Monthly Archives: December 2012

Model Making Process- 3D Printing

For many of the smaller details of my concept vehicle such as headlights and logos, these were much easier to be 3D printed rather than CNC machined out due to the accuracy needed in the shapes and the freedom with design you had. The two machines that I had access too were a Z- Corp and a Objet Printer.

The Z-Corp was a white powder printer which was able to print objects down to 2mm with quite alot of accuracy. The common working process with these parts was to collect the prints and then coat them in an Epoxy Resin which after drying allowed them to harden into a material that was much easier to sand and consequently paint with better strength. These prints were generally cheaper than the Objet Prints however the smaller you went, the weaker the prints were, my taillights originally being printed in Z Corp, had the consistency of a baked cookie, crumbling and bending at some points being generally far to fragile to work with.  Noting the weakness of the smaller parts, the 3 larger prints that I needed to create were completed on the Z- Corp Machine maintaining a wall thickness of minimum 3mm all around to ensure rigidity in the printed structure.

The Objet Printer was an additive manufacture printer which printed in a polymer like material that was alot stronger than the equivalent Z-corp of the same size. Being costlier due to the support material that surrounded each part that was created, strategically placing parts flat on the bed was crucial to saving money. The parts that came out of the Objet were a translucent yellow polymer/plastic that took a while to clean but felt much stronger and flexible to work with than the Z-Corp Prints. I ended up using the Objet Printer for all my smaller parts as whilst the cost was slightly higher, the strength of the parts paid off due to the easy of sanding and painting them.

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Model Making Process- CNC Machining Part 2

Realizing some parts of my model were quite tough to machine out without creating alot more individual parts than I already had, I had to look around for other machines that I could use. The RMIT TAFE up the road actually had access to a larger Roland CNC Machine that cut using 4 Axis. This meant that the parts that could be cut out on this machine could be rotated to allow the drill to access parts which were originally undercuts.  This machine being bigger was a great help for helping to create the outer wheel pods of my concept with the help of the Technician who allowed the machine to run overnight, saving me a bunch of time.

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The program used here was called Modela. This program was taught to the Product Design students at the Tafe and was extremely helpful. It was a simpler program compared to SurfCam only requiring experience to know how to push the machine to work that little bit smarter than usual

The RMIT Gossard Workshop also had a Roland Machine which was a 4 axis machine but was often used as a 3 axis. This machine which I ended up learning how to use by myself, had rather simple interface but still took a bit of fiddling about to get it working perfectly. This machine was able to create very good finishes on parts but being a smaller machine with smaller drill bits was quite a bit slower.  Through using this myself I was able to learn to run tool paths through the SRP Player and also where I could push the machine to work faster or slower depending on the complexity of the part. By the end of the project I felt confident enough to run the machine entirely by myself and was able to run other students project parts awell.

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Model Making Process- CNC Machining

The 4 Machines that I was lucky enough to use at RMIT’s workshop ranged from 2.5 -4 axis CNC machines of varying sizes. These included 2 Roland Machines, a Haas and an ART Router.

The ART Router or the big yellow CNC machine as i called it, was a large 2.5 axis machine that was relatively quick but at the expense of detail. Used to cut out the big sides of the 3d Model, the job took approximately 7 hours and wasnt without error and many tense moments. It had troubles cutting sharp gradients and sharp small corners as the step size between the tool paths were quite big meaning more sanding for myself afterwards. I was more happy just to see my model take shape! The files for this machine were IGES prepared through Rhino and toolpaths were run through RHINOCAM before being sent to the machine.

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The Haas Machine was a 5 axis CNC Machine converted to 3 axis which we made good use of. This machines bed size was alot smaller than that of the ART at about 300 by 300mm, but was a quick cutting machine with a very good finish requiring minimal sanding. This machine was great for the smaller more detailed areas of my model where drill bit size and length was an issue. Due to the speed of this machine almost 50% of the parts were cut out here as the post CNC work was minimal. Unfortunately this machine was alot more complicated than the others to run with tool paths needing a qualified technician to program. The program used for this was SurfCam.

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Model Making Process- CAD for CNC

After refining my final CAD model a number of times, cleaning up surfaces for rendering and updating and design changes, the 3D model was ready to be CNC Machined. Lucky enough our uni RMIT has a number of CNC machines at their disposale ranging from high speed small scale 4 axis machines to large (2.5m+) 2.5 axis machines able to churn out large parts in a matter of hours. Due to the size and axis limitation of these machines a full 3D model is unable to be cut as a single piece through to these machines. This meant splitting or ‘slicing’ up our 3d models into more manageable sizes that would make the best use of each machine. Examples of this were sending the more highly detailed parts onto the smaller machines which had the drill bits which were small enough to cut out the details needed.  This was also the case when a particular piece was easier to machine on a 4 axis machine rather than a 3, perhaps because it saved time or produced a higher quality result.
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The form that I had ended up with was quite long and had many undercuts which resulted the large number of CAD images you see above. Where as some students in my class were able to cut their model from less than 10 pieces, the design of mine included many undercuts which made splitting my model quite a task in itself. At the end of the CNC process I had cut out almost 25 pieces on 4 different CNC machines over 3 weeks. I had considered getting some parts outsourced to save time however the quotes that I received back were quite unreasonable, one place asking for upwards of $6000 and 3D printing being even more expensive. With the time constraints I was under and the  iffy nature of these machines, some parts did end up getting 3D printed to save myself time at quite a considerable cost at the university. In hindsight completing my CAD earlier would have prevented these extra costs but it was a good learning experience

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Model Making Process- CAD Process

Throughout the concept development process it was important for me to create CAD models to help visualizing my ideas through other mediums apart from sketching. This gave me the ability to block out forms quickly and utilize it as something that I could sketch over to refine certain shapes that I liked. 

I used Autodesk Alias to surface my model for my major project this year after learning to use it for a semester in 2011. I believed that this program was the best choice as it was a sought after skill in the automotive industry. Using online tutorials and the help of some friends who were also learning to use the program I was able to skill up to a level that was high enough to enable me to surface a form that could be transferred for CNC machining as well as CAD rendering. 

The top half of the images represent the earliest CAD models where the surfaces were created more to show form generation rather than clean surfacing. The later half represented a CAD model that I intended to use for both CNC Machining and Rendering with much cleaner surfacing and better reflections. 

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