Kinds of plastic for molded parts in a main frame as structure

[markpinto]

Hi Folks

I have a small machine to design that the client wants to use molded plastic in a larger role. previously they used molded parts for what I call inconsequential items, rollers knobs and things that are easily replaced and are usually wear items. now they want to use molded parts in the main frame as structure or as adjoining parts in a framing capacity . Has plastics progressed far enough for that? if so what kinds are being used successfully for these things, I envisioned the unit still having a light steel structure and use the plastic to fill out the bulk of a part so the plastic doesn't have to deal with as much force by itself. or even laminating the molded parts with steel. The units have to have a nice fit and finish like a consumer product when done. Ultimately they admitted they are going for a more flowing and rounded look. their competitors use thermoformed covers on ugly structure to get their look but thats not what they want, they want this look built into what would normally be pretty angular sheet metal bodies. Damn it's getting too busy ..

 

[Ninja]

I can't comment on types of plastics...not my forte...

But for design and "sexy" which seems to be in the mix, you may want to consider tolling out for 3D printing or "additive manufacturing". You have a lot more design freedom there, and don't need the molds.

Check it out and see if it is appropriate for your work...

 

[Ronen E]

Hi Markpinto,

Well, I'm a mechanical engineer by education and plastics happen to be my expertise on the engineering side... Sounds like you stumbled upon that field, but let me assure you that what your client is looking for is quite mainstream today.

Has plastics progressed far enough for that?

Definitely!!! The range of materials, design tools and techniques and array of applications and "precedents" are just astonishing compared to even 25 years ago (when I first entered the world of plastics). Today even under-the-bonnet automotive metallic parts are being substituted for plastics, not to mention things like home appliances and business machines (including frames and other load-bearing non-wear parts).

if so what kinds are being used successfully for these things

There's a wide range, and typically the best material is selected for each part. There are high-heat grades, high-strength grades etc., and if your strength / rigidity requirements are really high there are also composite grades, eg fibre-reinforced plastics (glass fibres, carbon fibres etc.). In a project like yours, a plastics design engineer is usually involved, both for material selection and for engineering analysis. In most settings I've seen, that person is also the part designer or works in tandem with an industrial designer (where looks are paramount).

I envisioned the unit still having a light steel structure and use the plastic to fill out the bulk of a part so the plastic doesn't have to deal with as much force by itself. or even laminating the molded parts with steel.

No need for any of that today, unless the application is super-demanding. Plastics are the material of choice for design and artistic flexibility, and with the right amount of engineering (not too much is required in most cases) functional / performance requirements can be met as well.

Cheers,
Ronen.

PS If you want to go deeper into specifics of the machine / project, please feel welcome to send me a private message.

 

[Ninja]

... things like home appliances and business machines (including frames and other load-bearing non-wear parts).

There's a wide range, and typically the best material is selected for each part. There are high-heat grades, high-strength grades etc., ...

At the risk of derailing the thread (which I hope I don't do)...

If there are high strength grades...I've been looking ofr high strength plastic floor joists...are they around yet?
Not suspended...sitting right on a damp concrete slab...just need to hold up the raised floor.

 

[Ronen E]

I've been looking ofr high strength plastic floor joists...are they around yet?
Not suspended...sitting right on a damp concrete slab...just need to hold up the raised floor.

Do you mean something like that?

 

[Ninja]

Do you mean something like that?

Yes, precisely...Thanks for the lead!

$80+ each for a 10' section...ouchers. I think I'll just strip a plastic deck board and put it on the bottom of a wood joist...

 

[NikkiQSM]

I work for a plastics compounder. While most of what we produce is medical, we do produce industrial plastics as well.

The first step is to determine the specifications you want.

What would be the minimum impact strength, or other physical properties?

What is the desired cost? Some resins you purchase could only be $1.00 a pound, while others can be $80.00 a pound. So you will want to pick and choose while keeping costs in mind too.

Are you molding this resin? If so, you may want to consider cycle time as well. You will want a resin that can quickly set before being removed. A resin with a long cooling time can result in slower progress.

I would recommend speaking with whomever does your design and development.

 

[Ronen E]

Are you molding this resin? If so, you may want to consider cycle time as well. You will want a resin that can quickly set before being removed. A resin with a long cooling time can result in slower progress.

I would say cycle time is affected much more by the geometrical design of the part and by the IM tool design than by the selected polymer grade (though that does have some effect too).

Cycle time really matters when the quantities are big and each piece is expected to be super cheap. For a machine / appliance housing I'm not sure it's that critical.