5. Mold Structure Bong-Kee Lee Chonnam National University the simplest and most reliable design has the fewest number of moving parts and is more straightforward to manufacture and run in production is usually cheaper to manufacture
Basic Two-Plate Construction Basic General Arrangement
locating or register ring circular ring, screwed to the front clamping plate enables the mold to be centered on the injection cylinder axis by locating it into a machined hole in the stationary platen good-quality low-carbon steel top plate or, front plate, fixed half front plate, fixed half clamping plate allows the mold to be secured to the fixed platen with cap screws to hole it in position low-carbon steel or alloy tool steel for very long-running jobs
split line or, parting line plane or position at which the mold separates into two distinct parts stationary and moving platens after the mold has split at this point, space is created for the molded parts to be pushed or ejected from the mold cavity insert or, mold insert, insert core circular or rectangular piece of alloy tool steel that carried the form of the molded part in it more convenient machining and prevention of distortion from the hardening
front cavity plate or, fixed half cavity plate to hold the front half cavity inserts in position in the stationary platen of the mold low-carbon steel or alloy steel for very long-running jobs rear cavity plate the same function and material as the front cavity plate makes the rear half inserts captive between it and the cavity support plate cavity support plate to withstand the force generated by the injection pressure of the melt that is exerted on the actual cavity parts alloy tool steel to resist the cavity inserts being embedded (or hobbed) into it must be of sufficient depth (or thickness) to prevent excessive plate deflection taking place
ejection system carries a number of ejection pins that push or eject the parts from the cavities as well as ejector pins, it may use sleeve ejectors and blade ejectors or may also operate stripper plates, double ejection systems, collapsible cores or other more complex devices ejection gap the amount that the ejector system can move towards the cavity support plate from its rest position support blocks or, risers connects the cavity support plate to the rear clamping plate or back plate good-quality low-carbon steel
guide pillar accurately align the front and rear platens of the mold hardened alloy tool steel return pins or, push backs to return the ejection system to its initial or rest position when the tool closes to prevent any damage to the more fragile ejector pins through contact with the front platen of the mold hardened silver steel or hardened alloy steel
Detailed Design Detailed Design additional features clearances around the ejection pins, ejector return pins and ejector bar bushes on guide pillars and return pins wears between the mold plates of soft mild or alloy steel and the repeated sliding of hardened components screws to hole the tool together support pillars taper tapped holes on water cooling channels stand-off buttons beneath the ejector system chamfers on rectangular cavity insert guide pillar and bush system completely aligns the mold
Multi-Plate Mold when an over feed gate is necessary, either for multipoint feeding parts or for gating parts to achieve balanced flow Multi-Plate Mold operation stages gate breaking or de-gating stage
Multi-Plate Mold operation stages Multi-Plate Mold operation stages
Multi-Plate Mold disadvantages long opening stroke is necessary to accommodate all the different openings both the speed and accuracy of the mold open stop must be good as variations in either can results in the failure of the mold to operate or, worse, in a breakage the limiting factor on most molds is nearly always the length of opening stroke required Multi-Plate Mold incorrect opening sequence
Multi-Plate Mold main requirements it must open in such a way that all possibilities of the molded parts sticking in the cavities are avoided the openings must be sufficient to ensure the runner, sprue, and the parts have sufficient room to fall freely from the mold the molding machine must have an accurate opening stroke, otherwise the pull rods and limit bolts may be broken or the parts and the runner system may not be stripped and ejected properly Multi-Plate Mold comparison with hot runner systems suitable for medium-length production runs, where the relatively higher cost of the hot runner mold would not be economic often more reliable owing to simpler nature and does not require expensive heating and control systems changing material and/or color is easier since this type of mold clears its complete feed system every shot thermal sensitivity of certain material such as PVC or acetals may prohibit the use of hot runner systems
Multi-Plate Mold for Drive Gear Multi-Plate Mold Multi-Plate Undercut Molds injection mold for valve housings
Multi-Plate Mold Multi-Plate Undercut Molds Multi-Plate Mold Stack Molds highly efficient, cost-effective production method of large projected areas shallow boxes, cassette cases, video cases, and Petri dishes alignment of projected areas in stack molds
Multi-Plate Mold Stack Molds simple design of stack molds