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Comment by kelukelugames | Hacker News Reader

Any manufacturing experts can help us understand why white plastic is difficult?

White plastic highlights defects including contamination with other colors (or materials), burn marks, and shrinkage. It is common for one injection machine to be used for many colors and types of plastic, but since white is such a pure color, it is very easy to see swirls or traces of other colors in the part. Even different batches of white plastic can cause unsightly marks; getting some nylon in your ABS part will certainly ruin it. Burn marks (which are dark) obviously stand out more against white than any other color, and are generally caused by either the mold or plastic being too hot. Shrink marks are caused by uneven cooling of the plastic because of machine settings or part design, and are most visible on white because of uneven reflections and small shadows. Even tiny scratches can ruin the glossy finish of a smooth part.

Since Apple has huge volumes, they can dedicate machines to injecting a single mold, and ensure that plastic colorants are matched across batches; the rest of us (with volumes of less than ~100-500k/yr) have to settle for grey.

If anyone wants to chat about part design and manufacture, let me know.

Is this still a thing?

I ask in seriousness, as commodity smartphones with small production runs, less than 100k, and earphones, even USB cables, now exist at very low prices, production runs and seemingly margins.

Or has the mold part got easier, allowing different shapes/sizes without burning, and the colourants / dedicated white production line now standardised?

Smartphone enclosures themselves are usually quite simple, and if you look closely, you will see that most small devices are designed much more simply than Apple products. Apple dedicates more effort into modeling plastic flows, shrinkage, and other manufacturing issues than most other OEMs. Apple also dedicates more effort to refining production techniques than most other manufacturers. Companies like Samsung and HTC have volumes almost as large as Apple's, and are not far off.

Molding parts has gotten a little easier over the last 10 years. Molding machines are more easily tuned, and CFD tools have gotten much better and easier to use. The Bolt post is addressing new companies with 1k-100k/yr volumes and less expertise than Apple, and the post is largely correct.

Thanks.

After reading further comments I decided to compare all of the white plastic devices I have, and they're all a often noticeably different colour, even on different parts of the same device.

I think several of us are interested in some insight into this world. It seems like you have it and are able to convey it in an easy to understand, compelling way.

I suggest you write a series of blog posts that explain interesting bits and quirks of manufacturing processes that the rest of us outside of the industry don't really think about.

It's a way that you can help inform the world, and also capitalize off of your knowledge! Please consider it :)

Seconded!

We manufacture large parts in Apple white, and it's not caused a huge number of problems. At least not yet.

What about white with texture? Definitely understand white shows artifacts on glossy textures very readily, but we've had decent luck with Mold-Tech textured whites at admittedly very small volumes (1-5K).

Color match is still rough though.

Texture makes any color much easier to deal with, as it makes mixed colors, materials, and shrinkage less visible.

Really glossy any colour is difficult. Glossy black shows sink much worse than light colours in my experience. Texturing fixes so many difficulties in injection molded parts.

I certainly am! Please tell more. :)

Black makes it easier to hide defects. White makes any tiny issue show up very clearly, it's hard to get the exact shade of white right, and you'll need to run lots of plastic through the machine to make sure no little bits of other colors are still waiting in there to ruin your new pieces.

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