Advance Mould Design

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Advance Mould Design

SPLIT MOULD


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SPLIT MOULD


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Split design constrains the following factors:

Amount of splits movement required.

Whether a delay period is required.

Length of a delay period.

Ease with the moulding can be removed.

Whether a short or long production run is required.

Whether the available machines are programmed for

ancillary cylinder control.

Whether moulding inserts are to be incorporated.


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TYPES OF SPLIT MOULD ACTUATION METHODS

Finger cam actuation method.

Dog-leg cam actuation method.

Cam track actuation method.

Hydraulic actuation method.

Angled-lift splits.

Spring actuation system.


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FINGER CAM ACTUATION:


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If the required movement is known from the amount of componentundercut, the following formula used to determine the finger camlength.

L = (M / sin) + (2C / sin 2) Where, M = splits movement.

= Angle of finger cam (10-25).

L = working length of finger cam.

C = clearance. The clearance C provided for

No direct force on finger cam pin.

Permits to open the mould to open a predetermined amount before thesplits are actuated.

The amount of delay movementD

before the splits are actuated Idetermined by the formula:

D = C/sin


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DOG-LEG CAM ACTUATION:

.


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The relevant formula for calculating the opening

movement, the length of cam, and the delay period are

given by

M = La tan - C , La = (M + C)/ tan ,D = (Lse) + (C/tan )

Where M = movement of each split,

La = angled length of cam,

Ls= straight length of cam,

= Cam angle, C = clearance,

D = delay,

e = length of straight portion of the hole


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CAM TRACK ACTUATION:

M+c

La = ----------

tan c 1 1

D = Ls + ---------- + r ------- - --------

tan tan sin

Where M = movement of each split,La = angled length of cam track,

Ls = straight length of cam track,

= cam track angle, 10-40

c = clearance, 1.5 mm

D = delay,

r = radius of boss


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The permissible angle of the cam track plate isbetween 10 and 400. The formula for calculatingthe distance required for each split, the length of

cam track, and the delay period are as follows: M =La tan - c


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HYDRAULIC ACTUATION:

The splits are actuated by hydraulic mechanism,The hydraulic actuation system is used for design oflarge shape split mould components as more lockingforce is required to keep the splits closed during theinjection phase.In this case more delay movement and large splitmovements can be achieved.The splits having a projection on the underside towhich the ram of the hydraulic actuator is attached.


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Angled guide dowel actuating systemG:

In this design, the guide dowels are fitted at an angle to theunderside of each split. These guide dowels are passes throughholes machined at an angle in the chase-bolster. When the

ejector system is actuated, the relative movements between theejector plate and the enclosed chase-bolster causes the guidedowels to move forward at an angle corresponding the splits areget to open, shown in figure


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The spring-loaded system:

It is an operating method confined to moulding has very shallowundercuts or projections. AS shown in Figure , a stud is fixed tothe underside of the split block and it is accommodated in a slot

machined in the mould plate. A spring or springs are fitted to theslot and cause the side core assembly to withdraw immediatelythe mould opens. The locking heel is used to progressively returnthe assembly when the mould is being closed


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MOULDING INTERNAL UNDERCUTS

These are three types of methods are usedfor releasing the internal undercuts asfollows:(1) Form pin(2) Split cores internal undercuts.

(3) Stripping internal undercuts.


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FORM PIN:

The amount of withdrawal obtained may be computed front the following

relationship:

M = E tan

Where M = the withdrawing movement.

E = ejection movement.

= fitting angle of the form pin.


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Split Core Actuation :


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Split coreangled action:


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Mould Designs for threaded components:

Basically, thread forms may be moulded by the followingmethods:Using loose tool insertsUsing splitsUsing collapsible coresAxially moving and static unscrewing coresUsing automatic unscrewing techniques


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Typical jump undercutdesign


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Two-segment collapsiblecore details

M ld D i f h d d


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Rotat ing core unscrewing too l

HOT RUNNER


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HOT RUNNER

Hot runner molds are two plate molds with a heated runnersystem inside one half of the mold. A hot runner system is

divided into two parts: the manifold and the Nozzles. Themanifold has channels that convey the plastic on a singleplane, parallel to the parting line, to a point above thecavity. The Nozzles, situated perpendicular to the manifold,convey the plastic from the manifold to the part.


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M if ld


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Manifold:

Types of Profi les

for Manifold s

Rectangular

and CircularManifolds

No le t pes


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Nozzle types:-

Extended nozzleBarb Nozzle

Antechamber Nozzle


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Advantages & Disadvantages\

The many advantages of insulated runner systems,compared with conventional runner systems, include:

Less sensitivity to the requirements for balanced runners

Reduction in material shear.

More consistent volume of polymer per part.

Faster molding cycles.

Elimination of runner scrap less regrind.

Improved part finish.

Decreased tool wear..


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However, the insulated runner system alsohas disadvantages. The increased level of

technology required to manufacture andoperate the mold results in:

Generally more complicated mold design.

Generally higher mold costs.

More difficult start-up procedures untilrunning correctly.

Possible thermal degradation of the polymermelt.

More difficult color changes. Higher maintenance costs


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Gas-Assisted I njection Molding


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Introduction

Gas-injection moulding has been developed to save

material, shorten cycle times and to improve the surfaceaspects of thick-walled injection-moulded parts.

General Principles

Gas-injection moulding uses a standard injection-moulding machine, extended with equipment to injectgas normally (Nitrogen) parallel or in series with theinjection of the melt .Gas injection can take placethrough the same nozzle as the melt (machine nozzle),or via one or more special gas injection needles locatedat the runner or where there are materialconcentrations (thicker walls). Special machine nozzledesigns are needed to ensure reliability.


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Stack mould

The stack mould is used for moulding shallow and smallparts in large quantity such as tape cassettes. In thistype of mould the cavities are located into two planescorresponding to the parting lines and are filled at thesame time. For moulding the stack mould it requires aninjection moulding machine with large opening strockand clamping force of 15% higher than a standard

mould. Stack mould were originally operated with coldrunner design, which has to be the moulded in eachshot. Further hot runner manifold is employed toincrease the productivity


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Reaction Injection Molding

RIM was developed with polyurethane toproduce large automotive parts such as bumpersand fenders

RIM polyurethane parts possess a foaminternal structure surroundedby a dense outer skin

Other materials used in RIM: epoxies, andurea-formaldehyde


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Advance Mould Design