Week 12

 This Blog: Reflection of what we had learned on Product development- 3D Printing

- Additive Manufacturing (AM)

What is AM?

Additive Manufacturing is a name describing the technologies that build 3D objects by adding layer-upon-layer of material. Material can be plastic, metal, concrete or even human tissue one day.

The use of computer is a common AM technology which involves 3D modeling software (Computer Aided Design or CAD), machine equipment and layering material. Once the CAD sketch is completed, the AM equipment reads the data from the CAD file and lays down or adds successive layers of liquid, power, sheet material or other, in a layer-upon-layer fashion to fabricate a 3D object.

The term AM encompasses many technologies including subsets like 3D Printing, Rapid Prototyping (RP), Direct Digital Manufacturing (DDM), layered manufacturing and additive fabrication.

Application of AM:

At the start, AM was use in the form of Rapid Prototyping focused on preproduction visualization models. More recently, AM is being used to fabricate end-use products in aircraft, dental restorations, medical implants, and even fashion products.

Advantages of AM: 

AM lower costs, save time, and transcends the limits of fabrication processes for product development. AM offer versatile solutions in a wide variety of applications. AM can fabricate concept models and functional prototypes in rapid prototyping to jigs, fixtures, or even end-use parts in manufacturing.

Moreover, over the last few years, AM has became much more affordable, easier to use and more reliable.

First example: Chemical plant companies are using AM to 3D print needed instruments such as valves. This can reduce the time taken needed for supplier to construct, build and deliver to the company from days to just hours.

Second example: When buying an old plant, the supplier to the instruments needed for replacement may have stopped operation. We can then use AM to 3D print the necessary products we need.

- 3D Printing Technologies 

3 methods: FDM, SLA, SLS

FDM ( Fused Deposition Modeling)

Fused deposition modeling (FDM) is the most widely used form of 3D printing. 

Operating Type: Process oriented involving use of thermoplastic (Polymers that changes to liquid upon application of heat and solidifies to a solid hen cooled) materials injected through indexing nozzles onto a platform. The nozzles trace the cross-section pattern for each particular layer with the thermoplastic material hardening prior to the application of the next layer. The process repeats until the build or model is completed and fascinating to watch. Specialized material may be need to add support to some model features. Similar to SLA, the models can be machined or used as patterns. Very easy-to-use and cool. 

Strength: FDM works with a range of standard thermoplastics, such as ABS, PLA, and their various blends. The technique is well-suited for basic proof-of-concept models, as well as quick and low-cost prototyping of simple parts, such as parts that might typically be machined.

Limitations: FDM parts tend to have visible layer lines and might show inaccuracies around complex features. FDM has the lowest resolution and accuracy when compared to SLA or SLS and is not the best option for printing complex designs or parts with intricate features.

SLA (Stereolithography)

Stereolithography was the world’s first 3D printing technology, invented in the 1980s, and is still one of the most popular technologies for professionals.

Operating Type: SLA resin 3D Printer use a laser to cure liquid resin into hardened plastic in a process called photopolymerization. The build occurs in a pool of resin. A laser beam, directed into the pool of resin, traces the cross-section pattern of the model for that particular layer and cures it. During the build cycle, the platform on which the build is repositioned, lowering by a single layer thickness. The process repeats until the build or model is completed and fascinating to watch. Specialized material may be needed to add support to some model features. Models can be machined and used as patterns for injection molding, thermoforming or other casting processes.

Strength: SLA parts have the highest resolution and accuracy, the clearest details, and the smoothest surface finish of all plastic 3D printing technologies, but the main benefit of SLA lies in its versatility. Material manufacturers have created innovative SLA photopolymer resin formulations with a wide range of optical, mechanical, and thermal properties to match those of standard, engineering, and industrial thermoplastics. SLA parts have sharp edges, a smooth surface finish, and minimal visible layer lines. SLA is a great option for highly detailed prototypes requiring tight tolerances and smooth surfaces, such as molds, patterns, and functional parts.

Limitations: Parts are affected by moisture, heat and chemicals. Limited to photosensitive resin. 

SLS (Selective Laser Sintering)

Selective Laser Sintering is the most common additive manufacturing technology for industrial applications, trusted by engineers and manufacturers across different industries for its ability to produce strong, functional parts.

Operating Type: SLS 3D 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. During the build cycle, the platform on which the build is repositioned, lowering by a single layer thickness. The process repeats until the build or model is completed. Unlike SLA technology, support material is not needed as the build is supported by unsintered material.

Strength: SLS ideal for complex geometries, including interior features, undercuts, thin walls, and negative features. Parts produced with SLS printing have excellent mechanical characteristics, with strength resembling that of injection-molded parts. Moreover, SLS has low cost per part and has a high productivity.

Limitations: SLS parts have a slightly rough surface finish, but almost no visible layer lines. Limited material option.

- 3D Printing Materials

Materials use for FDM: Standard thermoplastics, such as ABS, PLA, and their various blends.

Materials use for SLA: Varieties of resin (thermosetting plastics). Standard, engineering (ABS-like, PP-like, flexible, heat-resistant), castable, dental, and medical (biocompatible).

Materials use for SLS: Engineering thermoplastics. Nylon 11, Nylon 12, and their composites.

- Common Suitable materials for FDM 3D Printing

First Material: PLA

One of the most-used printing materials, PLA (Poly-Lactic Acid) is highly versatile. 

Limitation: PLS has a low melting point (around 150°F), it’s unsuitable for high heat work. Additionally, while it’s very versatile, the final products tend to be quite brittle, so if you’re building something that’s going to take a few hits, you might want to consider using something else instead.

Strength: PLA is made from renewable sources like sugar cane, which helps keep the price low. It’s a very forgiving material with a low chance of warping and good reusability. As a bonus, it produces a sweet, popcorn-like smell when melted.

Characteristics: Low-melting point, Brittle

Application: Low-cost rapid prototyping. Basic proof-of-concept models.

Second Material: ABS

Limitation: Poor UV resistance unless protected, maximum continuous use temperature approximately 160 °F, poor bearing properties (high friction and wear) and high smoke evolution.

Strength: More heat-resistant than PLA, but can be melted down and reused if needed. PLA is also a more durable plastic too, making it a strong choice for prototyping. You can sand, paint, and polish it without worrying about cracking or warping. It barely shrinks too, so you don’t have to compensate too heavily for that.

Characteristics: Higher melting point as compared to PLA, 221°F

Application: Low-cost rapid prototyping. Basic proof-of-concept models.

- FDM design requirement: Slicer setting for Quality Product

1) Temperature:  

The temperature of the nozzle is the single most important setting in your slicer because, without a Goldilocks level of heat (not too cool, not too hot), no print will work. Nozzle temperature should be the first thing you tune on your slicer whenever you begin printing with a new filament, and you can do this by printing a temperature tower to see which values work best.

Too high a nozzle temperature will cause over-extrusion with blobs and zits all over your print. At the other end of the spectrum, too low of a temperature will cause under-extrusion, where not all the layers are fully printed.

For printing quality products, use a Goldilocks level of heat.

2) Layer height:

Layer height is another very influential factor in your slicer and refers to the height of each layer of your print. The smaller the layer height, the more layers will be required in the overall print. This means your printer will have more room to generate finite detail on parts like miniatures. On the flipside, more layers also means longer print times and weaker parts.

When setting layer height, you want to find a suitable balance between printing time, detail, and part strength. Some makers subscribe to the “magic number” theory, where you set your layer height as a multiple of your stepper motor‘s natural step distance. On many common printers like the Ender 3, the step distance is 0.04 mm, so heights of .16, .2, and .24 mm work as good detailed, balanced, and quick values.

For printing quality products, the layer height is set as a multiple of our stepper motor's natural step distance.

3) Speed:

Speed is our third powerful slicer setting. As the name indicates, it’s the speed at which your printhead moves. When spoken of generally, “speed” encompasses many different settings, not just the default movement speed. For example, it can be useful to adjust specific speeds derived from the default value, such as the infill speed, wall speed, and so on.

Usually, it’s good to leave specific speed settings alone and only adjust the default speed. In most slicers, a particular speed will be chosen based on your chosen layer height and material, but if you think your printer is up to it, you can experiment with increasing print speed to reduce print times.

On the other hand, it can be good to reduce speed whenever you run into print quality issues. Slow speeds make it much easier to identify which setting is causing problems (if it’s something other than speed).

Travel speed is a different story, and you shouldn’t need to adjust it very often, if ever. Try to keep it close to its slicer default (probably around 150 mm/s) because too fast may cause nozzle run-ins where the printhead could knock over small structures while printing.

For printing quality products, a slower speed is preferred. 

4) Retraction:

Retraction is usually the first setting people think about when they see strings, hairs, or whisps on their print. Retraction determines how much and how fast filament is sucked back into the nozzle to prevent material from oozing out when it’s not being extruded. Retraction is controlled by a few specific settings, chief among them being retraction distance and retraction speed.

These settings should be adjusted when you see stringing, but be mindful that retraction isn’t the only solution to this problem and nozzle temperature also plays a role. You should change your retraction settings in small intervals and don’t make any significant increases until you’ve tried lowering the temperature. Too much retraction can cause nozzle jams, as the filament is more aggressively pushed in and out of the nozzle.

For printing quality products, higher retraction is preferred so that there will be lesser strings, hairs, or whisps on the print.

5) Flow:

Flow, sometimes known as the extrusion multiplier, determines the rate at which filament is extruded. For example, with a 100% flow rating, your printer might use 10 cm of filament for a particular part feature, but if you change the flow to 90%, the same feature would only require 9 cm. In the end, adjusting flow affects how many steps the extruder’s motor turns per millimeter of material deposited.

Flow can be used to account for over or under-extrusion on your printer without adjusting a printer’s E-step parameter, a value stored in firmware. While technically, flow and E-steps can both be used to solve the same problems, it’s best to tune the E-step value during printer calibration and adjust flow as required by particular print jobs.

Flow rate depends on the filament required.

6) Adhesion Resistant:

An adhesion assistant is a physical feature added to a print – auto-generated by the slicer when instructed to do so – which is designed to enhance bed adhesion. Bed adhesion is how well a part sticks to the build surface, and it’s typically most important for the first layer. An adhesion assistant comes in three main forms:

• Skirt: A skirt is a distant and detached perimeter that outlines a print. Skirts provide no real adhesion assistance for a model but help get material flowing through the nozzle in time for the first layer to start. They can also be useful for making last-minute manual adjustments to a bed’s levelness. Unless set otherwise, many slicers will automatically generate a skirt for every print.
• Brim: A brim is a set of lines attached to the outside of a print’s first layer, sprawling from its base. If your print were a cylinder, the brim would literally look like the brim of a top hat. As far as adhesion assistants go, this is the first step to take if a model is having bed  adhesion issues (because it has small “feet”, for example).
• Raft: A raft is a complete base upon which your model grows. When printing rafts, slicers generally attempt to save material by putting space between adjacent lines. This is the no-holds-barred approach to bed adhesion, as your print never has to touch the surface. (This is often useful when warping is an issue.)

As you might expect, a skirt takes up the least amount of material and print time, followed by a brim and then a raft.

In general, a hotter bed will provide better adhesion, while a cooler one could lead to warping. 

7) Support:

Supports are another significant slicer setting and, like adhesion assistants, are slicer-generated. Supports are structures that hold up overhanging features on models if they meet certain requirements, which can be set in your slicer.

These requirements include the overhang angle and the minimum support area. The former determines the minimum angle an overhang has to be before the slicer creates a support to hold it up. The latter governs the minimum area (in mm2) that a support structure has to have to be included in a print.

Other support settings and options are also very important. For example, part orientation plays a key role in how support structures are generated. Other support settings include print speed, support infill density, and more. You shouldn’t change these settings at all if your model doesn’t require supports in the first place, but when necessary, you can tweak them to find a balance between sufficient support and minimum material consumed.

For printing quality products, more and thicker support would be better.

8) Cooling:

Next up is cooling, which determines the power of the fans on your printer. While there may be fans around your printer’s mainboard, power supply unit, and hot end, cooling usually refers just to the speed of your part-cooling fan. This fan’s speed can typically be set and adjusted as a percentage of total power.

When adjusting the speed of your part-cooling fan, consider the material you’re currently printing with. For example, PLA requires moderate cooling from the part-cooling fan, but ABS shouldn’t have any (because cooling can lead to cracking). If your model has overhangs and you don’t want to use supports, you can try increasing cooling to more rapidly solidify printed overhangs.

In conclusion, when cooling overhangs product, cooling can be set to more rapidly to quickly solidify printed overhangs.

For printing quality products, the cooling rate depends on the material used.

9) Infill:

Infill is the internal filling in 3D printed parts and is a feature unattainable with traditional manufacturing methods like injection molding. Infill allows you to better control the strength, weight, material consumption, and internal structure of a part without having to adjust its appearance or external features. In a slicer, infill can be controlled using infill density, set as a percentage, and infill pattern, which is the infill’s structure or form.

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

For printing quality products, amount of infill needed depends on the desired material strength, weight, material consumption.

10) Shell Thickness:

Lastly, shell (or perimeter) thickness represents the number of lines in the walls of your prints, whether they’re at the sides, on the top, or on the bottom. If infill is the “inside” of a print, shells are the “outside”, which means they are completely solid and printed concentrically. Shell thickness is usually set as a value in millimeters or as a number of layers, individually for the walls and the top and bottom layers.

Shell thickness is an important setting to tune because it can significantly impact the strength of your model. The higher the shell thickness, the stronger parts will be and the longer they will take to print. That’s because the more shells you have, the more completely solid layers or walls your machine has to print.

For printing quality products, the shell thickness is dependent on the desired strength of your model.

- FDM design requirement: Slicer setting for Fast Printing

1) Temperature: Goldilocks level of heat (not too cool, not too hot).

2) Layer Height: The smaller the layer height, the more layers will be required in the overall print. For fast printing, larger layer height are preferred.

3) Speed: A higher speed setting will have a faster printing speed.

4) Retraction: Higher retraction, faster printing speed.

5) Flow: Higher flow of filament, the faster the printing speed.

6) Adhesion Resistant: Having no adhesion will have a faster printing time.

7) Support: Lesser support, the faster printing speed.

8) Cooling: Higher cooling speed, the printing solidifies quicker.

9) Infill: Lesser infill will have a faster printing rate.

10) Thickness: Thinner shell thickness will have a faster printing rate.