The development of new injection molding technology overview

The development of new injection molding technology overview---------------- Sichuan University College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering References
Abstract: The recent development of injection molding technology, introduces the new gas-assisted injection molding, multi-component injection molding, powder injection molding, microcellular foaming injection molding, micro injection molding and other technical features and the latest trends.
Polymer forming methods are extrusion, injection molding, blow molding, calendering, pressing, etc., which can be produced by injection molding and manufacturing shapes more complex products, and computer technology combined with easy, easy to automate production, etc., in the polymer material forming occupies an extremely important position. Injection molding is widely used in automobiles, home appliances, electronic equipment, office automation equipment, building materials and other areas. In recent years, the rapid development of these industries to the development of injection molding technology provides a powerful impetus to the development of injection molding technology in the speed, level of development have been rapid, especially for injection molding of new technologies to develop more is to play a strong role. This article looks at the latest injection molding technology developments, describes several use the more extensive injection molding technology. In recent years, injection molding of new technology developments focus on: new gas-assisted injection molding technology, multi-component injection molding technology, micro-foam injection molding technology, micro-injection molding technology and so on.http://www.prmindustry.com/Abstract...Articles section A new gas-assisted injection molding
     Gas-assisted injection molding (Gas-assisted InjectionMolding Technology) is a self-reciprocating screw injection machine since the advent of injection molding technology is one of the most important development. It is through high-pressure gas in the hollow plastic parts internally generated cross-section, the use of gas backlog, reduce the residual stress products, eliminating the product surface sink marks, reduce the use of materials, showing the traditional injection molding can not match advantage. General gas-assisted injection molding process is: first injected into the mold cavity through the accurate measurement of the plastic melt, and then injected directly into the compressed gas; gas surrounded by the plastic melt in the direction of least resistance along the forward spread of the plastic melt to penetrate and emptying, as full of power-driven plastic melt the plastic melt to the mold cavity and packing until the product solidified after cooling mold ejection. In recent years, gas-assisted injection molding technology is developing rapidly, there are some innovative technologies, such as water-assisted injection molding, gas-assisted cooling gas technology, gas-assisted co-injection molding technology, the external gas-assisted gas-assisted injection molding technology and vibration technology.
     1.1 Water-assisted injection molding
    Water-assisted injection molding (Water-Assisted Injection Molding Technology) is the University of Aachen, Germany, represented by the Institute of Plastics Processing researchers developed based on principles of gas-assisted injection molding out of the new injection molding technology. As the gas heat capacity is relatively small, poor thermal conductivity, gas-assisted injection molding, parts equivalent to one-sided cooling, so its injection molding cycle is often longer than the average. Water-assisted injection molding technology works with gas-assisted injection molding technology is basically the same, but with water instead of gas injected into the molten center. The process is: (1) melt filled cavity, a short dwell; (2) the melt water into the center, under the pressure of the water, melt back back to the parts center injection system; (3 ) after a period of time packing, vacuum the water from the parts. Drainage required pressure generated by the evaporation of water, adding water or by evaporation of CO2 produced. 30mm in diameter in the injection molding of PP hollow parts of the comparative tests found that water-assisted injection molding cooling time than the gas-assisted injection reduced by 75%. Forming process in accordance with the different water-assisted injection molding with short (less material injection) method, reflux method, the overflow method and four kinds of process flow method [1].
     1.2 cooling gas gas-assisted molding technology
      In the gas-assisted injection molding process, although gas-assisted molding plastic parts to reduce the wall thickness, but in the process, the cooling stage in the molding cycle, the largest proportion. When the gas (nitrogen) through the plastic, its cooling effect is very small. If the products in the mold cooling is not sufficient, then the residual heat will be formed within the surface recrystallization, resulting in lower product quality or distortion, severe air bubbles will appear when the product inside. To avoid the above happening, you can take to extend the mold cooling time or sub-cooling measures, but will increase costs. Cool gas-assisted molding technology for the above problems is the emergence of a new gas-assisted injection molding methods. In the cooling process in gas-assisted molding, gas is usually cooled to -20 ℃ ~ 180 ℃. Cooling gas formation process are: temperature gas through a chamber in which was cooled by liquid nitrogen. This cool gas-assisted molding technology, the main advantage: When the cooling gas through the melt, in the mold cavity will have a plug flow effect, plug flow generated by the residual wall thickness than conventional gas-assisted molding should be small; cooling gases to prevent a blistering internal parts, and can produce more smooth inner surface [2].
     1.3 Total gas-assisted injection molding technology
     Total gas-assisted injection molding technology (Co-Injection and Gas-Assisted Injection Molding) is a polymer of gas-assisted injection molding technology and a combination of technology and get a new process. Polymer co-injection molding technology is at the same time or successively injected into the mold cavity to different polymer melt to form a multi-layer structure of a molding technology, and sharing the injection molding process compared to more than a gas injection process; relatively gas-assisted injection molding concerned, is more of a multi-layer structure formation [3-5].
    Total gas-assisted injection molding process involves three stages: (1) Co-injection phase. This stage and the general co-injection molding process is similar, except in the form table / inner structure, when the inner surface and the total amount of material into the cavity of a certain percentage of the total volume, stop injection melt, this process can be described as gas-assisted process "material injection due to" just melt into two or more; (2) gas-assisted injection molding stage. Melt through the inner gas, with the advance of the gas, the gas was "crowding out" of the inner surface of the melt and bring forward the melt flow; (3) holding pressure cooling, release pressure stripping, access to products. In order to achieve a total polymer gas-assisted injection molding, must be the original co-injection molding equipment modified, that co-injection molding equipment, based on the increase of a gas-assisted system.
     1.4 external gas-assisted molding technology
      External gas-assisted injection molding (External Gas Molding Technology) is a traditional internal gas injection molding, a gas-assisted injection of different ways. Conventional gas-assisted injection molding technology is the gas within the melt to form hollow plastic parts or pipes, while the new gas-assisted injection molding technology is the gas injected into the mold cavity surface of the partial sealing position (equivalent to melt the plastic outer), so called "external gas injection" [6].
     Vibrating gas-assisted molding technology 1.5
     General gas-assisted injection molding process is non-dynamic shape, and vibration gas-assisted injection molding (Vibrated Gas-Assist Molding) process is to introduce the biggest difference vibration wave, the conventional gas-assisted injection molding into a "steady-state gas" into a certain vibration strength "dynamic gas", which use gas as the medium of vibration force field introduced into the gas-assisted injection molding filling, packing and cooling process, making it a dynamic forming process [7].
     2 Multi-component injection molding
     Multi-component injection molding (Multi-Component Injection Molding) by at least two different materials by injection molding to obtain the required components of the process, the integration of the components of superior performance, can produce an ordinary single-component injection molding process can not be achieved exceptional performance products. This consists of two or more kinds of material composition of products, from a material with conventional injection molding products have different physical properties compared. Multi-component injection molding is unique in that [8]: (1) may be different processing characteristics of the material composite molding; (2) increase the feel and appearance of products, a variety of performance in one set; (3) to shorten the product design, production and cycle time, reduce costs; (4) omit the traditional injection molding, secondary processing and assembly process.
    More than 2.1-component injection molding process
      Currently, there are multi-component injection molding of plastic injection molding, sandwich molding, two-color injection molding, overmolding, multi-color injection molding techniques [9], according to the various components in the molding process with its different forms, can be divided into sequential injection molding injection molding and stacking two categories.
     2.1.1 order injection molding
       Sequence is followed by injection molding process the material, this process is through a special multi-component nozzle to achieve. The process is first injected into the cavity in the molten composition to form the first product surface, and then switch the multi-component nozzle switching valve, injection of the second component, the formation of products of the core part of the process shown in Figure 1 . Sandwich on the common two-component injection molding, the two components can be a complementary aspects of performance, and avoid weaknesses, in order to achieve single-component products can not get the performance. Order of the most widely used injection molding has the following three categories: (1) for large volume products, core to use recycled materials, while the outer layer of decorative role of new materials; (2) required to withstand bending stresses and other loads of products, Use the outer layer of glass fiber reinforced materials, and the kernel can be used non-reinforced materials; (3) For thick-walled products, often made use of its core foam material2.1.2 stack injection molding
     Injection molding process is superimposed by a different gate or runner will be a variety of components (usually two) injection together, or one component superimposed on top of another component. Compared with the sequential injection molding, the mold is part of the key improvements and changes. Superposition of injection molding can be divided into "melting / fusion" injection molding and the "solid / melt" injection molding two [10]. "Melt / Melt," the general said injection molding is a common injection molding, which is characterized also by different components of the two kinds of gate melt into the mold cavity. "Solid / melt" is characterized by injection molding molten composition in the first part of curing, then the second injection, or even third, fourth component. Such as self-assembly injection molding mold is completely cured in the first component after passing through internal or external shape their transfer to the next position, into the next component, multi-component injection molding,More than 2.2-component injection molding equipment
     Different needs from the molding process to achieve the corresponding molding equipment. Corresponds to the multi-component injection molding process classification, the corresponding injection molding equipment main unit forms are: (1) a number of parallel horizontal injection unit or the layout of each other at an angle (L-or V-shaped) design or vertical distribution in the vertical plane; (2) The two share a nozzle injection unit, injection part of the alternating sequence to allow the two components are the order of injection molding or intermittent. Multi-component molding equipment representatives in Germany (Krauss Maffei) Krauss Maffei's Revolution • two-component injection molding rotating plate system [13].
     More than 2.3-component injection molding technology trends
     With the extensive application of plastic injection products, multi-component injection molding technology in contemporary technology has great opportunity and hope. With a single injection technique compared to the normal component, multi-component technology in the design and function has obvious advantages. A total of different thermoplastic molding, elastomers and thermosetting plastics were molded plastic, two-component super-wall molding, decorative molding lining is the trend of multi-component technology [14]. In addition, the system with a multi-component technology with magnetic, thermal or electrical conductivity and other features filled thermoplastic parts has become a hotspot of current research.
    3 powder injection molding
     Powder injection molding (Powder Injection Molding) is a modern plastic injection molding technology into the field of powder metallurgy and the formation of a new powder metallurgy molding technology. It is the plastic molding technology, polymer chemistry, metallurgy and metal materials science technology and other multi-disciplinary and cross-penetration of the product, the use of blank mold injection molding, and high density by sintering rapid manufacturing, high-precision, three-dimensional complex shapes structural parts, can be quickly and accurately design ideas materialized into a certain structure, certain features of the products, and direct mass-produced parts, the manufacturing technology industry a new change.
     3.1 powder injection molding process and technical characteristics
      Powder injection molding process, shown in Figure 3. (1) Select the line with the technical requirements of injection molding powder metal powder and organic binder; (2) under certain temperature, using appropriate methods to powder and binder mixture into a uniform feed; (3) injection molding machine made of granular feed into the mold cavity after forming after the condensation, has been molding blank; (4) of the molding blank for degreasing treatment; (5) sintering of blanks, the final product.

 Powder injection molding technology in the manufacture of complex shapes, uniform structure and high-performance, high-intensity, high-precision products shows a distinct advantage. Not only has less conventional powder metallurgy process, no cutting or less cutting, economic advantages, and overcome the traditional powder metallurgy products, uneven texture, low mechanical properties, easy molding thin-walled, complex structure of the shortcomings, particularly for mass production of small, complex shapes and with the special requirements of metal parts by powder injection molding for mass production have a greater cost advantage, the cost of traditional production processes of 20% to 60%. Powder injection molding technologies, design and manufacturing industries to provide a new design ideas and manufacturing techniques, the use of powder injection molding can safely use the original as processability and processing of the poor economy had to give up some of the complex structure design. Also allows the original due to the processing difficulties and had to use a combination of parts, assembling parts to complete the processing of a composite [15-16].
     3.2 Powder injection molding process of the new development
     In recent years, the powder injection molding technology has been rapid development. Its greatest feature is powder injection molding and other molding technology, has been a lot of excellent products. Micro-injection molding and two-component injection molding and powder injection molding with: the micro-tensile specimen for the study, that two-component injection molding powder products practical, examples of products developed as a micro-heating needle. Arburg injection molding a mass of 0.0679g the company's ceramic products, used as insulating materials [17-18]. Vibration-assisted injection molding: Yin Xiaochun [19] on the vibration-assisted injection molding process used in metal powder injection molding were studied. The results showed that: the vibration force field can make the different radial position of the maximum cavity pressure with vibration amplitude, frequency increases and decreases, and thus can not affect the product performance under conditions of reduced pressure injection molding, metal powder injection molding in order to broaden scope of application.
    In the future, powder injection molding technology research and development of main directions: the development of efficient, low-cost pre-mixed powder production technology; better performance in research and development process of new binder, binder design principles and establish a database [20]; development of powder injection molding process modeling and simulation technology for mold design and injection molding process to develop the theoretical basis; development of low temperature, quick skim and low-temperature sintering technology, reduce defects and distortion.
     4 micro-foam injection molding
     Porous foam (MCF) is a pore diameter of 0.1 ~ 10.0μm, pore density of 109 to 1 015 / cm3, the density than the foam material before the reduction of 5% to 98% of the foam. Compared with the non-foam plastic, porous foam with excellent impact properties, high fatigue life, low dielectric constant and thermal conductivity. As to the porous foam plastic material not only reduces the cost and the dual effect of improving its performance, cost-effective, it has great application prospect. The use of gas in the supercritical fluid state distribution of the polymer produced in uniform and uniform small pore size (based on polymers of different materials and applications, its size is usually 5 ~ 100μm) is a porous foam injection molding of technical characteristics. Microcellular foaming technology and traditional plastic injection molding foaming technology more [21], does not require chemical blowing agents, do not need to alkyl catalyst for the raw material of physical, foam agents and other additives. Rational use of micro-injection molding technology can expand the product structure, increase productivity, reduce production costs. According to the continuity of the molding process can be divided into micro-foam injection molding process gap microporous foam plastic injection molding and continuous porous foam plastic injection molding.
     4.1 gap-type porous foam plastic injection molding
     Gap-type porous foam plastic injection molding for micro-injection molding is an early one way process [22-23] is the first in the high pressure of the gas (CO2) uniformly dissolved in the solid polymer (a polymer glass state under) to form a solid polymer / gas saturation system, heated to a molten state. Then under high pressure injection molding, and reduce the temperature and pressure to a certain state, the polymer melt in the gas saturation, precipitated the formation of large bubbles nuclear, and finally rapid cooling to prevent bubble growth, thereby forming porous foam plastic . This pressure makes the use of solid polymer in the inert gas into porous foam molding method is only applicable to batch production, production efficiency is relatively low, less than other continuous microcellular foaming injection technology.
     4.2 continuous porous foam plastic injection molding
      U.S. Trexel MuCell technology provided by [24] is considered to be the first marketing of a suitable porous foam molding technology, the process can be divided into the following four steps: (1) super-critical state of the gas (eg CO2) Back stage at the screw through the barrel injection into the polymer melt to form a single-phase solution; (2) When the melt under high pressure injection molding machine barrel into the lower pressure mold, due to pressure changes, single-phase solution thermodynamically unstable state experienced a large number of bubble nucleation point chamber; (3) gas diffusion into the bubble, causing the bubble expansion; (4) When the bubbles grow to a certain size, the cooling setting. MuCell technological breakthroughs in injection molding, injection molding products for the production of other injection molding process do not have a great capacity for new products designed to optimize processes and reduce product costs to develop a new way.Other continuous porous foam plastic injection molding process are: Ergocell porous foam plastic injection molding [24], supercritical fluid microcellular foaming plastic injection molding [25].
     5 micro-injection molding technology
     In recent years, micro-system technology from microelectronic devices, micro-optics, micro-medical devices, micro-sensors to read and write to the disk expansion unit, ink jet printing. To be able to produce micro-components of practical value, resulting in many new manufacturing technology, including lithography, electroforming and mold technology (LIGA), UV lithography (UV), electrical discharge machining (EDM), micro-injection molding , precision grinding and precision machining, etc. [26-27]. Among them, micro-injection molding technology to easily achieve low-cost mass production of precision micro-structural components of the advantages of the world's manufacturing technology research focus [28-29].
     5.1 micro-injection molding process characteristics
       Micro-injection molding process, shown in Figure 4. Compared with ordinary injection molding, has the following advantages: (1) raw material utilization. Micro-injection system can significantly reduce the flow channel size, thereby enhancing the utilization of raw materials; optimized design flow, the material utilization rate up to 60%; (2) products with high precision. The injection volume can be controlled, reduced gate and runner are conducive to improving the accuracy of products, the size of the current micro-injection molding products can be controlled within 0.01mm of error, the quality of error is less than 0.00008g; (3) shorten the production cycle. Gate, reduce the size and flow temperature-control system to speed up the products of the filling, cooling rate, shorten the molding cycle. Commonly used with micro-injection molding parts, the molding cycle time of about 40% shorter than before5.2 micro-injection molding equipment
     Micro-micro-injection molding machine is the key. Compared with conventional injection molding techniques, micro-injection molding technology for the production equipment has many special requirements, mainly for the following aspects: (1) high injection rate; (2) injection volume precision measurement; (3) rapid response capability. Classified according to drive can be divided into hydraulic / pneumatic drive, all-electric drive and hybrid electro-hydraulic drive. Plasticizing and injection unit according to the classification of institutional design, can be divided into screw, piston, screw plunger hybrid and other special forms. Micro injection machine screw models are representative of the company's German Dr.BOY BOY12A, Nissei Plastic Industrial Co., Ltd. of HM7-DENKEY, tree research industry JMW-015S-5T and Toshiba EC5. Plunger type micro injection machine on behalf of the Spanish Cronoplast company Babyplast6/10, UK MCP's Rabbit2 / 3 and the American Medical Murray's Sesame. Mixing screw plunger injection machine on behalf of the decline of the British model MCP's 12/90HSP, Japan Sodick Corporation TR18S3A and Battenfeld's Microsystem50 [32].
     6 Conclusion
      Currently, plastic injection molding technology is the most commonly used processing methods can be used to produce very complex spatial geometry of the plastic parts. In recent years, a variety of injection molding technology has made significant progress, the general trend is to continue its development to meet the polymer system to the highly integrated, highly sophisticated, high-yield and other aspects of development required to achieve the state of aggregation of products, materials, phase form, organization and other aspects of state control, or to realize the products for heterogeneous composite materials, to maximize the characteristics of the polymer to achieve the purpose of high-performance products. In-depth study of plastic injection molding and injection molding equipment to overcome the shortcomings in the products of scientific and technological progress and high standard of living requirements of people is important.

 

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          Peter   Huang