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I’ve already shown how to accurately design simple living hinges in SolidWorks as a single part in a past blog article here: ( https://www.design-point.com/how-to-model-a-plastic-living-hinge-in-solidworks-as-a-single-part ). We are now going to take those concepts and techniques to the “edge” in this blog now that SolidWorks 2014 has introduced 2 critical new tools.
1. Fixed Length Spline -It is now possible in SW2014 to dimension the length of a spline. All you need to do is draw a spline, and click on it with the smart dimension tool to add a length dimension that will drive the length of the spline. This opens up many creative techniques that you can employ to model straps, ropes, chains, hoses, wires, etc that can be manipulated parametrically (AND STILL KEEP THEIR PROPPER LENGTH). Routing users are going to benefit hugely from this now that they can natively drive any spline length used for hoses, tubes, or wires.
2. Style Spline – These are probably my 2nd favorite new feature that I’ve found so far in SW2014. These are much different from the traditional splines that must go through “points” to shape them. This new spline allows you to dimension and constrain what used to be the “control polygon” points. The result is that it is much easier to fully define a spline (now that is a good thing in SW2014), and get a smooth, flowing spline as a result compared to the traditional, “control point” spline which was always difficult to fully define.
So these 2 great new tools now allow us to dynamically model something that was impossible with any other version of SolidWorks, a “butterfly living hinge”. These are mainly found on dispensing closure/caps and any plastic part where you need a 2 position or sprung hinge action. Sure, you could always design these in their open (as molded) state, but could you exercise the lid to show approximately how the hinge behaves (in a single part)? The answer was a big “NO”.
We are going to start with the same “fixed arc technique” in my earlier blog post to model the center of the hinge where the plastic hinge is short. We will also re-use the driving sketch to define the open angle of the lid. After that is complete, it is now time to use our new tools to model the outside edges of the butterfly hinge where the plastic acts like a flexible strap. This plastic stretches as the lid is rotated to give the 2 position, “snap” action. This transition usually occurs around an open angle of 90deg depending on hinge geometry.
Once we have our sketches for the center and edge shapes, we just need to create a boundary surface between them, thicken it to our desired hinge thickness, and combine the 3 bodies (base, lid, and hinge).
These 2 new tools have allowed us to quickly model something that most people would have thought was impossible to do as a single part. I have posted the files on GrabCAD and these are available for download if you want to check them out.
Please note that they are obviously SW2014 files so you will need SW2014 Beta (currently the latest version) to see the feature trees. The parts should be able to be opened in SW2013, but will only show as an imported body. You can download the part and assembly filed here on GrabCAD: http://grabcad.com/library/butterfly-hinge-closure-cap-1