We offered a new laboratory exercise in our Compute Aided Engineering class — Kiln Glass Casting.   We have been playing with direct 3DP molds for a little over a year now.   The way to know if you really understand something is to let students give it a go.

This lab allows you to experience direct mold printing (via 3DP) and kiln casting glass.  Your mold will be used once(it will be
distroyed during the Kiln casting process).

You will not need draft and you can have undercuts (if you have undercuts, you will likely need  vents due to trapped air).  
Also, if you have significant undercuts, there may be issues of de-powdering your mold.

Constraints:

You will not be constrained by mold boxes BUT you may use only 12000 mm^2 (~18.6 in^2) or less of plate cross-section and the max
height is 70 mm (about 2.75 inches).

No part of your resulting glass object can be more than 1 inch (25.4 mm) thick.

Mold must be 16mm (5/8 inches) thick everywhere.

Design Guidelines:

  • Consistency of honey.
  • Features on a surface (min 3-4mm).
    • Smaller features might break off in depowdering (similar to previous labs).
    • Some smaller features might not completely fill out, but they will leave an impression.
  • Extruded and thinner features must be greater than 3/8″ with proper gates to allow flow and air to escape.
  • Edges of smaller features will not be crisp.
  • Must be able to access all parts of the mold to depowder it.
  • Features on the top surface (especially open-faced) on the edge of the mold will be rounded because of the meniscus of the glass.

They designed!  We printed molds.  We set the firing schedule on the kiln to cast glass, loaded up the kiln, and pushed start…

The result was a 50% yield.   Even after all of the reading that we had done on kiln casting (and successful runs), the thicker parts were not annealing and cooling correctly.  We even had one explode with such force that it destroyed its mold!   Time for more research and reading.  After much more reading, we learned a new phrase — “lower strain points“.   While one could employ finite element analysis to run an annealing/cooling analysis to determine a furnace curve (perhaps another time), much of art glass is explored empirically.   We found an amazing book of furnace curves by Graham Stone called “Firing Schedules for Glass – The Kiln Companion”.   Biblical in firing schedule nature!  With several new firing schedules in hand, time to reprint molds and try again…

Yes, we know that you REALLY shouldn’t open the kiln when its glowing hot (so don’t) but we couldn’t resist taking this picture.  Our resulting firing schedule is a mixture of schedules from Bullseye Glass, Spectrum Glass, and Graham Stone’s Book.   We were casting regular (not premium) Spectrum Furnace Nuggets (a System 96 soda-lime glass) which is typically used in glass blowing furnaces (it is economical for class use).

Rate (F/hr)  Temp (F)   Hold Time
=================================
200           850       0.5 hour
500          1050        1 hour
500          1650        6 hour
9999          960        6 hour
  8           800        1 hour
 16           700        1 hour
OFF  to cool to room temperature

This schedule seems conservative and produced 100% casting success.

We believe that this curve works for objects of 2 inches (100 mm) or less in thickness.  (How one determines maximum thickness is completely another issue to be discussed another time).  

Results…

Our students had a great time (although if we’re not careful this could become the “shot glass lab”).  We still have a few more pieces in the kiln… We can’t wait to see them.


32 Comments on Student Glass Work

  1. dthorpe says:

    Great article! Thanks for posting.

    What material are you using for the 3D printed molds? Hydroperm?

  2. dthorpe says:

    Great article! Thanks for posting.

    What material are you using for the 3D printed molds? Hydroperm?

  3. What a chance for WU students !
    Long life and prosper !
    A glass friend !

  4. What a chance for WU students !
    Long life and prosper !
    A glass friend !

  5. Rand Launer says:

    Great information from a wonderful project. My question would be…Did you use a mold release of any kind? IE…How did you get a good release from the mold?
    Thank You,
    Rand

    • ganter says:

      Rand, the molds are one time use. We didn’t use any mold release. We (Laura West & I) have been experimenting with various mold
      releases but haven’t found that glass needs too much. Getting the top end firing temperature in the correct range gives large
      variations in surface finish. Thus, its worth you time to run many temperature tests. Charlie Wyman likes to run his molds as cool
      as he can as long as he gets adequate glass flow.

      • Rand Launer says:

        Thank you very much.
        I’m going to try to use the molds more than once.
        Why not? I just bought the Hydroperm. Excitement is hard to contain with a firing schedual!!
        I’ll use “Slide 1800 hi-temp mold release @ $18.00 a 10 oz. spray can. Next would be the high priced…”Tri-lox 5500” white graphite mould release @ $50.00 a 10oz can.

        Oh my, I wish I was able to participate in your classes!!
        Thank you.
        Rand

        • ganter says:

          Rand, please keep us posted. Laura West tried out some mold washes the last time she was in our lab but no clear winners.

  6. Rand Launer says:

    Great information from a wonderful project. My question would be…Did you use a mold release of any kind? IE…How did you get a good release from the mold?
    Thank You,
    Rand

    • ganter says:

      Rand, the molds are one time use. We didn’t use any mold release. We (Laura West & I) have been experimenting with various mold
      releases but haven’t found that glass needs too much. Getting the top end firing temperature in the correct range gives large
      variations in surface finish. Thus, its worth you time to run many temperature tests. Charlie Wyman likes to run his molds as cool
      as he can as long as he gets adequate glass flow.

      • Rand Launer says:

        Thank you very much.
        I’m going to try to use the molds more than once.
        Why not? I just bought the Hydroperm. Excitement is hard to contain with a firing schedual!!
        I’ll use “Slide 1800 hi-temp mold release @ $18.00 a 10 oz. spray can. Next would be the high priced…”Tri-lox 5500” white graphite mould release @ $50.00 a 10oz can.

        Oh my, I wish I was able to participate in your classes!!
        Thank you.
        Rand

        • ganter says:

          Rand, please keep us posted. Laura West tried out some mold washes the last time she was in our lab but no clear winners.

  7. Bert says:

    WOW ! GREAT !
    thanks for book link
    What power of you oven ?

    We believe that this curve works for objects of 2 inches (100 mm)
    2 inches not 100mm it only 50 mm

  8. Bert says:

    WOW ! GREAT !
    thanks for book link
    What power of you oven ?

    We believe that this curve works for objects of 2 inches (100 mm)
    2 inches not 100mm it only 50 mm

  9. Alice says:

    Hello, I’m very interested in all of your glasss 3D printing technologies. Do you have a phone number or direct email address at which I can contact Open3DP? I haven’t been able to find one on the site.
    Thanks!

    • ganter says:

      Alice, Sorry, We’ve been away enjoying the summer. We don’t have a phone number (due to state budget cuts). As for email, the comment stream works fine. RISD is well known for glass (so you should have great questions).

      • Alice says:

        Hi,
        Thank you for your response! I did some research into the 3D glass printing and discovered a couple things. One, that the process is still mostly in the research phase (thus happening experimentally at universities). Two, Shapeways did offer 3D glass printing at the commercial level but then retracted it. Three, that 3D glass printing is still at the lab level because we haven’t yet found a way to print where the result is transparent (which is the quality of glass that is desirable anyway.)

        Could you please confirm for me that these are true, and tell me about the next steps in terms of when the public can expect to have access to 3D printed glass that has vitreous qualities?

        Thanks!
        Alice

        • ganter says:

          Alice, 1.) anyone with a 3D powder printer and a kiln can do it. 2.) don’t know about Shapeways as many things have changed there. 3.) see answer 1.

          You might think of 3D printing glass as pate de verre with a super fine glass powder (think glass powder which is screened finer than 400 mesh). Yes are correct that given that starting point that clear glass will not likely result (but PDV wouldn’t be clear either). PDV with fine glass produces amazing work (just not clear generally).

          3D printing in glass already has vitreous quality as vitreous is a material property of glass.

          The next steps as to when the “general public” will have access to 3D printed glass (see #1). One can get a 3D powder printer on internet auctions for less than $5K which will print glass. If more groups engage 3D glass printing, then more interesting things will happen.

          Clearly RISD as a design school might likely have a 3D powder printer (start with our recipes and give it a go).

  10. Alice says:

    Hello, I’m very interested in all of your glasss 3D printing technologies. Do you have a phone number or direct email address at which I can contact Open3DP? I haven’t been able to find one on the site.
    Thanks!

    • ganter says:

      Alice, Sorry, We’ve been away enjoying the summer. We don’t have a phone number (due to state budget cuts). As for email, the comment stream works fine. RISD is well known for glass (so you should have great questions).

      • Alice says:

        Hi,
        Thank you for your response! I did some research into the 3D glass printing and discovered a couple things. One, that the process is still mostly in the research phase (thus happening experimentally at universities). Two, Shapeways did offer 3D glass printing at the commercial level but then retracted it. Three, that 3D glass printing is still at the lab level because we haven’t yet found a way to print where the result is transparent (which is the quality of glass that is desirable anyway.)

        Could you please confirm for me that these are true, and tell me about the next steps in terms of when the public can expect to have access to 3D printed glass that has vitreous qualities?

        Thanks!
        Alice

        • ganter says:

          Alice, 1.) anyone with a 3D powder printer and a kiln can do it. 2.) don’t know about Shapeways as many things have changed there. 3.) see answer 1.

          You might think of 3D printing glass as pate de verre with a super fine glass powder (think glass powder which is screened finer than 400 mesh). Yes are correct that given that starting point that clear glass will not likely result (but PDV wouldn’t be clear either). PDV with fine glass produces amazing work (just not clear generally).

          3D printing in glass already has vitreous quality as vitreous is a material property of glass.

          The next steps as to when the “general public” will have access to 3D printed glass (see #1). One can get a 3D powder printer on internet auctions for less than $5K which will print glass. If more groups engage 3D glass printing, then more interesting things will happen.

          Clearly RISD as a design school might likely have a 3D powder printer (start with our recipes and give it a go).

  11. Hi Alice, hi Ganter,

    Very happy that you’ve re-openend this subject. We’re also interested at Cerfav FR with this printability of transparent glass. We’re exploring laser possibilities. Here you can find some results (that turned pure silicium to vitrous matter)…. Let’s us know more of your background… (pages 7 & 8) http://issuu.com/cerfav-verre/.....e-infos-48

  12. Hi Alice, hi Ganter,

    Very happy that you’ve re-openend this subject. We’re also interested at Cerfav FR with this printability of transparent glass. We’re exploring laser possibilities. Here you can find some results (that turned pure silicium to vitrous matter)…. Let’s us know more of your background… (pages 7 & 8) http://issuu.com/cerfav-verre/.....e-infos-48

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