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Design and manufacturing of plastic injection mould

11 – Undercutted parts

Dr. Mikó Balázsmiko.balazs@bgk.bmf.hu

BAGIM1ENNB

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Undercutted part

� Hidden feature from the opening direction� Size / Shape / Matching of the inserts

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Example 1

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Example 2-3

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Design facilities

� Moving insert� Conventional ejection bar� Ejection rod

� 2 stage ejector� Slider� Lifter� Spring core

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Moving insert

� In case of proto moulds� Move with the plastic part� Ensure the position of the insert

� Fixture for disassemble of insert and part

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Conventional ejection

� Simple undercut, � Surface can be damaged.

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Ejection rod

� Ejection bar with form.� Simple undercut.� Demoulding can be problematic.

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2 stage ejection

� Small undercut.

� Part can be damaged.

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2 stage ejection

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Slider

� Insert, which is moved to the direction of the undercut

� Problems: � Closing� Moving� Guiding� Fixing

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Moving

� Moving by angle pin� Moving in time of

opening

Slider

Angle pin

Pressure insert

Stopper

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Geometric parameters

H

L

H

L

α

tg α = L

H

H = L * tg α

αmax = 30°(18°- 22°)14

Design

Guide railFlat guiding

stock

Pressure insert

Slider body

Wear plate

Angle pin

Holder insert

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Slider body

� Shoulder for guiding (5x5)

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Angle pin

� 1 or 2 pin

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Holder insert

� Egyszerőbb gyártás

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Guide of the slider

� Guide

� Fitting in mould plate (dowel pin and slot)

� Fixing by screws

� Self lubricated of hardened

� In case of wide slider more guiding elements can be used

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Pressure insert and wear plate

� Erı felvétele� Zárás beállítása� Formalappból

kialakítva

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Pressure insert

� Külön alkatrész� Megfelelı

illesztés és rögzítés

� Kopólappal vagy a nélkül

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Pressure insert

Additional insert incase of larger mould

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Recommended geometric par.

α < β α = β

α > βα = β + (2°- 5°)

� �

�

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Fixing the open position

� In open stage the position of the sliders have to be fixed

� The recommended slider direction is level

� Ball screw� Hole in the slider� Bottom of the slider or in the

side (not recommended)

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Fixing the open position

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Fixing the open position

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Fixing the open position

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Fixing the open position

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Fixing the open position

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Moving of sliders

� Z rod� Moving after the

opening

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Z rod

� Ensure alternative mould building

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Drive by hydraulic cylinder

� Long move� In the A side� Action before opening� In mould or standard cylinder

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Mini slider

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Special slider

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Special slider

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Special slider

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Lifter � Small undercut

� No space for slider

� Space for lifter exists

� Support the ejection

� The slip of the part must be eliminated

Cavity

Core

Ejector bar

Support plate

Lifter

Ejector base plate

Ejector retainer plate

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Typical application

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Design constrains

Lifter

Rib

Lifter will crash to the rib

Space required to the moving

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Drive by spring

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Moving by ejector plates I.

� Straight ejection � Drive by insert

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Moving by ejector plates II.

Assembled or one piece

Cylindrical or rectangular rod

Drive in insert or in plate

Drive in th ejector plate

Assembled or one piece

Close mould Open mould 42

Head design

� One piece� Hole + Dowel pin� Screw

� Taper surfaces are needed in the plate

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Guide of the lifter

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Lifter

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Spring core

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Spring core

Rugózó nyak

Rögzítı csavar

Lapolt szár

Bronz vezetı elem

Fej fokos kialakítással

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Spring core

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Spring core

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Spring core

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Spring core

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Double spring core

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Double spring core

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Double spring core

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Tulip ejector

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Examples

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Examples

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Examples

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Examples

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Examples

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Examples