This is the first edition of KnowHow Q &A Session focusing on Quality Molded Plastic Parts Design. Participants asked followed questions on various issues related to design and failures of molded plastic parts. Mr. Alex Lau addressed all the real questions/ issues raised by participants, which was held on 2 April 2021. The questions/issues addressed in this Q&A session are: # How does under-cooling of the molds cause warpage?; # I had dried the resins and checked the moisture content to specification before molding, why did the parts break in one batch of molding but not another batch?; # I’ve used FEA, found that it’s not accurate. Any suggestions why?; # Can I allow my toolmaker to add the draft angles for me, since he’s very familiar with the requirements?; # Should I use ribs to help reduce warpage?; # If I use FEA to accurately calculate the stress, and considered creep performance of plastics, the part should last a long time?; # What is nonlinear FEA?; # Theoretically, to eliminate warpage, can I leave the part in the mold until it cools down to room temperature?; # I measured the moisture content when the bags of resins were received. I rejected those that exceeded the limits, then used the remainder without further moisture content checks. Is this ok?; Can I have zero draft angle on some features?; Nonlinear FEA takes too long. Can I use linear FEA for fast answers?; The molded part broke but I don’t see those fatigue ‘beach marks’ on the surface of the break. Why?; # Can DFMA help to reduce cycle time of molding?; # I used hand calculation to determine the working stress in the plastic structural part. Is this good enough? # My toolmaker does the Moldflow analysis for me. Why not continue as is?; # What is MFR?; # I practice DFM and FMEA quality processes in my company. Why didn’t they identify potential fatigue failures?; # Why are the glass-reinforced plastics more resistant to creep?; # I don’t have an FEA analyst in my company. Can I out-source the job?; # I’ve done nonlinear FEA with mesh refinement. The production part was tested and its performance correlated with the FEA predicted results, all well and good. Some weeks later the production part still broke, how come?; If the molded part is not compliant to UL Flammability can I change to another grade that is compliant?; For a desiccant dryer machine can I set to -20C dew point?; My FEA reseller did not tell me about nonlinear FEA. Why was that?; My designs are out-sourced. How can I be sure the out-sourced designer had taken fatigue failure into account?; I used a jig to hold the warped part straight during cooling after ejection. Fortunately, I have not had problems with the parts warping back at a later time. Why was that?; In a plastic part that failed by deformation or breakage, why not just change to a stronger plastic?; Can I modify the gates, molding parameters, temperatures, etc. to eliminate fatigue failure?; Can cosmetic defects be removed by adjusting the molding parameters?; Is Conformal Cooling expensive?; How good is the Boothroyd & Dewhurst DFMA software?