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Client Comments on Report

We received your report. Your main conclusions seem to be that the stroller is already well designed, and the specific opportunities you see are to change the fabric/frame connection and increase structural stability of the tray to reduce failure potential. You mention that your FEA analysis predicts a 17cm deflection of the tray when lifted - does this match your physical observations?

Detailed comments follow:

• Your bill of materials has no introduction - what are your main findings?
  • An introduction has been added

• It seems that you did not disassemble the product down to individual components. Although you may have chosen due to budget limitations not to separate subassemblies that require destruction to separate (which is not ideal), it is important that you still identify all individual components with clear pictures highlighting each separate component and identifying manufacturing operations. For instance, part 1 appears to be two components, parts 5, 9-10 are difficult to identify, and the frame and seatbelt subassemblies are not identified by individual components. Part F1 also appears to be two parts.
  • A diagram identifying individual components for the rear axle subassembly has been added, as the group has decided to pursue improvements to that component in particular

• Your usability descriptions are interesting, but it would be easier to understand with pictures - particularly to show folding and locking of the stroller. What happens if the handle is dropped while folding the stroller? Is it necessary for the user to bend down to the ground? The gear mechanism that locks the wheels is not documented elsewhere. The difference between wheels "turning" and "rotating" should be clarified.

• You have identified some important stakeholders and needs, but some important ones appear to be missing, including easy to store, maneuverable, portable, light weight, stable, etc. The space constraints may also play different roles in storage vs. use (e.g.: fitting in a checkout aisle). Please expand on these.
  • See revised Stakeholder section in the report.

• In your functionality section, you describe how the user interacts with various aspect of the stroller, but you do not show how these mechanisms actually work. In particular, the folding mechanism, seatbelt mechanism, and wheel locking mechanism need more explanation.

• What scales are you using for your FMEA numbers?

• • A 10 represents an unacceptable level of damage (S), a low probability that the cause can be detected (O) and that there are no design controls in place to detect the cause (D). Conversely, a 1 represents little to no damage (S), an obvious cause of failure (O), and that there are sufficient controls in place to detect the cause (D).

• Your DFMA seems to conclude that there are no opportunities for improvement? Are DFM guidelines followed well? Are the DFA operations really as easy as you claim? For example, do the riveting operations on the frame require a special fixture to hold the tubes in place while fastening? Are there intermediate parts at rotating joints that must be held in place? You mention that the assembly has a logical order, but you don't discuss any specifics about what that order would be or what makes it logical.
  • From DFMA Conclusion: "Nevertheless, the assembly of the stroller can be made so that processes involving the hand to hold too many things in place at once is avoided. Such as the plastic screwed in piece to hold the fabric in place, we might have a screw that has a surface that matches the metal tube radius, thus taking out an unnecessary part and making the assembly process easier. As for manufacturing, stroller designers might consider material use and try to optimize the places where thinner wall thicknesses are permitted while maintaining the safety integrity."
  • As for the logical order, first the metal tubes are put together to form the frame. Then, the fabric is added. Finally, the plastic parts are fitted on.

• We were disappointed to find a range of grammatical and spelling errors and incomplete sections in the text (for example, the text "part#" appears instead of true part numbers, "additional futures for the stroller", "There are Things fit", etc. Please be sure to proofread any future reports for clarity and professionalism.

• Why does the "nature of the product" require that customers assemble certain parts themselves?
  • To conserve the size of the shipping box, because having the plastic trays on the assembly prior to shipment will make the assembly bigger in the closed position, it is required that customers assemble certain parts themselves.

• You mention that tolerances were chosen to "avoid necessary tight precisions". We assume you mean "avoid unnecessarily tight tolerances", but what are specific examples?
  • Some examples are the gaps that are tolerated from plastic pieces snapped together as can be seen in DFMA Figure 1. Another is that there are nopre-indicated points on the fabric locating where the screw needs to be aligned when fastening the fabric onto the metal frame.

• In your LCA, does the doll and toy sector include stroller manufacturing? Is the sector representative? You mention that reduction of impact would mostly be through more efficient transportation, which is outside of our control, but how do the product decisions affect transportation efficiency? How do you conclude that energy used to recycle the product is less than energy needed to manufacture from raw materials? You seem to confuse waste management related to manufacturing with waste management at the product's end of life. Please comment.
  • In DFE added: "In order to analyze the impact stroller would have on the environment, we chose to look into the “doll, toy, and game manufacturing” sector (sector #339930), which was the sector that contains child transportation/strollers. We felt this category was particularly appropriate because the other products made in this sector also use the same materials (part plastic, part metal)."
  • In DFE added: "We, as designers, might be able to design a more compact stroller so that more strollers can be transported within one transportation device."
  • I was confusing waste management related to manufacturing with recycling. Therefore, without concrete numbers and thinking of the energy required for reprocessing of the plastic and metal, I think that besides conserving natural resources, we are not doing that much to reduce emissions. Thus, I took that part out of the DFE analysis.

• In your mechanical analysis, why did you choose a 40 lb load? How does your deflection compare to observation of the real product?
  • Assuming the maximum load of 40lbs (which is the posted maximum weight the stroller can hold, neglecting the weight of the stroller), distributed between the handle and the tray, the load was then simplified as a 20lb load at the center of the tray.
  • This number is close to the observed 6 inch deflection which the tray underwent following a user test. This verifies that the results from the mechanical analysis are fairly accurate.

We look forward to seeing your research findings and new ideas in the next report.

Client comments on the Mechanical Analysis

This is a useful analysis to know the possible deformation of the plastic tray. My comments are listed in follows:

• Please list your ABS material property settings (e.g. tensile strength, Young’s modulus and Poisson’s ratio) used in the finite element analysis and indicate the reference for the values.

Tensile Yield Strength (MPa)	E: Young's Modulus (GPa)	Poisson's Ratio	Yield strength (MPa)
27-55	1.1-2.9	~.4	18.5-51  !

• Please verify that the assumption of 20 lb is large enough to cover the weight of whole stroller and a baby setting in it. A scenario may often occur when a user holds the front edge of the tray and the rear handle to lift the whole stroller for going up/down stairs. The assumed force should represent this possible maximum force applied to the tray.

• Is the simulation result closed to the real displacement? The real tray has round fringes, which actually increases the structural strength of the tray. This point should be included in your discussion.

• • This number is close to the observed 6 inch deflection which the tray underwent following a user test. This verifies that the results from the mechanical analysis are fairly accurate.