On Monday 4. May 2015 12.32.47 Luke Kenneth Casson Leighton wrote:
It looks rather promising, and I can see how the limitations of the printer might make prototyping difficult: I've also had people print me things, and it has required a lot of "post-processing" on their part to get mechanically- acceptable results.
I imagine that this would be adapted to more scalable processes once prototyped, however, which would infuriatingly eliminate some of the precision issues experienced during prototyping. Or would you first go through an iteration or two of higher-specification 3D printing first?
Paul
On Mon, May 4, 2015 at 5:29 PM, Paul Boddie paul@boddie.org.uk wrote:
On Monday 4. May 2015 12.32.47 Luke Kenneth Casson Leighton wrote:
It looks rather promising, and I can see how the limitations of the printer might make prototyping difficult: I've also had people print me things, and it has required a lot of "post-processing" on their part to get mechanically- acceptable results.
yeah tell me about it. i learned only recently that you have to switch on "antiooze retract".
one of the problems i'm encountering is that the inner walls are really quite thin. repsnapper isn't too smart, so it goes "i'll draw that inner part - 1mm thick - as a square, and right next to it i'll draw *another* inner part buuuut, because they're separate, i have to go zip-zip-zip (from 1st square to 2nd and back) to get the bit of oozing plastic off of the nozzle".
uuunfortunately, that "bit of oozing plastic on the nozzle" can be as much as 3-4mm long. it accumulates *per layer* on the exterior of a wall 1mm thick that's being built up 0.2mm at a time.
you can tell what's going to happen, can't you... :) yep you guessed it: that "bit of oozing plastic" makes the corner of the inner wall eeever so slightly higher by 0.2mm than the surrounding sides being built up... by the time you get 10mm high the corner is a whopping *4* millimetres higher than the height where the printer head is travelling!!
that ends up with a corner pushing the bed down, causing no end of problems including the entire part breaking free of the heated bed.
by switching on antiooze retract, the zip-zip-zip which causes 3-4mm of plastic to be dumped in a corner is replaced with "bzzz-zip-bzzz" which is:
* z-axis going backwards a couple of millimetres * x-y positioning to the new location * z-axis going forwards a couple of millimetres
and it carries on from there. it seems to work and produces much better quality work.
*if* however the walls on the parts i was printing were, say, the quotes normal quotes thickness - most people print 3D parts with walls *at least* 5mm thick, and *especially* if they were being printed as solid parts (which i am not), then there would *not* be the problems that i'm encountering.
looking at the parts that make up the mendel90, almost all of them are completely solid. holes are at least 8mm in diameter. any "interior walls", the smallest thickness i can see on any of the 100 parts is about... 4mm.
by contrast, i'm printing *hollow* parts where the walls are in some places only 0.7mm thick. certainly, the interior support struts are only 2 runs of the print head back-and-forth.
so it really really does depend on what you're doing, paul. i can say that now, after working with this mendel90 for... five months? :)
I imagine that this would be adapted to more scalable processes once prototyped, however, which would infuriatingly eliminate some of the precision issues experienced during prototyping. Or would you first go through an iteration or two of higher-specification 3D printing first?
right. ok, the plan is as follows:
* phase 1: get 3d printed parts working (as +ves) * phase 2: split all parts into two -ves * each 1/2 part will be subtracted from a "block" * this "block" will fit inside a metal container * the two 1/2 -ve parts will be fitted inside the metal container * low-viscosity injection mold plastic will be used to create a prototype part
phase 3:
* the two 1/2 -ve parts will be printed out on flash-thermal resin (on a DLP) * the two 1/2 -ve parts will then be flash-cast to metal. * the resultant 1/2 *METAL* parts will then be used for *production* injection molding.
the reason for using high-accuracy thermal resin to cast the molds in metal is that - i hope - they will be much more accurate, so will not require polishing.
if they *do* require polishing (i.e. not look good enough) then what i will do instead is investigate some casting methods that give the cast parts a "sandy surface" look, meaning that any blemishes simply won't show up as significant.
$USD 20k on polished injection molds when they're only going to last 2 to 3 thousand units before they wear out due to abrasion - it's silly. there has to be a better way.
l.
On Mon, May 4, 2015 at 6:00 PM, Luke Kenneth Casson Leighton lkcl@lkcl.net wrote:
I imagine that this would be adapted to more scalable processes once prototyped, however, which would infuriatingly eliminate some of the precision issues experienced during prototyping. Or would you first go through an iteration or two of higher-specification 3D printing first?
right. ok, the plan is as follows:
- phase 1: get 3d printed parts working (as +ves)
- phase 2: split all parts into two -ves
- each 1/2 part will be subtracted from a "block"
- this "block" will fit inside a metal container
- the two 1/2 -ve parts will be fitted inside the metal container
- low-viscosity injection mold plastic will be used to create a prototype part
so *right from the start* i have to design each part so that it can *either* be 3d-printed (as a +ve part) or that it can be split into two -ve halves.
these two halves will fit together, creating an inner space that can be filled with molten plastic... *but*, the tricky part is that it has to be possible to remove the two halves without destroying the plastic inside it.
so, having an inner space that goes round a corner is not possible to do, because at least one of the halves of the mold will be stuck. the two halves have to come out of the plastic *straight* - no overhangs are allowed.
i don't entirely know if this is ok, but i am counting on it being possible to pull one of the mold halves out at one end first, followed by the other. the reason is because i have some screw-holes and insets which i am *hoping* will not be destroyed or damaged when one half of the mold is pulled away from the plastic.
... we shall have to see!
l.
On Monday 4. May 2015 19.00.22 Luke Kenneth Casson Leighton wrote:
right. ok, the plan is as follows:
- phase 1: get 3d printed parts working (as +ves)
- phase 2: split all parts into two -ves
- each 1/2 part will be subtracted from a "block"
- this "block" will fit inside a metal container
- the two 1/2 -ve parts will be fitted inside the metal container
- low-viscosity injection mold plastic will be used to create a prototype
part
You're braver than I thought. ;-)
phase 3:
- the two 1/2 -ve parts will be printed out on flash-thermal resin (on a
DLP) * the two 1/2 -ve parts will then be flash-cast to metal.
- the resultant 1/2 *METAL* parts will then be used for *production*
injection molding.
the reason for using high-accuracy thermal resin to cast the molds in metal is that - i hope - they will be much more accurate, so will not require polishing.
if they *do* require polishing (i.e. not look good enough) then what i will do instead is investigate some casting methods that give the cast parts a "sandy surface" look, meaning that any blemishes simply won't show up as significant.
I think Bunnie had some interesting/amusing things to say about surface blemishes when they were making the moulds for Novena:
https://www.crowdsupply.com/kosagi/novena/updates/1330
$USD 20k on polished injection molds when they're only going to last 2 to 3 thousand units before they wear out due to abrasion - it's silly. there has to be a better way.
A while back, I became interested in these matters and surfed around looking at UK-based companies offering injection moulding services. Maybe I should dig some of those links out and see if there are any collaborative opportunities. Interestingly, I think one of them was actually publicly-owned (by a local council) and was technically a non-profit.
Paul
On Mon, May 4, 2015 at 10:08 PM, Paul Boddie paul@boddie.org.uk wrote:
On Monday 4. May 2015 19.00.22 Luke Kenneth Casson Leighton wrote:
right. ok, the plan is as follows:
- phase 1: get 3d printed parts working (as +ves)
- phase 2: split all parts into two -ves
- each 1/2 part will be subtracted from a "block"
- this "block" will fit inside a metal container
- the two 1/2 -ve parts will be fitted inside the metal container
- low-viscosity injection mold plastic will be used to create a prototype
part
You're braver than I thought. ;-)
or just ignorant of what could all go horribly wrong...
I think Bunnie had some interesting/amusing things to say about surface blemishes when they were making the moulds for Novena:
yyeah :)
$USD 20k on polished injection molds when they're only going to last 2 to 3 thousand units before they wear out due to abrasion - it's silly. there has to be a better way.
A while back, I became interested in these matters and surfed around looking at UK-based companies offering injection moulding services. Maybe I should dig some of those links out and see if there are any collaborative opportunities. Interestingly, I think one of them was actually publicly-owned (by a local council) and was technically a non-profit.
yes please!
On Tuesday 5. May 2015 01.07.40 Luke Kenneth Casson Leighton wrote:
On Mon, May 4, 2015 at 10:08 PM, Paul Boddie paul@boddie.org.uk wrote:
A while back, I became interested in these matters and surfed around looking at UK-based companies offering injection moulding services. Maybe I should dig some of those links out and see if there are any collaborative opportunities. Interestingly, I think one of them was actually publicly-owned (by a local council) and was technically a non-profit.
yes please!
OK, I'm not sure if any of these are useful, but I found them educational when I was trying to figure out what kind of services people were offering. My starting point was actually wondering what the state of the industry was in the UK: plastics always seemed to be a common feature of industrial estates, at least up in the north of England, and I wondered whether it still was.
I found the following interesting because they make the fact that the customer owns the tooling a virtue. Maybe that isn't the normal practice, or maybe it's because they're so confident of their own abilities that they make a virtue of it...
http://www.omega-plastics.co.uk/
The following people are the publicly-owned company I refer to above. I just found it interesting that such organisations are still around and haven't been closed down by the powers that be:
http://www.moorlandplastics.co.uk/
The last time I made anything with plastics was at secondary school, unbelievably, so I sought out more recent guides to the technology. Here's one I found rather useful:
http://www.bpf.co.uk/Plastipedia/Processes/Injection_Moulding.aspx
Perhaps I surfed many more companies' sites and didn't think it worthwhile to note them all down. Nevertheless, I hope you can get some ideas about possible routes to production from some of this.
Paul
Luke,
1) We print 3d parts with one professional company doing it on good equipment. I can give you contacts if you like and you can ask for quote. Usually best scenario is to print several parts on your printer and when you think you are done, pay for better prints (for example if you need to shoot video or present it to investors you need the best you can get, don't spare on this).
2) I had several bad attempts with the mold makers but I think I found qualified one in China (this is specialized shop only in molds, the guy has been working on parts of HTC, Apple etc.). if you like I can give you contact and you can send him parts for quote to see if you can lower cost for mass production. He can also produce. As a rule of thumb, if you are going to China for mold go in Shenzen area, the best molder makers are there and opposite and if you go to i.e. Ningbo area good chances are that you are going to finish with bad quality parts, looking cheap. If you are not sure what you are looking in term of finishes, go to some mobile phone store, find some telephone (that you have exact model that you can point to molder so you have same reference) and ask molder if he can do that and that type of finish. I am not a mold specialist, but making several thousands pcs of one mold is way too low. Mold should last at least 100k pcs, depend on the quality of material can last 200, 300k pcs. Again, speak to qualified molder, ask for quotation and ask for number of produced units, ask for advice and second opinion. if they still reply you this low number ask why.
Hrvoje
On Mon, May 4, 2015 at 7:00 PM, Luke Kenneth Casson Leighton lkcl@lkcl.net wrote:
On Mon, May 4, 2015 at 5:29 PM, Paul Boddie paul@boddie.org.uk wrote:
On Monday 4. May 2015 12.32.47 Luke Kenneth Casson Leighton wrote:
It looks rather promising, and I can see how the limitations of the
printer
might make prototyping difficult: I've also had people print me things,
and it
has required a lot of "post-processing" on their part to get
mechanically-
acceptable results.
yeah tell me about it. i learned only recently that you have to switch on "antiooze retract".
one of the problems i'm encountering is that the inner walls are really quite thin. repsnapper isn't too smart, so it goes "i'll draw that inner part - 1mm thick - as a square, and right next to it i'll draw *another* inner part buuuut, because they're separate, i have to go zip-zip-zip (from 1st square to 2nd and back) to get the bit of oozing plastic off of the nozzle".
uuunfortunately, that "bit of oozing plastic on the nozzle" can be as much as 3-4mm long. it accumulates *per layer* on the exterior of a wall 1mm thick that's being built up 0.2mm at a time.
you can tell what's going to happen, can't you... :) yep you guessed it: that "bit of oozing plastic" makes the corner of the inner wall eeever so slightly higher by 0.2mm than the surrounding sides being built up... by the time you get 10mm high the corner is a whopping *4* millimetres higher than the height where the printer head is travelling!!
that ends up with a corner pushing the bed down, causing no end of problems including the entire part breaking free of the heated bed.
by switching on antiooze retract, the zip-zip-zip which causes 3-4mm of plastic to be dumped in a corner is replaced with "bzzz-zip-bzzz" which is:
- z-axis going backwards a couple of millimetres
- x-y positioning to the new location
- z-axis going forwards a couple of millimetres
and it carries on from there. it seems to work and produces much better quality work.
*if* however the walls on the parts i was printing were, say, the quotes normal quotes thickness - most people print 3D parts with walls *at least* 5mm thick, and *especially* if they were being printed as solid parts (which i am not), then there would *not* be the problems that i'm encountering.
looking at the parts that make up the mendel90, almost all of them are completely solid. holes are at least 8mm in diameter. any "interior walls", the smallest thickness i can see on any of the 100 parts is about... 4mm.
by contrast, i'm printing *hollow* parts where the walls are in some places only 0.7mm thick. certainly, the interior support struts are only 2 runs of the print head back-and-forth.
so it really really does depend on what you're doing, paul. i can say that now, after working with this mendel90 for... five months? :)
I imagine that this would be adapted to more scalable processes once prototyped, however, which would infuriatingly eliminate some of the
precision
issues experienced during prototyping. Or would you first go through an iteration or two of higher-specification 3D printing first?
right. ok, the plan is as follows:
- phase 1: get 3d printed parts working (as +ves)
- phase 2: split all parts into two -ves
- each 1/2 part will be subtracted from a "block"
- this "block" will fit inside a metal container
- the two 1/2 -ve parts will be fitted inside the metal container
- low-viscosity injection mold plastic will be used to create a prototype
part
phase 3:
- the two 1/2 -ve parts will be printed out on flash-thermal resin (on a
DLP)
- the two 1/2 -ve parts will then be flash-cast to metal.
- the resultant 1/2 *METAL* parts will then be used for *production*
injection molding.
the reason for using high-accuracy thermal resin to cast the molds in metal is that - i hope - they will be much more accurate, so will not require polishing.
if they *do* require polishing (i.e. not look good enough) then what i will do instead is investigate some casting methods that give the cast parts a "sandy surface" look, meaning that any blemishes simply won't show up as significant.
$USD 20k on polished injection molds when they're only going to last 2 to 3 thousand units before they wear out due to abrasion - it's silly. there has to be a better way.
l.
arm-netbook mailing list arm-netbook@lists.phcomp.co.uk http://lists.phcomp.co.uk/mailman/listinfo/arm-netbook Send large attachments to arm-netbook@files.phcomp.co.uk
http://rhombus-tech.net/injection_mold/
paul, thanks. hrvoje, could you put links/info on there so that it's possible to refer to in the future, easily?
soft tooling (lower cost) is what i was referring to. hard tooling (what you are referring to) lasts much longer and, obviously, costs a hell of a lot more.
i'm looking for practical ways to get prototypes ready at a lower cost even than soft tooling.
l.
arm-netbook@lists.phcomp.co.uk
-
Hrvoje Lasic -
Luke Kenneth Casson Leighton -
Paul Boddie