Injection Molding Basic & Systematic Mold Proving ①

1. Introduction

The invention of plastic, which is a miracle material in the 20th century and greatly affected human life, as well as the development of an injection molding machine significantly contributed to the development of various products and industrial advancement. On the other hand, the domestic circumstance of South Korea was a pity because the injection molding technology, which is for mass-production of the molded products, was not designated as the Ppuri Industry* such as a metallic molding, nor there was no or lack of the specialized institution for systematic educational unlike other industries, as well as, no tests were available to qualify the specialists such as an engineer and a professional engineer. However, it is worth expecting a change at this time since the 8 categories were additionally included in the Ppuri Industry Act, which was completely revised by the government from the existing 6 categories.

* Definition of Ppuri Industry

The term, Ppuri Industry, was stemmed from the meaning that it forms a foundation of competitiveness in the manufacturing industry by being inherent in the final products even if it is not revealed like the roots of a tree. Ppuri Industry includes the fundamental processing industries that produce parts or complete products such as casting, mold, welding, plastic working, surface treatment, and heat treatment, etc. 

The existing root technology included major 6 processing technologies that utilize metallic materials such as casting, molding, etc. It has strategies of expanding the digitalization of Ppuri Industry in response to the 4th Industrial Revolution including the emergence of new raw materials and lightweight tendency, the demand-tailored high value-added technology in order to widen the global value chain(GVC), the improvement of increasing corporate competitiveness, and the establishment of the base in next-generation root base.                  

In line with this, under the vision of "cultivating the root industries for turning to the future-oriented structure", the central government of South Korea will escape from the industrial structures with labor-intensive and low valued-added natures and prepare the “2021 Action Plan for Ppuri Industry promotion” through focusing on the 4 main domains as shown in the table below to actively foster them by investing the government funds.

However, it has been a long time that the technicians who mastered molding skills in the injection molding industry have not been treated fairly, and moreover, from some point, most manufacturing works have been deemed as the 3D industry that implies difficult, dirty and dangerous, thereby no more new entry of young people and causing a replacement by the short-term foreign workers. In this perspective, it is a fact that the small and medium-sized companies in the injection molding industry designated as root industries look more pitiful at this time.

Despite the technologies and human resources in the plastic injection molding domain, which play the most important roles in developing products even in Industry 4.0, or the smart era, are absolutely needed acquiring the good talented resources to properly operate the injection molding plants is as difficult as picking a star in the sky because companies are going abroad with a stream of the recent globalization.

As having been known well, nothing is easy in the conditions and processes of injection molding for mass-production of the molding products with good quality. It is a fact that the technicians in the molding field having worked in the injection companies are manufacturing the molding products by setting their own molding conditions that they have learned from the seniors and experienced through trial and error. In other words, it is a widely accepted theory that no principle exists in the setting of injection molding conditions.

In the future, if the condition setting is automatically available by linking the injection conditions, which were produced by the injection molding analysis based on the characteristics of the resin used, designs of molding products, a mold and an injection molding machine, with the injection molding machine, and on top of the above mentioned, if the optimal injection conditions by Artificial Intelligence, Deep Learning, Machine Learning, and Big Data that conform to Industry 4.0 are added, it is anticipated that the day having no defective products anymore will not be too far away because of establishing the system to perform a mass production with good quality and enabling the adaptive control when the injection molding conditions of the machine are changing.  

While expecting the day to come true, it is hoped to establish a foundation that can minimize defective products in the future by actively employing the "basic principles of injection molding conditions and systematic molding tests" elaborated in this series of materials that can comprehensively address these issues.

2. Injection Molding Process

A machine variable is a setting value that is entered directly into an injection molding machine or an additional device to obtain the molding product with the required characteristics. It doesn’t allow the transmission of absolutely equivalent mutual data between the production conditions to another machine and the characteristics of molding products. The relationships between machine variables and mold process data are the same in terms of tendency, but the relationships between machines are absolutely different. Furthermore, those can be altered over time due to wear on screws, screw tips and hydraulic components.

A process variable refers to the variables related to an injection molding process from the perspective of producing the molding products within a mold cavity such as pressure, temperature, time, and mold wall temperature of molten materials. Process variables are the independent terms of a machine, which can actually be discovered and transmitted. The molding products have the same characteristics only when a process variable has reproducibility.

Internal characteristics are information associated with an internal structure of a molding product such as molecular weight, orientation, internal stress, and crystallization degree of raw material as well as the distribution and orientation of the additives.

The external characteristics of a molding product are functional characteristics such as dimensions, tolerances, shape, surface degree, and the mechanical, optical, and electrical characteristics of a molding product.

In the injection molding process of a specific machine, the process data are the important results obtaining from the setting values, injection molds, and plastic materials used. These can be measured and stored at the stages of individual works, thereby being employed for further evaluation and monitoring.

The followings are the most frequent hurdles in the injection molding process.

·         Changes in temperature and viscosity

·         Quantitative changes in measurement

·         Incorrect behaviors of screw tip

These factors can be recorded by process data and are used to ensure the quality of the molding products.

It is essential to know when, where, and how the process variables are measured in order for them to be evaluated correspondingly and to understand the conclusions about the disturbing factors. Thus, it is necessary to shed more closely light on the works and molds as well as the functions of an injection molding machine.

* Source: www.lsinjection.com