Of course, a mold designer should know which plastic characteristics will directly affect your mold design, for example:
a) Flow characteristics, easy following materials usually present no problem, but “stiff” materials require higher injection pressure and, therefore, heavier construction of the mold, this will also affect the need for more accuracy and strength of the alignment elements
b) Melt processing temperature, this temperature is more higher, the heating and cooling design become more important, the method of heat insulation between hot and cooled portions of mold as well.
c) Material degradation, every thermoplastic is to some degree sensitive or subject to degradation when exposed to high temperatures over a length of time.
Shrinkage is a characteristic of the polymer used to manufacture the part. The molded part will shrink down in size for up to 24 hours post molding effecting the part geometry. Determining the proper amount of shrinkage to use to design and build the mold is both art and science. Every polymer has a unique shrink rate that must be applied to the 3D part model. Unfortunately, shrink rate information is not always provided by the polymer vendor. In some instances when it is provided, it is typically a wide range. Careful thought must go into selecting the proper shrinkage and it is necessary that the grade of polymer be selected prior to designing the injection mold. A good Plastics Engineer has the experience to help make the best shrinkage decision for your product and polymer.
Material shrinkage can vary with part and mold design; thick walls will shrink more than thin walls, variation in part thickness or geometry will cause differential shrinkage and warping; flow direction will also effect shrinkage especially when using fiber filled polymers.
Shrinkage is also influenced by process conditions. As cavity pressures rise, shrinkage will normally decrease. The mold and melt temperature will also greatly effect shrinkage. Cooler molds will reduce shrinkage while hotter melt temperatures will increase shrinkage.
A significant part of the design process includes scheduling of critical milestones throughout each phase of development. Every project requires design activities to be synchronized with business plans associated with the product. These events include trade shows, clinical trials and regulatory compliance, as well as final product release. Close communication with a molder is an essential activity to ensure the project stakeholder will be able to attain his or her objectives. Critical project milestones directly associated with a molder include ordering steel, tool design, machining molds, texturing tools, sample shots, designing and building fixtures, establishing quality standards and optimizing production parameters. These critical tasks must be planned and coordinated with overall project objectives to avoid costly tooling revisions or production delays. Fully integrating these activities with your molder is an essential part of overall product development and design for manufacturing.
thanks for sharing your experience on this issue, very good post
this is a good post, I got something useful for my mold design
A qualified mold designer should have sufficient knowledge of polymer materials.
as an injection molding engineer, I agree you at all