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Additive Manufacturing > Pre- and Post-processing > Flashcards

Pre- and Post-processing Flashcards

1
Q

What are the characteristics of Pre- and post-processing?

A
  1. Often over-looked, or simply ignored, when talking about AM
  2. Can add cost and time to the production process
  3. In some cases, not considering these things can be catastrophic!
  4. If you are in the position to buy one or more systems – find out about these things first!

E.g. if specialist cleaning materials are required, what is cost of these? Do you need extra equipment? How much floor-space is needed? Any special atmospheric requirements?

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2
Q

When does Pre-processing start?

A

Pre-processing starts at the design stage: How can you effectively design something if you don’t understand the restrictions of the manufacturing process?

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3
Q

What is it important to consider during the design stage?

A

Production may be in-house (with or without a choice of which system to use), or may be out- sourced
• In any case, a quick chat with the person running the machine may save you a great deal of time later

Remember, if you have a choice of system and/or material, consider:

  1. Accuracy required
  2. Mechanical properties (a cheaper process may give lower properties, but does this matter?)
  3. Surface finish (may also include colouring procedures)
  4. Number of parts required
  5. Component size and complexity (particularly, how easily can you remove support material?)
  6. Total cost per part (including pre- and post-processing!)
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4
Q

Pre-processing

Remember, if you have a choice of system and/or material, consider:

A
  1. Accuracy required
  2. Mechanical properties (a cheaper process may give lower properties, but does this matter?)
  3. Surface finish (may also include colouring procedures)
  4. Number of parts required
  5. Component size and complexity (particularly, how easily can you remove support material?)
  6. Total cost per part (including pre- and post-processing!)
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5
Q

Pre-processing

Once you know which system/material combination you will use, some considerations will be:

A
  1. Minimum achievable feature sizes
    • Minimum wall thickness
    • Smallest reproducible hole diameter etc.
  2. What mechanical properties will you obtain, and how homogenous are these?
  3. What post-processing considerations do you need to be aware of?
    • E.g. support structures, powder removal
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6
Q

How do you create an .stl file and then print it?

A
  1. Generate 3D CAD model
  2. Save/export as .stl
  3. Import into Magics
  4. Check and repair file
  5. Save error free .stl
  6. Send to AM machine for printing
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7
Q

What are the features of .stl?

A
  1. Most machines build from .stl file format
    • Original format for Stereolithography
    • Provides a standard format for use on most machines
    • Approximates the part surface into a series of tessellated triangles
    • Some loss of accuracy during triangulation
    • Very difficult to edit – ‘dumb’ data
  2. Some new formats emerging
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8
Q

How does the .stl file format approximate the surface of a part?

A

It approximates the part surface into a series of tessellated triangles - Some loss of accuracy during triangulation

Each triangle defined by its normal and 3 vertices

.stl format only describes the surface geometry…
• Any other information from the CAD file will be lost (e.g. layers, colour etc.)

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9
Q

.stl format only describes…

A

…the surface geometry…

• Any other information from the CAD file will be lost (e.g. layers, colour etc.)

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10
Q

What happens when you convert a file to .stl in terms of the accuracy/tolerances of the end result?

A
  • Always some loss of accuracy during file conversion
  • Tolerance is specified during creation of .stl file
  • Select a sensible tolerance based on the requirements of the part to be produced
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11
Q

What does a .stl file depend on?

A

File sizes are directly related to the number of triangles (thus the accuracy) and may also have an effect on pre-processing time (bear in mind how accurate your system even is)!

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12
Q

What is the most used software suite to generate .stl files?

A

Magics but CAD programmes can export to .stl too.

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13
Q

Mention some functions of the Magics software?

A
  • E.g. tooling
  • Slicing
  • Support Generation
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14
Q

What is the most important function the Magics software?

A

File checking / repair

Relatively common for .stl files to have a variety of errors which may cause problems when building the physical part; This is especially common when exporting surface models

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15
Q

Common errors on magics?

A
  1. Inverted normals / flipped triangles
  2. Bad edges
  3. Bad contours – a group of connected bad edges
  4. Missing triangles
  5. Shells
  6. Noise shells
  7. Overlapping triangles
  8. Intersecting triangles

Always check for errors before submitting an .stl file
• Corrupt files can potentially crash an entire build!

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16
Q

What is the best approach to avoid errors on Magics?

A

By far the best approach is to ensure your original CAD model is robust and water-tight

Eliminating errors at this stage will save time and potential problems later on in the process

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17
Q

How is Orientation/Nesting carried out?

A

Often carried out in machine-specific build software
• However, these are often not particularly user-friendly (may only provide a 2D view, may not highlight collisions between parts, may be simply ‘unwieldy’!)
• You may prefer to do all of this in CAD/.stl software and then simply import into build software

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18
Q

Why is orientation really important when 3D Printing?

A

Orientation can have an effect on:

  1. Surface finish
  2. Mechanical Properties
  3. Build Height (and therefore time)
  4. Assembly (e.g. geometry often more accurate when produced ‘flat’ – if two things need to fit together, build both in this orientation)
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19
Q

What is the effect of orientation on surface finish?

A

Surface finish

  1. Certain processes perform better in certain orientations (e.g. top surface of a Stereolithography part provides best finish)
  2. Stair-stepping effects
20
Q

Which orientation results in high surface finish and which in low?

A
  1. Vertical orientation = high surface finish

2. Angled orientation = stair-stepping

21
Q

What is the effect of orientation on mechanical properties?

A

Many AM processes produce different properties when building in a horizontal or vertical plane

This may influence choice of orientation, whereby critical areas are oriented for
highest strength

22
Q

What is the effect of orientation on build height?

A

Often it is the height of a build that determines the total build time (and therefore cost)

Can be a trade-off between best finish and shortest build time

23
Q

Why is build height important for AM?

A

Often it is the height of a build that determines the total build time (and therefore cost)

24
Q

What is nesting?

A

Fitting all components of an assembly to be printed efficiently within an area or volume using supports where necessary.

25
Q

What are the considerations for nesting?

A 
1.  In general, we would like to fit as many parts into a build as possible.
Certain aspects (operator set-up time, warm-up etc.) are independent of number of parts. Higher cost per part if we produce less in one build.
  1. May wish to avoid positioning parts in certain areas of the build volume (E.g. uneven thermal distribution)
  2. Minimising build height may have additional benefits (E.g. recycling of powder in Laser Sintering)
26
Q

How do we nest?

A
  • Can be a very manual (irritating!) process
  • Some automated software solutions (research and commercial), e.g. Magics Sintermodule
  • Make sure you can specify orientations for certain parts, minimum distance between parts, etc.
27
Q

What do most processes require when nesting components or printing single components?

A

Most processes require some form of support structure for over-hanging geometries (how to get around the problem of gravity) –> SUPPORTS

28
Q

When do we need to include supports?

A

Reasons include:
• Steep inclines
• Fully flat overhangs
• ‘Islands’ within a part

29
Q

Which systems are self supporting?

A

Powdered-polymer systems are self-supporting

30
Q

What are supports made of?

A
  • Thin lattices to be broken off easily
  • Separate (weaker) support material

They can be water soluble

31
Q

What do we need to consider during the machine set-up process?

A

Machine setup is very process specific but may include:

  1. FILE PREPARATION
    (often slicing will be performed at this stage - possibly some extra operations)
  2. PREPARE BUILD MATERIAL
    (Ranges between snapping a ready-made cartridge into place, through to sieving/mixing/shovelling powder)
  3. WARM-UP
    (Some processes (e.g. polymer Laser Sintering) require build material to be brought to a certain temperature before processing)
  4. LEVELLING OF BUILD MATERIAL
    (E.g. bubbles in Stereolithography can cause build failures)
32
Q

Why is layer thickness important to consider during machine setup?

A

Layer thickness may be variable, and will determine:

  1. surface finish
  2. build time
  3. level of detail achievable
33
Q

What is adaptive slicing?

A

Slicing that determines automatically the parameters for each model to be printed.

34
Q

When is vital to use thinner layers?

A

Use of thinner layers when

surface is close to horizontal

35
Q

What are the typical processes that take place during post-processing?

A
  1. Cool-down procedure
  2. Post-curing
  3. Removal from base-plate
  4. Painting/colouring
  5. Infiltration

Postprocessing is of course PROCESS-DEPENDENT!

36
Q

Give an example of why we might need to cool down components after printing?

A

E.g. in High Speed Sintering process, removing parts before properly cooled (~Tg) can lead to warpage

37
Q

Give an example of why we might need to post cure components after printing?

A

E.g. Stereolithography parts require further UV curing

38
Q

Give an example of why we might need to infiltrate components after printing?

A

Sometimes necessary to improve properties

39
Q

Is support removal easy?

A

Time/difficulty/level of automation depends on process

40
Q

Is it advisable to remove supports manually?

A

Manual removal can cause certain problems

  1. Lower levels of part complexity (e.g. internal geometries)
  2. Poor surface finish when snapping away supports
  3. Possible part damage!
  4. Can be time and labour-intensive
41
Q

Why were water-soluble supports developed?

A

With water soluble supports, we eradicate the dangers of manually snapping the supports plus we can remove all of the support material.

These result in a much better finish.

42
Q

What are the benefits of water soluble supports?

A
  1. Removing all support material can give better finish
  2. May allow more intricate internal geometries
  3. Eradicates problems caused by manual removal.
43
Q

What are the methods of removing water-soluble supports?

A

Two general methods:

  1. Leave parts submerged in solution:
    a) Can be less manual
    b) May require chemicals/temperature/time
    c) Possible manual removal of majority of supports
  2. High-pressure water jets
    a) May still damage intricate areas of part
    b) Need line of sight
44
Q

Why is often necessary to modify the surface finish of finished parts?

A
  1. Smoothing, e.g. for visual or tactile purposes

2. Roughening, e.g. for certain paint/adhesives

45
Q

What are the methods for modifying the surface finish?

A
  1. Bead-blasting
  2. Machining
  3. Polishing
  4. Chemical treatment
  5. etc
46
Q

What does the choice of finishing method depend on?

A
  1. Part material
  2. Required surface finish
  3. Restricted chemicals
  4. Required accuracy (E.g. shot-blasting may round off sharp corners)
  5. Geometry (E.g. do we want blast media stuck inside our part?)
  6. Availability
47
Q

What’s the take home message for pre and post processing?

A

‘It’s not just the part manufacture stage that we need to consider!’

Additive Manufacturing (9 decks)

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