Plastic Injection Molding - Injection Mold Design

Plastic materials have registered an exceptional development over the last 50 years, which exceeds that of any other consumer material.

Currently in Western Europe, the volume of production of plastic materials exceeds the production of Steel.

The growth in consumption is mainly explained by the increase in consumer products, having replaced plastics in large part, metals and glass as materials as containers for packaging, building materials, electronics, etc.

The advantages offered by plastic materials compared to other materials are the following:

·They are lightweight and, therefore, reduce transport costs.

·They are durable and often more resistant and safe.

· They can be manufactured in many shapes and applications.

·They have excellent characteristics such as thermal, acoustic and electrical insulation.

·Application in the food industry.

Plastics are standardized based on DIN 7728 and DIN 16780 for plastic mixtures.

Plastics, are organic materials technically called polymers, derived from oil or natural gas, which are carriers of molecules of carbon C, hydrogen H, oxygen O and other molecules such as nitrogen N, chlorine CL, sulfur S or CO2 Currently, only 4% of the oil is processed into plastic materials.

The plastic is extracted from petroleum by thermal distillation (cracking), in which Ethylene, Propylene, Butylene and other hydrocarbons are cleaved.

The macromolecules or plastics, are formed by multitude of simple structural units, called monomers; while the combination of these aided chemical interactions gives rise to polymers.

Fundamentals Injection Molding Process:

The process of plastic injection molding involves passing under pressure thermoplastic material softened by means of temperature, with the help of a hot piston, towards a mold placed in a press. The extraction of the moderated plastic pieces is done by opening the 2 halves of the mold once the injection process has been properly carried out.

After the retraction of the injection piston, the part must be kept for a while inside the mold so that the piece cools down to the ideal extraction temperature.

Fundamental Principles of the Injection Process:

A good injected piece can only be achieved by the right combination of Material, Machine / Process and injection mold design.

To achieve a good finish and quality in the injected piece must take into account the following factors:

· Process conditions and suitable mold temperatures.

· Injection mold design.

· Proper sizing of the machine.

· Contractions of the material and evacuation of gases.

· Suitable part thicknesses.

· Proper parts extraction process.

· Mold filling process and adequate piece cooling.

Regulation and adjustment of the injection process:

In order to achieve an adequate Injection process, it is necessary to take into account both the characteristic factors of the material and the design of the piece. The plasticizing and injection process are the most critical steps of the injection process and therefore the parameters of temperature, speed and pressure that are programmed in the machine must be controlled very well. The manufacturers recommend a range of parameters of injection temperatures (profile temperatures process and mold), piston advance speed, counter-pressure, in order to ensure an adequate injection process and avoid possible thermal degradation due to excess temperature during the process.