Whether you call it design for manufacturability (DFM), design for manufacturing and assembly (DfMA), or the latest acronym, design for additive manufacturing (DfAM), learning and following its principles is a sure-fire way to improve manufacturing processes and produce higher quality products at a lower cost.
At first glance, it can seem like a lot to take in. That's because manufacturing is a deep subject, and there's much to know before people consider themselves experts.
Testing the DFM Waters
Fortunately, we can simplify the process and ease some of the pain customers might feel when struggling with DFM principles through our intuitive digital quoting platform. Begin a project on our website and experience it yourself!
Once you've selected the desired manufacturing process—CNC machining, 3D printing, or injection moulding—you'll be asked to upload a CAD file. After that, you'll need to answer some questions about the raw material, surface finish, part quantity, and so on.
Depending on the selected process, you might receive an immediate price and "Ready to Order" notice, but it's more likely that your quote and DFM analysis will arrive within an hour or so. With them, you might also receive one or more design advisories.
It's essential to read them and follow their recommendations. Design advisories provide helpful advice about the part’s manufacturability. Even though the part design might be okay as is—meaning it’s manufacturable—it could be improved. That's why it's crucial that if you have any questions or concerns, you should contact one of our customer service representatives for help.
Dealing with DfAM
At the risk of stating the obvious, the “A” in DfAM stands for additive. As anyone familiar with the technology will attest, 3D printing offers greater design flexibility than any other manufacturing process. It does, however, present some challenges. Check out some of our other design tips, and you'll discover a wealth of information about common mistakes, size and geometry constraints, and ways to improve part cost, quality, and lead time.
For example, holes smaller in diameter (about 1.5mm to 2.8mm) can be challenging with any manufacturing process, and 3D printing is no exception. The same can be said for narrow slots and tall walls, especially if they're many times deeper than they are wide. A design advisory might flag these areas as “Review and Accept”, while others throw up a big red “Remove from Quote” flag. Both of these indicate the feature’s level of non-manufacturability.
But what’s perhaps most unique about additive manufacturing (the “AM” part of DfAM) is its need for support material to keep part layers from curling or sagging during the print process. Exceptions exist, and part orientation plays a significant role in the number and spacing of these scaffold-like structures. Still, the fact remains that support management—though not strictly a DfAM consideration—is one area where a quick chat with one of our applications engineers can lead to better parts and fewer surprises.
DFM for Chipmaking
Additive manufacturing brings benefits in terms of complexity and ease of manufacturing, but one DFM rule that any designer should live by is this: If the part is easily machined, go with that production method. In fact, thick, blocky parts like hydraulic manifolds and the threaded fittings that go into them might be unprintable due to the amount of heat they acquire during the build. The bottom line is that if you can machine, mould, stamp, or form it, that’s probably the route you should take.
Speaking of screw threads, here's another tip that might not fall into a purist's DFM bucket but is a common reason for faults: avoid modelling that 1/4-20 tapped hole or 1/2-13 external thread. Yes, Solidworks and Fusion 360 make it easy to do it, but machine shops everywhere—us included—prefer a simple UNC or UNF-style thread callout.
There’s lots more to know about DFM for CNC machining. Don’t make tolerances any tighter than necessary. Square internal corners on vertical walls add significant cost. Text does, too, especially if it’s raised. Oh, and don’t choose titanium when steel or aluminium will do. Another thing to keep in mind is that very deep pockets and holes may make the part unmanufacturable. Also, just as with injection moulding and 3D printing, thin walls tend to bend or break.
Moulding and Beyond
Last but certainly not least on the DFM list is injection moulding. This champion of high-volume plastic part production has its own volume(s) of manufacturing guidelines, some of which contradict those already mentioned. For instance, thin walls won’t deflect during the moulding process like they will during machining and 3D printing, but the molten plastic might not flow into the mould’s harder to reach areas, leading to what’s called a short shot.
But make those walls too thick and you might experience a phenomenon called sink, which is just as big of an issue. Also, as with over-tolerancing of any manufactured part, overly smooth surface finishes drive up part cost.
Conversely, rough surfaces tend to reduce processing time with machining and 3D printing, but with injection moulding they can lead to dreaded ejection problems. Then, there are parting lines to contend with where mould halves meet, not to mention undercuts, gate placement, and more. Here's one area where a short chat with a moulding expert can pay big dividends later in the project.
It may seem daunting initially, but don’t worry! The good news is that, despite the seemingly huge number of DFM guidelines that apply to this and the other manufacturing processes, the design rules built into our quoting process will help to steer you in the right direction. The design advisories that accompany your quote, along with our extensive library of design tips, will also help. And if you need support, you know where to find us. You can speak with one of our application engineers at +44 (0) 1952 683047 or customerservice@protolabs.co.uk.