collapsible core for demolding/ejection system of internal screw undercut

one common way used in the ejection system for an internal screw is used collabsible undercut core, which requires collabsible core product generally has the undercut on the inside, for example an internal screw, pipe fittings, elbow pipe, use collabsibe core is not only on the core course , undercut the slider is also often used collabsible cores.
video below gives a simple explanation of how Collapsible cores working

http://www.die-moldtool.com/

Main Component
The three units are a Collapsible Core, center pin, and a positive collapse sleeve.

cenTer pin
The Center Pin serves to expand the segments of the Collapsible Core to their molding position and holds them at this diameter. A hole is provided inside the pin for cooling. The center pin is manufactured of a high alloy Type D-6 steel hardened to 60 to 65 Rockwell C or use SKH 51, SKD 11. Refer to the pin grinding instructions for machining directions. In use the pin must incorporate two design features. The pin must protrude beyond the face of the collapsing core segments by certain amounts. This protrusion keeps material from flowing under the face of the collapsing segments to ensure they properly collapse. A radius must be applied to the outside corner at the front of the center pin. The sharp edge resulting from cutting the pin to length will gall and subsequently destroy the inside surfaces of the collapsing core segments
collapsible core
The Collapsible Core is manufactured from A.I.S.I. Type A-2 steel hardened to 51 to 57 Rockwell C. It is designed to collapse independently when the center pin is withdrawn. The fit between segments is controlled to permit flash free molding. The location of the core on its pin is critical. The distance between the back of the core flange and the front of the center pin flange (Head Space) is critical and must be maintained.
If the Head Space (1.938 ±.005 on a CC 202 PC) is not maintained, unsatisfactory operation will result, or the core may be permanently damaged.
posiTive collapse sleeve
The Positive Collapse Sleeve (PC sleeve) is designed to function when the Collapsible Core fails to collapse independently upon withdrawal of the center pin. In normal operation, the PC sleeve is not functioning. It is essential to have such a unit for maximum safety and reliability in automatic and semi-automatic operation. Under no circumstances should a mold be placed into automatic operation without the use of the PC sleeve.

picture above shown collapsible core and the component, detail explanation about CC we can find it in DME standard part http://www.dme.net/dme/resources/FAQs/collapse_cores.html

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Runner Design in Injection Mold,

in designing the runner, first-time we must consider items that affecting  runnersize, some of which
- Volume of part, the greater the volume takes a larger diameter runners anyway.
- Weight of part, the heavier parts, it takes a larger diameter runners.
- Plastic materials, plastic materials with low viscosity, aqueous requires a smallerdiameter runner.
- Wall thickness, the thicker the greater the diameter of the runner is needed.
- Length of flow path, the longer it takes the flow of large diameter runner.

picture above shown some factor that we must consider before choosing right diameter of runner, 

Cross Section Area

various cross section area use on the market, It depends on the heat loss, machining requirement, but the most popular cross section area are circular, parabolic and trapezoid section area, picture below shows three

Diameter

to determine the diameter, based on the type of material and wall thickness, the following chart can help, for similar materials PP, PA, POM, PC, PE can use the following graph, first select the appropriate thick wall thickness and look heavy parts, and then pull the line down, the approximate diameter required will be obtained

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Lifting bolts hole design in injection mold

Plate transfer process occurs during the machining and assembly of mold, both for the cavity and mold base plate, especially for the plate with a weight greater than 20 kg, threaded hole necessary to facilitate the transfer process. cause may be in a mold plate having a various of machining processes with different types of machines. Base on position of hole the type of lifting bolts can divided became two, perpendicular to face, and parallel with face of plate.

perpendicular to face

beside transfer process, lifting bolts also important for lift out cavity insert from mold base, flat wide plate usually use magnet to lift from one machine to another machine or station, but if shape of plate doesn’t flat it need bolts hole to attach eye bolts, then use crane that connected to eye bolts for lifting the mold base plate or cavity plate.

Parallel with mold face.

Especially for mold base, this hole must available because transfer mold base usually use eye bolt that connected to crane, for mold base plate that use horizontal machining also use this hole to connected with crane, picture below shown mold base with metric bolt hole and eye bolts ready for transfer with crane

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runner components of injection mold

Runner components between the two mold plate and three plate mold because there are different functions of these components, but there are several components that can be used in general without looking at the type of mold construction.

1.Runner lock pin
The main function of the runner lock pin (RLP) is an pulling runner so
the gate can be disconnected/cut from the product, RLP fitted with a straight gate position, the head planted on the top plate, while in the body mounted on the cavity plate (3) up to the top
plate (1). RLP does not move during the injection process lasts, mold base plate
moves accordance with the mold opening sequence, the tip of the runner lock pin is the part that greatly affects the success or failure of the gate runner cutting process. Greater the undercut which is the stronger the ability of RLP to attract runners from the gate, the type of plastic material also influenced for selection of RLP.
2.RLP Lock
RLP lock have function to maintain RLP order not to loose from its position, there are various ways to lock them RLP
* closed with a locating ring or sprue bush or heat insulation board.
* using a plate
* use a screw plug
3. Bushing RLP
high cycle time mold or need durability are advised to use the bushing,the benefits include easy maintenance of RLP, more resistant to wear due to friction so it's can avoid direct contact between RLP and mold plate that can caused wears, this method will shorten maintenance time.
4. Ejector runner
Only used if the runners stuck on the stripper plate mold base or stuck on the cavity mold bases, the use of the runner ejector can help the runner release from the place that was not supposed to stick. Other components are collar to the head of RLP, and change flow components

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