SpoolHead
Release status: unknown
| Description | Spool-printing toolhead
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Contents
Introduction
I'm Jacob Bayless, and my team members are Mo Chen and Bing Dai. We're 4th year Engineering Physics undergraduate students at the University of British Columbia, and this is what we have chosen for our project course this year.
The Spool-printing toolhead ("spoolhead") is a Reprap toolhead for printing with spooled, non-extrudable materials. The main goal is to print with copper wire, but steel and nichrome wire may also be printable. Possibly thread will be as well, although we are not planning to test this.
While we would love to be developing this toolhead for Mendel, these printed parts were not readily available when we began our project, and Darwin was deemed sufficient for our needs. Modifications to adapt the toolhead for Mendel should be minor.
Schedule
The project began in August 2009. The release date is expected to be early April 2010.
Motivation
While Reprap can print with a variety of plastics, efforts are currently being undertaken to extend this ability to the extrusion of low-melting-temperature alloys such as Field's metal. However, even with this in place, the Reprap's ability to print "active" (electronic or electromagnetic) components will remain limited, due to:
- The inability to print thin insulated wire, essential for tightly-wound coils;
- The high cost and low availability of Field's metal and similar compounds;
- The difficulty of printing fine tracks from liquid metal, due to surface tension;
- The operating range of printed components would be restricted to temperatures safely below 62 degrees C, the alloy's melting point.
The last point implies, for example, that the Reprap will not be able to use Field's metal conductors in an extruder for Field's metal, as it would melt itself during operation.
In his Ph.D thesis, Ed Sells discusses the mechanical design of the Darwin model. In the section "Remaining challenges for pure self-manufacture", he writes that, of the Reprap's own parts, the most difficult to self-manufacture would be "electronic components, motors, conductive cable, solenoids, and the heating element". He adds that "it is unlikely the machine will be able to self-manufacture these parts for at least a couple of years". The challenging element that all of these parts have in common is the printing of copper (or Nichrome) wire.
It is therefore clear that the ability to include wire elements in a printed part would greatly expand the Reprap's capability of self-manufacture, whilst allowing it to manufacture a wider variety of active components for other purposes as well.
Further applications may include:
- Printing steel wire reinforcements to strengthen a part in crucial areas;
- Printing flexible threads within parts to create durable "living hinges".
Software
To get started in the right direction, our image of what such a toolchain may look like is one that works in the Scalable Vector Graphics (SVG) file format. First, a 3D model (STL) would be sliced in the traditional way by software like skeinforge. Then, the slices would be exported to SVG, in individual layers representing the Z height. Users would then draw lines representing wires in the part layers freely as desired (and, possibly, vias to connect Z layers). The SVG model, now incorporating bulk plastic and wire information, would then need to be translated into G-code.
Due to time constraints, we are not planning to create special skeinforge-like software for digesting 3D models with wires incorporated in them. This may form a future project in its own right, or other members of the Reprap community may join in to create an accompanying software toolchain.
Of course, any software produced by our team for this toolhead (such as firmware, or modifications to G-code interpreters) will be released with the hardware plans.
The Spool-Printing Process
Unlike extrusion of a thermoplastic, spoolhead printing allows for use of materials that are impractical to melt; for example, metal wires. The flexible wires are laid as continuous strands within the printed part. Doing this requires the following automated processes: 1. Controllably feeding the wire from the spool; 2. Bonding the wire to the printed part; 3. Cutting the wire at the desired location;
This process is sufficient to handle an arbitrary number of wires on arbitrary horizontal planar paths, allowing the printing of many desirable features, such as PCBs, routing. Further software developments may also open the possibility of printing a subset of 3-dimensional embedded wire figures, such as helical coils. Printing of arbitrarily complex 3D wire shapes, such as knots, would probably be impossible with the proposed methods; however, the vast majority of useful devices do not require this level of complexity.
Controllably feeding the wire from the spool
Three methods have been proposed for this. The first is a stepper-actuated pinchwheel extruder, or similar device (such as a stepper motor capstan feeder), functioning in a similar way to the thermoplastic extruder. This method should work reliably, and has the advantage of being able to accommodate a wide range of wire diameters. More importantly, it has a high level of compatibility with existing electronics and software, due to its similarity to the thermoplastic extruder. However, wires must be relatively stiff (such as copper). The stepper does not have a high torque/narrow shaft requirement like the thermoplastic extruder motor, because there is very little resistance to the wire's motion. A good grip is, however, important.
Due to the convenience of compatibility, and the ability to handle fine wire diameters, this is the method of choice for the first SpoolHead.
The second method uses a solenoid-actuated mechanical pushbutton-advance pencil to act as a sort of linear stepper. This has the advantage of being extremely cheap, as solenoids and mechanical pencils are very common. Also, solenoids are more likely to be printable in the future than stepper motors. For reverse feeding, two pencils could be used back-to-back. The main disadvantage of this method is that a given pencil can accommodate only a certain diameter of wire (eg. 0.5 mm, a fairly thick gauge). The spoolhead's first printed material is planned to be 0.3mm copper wire; 0.3mm pencils are (to my knowledge) hard to find outside of Japan. Furthermore, compatibility with existing hardware and software is not guaranteed.
The mechanical pencil method is therefore left as a promising area to be explored in the future.
The third proposed method is to integrate the SpoolHead into a thermoplastic extruder (presumably with a wider nozzle diameter than existing variations). The wire would be drawn in by the molten plastic's viscous flow, and extruded together with the plastic. If it worked, this would guarantee a strong bond between the wire and the printed part. However, it suffers a significant drawback in being unable to extrude wires without simultaneously extruding plastic; this might be acceptable for some applications but not all. Furthermore, the method has many associated uncertainties; for example, would the wires jam easily? As a result, given tight deadlines for this project, it is considered too risky to pursue at the moment.
Working Notes. This is a stub!
Everything below this point is working notes.
Entrepreneurship (Kits)
No plans exist to produce kits for this toolhead.
Photos and Drawings
Captioned
Links can be put in captions.
Working Notes
Forum thread?
Files
Tooling
Description of the tooling requirements
Process
What is making the part like?
