Ross, you said:
Hi There,
I am a new subscriber so forgive me if this question has been asked before !
Has anyone experienced growth of SL models over time?
We are an RP bureau in the UK with an SLA500 using SL5180 and utilising both ACES and TCW Build styles
Goodbye and many thanks
Ross Nicholls
ross@mnl.co.uk
Ross:
Yes, we have definitely experienced SL growth over time - especially if the SL spends any amount of time in an environment that is not temperature and humidity controlled. We had a SL mold pattern for a heater tube - it was used initially to make a paraplast mold and then inadvertantly set on a shelf in the shop. Several months later, another mold was needed so the toolmaker wanted to use the same pattern but he discovered his end-of-part (EOP's) dimensions were off by 1/8 inch! We did some further checking (CAD dimensions versus SL model dimensions) and found out that the tube mold (approximately 2 feet long) had indeed grown by at least 1/8 inch (approx. .005 in/in) due to exposure to a hot and humid shop environment. Wall thickness and geometry also play a part in SL model growth and distortion. If you create thick-walled SL models (e.g. .125 - .250 inch) with reinforcement webs they will hold up better than thin-walled (less than .125 inch) models. It is best to keep the model in a controlled environment as long as possible before releasing it to the shop environment - and when you do caution them to use it as soon as possible to maintain accuracy. Shipping is also a major concern - one afternoon sitting on a hot shipping dock in Phoenix, Arizona is all it takes to destroy a model. I've heard of packing dry ice around the model (not touching it though) to help it survive the trip. Also watch bubble wrap - I've received some models from places where they had tightly wrapped the SL model and the models were severely distorted and there were deep impressions in the model from the bubbles - what I call a "golf ball effect." Shipping from a hot location by air in an unpressurized cargo bay was to blame for this.
Also, the ACES build-style holds up much better in adverse environments - the WEAVE styles tend to absorb moisture more because of the non-overlapping scans - its structure is more porous.
Being in the UK, you might want to check out the newer humidity and temperature- resistant resins offered by either Ciba or DuPont.
Hope this helps.
Regards,
Glenn Whiteside
Cessna Aircraft Company
e-mail: siderwhite@worldnet.att.net
For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
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