Question of the Week: Footwear 3D Printing

Question of the Week: Footwear 3D Printing
Some partially 3D printed shoes [Source: Fabbaloo]

This week’s question relates to how best to perform 3D printing of footwear, specifically, flip flops.

Reader Daniel writes:

“My main business is flip flops with arch support, but I have some other products I am starting to look at with ladies shoes and so on.

However, now with the pandemic and the fact that I want to get these other products moving along, I am now looking at the cost to take the next step and do all of our R & D in house here in Australia.

As such, I am looking at getting a 3D printer. We just need basic resin prototyping so that we can see the shape and so on prior to opening a mould. We might also use it to create rapid moulds so that we can make wearable parts from polyurethane. Printing wearable parts would be amazing as that would save the polyurethane rapid moulds, however, it is not a necessity. It would depend on the extra cost.

My question is, if you had to spend any money on a new 3D printer, given what I have told you about our user requirements. What are 1-2 options that would represent the best value for money for a small footwear company like mine looking to try and take the next step in professionalism?”

This is an excellent question, Daniel, and one that many small businesses have when considering a move in 3D printing. As you say, even though you are already 3D printing, there are many different 3D printing processes and capabilities, and the game is to find the best match between function and budget.

There are several concerns here and these will have to be sorted out before choosing any options, and this is what comes to mind:

3D Printing Strategy

You must decide on which approach you wish to pursue: 3D printing the actual items, or 3D printing molds in which the items can be created. The answers could be quite different depending on which way you intend on heading.

Build Volume

The particular items you’re 3D printing are shoes, and that implies a certain build volume is required. But it’s not just getting a printer that’s “a foot” wide. There are some tricks to the build volume.

Assuming you wish to have an entire shoe printed in one piece, it will have to fit into the build volume. This is clear, but there’s different ways to do this. I’d first determine the maximum shoe length, as that will govern the selection. However, I’d also add at least another 10mm if you intend on 3D printing molds for casting as the shoe will have to fit inside the mold.

Build volumes are usually quoted in Cartesian dimensions, but that’s not how you necessarily use them. For example, the shoe could be positioned diagonally, thus gaining a bit of length within the same build volume.

Using these approaches it might be possible to fit the shoe into a smaller build volume, and that could save some cash.

Materials For 3D Printed Shoes

Another consideration is materials. If you are 3D printing molds, then this allows for the highest choice in materials: you simply pour them in the mold. The only consideration in that case would be the mold material.

Several manufacturers produce casting materials, particularly for resin 3D printers that can achieve high resolutions. You’ll have to decide whether the molds will be rigid or flexible, and that depends on the geometry of your shoe parts. A flexible mold can release more complex geometries than rigid molds.

It’s also possible to produce a negative of the mold itself, and then cast it in a friendly flexible material that can become the actual final mold. This is more steps, but is more flexible — in more ways than one.

On the other hand, if you are 3D printing the final shoe part directly, you have to be concerned with the materials available for the 3D printer in question. Also consider how much of the shoe might be 3D printed; only the midsole, or an arch support, or all of it? The bad news is that the choice of materials is extremely limited, particularly for flexible materials. You may not find a material that matches your needs for durability, flexibility, price and even color. This approach may be useful only for prototyping the general shape of the shoe, and little else. Why prototype in this way when you can use a casting approach to produce the prototype in the final material?

Another consideration with materials is the cost. 3D print materials are notoriously high cost when compared to traditional materials, and thus for this type of item there’s not a lot of reason to 3D print the final product unless there is a specific reason to do so, such as personalized fitting. This seems to me to be a prototyping scenario.

Build Speed

I don’t think this is a big concern, as virtually all options will be slow. And by slow, I mean you’ll likely get one print done per day, probably completed overnight. Because of that effect the fact that one machine might be slightly faster than another is essentially meaningless: you pick up the completed print in the morning anyway.

Cost

Machine cost is indeed a big factor, but there’s more to the story. I would use a “total cost of ownership” approach to budgeting this venture. This would include the cost of the machine, the expected cost of materials over a given time period, and the labor required to operate and especially post-process the prints. There is also the unknown factor of downtime — all machines will break. For this you might consider buying TWO machines to ensure there’s always at least one ready to roll. Alternatively you could consider a maintenance program from the manufacturer to handle such problems — if one is even offered.

Some companies, like Carbon, offer their equipment on a subscription basis. While this can provide some cost smoothing and certainty, it can also be expensive compared to some options. On the other hand, Carbon has perhaps the widest array of different industrial materials available for this type of application.

3D Printer Product Support

A big consideration is support. I’ve mentioned that machines do tend to break, and you must know what the plan will be when that inevitably occurs. This depends on several factors, including your tolerance for outages and whether you have someone on staff who’s “handy” and might be able to attempt fixing the device on their own with manufacturer’s support. If not, then you should consider companies that provide some level of on site or mail-in support.

Another alternative here is to acquire the device through a local or regional reseller. These organizations typically specialize in on-site service and so they could meet the needs of an operation that can’t afford to fix broken equipment themselves.

Daniel, I don’t know the answers to some of these factors, so I can’t really recommend any specific machines. However, I can suggest that there are certainly options to cover off any combination of factors.

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