Very low strength of HIPS prints - Why?

Question

I'm using a Prusa i3 MK3S printer. After ~8 months of printing PLA, PET-G, ABS I decided to buy some HIPS and print something with it. I cannot print >1 filaments at once, so I'm not using it as a support for ABS, I want to create some high durability working models, like gears, robot parts etc.

While the quality of my models is perfect, unfortunately their strength is disappointingly low. They easily undergo plastic deformation or break. I've tried lots of settings, some yielding better or worse results, but the problem is present regardless.

My settings:

• Printer: Prusa i3 MK3S
• Nozzle: Default 0.4 mm nozzle for Prusa
• Layer Height: 0.2-0.3 mm
• Temperature: 230-240 °C nozzle, 100-110 °C bed
• Slicer: PrusaSlicer 2.0.0

I've read lots of tutorials regarding HIPS printing and they did not give me the answer to my question...

Am I doing something wrong or is it normal for High Impact PolyStyrene? At this point, the High Impact Polystyrene seems less High Impact than generic PLA.

Answer 1

It might. If HIPS is a single material with consistent properties, it might have a narrower temperature range. Online references suggest up to 240 °C. Try that, then 245 and 250 °C. Maybe higher.

Answer 2

You might try upgrading your PrusaSlicer to 2.1.1. I don't know if the "Prusa HIPS" setting got updated since your 2.0.0 but it's worth checking.

For comparison, PrusaSlicer 2.1.1 uses these settings for HIPS:

Filament:

• First layer temp: 220
• Other layer temp: 220
• Bed temp, first layer: 100
• Bed temp, other layers: 110

Cooling:

• Fan speed: min 20%, max 20%
• Bridges fan speed: 50%
• Disable fan for first 3 layers
• Enable fan if layer print time is below 10 sec
• Other cooling settings same as for PLA

Advanced:

• Max volumetric speed: 11

There's also custom G-code for HIPS setting M900 K10.

I, too, want to print actual parts with HIPS. For me, it's because HIPS the lowest density of all the commonly-available stiff-plastic filaments, which is great for printing lightweight model aircraft parts where every gram matters.

Answer 3

The primary use of HIPS in 3D printing is to create sacrificial supports, which you're aware of. The material dissolves in lemon oil, making it popular for printing dense supports within complex shapes that can then be easily removed just by spraying the part down with Orange Clean.

I would not expect HIPS material sold for 3D printing use to have much if any strength, especially for moving parts. Outside 3D printing, most uses of the material are in expanded foam products like bike helmets, flotation products etc, and these applications require pressure-molding, which creates a higher-density object and hardens the foam's outer layer to make it tough enough for everyday use. Just extruding the stuff out into the open air gives you the same density (and strength) as a packing peanut.

If you want a styrene-type material that's strong, tough and relatively light, I'd stick with ABS. If you're looking for a challenge in a similar material, try nylon; it creates a lower-friction surface, is very tough but pliable, and its hygroscopy requires very careful handling of the filament (in some more humid climates, you have to feed it from a dry box through PTFE tubing straight into the printer; even the time out in the air between the box and the extruder is enough to get hydrolysis-related issues).

If you really want to print HIPS foam gears, the only thing I can suggest you try is an epoxy coating to give the object a harder shell while retaining the light weight. My wife does custom-applique vacuum tumblers (but who doesn't nowadays; my wife's making more money selling other people the supplies and equipment to do it), and her favorite stuff to use is Faux Rizzle; very durable, odorless, easy to mix and apply, and relatively inexpensive (many other art resins sell for about double what you can get FR for). Good luck to you.

Answer 4

I've been using HIPS for nearly 2 years now to print the housings of EDF units for RC planes. They come out light and strong but have poor layer adhesion, especially on thin-wall parts.

Normally I print at with a 260 °C nozzle and 100 °C bed but will try higher temperature when I upgrade my Ender 5 to a 32-bit board. Thin cyanoacrylate painted on the surface solves most issues. Sometimes I use a solution of ASA dissolved in acetone to paint the surface and bind layers together.

The EDF rotors I print from Apollo X which is a modified ASA that is easy to print but not soluble in acetone.