Saturday, August 30, 2014

HDPE Print Bed Adhesion Solution



3D printing using recycled HDPE (shredded gallon milk jug flakes) comes with many challenges, one of them being print bed adhesion. HDPE has become infamous to WOOF for its uncontrolled warping and shrinking, which causes prints to peel off of the print bed. To mitigate this, WOOF Officer Brandon Bowman began developing a process to create an HDPE print surface. 

The initial idea was to heat gun HDPE flakes onto steel plates (18” X 18” X 1/8"). This evolved into baking using a standard baking oven. Bowman initially baked HDPE flake onto a steel plate then applied force on top of the flake using another surface, his body weight and his feet.

Photo Credit: Brandon BowmanPhoto Credit: Brandon Bowman

This process produced inconsistent and non-optimal results. Size limits of the baking oven, the need to put plastic in an oven, and the need to apply spray on Teflon coating encouraged designing a different solution.
  
Over time the flake baking process evolved into a recipe reasonably perfected by WOOF’s Director of Operations Dana Henshaw. The following recipe utilizing a Wabash Hot Press has produced promising results:

Stack 4 plates prepared in the below manner with a 5th steel plate by itself as a barrier on top into a hot press.
To prepare each steel plate requires:

1 - 24” X 24” Steel Plate (1/8” thick)
Photo Credit: Dana Henshaw

3 - Pints of Recycled HDPE Milk Jug Flakes (cleaned and shredded) spread on the steel plate leaving an approximately 1" border.
Photo Credit: Dana Henshaw

1 – 24” X 24” Sheet of Porous Teflon Coated Fabric

Photo Credit: Dana Henshaw
1 – 24” X 24” Sheet of Breather Material

Photo Credit: Dana Henshaw


Finally top the sheet off with: 
1 – 24” X 24” Sheet of Non-Porous Teflon Coated Fabric (Not Pictured)


Then using a Hot Press:

Photo Credit: Mark Stamnes

Apply and maintain 400lbs of force
Increase temperature to 375 °F over 30 minutes
Hold at 375 °F for 40 minutes
Cool for 10 – 20 minutes
Remove the 400lbs of force and separate hot press platens
Then carefully remove the hot plates

After the plates are cooled, they are attached to the build surface and then used for printing.

Photo Credit: Mark Stamnes

This is an attempt to print a cylinder that was to be used as a potential floatation device.

Photo Credit: Mark Stamnes

Photo Credit: Mark Stamnes


This turned out to be a great learning experience. Here are a few things that were tried but did not work: 

Failure of first hot press: Used only non-porous Teflon coated fabric. It made sheets that were too smooth, and the first layer of printed HDPE wouldn't adhere well enough.

Failure of second hot press: holding pressure for 20 minutes with the breather material was not long enough for temperature to penetrate deep enough into the stack to allow full adhesion of HDPE flake onto each plate. The HDPE on the middle plates stayed as flakes.
 
In all, developing this process has allowed the WOOF team to achieve successful prints of the sections a multi-sectioned Kayak.

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