recoating methods

From: John Male (
Date: Thu Feb 12 1998 - 12:23:43 EET

Firstly, thanks to everyone who took the time to answer my question
about recoating methods and blade crashes.
I had responses from people with the following machines:
4 doctor blade machines (all SLA 250's)
10 zephyr machines ( 5 SLA 250's, 3 SLA 350's and 2 SLA 500's)
A constant source of blade crashes for all machines is erratic laser
power (or a faulty laser power sensor) which results in the resin not
being fully cured, so when the recoating arm moves over the part it
collects the uncured resin on the blade, and this builds up and crashes
into the solid part.
The doctor blade users reported that blade crashes due to geometry were
normally found on large flat areas especially with thin layers, so parts
were normally reoriented to avoid them. Trapped volumes could normally
be easily identified and parts reoriented so weren't too much of a
problem. To cut down on recoat times, some users just deep dip on parts
with small areas, with no blade sweep. Also, someone had experimented
with using the doctor blade without deep dip to cut out the deep dip
time (a deep dip of 8 mm using 0.2 platform velocity and acceleration
takes 16 seconds). However, this only works on parts with part widths up
to 10 mm, and even then can be risky, but it does save alot of time when
it works.
Peoples experience with zephyr varies from a 350 user who hasn't
experienced a blade crash since they got the machine (about 1800 laser
hours old) to a 500 with a retrofit zephyr arm, that crashes about once
a week (with the doctor blade, it crashed about once per month). Other
users have experienced a reduction in blade crashes since they got
zephyr from about 5-8% crashes to about 5%. About one crash a month
seems typical. Part support comes out as being an important factor in
avoiding crashes, with even small unsupported overhangs being able to
cause crashes. In our experience, Quickcast parts are much more prone to
crashes than solid parts. Has anyone else found this?
If anyone wants to add to any of these comments please email me, as I
would like to hear everyones experience.
Thanks again


John Male
Research Student
Centre for Rapid Design and Manufacture
Buckinghamshire University College
Queen Alexandra Road
High Wycombe
HP11 2JZ

Tel 01494 605085 Fax 01494 538593

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