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Additive Manufacturing General Study Guide, Exams of Nursing

University of Phoenix (UOPX)Nursing

Additive Manufacturing General Study Guide

Typology: Exams

2024/2025

Available from 04/17/2025

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Additive Manufacturing General Study
Guide - Midterm Exam
Why is additive manufacturing usually most cost effective for small production lots (as opposed to large
production lots)? correct answersConventional manufacturing has the cost of tooling (i.e. molds,
fixturing), but additive has no specialized tooling. Small production lots benefit from not needing this
high fixed cost. On the other end, this specialized tooling can help produce a large amount of parts faster
than AM, which brings the part cost down for large production lots.
What are two security concerns related to the build file used in AM processing? correct answers1.
Someone steals your build file and can make your part because it contains all the commands to build
your part.
2. If someone intercepts your build file, they can change a few lines of code to intentionally cause a flaw
in your part without you knowing. Sabotage.
What is HIPping and how is it used in additive manufacturing? correct answersHot-Isostatic pressing is a
process that places a finished part under high temperature and pressure for a fixed period of time; it is
used to reduce the size of internal pores.
Give two reasons why the FDM process "took off" in popularity in the 1990s compared to the other
major polymer AM processes (SLA, DLP, SLS). Hint: One of the reasons is also why FDM was quickly
adopted as the basis for maker machines. correct answers1. The process was simpler, and thus the
machines were simpler and cheaper as a result.
2. The machines used commonly available materials (ABS, PLA), making their continued use cheaper
than existing methods.
What was roughly the cost difference between FDM machines made by Stratasys and the first Makerbot
machines based on the FDM process? correct answersThe cost of the makerbot was about 2.5k and the
real FDM machines were 25k, so a factor of 10
Give 3 ways you can come up with a CAD model of a part which can then be printed in an AM machine.
correct answers1. Off the internet (GrabCAD)
2. Create one from scratch
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Additive Manufacturing General Study

Guide - Midterm Exam

Why is additive manufacturing usually most cost effective for small production lots (as opposed to large production lots)? correct answersConventional manufacturing has the cost of tooling (i.e. molds, fixturing), but additive has no specialized tooling. Small production lots benefit from not needing this high fixed cost. On the other end, this specialized tooling can help produce a large amount of parts faster than AM, which brings the part cost down for large production lots. What are two security concerns related to the build file used in AM processing? correct answers1. Someone steals your build file and can make your part because it contains all the commands to build your part.

  1. If someone intercepts your build file, they can change a few lines of code to intentionally cause a flaw in your part without you knowing. Sabotage. What is HIPping and how is it used in additive manufacturing? correct answersHot-Isostatic pressing is a process that places a finished part under high temperature and pressure for a fixed period of time; it is used to reduce the size of internal pores. Give two reasons why the FDM process "took off" in popularity in the 1990s compared to the other major polymer AM processes (SLA, DLP, SLS). Hint: One of the reasons is also why FDM was quickly adopted as the basis for maker machines. correct answers1. The process was simpler, and thus the machines were simpler and cheaper as a result.
  2. The machines used commonly available materials (ABS, PLA), making their continued use cheaper than existing methods. What was roughly the cost difference between FDM machines made by Stratasys and the first Makerbot machines based on the FDM process? correct answersThe cost of the makerbot was about 2.5k and the real FDM machines were 25k, so a factor of 10 Give 3 ways you can come up with a CAD model of a part which can then be printed in an AM machine. correct answers1. Off the internet (GrabCAD)
  3. Create one from scratch
  1. Use a laser scanner to scan an existing part and turn it into a model What were the two major breakthroughs that occurred approximately 12 years ago that greatly increased interest in AM? correct answers1. The expiration of the FDM 2009 printing patent. This opened the industry to other competitors and started the "maker movement" in polymer AM.
  2. For metal, the automation of laser powderbed and electron beam powderbed made the processes easier to use and plan for. Roughly what is the range of yearly production volumes that AM processes target? correct answersProduction lots usually target a max of 30k parts per year, 1 to 20,000 is acceptable. Why is it an advantage to use AM to combine parts in a component design? correct answersEach part has a design team, standards for that part, processes for that part, specifications for joining those parts, etc. Joining those parts into a single component removes the product development costs and the final assembly costs. Another reason: AM removes the need for some fasteners and joining techniques, which are common failure points. This could also reduce the weight by a significant amount in some cases. Original SLA printers printed a part by polymerizing a layer with an overhead laser, then moving the part down one layer thickness into the photopolymer. Current SLA printers print a part by polymerizing a layer using a laser source below the part, followed by moving the part up one layer thickness. What is the reason for this change in approach? What complication does this approach add to the process? correct answersParts used to be printed from the other direction because it required that there was enough liquid to cover the entire part while printing. The photo-curing resin is very expensive, so this is wasteful. With the other design, only enough polymer is needed to fill the gap between the part and the glass. The complication with this method, however, is that the part will adhere to the glass after curing. Moving up each layer requires a delicate removal process that won't damage the part. What was the first commercially available 3-D printing process? When was it invented? Who invented it? correct answersSla, 1984, Chuck Hull What is the main difference between the SLA and DLP process? correct answersBoth involve curing of photocurable polymers, but they differ in that SLA uses a moving laser to cure the polymer and the laser must trace out the shape of the layer, where DLP uses bright light reflected off of a micromirror array to cure the entire layer at once.

What is the traditional process used to fabricate injection mold tooling? Roughly how long does it take to go from concept to manufactured molds and what are the steps typically taken to manufacture the molds? correct answersThe traditional process is CNC machining Turn-around is on the order of 2 weeks Steps: 1) create the mold CAD design

  1. send it to a low-cost off-shore machining site (China is a major destination).
  2. The mold is CNC machined at the off-shore site.
  3. The finished mold is shipped back to the US. Describe a specific problem for AM caused by residual stress and a currently used fix for that problem. correct answersPossible Issues and their solutions
  • Dimensions out of spec; you can preheat your build plate to reduce thermal stresses, thereby reducing the deformation. You can also use predictive modeling to predict these deformations and adjust your geometry to compensate. Supports are another option to keep overhangs under control.
  • Decreased strength or life; Stress relief at end can help, but it is also good to preheat your build plate. Sometimes, machining the surface may remove pits that would cause issues with fatigue lifetime (you aren't expected to know this specific fix though)
  • debonding from build surface; This one is related to thermal stresses that pull the part from the plate. The best fixes are preheating and/or an adhesive on the build plate, in the case of polymer printing.
  • Recoater Blade collisions; replace your hard recoater with a soft recoater to avoid the worst collisions. You can also orient your parts at an angle, so that the recoater has a higher chance to glide over the edges of the part. The final thing you can do is place the parts where you expect the most deformation/highest chance of collisions near the end of the recoater's path. For metals AM, why is it important to heat treat your build plates after they are used in a build? correct answersThe Heat Affected Zone (HAZ) is brittle near the top of the build plate, so if you do not heat treat it, you can have a brittle zone for the next time you use it. Parts will not adhere as well. In a specialized, low production volume small-scale air pump design application, a small cylindrical component is to be used as a reservoir that can be subjected to up to 50 psi. It is proposed to make the cylindrical component by FDM. The material to be used (ABS) is easily able to handle the pressure load. Why is this likely a bad choice of process? correct answersFDM components are typically not air-tight (at least not thin-walled ones). This is due to porosity that exists from occasional incomplete overlap between extruded beads.

What company was founded based on the FDM process? correct answersStratasys Polymers and metals have temperatures above which temperature gradients induce thermal strains, but they don't induce thermal stresses. What is the rule of thumb value for this temperature in metals? correct answersTmelt/2 or Tmelt/3 where Tmelt is the melting temperature on an absolute scale. In laser powder bed (SLS) AM builds for metals (and for some thermoplastics) you often see parts oriented on a build plate so that if you look from above the parts are at a slight angle to the build plate edges. Why is this? correct answersThis is so if the spreader blade or roller impacts the top surface of the part, it will first hit at one location and then hopefully "ride over" the rest of the part. This is in contrast to the blade or roller hitting an entire edge of the part at once. This small change can make the difference between a failed build and one that succeeds. Describe what the hourglass shape is for AM parts and describe why it happens correct answersThe hourglass shape is one of two overall shapes that all parts assume after being built (the other overall shape is a cup-shaped warping caused by bending). The hourglass shape is caused by axial compressive deformation in the plane of a layer. Each layer that is deposited in a part wants to contract as it cools. Layers at the bottom of the part want to contract, but the much larger and stiffer build plate does not allow them to (at least not by much). In the middle of the part height, layers are away from the build plate and can contract more freely as they cool. More importantly, additional layers deposited on top of a layer can cause it to contract even more. At the top of the part, a new layer can contract more freely, but there are no additional layers deposited on top, so the contraction is small. The net result is that in-plane layer contractions at the top and bottom of a part are small, but they are large in the center of the part. This creates the hourglass shape. If you were to use one word from sophomore-level mechanics to describe the mechanism behind stress- induced warping in AM what would it be? correct answersBending Software companies are investing significantly in developing analysis software to predict stress-induced distortions in AM processes. The idea is to have a tool that a machine user can use before starting a build, to see if the build might fail. Why is this software development effort not a very good long-term business plan? correct answersLong-term it is expected that thermal AM processes will increase their preheat temperatures (in fact it is already happening). As this is done, residual stresses will be reduced or eliminated. As a result, the number 1 cause of failed builds in such processes may soon become a minor concern or go away entirely.