Topic outline

  • General

    This course in an introduction to the Injection molding process for producing thermoplastic and metal materials. It focuses on the basic of injection molding machine and its mold, proper selection of thermoplastics, binders, metal materials, and calculations on the proposed product design. It uses CAD software for designing and modeling of the mold and uses CAE Moldflow simulation tool to optimize the correlation of the mold design with the injection molding process. Finalized design mold would be fabricated and molded parts are produced by actual injection molding machine.

  • Introduction

    This chapter is intended to provide the "hands on" injection molding personnel, the machine operators, technicians and mechanics, with an improved understanding of the basics of injection molding. Although injection molding has been used since the 1930's, the operating personnel have generally learned the process from their supervisors, who either learned from their predecessors or gained the knowledge by "trial and error." The chapter will explore the elements of the molding process at the most basic level in the hope that it will contribute to the productivity and job satisfaction of those injection molding machine personnel. The residual benefit to the managers and owners of molding operations....improved profitability.

  • Plastics

    Although a technical discussion of plastics is clearly not within the intended scope of this chapter, anyone attempting to learn the basics of injection molding must first have an understanding of the raw materials used. There are two types of plastic used in injection molding. Most injection molding is performed using thermoplastic material.  However, some injection molding uses thermoset material. There is considerable difference between the two types.

  • Additives

    In addition to the raw plastic materials discussed in the last chapter, there are a number of other ingredients that may be added to the plastic to modify its properties. These other ingredients are referred to as additives and include plasticizers, fillers, reinforcements, stabilizers, flame retardants, colorants, lubricants and many others. Although it is not vital to remember all of the various types of additives, it is essential that the molder understand the need for some of the additives and their impact on the molding process.  The more important and commonly used additives are discussed in the following pages.

  • Loaders and Dryers

    The next step in the molding process is to dry the plastic (if required) and move it from its storage location to the injection molding machine hopper. This is accomplished by one or more pieces of equipment categorized as dryers and loaders.

  • Injection Unit

    The injection unit of an injection molding machine consists of the elements shown below;

    1. Barrel
    2. Non-return Valve
    3. End Cap.
    4. Hydraulic or Electric Screw Drive
    5. Screw
    6. Nozzle
    7. Heater Bands
    8 Hopper

  • Clamp Unit

    The clamp unit of an injection molding machine performs the following essential functions:

    1. Holds the mold
    2. Closes the mold
    3. Keeps the mold closed under pressure during injection
    4. Opens the mold to allow the parts to be ejected
    5. Accommodates the ejector system which ejects the parts out of the mold.

  • Mold

    The injection mold is the element of the injection molding system that receives the molten plastic from the injection unit, forms the shape of the desired plastic part, provides the necessary cooling to solidify the part and ejects the part. Regardless of the type, molds consists of several components, each of which fulfills a vital function in  the molding of parts.

  • Control

    Most of the functions of the injection molding machine have been discussed in prior chapters, such as the clamp unit, the mold and the injection unit. in order to cause those functions to perform properly with any degree of automation, a control system on the machine is required. Because there are more types of controls than there are machine manufacturers, this chapter will discuss the types of control elements that are present on most machines. The information  presented will also differentiate between older types of machines where the controls are more mechanical and rudimentary and the newer machines where microcomputers are used to automate many of the control functions. Because controlling and monitoring are both essential elements of the control system, each will be discussed separately.