Wednesday, March 20, 2013

Open Manufacturing: Laser Cut Packaging Solutions

I don't believe anyone can argue against the merits of attractive and functional packaging on a product.  Sometimes, the way a box looks may even be enough to persuade a potential customer.  There are thousands, maybe millions of unboxing videos posted to Youtube. Great packaging delivers its contents safely and gives its consumer a reason to smile.  But, we aren't here to discuss the merits of aesthetically pleasing packaging.  This is a post about building packaging that protects the integrity of the product being shipped and how to prototype that on your laser cutter.

At I Heart Engineering, there have been a few cases in which a TurtleBot 2 was damaged during shipping.  One problem is that we currently do not manufacture our own boxes.  However, what we can do is come up with our own structural packaging solutions to protect our products working within the constraints of "stock" boxes acquired from elsewhere.  The first effort was directed at protecting the Kobuki base of the TurtleBot 2 during shipping.  Currently, the shipping department modifies the already existing Kobuki packaging to fit inside of a commonly available box and uses foam inserts to protect the plates. Our question now, is how to create support for the Kobuki base using our digital manufacturing tools, or if you prefer, the Epilog Helix Laser.

First, we need to understand the process of creating a "box."  Well, the unfolded form of packaging is referred to as a net.  This closely resembles the term flat-pattern which is used in sheet metal work.  Some techniques used by sheet metal workers can be applied when making your net out of certain materials.  In our case, we are limited to the use of 24" x 18" C-Flute Corrugated Cardboard which provided a few interesting issues.  Before you begin to CAD your net or flat-pattern, you should create a scale model of what you intend to build out of card stock. I recommend reading Paul Jackson's Structural Packaging Design Your Own Boxes and 3-D Forms for a full understanding of that process. The end results produce something similar to the picture below.

At this point, it is now okay to create your net in a CAD program of your choosing.  I should note that there is software available designed for this specific purpose, but it is not Open Source nor does it seem to be made for work with laser cutters and is geared toward industrial designers.  Parametric CAD suites like Solid Works and Creo [Pro/E] meet our needs in addition to tools such as Inkscape, GIMP, and Corel Draw.

Folding is key, how the material folds and the method of folding make all the difference in the actual design of your net. There are sheetmetal formulas for calculating the proper lengths of your folds legs.  However, in the case of cardboard and a laser cutter as a tool, things don't quite work exactly the same by our experiments.  Sheetmetal work has a principle of the neutral axis, that is, the axis between the tangent points of  a bend that is neither compressed nor stretched. In those formulas, this neutral axis is represented in what's called the K-Factor and Y-Factor [used in CAD software usually multiplying the K-Factor by number.] For this cardboard, the K-Factor is effectively 0 as all of the material compresses or stretches when bent at a 90deg angle.  This means that bend radius on the inside and outside of the bend are very close to 0 for all intents and purposes, but you still have to account for the material thickness when designing the actual folds in the net.  In other words, it is a good idea to offset some of your fold lines by some of the material's thickness to get a better fit.  I also recommend that you shorten the lengths of your tabs to avoid fold interference and using corner reliefs everywhere applicable.

In terms of cutting the net and fold lines, Vector cutting the entire net is your best option for rapid and mass production.  Using the raster feature to whittle away at the fold line would consume far too much time to make it useful in production.  Also, because the cardboard is corrugated, it doesn't provide any actual advantage at all in this situation.  There was no point in trying to vector the fold lines on low power to mimic a raster for that reason.  Instead, I opted to test various methods of vectoring the fold lines from replicating the SNIJ Hinge to dashed lines of various lengths.  I found that for our purposes a series of dashed lines similar to perforation were most effective in getting the cardboard to fold in a suitable manner for our purposes.

After many iterations, a version was made that is sufficient for packaging our TurtleBot more safely than it was before.  I will continue to iterate on it's design to make it even more effective, but this version was found to be sufficient.  Also, it would be greatly appreciated if anyone knows where we can purchase E-Flute corrugated cardboard in 24" x 18" sheets.  I have reasons to believe that it may be the most suitable size for this operation.

Here is a link to the net posted on Thingiverse:


Anonymous said...

Nice! But why is this Kobuki so dirty? :-)

I Heart Robotics said...

If you look at the connectors, you can see that it is a pre-production model.

Also, someone decided to attempt to upgrade it to the latest firmware, this did not work.