Why we still need machined prototype, injection molding, die casting?

Everyone's now aware of 3D printing — they’ve read about it in the papers, on blogs or seen it on TV. The mentality now seems to be that, in the future, we'll be able to download our products or make them ourselves with CAD programs, apps and 3D scanners, then just print them out, it seems the traditional industrial will be changed a lot, ’3D printing’ makes it sounds so easy, doesn’t it? Do you think if it were still called ‘rapid prototyping,’ people would be saying “I can’t wait to get a rapid prototyper in my house’? But …

Strength: 3D printed parts are not as strong as traditionally-manufactured parts. Their layer-by-layer technique of manufacturing is both their biggest strength and their greatest weakness. In something like injection moulding, you have a very even strength across the part, as the material is of a relatively consistent material structure. In 3D printing, you are building it in layers — this means that it has laminate weaknesses as the layers don’t bond as well in the Z axis as they do in the X and Y plane. This is comparable to a Lego wall — you place all the bricks on top of each other, and press down: feels strong, but push the wall from the side and it breaks really easily. Machined prototype, it is machined from metal or plastic board, so the raw material strength is as it is, After machining, do some finishing, the strength can be very good as long as your choose the best raw material, and for injection & die casting, the process is that the material mixed completely, with chemical reaction, so obviously the strength is good.

Surface finish: People hear you can print in plastic, so they visualise a plastic item. This is likely to be gloss and smooth. They don’t visualise a matt finish with rough layer lines all over. Many companies offer a ‘smooth’ surface finish, but often neglect to add the suffix ‘for 3D printing’. You can also post-process parts, but this generally involves labour and/or chemicals like acetone (really nasty stuff) and loses detail and tolerance on parts.

Materials: Generally speaking, you can only print in one material, and this is generally a plastic. Now look around you…how many items are in your room that are made up of a single piece of plastic — just plastic, nothing else? I can see two things; a cup and a lens cap. The cup cost 5p. The lens cap was expensive, but requires very high accuracy and acute clips (not great on a 3D print thanks to the layers causing weaknesses). Would I 3D print it? No. Most items in the house are made up from multiple materials, and most of them are both metal and plastic. Those two cannot be made together as their melting temperatures are hundreds, if not thousands of degrees apart. I’d not like to smelt in my living room either.

So, 3D printing could not print anything, our traditional manufacturing is still on. When some parts we need to have strength and good finish or show it is real situation, we still need machined prototype process, injection molding process and die casting etc.. The future for consumer 3D printing lies in the potential for people to create, invent and share ideas. Since starting this business I’ve helped hundreds of designers make their ideas come to life, and am proudly watching as they arrive in the marketplace. These products are now being mass produced and not 3D printed, so the quality is much higher. 3D printing will continue to grow in areas like the prototyping market, medical, aerospace — the list goes on. But as an everyday household object? I’m not convinced. We are still firmly in the honeymoon period with 3D printing — we’re in aware of it and what it can do. But when you look at just the parts produced and not the way they were produced, printed parts are a long way behind in terms of quality, and when there often is no cost advantage, Captain Everyday will always go for the mass-produced one.

Xiamen Nieltec Metal & Plastic is your machined prototype specialist , Injection molding and die casting partners.