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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Stripper Ejector Construction (step by step mold design) part 5

next step let's put sprue bush at top plate until directly to product, beside sprue bush i put locating ring, this two part important become guide between mold and injection machine, sprue bush will guide molded plastic to runner, because this product use direct gate, runner also direct from runner to product. see picture below for detail



Locating Ring Type
i use 120 mm diameter of locating ring, with height 15 mm, from that height, 5 mm i put on moldbase, and 10 mm become guide when mold base attach to injection mold, 3D picture below will give briefly image of locating ring.



Sprue Bush

What is Gate ?
The entrance through which molten plastic flows into the cavity of the mold from the runner. This is where the flow or melting of molten plastic is controlled by control type of gate or gate dimension. It is positioned at the thickest area of a part.
other function of gate is the gate makes it easier for the runner, which will be unnecessary after molding, to be separated from the part.is recommended to consider gating options early in part design.

Direct Gate
direct gate or sprue gate we can define as connecting directly end sprue to the molding and used as a gate,
this type of gate is commonly used for single cavity molds, where sprue feeds the material to cavity molds directly rapidly with minimum pressure drop.
see more explanation of direct gate at link below
http://mould-technology.blogspot.com/2008/02/direct-gate-or-sprue-gate.html

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Stripper Ejector Construction (step by step mold design) part 4

on the step below we design bolts position to hold the cavity insert to top plate of mold base, i use M10, or you can use other bolts base on your strength calculation and available market, there are various bolts type available on the market, i prefer use socket head screw in mold design, see link below for reference about this type of bolts
http://www.engineersedge.com/iso_socket_head_screw.htm

Picture below shown Socket Cap Head Screw.























picture below shown cavity main insert and bolts position, i attach the bolts in 4 side symmetrically,



for easy machining process, don't forget this little tips but very important when designing mold, at corner side of pocket make sure you make Radius or half circle, so pocket can be process use in MC easily. i use half circle type in each corner.



Chamfer in Insert
to prevent accident when assembly process, safety reason and easy assembly of mold we need to make little chamfer in each edge of mold, with chamfer it also became guidance when assembly the cavity insert to mold base. see picture below for detail picture, i use C5 in symmetric chamfer and 3-10 in asymmetric chamfer.

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Circular H type Runner Layout in Mold Design

It’s called H type because the runner shape from the top similar with “H”, it’ use in both circular layout and rectangle layout system, in circular type the runner doesn’t similar with H but it more similar with fork, circular type use in various type of product, like gear, cylinder shape, etc.
Total length of H circular type in each part of runner
8.801 x 16 = 140.816
7.491 x 8 = 119.856
18.83 x 8 = 150.64
Total length of runner in H circular type runner system
140.816 + 119.856 +150.64 = 410.912
Let’s compare with previous type runner system, direct runner system both circular and rectangle type,
Direct circular type = 448 mm
Direct rectangle type = 495.04 mm
H circular type = 410.912 mm
So the conclusion is from three example runner systems for these part and layout type, H circular type has the minimum length of runner,


Advantage
1.Flow length in the runner more stabile, cause we can add runner slug before branched the runner, see picture above
2.When designing the runner, runner volume is made small as possible, this type is smallest than two type runner before.
3.All the cavities fill at the same time possibility is high, balanced runner have an equal flow length and runner size form sprue to all cavities also same, so that each cavity can fill in nearly condition.

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direct circular runner system and direct rectangle runner system in mold design

continuing previous post about sleeve ejector system in mold, now let's learn how to choose runner layout, and lay outing the cavity and core,

From picture above space that available for layouting cavity core is 40 mm X 40 mm, from those available space we must design effective and cheap runner cost, effective design for runner mean that total runner length designed as short as possible, and runner, product weight ratio is small, so it’s your product will contain only short runner, that can reduce cost of material. Here some layout that I tries to make from available space 40 mm X 40 mm.

Direct Circular Type
This type is easy to layout, because we only design for one runner, straight between center of sprue bush to gate position, then copy those runner base on amount cavity that can be layout, from space that available 40 mm x 40 mm, we can arrange the cavity until 16, so the angle between one cavity and other is 360 / 16 = 22.5, to arrange more detail copy and rotate your runner design with those angel (22.5) until you get 16 runner, each runner length is 28 mm, so total length of runner are 28 x 16 = 448 cm.
See picture below for detail construction and dimension of circular runner system for this mold



Top view


Direct rectangle type
Simple way to layout cavity core and runner is using direct rectangle, this type common use in imprecision part, 8 cavity will have length 28.6 mm from center sprue bush, and the 8 cavity others will have length 33.28 mm, see picture below for detail sketch of runner. From this condition total length of runner are (28.6 x 8) + (33.28 x 8) = 228.8+266.24=495.04 mm, this runner type have 47.04 longer than previous type.
The other’s disadvantage of this runner type is flow material will not same to all cavity, because distance between cavity and center of sprue bush for all cavity have 2 type, first type have 28.6 mm, second type have 33.28 mm in length, if the injection pressure too high or injection volume of material too much, it possibly flash at the first type (28.6) cavity. And if volume injection doesn’t enough shot mold possibly appear at second type cavity (33.28)



so, in this case, circular type of runner layout still the best to be implemented, how about the other runner layout type, such us H type, let's see on the next post

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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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Sleeve ejector system

This system use when part have tolerance or good dimension so, so we can’t put ejector in those face, or ejector prohibited in that face other reason is part have hole and face that can touch with ejector is very small and surrounding the hole. Look at picture below

Red face indicated that ejector is prohibited, for that reason the only way to eject those part is using sleeve ejector that will located at green face (look at picture)

Basic construction of sleeve ejector system is like picture below

 

How Sleeve Ejector Works

Basic mechanism of sleeve ejector is how to make insert pin doesn’t move when sleeve ejector move to eject the product.

Picture above shown step by step when sleeve ejector moving to eject part, the main part on those picture are product (yellow) sleeve ejector (green), core insert pin (white at center of sleeve ejector) mold base core (light blue at side sleeve core), cavity insert (dark blue), cavity pin insert (pink at center of dark blue), and cavity mold base (light blue surrounding cavity insert pin.

A.     After plastic material injected at cavity insert then cooling water/liquid will flow to transfer heat from mold to liquid. At this position mold base still close, just seconds before ejecting process begin.

B.     Ejecting process begin, first mold will open, core insert include cavity insert will move to backward, because shrinkage of material always move to inner side, product will stick in core insert pin.

C.     Sleeve core move forward when ejecting process begin, sleeve core will eject the product, and the product will leave core insert pin, because core insert pin doesn’t move forward.

After sleeve core move same as ejector stroke, product will drop, and.. Gotcha.. you get the product.

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Stripper Ejector Construction (step by step mold design) part 3

after make insert like in posting number 2, let's make main construction of ejector stripper plate, simple ejector stripper plate consist of three main part
1. ejector plate
2. bolts for clamp
3. ejector pin

those plate main function is to push product when ejecting, isn't need much part of plate surface that contact with bowl surface, only 0,8 mm product will able to eject from core insert side.


clearance and dimension tolerance
below is picture and some explanation where and when we set the clearance between insert part.


1. between insert core and core block, fit tolerance about 0.010 mm with height about 15mm from parting line, and after that make clearance about 0,5 until 2 mm.
2. between stripper and core block, give it free tolerance about 0.5 mm each side
3, between stripper plate and insert core, give it fit tolerance about 0.005 mm until 0.010 mm, it to prevent plastic product flash.
4. between ejector pin bolts and stripper plate, give it free tolerance from 0.5 mm until 1 mm.
5. ejector core pin and core block, give it fit tolerance about 0.010 in top side with height 10 mm, after that give free clearance about 0.5 mm in each side.

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