my present

[marioserafica]

Good evening to all,
...any time ago, in my first presentation I had greeted with "good morning to all", but for some reason the draft disappeared while trying to insert a drawing. It's a pleasure to take me back.
My name is marioserafica, I worked as a technician in the design of thermoelectric plants, after sailing eight years .
I have been retired for years now and in '94 together with others we have "founded" a modest voluntary association to bring effective aid to victims of the war in the territories of the former Yugoslavia (no one excluded).
for about 15 years we are engaged in the design, construction and application of orthopedic prostheses for.. who needs it and cannot afford it. . .
(no one of us is technical prosthetic, except for professional prosthetic friends who accompany us in our laps, but studying, asking and looking... we arrange.) for those who want to know more about our site is <timeforpeacegenova.org> and also on facebook.
we are updating our knee project, which we thought to realize, as for other components, through injection molding in delrin/pom,
but being the cost of the mold rather high (!!) and having tried the prototype ( verified with analysis to the finite elements) only in place with the help of an amputated friend, we do not feel to face such expense, if not after long and challenging tests on site, where conditions are much more severe.
change would mean .. another mold !!!
alternatively we bought a handcrafted cnc cutter and self-built a 3d pantograph, we are still perfecting parameters etc, but the results are positive.
but we did not abandon the idea of molding, also because motivated by a more complex project (precious plastic - </timeforpeacegenova.org>https://davehakkens.nl/community/forums/forum/precious-plastic/),
to verify the possibility of obtaining good results, by means ..modesti, we thought to try with the upper part of the knee, with simplified mold formed by external shell of adequate thickness aluminum and internal footprint in epoxy resin. the geometry of the mold will have to, clearly, allow the extraction of the print. the model is simple and we have an idea, but we would be grateful if you would like to suggest the optimal solution.
drawing allego for evaluation.
thanks and cordial greetings for time for peace-genova
mario seraphic
marioseraficaatyahoo.itwww.timeforpeacegenova.org

 

[TECNOMODEL]

And that piece would you like to get it with a "simple" mold?
You need at least two side trolleys to extract everything.
Have you thought of a 3d printing prototyping?
Alternatively you could make the mold always in 3d printing, if you don't have to print loaded materials or especially technical for pulling a few pieces you do quietly.

 

[marioserafica]

good day and thanks for the immediate answer.
...simple. We'd like to try. we thought of an aluminum mold divided into two parts by a passing plane for the satiate section.
in fact aluminum would be only the containers, while the imprint would be made by colando, in two times, of the epoxy resin.
the space between the two dense sectors would be maintained by inserting a suitable thickness, both to form the footprint, and during the injection; "eyely" should not be subsquadri...but the expert's eye could find them.
We tried with 3d printing, making us print the whole knee with better printers than we could afford, but the results we
they convinced that technology, at the moment, would not guarantee the necessary security.
in fact the material used today for other prosthetic components is the delrin. as mentioned we verify the project with analysis of the finished elements
In addition, we have built an electropneumatic equipment to test prototypes cyclically, as provided for in ISO 10328.
we try to get, as far as we can, reliability, simplicity and economics and following these principles we considered interesting as expected from the dave hakkens website.
sometimes professionals are suspicious if not contrary to "simplifications", concussi da qualità e tempi di produzione parameters inevitabili nel Mercato. we can also try to optimize the limited resources (only provided by friends).
we thank you again for the collaboration and any future proposal will be well accepted.
for tfp-genova mario serafica

 

[TECNOMODEL]

What is the sagittal plan for you?
if we consider the orientation of his design as the classic x-y-z and divide the mold to the bottom wire of the cylinder there are all or almost the teeth in the underframe, the same said for the holes of the two dentate fins. This would require two trolleys to extract the part of the two wings with relative souls forming the holes.
if instead we go to divide the mold on the axis z the correspondence with the half-works of the piece we have the central cut between the two wings, the upper concave part and its holes in subsquadro.
Also in this case it is solved with the construction of two trolleys, but the thing is complicated by the presence of holes on the wings. it would serve an oleodynamic closure of the carts in order to be able to close them before the press closing, on the dua matrices would then be present the souls that form the holes and that they would go to slip into the carts.
as you see both solutions are feasible but not simple as understood by you.

 

[Meteor02]

I see particularly difficult to get a simple mold to get the particular seen above. resin castings are not compatible with injection molding due to the forces in play, it is necessary to insert movements, to the eye there is no sform. the cheapest version that comes to mind is aluminum mold with housing and sleigh steel trolleys.
I have some doubt about the project, I would not be so sure that the dentate parts if made in pom can support the weight of a man who submits them to twist and bending during the walk. before thinking about a mold I would test the prototype much more carefully, perhaps thinking it already for injection molding so that once tested it should not undergo further modifications to make it feasible.

 

[marioserafica]

I see particularly difficult to get a simple mold to get the particular seen above. resin castings are not compatible with injection molding due to the forces in play, it is necessary to insert movements, to the eye there is no sform. the cheapest version that comes to mind is aluminum mold with housing and sleigh steel trolleys.
I have some doubt about the project, I would not be so sure that the dentate parts if made in pom can support the weight of a man who submits them to twist and bending during the walk. before thinking about a mold I would test the prototype much more carefully, perhaps thinking it already for injection molding so that once tested it should not undergo further modifications to make it feasible.

Good morning,
I'm glad that the problem raises a little interest, thank you.
I came up with the idea of resin (to overcome the costs of a print made directly from an aluminum block) because I had seen something like that in the past. clearly can not guarantee hundreds of printings (some say thousands!!) but for us a hundred a year could suffice... and then start again. .
the dense sectors come into contact with other fixed teeth, obtained in a separate block, only when the weight of the body is loaded on the amputated leg, winning the strength of an antagonist spring and blocking the joint (to avoid undesirable yields, especially descending stairs or steep terrain).
the construction of molds involves a particular technology..quasi an art, that we can not afford, as well as carts, sleds and every well of god. Therefore I also propose as an answer to technomodel, which undoubtedly reads at the same time, the "completely manual simplification, specifying that I forgot to mention the "shaped cover" and therefore the mold would be in three parts and that the various holes can be made after with column drill and a blade... not scandalized... but when there are no horses trot the donkeys and this fits perfectly to us (I)
....I thought I had already sent and attached drawings, in a second time, but I do not find trace ..!

 

[marioserafica]

 

[Meteor02]

Now an aluminum mold made to make maybe in wool has really low costs. mold closures have to lean in figure and close with several tons, to the eye I would say at least a 70 t press and I do not think there is a resin able to endure such pressures, moreover a fusion still needs to be resumed to cnc and need manual adjustment like a "real" mold, in short save a few hours of milling going to meet countless problems. then you already have a printer willing to take charge of such a bitch? using a resin mold is definitely not something from everyone on... in the workshop we have some old caiem mold (zama) that we use only internally seen the difficulty to find printers willing to treat so delicate molds. about the project I do not question the ability to hold vertical compression (assisted by spring) but the transversal stresses and twists, a man does not have a perfect balance, much less if forced to use prostheses, should he stumble as it would behave that prosthesis? and in front of a movement that would cause the distortion of a healthy knee?

 

[TECNOMODEL]

I understand your needs and I also find your intent commendable.
I think you're on the wrong road. As you schematized that piece will never get out of the mold, you have all the teeth in the subsquadro.
as I said in a previous post there is the possibility to make the matrices through 3d printing, there are printable materials quite resistant to realize limited productions. the thing, however, does not eliminate the need to have the two parts of the mold in steel or aluminum.
the matrices should be housed within this last in special locations.
even with this technique, however, the complexity of the geometry of the piece does not allow you to realize it through a simple mould with fixed and mobile matrix.
I am not clear what it means by completely manual simplification.
You don't think you're assembling the resin mold and pouring in molten plastic, do you?
the molding process requires adequate pressure for filling and, above all, compacting.
These pressures, to be contained, require solid structures that should not deform under the pressure of the material.
if the mold is not suitable you would find details full of bave and with geometries different from the desired one.

 

[marioserafica]

I read yours carefully (they are Genoese...but there is no difference in price between yours and then...) reply and I capitalized the highlights. But I do not see any particular difficulties in extracting the piece. I have the mold in three parts, the two side and the "coperche" and between the dense sectors I insert a suitable diaphragm. lever the cover, then free the top cup

How come today 14/12/2017 do not find the full text sent yesterday, but only a scampolo? and how do I know if it was received? thank you

 

[TECNOMODEL]

But how did the three parts of the mold keep them closed?
If you think you can put them in a box, leave it alone. The games you need to do would make you fearful.
how do you hold it in the two semi-tastes? the forces at stake are relevant, if it is not sufficiently robust it goes around the mold compromising the size of the piece.
Finally, once properly printed and compacted, the piece will have a big resistance of the same to separate from the two seeds, especially due to the teething.
How do you think you're "shoulding" the two semi-tastes from the piece?
other thing, how would you get the two resin semiguscs? mechanical processing? Those pointed teeth are a beautiful snare, both for processing and for the finished piece that at that point will be fragile.
I think the only way cheap enough is to find someone who has an interchangeable matrix mold with two side openings.
In that way, if the dimensions allow it, there would only be to build the matrices. Given the numbers it would be enough to make them aluminum.
the costs would be very reduced and the good result.
Then, of course, you have to see if the amount of cost falls into your possibilities.

 

[marioserafica]

I would start from the end, that is, "to find someone who has a mold...etc" "the costs would be very reduced..." and the most important point "the amount of cost"??????????????????????????????? If someone comes forward... well, indeed very well!

This is not a box in which to insert resin footprints, but a robust (we will calculate later the necessary thicknesses) aluminum body (in three parts) in which to drain the epoxy resin, drowning the model, in two stages, interrupted by a detachment application to ensure separation. follows a heat treatment in the oven to obtain the expected qualities. in these phases the model is maintained mechanically, for example with a passing pin in the lid. .
once the injection is completed (heated cylinder at controlled temperature, piston driven by pneumatic cylinder, closing force guaranteed by hydraulic cylinder ...) we hope to convince the two shells and lid to detach with the help of pressure pins (vulgo bolts) (we will certainly try to intervene, minimally, on the profile to make it more "fuggente! ).
as already said is a bit a bet and you will need many tests. ..always distances from acceptability are not astronomical. I'm going back. .
I can't tie sketch, I'll try later or tomorrow good night

 

[marioserafica]

I hope this time goes well

 

[TECNOMODEL]

You're practically thinking about working as you do in the foundry on earth.
In the absence of the appearance of the epoxy resin that I do not know about the characteristics, I can say that with all the time you use to do that little work you can easily make an aluminum mold.
we come instead to the speech injection: Are you talking about a cylinder heated with pneumatic piston, but is it an injection mould so equipped?
It's a primordial injection method, it's been replaced for decades by screw cylinders.
with a heated cylinder it is impossible to obtain proper plasticization of the material, the result is a non homogeneous casting that creates several problems to the finished piece.
However, I understand that the decisions you have already made, I would be curious to see the results of the work.
If you want to share them, I'd be grateful.
Good job.

 

[Lettore espatriato]

Good morning.
hoping I didn't mess with the posts and not repeat the same message for 2 times, I wondered if it wasn't possible to use molds in "silicone".
i have seen used in automotive models and small production batches (20-30 pieces).
After this issue, they usually have to be rebuilt, but probably, compared to an aluminium mold and 100 pieces per year, they are likely to be cheaper.
without considering that they can solve small subsquadro problems.

 

[marioserafica]

I once again stress that I responded to both you and the "expatriate reader", but once again everything disappeared
...I asked for explanations about where... I'll be early