We have had very good results casting RP parts. We have a 3 hour dwell time at 300 degF. This seems to let everything settle down. The thermal expansion rates of investment and cured resin are very different from each other. We have seen problems with small cracks in the investment if this step is not done. That can not only show up in the casting, but bits of investment can flake off resulting in pits in the metal casting. We regularly cast small parts in stainless steels and other refractory alloys using R&R Astrovest in flask casting (not shell casting) with a highly modified centrifugal machine. We even use Astrovest for bronze/brass because we are used to it (we could use Kerr Satincast if we wanted to for these alloys). We are probably using much larger flasks than the normal user and this may account for the extended dwell time we need.
We cast steel et al at between 800 and 1200 degF depending on the section thickness. Clearly, we are not casting jewelry, but take this for what it is worth.
I have seen photos here with poor surface finish and it appears to me that the caster is not even using the brief low temperature dwell recommended by Formlabs or the part has not been properly UV postcured. Even our large parts have better surface finish than the photos.
Bill, do you mean that youâre casting at 300°C? Casting steel between 800 and 1200°F seems low? Also, what is a âdwell time?â Is this the final temperature before you cast, or the temp you hold at when youâre doing the initial melt of the wax? Iâve never heard this term used in jewelry, but I see youâre using steel. Can you describe where this is in the burnout cycle?
Also, has anybody here used Kerr Satincast? Iâm familiar with R&R, but would to prefer to use Satincast because thatâs what I have a lot of.
Romanoff in NY has all sorts of investment materials, good prices and really nice people to deal with.
Back to the parts being rough, I was wondering if they followed the burnout schedule properly or not. Thinking there is some residue in the mold cavity causing this. I am not a lost wax expert by any stretch but do know that the burnout process is different with resin parts than wax.
Sorry for the confusion. By âdwell timeâ I mean that during the early phases of burnout we keep the temperature of the oven constant at 300 degF . this seems to stabilize things as I posted in the forum. Investment fracture is a major problem we are dealing with here.
Most (but not all) of our castings are larger than a typical jewelry piece. ( but still, we can only cast 3 pounds of steel at a time). This makes things worse. We also had a big problem with voids in our castings at the sprue. It helped if we improved the sprue to part connection, but we could only get it under control by reducing the mold casting temperature at the end of burnout as described.
We use a duel beam optical pyrometer to measure melt temperatures. We typically cast about 100degF above the melting temperature of the alloy. Most people do not need this exotic equipment to get good castings. Run experiments to determine the length of time you spend after the metal is completely melted to when you cast. We use induction heating so the metal is getting hotter the longer it is being heated. Yes, it is dependent on the weight of metal, etc. We cannot afford to run these experiments on every part metal weight so we use the pyrometer.
In the past we have had very good results with Kerr Platinite (Spelling?). It has a completely different chemistry than the usual high temperature (phosphate bonded) investment. It is also very forgiving. Go to their web pages if you want to know more.
I do not want to stir up a storm here, but I do not think there is a great deal of difference between low temperature gypsum bonded investment brands (Satincast et al.) as long as the maker is reliable.
Bill
I know that this is obvious, we all need to keep in mind that our patterns DO NOT melt at all (unlike wax) - they oxidize and decompose. So most of the pattern is being removed at much higher temperatures. This means that there must be lots of oxygen around so it can do its thing. We open oven vent as long as we can maintain temperature.
Thermal expansion differences at all temperatures put the investment under stress. This can show up as investment flaking off and causing voids in the part to investment fracture.
I think it is very important to follow Formlabâs burnout cycle instructions.
Does the resin after post-curing change its properties?
I mean is it visually noticeable by eye or touch?
Is it more stronger?
Have bought nail-spa 365nm (36W) and LED 405nm (30W). Post-cured by both lamps to be sure.
By donâ;t know how to check post-curing desired result. Anyone knows?
Or maybe it is just 2 hours of post-curing and thatâs all
Peter
Tomorrow will send prints for 2 different casting companies. (pink, yellow 18k ; white 14k)
Soon i post results with design screenshots, print result and casting result.
Okay, here are my first prints from a local distributor. We used one of the nail salon-type UV curing units, with 36W bulbs on sides and top (it was this $70 USD unit)âŠyou can see that the top of the model, which was cured for a couple of hours, is much crisper. The second image, if you look carefully, is not clear at all. This was on the bottom of the âferris wheelâ as I had it laid out.
I think itâs a combination of a bad layout that could be corrected if I tilted the wheel at an angle, but the top of the wheel that was completely cured was harder and clearer, and the bottom of the wheel was soft and cloudy. This was also with the older version of the castable resin (that the distributor ordered last weekâŠand got the old stuff!)
Iâm brand new at this, so take my experience with a grain of salt. But I think my assessment is accurate. When cured correctly, the model is clearer and harderâŠ
@katkramer
When I see second picture a question arises:
did you extra treat the surface of the resin with abbrasives?
(I mean polishing tools) because it looks like that, or maybe it s the light.
We have build a new post-curing lamp recently.
Resin after post-curing seems to be fragile. Hope it is a good sign.
Sent today the samples to cast in silver.
next week will have results in my hand.
We are working on lamp with shorter time of curing.
second one is 30W LED lamp (for outdoor lightning purpose) with changed chip. Than received 405 nm light.
The problem is the shorter lightwave = the highier temp
(nail spa has 365nm and generates some amount of heat)
but we all need 405 nm= this is cool light - as read in the article from FormLabs.
cool light provides really small amount of temperature.
I used both lamps for 4 days (8 hours per day) to be sure that it has been post cured.
one of the tests : after 4 hours with 405nm lamp the resins changed its structure from flexible to much much more harder. It was good result but not so fragile as after few days. Now we think about acceleration of all process. Also we find out if post -curing is good after caster will do his job.
Hello Peter, I have been looking into 405nm uv led alternatives⊠I ordered the 5050 lightstrip but i think it will not be powerful enough⊠Can you please share where you found a 30w led lamp, so you had to modify it? chip? please explainâŠ
@survivalist
First time I did that post-curing process,
so maybe letâs wait few days when i receive gold and silver samples from 3 different casting companies.
Than we compare results of that post-curing process if good or not.
Hey PeterG, yes, I did try sanding it slightly with fine sandpaper. However, the dull blue is âmushyâ looking, whereas other parts of the model directly exposed were transparent and hard. I think itâs because the curing light could not get to the underside of the model with the stilts attached. I think tilting the model would be a better configuration for the next prints.
I donât have the Form 2 yetâŠIâm working with a distributor here in Austin, and I should have it within the next couple of weeks.
survivalistâŠI noticed that a lot of the reviews on Amazon of light strips talks about them âlosing their strengthâ after a while. I donât know how accurate this isâŠ
to be sure.
