What is injection molding machine | definition | types | advantages , disadvantages and applications | - kcrtoy

Introduction

Injection molding is a major processing technique for converting thermoplastics, and  thermosetting materials, into all types of products. Approximately 25% of the 13 billion pounds of thermoplastics sold in the United States in 1971 were injection molded, and about 36% (4320) of the 12,000 processing plarnts in the United States injection molded. Furthermore, in 1970 about 5O00 injection molding machines were purchased in this country which brought the total of injection machines in-place to about 58,000.

Definition “Injection molding is a forming process using molds. Materials such as synthetic resins (plastics) are heated and melted and then sent to the mold where they are cooled to form the designed shape”

 Since there were 130,000 processing machines, injection machines represent close to 45% of all processing units. Sixty percent of the machines use a reciprocating screw, 35% a plunger (concentrated in the smaller machine sizes), and 5% a screw pot.

Cost of the machines

 This reinforces the fact that only 20% of those responding to the survey indicated that obsolescence was important. The average plant had 12.5 machines. Custom molding plants tended to cluster in 12 machine units (12, 24, and 36 machine plants), as this is an economical management unit. The average age for smaller machines was 6.3 years, for medium size machines S.0 years, and for larger machines 4,8 years. Also 52% of injection molders processed plastics by another method, and 20% used two or more different processes. In view of the high capital cost of injection machinery, it is surprising that for all plastic processing plants, 24% worked one shift, 18% two shifts, and 58% three shifts.

History

 The process is not new. John and Isiah Hyatt received a patent in 1872 for an injection molding machine, which they used to mold camphor-plasticized cellulose nitrate (celluloid). In 1878 John Hyatt introduced the first multicavity mold. In 1909 Leo H.Backeland introduced pheno-formal dehyde resins which are now injection moldable with the screw molding machine. The experimental and theoretical works of Wallace H. Carothers led to a.  General theory of condensation-polymerization that provided the impetus for the production of many polymers, including nylon. At the end of the 1930% modern technology began to develop and great improvements in material permitted injection molding to become economically viable. A similar advance it machine technology is developing now.

Four basic part of the injection molding

·        Plasticizing and injection system

·        Clamping system

·        Ejection unit

·        Electrical and hydraulic control system   

Types of injection molding machine

Machines vary in size and mode of operation Some of themost common types of injection molding machine are describe in below

Hydraulic machines use hydraulic forces to inject the short of plastic and to exert clamping forces. They can create very high clamping forces

Electric injection molding machines use servo motors to control injection clamping forces. They are fast and energy efficient

Vertical injection molding machine can be hydraulic, electrical, or hybrid, and take up a smaller footprint due to their orientation. They are highly suited to insert molding

Desktop injection molding machine are low cost molding machine suitable for simple diy plastic product. They lack the clamping forces and high precision of industrial machines

Material use in injection molding

             Mainly two types of materials are use in injection molding process

1)                Thermoset plastic

2)                  Thermoplastic

Advantages of Injection Molding

·        Parts can be produced at high production rates

·        Large volume production is possible

·        Relatively low labor cost per unit is obtainable

·        Process is highly susceptible to automation

·        Parts require 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 of 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 reused

·        Same item can be molded in different materials, without changing the

·        machine or mold in some cases

·         Close dimensional tolerances can be maintained

·         Parts can be molded with metallic and nonmetallic inserts

·         Parts can be molded in a combination of plastic and such fillers as 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.

 

Disadvantages and Problems of Injection Molding

·        Intense industry competition often results in low profit margins

·        Three shift operations are often necessary to compete

·        Mold costs are high

·        Molding machinery and auxiliary equipment costs are high

·        Process control may be poor

·        Machinery that is not consistent in operation, and whose controls are not

·        directly related to the end product

·        Susceptibility to poor workmanship

·        Quality is often difficult to determine immediately

·        Lack of knowledge about the fundamentals of the process causes problems

Application of injection molding

• Medical and pharmaceutical

• Food and Beverage

• Automotive parts

• Household product

• Agriculture

• Electronic parts