New to molding, need some advice please!!

[shmuck2002]

Hi guys,

I have been developing a product that, I believe, the best route is to make it out of injection molded plastic. The part is a single piece, approximately 8" wide, 6" tall, and about 1" thick, no moving parts, no heat resistance condiderations to worry about, and it is not a high-strength part either.

I did some research online and found having it professionally injection molded would be cost-prohibitive at this stage, maybe an option later on. Right now, I need to make a few just as prototypes, and to get a patent issued.

I have seen some chatter about people making DIY injection molding machines, seen a few pictures etc, but they look like they are designed to make parts much smaller than I need. Things like golf tees and knobs for automotive use, etc. The item I need to make is obviously bigger.

So, I have a few questions: First, I intend to use a recycled material such as oil bottles or 2-liter bottles, things of that density. Would I be able to make a mold out of something like epoxy or concrete? I do not have access to any sort of CNC machine that would allow me to make a mold from aluminum, and from a practical standpoint, the only way for me to make this would be to cast one of my hand-built prototypes to use as a master copy. I have seen brief mention of using epoxy or cement, but I cannot find anything in particular if people have used it for molding plastics. If this is feasable, then by all means... do tell

Having no experience in this field, it's entirely possible I am overlooking another production method more suited for DIY'ers, any suggestions on that level? And again, having no experience in this field, am I attempting something that is impossible for the DIY'er, by trying to mold something too large for a home-built unit? I ask that question because the home built units I have seen are making very small items.

A final question - do people make home-built CNC machines? bastardizing a drill press with a dremel and a X-Y axis tray? I am a computer engineer by trade, so the hardware to software interface is no issue, if building a computer-controlled CNC is the desire.

[rd1001]

Hi schmuck2002,

Your part is probably a little to big for one of those manually operated machines you may have seen. I just finished building my own bench-top injection molder for making prototypes, but the maximum mold size is only 2 1/2" x 2 1/2" x 4". In general, a larger part will require a more powerful machine. Its not just the injecting force you have to consider, its also the clamping force to hold the mold closed. The machines sold by http://www.Morganindustriesinc.com could possibly do it.

I think the best way for you to proceed from here will depend on what your objective is. Are you building the prototypes to prove functionality before applying for a patent? If so, they don't have to be pretty, they just need to function. So, you may be able to just assemble multiple pieces of plastic together by screwing them or gluing them, or whatever. I've already made numerous prototypes by just using a soldering iron to weld the various pieces of plastic together, and then shot a heat gun or micro-torch on certain areas until it gets soft enough that I can bend it into a desired shape.

On the other hand, if your prototypes don't need to function like the final production parts will, but just need to look good, you can probably make nice looking models by using a "plastic like" urethane resin.
http://www.Smooth-on.com sells everything you would need.

Focusing on building your own molder or cnc machine just for one part could easily get you sidetracked from completing your invention. http://www.Sherline.com sells small CNC machines controlled by PC. Occasionally you'll find used ones for sale on Ebay.There's also a popular book on how to build you own injection molder. Just google "ISBN: 1878087193"

The good thing about having to work on an invention when you don't have any money is it forces you to find ways to make things as simple and cost effective as possible. I would suggest taking another look at your part. Is there any way you can simplify it even more? Perhaps one side could be completly flat. That would allow you to make it in a half mold. Basically just pouring the urethane resin into a cavity until it reaches the level top. Maybe instead of injection molding the whole part, a portion of it could be made from something that is bought off the shelf and then mechanically attached to a more simplified injection molded piece. Maybe the part could be thermoformed instead of injection molded, Which is alot cheaper.Etc, Etc,

Hope this helps. Good luck.

Dave

[shmuck2002]

Thanks for the detailed info Dave, and I think you are absolutely right - I could very easily get side-tracked from my goal if I start horsing around with making the molding machine, or any other type of DIY tooling setup. What is important now is to build a prototype, probably from fiberglass resin and elbow grease and see how it goes. Once I do that, apply for patent, and put my web site and other advertising facets in place, and see what kind of interest I generate for the project, I will have a better idea of weather I want to find a DIY method for production, or if volume is high enough, bite the bullet and have a commercial outfit make my mold and have a few hundred units made.

Once that is off the ground, or as a seperate project completely, I may start fiddling around with a DIY moulding machine or even a CNC

Cheers, and thanks again for the detailed information!!

Joe

[bengomez]

I think you may need a prototyping machine for your molding... some rapid tooling..




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Rapid Tooling

[rs_shadow0000]

The acceptable affair about accepting to plan on an apparatus if you don't accept any money is it armament you to acquisition means to accomplish things as simple and amount able as possible. I would advance demography addition attending at your part. Is there any way you can abridge it even more? Perhaps one ancillary could be completly flat. That would acquiesce you to accomplish it in a bisected mold. Basically just cloudburst the urethane adhesive into a atrium until it alcove the akin top. Maybe instead of bang abstraction the accomplished part, a allocation of it could be fabricated from something that is bought off the shelf and again mechanically absorbed to a added simplified bang molded piece. Maybe the allotment could be thermoformed instead of bang molded, Which is alot cheaper.Etc.

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Stereolithography

[pincplastic]

I cannot find anything in particular if people have used it for molding plastics.


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Plastic training

[msmou]

Mingsheng Mould is one of the leading plastic mould manufacturers in China, can offer you top quality moulds with reasonable price and on time delivery.Please feel free to contact me for any further information.

MSMOU INDUSTRY CO.,LTD www.msmou.com www.tsmp.cn

[www.pmolds.com]

we will use the plastic mold

[levon606]

I worked for the Patent Office for two years, and one thing I know for sure you do not need an actual prototype to apply for a patent. All you have to do is demonstrate in your drawings and description that your part is fully functional, a constructive reduction to practice so to speak.

You don't even need to apply for a patent to lock in your invention date. You can either file a provisional application (costs $100), which will contain all of your disclosure, or you can simply make your full disclosure public. US is a first to invent country, and you have exactly one year to apply from the date of making your invention public before your own work can be used against you (statue 102 (b)).

As of injection molding your part, your volume is far more often your limiting factor than the mold size. Even some of the heavy duty indsutrial machines are limited by 2-3 oz of shot volume. Did you consider having your part printed using some of the 3d printing services to make the prototype?

You can check out the injection molding machine I made on youtube, under the same username.