mold design -...
TRANSCRIPT
Bong-Kee LeeSchool of Mechanical Engineering
Chonnam National University
Mold Design
5. Mold Structure
School of Mechanical EngineeringMold Design
Two-Plate Mold
Two-Plate Mold– 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
School of Mechanical EngineeringMold Design
Two-Plate Mold
Basic Two-Plate Construction
School of Mechanical EngineeringMold Design
Two-Plate Mold
Basic Two-Plate Mold General Arrangement
School of Mechanical EngineeringMold Design
Two-Plate Mold
Components– 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
School of Mechanical EngineeringMold Design
Two-Plate Mold
Components– 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
School of Mechanical EngineeringMold Design
Two-Plate Mold
Components– 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
School of Mechanical EngineeringMold Design
Two-Plate Mold
Components– 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
School of Mechanical EngineeringMold Design
Two-Plate Mold
Components– 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
School of Mechanical EngineeringMold Design
Two-Plate Mold
Components– 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
School of Mechanical EngineeringMold Design
Two-Plate Mold
Components– 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
School of Mechanical EngineeringMold Design
Two-Plate Mold
Components– 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
School of Mechanical EngineeringMold Design
Two-Plate Mold
Components– guide pillar
• accurately align the front and rear platens of the mold• hardened alloy tool steel
School of Mechanical EngineeringMold Design
Two-Plate Mold
Components– 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
School of Mechanical EngineeringMold Design
Two-Plate Mold
Detailed Design
School of Mechanical EngineeringMold Design
Two-Plate Mold
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
School of Mechanical EngineeringMold Design
Multi-Plate Mold
Three-Plate Mold– when an over feed gate is necessary, either for
multipoint feeding parts or for gating parts to achieve balanced flow
School of Mechanical EngineeringMold Design
Multi-Plate Mold
Three-Plate Mold– operation stages
• gate breaking or de-gating stage
School of Mechanical EngineeringMold Design
Multi-Plate Mold
Three-Plate Mold– operation stages
School of Mechanical EngineeringMold Design
Multi-Plate Mold
Three-Plate Mold– operation stages
School of Mechanical EngineeringMold Design
Multi-Plate Mold
Three-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
School of Mechanical EngineeringMold Design
Multi-Plate Mold
Three-Plate Mold– incorrect opening sequence
School of Mechanical EngineeringMold Design
Multi-Plate Mold
Three-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
School of Mechanical EngineeringMold Design
Multi-Plate Mold
Three-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 acetalsmay prohibit the use of hot runner systems
School of Mechanical EngineeringMold Design
Multi-Plate Mold
Three-Plate Mold for Drive Gear
School of Mechanical EngineeringMold Design
Multi-Plate Mold
Multi-Plate Undercut Molds– injection mold for valvehousings
School of Mechanical EngineeringMold Design
Multi-Plate Mold
Multi-Plate Undercut Molds
School of Mechanical EngineeringMold Design
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
School of Mechanical EngineeringMold Design
Multi-Plate Mold
Stack Molds– simple design of stack molds