Category:Mould design and technology’

Mould Standard Parts – 8

 - by Phoebe

Fastening and closing elements, elements for lifting the mould
Injection moulding moulds and die casting dies are fastened to the machine platens
with similar components. The two most common components are clamps and
screws or only screws. High pressure die casting machine platens are typically
equipped with T-slots. Injection moulding machine platens with threaded holes.
The clamps and fastening screws are quite similar (See images).

Some manufacturers have also different quick-clamping systems. These systems
include magnetic and hydraulic clamping systems and different mechanical systems.
Moulds and dies are quite often lifted to the machine with a
crane. To make short work of the lifting, the plastic mould and dies
are equipped with at least two pairs of eyebolts. If it is necessary
to lift the mould or die halves separately, it is important
to place two eyebolt pairs to the moving half and one pair to
the fixed half. Otherwise the heavy moving half will not be
balanced

Injection moulding machines typically have several different ways of clamping the
mould ejection plates to the machine ejection system. There is only one point of
attachment, but the equipments for attaching are numerous. The simplest clamping
system is one ejector rod. But there are also different couplings for pneumatic or
mechanical quick-clamping devices. (See images.) The point of attachment is in the
middle of the mould ejector plates.

High pressure die casting machines use different system. The machine ejection
system is hydraulic. There are four ejector bars, which are attached to the machine
ejection cylinders through holes in the machine moving platen.

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Mould Standard Parts-7

 - by Phoebe

Tempering channel fixtures and other components

 
Injection  mould tempering is typically done with straight and/or conformal
cooling channels. The cooling liquid is water. High pressure die casting die
tempering liquid is some heat transfer oil. The channels are similar, but due to a
higher strength demands, simpler.

Mould and die standard part manufacturers
have different small equipments
for building the tempering channels.
These equipments include fittings for
connecting the tempering machine to the
channels with pipes and also for connecting
channels with each other. It is
common to extend the tempering channels
externally with pipes.

There are also equipments to cascade the tempering liquid with the aim to
strengthen the cooling effect. These equipments include cascading liquid junctions,
cooling baffles and cooling cores. Typically these equipments are placed inside high
and relatively narrow cores.

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Mould Standard Parts-6

 - by Phoebe

Runner system components for injection moulding moulds


The purpose of the injection moulding mould runner system is to provide the
melted plastic a route from the injection moulding machine nozzle to the mould
cavities. There are basically three runner types: cold runner, hot runner and combined
system. The plastic solidifies inside the cold runner system. For that reason
the cold runner system is removed from the mould cavity with the moulded part.
Hot runner system keeps the plastic in liquid form and only the part is ejected.
Cold runner system consists of a central gate (sprue bushing), runners, gates and
ingates. Runners, gates and ingates are mainly machined channels in the mould
plates. The most common standard cold runner system parts are sprue bushings
and rings for centering the injection moulding machine nozzle to the sprue head.
Some standard part manufacturers produce also special tunnel gate components for
injecting the cavity below.

Hot runner system consists of a sprue bushing, manifold, nozzles and gate bushings.
There are basically three hot runner system types: externally heated system,
internally heated system and combined system. In the image below there are some
typical components of an externally heated system.

Internally heated system is constructed with the similar components. The difference
is in heating the channels. Internally heated system has internally heated channels.
Externally heated system has externally heated channels.

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Mould Standard Parts – 5

 - by Phoebe

Cavity supporting elements

 
Usually the ejection side mould cavity is supported with supporting pillars. The
fixed cavity plate has enough support from the moulding and casting machine
base, but the ejection side cavity plate faces an open ejection box construction. The
supporting pillar is placed between the clamping plate and the cavity or back plate
under the cavity.

Core pins
Core pins are similar to the ejector pins, but the material is different. The core pins
are placed to the mould cavity to shape deep and narrow holes in the part. (See
image.)

Core moving elements
Core moving elements are different hydraulic or pneumatic cylinders, electric
equipment or slide mechanisms, which will move the moving core out of the mould
cavity to enable part ejection.
Slide mechanism is pure mechanical. It moves by the mould opening movement.
Main parts in the slide mechanism are angle pin, slide locking parts, slide guiding
and slide. Moving faces are typically covered with war plates. Some of the standard
part manufacturers sell complete slide sets with all necessary parts in them. Some
sell only angle pins and wear components. There is also a special standard mould
set for constructing sliding core moulds. (See images.)

If the moving core is relatively long, it is more practical to use core pulling cylinders.
The slide opening movement is restricted by the angle pin length. In average
size moulds and dies, the typical core movement is less than 50 mm. Core pulling
cylinder stroke varies between 100 – 250 mm, even 300 mm if required.

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Mould standard parts – 4

 - by Phoebe

Ejector set guiding and returning elements


Injection moulding mould ejector set is fixed to the moulding machine with one
element in the centre of the mould. Without guides, the ejector pins are sole elements,
which support these plates along with the fixture. Compared to the ejection
pins strength and stiffness, the ejector set produces a relatively high load. Even the
smallest imbalance will bend and in the worst case break the pins.
High pressure die casting die ejector set is fixed to the casting machine with four
ejection bars. Four bars give rather good support, but it is still possible that the
ejector set bends – for example if the part sticks to the die cavity from one side or
there is some other kind of imbalance in the ejection. Usually the high pressure die
casting machine ejector mechanism works with hydraulic cylinders. It returns the
die ejector set to the back position with a cylinder backward movement.
In some injection moulding machine types the ejector mechanism is returned with
the mechanism backward movement. In some machines the returning movement is
done with a spring in the fixture. High pressure die casting hydraulic cylinders
typically produce also the backward movement. In any of these cases it is recommended
to place four ejector set returning pins to mechanically return the ejection
system to the initial position.
The set of returning pins is also the lightest guiding construction. Returning pins
are thick ejector pins, which are placed outside the cavity and extended to the
mould parting surface. If the ejector set returning system does not work properly,
these pins secure the ejector set to the initial position.

If it is necessary to guide the ejector set more reliable and accurately, there are
different guiding elements. Guide pillars and sleeves are available with or without
bearings.


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Mould Standard parts – 3

 - by Phoebe

Ejector pins and special components for ejection
Basic parts in the mould ejection system are ejectors and sprue pullers. There are
different types of ejectors. The main types are round ejector pins, flat ejector pins
and ejector sleeves. Sprue pullers are specially shaped or specially placed ejectors,
which stick to the sprue and pull it out from the sprue bushing. (See images.)


Ejectors are attached between the ejector set plates with the collar in the end of the
ejector. If the mould cavity surface is shaped, it is common to grind a flat surface to
the collar. This flat surface sets the ejector to a fixed position. (See image below.)

Sprue pullers are either special components or specially shaped ejector pins. (See
images below.)

There are also some special ejector types like tilting ejectors and stripper plates.
Tilting ejectors are suitable for moulding small back draft details like snap fits and
small slots. Stripper plates are very useful in ejecting high cup shaped parts. (See
images.)

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Mould Standard Parts – 2

 - by Phoebe

Standard mould set with guide bars, guide sleeves and other guiding
elements

Standard mould set consists of two clamping plates, two cavity plates, an optional
back plate, risers and an ejector set (See image.). Core and cavity side are 3D-CAD
terms. Most of the cavity is typically placed into the fixed side and most of the core
into the moving side of the mould. This assures that the part is in the ejection side
cavity after the mould has been opened.

 

Ejector set consists of two plates: an ejector retaining plate and an ejector plate.
These are fastened together with four bolts and the ejectors are placed between
them. Usually there are bumper plates between the ejector set and the clamping
plate. (See image.) Risers determine the longest possible ejection distance.

Moving and fixed mould halves are guided towards each other with different
guiding elements. Basic guiding elements, which usually are a part of the standard
mould set, are guiding pillars, guiding sleeves and centering sleeves. If it is necessary
to locate the cavity halves with more accuracy, the mould is equipped with
cavity interlocks: straight side interlocks or tapered interlocks.

 

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Mould standard parts-1

 - by Phoebe

These day I would like to share about the mould standard parts. And this is including many kinds of parts, so I will use several article to share mould standard parts.

Mould standard parts can be divided into the following groups:
− Standard mould set with guide bars, guide sleeves and other guiding elements
− Ejector pins and special components for ejection
− Ejector set guiding elements
− Core pins
− Core moving elements
− Cold runner system components
− Hot runner system components
− Tempering device fixtures, insulating elements
− Fastening and closing elements, elements for lifting the mould
There are several mould standard part manufacturers, who have sales offices in
Europe. (See table.)

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Subsurface gate

 - by Phoebe

The subsurface gate is a circular or oval gate which submerges and ‘feeds’ into the impression below the parting surface of the mould. While similar to the round edge gate in that it is of similar or nearly similar shape and feeds into the side of the impression, it has several advantages over the round gate.
1. The from, being in one mould plate, has no matching problems and precise dimensions can be achieved.
2. If the more oval form is used the filling rate if the impression can be conrrolled independently of the gate seal time

 3. The gate is sheared from the moulding during its ejection.

The basic design is shown in figure 1. The runner is terminated a distance X from the impression. A secondary runner, usually of conical form, is machined a an angle Φto the impression wall and is stopped short of the impression wall by a distance L ( Note that this corresponds to the gate land length). The gate is then machined at the same angle Φ to join the secondary runner to the impression.

The moulding and feed systems are removed separately from the mould and this means that a separate runner ejection is advantageous, particularly as a certain amount of deformation of the runner is necessary to remove the secondary runner from the mould.

The gate dimensions which must be considered are land length which because of the form, needs to be L (minimum)=1.9mm. Φis the angle between the centre-line of the secondary runner and the impression wall. This angle is normally between 30 degree and 45 degree. The dimensions for the gate cross-section can be estimated from either the equation suggested for the rectangular gate, if an oval gate is adopted, or the equation for the pin gate, if the circular gate is used,

The subsurface gate can be adopted for feeding into the inside surface of a component, providing at least one of the following conditions are met:

1. There is a suitable member which projects below the general parting line surface and which is also located relatively close to the component wall. The subsurface gate feeds directly in to this member.

2. In designs where it is possible to incorporate a small diameter peg relatively close to the component wall, the subsurface gate feeds directly into the peg and thereby into the impression. The peg is subsequently removes as a post moulding operation.

An example of the latter design is illustrated in Figure 2. The component impression (1), with added ‘peg’ impression (2) is shown in the moulding position at (a). The subsurface gate (3) feed under the base of the component wall, into one side of the peg. The reason why the peg (or other projection) must be relatively close to the wall will now be apparent to the reader. This distance control the length of the subsurface gate, and for practical reasons the gate length must be as short as possible.

An ejector pin (4 is provided immediately below the peg, in addition to the normal ejector system, which in this example is also by means of ejector pins (5). An undercut type ‘ puller’ (6) and associated sprue pin (7) is situated relatively close to end of the runner (8)

During the moulding phase the melt flows into the impression via the runner, subsurface gate and peg (gate) respectively. The moulding, and feed system remain in the moving half as as the mould opens. (figure 2(a)).

Ideally, although not an essential feature of the design, the ejection should take place in two stages. During stage one, the moulding and peg is ‘sheared from the subsurface gate in the process. The undercut type puller ensures that neither the runner or gate is dislodged during this first phase.

Finally stage two ejection occurs, which cause the undercut sprue puller to be ejected, and thereby extract the complete feed system from the mould plate as shown at (c)

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Mould design

 - by Phoebe

Well, Finished the national holiday, back to working. Fighting! We do many things should be step by step.  The mould design also need to make step by step.

Mold design & construction requires special attention for optimal product quality and reliable molding. A detailed specification is required in advance:
 -product shape and tolerances
 -mold in relation to moulding equipment
 -parting lines; venting
 -number of cavities
 -runner lay-out and gating system
 -ejection system
 -cooling system lay-out
 -type of tool steel
 -surface finish.

Posted By Phoebe

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