Optimizing Part Quality on Stratasys Production Series 3D Printers
When using Stratasys' Production Series systems, which employ Fused Deposition Modelling (FDM) technology, there are multiple paramaters that can be modified in order to improve part quality. This week we will focus on two easy methods that prevent part distortion, for both smaler and larger builds, to improve the quality of parts that come off of your machine.
Positioning Parts In Relation To Airflow to Improve Part Quality
Although often not thought of as a 'paramater' that can be altered, the positioning of the part on the build tray can make a large impact on the quality of parts coming off of your machine. Lack of airflow around the part as it builds can result in distorted parts and poor part quality; understanding how this can happen will help you position parts in the build area for best results.
First, we will discuss airflow on the different production grade systems from Stratasys. The airflow in a Fortus 200mc moves from both sides of the top of the chamber, acrossthe build area and then to the bottom. The air is then sucked into the sides and circulated back to the top after passing across the interval heating elements. The airflow on Fortus 360mc, 400mc, and 900mc systems moves from left to right.
Figure 1: Part Distortion
Figure 2: Optimal alignment of multiple part prints.
The air passes through heaters located on the sides and near the bottom of the build chamber and blows across the build area at the top of the chamber. This airflow serves two purposes during the build process, providing a uniform thermal gradient throughout the build chamber, as well as carrying the heat generated by the head and tip away from the part. Part distortion, seen in Figure 1, occurs when the part and support materials are not able to cool down to the envelope temperature when it is building.
Small parts are more susceptible to heat distortion because the head is radiating heat as the part is building, and the head does not move away from the part, meaning there is less time for it to cool. To minimize distortion on small parts, it is best to run multiple parts on the build platform. The parts can be the same as long as they are positioned in the build area properly. By doing this, you are moving the heated head from part to part, therefore allowing time for each part to cool as it is built. When building multiple parts, it is best to align them along the "Y" axis, spaced roughly 1" apart, as seen in Figure 2. Doing so maintains adequate airflow between the parts, allowing them to cool to envelope temperature.
Overcoming Part Curling with Large Builds
Now that we have discussed overcoming part distortion with smaller parts, we will address this issue with larger builds. Large parts can curl up from the foundation sheet while building, affecting part quality and potentially causing machine problems. A large mass of material retains a lot of heat in the middle of the part, whilst the edges cool much faster. This differential of cooling causes the edges to pull up off of the build sheet, as there isn’t enough holding power to hold the edges down. This can be overcome by modifying certain parameters within Insight, a process that is outlined below.
Orient your STL file and slice it as you normally would.
Before generating Supports, open the Support Parameters dialog (from the Main Menu, select Support > Setup, then click on the Access Advanced Support Settings icon) and increase the Base Oversize setting (Figure 3). This parameter can be set at up to .500”, and will provide a larger base area to bond to the build sheet. As a result, when the part is being built and the large base layers of the part are shrinking, there will be more area contacting the build sheet to hold it flat. Another way to achieve this, if an even larger base is desired, is to use the Offset command. Once you have generated the standard supports and base, select Edit > Offset from the main menu (Figure 4):
a. Make sure the “Offset Direction” box is set to Outside Closed Curve.
b. Enter a measurement in the “Offset Distance” field.
c. Make sure the “Destination Group” is set to Same as Selected.
d. Important: Select No in the “Keep Original” field! Otherwise, the offset curves will form a new inner / outer relationship with the existing base curves, and no base will be created under the part!
e. Select all the light blue (base) and dark blue (base top) curves at the bottom of the part and click OK. A new larger base has now been created.
Continue to process the part as normal, creating toolpaths and saving the job. The larger base layers will have more holding power and hold the part flat while building.
An alternative method, for Vantage and Titan systems running ABS or ABSi materials only, is to use the ‘Brick Mode’ function in Insight. To turn this option on, you must access the Modeler Configuration (the icon that resembles your machine) and click on the “Special Modeler Options” dialog box. Once in there, put a check mark next to Brick Mode (Figure 5), then make sure to click on the green check mark to save this setting You may now process your part normally; brick mode applies special parameters to your part to help overcome curling. It is important to note that it is not possible to mix non-Brick Mode parts with Brick Mode parts.
- Cimetrix Staff
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