1 - Is 3D Printing Right For Your Project?
Enclosures can be made of metal, wood, ceramics, plastic and other meterials too.
Nearly all electronic enclosures are fabricated from metal or plastic.
Metal cases may be necessary for ruggedization, shielding, or other reasons.
Metal cases are generally stronger, heavier and more expensive than plastic cases.
They are usually formed from sheet metal by folding, bending, cutting and drilling.
Plastic is a good choice of enclosure material unless you cannot use it.
Plastic is inexpensive, readily shaped, fairly long-lasting, and available in countless colors.
Many kinds of plastics are available with special characteristics:
- flexibility
- strength
- transparency
- biodegradability
- acid-resistance
- heat resistance
- non-toxicity
- conductivity
and more.
Even 10 years ago, the only practical method for producing plastic enclosures was injection molding.
Injection molding remains the most common manufacturing method for plastic enclosures,
but today 3D printing is an option to consider.
Injection Molding
Injection molding has been around for almost 150 years (first patent in 1872), so it is tried and true.
The injection molding process works by squirting molten material (usually plastic) into a mold.
Simple molds are two pieces which fit together and include one or more holes into which the molten plastic is injected.
Injection molding is a multi-step process:
- a two-part mold is machined from metal
(molds made from hard steel can be used hundreds of thousands of times)
- the molds are clamped together
- the molten plastiic is injected under pressure to fill the mold
- the plastic is allowed to cool
- the two halves of the mold are separated to release the newly formed part
To learn more about injection molding, with diagrams, see:
injection molding.
3D Printing
3D printing refers to a diverse collection technologies:
FDM, SLA, DLP, SLS, EBM and more.
3D printers do not use molds. Instead, they squirt molten plastic from a moving nozzle (FDM),
or cure photosensitive resins (SLA and DLP) with a laser or LED aray,
or sinter polymer powders (SLS) or metalic powders (DMLS) with a laser,
or fuse metal powder or wire by heating it with an electron beam (EBM)
All of these are additive processes because each proceeds by building up (adding) one thin layer of
material atop another until the part is fully printed.
Pros and Cons of Injection Molding
To produce one additional part by injection molding requires the execution of steps 2 - 5 of the process described above.
Steps 2, 3, and 5 take only a few seconds.
Step 4, waiting for the molten plastic to cool, typically consumes 90% of the total cycle time.
The overall size of a part does not necessarily affect cooling time but, rather,
cooling time depends on the wall (or other) thickness, and the efficiency with which the mold dissipates heat.
The total cycle time for an enclosure is likely to be less than 30 seconds.
We will see that 3D printing takes much longer.
Injection molding, obviously, requires a mold.
It typically takes about eight weeks (after the mold is designed) to have it manufactured,
and even a simple mold typically costs $10,000 - $20,000.
After a mold is milled, only the most minor changes can be made to it.
Beyond very minor changes a new mold must be made for another $10k - $20k.
Some products may require mulitiple parts or enclosures and therefore multiple molds.
Also, consider that if you are creating a new product, especially an electronic one,
it is possible—even likely—that one of your engineers' design goals will be to
reduce the cost and size of the circuit boards in subsequent releases.
If they are successful, you will need a new, smaller mold.
Pros and Cons of 3D Printing
3D printing uses no molds. The same 3D printer can produce any number of different cases with no retooling.
Switching production from one part or case to another requires nothing more than selecting a different file from
the printer's menu interface.
Modifying a 3D part requires no physical changes.
Whether the change is large or small, the 3D model gets tweaked using the same program used to create the model.
The model gets processed by another program (called a "slicer") and the same old 3D printer, using the new, modified
model produces a modified part.
The major drawback of 3D printing is that it is very, very slow.
Rather than injecting all the molten plastic for a part into a mold in a second or two,
3D printers lay down (or cure, or sinter) material bit by bit.
Printing time is directly proportional to the amount of material,
so a 100 gram (~4 oz.) case will take twice as long to print as a 50 gram case.
The cycle time needed to produce a case by injection molding is likely to be less than 30 seconds.
3D printing a 50 gram case will likey take 2 - 3 hours.
A 3D printed part or case, depending on the printing technology,
may not be as strong as an injection molded part—even when produced using the same plastic material.
Injection molding generally produces consisent, high quality, highly detailed parts.
3D printing, again depending on the particular technology, may not be capable of producing the consistency and detail
routinely achieved with injection molding.
Injection Mold or 3D Print?
An injection molding machine gets "fed" plastic pellets and produces plastic parts. Those plastic pellets, gram for gram,
are cheaper then identical plastic on spools (for FDM printers), or resins or powders used by 3D printers.
So, the material cost for injection molding is lower than for any 3D printing process, typically 40% - 80% less expensive.
The raw material cost for a single, injection molded, 50 gram case might be 75 cents.
The material cost for a similar 3D printed case might be $1.30 - $4.00.
However, even though the material cost of injection molding is lowest,
a mold is required, and that may tip the unit cost heavily against injection moldiing.
For example, the mold cost per case to injection mold 100,000 cases using a $20,000 mold is:
$20,000 / 100,000 cases = 20 cents/case
Adding in the materical cost of 75 cents, the total cost per case is 95 cents/case,
which remains less than just the raw material cost for 3D printing.
If, however, you only need 100 cases then using the same mold, the mold cost per case becomes:
$20,000 / 100 cases = $200/case
Adding in the raw material cost of 75 cents, the total cost per case is $200.75/case.
Of course, 3D printing uses no mold, so the cost per case is the same in any quantity.
Don't forget, however, that even though the cost per case to 3D print 100,000 cases might be as low as $1.30,
at 2 hours/case it would take 200,000 hours (23 years) to print them.
Of course, one could run 23 printers simultaneously and print them in only one year.
The obvious point here is that 3D printing is simply impractical for high-volume production.
Please note that the above examination of price looked only at mold and material costs.
In practice, injection molding charges will likely be 3 or more times the material (plastic) cost,
3D printing will cost quite a lot more because each print ties up a printer for so long.
