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Attributes linked to this design project (CEAB's Graduate Attributes):
> Problem analysis
> Design
> Use of engineering tools
> Communication skills
> Life-long learning
We were assigned the task of designing a 3D printer catering to hobbyists and amateur users, aiming to outperform existing models such as the Bambu Lab X1C and the QIDI TECH X-Max 3. Our objective was to align with the competition in terms of product and usage price ranges, print speeds, and sizes.
To achieve this, we initiated an extensive market research project to delve into the nuances of the prevailing 3D printer market. The formulation of precise engineering specifications was grounded in the findings from this research. Simultaneously, we engaged in an iterative design process, generating a range of potential designs. Through systematic analysis and comparison, we narrowed down these options to a singular design that not only met but exceeded industry standards.
To ensure the viability and competitiveness of our chosen design in the market, we subjected it to further optimization and refinement using SolidWorks. Employing an iterative approach founded on engineering precision and market insights, our 3D printer project was strategically positioned for success in a competitive and ever-evolving market.
Teamwork was crucial for this project as there were too many little details needed that it would have been easy for me alone to have missed them and not realized until team members highlighted them. As you can see later on, several iterations were needed to come up with a fully functional, appropriate, and efficient design.
SELECTED CANDIDATE DESIGN:
Cartesian Motion with Thread Rod and lead screws - V4 OF 4
Chosen design's iterations:
Cartesian Motion with Thread Rod and lead screws - V3 OF 4 (before CAD)
I made major iterations to the design four times. After every iteration, I consulted with my team to get their opinion on what they thought of each, and if they could think of any way to improve the design.
I initially came up with v1, but before proceeding to 3-D model it, realized that it had too many rotating parts, which would eventually cause the system to fail or weaken at some point in time; that's when I came up with v2, a design with fewer moving/rotating parts, but designed in a way that would allow the model to last practically much longer.
V2 also had its flaws. There were four stepper motors controlling the same movement in one direction, and so if any of the four motors failed or misaligned with the rest, the entire product would be defective. This made me move to v3, which still being advanced, but with fewer moving parts.
I consulted with my team on my final v3 design and one of the members highlighted a major flaw: the rotational movement of the extruder's screw rod coincided with it's linear motion, and so the user would not be able to control the extruder linear motion without affecting its rotational movement, and vice versa. With time being short, I quickly brainstormed viable ideas and discussed them with my team by using visuals during the same meeting, and ended up with the perfect solution to the problem, v4.
Cartesian Motion with Thread Rod and lead screws - V2 OF 4
Cartesian Motion with Thread Rod and lead screws - V1 OF 4
Design 1 (selected design): Cartesian Motion with Thread Rod and lead screws
Pros:
The nozzle can rotate, meaning they can save time and material by not building as many supports.
Cons:
The nozzle has to rotate meaning there are more components to the printer.
Design 2: Cartesian Motion with Belts
Pros:
Relatively easy concept to reproduce.
Similar concept to other printers on the market. This means that it has already been tested and done by the market.
Cons:
Print bed cannot move in the x and y direction at the same time.
The belts moving the print bed must be very long, meaning the printer is a lot larger than the print bed .
Design 3: Cartesian-Polar Hybrid Motion with Linkage Mechanism
Pros:
Similar designs exist on the market.
Is relatively fast (in terms of movement).
Cons:
Different coordinates, meaning it can be harder to program.
Relatively more components needed.
Design 4: Pulley-String Mechanism
Pros:
Not many moving components
Cons:
Not very common in the market
Different models mean more custom parts are necessary
The decision of design selected:
The team decided to continue the project with Design 1. We selected the design to be the top candidate because it is relatively fast, has a similar design on the markets, meaning parts can be found relatively easily, and has a simple design. It also has a lower operational cost than other printers on the market and is the middle ground between all the options.
Components of the selected design:
Types of Screw:
Lead Screw:
Designed to move something rather than hold something in place.
Lower friction because of the reduced contact ratio
Trapezoidal in shape (in order to lower friction)
Lots of backlash in x and y directions (gravity helps go against backlash
The Lead of a Screw
As opposed to other types of screws, the pitch of lead screws is not necessarily the same as the lead of the screw.
Definition: The lead of a screw: how far a nut will travel in 1 rev (mm/rev).
Because lead screws can be multi-start screws, the lead of the screw will be the pitch of one of the starts times the number of starts.
Example: 4 Start Lead Screw:
These types of screws will have 4x the lead of the screw compared to a single start lead screw. There is also 4x the amount of contact area, which helps prevent backlash.
Supporting the Screw:
Lead Screws should be combined with guide screws/rods that support the motion of the lead screw (one rod on either side of the screw). The lead screw should be mainly for the motion aspect, NOT the supporting part.
Size of the Screw:
6mm, 8mm, and 10mm diameter will be good
A 2mm lead screw could be used for the z-axis since it is the most precise and the axis with the least motion as opposed to something with a higher lead
The direction of movement:
Z Direction:
Using a 1.8-degree step motor, the following can be determined:
Note that with a 2mm lead, there will always be a full number of steps to get an accuracy of 0.05mm.
To check that 2mm lead is the correct choice, the power exerted by the motor in order to achieve the desired print speed can be determined. In the z-axis of a 3-D printer, the maximum speed and acceleration are significantly lower compared to the x and y directions, where most of the motion is occurring. Especially because the z-axis moves in discrete movements, it is important that the smallest step size (leading to the highest quality of print) can be achieved. In this case, a step size of 0.05 mm can be achieved by using a lead of 2mm.
X and Y Directions:
If the 2mm lead screws were used in the x and y directions, it will most likely require a very powerful stepper motor. This can be shown through the following:
Motor 200 steps/rev
The range of speeds that current 3-D printers operate is approximately 50 - 150 mm/s
Calculating RPM needed by the motor to achieve speeds of 50 and 150 mm/s
For the 2mm lead screw:
We want to test the limits: 50mm/s and 150mm/s
For 50mm/s with 2mm lead:
50 mm/s 2 mm/rev =25 rev/s = 1500 RPM
Even at the lower end of the speed requirements, the motor would need to run at 1500 RPM. A typical stepper motor has a maximum speed of around 1000 RPM [CC], so this stepper motor with this type of lead screw will not work for the X and Y directions.
To adjust for this, a larger lead must be used. The speed of the printer will increase, but the print quality will decrease slightly.
Try 50mm/s and 150 mm/s with 8mm lead:
50 mm/s 8 mm/rev = 6.25 rev/s =375 RPM @ 50 mm/s
150mm/s 8 mm/rev = 18.75 rev/s=1125 RPM @ 150 mm/s
Where does the speed max out with the stepper motors?
x mm/s 8 mm/rev = 1000/60 rev/s => x = 133 mm/s
In the current market of 3-D printers, 133 mm/s would be considered relatively high printing speed. To check that the quality of the print was not impacted, the distance travelled by the axis per revolution can be calculated:
2 mm/rev 200 steps/rev = 0.01 mm/step
The filament of a 3-D printer is generally 0.4mm, meaning that the distance travelled per step is 40 times smaller than the thickness of the filament. This difference is significant enough that the print quality of the machine will not be affected.
When the lead of the screw is 8mm, the design is able to operate comfortably in the x and y directions with speeds up to 133mm/s. The z-axis is controlled through a screw with a lead of 2mm, as the maximum speed and acceleration of the z-axis is significantly lower.
Threaded Rods:
Gives the highest holding force due to a higher contact ratio
V shape provides a high contact ratio (with lots of friction)
Therefore, it should not be used for motion transmission.
Build Platform:
Material: Aluminium
References:
[AA] https://grabcad.com/library/tr8x8-4-8mm-4-start-lead-screw-1
[BB] https://www.youtube.com/watch?app=desktop&v=YU5SdzRVtv0
[CC] https://www.youtube.com/watch?v=o_0xdrKUYVU
[DD] https://www.telcointercon.com/blog/max-speed-for-stepper-motors-and-gearmotors/
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