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MET 328 Class Credit Additive Manufacturing Project

Joe Legan

Executive Summary

This project is being performed in an effort to use life experience and experience gained from an internship as a substitute for the MET 328 class.The purpose of this report is to document the processes and technologies that can be used in modern additive manufacturing.

This project used a 3D Systems Capture scanner that uses white/blue light to digitize an artifact. This was followed by the use of Geomagic Design X to manipulate the scan data and to model the solid. The last software used was Cura. It was used to create the G-Code for an Axiom Airwolf Dual Head 3D printer.

As with most 3D printed material, the finished product is a likeness of the actual artifact. The surface finish cannot always be duplicated due to the nature of the process. This surface finish discrepancy can lead to some errors in the printed part.

It has been discovered that there is a problem with the 3D printed part. There is a small hole from between the central hole and one of the side angled holes. It is unclear if this error is caused by a defect in the model or if this was caused during the actual printing process.

Even with the mentioned error the overall quality of the print is high considering that the Axiom Airwolf printer is an entry level unit. The print could easily be put into use as a mock up prototype.

This project is an example of some of the technologies and their respective processes that are available to the manufacturing industry. The scanning and modeling processes are not exclusive to additive manufacturing and are often used in subtractive as well. I believe that this project has been a success in thoroughly demonstrating the technologies and processes used.

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Introduction

This project is being performed in an effort to use life experience and experience gained from an internship as a substitute for the MET 328 class.The purpose of this report is to document the processes and technologies that can be used in modern additive manufacturing. More specifically the processes of reverse engineering a given artifact, modeling a solid and using a 3D printer to recreate the artifact. This project used a 3D Systems Capture scanner that uses white/blue light to digitize an artifact. This was followed by the use of Geomagic Design X to manipulate the scan data and to model the solid. The last software used was Cura. It was used to create the G-Code for an Axiom Airwolf Dual Head 3D printer.Each of these steps is covered in more detail in the following section.

Procedures

The procedures have been segmented into 6 functions. These are:1. Scanning the artifact2. Mesh manipulation3. Modeling a solid from the mesh4. 3D print preparation5. Slicing the artifact and G-Code creation6. Operation of the 3D printer

The first step to all of this is setting up the scanner. The scanner chosen for use with this artifact, a remote oil filter base, is the 3D Systems Capture scanner. The Capture scanner is a desktop scanner that is intended for use with items no larger than a softball or large grapefruit. It uses white and blue light displayed in a series of patterns along with 2 cameras to digitize portions of the artifact. After each image is captured a synced turn table rotates the artifact to next position and the process is repeated.The actual steps used for this project are listed below.

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1. Open Geomagic Design X and setup the scanner and turntable.2. Setup the registration target for calibration

3. Click on Auto Exposure and, once complete, select Register.4. Adjust the location of the turn table and the angle of the scanner in order to obtain a successful

registration. This ensures the accuracy of the data recorded by the scanner.

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5. Replace registration target with artifact to be scanned and select Auto Exposure again.

6. Select number of scans required to fully scan the artifact. Rule of thumb: The more complex the artifact the more scans will be needed.

7. Click the scan button.

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8. Once the scans are completed, click the check mark on the scanner dialog box.

9. Select Yes to run the Mesh Buildup Wizard and proceed through the 5 steps.

10. Save the newly merged scans to your selected location.11. Repeat this process until all desired features on the artifact are fully scanned.

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The next step or process is manipulating the meshes of the individual scans. This must be done in order to combine the data from multiple artifact positions into a single cohesive mesh. There may be as few as 2 artifact positions and up to as many as needed for the scanner to fully digitize the artifact. For this artifact a total of 3 scans were required. Again the actual steps used are listed below.

1. Import each scan so that they can be aligned together to build a complete mesh.2. Select 2 of the total scans and select under the Alignment tab the Align Between Scan Data.

3. For this set of scans I have used the Local Based On Picked Point method.

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4. The result can be seen. Repeat this process until all scans are consolidated.

5. Select the Polygons Tab and select Combine to create a single entity out of the multiple scans.

6. Decimate the data down for quicker processing time. This doesn't affect the quality of the mesh. Usually, the ideal number of polygons is around 1 million polygons. This project was upwards of 4.3 million before decimation.

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7. Once combined and decimated the mesh needs to be segmented into regions for simpler modeling. Select the Auto Segment feature from the Region Tab. Set the Sensitivity low for speed and simple features and higher for more complex features.

8. Result of the Region segmentation. Each color represents a distinct shape or feature such as a revolution, sphere, plane or cylinder.

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Features that are known from inspection of the artifact to be congruent can be merged as illustrated by the Cylinder regions before and after. Merging regions allow dumb solids to be extracted with ease from the regions.

Cylinder regions to be merged.

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Cylinder region merged

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9. Select the Alignment tab and use the alignment method of choice. For this project I used the Align Wizard which used the intersection of the central hole axis vector and the bottom surface as the origin and assign the reference planes as pictured below. By aligning the scan to origin and reference planes, orthogonal views can be used and defined.

The next process is the modeling of a solid for use in later procedures. For this project a sketch was created using a plane on the mesh itself as the reference geometry. In fact, for all features of this artifact, each sketch was created directly onto the mesh. From these sketches, solid features were created. These features include extruded bosses, extruded cuts, swept cuts and finally some fillets. The modeling follows the same set of rules as programs such as SolidWorks. Meaning that each sketch must be a closed contour and cannot be self-intersecting in order for a solid or surface operation to be performed upon it. Lastly, care must be taken when using the mesh as the basis for a sketch. Each edge may project multiple contour lines from the overlapping of scan data or from the camera catching a reflection. When there are multiple contour lines it is possible to create sketch geometry that is different from the actual artifact. This necessitates some classical metrology with radius gauges, hole gauges, micrometers and Vernier calipers in order to ensure that dimensions are accurate. Listed below is a quick summary of the steps taken to create the solid model.

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1. Modeling begins with a Mesh Sketch derived from the regions of the mesh. The result is a polyline on the base plane as evident by the pink line.

2. Start tracing the polyline with solid lines in order to start the solid modeling.

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3. Solid extrude based upon the sketch.

4. Repeat this process for each feature, adding reference planes if needed.

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5. Final Model

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Before the oil filter base can be 3D printed, the solid model needs to be converted back into a mesh .STL file. To do this the Convert To Mesh tool was used. The steps are listed below.

1. Select the Solid Bodies in the view control panel in the lower left of the screen. This ensures that only the newly modeled features are converted back into a generic .STL file.

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2. Select the Polygons tab at the top of the screen and select the Convert To Mesh feature. Select the solid body and click the check mark. A new item will appear at the bottom of the tree that is the new mesh. Export this as a .STL file in order to use it with the 3D printer software.

The next operation uses the Cura software to slice the .STL file and create the G-Code for the printer. With the Axiom Airwolf Dual Head printer there are specific initiation files for each type of material that can be used. For this project ABS plastic was chosen due to the low cost and the fact that the printed oil filter base will never actually be put into service. The actual steps involved in this process are listed below.

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1. Launch the Cura software. The checkered board is the build plate that is printed upon and the vertical walls represent the volume that is printable space.

2. Load the .STL file that was exported from Geomagic Design X.

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3. Rotate and move the model into the desired orientation and position. Keep in mind that all overhangs will need support so material can be saved or wasted depending upon the orientation selected. For this model it was rotated to minimize the amount of support required. This saves on material cost and time required for the print.

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4. Because the swept cut was facing down towards the build plate it was required to add support for the entire cut. The orientation minimizes the amount of features that require support. The support options can be toggled as shown.

5. The last software process required is to double check the actual G-Code. Through use we have found that the Airwolf printer is sensitive to requiring an auto-leveling sequence prior to the actual printing. This sequence was thought to be included in the firmware of the printer, several incorrect prints later we discovered it was not. This sequence is required to be included in the beginning of the G-Code and is contained in the initiation file that is loaded before importing the STL file.

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6. The last step is to load the actual file into the printer. The Airwolf printer used can either use files from a MicroSD or wirelessly if it is networked.

Results/Analysis

The result of this project is the actual 3D printed oil filter base that has been submitted along with this report, the merged scan data as a STL file and lastly the STP and IGES file of the modeled solid body.

Conclusions

This project has been an example of some of the modern technologies that can be used for additive manufacturing. Additive manufacturing shares many processes with subtractive such as reverse engineering and CAD modeling. One major difference between additive and subtractive manufacturing is the number of required axis for some complex geometry. One example of this is this oil filter base. The angled faces and threaded holes that are perpendicular to them require either a 5 axis mill or multiple fixtures for use with a 2.5 axis mill when machined. Whereas a 3D printer can create this with only 3 axis. This ability could help create a push for 3D printers with the capability to print metal to become more popular and therefore more affordable. This could also take the 3D printer out of the prototype room and into the manufacturing area.

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