Pin Point Gate Construction

pin point gate is commonly used in 3 plate mold types, see explanation more about 3 plate more here, basically the pin point gate part is like picture below
































those picture is pin point gate picture, to make gate like that we can buy pin point gate bush in mold manufacture company or we make it by EDM (electronic Discharge Machine) Process, the special EDM torch for Pin Point gate also available in mold part markets.
Pin Point gate Bush
picture below shown simple pin point gate bush,




































the construction to assembly the pin point gate bush in mold is like picture below
straight, without extended bush, picture below shown, locating ring, pin point gate bush, runner lock pin, runner, product and mold base plate (top plate, stripper plate and cavity plate)



some times, we need extended pin point gate bush, why when plastic material have high shear rate, we need to assembly extended bush, so from diameter gate until runner plastic material will easy to flow the cavity.
see the construction at picture below


here some good link of standard component of gate,
http://www.misumi-europe.com/www/lang/catmold_eng/nav/006/hl/007/menu/catalogues/fn/21/content.html

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Opening Construction of 3 Plate Mold Type

previous post http://mould-technology.blogspot.com/2008/08/main-construction-pin-at-3plate-mold.html
we can see closed condition of three plate molds

picture below is shown three plate condition when open


basically there are three opening type in 3 plate molds base
1. Sprue Cut Opening
2. Runner Opening
3. Product Opening

below i try to explain in simple words
1. sprue cut opening
this opening will cut sprue from nozzle, so the feeding runner can take easily by arm robot or manually by hand, this opening use puller bolt and runner stripper plate to cut the sprue. the stripper plate will move after puller bolts pulled by cavity plate, remember that puller bolts also end mounted in cavity plate.
the opening length between 5mm until 10mm.
2. runner opening
this opening use tho open runner system, than runner will take by robot or manually,this opening will make space between stripper plate and cavity plate.
to make sure this runner opening safely, attach spring in puller bolts between stripper plate and cavity plate, or use other methods like attach spring in out of puller bolts. length of this opening is same with runner length + 20 mm.

3. product opening, as we know this opening is to open the product, make space so the product can be ejected from core.
this opening length is about length the product + length robot arm + 10 until 20 mm to make save space when product ejected.

Opening Sequence

actually to pull the cavity plate, so the cavity plate can pull the puller bolts than open the stripper plate have two types, using tension link and magnet.
OK, at this post let's learn when using tension link.
1. first Opening is Runner Opening
why ? becouse between stripper plate and cavity plate,some springs always attached at there, some mold designer attach at puller bolts, and the other attach in each side using pin and make some hole to attach the spring. but i prefer attach the spring in puller bolts, it more easy in process.(sorry at picture above i don't write some spring)
2. Second Opening is Product Opening
Parting Line between core - cavity plate always easy to open, when moving plate at the injection machine pull the bottom plate until core plate, it will make Product Opening open.
3. Sprue Cutting Opening
after moving plate pull the core plate, with tension link core plate will pull the cavity plate until cavity plate pull the puller bolt, and make some space to cut the sprue from nozzle.

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Main Construction Pin at 3Plate Mold

I take those topic, to start learning about kind of pin on 3 Plate Molds, becouse between 3plate and 2 plate mold have several different function of Pin.
Basically 3 Plate mold to support the main construction have 3 kind of Pin.Look at picture below


(click the picture to enlarge)

3 Part Pin are
1. Main Support Pin
2. Positioning Pin
3. Puller Bolts

those pin will support both opening and closing process of 3 plate type of injection Mold. the function each pin are

Main Support Pin
this pin is totally support cavity, and runner plate when molds in open,when we buy mold base plate from fabricator, they always have exact diameter of Support Pin that we needed, it was calculated, but if your part is precision ensure it by calculating the deflection of those pin caused by cavity plate and runner plate.
make sure the deflection of pin not larger than 0.1 mm, choose more large diameter of Support pin when deflection is large.

Positioning Pin
Because support pin doesn't precision when closing, we need more precision guide part, this part also named Guide Pin, becouse it will guide core and cavity matching together. use this part with the Bush, in high precision part, some times we need more than one Positioning Pin, we can also add block guide, taper block set, taper pin set and other high precision positioning tools.

Puller Bolts
puller bolts doesn't support any plate, this part actually include in opening part of three plate molds.
working together with tension link or magnet block, this part will make parting line at stripper plate and top plate, this parting line used to make sure that sprue was cut from nozzle.

Parting line Opening is about 5-10 mm, depend on large of molds.

look at picture below to learn the length of each Pin.

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Sprue bush cooling design and construction

some times sprue bush need cooling to cut the cycle time of injection process, when diameter of sprue is large cooling in sprue bush is important. some fabrication of mold part have their own sprue bush that containing cooling pipe. like picture below


from those picture some standard part mold company have their own methods to make inner cooling at the sprue bush, we can by cutting in some part that weld together again, or by other method.

the other way to make cooling in sprue is like picture below


by those type of sprue we change the entrance and exit flow by using stopper buffle, for example like picture below


or you can make the flow straight, the other cooling method in sprue is like picture below, by using this type is easy to attach the O ring, becouse in and out flow from below side that contact with moldbase. becouse when assembling of ring to moldbase is more easy by attach the O ring in Moldbase then put the sprue bush than attach the O ring in sprue bush and assembling it together in moldbase.

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Locating Ring Design and Construction in Injection Mold

Locating ring is simple part but, very important when mold base attach to injection machine, ok here the construction of locating ring after assembled in mold base.



















then after attach in injection mold, the position of locating ring is like below


Basic Rule Design
1. when design locating ring, first rule is look at your injection machine catalog or hand book, and find the dimension of locating ring. like picture below

from picture above we know that locating ring diameter is 200 mm and diameter of nozzle is 52 mm, so your locating ring outer diameter must same with those injection machine locating ring hole.

2. don't worry about the tolerance, at the injection machine tolerance always about minus 0.01-0.1 mm, then the locating ring tolerance if we buy in standard mold part company is about minus 0.01-0.05.

3D Modeling various Locating Ring
below is some picture of locating ring that was i sketch using Google sketchUp, now i provide two type of locating ring. to choose right locating ring in mould is depend on injection machine nozzle, locating hole diameter, nozzle length in other factor.


Second type





















Third type
this type have large chamfer from top to bottom in inner hole, those chamfer provide shape so nozzle can touch the sprue more precise and easier.


and below is sample picture of locating ring base on Mold Part Industries

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Sprue Bush Design in Injection Mold

The molten plastic injected from the injector nozzle will go through a sprue (sprue bush), a runner, and a gate and fill up in the cavity.
As the temperature of molten plastic is lowered while going through the sprue and runner, the viscosity will rise; therefore, the viscosity is lowered by shear heat generated when going through the gate to fill the cavity.
so learn Sprue bush design is important, becouse sprue bush is part that contact first time with melted plastic, bad design of sprue bush can make plastic product broken, especially sprue broken and runner broken.
picture below shown mold basic construction with sprue.



























below is 3D model of sprue bush with 2 bolts
































this type is commonly use in small mold size, until 350 ton injection machine is still used.

the other construction is 4 bolts, this sprue bush type commonly use in large mold type and mass production, more than 200 ton






























and below is sprue bush with ring attachment, this type use when top plate thickness is width, but some designer prefer use large chamfer in top plate so with first model sprue bush is still can be attach


































Sprue Bush Design Rule
1. Ball radius of sprue must larger than ball radius nozzle, so don't forget to check diameter of nozzle of injection machine, or you can look at injection machine catalog. for example when ball radius of nozzle of injection machine is 10 mm use ball radius sprue bush 11 until 13 mm.
2. Hole diameter inner must be larger than hole diameter nozzle, diameter nozzle is variating base on machine injection type and manufacture, is about 2 mm until 5 mm. use 0.5 mm more larger than hole diameter of nozzle.
3. check your plate thickness, make sure that length of sprue bush fit with the plate thickness.

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