The Tech Team is excited to introduce a brand new feature to the product evaluation process: Most Active Sort!
The purpose of this sort is to continuously surface ideas that are interesting and worth further evaluation. The sort will provide an hourly ranking of the community’s engagement with an idea. We want to show you what’s the most pop– we mean, the most active ideas on the site.
Let us know what you think!
Due to popular demand, the Tech Team has decided to REMOVE the controversial Most Popular sort from the Product Evaluation process, effective immediately.
Without machining, most of the modern manufacturing methods would not be possible. Machining is a subtractive process, meaning that you start with some block of material and cut away until you have the part you want. Carving marble (or ice or pumpkins) would be a subtractive manufacturing method; 3D printing and knitting are two examples of additive manufacturing methods.
When people talk about machining, they are generally referring to two machines: the mill and the lathe. Both leverage the power of mixing sharp things and spinning really fast. The mill spins a (more or less) stationary cutting tool while moving a non-spinning part into it to be cut; the lathe spins an otherwise stationary part to be cut while moving a non-spinning cutting tool in for cuts.
Milling machine.
Most machining these days is CNC machining (Computer Numerically Controlled). The motions the machine makes and the speeds everything moves at are all programmed in. With CNC machining, all of those movements are insanely repeatable. What isn’t necessarily as repeatable is how you’re holding the material you’re cutting. You need to establish datums and often even cut in the features you want to measure everything against to ensure precision. Another limitation of machining is that you often have to reposition parts to cut all of the features you need – if you’re holding a part by one side, you need to flip it over to cut the other side. That can also mean losing exact datums.
The molds and tools for a lot of manufacturing methods are made by machining – certainly for injection molding and extrusions, the first two methods I talked about. And, like I mentioned in the extrusion post, often parts made through other manufacturing methods need to be post-machined. That may be because the manufacturing method used first couldn’t add a feature (like the hole for the switch on the Split Stick) or because the original manufacturing method doesn’t have high enough precisions. If you have holes that need to be very precisely located, sized, or round in an injection molded part, that will often be a post machining step. Post-machining means more time spent handling every part, which adds cost. However, machining is used as the primary manufacturing method on parts as well, particularly on things that are truly round, like axles, or things that require precision, like tools. It’s too time intensive for most mass produced products, though.
Lathe.
How expensive something is going to be to machine is generally based on 3 things – material, how much needs to be cut away, and how many times the part needs to be repositioned. For any given material, there’s usually a maximum depth of cut – if you try to make a deep cut into steel, for example, you risk breaking the tool instead. Machining often involves making multiple passes over the same area to cut to the right depth. So, machining a hard plastic takes less time and causes less wear to the cutting tools than machining steel.
If some of this post has been a bit general, that’s because machining is so versatile. It’s so integral to manufacturing that there are a lot of variations on how it can work. Mostly it’s used on metals and hard plastics, but there are workarounds for machining other materials too. There are combination mill/lathes. There are milling machines where the spindles can rotate to cut at angles. If you want to learn more about machining, there are lot of videos on the web that that demonstrate the basics.
The best idea in the world will stay just that – an idea – if you can’t figure out how to make it. Understanding manufacturing methods helps you see how difficult it will be to make a design (which, of course, usually relates to the bottom line).
Although pasta is also an example of something that’s made through extrusion, the first thing I think of when I hear “extrusion” is always the Play Doh Fun Factory.
Extruding material is a way to make something with a uniform cross section. Material is pushed through a tool called a die that has the desired cross section cut out, and comes out as a continuous piece that has the same shape all along its length. A wide variety of materials can be extruded, but the process for extruding plastic is a little different than the process for extruding metal, so we’ll start with metal.
For metal extrusion, you start out with round bar stock, so the size (and therefore cost) of the die depends on how big the smallest circle you can draw around your desired profile is. That circle is called the circumscribing circle. Sometimes the metal is heated, which lowers the forces involved, but changes the properties of the metal. (Like when you leave chocolate in the car, and it melts and then resolidifies. It is still chocolate, but it tastes a little bit different and has those white specks.)
If you have ever used the Play Doh Fun Factory, you might remember that, for example, when you tried to make the asterisk profile, the plastic bowed out a lot. So when you thought you were going to get this skinny little profile, you got this big fat one instead. That demonstrates the reason behind a few of the things that go into design for extrusion.
-The dies aren’t thin, and they don’t have the same profile all of the way through. The profile on the side of the die where the material enters is bigger, and sometimes less detailed, than the profile on the exiting side. This reduces the stress on the die because it sort of eases the material into the final shape, and (as with people) reducing stress extends life.
- You want your profile “wall thickness” to be somewhat uniform. The thinner a gap you’re trying to push the material through, the less it’s going to want to go. If you have a big fat section section next to a skinny section, the same amount of force is going to push the material through faster in the fat section.
-There’s only so thin you can go. That limit mostly depends on the material you’re trying to extrude, though the size of the circumscribing circle also comes into play. The absolute smallest for steel would be around .15″, but aluminum would be more like .05″.
The body of the Split Stick is made out of an aluminum extrusion. But it’s a hollow extrusion. So you might think that would be a problem. How would you support the center of the die? If you think about extruding a metal pipe, you would actually start with a “C” shaped die, and then move the center of the C over into the middle of the circle as you get closer to where the material exits.
Another thing you might notice about the Split Stick is that there’s a slot on the top face. One of the limiting things about extrusions is that you often have to machine parts afterward to add features, like we have to do to make that hole.
That should be a little glimpse into how extrusion works – again, if you want to know more, the Internet is your oyster!
One of the strengths of the Quirky community is the broad range of backgrounds that our members bring to the table. That variety does mean that some community members are intimately familiar with what happens “from sketch to store,” and others might be getting a bit lost when the conversations get more technical. So for my next few bi-weekly blog posts, I’ll be trying to explain the basics behind some of the most popular manufacturing methods we use. For those in the know, please excuse some broad generalizations.
Far and away the most common process we use is injection molding – it’s probably the most common manufacturing method for any plastic or rubber. Molten plastic is shot into a steel mold at high pressure, allowed to cool slightly, and then ejected from the mold. The steel mold is called the tool, and tooling costs tend to be pretty high for injection molding ($1K-$80K) because steel is expensive and labor intensive to cut. On the other hand, the part cost (basically the cost of the plastic used) is pretty low, because it’s pretty easy to automate. The most basic mold would have two sides and no moving parts (except opening and closing). For more complex geometries, or to add features like threads, mold makers add more parts to the mold (which, of course, adds more cost).
While the plastic is cooling, it also shrinks, and that’s the basis of most of the limitations involved in injection molding. One example is wall thickness. Because the cooling occurs at different rates depending on how thick the part is, parts need to have more or less even thickness – otherwise the part warps, because the middle of thick sections are still liquid while the thinner sections are trying to shrink. If you want to know more about different design constraints for injection molding, just google it – there are tons of guides out there.
Two of the most powerful things you can do with injection molding are overmolding and insert molding. For overmolding, you mold two different materials in the same mold – that’s how you get all of those objects that have rubber grips permanently attached attached to hard plastic. Overmolding is very popular in toothbrush and sneaker design. Insert molding is where you take something and put it in the mold before the process starts, so that it ends up embedded in the part. For example, Cordies has an insert molded steel piece that adds weight to the ends.
There are lots of books out there on injection molding, and lots of slight variations on the process, but that’s the general gist of how it works.
Addendum from Ben: How does this all work in the real world? Check out our awesome PowerCurl molds!
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