Evaluation criteria
| Criteria | Description |
|---|---|
| Tool forces | When moving the extruder relative to the substrate the friction induces tool forces. These forces can be reduced by minimizing the contact area of die outlet. Low tool forces can ultimately allow the extruder to be controlled by less rigid robots like Scara-arms |
| Process control | The tuneability of the process relates to whether parameters like rotational speed, feed-rate and temperatures can be controlled independently |
| Flash formation | Due to the pressure level inside the extruder and the clearance between the moving parts some flash will be generated. However, the design should seek to minimise this by using the lowest possible extrusion pressure combined with stiff components and tight clearance fit between the moving parts. Furthermore, the design should allow flash to be removed continuously to reduce friction between moving parts and build-up of excess material |
| Oxide removal | Proper removal of oxides is crucial for bonding between extrudate and substrate. Any oxide layer on the mating surfaces will reduce the bond quality |
| Resolution | The cross-section of the deposited stringer dictates the level of details that can be deposited. A coarse structure will cause more material wastage during post machining and is not preferred |
| Wire slip | If the extrusion chamber is too short compared to the required extrusion pressure the wire will slip |
| Contact friction | The contact area between spindle and housing should be reduced to avoid excessive work and heat generation during extrusion |
| Serviceability | When used for aluminium, the parts that are in contact with the feedstock will bond by the sticking aluminium and will need to be disassembled prior to sodium hydroxide cleaning |
| Deposition quality | The density and visual appearance of the deposited structure. The structure should be continuous and void-free |
| Criteria | Description |
|---|---|
| Tool forces | When moving the extruder relative to the substrate the friction induces tool forces. These forces can be reduced by minimizing the contact area of die outlet. Low tool forces can ultimately allow the extruder to be controlled by less rigid robots like Scara-arms |
| Process control | The tuneability of the process relates to whether parameters like rotational speed, feed-rate and temperatures can be controlled independently |
| Flash formation | Due to the pressure level inside the extruder and the clearance between the moving parts some flash will be generated. However, the design should seek to minimise this by using the lowest possible extrusion pressure combined with stiff components and tight clearance fit between the moving parts. Furthermore, the design should allow flash to be removed continuously to reduce friction between moving parts and build-up of excess material |
| Oxide removal | Proper removal of oxides is crucial for bonding between extrudate and substrate. Any oxide layer on the mating surfaces will reduce the bond quality |
| Resolution | The cross-section of the deposited stringer dictates the level of details that can be deposited. A coarse structure will cause more material wastage during post machining and is not preferred |
| Wire slip | If the extrusion chamber is too short compared to the required extrusion pressure the wire will slip |
| Contact friction | The contact area between spindle and housing should be reduced to avoid excessive work and heat generation during extrusion |
| Serviceability | When used for aluminium, the parts that are in contact with the feedstock will bond by the sticking aluminium and will need to be disassembled prior to sodium hydroxide cleaning |
| Deposition quality | The density and visual appearance of the deposited structure. The structure should be continuous and void-free |
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