Lift Cart
Figure 1 - A side photo of the custom forklift before making changes.
At Desktop Metal, I had to solve an interference issue with a custom forklift. This was my first major engineering challenge outside of school. I used beam deflection and bolt calculations to validate my design changes with analyses. With these analyses, I was able to verify that the structural safety factors were above two. Furthermore, I was able to back up my work during a design review in front of senior engineers. After the design review, I developed my GD&T skills with technical drawings of parts.
First Time Using GD&T
My first part had to lengthen the arms of the forklift without changing the existing parts. So, I designed a simple extension block out of aluminum. This was my first time practicing GD&T and applying technical drawing standards.
Figure 2 - My first technical drawing of a part I designed using GD&T drawing standards.
Figure 3 - My technical drawing of a foot extension, done with manufacturability in mind.
We Need More GD&T
I then designed an extension for the forklift’s feet and created another technical drawing. My part’s drawing included more GD&T standards such as perpendicularity, true position, and datums. Furthermore, I designed with manufacturability in mind. So, I placed reference dimensions to make machining and inspection easy. I also analyzed tolerance placement to guarantee the part would fit with other components.
What Does the Simulation Say?
Figure 4 - Top left, a simulation of the forklift’s arm under the weight of the payload. Right side, a simulation of my extension blocks under load. Bottom left, a simulation of an eyebolt for added support.
To support my designs, I hand-calculated a cantilever beam to find the shear force, bending moment, and maximum deflection of the forklift arms under a load. To cross-check my hand calculations, I performed a SolidWorks FEA analysis of the forklift’s parts and assemblies. Not only were my calculations valid, but the analyses improved my simulation skills and uncovered points of stress concentration.
Let’s See What They Look Like
Figure 5- On the left side, there are machined extenders, one of which has a threaded bumper and spring pin. Top right, is one of the extenders onboard the forklift. Bottom right is one of the extenders without hardware.
Under the supervision of our in-house machinist, I took one piece of 6061 aluminum and machined the foot extenders I designed. I used a manual mill to create clearance holes, tapped holes, fillets, and chamfers within my designed tolerances. These features allowed the forklift to properly house a threaded bumper, spring pin, and threaded bearing. Although one of the holes was slightly beyond the tolerance range, the blocks snuggly fit into the forklift, and all other dimensions were within specification.
Other work at Desktop Metal
Other notable work I did at Desktop Metal included solving a gasket leak and performing a tolerance stack-up on a dozen-part assembly. Onboard one of the printers, there were sealing issues with the bulb gaskets. So, I looked at the tolerances of the specified gasket and compared them to the perimeter of the slot it covered. After checking several printer frames and comparing them to the specified gaskets, the gaskets were out of the acceptable tolerance range. So, I experimented with gasket lengths and found a general rule for applying gasket lengths for any slot perimeter.
Additionally, there was a component that needed to be changed in a large assembly, but this new component was 10mm longer than the original. So, with the help of a senior engineer, I analyzed multiple part drawings and identified key dimensions and their tolerances. I then cumulated these values to calculate the tolerance of the new component’s position and whether there was a possibility of interference. Through these projects, I learned how to use part drawings to determine the cause of a leak. Plus, I learned how to analyze multiple parts in a tolerance stack-up.
Figure 6 - Data from the tolerance stack up alongside the final minimum and maximum dimensions.