HOW TO SELECT AN

INJECTION MACHINE
“FOR A MOULD”
IN MY ENTERPRISE OR TO BUY
- INTRODUCTION

- ATTRIBUTES TO BE CONSIDERED

- SOFTWARE DEVELOPED TO SELECT AN

INJECTION MACHINE

- EXAMPLE
 - THERE
CAN BE PROBLEMS AND FLAWS DURING THE
MANUFACTURING OF PLASTICS PARTS DUE TO A WRONG
SELECTION OF THE MACHINE.
WE MUST AVOID THEM WITH THE RIGHT SELECTION PROCESS .
SOMETIMES THESE FLAWS CAN GO UNNOTICED.
- WE MUST NOT CHECK ONLY THE CLAMPING FORCE AND THE
SHOT TO SELECT THE MACHINE WE ARE GOING TO INJECT A
MOULD WITH. WE MUST ALSO CONSIDER OTHER FACTORS.
-THE MACHINE CAN OPERATE IN BAD CONDITIONS
WITH MOULDS THAT ARE TOO BIG OR TOO SMALL
- OPTIMUM CYCLE TIMES CAN ONLY BE OBTAINED
WITH THE APPROPRIATE MACHINE
- BUYING AN INJECTION MACHINE IS A BIG INVESTMENT
 ATTRIBUTES TO BE CONSIDERED
EXCLUSIVE ATTRIBUTES => NON- EXCLUSIVE ATTRIBUTES =>

MAXIMUN INJECTION PRESURE SPACE BETWEEN TIEBARS

THEORICAL INYECTION VOLUME MAXIMUN MOULD WEIGTH

INJECTION RATE PLATENS DIMENSIONS INJECTION POWER

PLASTICIZING CAPACITY CAVITY PRESURE CONTROL

EJECTOR STROKE / FORCE
TYPE OF NOZZLE OPEN/CLOSED
CLAMPING FORCE MACHINE WITH NC (NUMERICAL CONTROL)
NUMBER OF INJECTION SPEEDS
AUTOMATION NUMBER OF PRESSURES...

MOULD MAXIMUM AND MINIMUM THICKNESS/HEIGHT

NUMBER OF CONTROLLABLE CORES MACHINE WEIGH/DIMENSIONS

MOULD OPENING STROKE/MAXIMUM DELAY NOISE AND VIBRATION

 T. INJECTION VOLUME SHOT WEIGHT
AN INJECTION MACHINE HAS TO BE ABLE TO PREPARE ENOUGH
MATERIAL TO FILL AND HOLD THE MOULD

THEORETICAL VOMUME: IT DEPENDS ON MATERIAL WEIGHT X ρ OF MATERIAL AT

INJECTION
RECOMMENDED: TEMPERATURE

% V machine ≤ V part ≤ %V machine

0-10% 90-100%
 MAXIMUM INJECTION PRESSURE
INJECTION PRESSURE: IS THE PRESSURE NEEDED TO FILL THE
MOULD WITH THE CHOSEN PARAMETERS.
THE INJECTION PRESSURE IS RELATED TO THE RATIO OF THE
SCREW CROSS SECTION AND THE INJECTION CYLINDER AREA.

Injection Maximum Injection Maximum Hydraulic Pressure

pressure Machine Specific
Pressure x ( S cylinder /S screw )
needed
It depends on:
-Thickness
-Length
-Filling conditions
-Viscosity of
material

∆P total = ∆P part + ∆P runners + ∆P nozzle

 INJECTION SPEED
THE INJECTION SPEED IS THE MAXIMUM SPEED AT WHICH THE SCREW
OF THE MACHINE IS CAPABLE OF OPERATE. IT AFFECTS THE
INJECTION TIME. MOULDING THIN-WALLED ARTICLES REQUIRES HIGH
INJECTION SPEED SO THAT THE MELT DOES NOT SOLIDIFY BEFORE
THE CAVITY IS COMPLETELY FILLED.
EACH PART NEEDS
EACH PART HAS OPTIMUM TIME A MINIMUM
INJECTION SPEED

IF INJECTION MACHINE MATERIAL

SPEED INJECTION FILLING TIME
NEEDED SPEED GETS COOL
SHORT SHOT
SOME I M HAVE AN ACCUMULATOR AS AN OPTION TO
BOOST INJECTION SPEED POOR
QUALITY
 PLASTICIZING CAPACITY
PLASTICIZING CAPACITY IS THE AMOUNT OF PS THAT A PIMM CAN UNIFORMLY
PLASTICIZE AT MAXIMUM SCREW ROTARY SPEED AND ZERO BACK PRESSURE.
IN ORDER NOT TO WASTE TIME,

PLASTICIZING TIME COOLING TIME

SEPARATED HYDRAULIC SYSTEM

CLOSED NOZZLE

PERMITS PLASTICIZING
MATERIAL DURING CLAMPING TIME
AND EJECTION SAVING
 CLAMPING FORCE
CLAMPING FORCE IS THE MAXIMUM FORCE THE MACHINE IS CAPABLE OF TO
KEEP THE MOULD CLOSED AGAINST THE CAVITY PRESSURE DURING
INJECTION. INSUFFICIENT CLAMPING FORCE GIVES RISE TO FLASH AT THE
MOULD JOINT.

OTHER CLAMPING
PARAMETERS FORCE

THERE IS NO DIRECT RELATIONSHIP

CLAMPING FORCE ESTIMATE

THERE ARE SEVERAL WAYS:
-FIGURES
-SIMULATIONS. THE MOST ACCURATE
ESTIMATE OF CLAMPING FORCE IS
DONE BY COMPUTER SIMULATION
AFTER THE MOULD IS DESIGNED. AN
EXAMPLE OF SUCH PACKAGE IS C-
MOLD.
 MOULD MAXIMUM AND MINIMUM
THICKNESS/HEIGHT
Moud height is expressed as a range in a toggle clamp I
M specification, from the minimum to the maximum
height the machine can accomodate. The difference is
the mould height adjustment the machine is capable of.
Mould height is experessed as a number in a direct
hydraulic clamp IM specification: the minimum mould
height the machine can accomodate.

Mould thickness
The actual mould height must be bigger than the
machine minimum mould height for the mould to be
closed and clamped.
Otherwise, a smaller machine (tobe exact, a smaller
clamping unit) is called for.
It also must be less than the machine maximum mould
height for the mould to fit in. Otherwise, a bigger
machine is called for. The minimum thickness can be
solved with additional plates.

FRAME OF SWITCH
 MOULD OPENING STROKE
IT IS THE MAXIMUM OPENING BETWEEN THE FIXED AND MOVING
PLATENS WHEN THE CLAMP IS WIDE OPEN.

MINIMUM OPENING STROKE 2’5 PART’S DEPTH

PART DEPTH

TOGGLE SYSTEM MOVEMENT OF TOGGLE

HYDRAULIC SYSTEM MAXIMUM DAYLIGHT = MOULD OPENING STROKE +
MINIMUM MOULD HEIGHT
 SPACE BETWEEN TIEBARS
THE MOULD MUST FIT WITHIN THE SPACE BETWEEN TIEBARS. THIS SPACE IS
EXPERESSED IN HORIZONTAL AND VERTICAL DIMENSIONS.

THE MOULD WIDTH MUST FIT WITHIN THE HORIZONTAL SPACE BETWEEN TIEBARS IF
THE MOULD IS LOWERED FROM ABOVE. THE MOULD LENGHT MUST FIT WITHIN THE
VERTICAL SPACE BETWEEN TIEBARS IF THE MOULD SLIT IN FROM THE SIDE.

IT IS ADVISABLE THAT THERE

IS A CLEARANCE OF 25 MM ON
EACH SIDE FOR A SMALL
MOULD, AND 50 MM FOR A BIG
MOULD. THIS IS TO AVOID
BANGING OF THE HEAVY
MOULD AGAINST THE TIEBARS
DURING LOADING,
 INJECTION POWER

HYDRAULIC MOTOR POWER

% Inyección

100 Plastificación
Compactación

Apertura del
molde
Acercamie
Cierre nto boquilla Pausa

Pausa
SOME INJECTION MOULDS CAN
WORK WITHOUT PRESSURE SENSORS.
THERE ARE I M EQUIPPED WITH A SYSTEM TO
RECEIVE THAT KIND OF SIGNAL
 PLATENS DIMENSIONS
THE PLATENS ARE THICK STEEL PLATES TO HOLD UP THE
MOULDS WITH. IT IS ADVISABLE THAT THE MOULDS, OR AT
LEAST THE PART AREA, DO NOT PROTRUDE BEYOND THE
PLATEN LIMITS. TOO SMALL A MOULD WOULD PUT UNDUE
BENDING STRESS ON THE PLATENS, BREAKING THEM IN THE
EXTREME CASE. SOME MANUFACTURESRS OFFER A CHOICE OF
PLATEN SIZES FOR MACHINE OF A GIVEN CLAMPING FORCE.
 TYPE OF NOZZLE OPEN/CLOSED
SIMPLE NOZZLE, SPRING-SHUT-OFF NOZZLE
AND HYDRAULIC SHUT-OFF NOZZLE ARE THE
COMMON TYPES. SIMPLE NOZZLE IS SUITED TO
PLASTIC MATERIALS THAT DEGENERATE WITH
HEAT PRODUCING GAS.
GAS-GENERATING PLASTICS NO GAS-GENERATING PLASTICS

PA POM PVC PP PS PE ...

 MACHINE WITH NC (NUMERICAL CONTROL)

THE POSSIBILITY OF PROGRAMIMG SPEEDS,

PRESSURES AND MOVEMENTS BY NUMERICAL
CONTROL IS ESSENTIAL ON MANY OCCASIONS
TO OBTAIN AN OPTIMUM PART.
WITH AN APPROPIATE NUMERICAL CONTROL
WE CAN OBTAIN
-AN OPTIMUM SPEED PROFILE FILLING
-AN OPTIMUM PRESSURE PROFILE HOLDING
-SEVERAL EJECTION SHOTS, ...
 NUMBER OF CONTROLABLE CORES
INJECTION MACHINES CAN BE EQUIPPED WITH A
HYDRAULIC SYSTEM TO MOVE DIFFERENT QUANTITIES OF
CORES. IF THE MOULD TO INJECT HAS A HIGHER NUMBER OF
MOVEMENTS, IT WILL BE IMPOSSIBLE TO INJECT, OR AN
ADDITIONAL HYDRAULIC SYSTEM WILL BE REQUIRED.
 AUTOMATION

SOME MOULD NEEDS THIS OPTION

THERE ARE IJECTION MACHINES THAT
CAN WORK WITH MANIPULATING
ROBOTS FOR REMUVAL OF PART OR
INTRODUCING CORES