CAD/CAM Inquiry: Thermoforming Over CAD Urethane Foam Models
Description
Collection
Title:
CAD/CAM Inquiry: Thermoforming Over CAD Urethane Foam Models
Text:
List Members.... My apology for the second post, as I did not include my name
or credential with the original post on this subject!!
John N. Billock, CPO/L, FAAOP
Orthotics & Prosthetics Rehabilitation Engineering Centre
Warren, Ohio
========================================================
Anyone using CAD/CAM technology in design and fitting of lower/limb
prosthetic interfaces appreciates the finite dimensional control this technology
provides. Despite the finite control CAD/CAM offers, one of the more nagging
uncontrollable factors we experience are urethane model compression and/or
thermoplastic shrinkage.
The familiar problem with unwanted compression of the urethane foam model
occurs during the vacuum forming process for a diagnostic interface and
eventually the definitive interface. As you know, this occurs due to the simultaneous
presence of heat and negative pressure during the forming process. Also,
dependent upon the type and thickness of the thermoplastic being used, a varying
degree of positive model compression (reduction) occurs, resulting in a loss of
the desired volume or circumferential dimensions you achieved in the CAD
model rectification process.
For those of you who are CAD/CAM users, given the above characteristics, I am
would be curious to know thoughts to the following questions:
What other techniques are being used, beyond “upsizing” the model, prior to
the forming process to maintain the desired fitting dimensions of the
interface?
If you do “upsize” the CAD model to accommodate shrinkage in the model
and/or the thermoplastic being used, would you please comment on the dimensioning
technique or guidelines you are using?
Do you use any mold release agents, such as power or silicone spray?
What are you doing to prep the urethane CAD model for the thermoforming
process, if anything, such as use a nylon socks and/or a PVA bag over the model?
Do you cool down the model before thermoforming process either with water or
refrigeration?
I will gladly compile the above and share it following a 1 week of response
time to the questions posed!
or credential with the original post on this subject!!
John N. Billock, CPO/L, FAAOP
Orthotics & Prosthetics Rehabilitation Engineering Centre
Warren, Ohio
========================================================
Anyone using CAD/CAM technology in design and fitting of lower/limb
prosthetic interfaces appreciates the finite dimensional control this technology
provides. Despite the finite control CAD/CAM offers, one of the more nagging
uncontrollable factors we experience are urethane model compression and/or
thermoplastic shrinkage.
The familiar problem with unwanted compression of the urethane foam model
occurs during the vacuum forming process for a diagnostic interface and
eventually the definitive interface. As you know, this occurs due to the simultaneous
presence of heat and negative pressure during the forming process. Also,
dependent upon the type and thickness of the thermoplastic being used, a varying
degree of positive model compression (reduction) occurs, resulting in a loss of
the desired volume or circumferential dimensions you achieved in the CAD
model rectification process.
For those of you who are CAD/CAM users, given the above characteristics, I am
would be curious to know thoughts to the following questions:
What other techniques are being used, beyond “upsizing” the model, prior to
the forming process to maintain the desired fitting dimensions of the
interface?
If you do “upsize” the CAD model to accommodate shrinkage in the model
and/or the thermoplastic being used, would you please comment on the dimensioning
technique or guidelines you are using?
Do you use any mold release agents, such as power or silicone spray?
What are you doing to prep the urethane CAD model for the thermoforming
process, if anything, such as use a nylon socks and/or a PVA bag over the model?
Do you cool down the model before thermoforming process either with water or
refrigeration?
I will gladly compile the above and share it following a 1 week of response
time to the questions posed!
Citation
“CAD/CAM Inquiry: Thermoforming Over CAD Urethane Foam Models,” Digital Resource Foundation for Orthotics and Prosthetics, accessed November 5, 2024, https://library.drfop.org/items/show/222639.
