Mechanical Engineering Project related to RepRap

Hello all,

I am a penultimate year Mechanical and Manufacturing Engineering student, and am very interested in Open Design, which I first became aware of after reading the RepRap article in Make a couple of years ago.

I hope to base my final year project on the RepRap, and have found a lecturer who is interested in supervising it. I could of course build one and spend the project trying to modify things here and there. However I thought it might be more beneficial to the RepRap project as a whole if I picked one particular aspect of the design to focus on.

So I'm wondering if there's any areas that the RepRap community think would benefit from being the subject of a research project. I'm not looking for anybody to come up with my ideas or do my work for me, I just don't want to reinvent the wheel. I figure there's people here with a lot better knowledge of what's going on than me...

As I said, I'm studying mechanical/manufacturing engineering but I'm pretty good at programming and am interested in Mechanical/Electronic overlaps. So suggestions related to any aspect of the design are extremely welcome.

If there's enough scope in the project, I will try to continue the research at a postgraduate level. Of course, if people think that there's not a need for this, or that it would not be particularly beneficial to the RepRap project/community, I would very much appreciate being told that too

Thank you all in advance,

--Dónal

PS. I live in Ireland and study in Trinity College Dublin

Hi Donal.
I can't speak for the project officially, but for me it RepRap clearly splits into two main areas: the 3d-cartesian robot, which can be used for CNC machining, reprapping, and a bunch of other purposes, and the plastic extrusion unit - which is specific to RepRap. The robot platform seems to be well-supported and used for a wide variety of projects. The extruder might be a good 'chunk' to concentrate on.

The extruder splits further into the heater and drive unit - there's a whole bunch of different configurations that have been tried. There are pinch wheel and screw thread drives, variations using diagonal screw threads, different threads (e.g. a coach bolt) and different pinch wheels.

The heater/nozzle has also been made in many different versions - nichrome wire, wirewound resistors, different insulators, insulation materials (tapes, fire cement, JB weld, etc).

Nophead has done some good work to try and measure the strength of different drive units, and trying out different barrel/nozzle designs. Check out his blog
[hydraraptor.blogspot.com]

I reckon there might be a good project examining the behaviour of plastic as it melts and gets forced through the nozzle, and which drive system/heater/nozzle design produces the best, most reliable flow. It's probably a damn good excuse for building a reprap too :-)

Also, looking forward, recently there has been some excellent work on RepRapping electronic circuits - laying down solder into a plastic mask and adding components. That would be an interesting area to research.

I hope you can find something interesting to investigate!

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Reprapping blog and other rants: [renoirsrants.blogspot.com]
My Reprap: [sites.google.com]

Like David said, the extruder is a good way to start. Maybe try to find a way to change the extruder to a drilling mill? I know that someone from the core team made a design to have multiple extruders in the machine, why not make a drillhead for the reprap and write the software to use it?

It depends what your budget is.
The recommended/official parts are all very modular, so a high cost is allocated to extra connectors and PCB space, holes to house them, and repitition of things like mounts, mounting holes etc.

You could go down the road I am, and make a new motherboard with higher integration, that can certainly bring the costs down. There are a lot of decisions to be made down that path. I have been considering a smaller version, with less drive capability and an ultra small PCB foot print, but at the moment I'm just about to start software on mine, and it's manufacturable with only subset components if required, for less demanding applications.

If you want a preview of some of the issues I've faced, I'd recommend you look through my build thread over in electronics:
[forums.reprap.org]

However, if it's the mechanical side that is critical to you, then I'd second the above opinion from David Renyolds.

I would agree that the area of RepRap most in need of attention right now is the extruder, I would even go so far as to specify the heater/nozzle component.

It would be nice to have a good characterization of the effect of various factors on the thread produced. The important inputs I can think of are plastic type, tube temp, feed pressure, and nozzle size. The outputs might be output rate, thread temp or adhesion vs sag, and thread diameter. This is also an area where your interest in M/E overlaps is likely to be rewarded.

Another area of difficulty with the current designs is heat conduction back from the nozzle damaging the plastic parts of the extruder and the related problem of back pressure from the molten plastic forcing extruder components apart.

There are a lot of people working on extuders. I'd question whether you bring anything new to the effort. Two areas that really need attention is 1) in the recycling of scrap plastic and turning it into new filament and 2) making printable stepper motors.

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Hell, there are no rules here - we're trying to accomplish something.

Opportunity is missed by most people because it is dressed in overalls and looks like work.

Thomas A. Edison

Quite true, but since this is a Mechanical/Manufacturing Engineering Final year project, Donal has some focused effort and some university backing, plus a certain level of training and skill. A research project like recycling plastic, printable motors or printable circuits is open-ended, opening up a new area - which suits some people. Others (like myself a long time ago) might like a tighter, more defined area, where there's a bit more of a trodden path to follow - but it's still fresh ground.

If I were Donal, I'd have several goals:
1) GET ENOUGH MARKS TO PASS MY DEGREE
2) Anything else: including:
a) Learn a bit more about things I find interesting (mechanical/electronic overlaps, programming?)
b) Build a reprap and have some fun printing stuff out
c) Contribute something back to the project.

I felt there might be a good project investigating the extruder, measuring the drive systems, different nozzles, heaters (like NopHead's results), and analysing the flow through the heater and nozzle.

Things you could do:

Embed several thermistors into the nozzle, so you can get several temp readings - where's the best place for a single reading to be taken?

Thermal modelling of the nozzle - does the theory match up with actual readings? is there a better design? how long does a barrel have to be to get from 200C at one end to 60 at the other?

Examine the warm-up/shutdown cycle - when the nozzle thermistor first reaches target temp, has it reached a stable state? do parts continue to warm up? what effect does extruding at a certain rate take energy out of the system?

The actual behaviour of the flow is sometimes not clear - at what temp does ABS start to widen out as it gets softer? (i.e. how far up is this)? Is the best heater a straight tube, or a larger melt chamber?


Sorry, just thinking aloud.. Ignore any ramblings...

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Reprapping blog and other rants: [renoirsrants.blogspot.com]
My Reprap: [sites.google.com]

Greetings Donal (and other readers),

I agree that the extrusion process is much less well understood than making an X/Y/Z positioner, so there are numerous research projects that can be based on improving understanding of how the plastic melts/flows/adheres/solidifies. Note that these poorly-understood processes are not confined to the extruder itself.
So, analysis, modeling/simulation, instrumented experimental designs are all good candidate project areas.

Having said that, support materials (and their placement, e.g. by a different extruder) is also an an area deserving of more exploration.


Here are some questions to consider, when weighing project alternatives:

What are you interested in?
What skills do you have?
What tools (hardware and software) do you have available?
Which projects are of appropriate scope (neither trivial, nor too !@#$% tough?)

On that latter one, think carefully!
I wouldn't want your enthusiasm to lead you to bite off too much. Personally, I'd rather you do well on a smaller issue, than get stuck trying to solve something that's too big/tough.

For example: many people have thought about making a granule-based extruder, since granular plastic is cheaper and more available than welding rod. However, nobody has built a usable granule-based extruder, despite a number of attempts. Prof. Boyer, himself, has done some work on this, but it's still (from what I've read) in the concept stage. So, I think this (developing a granule extruder) would be a too-ambitious project area. On the other hand, a good, usable model/simulation of granule melting (and what happens to the air between the granules) might be reasonable, if you happen to be a simulation/heat flow type of guy.

Good Luck (and let us know what you pick),

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Larry Pfeffer,

My blog about building repstrap Cerberus:
[repstrap-cerberus.blogspot.com]

#$#%$#%# risk averse Americans. :-p

Edited 2 time(s). Last edit at 05/04/2009 12:08AM by Forrest Higgs.

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Hell, there are no rules here - we're trying to accomplish something.

Opportunity is missed by most people because it is dressed in overalls and looks like work.

Thomas A. Edison

:-)

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Reprapping blog and other rants: [renoirsrants.blogspot.com]
My Reprap: [sites.google.com]

Hi Donal(and everyone else )
I've just finished my 4th year engineering project on creating RepRapped Electronic Circuits (It's been mentioned in the blog). All of the suggestions made I would say are valid. however, I would say if your trying to implement an extruder or other practical device, You should try to have two mini projects, just to have one as a backup. Specifically, with my project at times I thought I'd bitten off too much with the circuits. To say I was banging my head against a brick wall on times was the understatement of the century. But it was a relief as I was also looking into UV resins (this was never finished though)

Hello again,

Thank you all for your suggestions, you've given me a lot to think about and look into...

Unfortunately (or fortunately?) in my course we are quite constrained as regards projects. The department compiles a number of projects related to the research currently ongoing and students compete for their choice. However, if a student can come up with a proposal that is in keeping with the department's criteria, and find someone interested and able to supervise it, they may be allowed to do it.

This is what I am currently trying to do. So on the one hand, I'm not really free to dictate my own project, but on the other it's unlikely that I'll be able to bite off too much, as Mr. Pfeffer put it above...

An investigation of the extruder seems like a very well bounded problem, while the more open-ended suggestions, e.g. printable motors, seem very interesting. Great suggestions all round! I'll now go and talk to my department with these things in mind, and see what they think.

Thank you all for your help, and I'll keep you updated!