Mechanical Design
Preliminary Designs
Full Scale View
The view above shows the entire prototype with the blade that cuts the Plasticine into the desired length. The goal of this prototype is to allow continuous loading.
Cross Section View
The view above shows the different moving mechanisms used in the prototype. Part (1) cuts the Plasticine into desired length and acts as a blockage, part (2) is the ejector mechanism and part (3) is the die that forges the head of the bolts.
Isometric View
The view above shows the machine with the frame structure. The frame structure will be made of aluminum 80/20 T-slot extrusion and 0.25" thick acrylic plates. This will provide stiffness in the machine and prevent the moving dies and mechanisms from misalignment.
Cross Section View
The view above shows the different moving mechanisms used in the prototype in more detail. The two dies will separate, and the billet will enter the die. Once enough billet enters the die, the blade will cut the billet and move downwards. The dies will both close and head the bolt against the surface of the blade.
Design Consideration
Die Constrainment Feature
One of the most important design considerations for our machine was how the two dies would stay aligned. Due to tolerancing fit and play and deformation that occurs in the machine, there will be forces that will push the upper die out of alignment during heading. Our first approach was inspired by sliding drawers, called guide rails. However, with deflection calculations and tolerancing considerations for metal and plastic materials, we concluded that the maximum misalignment from the guide rail concept would exceed our final bolt dimensional tolerancing specifications. Consequently, we proceeded with A2 tool steel alignment rods, which will minimally deflect during heading and keep the dies aligned.
Alignment Rods
Pros:
Maximum Misalignment of ~0.2mm
Misalignment of 0.2mm for largest expected frame deflection and loosest component fits. (Dimensional Tolerance Specification for bolts is +/- 0.25mm for concentricity)
Long Wear and Fatigue Life
Tool Steel can be heat treated and hardened in order to reduce wear on the rods. The alignment rods will be useful for a long time. Endurance life of the alignment rods is higher than expected forces, so the rods can withstand a large number of bending cycles.
Cons:
Harder to replace rods
The rods are press-fitted into the die.
Guide Rail
Pros:
Easier to replace parts overtime due to wear and tear
Since the guide rails are held in by screws, they can easily be taken out and installed
Cons:
Maximum Misalignment >0.25mm
More play for gaps in the design since there are more interfacing features and dimensions. We considered high stiffness plastic, such as Stratasys ABS-M30, however the deflection during bending would lead to too much misalignment. We then considered aluminum, however, the 3D geometry for the rails could not be feasibly made by traditional machining processes.
Final Design
(All dimensions are in mm)
Table of Joints
Full Assembly
Parts
Sub-Assemblies
