Three months later, I am finally getting back to writing about some of the things that I’ve been working on. This one is all CAD based, and was a collaboration between myself and two others. We were tasked with reverse engineering a product using SolidWorks, and we chose to model an old staple gun that I had laying around.
This project was for ME 5680 at the Ohio State University. The class title is “Computer aided design and manufacturing”, and is a highly sought after technical elective at OSU. If you are an ME at OSU, you should so totally take it. It is awesome. You get to learn SolidWorks, get certified in SolidWorks AND the labs use Tormach CNC machines! Seriously, take the course.
We were required to find a product that we could disassemble, measure (fairly) accurately, and have a minimum number of parts with some complexity. The project began around the 3rd or 4th week of our 15 week semester, and we managed to keep a very steady pace throughout the time we had to work on it. My group members for this project were Caitlin Boone and Hamed AlGendy, both of whom did great work the whole semester, thanks guys! This was one of two large project groups I was a part of during my final semester and both of them were seriously great. Both projects did such a great job of pacing the projects that we barely had any late night or weekend meetings and we even finished with spare time before the due date!
After taking apart the stapler, we counted 21 unique parts, most of which were fairly complex sheet metal components. This satisfied the requirements for the project so we split up the stapler into three main sub-assemblies: the hammer, the magazine, and the body. My portion was the hammer assembly. After we split up the parts we proceeded to work on the project over the next 11 weeks very consistently by dedicating 3 hours a week to meeting with each other and working on our parts.
HAMMER ASSEMBLY MODELING
Modeling the hammer assembly was very interesting. I had used sheet metal tools previously, but this sub-assembly had some very complicated components in terms of features and dimensions.
The hammer itself is only a flat piece of steel with a couple squares punched out of it. The stops, both the steel and rubber one, were simple shapes again. Where this one got interesting is the hammer carriage, the springs, and the hammer body.
The hammer uses two coaxial springs, and I wanted to model them in such a way that they would animate when I moved the hammer carriage in the model. I accomplished this by defining the helix of the spring with it’s center line, but leaving the top end of the line undefined. By defining the end of the line with its mating component at the assembly level, the springs would recalculate each time the hammer carriage was moved, meaning animation was possible! The spring itself is a sweep feature using the previously mentioned helical sketch, with special sweeps and cuts on the ends to create the ground/flattened ends like a real spring.
The hammer body and the hammer carriage are both purely sheet metal features. This speaks to how they are manufactured, and means that the part starts it’s life out as a flat sheet of metal. Specific to these two components, the manufacturing methods involved are most likely performed by die presses to deform, punch, bend or cut the sheet metal into the final form. The important part about this concerning a 3D design is that it is important to get the flat pattern of the part prior to manufacturing so that you know how much material to use. In SolidWorks, if you model it correctly, the software can do this unfolding for you! Staying true to the manufacturing process and wanting it to be as accurate as possible, I used the sheet metal tools in SolidWorks.
The main part of the hammer body is a series of sheet metal bends and plain old cuts. This wasn’t too crazy until I got to the back end where there was a curved bend, which is a little bit of an oddity as far as the flow of material is concerned when you actually form it. SolidWorks handled it just fine and it still worked great with unfolding the feature.
The rest of the features were made with forming tools. Forming tools in SolidWorks allows you to create the solid that defines the press tool that would be used in real life, place it on your model where it would be used, and then actually execute the forming operation to deform the material and show how it looks in the model. The key to using this instead of just making it a solid extruded feature goes back to the sheet metal part stuff. Sheet metal parts have the same material thickness throughout the whole thing (except where material has flowed due to excessive deformation). This means that the forming tool features don’t add or remove thickness to the material, but “displaces” or deforms the metal, just like it would in real life.
Whew that’s a lot of text. Enjoy some renders of my parts instead, they are more fun to look at!
THE REST OF THE MODEL
Caitlin and Hamed did a great job on their sub-assemblies as well. One of the mating parts that Hamed and I worked on separately even fit together within .05″! That is pretty impressive considering the difficulty of measuring some of the features.
I took care of the final complete assembly, and animating the model for our presentation. I spent probably 2-3 hours just on fighting with the motion study feature in SolidWorks to make the animation play in the way I wanted it to. I was pretty happy with the result. The animation consisted of the stapler disassembling, reassembling and then finally shooting a staple (with all the inner workings showing and working as they really do!).
We did make a fancy powerpoint presentation that you can take a look if you are interested. I felt we did very well, and our professor must have agreed, because we got an A on the project! Working on this project with Hamed and Caitlin was one of the most pleasant project group experiences that I had while at school. We kept such a great pace and the quality of work was just wonderful.
Oh. I also uploaded the assembly to GrabCAD just in case anyone needs a super complex staple gun model for some reason. Unnecessary levels of detail!