Document Description

 Utilizes a ram or screw-type plunger to force molten plastic material into a mold

cavity

 Produces a solid or open-ended shape that has conformed to the contour of the mold  Uses thermoplastic or thermoset materials

 Produces a parting line, sprue, and gate marks  Ejector pin marks are usually present

3.2.1 Introduction

Purpose:

The purpose of the injection molding is used to produce thin-walled plastic parts for a wide variety of applications, one of the most common being plastic housings. Plastic housing is a thin-walled enclosure, often requiring many ribs and bosses on the interior. These housings are used in a variety of products including household appliances, consumer electronics, power tools, and as automotive dashboards. Other common thin-walled products include different types of open containers, such as buckets. Injection molding is also used to produce several everyday items such as toothbrushes or small plastic toys. Many medical devices, including valves and syringes, are manufactured using injection molding as well.

Scope:

Injection molding is used to create many things such as wire spools, packaging, bottle caps, automotive dashboards, pocket combs, some musical instruments (and parts of them), one-piece chairs and small tables, storage containers, mechanical parts (including gears), and most other plastic products available today. Injection molding is the most common method of part manufacturing. It is ideal for producing high volumes of the same object.[5] _{Some advantages of injection molding are high}

production rates, repeatable high tolerances, the ability to use a wide range of materials, low labor cost, minimal scrap losses, and little need to finish parts after molding. Some disadvantages of this process are expensive equipment investment, potentially high running costs, and the need to design moldable parts.

Summary:

There is no mystery in injection moulding of plastics. Each and every phenomenon has its scientific reasons. Since injection moulding involves Polymers, Mould and Machinery, it is necessary to understand all of them; their role and their limitations. We explore in this book

–Cavity pressure profile, pvT diagram, Shear thinning of plastics, Flow mechanism- simultaneous flow and freeze of melt with skin formation and fountain flow.

We also appreciated the root cause of most of the quality problems lie with three balancing tricks in the process.

• Flow balance in part,

• Heat balance in mould,

• Uniform freezing in mould.

• Moulding process in this book is not discussed in lay man's point of view but it is discussed in terms of physics of plastic melt, which is best described by pvT characteristic, shear thinning characteristic and orientation characteristic of melt.

• This book provides technical perspective to the process that is relevant to

understand CAE technologies. You can develop skills to visualise the happenings inside the Screw-Barrel and inside the Mould. This knowledge can help you to understand the root causes of all the quality related problems.

• Very vital information are provided with figures and tables about Screw Design, Machines, Support Equipment, Service lines, Injection Moulding Process, Quality related Problems, Mould, Hot Runners, Mechanical failures in Moulds, Energy efficiency, Testing of Machines, Robot, Multi-component Moulding, Gas assisted Moulding, Thermoset Moulding, CAE, CAD, CAM Technology. A chapter on Myths and Truth clarifies the most misunderstood aspects in the industry..

3.2.2 System Overview

Injection molding of plastics is one of the most cost effective processes for manufacture of parts in volume. While mold costs can be significant, amortization over many parts can make the overall cost of injection molding highly competitive with other manufacturing processes. The wide range of available polymers multiplied by the huge array of specific blends offer a tremendous range of physical, thermal, electrical, and chemical properties. Engineering plastics, classified by mechanical properties such as stiffness, toughness, and low creep, increasingly replace metals on a cost and performance evaluation. Designing for injection molded plastics requires planning. Too often parts will be presented to a molder or tool designer late in the product development process only to be confronted with feasibility issues. If that happens the developer faces decisions to rework part designs or to face higher tooling and part costs. Leaving design for manufacturing and assembly (DMFA) considerations until late in the development program is a common mistake the misses out on optimization and disrupts the transition to manufacturing. Planning begins in preliminary design. Some will argue that consideration for manufacturing early in the program will inhibit creativity; the reality is that it does not if perspectives are kept in balance. In fact design committee often err in committing to a design that later reveals feasibility and cost issues. While designers and engineers need to be free to brainstorm potential solutions, taking time to evaluate for manufacturing options

Design concept modeling is a vital step in preliminary product design. Form and function can be evaluated in blocked-out quick CAD studies. Drawings produced from 3D CAD model studies can help evaluate the size, cost, and architecture of a proposed design. Multiple preliminary model studies are a good use of time because many factors can be evaluated after a few hours of work. Such studies can include component packaging, part break out, and overall size and weight. Concept parts can be submitted for preliminary price quotations. DMFA (design for manufacturing and assembly) has become a hot buzz word in product development the truth is that consumer products manufacturers have been doing DMFA for decades as a means of competitive survival. Injection molding is particularly advantageous for assemblies wherein components can be mounted using ribs and bosses inside the shell of the parts allowing to easy assembly most commonly using screws, push nuts, snap latches, or heat staking. Components are commonly captured between two shells. Consideration for assembly procedure in part design is critical to reducing cost and boosting assembly line yields. In many industries, cost competitiveness is key factor in market success. Secondary assembly operations can include sonic insertion of threaded fasteners and plastic welding operations such as thermal welding, ultra-sonic welding, spin welding, vibration and laser welding. Consumer product industries were the first to focus on aesthetics for competitive advantage wherein one product would out-sell another primarily because of form and function. The field of Industrial Design sprung up wherein artistic individuals entered into product design realm bring their drawing, rendering, model sculpting skills and aesthetic sensibilities into the product development process. Early pioneer Raymond Loewy in the 1930s came from the fashion industry and proved to be a fastidious designer with great attention of detail and construction. Solid modeling CAD systems offer powerful 3D (three dimension) surface modeling capabilities that can satisfy high expectations for appearance in the field of Industrial Design. Surface modeling provides the tools to capture complex surface geometries for seamless data transfer to machine tooling operations for injection molding. CAD data is captured electronically and interpreted by CAM (computer-aided-machine) operations. CAM software programs define specific cutter tool paths for efficient and accurate cutting of mold cores and cavities. CAD/CAM processes can capture virtually any surface configuration that a designer envisions. CAM data is used for CNC (computer- numerical-control), EDM (electro-discharge-machining or spark erosion) and wire EDM cutting methods.