Loose cavity inner undercut release method in injection Molding

one way to release the undercut is to loose cavity, the opposite of loose cores, loose inner cavity is used to remove the undercut in the cavity area, note the image below for more details,

1 = top plate
2 = runner stripper plate
3 = cavity plate
4 = core plate
5 = locking block for loose cavity
6 = angular pin for loose cavity system
7 = loose insert cavity

 

some designers also say that with the inner mold cavity slider, whatever his name is, in essence, functions and works the same way. when the first opening between the top runner stripper plate (2) with the cavity plate (3) top plate will pull locking block (5) together with the angular pin (6), aided by the spring on the insert cavity, this movement causes the loose insert cavity to move straight straight to the angular movement of the pin, as a result of friction between the angular pin with a hole in the loose insert cavity.

when construction is used, ie if your product has undercut formation on a position in the cavity region, angular corners and locking block commonly used ranged from 8 to 20 degrees, above the angle can cause angular cartilage pin was broken, because the force that fought too large.
Another thing to note is the stroke, you must ensure that the stroke of movement of loose cores must be secure, which is about the length undercut products coupled with the 5-10 mm.

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Stripper Ejector Construction (step by step mold design) part 6

now, after put sprue bush and locating ring at top plate, let's design core side, like cavity block, core block also need bolts to attach the core block to core plate, see picture below


at those picture i use M10 bolts type, this bolts use to attach the core block to mold base plate, don't forget to give chamfer of each side of core bolts, this chamfer very useful in assembly mold processing, this chamfer will become guide of core block when assembling to mold base plate.
for safety reason, you must also consider chamfer for other side to prevent scratch accident of operator when doing assembly process.



at last make packet at mold core plate, at those pocket give some Radius for machining process, this radius is must equal or more bigger than milling cutter radius that you want use in machining process, commonly more deep your pocket more large the radius of milling cutter.

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Mold Cavity Core Construction for Sleeve Ejector System

continuing from previous post about sleeve ejector system, below the explanation of cavity and core constructions

Cavity Construction
Basically cavity consist of : cavity main insert, and cavity insert, for this product, we use cavity main insert shape like pin, and to release air trap, we put cavity insert pin (pink color) with gas vent land. Gate located at cavity main insert that one position with parting line

Gas vent construction
At this mold type contractions gas vent very important, to prevent product burning and unfill (shot mold), see at those picture between gate position and top product distance is to high, base on my experience more than 10 mm plastic material can not fill until top of part (shot mold), although it depend on thickness of product, this product have thickness only 0.5 mm in each side, they are various ways to make gas vent for pin construction, picture below shown the other one.
At the top of product we cut to make gas vent land, give distance about 5-10 micro mm, see picture below, P1 as pin length have maximum length 19.992 mm (orange color) mm and P2 hole at the grey pin have length 20.000 mm (grey color), so distance between other is only 8 micro mm, gas can exit with this distance but plastic material can’t fill at this distance, almost plastic material in injection process, can fill if 20 mm space available, it cause plastic product defect that called flash.



























other picture for gas vent land and groove construction



At second picture, gas vent groove release at cavity main insert pin, gas vent groove depth is about 0.1 – 0.5 mm. when designing gas vent the important point is make sure that gas can release to out of mold.

Cavity insert

The main part of cavity insert is only cavity pin, because this product can be formed only by pin at the cavity side (see picture below), cavity pin located at center of product (grey color), product color is yellow, don’t forget to make some taper at this pin.

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Coring uniform wall thickness

when design a mold then we find nonuniform wall thickness, we can make little graduation translation using core, of course if there was not function parts,
ordinary parts like not cosmetic parts, touching with others parts, sliding and etc, should we change by making insert in core or cavity side. look at picture below
when a parts have no uniform thickness after injection process, sink marks and unfill product like void will occurs,




Different wall thicknesses in the same component cause differential shrinkage which, depending on component rigidity, can lead to serious warpage and dimensional accuracy problems To attain uniform wall thickness, thick-walled areas of the moulding should be cored like picture above,
the best core for graduation translation and easier material flow is by make radius in every corner, beside flow more easier there will easy when machining process used,and no need EDM process so it's should cost down the price of product.

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