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The three main components of a mandrel tube extrusion machine are the die, mandrel, and container. They require meticulous material and process selection to meet demands and specifications.
Full Scale Machine
Full Scale Machine
Die
Die
The die withstands the greatest pressure in the extrusion process while requiring the tightest tolerances. As such, the most important properties to maximize are fracture toughness, strength, and hardness.
The Ashby Chart shows that optimal materials for the die include Steels, Ni Alloys, and Ti Alloys. Since cost is a factor as dies need to be replaced after extensive wear, Steel is the optimal material choice.
The Wear Rate-Hardness graph further shows that minimizing wear and maximizing hardness is best left to Nitrided Steels or High Carbon Steels.
The best process selection for die production would be forging of a steel billet and CNC machining to produce the final geometries. Nitride treatment or carburization heat treatment is then added for extra hardness.
Scaling down from full scale production to a small scale prototype, stresses experienced are less strong. As a result, light metals such as Aluminum may be used to create the die.
Mandrel
Mandrel
The mandrel faces similar stresses and friction to that of the die. As such, material selection is similar meaning the optimal material choice is Nitrided or High Carbon Steel.
Mandrel production would ideally start as a forged steel billet. Final measurements are created through lathing as Mandrels generally have simple geometries. Nitriding or carburization can then be added.
On a small scale prototype, reduced friction requires less rigorous material selection. As such, aluminum can be used instead of steel for the mandrel.
Container
Container
The container experiences pressure as a result of the Poisson Effect due to the load applied by the ram. Though the pressure is lower than that experienced by the die and mandrel, steel is still the most optimal choice taking performance and price into consideration. Due to lower stresses, Medium Carbon Steel is a good choice.
The container production process would start with forging a cylinder out of Medium Carbon Steel and then hot rolling the billet into a tube shape. Using a lathe, the interior can be brought to the specified diameter.
Scaling down production to a small scale prototype while using a clear material to see the inner mechanism results in a different number of material specifications. Optimal materials include Polycarbonate, Acrylic, and PVC.
Prototype Machine
Prototype Machine
The prototype extrusion machine experiences forces on a much smaller scale due to its difference in size and the billet material of Plasticine. As a result, the material properties of the parts can be less demanding which saves cost in material and processes. As per the project's requirements, the container will be constructed out of Acrylic to allow one to observe the deformation of the billet. All other parts can be constructed out of 6061 Aluminum Alloy. Stress simulations indicate that this material selection is more than efficient for the forces experienced during extrusion.
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