Injection

AEROSPACE MATERIALS

Injection

Project 4

Núria Escorihuela, Arnau Garriga, Aleix Megías

2/12/2010

Index

1. Introduction.

2. Injection Machine.

3.1. Injection unit.
3.2. Clamping unit.
3.3. Control Unit.
3.4. Mold.

3. Injection cycle.

4. Parameters that influence the injection process.

5.5.Temperatures.
5.6. Speed.
5.7. Pressures.
5.8. Distances.
5.9. Times.

5. Sealing point curve.

6. Conclusion.


1. Introduction

Injection molding is one of the most popular plastic processing technologies, accounting for a relatively simple to manufacture components with highly complex shapes.

The popularity of this method is explained withthe versatility of parts that can be made, the speed of manufacturing, design scalable from rapid prototyping processes, high cost production and low or very complex geometries that are impossible to produce with other techniques. The finished parts require very little because it has the desired surface roughness, colour and transparency or opacity in addition to good dimensional tolerance.

Itis a semi-process that involves injecting a polymer or ceramic in the molten state in a closed mold under pressure and cold, through a small hole called the gate. In that mold the material solidifies and the final piece or part is obtained by opening the mold and removing it from the cavity.

This project will study the parts of the injection machine and injection cycle in addition to consideringthe most important parameters to control. Finally, it will be discussed the use and application of the sealing point curve in the injection process.

2. Injection machine

The most important parts of the machine are:

3.1 Injection unit

The main function of the injection unit is to melt, mix and inject the polymer. To achieve this, use screws with different characteristicsdepending on the desired polymer melt.

The injection unit is originally a machine with a single screw extrusion, having the camera heaters and sensors to maintain a constant set temperature. The screw channel depth decreases gradually from the feed zone to the metering zone. Thus, the chamber pressure increases gradually. Mechanical stress, shear and compression produced by the turn of the screw,add warmth to melt the polymer system and more efficiently than if there were only warming.

During dosing spindle carrying the material back toward the front of the camera. This is where the molten polymer is accumulated to be injected. This camera acts like a piston, the screw then acts as the plunger that pushes the material.

The nozzle connects the cylinder to the mold, forming a latch toprevent the escape of material during the latter transferred to the mold.

3.2 Clamping unit

It is a mechanical or hydraulic press with a closing force sufficient to counteract the force exerted by the molten polymer to be injected into the mold. Localized forces can generate pressures of hundreds of MPa, which are only found on earth naturally only in the deepest points of the ocean.If clamping force is insufficient, the mold tends to open and the material will escape by the union of the mold. It is common to use the projected area of a piece (area unit is perpendicular to the total closure of the cavity) to determine the required closing force, excluding any gaps or holes in the piece.

F = Pm·Ap

Where:
F = Force (N)
Pm = mean pressure (Pa)
Ap =Projected Area (m2)
3.3 Control Unit

The control unit is based in a computer system that lets you change quickly and in a controlled way the variables by acting on valves and electric or hydraulic drives.

3.4 Mold

The mold is the space where the piece is generated, to produce a different product, simply changing the mold, being an interchangeable piece that is screwed into the...