossible. For instance, CNC cutting makes it possible to produce parts where there are wall thicknesses that are narrower than the thickness of the material, whereas die cutting does not.
Material thickness is also a big factor in making CNC cutting a good fit. Materials over 1 inch thick are not a good fit for CNC cutting. It is however a great fit for materials that are between 1/8th of an inch (about the thickness where die cutting no longer works) and 1 inch.
Design and Quality Considerations
Up next in the list is the design of your part itself. Arguably this factor has the most sway over which manufacturing process will be the right fit.
When a design comes our way for DFM, the first thing we will look at is the tolerances listed in the design. Often a big part of the communication that happens with a customer during the DFM process is to understand if there is leeway on any of the tolerances listed (and in many cases there is).
Understanding what is a hard and fast requirement, and what can be adjusted helps us determine the right manufacturing process that will also help balance other important factors like cost and lead time.
CNC cutting is able to maintain tighter tolerances than die cutting in certain situations, however one consideration to keep in mind is what is referred to as “overcut.” When the oscillating knife is raised and lowered into the material, there will be small overcuts (particularly around corners) that are the width of the knife, which become more noticeable with thicker materials.
In many cases this is perfectly acceptable, but may not be in others. It is truly a matter of understanding your design and production needs in great detail on a case by cases basis.
The next consideration in what is beginning to feel a bit like a mile long list is your cost. CNC cutting has not traditionally been thought of as the “lowest cost” manufacturing process, but, depending on the situation it can be.
Part nesting: One such instance where CNC cutting can reduce costs is through part nesting. If your part design can be nested in such a way that CNC cutting allows us to produce more parts from the same size sheet of material, then it can reduce material costs significantly.
Small volumes: Because there are no hard tooling costs with CNC cutting, if volumes are low enough, it can be cheaper to produce your parts with digital cutting than die cutting (where there is the additional hard tooling cost to build the die).
Changing designs: During rapid prototyping, design changes are happening frequently. CNC cutting allows a lot of flexibility to update and adjust the part design to be able to quickly test variations in the design. You also won’t have to pay hard tooling each time there is a change to the design.
Lead Time Considerations
Yet another item to consider is lead time. CNC cutting is generally one of your best options if you need your part like yesterday.
It is much easier to turn around parts with short notice using digital cutting techniques than those that require hard tooling, like die cutting.
In addition, using the layering and nesting techniques listed in the previous section, it can also help to bring down the total time to run a large volume of parts.
The Bottom Line
There is no easy way to say CNC or digital cutting is or isn’t a fit in general terms. It always comes down to a review of the interplay between your design, selected material, and production requirements.
Hopefully this article provided you with some clarity on what we review in order to determine if CNC cutting might be a fit, but if you are looking to see if it works for a specific design, we highly recommend submitting it to us for a DFM review.