Guideline3

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School

University of Maryland, College Park *

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Course

489O

Subject

Mechanical Engineering

Date

Dec 6, 2023

Type

docx

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2

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ENME 489O – Fall 2023 DFM Rules Name: Nathan Gernand Date: 10/1/2023 Rule Name: Parts with low flow resistance Rule Number: 1.3 Rule Description: Injection molding/die casting: Low flow resistance rule This set of rules will give guidance on the choices of varying rib/wall thickness, changes in sections, and other things that affect the consistency of a part to create the most flow resistant part possible. Background of Rule (Context): When designing and creating parts using injection molding, there are a lot of decisions that the designer must make. One of these is to make sure flow is as consistent and smooth as possible. If the flow is consistent and smooth, there will be no hiccups with the metal that is transported into the die/mold for the part to be created. This leads to better consistency throughout the part. Things that can cause these inconsistencies in flows are differences in section thickness, abrupt changes in sections, etc. These things can also cause uneven cooling, which creates a part made out of very inconsistent material. Shrink cavities, voids, and stresses are also things that can be caused by these discrepancies in wall thickness and section thickness. Having something such as a sharp corner can cause flow problems which can build up the material from the metal alloy in ways that are not intended. These shrinkages can cause material weakening as well as destroying some of the parts aesthetic appearance and worsens the corrosion resistance of the part. So, by controlling the consistencies of the surfaces, thicknesses of ribs/walls, and other things that affect the flow of the material into the mold, the parts will be as consistent as possible. Rule Condition (If statement): a) If ribs are required to be used when creating a part b) If a sharp turn must be made on a part Rule Consequence (Then statement): a) Make sure that if the difference in thickness is not big, the ratio between thickness should be very close to 1 b) Try and make the turn smooth rather than a sharp corner Rule Illustrations (if needed):
Rule Justification: By following this set of rules designers and engineers can improve: Manufacturability: By using these guidelines a designer can create his own set of dimension parameters for the mold to meet Cost: If the flow is consistent for the part, it is much less likely you will have parts that have to be discarded due to inconsistencies Rule Source: Poli, C. (2001). Design for manufacturing: A structured approach . Butterworth-Heinemann.
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