reprap-granule-extruder-tudelft1

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4 | From granule to extrusion can cause material to chip from the screw of the tube. When the extruder was disassembled it became clear that the screw was full of small metal parts, demonstrated by a piece of paper turning gray from the metal filaments when wrapped around the screw. This significant pollution is most likely due to the wear between the screw and the inner surface of the tube. These findings make it clear that is of great importance to produce the screw and extrusion tube with narrow tolerances. Diameter expansion after exiting the nozzle It was noticed that the material is expanding after it exits the nozzle. With the nozzle hole having a diameter of 2.3 millimetres, the extrusion rod has a diameter of 2.6 to 2.9 millimetres. This is due the fact that the material wants to get back in its original shape. The extrusion nozzle forces the material into a certain shape. When the material exits the nozzle, the forces of the extrusion tube disappear. The material tends to get into force equilibrium and expands a little. Larger granule causing a darker output colour When larger pieces of granule are fed to the extruder the extruded material becomes darker. This can be caused by two phenomena. The larger granules could have more problems to get into the extrusion tube, which can lead to less material in the extruder. The wear between the tube and the screw stays the same and therefore there are comparative more iron particles in the melt. The second cause is that the bigger granule causes the screw to bend a little, because of wrong alignment. This causes the screw to touch this inner surface of the tube, which causes al larger wear. Concluding, it can be questioned if the argumentation for choosing a screw based extruder was solidified. It seems that due to the small dimensions of the screw the fractional heating is very low. Another reason for this can be that the screw is not stiff enough to counter the force put on it by the material. Still the material blending and heat spreading properties of the screw based design are big advantage. 4.5 Research suggestions Because of time restraints, there was no time left for any structural testing. Therefore, some suggestions for testing the setup described before are given. When the extruder works well and controlable, different parameters have to be investigated: motor power, couple, motor rpm, external heating, kind of materials, nozzle diameter, screw design, density of the granule, screw size, screw tube fit, frictional heating, extrusion speed etc. As one can see there are a lot of different variables, which makes testing a difficult and time consuming process. When conducting this research one should know that the expected controlable variables are: temperature of the heating element, type and size of the input materials and motor speed (depending on the kind of motor). The chosen input material will request certain circumstances, which can be met by adjusting the motor speed and temperature. This statement is only valid when one decides to use one kind of machine and one does not vary the extrusion screw. At the end of this process the relations between the different parameters and the ideal values of the different parameters can be derived. The final phase of the research will be the exploration of things as accuracy, reliability and lifespan of the product. 22 | Prototyping Lab (IO3028) - RepRap Recycle Add-on
5 Ȧdapting the prototype to the RepRap Unfortunately, the time given for this project turned out to be too short to be able to adapt our findings for a RepRap ready prototype. A rough concept was created for our presentation, to show what the ultimate goal of the project is. This concept reflects our vision on how the extruder will look in a RepRap setting, yet it tells little about the actual feasibility of it. The feasibility will be discussed in our conclusion. RepRap mounted extruder In figure 5.1, a concept drawing of the granule extruder can be seen. For this concept, the design of the current Thermoplastic extruder 34 has been analysed and adapted. The different parts will be discussed below. Base The base is the part that joins everything together. As with the current extruder, it should be designed to be printed with a RepRap, to maximise the number of parts that are printable. Most other parts in the extruder are not that likely to be printed, because of tolerances and heat development. The mount displayed in the figure is based on the current mount to the so called ‘X carriage’, the module that makes sure the printer head can move in the X-axis direction. The Bits From Bytes RapMan, that is available at Delft University of Technology, has a different kind of mount. The base can be easily adapted or redesigned to fit everything on that (or every other) mount. Motor For this concept, we added a stepper motor to the side of the base. The size and weight correspond to the stepper motor that is currently used in the Thermoplastic extruder 35 . However, it is questionable if this standard RepRap stepper motor is sufficiently powerful for this type of extrusion (see chapter 6. Conclusion and discussion). Electronics Little is known about the required electronics at this moment. The circuit board should take care of the communication with the main RepRap control board. It is wired to the heating element, a temperature Base Circuit board for motor and heating control mounted to base Funnel (Stepper) motor Mount to standard X-axis carriage Tube/ Thermal barrier Thermocouple wire Heating element Worm wheel transmission Screw Nozzle Figure 5.1 - Concept drawing of the extruder with different parts named. 23 | Prototyping Lab (IO3028) - RepRap Recycle Add-on
Page 1 and 2: Developing a plastics recycling add
Page 3 and 4: Table of Contents 1. Introduction 5
Page 5 and 6: 1 İntroduction The RepRap is a 3D
Page 7 and 8: 2 | The RepRap project Fused deposi
Page 9 and 10: 3 | From product to granule Possibl
Page 11 and 12: 3 | From product to granule Figure
Page 13 and 14: 3 | From product to granule As for
Page 15 and 16: 4 | From granule to extrusion decre
Page 17 and 18: 4 | From granule to extrusion threa
Page 19 and 20: 4 | From granule to extrusion screw
Page 21: 4 | From granule to extrusion Figur
Page 25 and 26: 6 Ċonclusion and discussion The ma
Page 27 and 28: 7 Ṙecommendations for further dev
Page 29 and 30: 8 Ṙeferences 1 - Bowyer, A. 1992.
Page 31 and 32: Appendix A Blender granule tests 1.
Page 33 and 34: A | Blender granule tests 5. Blendi
Page 35 and 36: - Granule still bounces up without
Page 37 and 38: A | Blender granule tests 13. Blend
Page 39 and 40: Appendix B. Technical drawings of t
Page 41 and 42: 50 5 5 10 25 50 50 10 R8 5 25 1 10
Page 43 and 44: M16 20 25 14 2 30° 7 nozzle benami
Page 45 and 46: Appendix C. Extrusion screw manufac

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