Sharp edges design for injected molded parts


I noticed expanding trend regarding designs based on sharp(non rounded) edges for injected molded parts. the examples are jbl speakers or some products especially from Home Secure or home entertainment systems.

First question is - how do the manufacturing facilities produce those parts which seem to have minimal drafts and no rounds on edges?

  • is it extra materials related?

  • is it injection mold construction related?

Second question - how these quasi transparent parts are made? I mean the parts where indicated areas seem to have LED beneaf?

Well, often there will be a radius, up to 0.35mm or whatever else the toolhead can reach, enough to give a sharp appearance.
For some sections there may well be toolheads that can produce a straight transition.
Also instead of zero draft you can use 0.25 degrees which up to three inches will look virtually straight.
Unlike what textbooks say, a lot more is possible with injection molding nowadays.
It is a combination of smart tooling and part design strategies. You may design a partial draft on the inside so while the part is in cooling phase it shrinks onto the core but also away from it in mold release direction.
Gas/air assisted ejection is another option.

As for the LEDs, many plastics are by themselves somewhat translucent. White PS is a good example but also PP will work.
You can design specific lighting modules inside but even if you place an LED behind a thin matte translucent acrylic part so it catches and diffuses the light you can see it as a defined shape on the outside.

You can see the small radii (look at the edge of the power strip for example) in most of these examples. You can get very small and tight radii on parts. You will get a sharp edge if you put the parting line of the tool on the edge of the part where the core meets cavity.

Low draft parts have been possible for a while. It may reduce part yield, require a polished finish which created complexity in handling and tooling design to avoid drag marks, but most vendors are willing to be aggressive down to .5 degrees of draft on polished parts which looks virtually square even it if it isn’t. You can also use side pulls in the tooling to get a perfectly perpendicular wall.

For translucent light pipes there are tons of options. But usually there is either an inserted clear/frosted part placed in from behind, or the part is two shot injection molded where the clear and opaque parts are molded together for a completely seamless look.

small drafts max 0.5 plus high gloss surfaces make the solution, am I right? it makes the design some kind driven: top surfaces textured and adjacent side ones high glossed? it makes sense while comparing this to attached picture

There are ways to get the manufacturer to reach more, it is a matter of finding the right party and setting up good communication lines, preferably directly with engineering. Side sliding cams and cryogenic deburring are definitely a great option to look into as well. And please understand, if you angle the surfaces of the mold core, since the part shrinks away from the cavity, it will still release from the core even at low or zero draft for some geometries. It is a matter of the risk and time you want to invest to reach these solutions. I have had a part with 0.25 draft over 3 inches approved for injection molding - does it look exactly straight, no, but still very good and the general eye does not pick up that difference especially if it is well surfaced.