Additive manufacturing, often called 3D printing, builds parts layer by layer from a digital model. This cheat sheet covers the main 3D printing processes used in engineering, including material extrusion, vat photopolymerization, and powder bed fusion. Students need these ideas to connect design choices with strength, accuracy, surface finish, cost, and printing time.
It also helps students compare processes when choosing how to prototype or manufacture a part.
The most important concepts are layer height, build orientation, infill, supports, tolerance, and post-processing. Print time often increases when layer height decreases because the machine must create more layers. Part strength depends on material, process, orientation, bonding between layers, and the amount and pattern of infill.
Good engineering design for additive manufacturing uses the process limits, not just the shape of the final part.
Key Facts
- Additive manufacturing creates parts by adding material layer by layer, while subtractive manufacturing removes material from a solid block.
- For a simple estimate, number of layers = part height / layer height.
- Smaller layer height usually improves surface finish and detail but increases print time.
- FDM, or fused deposition modeling, melts and deposits thermoplastic filament through a heated nozzle.
- SLA, or stereolithography, cures liquid resin with light and usually produces smoother surfaces than FDM.
- SLS, or selective laser sintering, fuses powder with a laser and often does not need separate support structures because loose powder supports the part.
- Infill percentage = interior material volume / total interior volume x 100%, so higher infill usually increases mass, strength, and print time.
- Clearance is the intentional gap between moving or fitting parts, and required clearance must be larger than the printer tolerance.
Vocabulary
- Additive manufacturing
- A manufacturing method that builds an object by adding material in layers from a digital 3D model.
- FDM
- Fused deposition modeling is a 3D printing process that extrudes melted thermoplastic filament through a nozzle.
- SLA
- Stereolithography is a 3D printing process that uses light to harden liquid resin into solid layers.
- SLS
- Selective laser sintering is a 3D printing process that uses a laser to fuse powdered material into solid layers.
- Layer height
- Layer height is the thickness of each printed layer, which affects detail, surface finish, and print time.
- Build orientation
- Build orientation is the direction a part is positioned on the print bed, which affects strength, supports, accuracy, and surface quality.
Common Mistakes to Avoid
- Choosing the smallest layer height for every print is a mistake because it can greatly increase print time without improving a part that does not need fine detail.
- Ignoring build orientation is a mistake because many printed parts are weaker between layers than along continuous printed paths.
- Designing zero-clearance moving parts is a mistake because real printers have tolerance limits, so parts may fuse together or not fit.
- Forgetting supports for overhangs in FDM and SLA is a mistake because unsupported material can sag, fail, or cure in the wrong shape.
- Comparing print processes only by cost is a mistake because accuracy, material properties, surface finish, safety, and post-processing can be more important.
Practice Questions
- 1 A part is 60 mm tall and printed with a layer height of 0.20 mm. How many layers are needed?
- 2 A solid part would use 80 cm3 of plastic, but it is printed with 25% infill inside the interior. Estimate the interior plastic volume used if the whole part is treated as infill space.
- 3 A printer has a dimensional tolerance of plus or minus 0.20 mm. What minimum clearance would you recommend between two moving parts if the design should avoid sticking?
- 4 A student needs a smooth, detailed model for a small medical device prototype, while another student needs a strong nylon bracket with complex internal shapes. Which additive manufacturing processes are better choices for each case, and why?
Understanding Additive Manufacturing (3D Printing) Processes
A printed object begins with a digital design, but the design file is not sent straight to the machine. Software first converts the shape into many thin slices. It then plans the tool path for each slice, including travel moves, wall paths, fill patterns, and support material.
This planning step is called slicing. Small settings in the slicer can change a result greatly.
A model with a thin wall may look solid on screen but fail if the wall is narrower than the printer can make. Curved surfaces are stored as many tiny flat faces, so a low quality model can show visible flat spots even on a very accurate printer.
Material behavior explains many printing problems. In filament printing, each new strand must stick well to the strand below it. If the plastic cools too quickly, the bonds can be weak.
A part can therefore split along its layer lines more easily than across them. This is called anisotropy, meaning properties differ by direction. Warm air around the print, a clean build plate, and suitable nozzle temperature help reduce warping and poor bonding.
Large flat parts are especially likely to curl upward as cooling plastic shrinks. Adding rounded corners, narrow relief gaps, or a wider first layer can help keep them attached.
Resin printing has different limits. Light must reach the correct areas of liquid resin, yet light can spread slightly beyond the intended edge. This can make narrow gaps close up or small holes become smaller.
Fresh resin parts need washing before extra light hardens them fully. Too much final curing can make some resins more brittle. Powder processes use heat in a bed of powder, and the finished part must be removed carefully from loose material.
Powder trapped inside hollow shapes needs escape holes. Each process has a useful range of feature sizes, surface quality, materials, and part sizes. The best process depends on what the part must do, not only how it looks.
Fit is usually learned through testing rather than trusting a single number. Printers can make outside dimensions slightly too large while making holes too small. Heat, material shrinkage, machine calibration, and the direction of a feature all affect the result.
Engineers often print small test pieces with several gaps, pegs, and holes before making a full assembly. These test coupons save material and reveal the actual capability of a machine.
Parts that must slide, snap together, or spin need deliberate space between surfaces. A tight fit in a computer model can become a jammed fit after printing.
Post-processing is part of the engineering plan. Support removal may leave rough marks, so critical faces should be placed where supports are unnecessary when possible. Sanding, polishing, painting, machining, or heat treatment can improve appearance or function, but each step changes time, cost, and dimensions.
Students meet these decisions when making phone stands, gears, robotics brackets, medical model parts, or replacement knobs. Pay attention to the purpose of every feature.
A decorative model can use different settings from a load-bearing bracket. Good results come from recording settings, measuring printed parts, noting failures, and using that evidence to improve the next design.