3D Printing

 

WEEK 7 (TUTORIAL)

 

What is 3D Printing?

 

3D-Printing is described as Additive Manufacturing. Additive Manufacturing refers to objects built by adding layer-upon-layer of material. The material used can be any type of material, such as plastic, metal or even water-soluble materials such as Polyvinyl Acetate (PVA).

 

Once a CAD sketch is done, the 3D-Printer reads in data from the G-Code file, made using a slicer software and lays down or adds successive layers of liquid, powder, sheet material or other, in a layer-upon-layer fashion to fabricate a 3D object.

 

A slicer is a software that slices our CAD drawing into different layers, and these layers will be made so thin that it can be read/ represented as X, Y, Z coordinates information. This will give an output, G-Code file.

 

Types of 3D Printing technology

 

1. Fused Deposition Modelling (FDM)

 

Also known as Fused Filament Fabrication (FFF), it is the most widely used form of 3D Printing at the consumer level. FDM 3D printers build parts by melting and extruding the thermoplastic filament, which a printer nozzle deposits layer by layer in the build area.

 

FDM works with a range of standard thermoplastics such as ABS, PLA, and their various blends.

 

Advantages	Disadvantages
Quick	Layer lines tend to be visible
Low-cost prototyping of simple parts	Shows inaccuracies around complex features

 

FDM is not the best option for printing complex designs or parts with intricate features. Higher quality finishing may be obtained through chemical and mechanical polishing processes. However, if it is only used to print prototypes or a simple design, FDM is a good choice.

 

2. Stereolithography (SLA)

 

This was the world's first 3D printing technology, invented in the 1980s. SLA resin 3D printers use a laser to cure liquid resin into hardened plastic in a process called photopolymerization.

 

SLA has the clearest details and the smoothest surface finishes of all plastic 3D printing technologies. However, the main benefit of SLA lies in its versatility. SLA photopolymer resin formulations were created to have a wide range of optical, mechanical, and thermal properties to match those of standard, engineering, and industrial thermoplastics.

Advantages	Disadvantages
Tight tolerances	Parts are affected by moisture, heat and chemicals
Smooth surfaces	Limited to photosensitive resin
Minimal visible layer lines	-

 

SLA parts have sharp edges, a smooth surface finish, and minimal visible layer line. SLA is a great option for highly detailed prototypes requiring tight tolerance and smooth surfaces and is widely used in a range of industries.

 

3. Selective Laser Sintering (SLS)

 

This is the most common additive manufacturing technology for industrial applicators. 

SLS printers use a high-powered laser to fuse small particles of polymer powder. The unfused powder supports the part during printing and eliminates the need for dedicated support structures. This makes SLS ideal for complex geometries, including interior features, undercuts, thin walls and negative features.

Advantages	Disadvantages
Excellent mechanical characteristics with strength resembling that of injection-molded parts	Slightly rough surface finish
Almost no visible lines	-

 

The most common material for selective laser sintering is nylon, which is a popular engineering thermoplastic with excellent mechanical properties. Nylon is;

• lightweight
• strong and flexible
• stable against impact
• stable against chemicals
• stable against heat
• stable against UV light
• stable against water
• stable against dirt

 

The combination of low cost, high productivity and establish materials make SLS a popular choice among engineers for functional prototyping and a cost-effective alternative to injection molding.

 

 

Slicer Settings

Slicer settings are important as every 3D printer is different, every material is different, and every 3D model is different. Slicer settings will affect the product properties. Thus, choosing the correct slicer setting is important. Some important settings are, Temperature, Layer Height, Retraction, Supports, Infill and Shell Thickness.

 

Temperature

The temperature of the nozzle is the most important setting in slicer because without a perfect level of heat, no print will work. Nozzle temperature should be tune when we begin printing with a new filament. Different filament will have different melting point.  We can check the temperature by printing a temperature tower to see which values work.

Too high a nozzle temperature will case over-extrusion with blobs and zits all over the print.

Too low a nozzle temperature will cause under-extrusion, where not all the layers are fully printed.

For the bed temperature, generally, a hotter bed will provide a better adhesion, while a cooler one could lead to warping.

Some methods we can do to improve adhesion is using Skirts, Brims and Rafts.

Skirts are used to provide an outline - no adhesion

Brims allow some adhesion to the print perimeter

Rafts are full platforms on which the 3D print is places. Print adhesion is onto the bed raft instead of the bed.

 

Layer Height

Layer height is important as it affects the printing time, detail and part strength.

A smaller layer height will have more layers to the overall print. This means that the printer have more room to generate finite detail on parts but take a longer printing time and have a weaker part strength.

A bigger layer height is the opposite of a small layer height.

 

Retraction

Retraction determines how fast filament is sucked back into the nozzle to prevent material from oozing out when it is not being extruded. Retractions affects how the overall print looks as it may have strings, hairs or wisps.

Supports

Supports are structures that holds up overhanging features on models. Without supports, our printing will go haywire. Supports are printed out together with the product. They are usually very thin so that we can snip them off once the final product have been printed. There is also another way to print support. If our 3D printer has 2 nozzle, one of the nozzle can be used to print water soluble materials.

Water soluble materials such as PVA are use as supports. When our product has been printed, we can dunk our product into water for awhile. PVA being water soluble, will dissolve away. This allow our product to be cleaner as we do not need to snip off any excess parts.

 

Infill

Infill is the internal filling in the 3D printed parts. Infill allows for better control of the strength, weight, material consumption, and internal structure of a part without having to adjust its appearance or external features.

In the slicer settings, infill can be controlled using infill density and infill pattern.

More robust infill patterns and larger infill densities will extend printing times and consume more materials but will help to increase a part's strength and weight. There are many infill patterns, with its own design and characteristics, like concentric (for flexible parts), cubic (strong), and lines (fast). The infill density can be set to achieve our desired mix of printing strength, material consumption, and printing time. 

 

 

Shell Thickness

Lastly, shell thickness represents the number of lines in the walls of our prints. Infill refers to the inside of the print while the shell is outside of the print. This means that they are completely solid and printed concentrically.

Shell thickness is an important setting to tune because it can significantly impact the strength of the product. The higher the shell thickness, the stronger parts will be and the longer the printer duration.

 

 

INDIVIDUAL ACTIVITY

 

For this activity, we were required to design in Fusion360, and 3D print an object that could not be easily made subtractively. The object should be small in size should require no more than 1 hour of printing.

 

I decided to go with a simple design of a ball in a box. Below are the steps to design it in Fusion 360.

Step 1: Create a sketch and select any plane for you to work on

Step 2: Create a square of 32mm x 32mm

Step 3: Extrude the square by 32mm such that you get a cube

Step 4: Create a sketch of another square of dimension 28mm x 28mm

Step 5: Extrude the smaller square by 32mm such that you get a hole.

Step 6: Repeat steps 4 & 5 on every surface of the square.

Step 7: Create a sphere of diameter 31mm

Step 8: Using the Move/Copy function, move the box such that the sphere is in the middle of the box

Figure 1: What the final design should look like

Step 9: Open Cura and upload the STL file. Ensure that supports and adhesions are turned on. If necessary, change the settings of the support and adhesion to suit your own needs. For my design, the Support Structure Type is "Tree" and the Build Plate Adhesion Type is "Brim".

Step 9: Slice the design into layers. Take note of the time required to print the design. For my design, since the time required to print it was more than 1 hour, I had to scale it down to 70% of its original size so that it could be printed fully within an hour.

Why can’t this design be made subtractively?

It cannot be made subtractively as the diameter of the ball is larger than the dimensions if the holes, hence it will be physically impossible to carve or laser cut such an object.

Figure 2: 3D Printing process

Figure 3: Failed product (Ball did not print out :/)

Figure 4: How the product would have looked like

Reflection

Overall, even though my product was not printed successfully, I feel like it was a great learning experience for me as I was able to better understand the way a 3D printer functions. I will definitely try to print my product again, hopefully this time it will be successful. I also hope to be more proficient so as to be able to design more complex objects and 3D print them.

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