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Jul 13

Thursday Tech Tip: Polyjet Head Maintenance

This week we're returning to our Tech-Tip Thursday series - every Thursday, a member of our Applications Team will be providing you with tips, tricks, and insights to help you make the most of your Stratasys 3D Printing solution! This week we have our Applications Specialist and Polyjet guru, Stefan Bullock, outlining the importance of print head maintenance on Stratasys Polyjet 3D Printers.

A multi-material medical model used for pre-operative planning. This was produced on the J750 using Connex technology.

As many of us may already know, our Stratasys Polyjet systems - including the J750, Objet Connex Series, and the Objet Desktop Series - are capable of very high resolution printing. With high accuracy also comes high responsibility for ensuring that this accuracy is up kept and print quality stays optimal. A large portion of this up keep is achieved in the simple process of cleaning heads and general machine cleanliness.

First let’s take a deeper look into the intricacies of a Polyjet print head. These print heads are constantly being filled with liquid resin which is heated to achieve a specific viscosity for printing. This heated viscous resin is held in the head by a specified level of vacuum.

Resin is precisely fired out of the heads by a firing mechanism similar to the vibrations of a typical conical speaker vibrating under specific voltages, jetting resin through nozzle openings that are microns in diameter.

An example of Connex Multi-Material Jetting.

Now that we have a sense of the general processes that are taking place, let’s take a look at the possible issues that may arise from improper care. The resin that is being used for printing is cured by UV light; from the material cartridge, through the pumps and material tubes all the way to the heads, the resin has no chance of being in contact with any light source. However, resin can become cured at the surface of the heads, effectively blocking the nozzles from jetting material. Blocking of nozzles are acceptable for one or two nozzles, but beyond this, part quality starts becoming less than optimal. Our first goal is to look at the wiper that cleans the heads.

  • If they do not perform up to spec, resin will be left on the heads, clogging it or even dripping onto printed parts, causing less than ideal part quality
Print Block Assembly on the Connex Systems - a focial point for user maintenance procedures.

After every print, ensure that you run the Wiper Cleaning Wizard from the Options menu.

  • Soak a lint free cloth in Isopropyl alcohol and gently scrub the leading edge of the rubber wipers. This dissolves any leftover material from previous wipes, especially when dealing with rubber-like Tango/Agilus

Next we can look at cleaning the heads themselves. The User Guide from Stratasys does a great job in explaining how head cleaning should be done during the Head Cleaning Wizard. Here at Cimetrix have found a few additional notes that will ensure even better performance from your Polyjet system.

  • Clean the heads
  • Soak a lint free cloth in isopropyl alcohol. Using a different section of the cloth for each head, slowly wipe the head, starting at the back of the head and wiping towards you. The key is a nice slow wipe, allowing the nozzles to soak in the isopropyl alcohol and dissolve semi-cured resin from blocked nozzles.
  • Run the machine through the Purge function from the Options menu 5 times in a row, allowing any more blockages that were not dissolved through cleaning to be cleared.
  • Follow this up with one more head cleaning as the Purge cycle can become messy from the material splashing while purging.

Following this process on a daily basis should take 5 minutes total, but will go a very long way in up keeping the quality of your prints. Proper care of heads with our prescribed method ensures that your print quality stays up to par and can even extend the life of your print heads.

Keeping your heads active also goes a long way in the longevity of your print heads. We recommend the same as Stratasys, which is one part per week minimum. Even if you do not have any intended print jobs for your printer, a small scaled down sample part of just 2 grams of material is enough to keep the print heads in a good working condition. Hopefully this week's post has provided you with some additional background and information to keep your Polyjet machine running. Be sure to keep on the lookout for my next Tech Tip segment where we discuss proper roller bath/blade cleaning.

- Stefan B