Dan:
Your ideas would probably work OK. I think one of the toughest areas would
be in designing the mold correctly, figuring out the "expansion factor"
necessary to accomodate for the water-to-ice transition multidirectional
growth.
Regards,
Glenn Whiteside
>Glenn & Andy,
>
>I wonder if following will make for a repeatable process, without air
>entrapment:
>
>1. place the mold and water in a vacuum casting machine (Kugelgen, MCP,
>etc.)
>2. degass the water in a vacuum chamber
>3. after degassing, but before the water freezes, pour water into mold
>4. contiune applying vacuum until frozen
>
>Any thoughts?
>
>---
>Regards,
>Dan Davis
>PROTON Rapid Prototyping & Manufacturing Center
>Hicom Industrial Estate, Batu Tiga, PO Box 7100
>Shah Alam, 40918 Selangor MALAYSIA
>+60 3 515-2380 phone/fax
>http://www.protoncar.com/rapid/index.htm
>
>
>> -----Original Message-----
>> From: Monica & Glenn Whiteside [SMTP:SiderWhite@worldnet.att.net]
>> Sent: Thursday, April 08, 1999 8:57 AM
>> To: Rapid Prototype Mailing List
>> Subject: More info on freeze cast process (FCP), ATTN: Andy Scott
>>
>> Andy:
>>
>> In reply to your question I have quoted some more information from the
>> article that might answer
>> some questions that people may have:
>>
>> "Fine-tuning the process:"
>>
>> "Not surprisingly, many problems were encountered during the
>> development
>> of the freeze cast process.
>> Mold design was particularly challenging, because water expands as it
>> freezes. Fortunately, ice exhibits the same linear expansion
>> repeatability,
>> if frozen at the same temperature. However, the expansion is
>> multidirectional (I take this to mean that water is isotropic - GW).
>> Therefore, the elastomer mold must be designed to provide enough extra
>> volume to absorb multidirectional forces. Moreover, the thickness and
>> consistency of the elastomer must be correlated with the different
>> modules
>> for the different shapes of the castings".
>> "After conducting hundreds of tests and measurements, problems
>> involving
>> the morphology of castings and the induced stresses were resolved. A
>> system
>> was developed in which several basic geometries were designed, to
>> which
>> certain semi-constants could be applied in the design of a specific
>> mold. A
>> major breakthrough came when directional solidification was viewed in
>> terms
>> of expansion rather than shrinkage".
>> "Another major problem was how to prevent the cracking caused by
>> stresses induced in the ice pattern by constricted freezing. This was
>> studied and attacked from three different directions: mold design, the
>> freezing medium's velocity and temperature, and air content in the
>> water/ice
>> system. It was discovered that
>> extremely low temperatures trigger cracking, particularly when the
>> patterns
>> are stripped at higher temperatures. This problem was adressed by
>> "conditioning" the ice, just as wax is conditioned prior to being
>> injected.
>> Conditioning involves controlling the air content of the ice and
>> regulating
>> additives (amount and chemistry) in the water".
>> "Warmer mold temperature was found to be crucial for fast, clean
>> stripping of rubber molds. Parting sprays that do not freeze,
>> pre-chilling
>> the water solution, and higher temperatures are used for
>> fast-stripping of
>> the molds".
>> "Air bubbles trapped on the surface of the ice were a recurring
>> and
>> persistent problem, in spite of molds designed to permit air bubbles
>> to
>> escape. Unfortunately, these bubbles would be reproduce on the
>> surface of
>> the casting. This problem was minimized by controlling turbulence and
>> counter pressure within the mold, through proper mold design and
>> venting. A
>> vacuum was also applied in a sealed chamber, prior to and during the
>> mold-filling procedure. A combination of these methods, along with
>> special
>> additives for the water, finally eliminated the air bubbles".
>>
>> Fascinating process!!
>> Hope this additional information helps.
>>
>> Best Regards,
>>
>> Glenn Whiteside
>>
>>
>>
>> >In a message dated 99-04-05 19:39:55 EDT, SiderWhite@worldnet.att.net
>> writes:
>> >
>> ><< Then water
>> > (with "special" additives to minimize air bubbles) is poured into
>> the
>> rubber
>> > mold and frozen. >>
>> >Water expands when it freezes. Is it isotropic? Then you need to
>> compensate
>> >for the metal shrinkage as it cools. Sounds to me, it might take a
>> few
>> >iterations to get the numbers dialed in.
>> >Andy Scott
>> >Lockheed Martin Aerospace
>> >
>> >For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
>> >
>>
>>
>> For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
>
>For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
This archive was generated by hypermail 2.1.2 : Tue Jun 05 2001 - 22:51:26 EEST