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Intelligent Injection Molding on Sensing, Optimization, and Control
The term quality has become a “catch all” term used in describing the various characteristics of an object. It is nearly impossible to define the term consistency. The quality is any particular or specific characteristics of a product development design object that contains or relates information about the object. This is primarily a chunk of geometry distinguished by its ability to perform a function with one or more other. In this primary processing conditions are studied from concept development to manufacturing of the product. Effect of different factors studied on the basis of processing parameters. Since quality and productivity are the two important contradictory objectives in any machining process. Some extent of quality has to be compromised while assurance giving for high productivity. Similarly productivity will be decreased while the efforts are channelized to enhance quality. To ensure high quality and productivity, it is necessary to optimize machining parameters. Various responses of quality of injection moulding process has been studied on the basis of performance parameters and methods. This paper aims to present plastic injection moulding process conditions. The processing conditions satisfied quality based product manufacturing.
Temperature control prevents quality issues such as shrinkage, warping and stresses from developing in the injection-molding processes.
From manufacturing personal items like toys and toothbrushes to industrial parts like plastics utilized in automobiles, injection molding is one of the most relevant manufacturing techniques in use today. This article will define what injection molding is, outline the steps involved, and explain the need for temperature control in the process.
Injection molding is a specialized manufacturing technique used for fabricating plastic parts and items. It allows for the mass production of several thousand — or even millions — of identical parts of a specific dimension and quality.
Plastic injection molding involves injecting molten plastic into a mold (or cavity), which defines its molded part’s shape after it solidifies. The basic requirements for the process are the injection-molding machine, raw plastic material and the mold.
The injection-molding machine consists of a hopper, through which pelletized plastics are fed into the machine; a heating barrel with a reciprocating screw; and an injection nozzle. The most common thermoplastics utilized in injection molding are nylon (PA), polycarbonate (PC), polypropylene (PP) and acrylonitrile-butadiene-styrene (ABS). Molds used can be single- or double-cavity type, depending on the application.
Tooling Investment Costs. When a electric car mould part is being manufactured for the first time, the design is first prototyped with a test material to ensure accuracy using techniques such as 3D printing or CNC machining. The mold tool is made of steel or aluminum material and must be designed to precise dimensions.
Prototyping and Testing. With injection molding, manufacturing companies must carry out extensive testing and prototyping of the entire system using replicas. Any subsequent modifications to the final design will require either modifying the tools or scrapping them completely — both of which could add significant costs to the production budget.
Size and Thickness Limitations. Because injection-molding machines and molds typically have limited sizes, injection molding may not be suitable for designing large plastic parts. Also, injection molding tends to create mostly molded parts of a uniform thickness. This characteristic may be undesirable to some manufacturers that require variation in this aspect. This is because injection-molded parts must be created with a sufficient wall thickness (at least 1 mm) to prevent problems with filling the mold.
Many manufacturers use cooling tower water to cool the small channels within the mold with a temperature regulator attached to the injection-molding machine, regulating its temperature. While this technique is effective and incurs a lower operating cost, the mold will be prone to contamination. Cooling towers are open-loop systems. By contrast, an industrial chiller can be used to regulate the temperature via closed-loop cooling, ensuring a higher degree of product purity.
When plastics for the injection-molding process are being heated and mixed inside a machine, a specific temperature limit must be maintained as the temperature of the process will directly impact the quality of the final mixture.
If the temperature is too low, the components may not mix properly. Alternately, when the temperature is too high, the mixture might become burned. Thus, there is typically an ideal point, or a prescribed temperature at which the process must be maintained.
Mold Temperature. The temperature of the precision mold is another essential consideration that affects the quality of the injection-molded part. Getting the best quality mold is a balance between heating the mixture sufficiently to create a homogeneous mixture and cooling it down at an ideal rate. Anything else would be undercooling or overcooling.
Undercooling and Overcooling Issues. Improper polymer flow is a direct consequence of under- or overcooling issues in plastic injection mould. When the mixture is not cooled sufficiently, it may not solidify completely before being ejected. This may leave residual plastic in the mold.
Conversely, excessive cooling causes a lack of uniformity in the plastic material. This may cause further problems down the line such as shearing, cracking and cavities that do not fill up completely. Maintaining the mold temperature at a set temperature will yield the most optimum results.
Temperature Control with an Industrial Chiller System
Close tolerance temperature control units can be used with industrial chiller systems to provide close temperature tolerances for process water. When combined with a compatible and suitably sized industrial chiller, the temperature control unit can maintain the process temperatures at ±0.5°F of the set 33°F value, ensuring a stable injection-molding process without catastrophic freezing failures.
The close tolerance temperature control units come in varying flow variations and configurations and standard models have a pump and heat exchanger with a jacketed tank or a heat exchanger.
Plastic moulding is the process of pouring liquid plastic into a certain container or mould so that it hardens in that customized shape. These plastic moulds can then be used for a wide range of purposed. There are 5 types of plastic moulding that is considered to be the most effective and most popular.
These 5 types are extrusion moulding, compression moulding, blow moulding, injection moulding and rotational moulding. We will look at the details pertaining to each of these methods so that you can decide which one will be the most effective for you to use.
1. Extrusion Moulding
With extrusion moulding, hot melted plastic is pressed through a shaped hole to create a lengthy shaped plastic part. This customizable shape that the liquid plastic gets pressed through is called a die. This die is custom made for the particular outcome that is desired. It is almost like pressing dough through a press to make shaped cookies.
The other forms of plastic moulding also use extrusion so get the raw liquid into the commodity mould, the difference here is that other methods use the moulds to make the desired shape and here the extrusion itself is making the shape with the use of the die’s shape.
When using this method your outcome product will continuously have the same shape along the length of it. These can be things like straws or PVC pipes. These types of parts can be made at very high volumes because it can just keep producing the same shape without end.
In comparison, this type of moulding is low cost because the equipment is fairly simple and can have high productivity. The downside to this method is that you are very boxed in when it comes to the variety of parts you can make.
Injection molding is one of the most significant material processing methods for mass production of plastic products. It is widely used in various industry sectors, and its products are ubiquitous in our daily life. The settings and optimization of the injection molding process dictate the geometric precision and mechanical properties of the final products. Therefore, sensing, optimization, and control of the injection molding process have a crucial influence on product quality and have become an active research field with abundant literature. This paper defines the concept of intelligent injection molding as the integral application of these three procedures—sensing, optimization, and control. This paper reviews recent studies on methods for the detection of relevant physical variables, optimization of process parameters, and control strategies of machine variables in the molding process. Finally, conclusions are drawn to discuss future research directions and technologies, as well as algorithms worthy of being explored and developed.
The Society of the Plastics Industry (SPI) has reported that, in the United States, the plastics industry is the third largest manufacturing industry. In 2017, the US plastics industry accounted for $432.32 billion in annual shipments and directly employed nearly one million people [1]. Hence, the plastics industry has a large contribution to the nation’s economy. Plastics are now among the most widely used materials and their use covers the entire spectrum of industries worldwide [2]. Injection molding is regarded as the most important and efficient process used to manufacture plastic products. It accounts for approximately 80% of the plastic merchandise in the modern plastics industry [2], and as such, it is one of the important pillars of the manufacturing industry. As a highly complicated process, plastic injection molding can be divided into three stages: filling, packing, and cooling. During the entire process, the polymer is subject to large and dynamic changes in pressure and temperature. The whole process is complicated because the process variables are strongly coupled and hard to analyze accurately. For now, manufacturing of qualified products by injection molding still mainly relies on manual operation and trial-and-error methods [3–5]. Obviously, this traditional approach has disadvantages of low production efficiency, poor reliability and repeatability, and dependence on prior experience. Therefore, it is imperative and crucial to develop an advanced injection molding method that is science based and technology oriented.
Recently, much attention has been focused on intelligent (smart) manufacturing, which represents an in-depth integration of next-generation artificial intelligence (AI) technology and advanced manufacturing technology. It runs through every link in the full life cycle of design, production, product, and service [6]. Intelligent injection molding refers to the production process that employs AI technology—such as extracting information from production, computer optimization methods, and control strategies—to develop an online production optimization system. Through the comprehensive use of sensing, optimization, and control methods, the intelligent injection molding production process can increase production efficiency and product quality.
During the production process, when material and mold are preselected, an intelligent injection molding method is required to obtain high quality and stable production. As shown in Figure 1, intelligent injection molding contains three phases—sensing, optimization, and control—all of which are interrelated. Process sensing is first needed to realize real-time detection of variables from the injection-molding process and further on to diagnose and guide the manufacturing process. Moreover, optimal process parameters should be determined by process optimization since it is the key to obtaining high-quality injection molded products with high precision. Finally, sufficient machine control accuracy and repeatability—which means robust control over machine parameters—are required. Furthermore, advanced control strategies will help to conserve energy in manufacturing [7]. Integrating these three phases into an effective online quality control model, which is the section in the dotted-line frame in Figure 1, is one of the major goals of intelligent injection molding. It has attracted extensive attentions from many researchers in the field of injection molding.
In a 2005 review article, injection molding control [8] after process setup was classified into three levels—machine control, process control, and quality control. Due to the lack of quality sensors and the process and quality relationship model, there is a potential opportunity for advancement in the optimization and control of the product quality in injection molding. Moreover, with further development of science and technology in injection molding, and the fact that there has been very little review of process sensing, this paper aims to review and summarize the research on intelligent injection molding in recent years. It will focus on sensing, optimization, and control so that readers will be able to obtain useful information and an overview of the intelligent injection molding process. This paper is outlined as follows. Section 1 provides a brief introduction of intelligent injection molding. Sections 2, 3, and 4 discuss sensing, optimization, and control methods for the injection molding process and present up-to-date developments in these fields. The last section provides a summary of and future directions for intelligent injection molding.
The sensing of the injection molding process is focused on the temperature, pressure, position, speed, etc., which reflect the physical state of the process. Temperature and pressure are the two fundamental physical variables that are the most important in the injection molding process. Furthermore, among various sensing technologies, temperature and pressure sensors are the most well developed and the most widely utilized. By means of sensing the temperature and pressure, one can obtain abundant information about the mold and polymer melt. With continuing technology development, some new methods have emerged in the field of injection molding. Some of them are capable of characterizing more variables besides temperature, pressure, position, and speed. This section will briefly introduce the conventional and emerging methods used in injection molding processes and the up-to-date research progress. Finally, a conclusion and analysis will be put forward and discussed. |
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