I'm seeking input from mold designers, mold makers and injection molding experts on common mistakes designers make when designing parts for plastic injection molding. What common mistakes take the most time and effort to fix? Issues may include inconsistent wall thickness, coring or lack-there-of, absence of radii, impossible undercuts and so on. I'm putting together a plan to develop a designers knowledge of creating great plastic parts for injection molding - you're input would be very much appreciated!

Gate design is always a big one. There is also the mold being built for one material and then a different material is used. A big problem that I have also run into is molds that are built larger then they need to be there for making it go in a larger press then the part really needs.

Thank you Frank!

Zero draft angle and Kiss-off steel surface. Putting too many GT& D requirement in the drawing.

Zero draft, indefenition of parting line, ribs too thin .

use servals of simple parts assembly to instead of a complex part design.so then moding is more easy,dimension is more precision,quality is more stably too.

parting line position, inconsistent wall thickness, over-designed part, material and as Frank says - gate design. It is still a big deal even tons of literature and articles have been written.

Designing a best plastic part requires a designer that have knowledge of general moulded part desing, mould design (mould construction desision made) good experience of resins and their requrements and properties and knowledge of requirements for the part itself.. OR it must be made in co-operation with the designer - the mould maker - the moulder, of course all of them must be good professionals. I have seen many times that the second option produces in practice best parts/tools.
In the process of making a plastic part usually have so many variables that the number of possibility to make a mistake is high.