Pattern Orientation for Printing

p/n 31-D096 Rev C

 

Pattern Orientation for Printing

3D Systems MultiJet (MJP) Printing as deployed in the ProJet® 2500 IC is a robust and mature 3D printing technology with many unique values. MJP is well known for its world-class high precision and high fidelity capability allowing patterns to be printed true-to-CAD and with good surface quality. VisiJet® M2 ICast real wax material is intended for investment casting. It has a high contrast color and melts out completely to provide the highest quality casting patterns of any printing technology. MJP’s support structures are automatically created regardless of pattern geometry and/or complexity, and are removed quickly and easily in a solvent bath without leaving behind surface defects that must be sanded or burnished. No two use cases are the same and each will leverage different aspects of this technology for their specific application.

When setting up a build, it is important to arrange your patterns in accordance with intent. Intent is determined by user needs, and can often conflict or be mutually exclusive. Optimization of dimensional accuracy, printed pattern quality, material use, single pattern build speed, and maximum throughput are covered in this document. Max print quality does not always mean minimum material usage, and you must trade off what is most important for your specific process.

Before optimizing build setup, it is important to know how the machine operates. The ProJet® MJP 2500 IC printhead has 880 individual jets (440 each for build and support) and are packed into an approximately 2.75 inch (7 cm) array at 75 jets per inch (1/3 the total build width).

To produce patterns/jobs larger than the head width, the printhead is translated from the front to the back of the build plate to make larger patterns (~6” or 9” width jobs for the 2500 IC). These lanes are shown in 3D Sprint by the dotted lines on the build plate.

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Dimensional Accuracy:

  • Set default units to inches and place patterns such that true absolute position values do not go past 2 decimal places because printer resolution is 600 DPI in X, Y, Z and you want to avoid rounding off to the nearest pixel on each side. Rounding can change pattern size by as much as one pixel in each direction. In 3D Sprint, selecting Transform->Move->Absolute Move will allow you to do this. The copy tool also can be used in this manner. To determine if your patterns are placed on a pixel boundary, open Settings and adjust default length units to 123456. If length is set to .12, 3D Sprint will round shown values to the nearest hundredth.
  • There is a default scaling factor set in 3D Sprint for each printer, accessible in 3D Sprint by selecting Printer Tools->Printer Settings->Add. To optimize this factor for your particular pattern or environment, you should print several patterns or a calibration pattern that is roughly the size of the patterns. Measure the printed pattern and adjust scaling factors. (Link Shrink Compensation)
  • If a pattern’s x or y extent is less than the lane width, rotate or position the pattern to occupy a single lane. This will avoid any possible lane joining error and significantly increase print speed.

Print/Pattern Quality

  • Fine features like embossed/debossed text are best oriented facing up, or facing down if necessary. Orienting text to stand vertically (text faces in X or Y direction) can reduce the sharpness of the pattern.
  • Flat surfaces with a large area (greater than 2-3 square inches) should be oriented so they are non-parallel with the build plate. This avoids delamination between support and build. Generally, putting the patterns at a “compound-angle” (rotated ~10 degrees in the x and y axes) will reduce surface area on a single layer and produce optimal quality.
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Left: Compound Angle Demonstration, Right Top: Delamination on Flat Surface, Right Bottom: Fixed with Compound Angle

 

To reduce the effect of “stair stepping”, surfaces of patterns should be exactly parallel/perpendicular to the plate, or more than 10 degrees from parallel/perpendicular. Shallow angles (general rule less than 10 degrees) will cause increased visible “stair stepping” effect. The Orient->Manual tool can be used to select a flat surface that you would like to mate parallel with the build plate. If the surface is too large, you must again worry about delamination and should not print flat on said surface.

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Manual Orientation Tool, Selecting Bottom Surface

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After Manual Orientation

   

 

  • Patterns also should be rotated about the Z-axis. Curved or vertical surfaces that are almost parallel with x- or y-axis can be improved by increasing z-axis rotation 15-45 degrees away from parallel.
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NOTE: Patterns with surfaces that are perfectly parallel with the X/Y-axis do not need to be rotated.

 

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Example Orientations

Effect of Different Orientations

 

  • Maximizing the poly count or triangle count in an STL file during export from your cad software can provide the smoothest possible surfaces. STEP, IGES, or SLC files can also be utilized to reduce lossy export from cad software. Upon importing STEP files into 3D Sprint, select the lowest possible import tolerances to keep the model as detailed as possible.
  • If you notice signs of over-heating on the top surface of a pattern, you can enable the ECM build style in 3D Sprint. The default print speed on the 2500 IC is set to maximize productivity with minimal thermal effects. However, some patterns may be more sensitive. ECM is particularly beneficial for patterns placed in only one lane, with a small x extent (uses only a fraction of one lane, especially near the verification wall), and has large flat horizontal areas. Occasionally the tallest sections of a multi-lane pattern will be contained all in a single lane, allowing layers at the top of the pattern to print much more quickly and at too high a temperature. Selecting ECM from 3DSprint will avoid overheating near the end of these jobs. Also, maintaining a cool ambient temperature of 65-68°F (18-20°C) in the room where the printer is located can help provide optimal print quality.
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Evidence of Running Hot.  Notice Contrast on Top Surface After Printing

(Before Support Removal)

 

Material Use

  • Build material usage remains constant regardless of pattern location on the build plate or pattern orientation; however, support material usage is affected. For example:
    • A hole or large opening would be oriented with concave side up, as overhangs will require support material underneath. A table is best oriented with the legs up, since it will otherwise require support material under the overhanging patterns.
    • Thru-holes should be oriented parallel with the z axis because no support material is needed in the hole.
    • If you print a flat rectangular prism or control arm, it should be stood up so the side with the smallest surface area is facing the build plate.

 

  • Use the estimate tool to test material and time reduction of various trial orientations.
  • Minimize number of lanes used to reduce the size of the verification wall.
  • Stacking patterns is not recommended, as this tends to use more support material, reduce pattern quality and increase post-processing difficulty.
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Examples of Orientations for Support Use Reduction

Throughput Maximization and Print Speed

  • Minimize number of lanes (if possible). The lanes are separated by dotted lines in 3D Sprint.
    • Increasing the number of patterns in a single print lane will not significantly increase print time. Height of patterns and number of lanes are the main factors that can extend print time.
    • If possible, localize tall sections of patterns to the fewest number of lanes. Once the maximum pattern Z-extents has been reached in a lane, the printer will skip that lane for the rest of the job. Subsequent layers with fewer occupied lanes will skip unused lanes, which can significantly reduce print time.
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Orientation Maximizes Print Time Print Time Significantly Reduced Print Time Reduction Explained

 

  • Use the Estimate tool to test each layout because results can sometimes be surprising.
  • After minimizing number of lanes and build height, put patterns as close to the verification wall as possible and minimize the extents in the X- axis from the wall as much as possible.
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Note: that 3D Sprint will outline a pattern in red to alert you if it is too close to the verification wall, or extends beyond the print area in any direction. However, there is no warning when manually placing patterns to alert you to overlap or patterns that have been placed too close together. We suggest a 2mm (0.080 inch) spacing between patterns, as is provided when using the AutoPlace function. Sometimes it may be difficult to know if patterns are too close; it is often useful to create a temporary 2mm (0.080 inch) thick disk or 2mm (0.080 inch) thick rectangular bar with the Generate Geometry tool, and manually move it in between patterns much like using a feeler gauge.

  • Orient to minimize x extent in all 3 lanes.
  • When your goal is maximum throughput, print time can sometimes be less important than number of patterns in a build. For example, a build with fewer patterns may print faster but a longer job with more patterns can print overnight, making efficient use of time.

Example:  5 patterns in 8 hours, or 15 patterns in 16 hours.

  • 15 patterns in 16 hours will give you maximum daily throughput because the job will print overnight unattended.

 

Thin Sections / Delicate Structures

Thin features such as cooling fins provide a challenge to handling and post processing due to the inherent brittleness of wax. Small forces perpendicular to thin elements can quickly crack and fracture the wax pattern, so they require care when gripping and placing. One natural way to orient an object such as a piston cylinder is with the internal bore vertical in Z, and the fins horizontal in the X-Y plane. In most instances, it is better to rotate the pattern so that the fins are vertical in Z. This provides the advantage of easier and quicker post-processing of the support wax, since long bath times are required to remove support from the deep, narrow passages between close-spaced horizontal fins. The bulk of the support wax in the large central bore is easy to remove manually and the bore will post process more quickly than the spaces between the fins. This is a case of a trade-off in demands: the rotated pattern will use more support wax, but the post processing times will be shorter, and the post processing yields will be better which generally is an overall win.

It is often prudent to use a fixture to transport and hold patterns with delicate features – see ProJet® 2500 IC Post Processing Best Practices Guide for more information. Also consider adding some auxiliary gates/support bars to the outside of a pattern across thin features. This will provide a sturdy location for handling the pattern while it is in the bath or transporting. These auxiliary bars could be part of your gating and will be removed after casting.  Take care to design and place these so as not to interfere with proper metal flow during casting and to meet your process requirements.

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Orientation Maximizes Post Processing Time

Post Processing Issues Significantly Reduced

 

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Adding Auxiliary Bars to Protect Delicate Features