Optimization of Process Parameters for L.D.P.E. Material in Injection Moulding Machine Using Taguchi Methodology
A dissertation work
Submitted in partial fulfillment of the requirement for the award of degree of
Master of Technology
In
MECHANICAL ENGINEERING
Submitted to
RAM KRISHNA DHARMARTH FOUNDATION UNIVERSITY BHOPAL (M.P.)
Submitted by
MOHAMMAD MASHUK ALI
Enrollment No -0211PIE16PG008
Under the guidance of
Prof. Amitesh Paul
Department of Mechanical Engineering
SRI SATYA SAI COLLEGE OF ENGINEERING GANDHINAGAR BHOPAL (M.P.)-462033
JUNE-2018
Sri Satya Sai College of Engineering, Bhopal
Department of Mechanical Engineering
CERTIFICATE
This is to certify that dissertation entitled “Optimization of Process Parameters of LDPE Material in Injection Moulding Machine Using Taguchi Method “submitted by Mohammad Mashuk Ali has been carried out under my guidance and supervision. The dissertation is approved for submission towards partial fulfillment for the award of degree of Master of Technology in Department of Mechanical Engineering.
Guide & H.O.D Principal
Prof. Amitsh Paul Dr. A.C. Nayak
Department of Mechanical Engineering Sri Satya Sai College of Engineering
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CHAPTER 1 INTRODUCTION 1-23
1.1 Preface ……………………………………………………… 1
1.2 Basic Concept Of Injection Moulding Machine…………….. 2
1.2.1 Types of injection moulding machine……………. 2
1.2.2 Advantages of injection moulding machine……… 4
1.2.3 Disadvantages of injection moulding machine…… 5
1.2.4 Glossary (Terms related to injection moulding machine). 5
1.3 Elements Of Injection Moulding Machine…………………… 12
1.3.1 Screw – Nomenclature…………………………… 12
1.3.2 Zones of screw………………………………….. 13
1.3.3 Nomenclature of injection moulding……………. 14
1.3.4 Types of moulds………………………………… 15
1.3.5 Clamping system- Function…………………….. 16
1.3.6 Types of clamping system……………………… 16
1.4 Plastic Materials……………………………………………. 19
1.4.1 Introduction…………………………………….. 19
1.4.2 Types of plastic materials………………………. 20
1.4.3 Low Density Polyethylene……………………… 20
CHAPTER 2 PROCESS PARAMETERS 24-29
2.1 Introduction……………………………………………….. 24
2.2 Injection Pressure…………………………………………. 24
2.3 Setting Of The Injection Pressure………………………… 24
2.4 Injection Speed…………………………………………… 26
2.5 Setting Of The Injection Speed…………………………… 26
2.6 Holding Pressure………………………………………….. 26
2.7 Setting Of The Holding Pressure…………………………. 26
2.8 Back Pressure…………………………………………….. 27
2.9 Setting Of The Back Pressure……………………………. 27
2.10 Hydraulic Oil Temperature……………………………… 28
2.11 Screw Rotary Speed……………………………………. 28
2.12 Setting Of Screw Rotary Speed………………………… 28
2.13 Mould Temperature…………………………………….. 28
2.14 Cooling Time…………………………………………… 29
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2.15 Setting Of Cooling Time…………………………………… 29
CHAPTER 3 LITERATURE SURVEY 30-38
3.1 Historical Background……………………………………… 30
3.2 Literature Review…………………………………………… 31
3.3 Research Gap……………………………………………….. 38
CHAPTER4 RESEARCH OBJECTIVES AND WORK PLAN 39-41
4.1 Research Plan……………………………………………… 39
4.2 Work Plan…………………………………………………. 40
4.3 Objectives Of The Study………………………………….. 40
CHAPTER 5 EXPERIMENTAL DESIGN METHODOLOGY 42-48
5.1 Introduction……………………………………………… 42
5.2 Taguchi Experimental Methodology…………………….. 42
5.2.1 Taguchi’s philosophy……………………………… 43
5.2.2 Experimental design strategy……………………… 44
5.2.3 Loss function……………………………………… 47
5.2.4 Assumption of the Taguchi method………………. 48
CHAPTER 6 EXPERIMENTATION 49-66
6.1 Machine Start-Up Procedure…………………………….. 49
6.2 Machine Operation (Setting Of Process Parameters)……. 49
6.3 Sample Preparation………………………………………. 56
6.4 Fundamentals Of Testing………………………………… 57
6.4.1 Specifications and standards……………………… 57
6.4.2 Important testing standards………………………. 57
6.4.3 Sample conditioning and test atmosphere………… 57
6.4.4 Important testing properties (mechanical)………… 58
6.5 Determination Of Tensile Strength………………………. 58
6.6 Machine Shut Down Procedure………………………….. 59
6.7 Selection Of The Definite Value Of Process Parameters… 60
6.7.1 Design: Application of Taguchi Methodology………. 60
(With the help of MINITAB 17 SOFTWARE)
6 . 7 . 2 Experimentation………………………………… 60
6.8 ANOVA (Analysis Of Variance) Calculation…………… 64
6.9 Concluding Remarks…………………………………….. 66
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CHAPTER 7 SUMMARY OF MAJOR RESEARCH CONTRIBUTIONS 67-69
AND SCOPE FOR FUTURE WORK
7.1 Summary Of Work Done……………………………… 67
7.2 Key Finding Of Research Work………………………. 68
7.3 Scope For Future Work……………………………….. 68
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LIST OF TABLES
S. No. Table No. Title of Tables Page No.
1 1.1 Properties of LDPE………………………………. 21
2 2.1 Factors that influence injection pressure…………. 25
3 2.2 Screw rotary speeds for various plastic materials… 28
4 4.1 Work plan………………………………………… 40
5 5.1 Layout of L9 Orthogonal Array………………….. 44
6 6.1 Selected values of process parameters…………… 60
7 6.2 Experimental result for tensile strength and S/N… 61
ratio as per L9 orthogonal array arrangement
8 6.3 Response Table for Signal to Noise Ratios……… 61
9 6.4 Response Table for Means………………………. 62
10 6.5 Response Table for Standard Deviations……….. 62
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LIST OF GRAPHS
S . No . Graph No . Title of Graphs Page No. Page No .
1 6 . 1 Temperature-Time Curve at Various……… …..51 51
Locations in the Mould
2 6 . 2 Main Effects Plot For Means…………………….62 62
3 6 . 3 Main Effects Plot For Standard Deviations……63 63
4 6 . 4 Main Effects Plot For S/N Ratios………………63 63
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INTRODUCTION
CHAPTER 1
1.1 PREFACE
Competition is the life-blood of our present day industrial civilization. This fact is apparent everywhere ranging from the user of the smallest domestic appliances to those responsible for the management of the largest industrial concerns and technological projects. Many of the products those are the part of everyday life go unnoticed, either because they are components of larger items or they are so commonly used that a little thought is given to their existence. Those items which have manufactured by plastic injection moulding often all falls into this category. We looks around a home or business, we will find many products that exist because of the injection moulding process. From cars to toys, hence plastics play an important role. Hence the plastic injection moulding is a method for preparing this durable, resinous materials in to about any form of required imaginable. Hence the first injection moulding machine was invented and made by brothers John and Isaiah Hyatt in 1872. It resembled a large hypodermic needle, with a heated cylinder through which a large plunger forced the gooey mass into a mould. Therefore today, this process is more complicated although the basic principles of plastic being injected into a waiting mould are still the same. One of the biggest advantages has come by way of the materials used, and there are now thousands of different formulas available for making ‘plastic’. Raw materials used in the plastic injection moulding process including thermoplastics, thermo sets and elastomers, also called polymers or resins, there are more than 20,000 unique formulations that could be injected in to moulding to produce various parts with the particular characteristics to be used for the particular objective. The examples of common thermosetting plastics include polymers such as epoxy and phenolic. The normal thermoplastics are nylon, polyethylene and polystyrene. Injection moulding is the most common plastic moulding process and is used to create a huge variety of complex parts of different sizes and shapes. However it is a snow board & a vinyl window thing being produced, injection moulding is an efficient & economically, particularly if the maximum quantity of things are being made. The highly complex parts can be produced at a low cost. The only demerit is the initial start-up costs of Injection Moulding Machine.
1.2 BASIC CONCEPT OF INJECTION MOULDING MACHINE
One of the most common methods of converting plastics from the raw material form to an article to use is the process of injection moulding. So this method utilized for thermoplastic materials & other various polymeric materials, which may be consecutively, could be melt, reshaped & cooled. The injection moulded components quality of most each & every functional manufacturing object in the modern world.
1.2.1 Types of Injection Moulding Machines-
There are different variants of Injection Moulding Machine available on respective to their functions & utilization. Therefore the cost of the machine could be more depending on their function & size. So the simplest Injection Moulding machine is a hand injection moulding machine with very low cost & costliest machine may be a screw type automatic microprocessor injection moulding machine.
Hand Injection
Plunger Type
Screw Type
Plunger-Plunger
Screw-Plunger
Hand Injection Moulding Machine
Figure 1.1: Hand Injection Moulding Machine
There are various types of injection moulding machine available which carried with of barrel, Plunger, Band Heaters included with energy regulator, Rack and Pinion systems for injecting material through by the plunger, a torpedo and nozzle. Therefore the clamping is done manually on a worked bench. So the machine has to be fixed on the working bench. The heating has to be setted manually. Hence the strength of the machine can be available from 0.5 Oz to 2 Oz. Hence if once heating has received the production originates manually. So the quality of product is
Completely depend upon the skill of the operator. Therefore the heating set point is achieved by heat & trial method. Even though the temperature controller may be fitted on the machine, but the set point is completely depend on the quantity of product produced by the operator. The cycle (revolution) time is completely variable and it depends on the competence of the operator. The main function of the torpedo is to help the material for proper melting and create a back pressure for help in mixing.
Plunger Type Injection Moulding Machine
Figure 1.2: Vertical & Horizontal Plunger Type Injection Moulding Machine The Plunger type injection moulding machine is available horizontal or vertical type and operated pneumatically or hydraulically. The clamping and Injection may be Semi or automatic. In a semi Automatic type the clamping cylinder & the Injection cylinders are operated by levers which is connected the pneumatic or hydraulic cylinders. In Automatic type the cylinders are actuated automatically to set timers.
Screw Type Injection Moulding Machine
The Screw type Injection Moulding Machine consists of a hopper, a reciprocating screw, barrel assembly and an injection nozzle.
Figure 1.3 (a): Screw Type Injection Moulding Machine
Plunger-Plunger Injection Moulding Machine
The plastic industry developed a second type plunger machine appeared, known as two stage plunger. This type of equipment involved two plunger units set on top of other the one to plasticize the material and feed it, to another cylinder that consist of a chamber to heat the plastic material by conduction and plunger that operates as a shooting plunger and push the plasticize material into the mould.
Screw-Plunger Injection Moulding Machine
The variation appeared in which first plunger stage was replaced by a rotating screw. In this type of cases the action of the screw serves to work and melt the resin and feed it, into the second plunger unit where the injection ram forces it forward into the mould.
1.2.2 Advantages of Injection Moulding Process-
Parts can be produced at high production rate.
Large volume production possible.
Relatively low labor cost per unit obtainable.
Parts required little or no finishing.
Many different surfaces, colors, and finishes are available.
Good decoration is possible.
For many shapes this process is the most economical way to fabricate.
Process permits the manufacture for very small parts which are almost impossible to fabricate in quantities by other methods.
Minimal scrap loss result as runners, gates, and rejects can be reground and can be reused.
Same item can be moulded in different materials & without changing the machine or mould in some cases.
Closed dimensional tolerances can be obtained.
Parts can be moulded with metallic and non-metallic inserts.
Parts can be moulded in a combination of plastic and such fillers as a glass, asbestos, talc and carbon.
The inherent properties of the material give many advantages such as high strength-weight rates, corrosion resistance, strength and clarity.
1.2.3 Disadvantages of Injection Moulding Process-
Intense industry competition often results in low profit margins.
Mould costs are high.
Moulding machinery and auxiliary equipment cost high.
Lack of knowledge about the fundamentals of the process cause problems.
Lack of knowledge about the long term properties of the materials may result in long-term failure.
1.2.4 GLOSSARY (Terms Related To Injection Moulding Machine)-
ADDITIVE – A substance added to a plastic compound to alter its characteristics. Examples are plasticizers, and flame retardants.
ALLOY – A combination of two or more plastics which form a new plastic. AMORPHOUS – A plastic material in which the molecular structures is random and become mobile over a wide temperature ranges.
ANNEAL – To heat a moulded part up to a temperature just below its melting point and slowly cooling it back; down to room temperature. This relieves moulded stresses.
ANISOTROPIC SHRINKAGE – Shrinkage that occurs more in one direction (usually as the direction of flow; reinforced materials shrink more across the direction of flow) than another.
AUTOMATIC OPERATION – The term used to define the mode in which a moulding machine is operating when there is no need for an operator to start each cycle.
BLEND – A mixture of two or more plastics.
BOSS – A projection of the plastic parts, normally rounded, which are used to: strengthen an area of the part; provided a source of fastening; or to provide an alignment mechanism during assembly.
CAVITY – A depression or female portion of the mould which creates the external plastic part surface.
CHECK RING – A ring shaped component that slides back and forth over the tip end of the screw. This removes the flow of molten materials reverse over the screw during the injection time.
CLAMP FORCE – This force measured in tons, if clamp unit of a moulding machine create to keep the moulding closed during the injection processes.
CLAMP UNIT – The section of moulding machine contains clamping method. That can be utilized to close mould & keep it closed w.r.t injection pressure started through the injection processes. Hence the clamping unit as well contains the ejection mechanism.
COMPRESSION RATIO – A factor that determines the amount of shear that is imparted to plastic material as it travels through the barrel. It is determined by dividing the depth of the screw flight in the feed section by the depth of the screw flight in the metering section.
CORE – A pin or protrusion designed to produce a hole or depression in the plastic part.
COUNTERBORE – A recessed circular area. Normally utilized to fit the head of an ejector pin in the ejector plate.
CRYSTALLINE – A plastic material in which the molecular structures becomes mobile only after being heated above its melting point.
CYCLE – The total amount of time required for the completion of all operations needed to produce a moulded part. Sometimes referred to as the "gate-to-gate" time, meaning the time from when an operator first closes the gate until the time the operator closes the gate again for starting the next cycle.
DECOMPRESSION – A method of relieving pressure on the melt after preparing it for injection during the upcoming cycle. This minimizes the drooling that occurs when a shut-off nozzle is not utilized.
DEFECT – An imperfection in a moulded part that results in the product not meeting original design specifications. These defects can be visual, physical, and/or hidden.
DRAFT – An angle (or taper) provided on the mould to facilitate ejection of the moulded part.
EJECTOR-HALF – The half the mould which is mounted to the moving platen of the injection machine. Sometimes called the "live" half or the "moveable" half because it moves. The half of the mould generally contains the ejection method:
FEED ZONE – Area of the screw that is at the rear and receives fresh material from the feed throat.
FILLER – Specific material added to the basic plastic resin to obtain particular chemical, electrical, physical, or thermal properties.
FLASH – A thin film of plastics that tends to form at parting line areas of a mould may also be found in vent areas and around ejector pins. Flash is caused by more great a clearance between mating metal surfaces, which allows plastic material to enter.
FLIGHT – The helical metal thread structure of the injection screw.
GATE – An opening found at the entrance of a cavity (end of the runner system) which allows material to enter.
GRANULATOR – A machine designed to grind up rejected pre-moulded plastic (products or runners). The material generated by this process is called REGRIND. GUIDE PINS – A pin (usually circular) which normally travels in a bushing in order to provide alignment of two unattached components, such as the two halves of an injection mould also called LEADER PINS.
.
HEATING ZONE – An area of the heating barrel that is controlled by a temperature controller attached to a set of heater bands. The four major zones are front, centre, rear and nozzle.
HYGROSCOPIC – A term applied to those plastics (such as ABS and NYLON) which absorb moistures from the atmosphere.
INJECTION PRESSURE – That pressure which performs the initial filling of the mould. It has provided by the injection screw as it is pushes material out from the heating barrel and in to the moulding.
L/D RATIO – The result of a calculation which divides the entire length of flighted area on a screw by its nominal diameter.
MANUAL OPERATION – The term used to define the mode in which a moulding machine is operating when there is a need for an operator to start and finish each phase of the total cycle.
METERING ZONE – That area of the screw at the front end which contains properly melted plastic that is ready to inject.
MONOMER – A molecular unit of an organic substance, usually in the form of a liquid or gas.
MOVING PLATEN – The moving platen of the moulded machine of which opens and closes. Hence it is connecting to the clamp unit & the mounting place for the B, of travelling, halve of moulding.
NON-RETURN VALVE – A mechanism mounted in (or at) the nozzle of the injection machine, which operates to shut off injection flow at the end of the injection cycle. This eliminates material from the upcoming shot from drooling out of the nozzle when the mould opens to eject parts from the previous shot.
NOZZLE – The device mounting at the end of the heating barrel, of which focuses the plastic material to flow from the machine in to the moulding.
PARTING LINE – A plane at which two halves of a mould meets. Also applies to any other plane where two moving sections come together and form a surface of a moulded part.
PLASTIC – A complex organic compound (usually polymerized) that is capable of being shaped or formed.
PLATENS – The flat surfaces of a moulding machine onto which the two halves of the mould are mounted. One is stationary and the other travels. There is a third platen (stationary) at the clamp end of the machine which serves as an anchoring point for the clamp unit.
PLUNGER – Injecting member of a non screw designed mould machine. So the plungers do not revolves, to bring material forward in readiness for the next phase. Hence nor do they blend the material as a screw does as per described.
POLYMER – A group of long chains of monomers, bonded together in a chemical reaction to form a solid. This term is often used interchangeably with PLASTIC, but there can be a difference.
PURGING – The method of injecting not needed plastic material from the injection cylinder in to the atmosphere for the aim of changing materials, changing colours, or removing degraded material also the nomenclature given to the mass of material that has to be purged.
RECIPROCATING SCREW – The metal shaft which can revolves in between the heating cylinder of a mould machine, shearing, blending and advancing so plastic material. Thereafter revolving the screw is pushing forward which can injects a plastic in to the moulding, & simply referred to as Screw.
REGRIND – The plastic material formed by the granuling pre moulding material. The regrind is newly material that has exposed to at least single heating cycle.
RUNNER – The place (Groove) cutting in to either both half of injection moulding provide a way for the molten plastic material to be carrying from the sprue to the gate of the cavity as per experimentation.
SCREW SPEED – The rotating speed of the screw as it augers new material towards the metering zone is expressed in RPM (revolutions per minute).
SECONDARY OPERATION – Any activity performed after the moulding process required f produce a finished product suitable for its designed purpose.
SEMI-AUTOMATIC OPERATION – The term used to define the mode in which a moulding machine is operating when there is a need for an operator to start each cycle.
SHOT – A term given to the total amount of plastic material is injected (or shot) into a mould in a single cycle.
SHUT OFF LAND – A raised area of the mould surface surrounding the cavity image. This area is usually between 0.002 and 0.003 inch high, approximately 1/2 inch wide and is used to focus clamping pressure on the mould. Hence the utilization of a shut off land neglects the quantity of ton age needed to keep a moulding closed against the injection pressure.
SLIDE – A section of the mould which is made to travel at an angle to the normal movement of the mould. Used for providing undercuts, recesses, etc.
SPRUE – In this the plastic material which joints the runner method to the nozzle of the heating cylinder of mould machine. This is formed through the internal surface of a bushing that joins the moulding to the machine nozzle.
SPRUE BUSHING – A hardened bushing connects to the mould to the moulding machine nozzle and allows molten plastic to enter the runner system.
STATIONARY PLATEN (A) – In this the platen at the injection end of the moulding machine, which does not travel through. This consists the A half of the moulding & locates the moulding to the nozzle of the injection unit. Hence the moving platen travels in between this platen and stationary platen B.
STATIONARY PLATEN (B) – In this the platen at the clamp end area of the moulding machine which does not travel. The moving platen travels between this platen and stationary platen "A".
THE STRESS – Hence the obstruction to demodified from the applied forces. The moulded plastic outcomes tend to consists stresses moulding in as a final outcome of forces parameters applied in between the injection process. Therefore these stresses could result in fracture, crack, & breakage, if all are escaped during utilization of the product obtained.
THE SUPPORT PILLAR – The circular rod moulding factor used to support the evictor halves of the moulding. Hence it is needed because of the terrible quantity of the pressure draw up against the "B" plate, so through the injecting phase of the moulding processes.
THERMOCOUPLE – A device made of two dissimilar metals which are used to measure the temperature of a heated area such as a barrel or nozzle. It sends a signal to a controller which then turns off or on to control the temperature of that area.
THERMOPLASTIC -A plastic material which, when heated, undergoes a physical change. It can be reheated, thus reformed, over and over again. See THERMOSET. THE THERMOSET – The plastic material when heated undergoes a chemical changes & "cures". This could not be rechanged, & re-heating only degrades this. Please see THERMOPLASTIC.
TIE BARS – Large diameter rods that connect stationary platen "A" to stationary platen "B". So the rotating platen consists bushings, which can be utilized for sliding over the tie bars, permissible the moving platen to travel between the 2 fixed platens.
THE TOGGLE CLAMP – Hence the term utilized to describe the use of mechanical "scissor action" method to open & close the clamped unit of moulding machinery. It has to controlled by the relatively little hydraulic cylinder.
TRANSITION ZONE – That area in the centre of the screw (between the feed zone and metering zone), this section has a tapering flight depth condition which compresses the plastic material in preparation for injection.
UNDERCUT – A recess or extension on the moulded part, located in such a way as to prevent or impede ejection of the part by normal moulding machine operation.
VENT – A shallow groove machined into the parting line surface of a mould in order to allow air and gases to escape from the cavity, or runner, as the molten plastic is filling the mould. Sometimes it is also located on ejector and core pins.
THE VENTED BARREL – The heated barrel modified with an automatic venting port which may permit moisture & gases has to be escaped from the molten plastic antecedent to be injected in to a moulding.
1.3 ELEMENTS OF INJECTION MOULDING MACHINE
1.3.1 Screw Nomenclature (profile)-
Figure 1.3 (b): Screw Type Injection Moulding Machine
The standard metering screw has three zones with a ring-plunger assembly. The input zone or place, so where the plastic first of all enters into the screw & has conveyed towards a fixed root
Diameter, so the intermediate zone or place, & where the plastic has conveyed, compressed & melted onward a root diameter that increases with a constant or fixed taper; & hence the metering zone area, where the melting of the plastic has finished & the melting is conveyed forward onward a constant or fixed root diameter reaching the temperature & viscosity to form parts at various research work.
Therefore the screw outline has stated as the length, in diameters or flights, of each of the 3 parts of the screw. The ten-five-five outline hint ten diameters in feed, 5 diameters in transition & 5 diameters in meter. In common purpose screws typically used a 10-5-5 profile.
1.3.2 Zones of screw-
• Feed Zone
The feed section is located under the hopper and in the rear section of the screw. Therefore the set-to depth is at its higher, & the material from the hopper fills the flight of the screw. The feed section has a constant channel depth throughout its entire length. Since the conveying action is caused by the difference in friction between the plastic and the barrel wall and the plastic and the screw, the screw is always more highly polished than the barrel. Normally, the barrel temperature is higher than the screw temperature. Consequently, the material adheres to the barrel as it softens and slips upon the cooler screw. The material is then compacted in the feed section and begins to melt. The majority of the melting occurs in the compression or transition section. In most moulding metering screws, the feed section is approximately half the screw length.
• Transition Zone
The transition or compression section where the channel depth is continually decreased completes the compacting and heating of the plastic granules. Here all the remaining air is released as a result of heat supplied by the cylinder heaters and mechanical energy supplied by the rotation of the screw.
Normally a transition zone encompasses approximately 25% of the screw length. When the material leaves the area under the hopper, it only partially fills the screw. After about four turns the material is fully compacted. The material touching the barrel melts by conduction.
Two types of heating are occurring. One is the convection of heat from the heater barrel. The second is the conversion of mechanical energy from turning the screw, into the energy, by shearing the plastic. Since the same weight of material per unit cross section must flow through the whole length of the extruder and since the
bulk density of the non-melted portion is less than that of the melted portion, the non- melted portion must be moving at a faster rate.
• Metering Zone
The metering section is also known as mixing zone helps for homogeneous mixing of the materials and acts as a pump, removing the material plasticized in the transition zone.
1.3.3 Nomenclature of Injection Mould-