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A Guide to

Injection Moulding of Plastics


Contents at a glance


PART I: MACHINE for Injection Moulding

PART II: INJECTION MOULDING PROCESS

PART III: QUALITY RELATED PROBLEMS

PART IV: ENGINEERING and; TECHNOLOGY

PART I: MACHINE for Injection Moulding

Overview of Injection Moulding of Plastics

This chapter lists topics that you should know to understand Injection Moulding process in-depth. It discusses about the advantages and disadvantages of this process.

Injection Moulding Machine

This chapter describes basics of Injection Moulding Machine, various design options (Injection and; Clamp units) available in the markets, modular design, Tie-bar-less machine, All electric machine, Developments in machine controls, quick change system and automation. Power saving and achievable accuracy with all electric machines.

Screw Plasticating

This chapter discusses screw plasticating, screw geometry, influence of various elements of screw design on quality of melt and various types of screw. It explains the influence of metering stroke on homogenety of melt.

Guidelines for Selection of Machine

This chapter exlains significance of machine specification, the reason for different maximum shot weight for different material for a given machine, Significance of percentage shot capacity utilisation, Intensification ratio, Injection power and connected power, Method of calculating clamp force etc.

Support Equipment and; Service lines

This chapter describes support equipment for polymer handling, scrap reclaim, Mould temperature control and Part handling. It discusses the estimation of service line capacity requirement for cooling water, chilled water and compressed air.

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PART II: INJECTION MOULDING PROCESS

Polymer Characteristics

This chapter discusses all the characteristics relevant to processing like MFI, Melt viscosity, Shear thinning, moisture, significant temperatures, Shrinkage, Maximum flow ratio, Crystalline and amorphose, pvT relationship, Process limitation imposed by the characteristics for various polymers.

Injection Rate

This chapter explains the significance of injection rate, freezing time and Melt flow mechanism.

Screw RPM and Back Pressure

This chapter explains the significance of Screw RPM and Back Pressure and Screw surface speed / Peripheral speed. It explains relationship between Screw RPM and Screw Diameter.

Process - Cavity Pressure Profile

Cavity pressure profile describes the moulding cycle. It explains methodology for setting speed and pressure profile.

Process - pvT Diagram

This chapter explains the significance of pvT relatioship in processing and methodology for speed and pressure profile.

Maximum Shot Weight

It explains the logic behind the shot weight calculation for different polymer.

Residence Time and; Thermal Stability

This chapter highlights the significance of residence time in the process. This limitation in processing is set by the time dependent Thermal Stability of the polymer.

Barrel Temperature Profile

This chapter explains the logics behind the barrel temperature profile. It explores the heat sources and baancing of heat sources and explains the various types of barrel temperature profile.

Mould Temperature and; Cooling

It discusses the importance of heat balancing required in the mould and need for well thought out design of cooling circuit. It enables you to see the mould in terms of isothermals.

Cycle Time and; Productivity

It explains dependeance of producitivity is on the three balancing tricks involving good part design and mould design (Cooling circuit).

Trouble Shooting

This chapter provides tips on trouble shooting. It also describes steps for machine setting.

Overview of Process Setting

This chapter provides tips on process setting. A table of typical process parameters for various material could be very useful. A Table explains limitations for cooling time reduction.

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PART III: QUALITY RELATED PROBLEMS

Overview of Quality

This chapter lists the factors relevant to achieve quality mouldings and provides overview of design related quality problems which can not be corrected on moulding machine. It lists the problems in performance of plastic parts and comes to the conclusion that stress cracking is the major cause of plastic part failure. It is related to part design and selection of right material.

Sink Mark

This is the part design related problem. The temperature dependent volume change in polymer melt is not compensated by volume change due to compressibility of melt in side the mould. Therefore part should have uniform wall thickness.

Warpage and; Mould Cooling

Reasons for warpage is discussed in this chapter.

Shrinkage

Dimensional changes of an injection moulded part in course of time, Influence of process paramer on shrinkage, Various factors influencing tolerance, are explained in this chapter.

Stress Cracking

Stress cracking is the main cause of plastic part failure. It happens when moulded-in stresses are present on the part in the aggressive environment of chemicals. If you remove one of then - moulded-in stress or the chemicals, then the part failure does not occur.

Weld Lines

This chapter describes how to strengthen weld line and also how to shift weld lines to convenient position.

Orientation

This chapter describes the factors influencing degree of orientation.

Moulding Quality

This chapter highlights the moulding constrains and contribution of part design and mould design in achieving quality of mouldings. It discusses the tolerance possible with moulding and the role of machine in the process.

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PART IV: ENGINEERING and; TECHNOLOGY

Mould

All types of moulds, gates, runner system, cavity layout etc. are described in details in this chapter. Various check lists, mould design tips, cooling systems, ejector mechanism, core pull, steel for mould, heat teatment tips are also provided.

Hot Runner Mould

Features of hot runner system, Comparision of Terminology of various manufacturers, Manifold expansion under heat, Various types of gate nozzles are included in this chapter.

Mechanical Failures in Mould

Reasons of mechanical failures and significance of Fatigue failure are discussed in this chapter.

Energy Efficiency

Various strategy of energy efficiency, Comparative energy consumption of various power system and machines are discussed in this chapter.

Testing of Machine

This chapter highlights the inspections to be carried out while taking delivery of the machine.

Technology

Here Technology is defined and technology of part design (CAD and; CAE), mould design (CAD), mould manufacturing (CAM), machine's microprocessor control features, Advantage of CAE analysis, etc. are discussed.

Robot

This chapter explains robot terminology, its classification, its limitations and scope for automation in moulding shop.

Multi Component Moulding

Two colour moulding and Compatibility of different polymers are discussed in this chapter.

Gas Assisted Moulding

Various techniques of Gas injection moulding, Machinery and trouble shooting are discussed in this chapter.

Thermoset Injection Moulding

Theory behind thermoset injection moulding is discussed in this chapter.

Myths and; Truth

General belief prevailing is listed and the truth is explained.

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HOME-book

Foreword Preface Contents Introduction Summary
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