Post Processing Best Practices

p/n 31-D093  Rev B

 

Post processing best practices for the ProJet® MJP 2500 IC. After reviewing the ProJet® MJP 2500 IC post processing procedure, use the following best practices/tips to further hone your process.

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Note: Wax patterns are fragile and should always be handled and processed with care. Expect a slight learning curve in developing the best techniques for working with these patterns. The following best practices will help you develop post processing techniques.

 

Pattern De-Plating: Best Practices

If you are using a heat gun to de-plate your patterns, focus the heat on one pattern at a time. Once you see the edges of the pattern beginning to melt, the pattern can be removed from the plate and placed on a non-stick mat, or on its side. The melted surface will firmly re-attach to bench tops and smooth surfaces if you are not careful.

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For Large Patterns: Leave the heat on one portion of the pattern at a time. After the pattern begins to melt (as shown above), move to another area of the pattern. This will uniformly heat the pattern so one side is not stuck to the plate.

For Small Patterns: Apply heat slowly and hold onto the pattern which you are heating. Small patterns have a tendency to fall over onto the build plate. If this happens your pattern can be ruined. Remove patterns quickly and keep a close watch on when the patterns begin to melt.

Small patterns can also be pinched together and removed in groups rather than one at a time. This must be done carefully—small features on these patterns could be damaged during this process.

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When de-plating patterns try to remove the patterns by lifting vertically or tilting slightly. If you slide the patterns off of the plate you will tend to create a flat layer of wax on the bottom of the pattern. This makes breaking the support away more difficult and causes IPA flow to be restricted. You may experience issues of buoyancy in the bath if this is the case.

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After all patterns have been removed from the warm plate, it is ideal to remove the liquid wax still left on the plate. This can be done by wiping the surface of the plate gently with a paper towel. Doing so will save you time when cleaning the plate later.

 

Pattern De-Bulking: Best Practices

Wax carving tools are useful for reaching hard-to-get places. Use caution when working with wax tools. It is very easy to scratch and gouge the build material, or your hand.

It is useful to “break the skin” of the support material for areas which are hard to reach, such as long blind holes. This allows the solvent to reach the inner structure easier and dissolve out more support wax.

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When de-bulking by hand be careful to not “chip” the build material away when removing support material. Support material can fracture (in the direction of the columns) which can remove some build material. To negate this you can score the support near the edge of the build material. This gives the material a clean place to break when removing support material by hand.

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Typical amount of support removal is 50%. This is heavily pattern dependent. If your pattern has thin, fragile, or complex features it is recommended to NOT debulk your pattern. This will reduce the risk of breaking your pattern during this step.

     A non-complex pattern de-bulked vs. not de-bulked A complex pattern not de-bulked
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Some geometries may have both large and small portions to de-bulk. It is ideal to de-bulk the large portion first and then follow up with the small portion. Leaving support on small features until the very last moment will ensure they have maximum strength throughout the process.

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Solvent Support Removal: Best Practices

Monitor your temperature and agitation settings carefully. The ideal bath temp should always remain in the range of 95 +/-4 °F (35+/- 2 °C). Agitation should be enough to create a small whirlpool at the surface only. Too much agitation can cause the patterns to move around in the bath which can result in dings, dents, and distortions.

Create a rack for your specific set up. Ideal materials are wire mesh covered in PVC coatings (such as McMaster-Carr # 6622T11). This helps prevent the wax from being damaged during processing (reduction of dents and dings in the patterns). Too small of a mesh material, such as a window screen, can inhibit flow and increase processing times. Mesh opening size should be a minimum of about 0.4 inch (10 mm) x 0.4 inch (10 mm).

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Patterns become more delicate once warmed up in solvent bath; handle carefully with nitrile gloves when changing pattern orientation or inspecting.

Only place the number of patterns in the bath that fit comfortably—overloading the number of patterns in the bath can cause problems with the patterns running into each other and leading to damaged patterns. Additionally this will inhibit agitation and increase processing times.

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Place patterns in bath with the majority of the support wax facing down, towards the source of agitation.

Some patterns should be flipped during processing to place the majority of the support wax toward the source of agitation. Depending on geometry this will allow the agitation to reach different areas of the pattern more effectively. For simple geometries it’s ideal to flip the pattern halfway through typical processing times. For patterns with fragile features, or patterns which can’t physically stand when flipped, it is not advisable to flip. You can lift up the rack and rotate it 90 ° or 180 °.  This will lead to longer processing times, but you will preserve the integrity of the pattern.

A typical pattern which would be flipped part-way through the bath
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Difference between top and bottom surfaces during post processing
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This pattern would be flipped due to the ability to lay it flat on its face in two orientations. This allows the IPA to target the recessed area inside of the pattern on both sides. Approximately halfway through post processing the bottom side has all of the support wax removed. Some areas of the top portion still have support wax and would benefit from being flipped.

 

A typical pattern which would NOT be flipped:

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This pattern would not be flipped due to the minimal support wax on the upper surfaces. Flipping of this pattern also causes the pattern to rest in a position which is not stable. This can lead to the pattern moving around during processing, causing damage to the final pattern.

 

When submerging patterns you may find that some patterns float—especially if you have not done any de-bulking of the pattern. This is due to air being trapped within the support structure. To alleviate this problem, puncture some “air holes” in the support skin. Submerge the pattern and you will see bubbles rising from the pattern, such as the hollow cylindrical tube shown below. Once the bubbles have stopped you will find that the pattern does not float anymore.

IMG_3357.JPGAdditionally, some patterns may float due to infill settings. A plastic mesh material is useful for holding patterns to the basket. This mesh can attach to the four corners of your basket.

IMG_3799.JPGSome patterns may need to be supported during post processing to aid in handling delicate features and to minimize damage. Fixtures for patterns are useful to hold them in a specific orientation during post processing. Here is an example of a pattern that benefits from a fixture for holding the pattern off of the basket material:

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When refreshing the dirty bath use IPA from the rinse bath. This will save IPA in the long run and keep your rinse bath clean to effectively remove any excess support material left on the patterns.

When removing patterns from the bath place on an absorbent cloth to avoid spills.

The longer you leave the patterns in the solvent the more “white” you will see on your patterns.

 

STEP: PATTERN RINSE

Pattern cracking is most common during this step; be very conscious of the temperatures your patterns are experiencing. Only go from warm to warm, never warm to cold. Always wash your patterns in water before letting them dry.

Patterns should be rinsed in heated IPA. Do not go from warm IPA cleaning bath to IPA at room temperature. Your patterns can go from room temperature to room temperature IPA, but they will clean slowly.

 

STEP: PATTERN DRYING

Allow patterns to dry in a room with a minimal draft; do not place in front of a fan/air conditioning, etc. Large patterns may benefit from a cover to slow evaporative cooling and prevent thermal shock from inducing cracks.