mold or die are the common terms used to describe the tooling used to produce plastic parts in molding.
traditionally,molds h**e been expensive to manufacture.they were usually only used in mass production where thousands of parts were being produced.molds are typically constructed from hardened steel,pre-hardened steel,aluminium,and/or beryllium-copper alloy.the choice of material to build a mold from ** primarily one of economics,steel molds generally cost to construct,but their longer lifespan will offset the higher initial cost over a higher number of parts made before wearing out.pre-hardened steel molds are less wear res**tant and are used for lower volume requirements or larger components.the steel hardness ** typically 38-45 on the rockwell-c scale.hardened steel molds are heat treated after machining.these are by far the superior in terms of wear res**tance and lifespan.typical hardness ranges between 50 and 60 rockwell-c(hrc).aluminium molds can cost substantially less,and when designed and machined with modern computerized equipment,can be economical for molding tens or even hundreds of thousands of parts.beryllium copper ** used in areas of the mold which require fast heat removal or areas that see the most shear heat generated.[12]the molds can be manufactured by either cnc machining or by using electrical d**charge machining processes
the mold cons**ts of two primary components,the injection mold(a plate)and the ejector mold(b plate).plastic resin enters the mold through a sprue in the injection mold,the sprue bushing ** to seal tightly against the nozzle of the injection barrel of the molding machine and to allow molten plastic to flow from the barrel into the mold,also known as c**ity[13]the sprue bushing directs the molten plastic to the c**ity images through channels that are machined into the faces of the a and b plates.these channels allow plastic to run along them,so they are referred to as runners.[14]the molten plastic flows through the runner and enters one or specialized gates and into the c**ity[15]geometry to form the desired part.
the amount of resin required to fill the sprue,runner and c**ities of a mold ** a shot.trapped air in the mold can escape through air vents that are ground into the parting line of the mold.if the trapped air ** not allowed to escape,it ** compressed by the pressure of the incoming material and ** squeezed into the corners of the c**ity,where it prevents filling and causes other defects as well.the air can become so compressed that it ignites and burns the surrounding plastic material.[16]to allow for removal of the molded part from the mold,the mold features must not overhang one another in the direction that the mold opens,unless parts of the mold are designed to move from between such overhangs when the mold opens(utilizing components called lifters).
sides of the part that appear parallel with the direction of draw(the ax** of the cored position(hole)or insert ** parallel to the up and down movement of the mold as it opens and closes)[17]are typically angled slightly with(draft)to ease release of the part from the mold.insufficient draft can cause deformation or damage.the draft required for mold release ** primarily dependent on the depth of the c**ity:the deeper the c**ity,the draft necessary.shrinkage must also be taken into account when determining the draft required.[18]if the skin ** too thin,then the molded part will tend to shrink onto the cores that form them while cooling,and cling to those cores or part may warp,tw**t,bl**ter or crack when the c**ity ** pulled away.[19]the mold ** usually designed so that the molded part reliably remains on the ejector(b)side of the mold when it opens,and draws the runner and the sprue out of the(a)side along with the parts.the part then falls freely when ejected from the(b)side.tunnel gates,also known as submarine or mold gate,** located below the parting line or mold surface.the opening ** machined into the surface of the mold on the parting line.the molded part ** cut(by the mold)from the runner system on ejection from the mold.[20]ejector pins,also known as knockout pin,** a circular pin placed in either half of the mold(usually the ejector half)which pushes the fin**hed molded product,or runner system out of a mold.[21]
the standard method of cooling ** passing a coolant(usually water)through a series of holes drilled through the mold plates and connected by hoses to form a continueous pathway.the coolant absorbs heat from the mold(which has absorbed heat from the hot plastic)and keeps the mold at a proper temperature to solidify the plastic at the most efficient rate.[22]
to ease maintenance and venting,c**ities and cores are divided into pieces,called inserts,and sub-assemblies,also called inserts,blocks,or chase blocks.by substituting interchangeable inserts,one mold may make several variations of the same part.
complex parts are formed using complex molds.these may h**e sections called slides,that move into a c**ity perpendicular to the draw direction,to form overhanging part features.when the mold ** opened,the slides are pulled away from the plastic part by using stationary“angle pins”on the stationary mold half.these pins enter a slot in the slides and cause the slides to move backward when the moving half of the mold opens.the part ** then ejected and the mold closes.the closing action of the mold causes the slides to move forward along the angle pins.[23]
some molds allow previously molded parts to be reinserted to allow a new plastic layer to form around the first part.th** ** often referred to as overmolding.th** system can allow for production of one-piece tires and wheels.
2-shot or multi-shot molds are designed to"overmold"within a single molding cycle and must be processed on specialized injection molding machines with two or injection units.th** process ** actually an injection molding process performed twice.in the first step,the base color material ** molded into a basic shape.then the second material ** injection-molded into the remaining open spaces.that space ** then filled during the second injection step with a material of a different color.[24]
a mold can produce several copies of the same parts in a single"shot".the number of"impressions"in the mold of that part ** often incorrectly referred to as c**itation.a tool with one impression will often be called a single impression(c**ity)mold.[25]a mold with 2 or c**ities of the same parts will likely be referred to as multiple impression(c**ity)mold.[26]some extremely high production volume molds(like those for bottle caps)can h**e over 128 c**ities.
in some cases multiple c**ity tooling will mold a series of different parts in the same tool.some toolmakers call these molds family molds as all the parts are related.[27]
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