Injection Mould Machine Structure-Topic 5

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Topic 5

INJECTION MOULDING MACHINE STRUCTURE

Fundamentals 2

History And Development .......................................................................................... 3

Evolution Of Injection Moulding ................................................................................. 5

Types 9

Basic Machine ......................................................................................................... 10

Multi-Shot ................................................................................................................ 11

Rotary Table ............................................................................................................ 13

Tandem.................................................................................................................... 15

Gas-Assisted............................................................................................................19

Classification 22

Open-Loop Control .................................................................................................. 23

Closed-Loop Control ................................................................................................25

Basic Components 27

The Injection Unit .....................................................................................................28

The Clamping Unit...................................................................................................30

Drive System ........................................................................................................... 35

Control System ........................................................................................................ 37


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INJECTION MOULDING MACHINE STRUCTURE

Terminal Objective:

Identify different sections of the moulding machine and their functions.

Fundamentals

Enabling Objectives

Knowledge:

Brief history of moulding machine and its evolution / development.


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1. History And Development

Injection moulding machines for plastics were derived from metal moulding or

diecasting machines.

The first injection moulding patented was granted in the United State in 1892 to

John Hyatt, for what was termed a stuffing machine plunger injection moulding

machines.

This is developed for demonstration only, not for production.

FIRST PATENT FOR MOULDING 1872, JOHN HYATT


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Injection moulding developments occurred worldwide. In Germany in 1920

injection moulding thermoplastics and in 1927 a press operated by pneumatic

jacks, permitting operation at higher injection pressure; in Italy in 1939 self-

contained hydraulically operated machines, etc.). First picture shows the United

State machine built by HPM in 1931.

A major development occurred in 1951 when William H. Willert (United State)developed the reciprocating screw plasticiser (RSP) for injection moulding

machines; Willert U.S patent 2,734,226 was issued on February 14, 1956.

US INJECTION MOULDING MACHINE BUILT BY HPM CORP. IN 1931

FIRST PATENT IN RECIPROCATING SCREW PLASTICATOR ISSUED TO

W.H. WILLERT, FEBUARY 14,1956


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2. Evolution Of Injection Moulding

1868- John Wesley Hyatt injection moulds celluloid billiard balls.

1872- John and Isaiah Hyatt patented the injection-moulding machine.

1937 - Society of the Plastics Industry founded.

1938- Dow invented polystyrene (still one of the most popular materials).

1940- World War II created large demand for plastic products.

1941 - Society of Plastics Engineers founded.

1942- DME introduced stock mould base components.

1946- James Hendry built first screw injection-moulding machine.

1955- General Electric began marketing polycarbonate.

1959 - DuPont introduced acetal homopolymer.


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PLUNGER TYPE INJECTION MOULDING MACHINE


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1969- Plastic landed on the moon.

1972- The first part-removal robot is installed on a moulding machine.

1979 - Plastic production surpassed steel production.

1980 - Apple uses acrylonitrile-butadiene-styrene (ABS) in the Apple IIE computer.

1982- The JARVIK-7 plastic heart kept Barney Clark alive.

1985- Japanese firm introduced all-electric moulding machine.

1988- Recycling of plastic came out of age.

1990 - Aluminum mould introduced for production moulding.

1994- Cincinnati-Milacron sold first all-electric moulding machine in the U.S.


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RECIPROCATING SCREW INJECTION MOULDING MACHINE


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Types

Enabling Objectives

Knowledge:

Expose students to different types of machines and their unique features.

Skills :

Identify different types of machines.


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1. Basic Machine

The machine consists of an injection unit to inject the material and a clamp unit

that is used to hold the mould closed during the injection phase. This basic

machine concept is shown in the figure.

BASIC INJECTION MOULDING MACHINE


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2. Multi-Shot

Multi-shot Injection Moulding with Rotary Unit

The mould for automatically functioning two-component injection mouldingcontains two stations in which the moulded part is pre-injected and then finished

in a second injection. In the first process step, a pre-moulded part is initially

created in a cavity, and then transferred to a second working position.

At this step, the mould is opened, and the necessary change in position is

completed by a rotary motion of 180. After the mould is closed, the pre-moulded

part is located in the second position for final injection with the second

component.

Simultaneous to this second step, the next pre-moulded part is already being

created in the first mould cavity. During the next opening of the mould, the mould

cavities are turned back by an alternating rotary motion.

The finalised part is now demoulded from the second cavity, while a new pre-

moulded part is placed into position from the first cavity.

EXAMPLE OF PRODUCTS


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MULTI SHOT INJECTION MOULDING FOR ROTARY UNIT

ARRANGEMENT OF INJECTION UNITS


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3. Rotary Table

This solution allows loading and ejecting operation made during injection and

cooling time, and permits a great reduction of cycle time. Also a perfect use of

robots for automatically operation.

Possibilities of rotation are: clockwise of two positions for 180, clockwise of

three positions for 120 alternatively the rotation may be either clockwise or anti-

clockwise of 180 and 120 (optional).

ROTARY TABLE


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ROTARY TABLE


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4. Tandem

These machines are capable of accepting two moulds in tandem, one behind the

other. This makes for a certain similarity with the stack-mould technique. With

such a design the economics of injection moulding can be improved with

machines of more than 5000 kN clamping force and cycle times of more thanabout 20 sec.

The tandem machine has a movable centre machine platen. Injection is done

laterally through this centre platen, which carries a female mould half on each

side. The projected areas of the two parts should be approximately the same.

The advantage results particularly from that stage during which the moulding in

cavity B is cooled, while the moulding in cavity A is moulded. This means a

high degree of utilization with efficient use the space. Equally shaped parts offer

an additional advantage.

TANDEM


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Injection moulding machine with clamping unit in tandem arrangement (System Husky).

A: Centre platen with hot-runner system.

B: Process sequence.

a: Both moulds are closed, injection into mould B, cooling of mould A,

b: After injection and holding-pressure time for mould B, mould A is opened and

part ejected, mould B remains closed. The injection unit moves to mould A.

c: Mould A is closed and injection starts, mould B is cooled.

d: After filling mould A, mould B is opened and mould A is cooled.

TANDEM - PROCESS SEQUENCE


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5. Gas-Assisted

Gas-assisted injection moulding enables the moulder to produce parts with a

combination of thick and thin sections.

The first stage of the cycle is the flow of molten polymer into the mould cavity

through a standard feed system. Before this flow of polymer is complete, the

injection of a predetermined quantity of gas into the melt begins through a

special nozzle located within the cavity or feed system as shown.

The pressure at the polymer gate remains high and, therefore, the gas chooses

a natural path through the hotter and less viscous parts of the polymer melt

towards the lower pressure areas. The flow of gas cores out a hollow centre

extending from its points of entry towards the last point of fill. By controlling theamount of gas injected into the hollow core, the pressure on the cooling polymer

is controlled and maintained until the moulding is packed. The final stage is the

withdrawal of the gas nozzle, prior to mould opening, which allows the gas held

in the hollow core to vent.

GAS - ASSISTED


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GAS - ASSISTED

GAS - ASSISTED


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GAS - ASSISTED

GAS - ASSISTED


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Classification

Enabling Objectives

Knowledge:

Identify the 2 broad classifications have and what they mean.

Skills :

Explain the effect at the moulding and operation of each type.


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1. Open-Loop Control

One or several input (reference) signals are modulated into an output (control)

signal in accordance with the inherent interrelations of the system.

The speed of the screw advancement x. It is controlled by the valve position y.

The oil pressure z1 as well as the oil temperature z2 and the force z3 acting

against the screw displacement affect the speed.

The speed of the advancing screw can be kept constant by adjusting the valve

accordingly with a control mechanism.

A:Control circuit (schematic)B:Block diagram of control

OPEN - LOOP CONTROL OF SCREW - TRAVEL SPEED


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OPEN - LOOP CONTROL OF SCREW - TRAVEL SPEED


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2. Closed-Loop Control

A closed-loop system feeds back the output (controlled) signal and continuously

compares its magnitude with the input (reference) signal. Any resulting deviation

from the set value produced by interference in used to correct the controlled

output.

The variable x (actual speed of displacement) should be kept constant and is

compared with the set speed value w. A controller determines the difference

between set point and actual value affects the valve position y in such a way that

the difference becomes zero. Thus the influence of the oil pressure z1 but also

the other interferences z2 and z3 are caught and eliminated.

In closed-loop control, the output signal, which has to be controlled, is measuredand the controller can compensate the effects of several disturbances.

CLOSED - LOOP CONTROL OF SCREW - TRAVEL SPEED


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Basic Components

Enabling Objectives

Knowledge:

Identify the structure and different sections of the moulding machine.

Skills :

Identify the different sections of the machine and their functions.


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1. The Injection Unit

The injection unit has to carry out the process by accepting free-flowing plastics

material (pellets) in the hopper, heating and plasticating them inside the barrel,injecting the plastic melting through a nozzle into a shape-providing cavity, and

keeping it there under pressure (holding pressure).

The most important elements of an injection unit:

a. Feed hopper

b. Reciprocating screw

c. Thermocouple

d. Barrel

e. Heater bands

f. Non return valve

g. Cylinder head

h. Screw tip

i. Nozzle

PICTURE A - THE INJECTION UNIT


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2. The Clamping Unit

The clamping unit of an injection-moulding machine accommodates the injection

mould, it provides the motion needed for closing, clamping, and opening, andproduces the forces, which are necessary to clamp and open the mould.

There are two basically different design concepts: -

a. Toggle clamping systems (positive locking with toggles actuated by a lead

screw or hydraulic cylinder).

b. Hydraulic clamping systems (force locking with hydraulic cylinder).

EXAMPLE OF CLAMPING


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a. Toggle Clamping System

The mould-clamping cylinder closes the mould at rather a high speed under a

low pressure.

After the mould clamping start position is reached, the cylinder exerts a heavy

force boosted by a toggle mechanism to the mould so that the mould is clamped

slowly under high pressure until the desired mould clamping force is attained.

i. Mould opened.

ii. Mould clamped.


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TOGGLE CLAMPING SYSTEM


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b. Direct Hydraulic Clamping System

Hydraulic oil under pressure is fed to the auxiliary cylinders to advance the

moving platen to close the mould.

After the mould clamping start position is reached, feed of oil to the auxiliary

cylinders is shut off and feed of oil to the mould clamping cylinder starts to clamp

the mould until the desired mould clamping force is attained.

i. Mould opened.

ii. Mould closed.


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DIRECT HYDRAULIC CLAMPING SYSTEM


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3. Drive System

The standard drive for an injection-moulding machine is the single electro

hydraulic drive, which consists of an electric motor and a hydraulic pump. Centralenergy supply with oil hydraulics or mechanical drives and pneumatic drive is

used exclusively for mini plunger-type machines.

A drive can consist of electric motor, transfer elements (e.g. Couplings), energy

transformer (e.g. hydraulic pump), and gear transmission. The kind of use

(rotation or translation) as well as the number of uses in one machine decide on

the individual arrangement in each case.

Diagram shows the principal hydraulic system of an injection moulding system.

The hydraulic pump delivers oil through a non return valve into an accumulator.

As the accumulator fills, the gas inside is compressed. When the accumulator is

completely filled, the pump pushed the oil, without pressure, through the

pressure relief valve into the oil tank. The various units draw oil from the

accumulator while it is refilled by the pump. The necessary pressure or volume

flow in the various units can be regulated by the valves.


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HYDRAULIC SYSTEM OF AN INJECTION MOULDING MACHINE


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4. Control System

It functioned to coordinate the machine sequences, to keep certain machine

parameters constant, and to optimise individual steps in the process.

All motion sequences of the machine, the correct order of these sequences, their

initiation, the signalling of positions reached (such as by limit switches), and the

reaction at predetermined times within a cycle have to be achieved, initiated, and

coordinated.

Specific values that must be controlled, by either open loop or closed-loop

control, are: -

a. Barrel temperature

b. Melt temperature

c. Temperature of hot runner systems

d. Screw rotation

e. Injection speed and

f. Holding pressure

The various parameters to be controlled by the control unit.


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PARAMETERS OF AN INJECTION MOULDING

MACHINE TO BE CONTROLLED

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Injection Mould Machine Structure-Topic 5