ABS vs Polycarbonate

Question

ABS vs Polycarbonate

LONDONDERRY (Mechanical)

(OP)

9 Sep 14 14:52

Greetings-
Recently, I inheriated a design project from a previous mechanical engineer no longer with the company. The design is a mobile suit case that is approximatley 20"x30" x 10". Inside is a laptop, docking station, camera, flash and other electronic devices. All of the previous mentioned items are mounted on top of an isolation plate (ABS plastic) with cylinder dampers on the other side that mount to the inside shell of the case. The isloation plate is 19x 29 x 3/8" thick and to reduce the weight, machine webbing was done on the other side. Recently, we have been getting customer feedback that the isolation plate flexes to much, feels cheap, and some of the elctronics devices also flex. I was considering changing the material from ABD to aluminum, but the quote I got back was really expensive. I'm now considering changing the material from ABS to polycarbonate but my question is will I gain anything by going from ABS to PC?

Demon3 (Materials) · Answer 1 · 2014-09-09 15:17:59

If your amount of flex is too high then you need a material with higher stiffness (modulus). PC and ABS have similar modulus. For your convenience I have provided a download from one of my plastic training web seminars. It compares the modulus and cost of most of the common thermoplastic materials.

http://ppl.ug/Q1GFlP1yBG4/

As you will see, for unfilled plastics ABS and PC are good options. Adding glass fiber or mica as reinforcement will improve modulus but you may lose some impact resistance. Adding ribs will improve stiffness too. I have included a link to a slide showing what happens to modulus as you add fillers to PP as an example.

http://ppl.ug/hzXJYBv5QyI/

Chris DeArmitt PhD
President - Phantom Plastics LLC

Consulting, ideas and training on plastic materials
www.phantomplastics.com

Pud (Mechanical) · Answer 2 · 2014-09-09 16:02:53

There are squillions of grades under the title ABS. Find out what it's currently made from and try a higher modulus grade.
Or try a 10% glass filled PC - or a 30% GF nylon. Nylon 6 is pretty cheap and will cycle faster than ABS.

I (and I guess Chris) are assuming that this is an injection moulding and not a thermoforming of some sort?

Cheers

Harry

www.tynevalleyplastics.co.uk

It's ok to soar like an eagle, but weasels don't get sucked into jet engines.

Demon3 (Materials) · Answer 3 · 2014-09-11 09:26:06

One material to consider is Curv. It's 100% polypropylene but with a 5GPa modulus (double that of ABS or PC). Unusually for PP it has amazing impact resistance even down to very low temperatures. Samsonite make their top suitcases out of it (I have one at home). It's available in sheet that can be thermoformed if needed.

http://www.curvonline.com/

Chris DeArmitt PhD
President - Phantom Plastics LLC

Consulting, ideas and training on plastic materials
www.phantomplastics.com

MikeHalloran (Mechanical) · Answer 4 · 2014-09-11 13:26:44

OP seems to suggest part is machined from 3/8" ABS sheet.

ABS sheet is definitely not as stiff as aluminum tooling plate, especially after you finish pocketing it for lightness.

Simplest fastest way to gain stiffness is to double the sheet thickness.
... and double it again if there's room.

While that's percolating through the change process, you need to check the current local stiffness around all the mounted stuff, either by analysis or by test with a dummy mounted item, a force gage and a dial indicator. Localized flexibility that comprises a perceived quality issue may guide you in revising the pocketing pattern.

Mike Halloran
Pembroke Pines, FL, USA

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ABS vs Polycarbonate