Increase in production with automation in injection molding machine

1 CHAPTER 1 INTRODUCTION This chapter proves a review of the concept of injected parts and methods of parts developments. This chapter also relates how parts were produced by using specific tools that provided in the laboratory. Besides that, this chapter also includes the information about parameter involves and the material that used in this project. The injected parts also are chosen so that the sample can be taken nicely to do some analysis. 1.1 HISTORY OF INJECTION MOLDING Injection is a manufacturing process for producing parts from both thermoplastic and thermosetting plastic materials. Material is fed into a heated barrel, mixed, and forced into a mold cavity where it cools and hardens to the configuration of the cavity. After a product is designed, usually by an industrial designer or an engineer, molds are made by a mold maker or toolmaker from metal, usually either steel or aluminum, and precision-machined to form the features of the desired part. Injection molding is widely used for manufacturing a variety of parts, from the smallest component to entire body panels of cars. (Todd, 1994) Am injection molding machine, also known as an injection press, is a machine for manufacturing plastic products by the injection molding process. It consists of two main parts, an injection unit and a clamping unit. Injection molding machines can fasten the molds either a horizontal or vertical position. The majority of machines are horizontally oriented, but vertical machines are used in some niche applications such as insert molding allowing the machine to take advantage of gravity. The first man-made plastic was invented in Britain in 1852 by Alexander Parkes. He publicly demonstrated it at the 1861 international exhibition in London; calling the material he produced “parkesine.” Derived from cellulose, Parkesine could be heated, molded and retain its shape when cooled. It was, however, expensive to produce, prone to cracking, and highly flammable. 2 In 1856, American inventor John Wesley Hyatt developed a plastic material he named Celluloid, improving on Parkes’ invention so that it could be processed into finished from. Together with his brother Isaiah, Hyatt patented the first injection molding machine in 1872. This machine was relatively simple compared to machines in use today. It worked like large hypodermic needle, using a plunger to inject plastic through a heated cylinder into a mold. The industry progressed slowly over the years, through a heated cylinder into a mold. The industry progressed slowly over the years, producing products such as collar stays, buttons, and hair combs. (U.S. patent, 1872) The industry expanded rapidly in the 1940s because World War II created a huge demand for inexpensive, mass-produced products. In 1946, American inventor James Watson Hendry built the first screw injection machine, which allowed much more precise control over the speed of injection and the quality of articles produced. This machine also allowed material to be mixed before injection, so that colored or recycled plastic could be added to virgin material and mixed thoroughly before being injected. Today screw injection machines account for the vast majority of all injection machines. In the 1970s, Hendry went on to develop the first gas- assisted injection molding process, which permitted the production of completed, hollow articles that cooled quickly. This greatly improved design flexibility as well as the strength and finish of manufactured parts while reducing production time, cost, weight and waste. The plastic injection molding industry has evolved over the years from producing combs and buttons to producing a vast array of products for many industries including automotive, medical, aerospace and consumer products. (Douglas, 1996) 1.2 INJECTION MOLDING MACHINE For thermoplastics, the injection molding machine converts granular or pelleted raw plastic into final molded parts via a melt, inject, pack, and cool cycle. A typical injection molding machine consists of the following major components:  Injection system  Hydraulic system  Mold system  Clamping system  Control system 3 Figure 1.1: Injection molding machine for thermoplastics. For the machine specification, the clamping tonnage and shot size are commonly used to quickly identify the size of the injection molding machine for thermoplastics. Other parameters include injection rate, injection pressure, screw design, mold thickness, and the distance between tie bars. The major equipment auxiliary to an injection molding machine includes resin dryers, materials-handling equipment, granulators, mold-temperature controllers and chillers, part- removal robots, and part-handling equipment. Injection molding machines can be generally classified into three categories, based on machines function which are:  General-purpose machines  Precision, tight-tolerance machines  High-speed, thin-wall machines 1.2.1 Injection system The injection system consists of a hopper, a reciprocating screw and barrel assembly, and an injection nozzle, as shown in Figure 1.2. This system confines and transports the plastic as it progresses through the feeding, compressing, degassing, melting, injection, and packing stages. Figure 1.2: A single screw injection molding machine 4 I. The hopper Thermoplastic material is supplied to molders in the form of small pellets. The hopper on the injection molding machine holds these pellets. The pellets are gravity-fed from the hopper through the hopper throat into the barrel and screw assembly. II. The barrel As shown in Figure1.2, the barrel of the injection molding machine supports the reciprocating plasticizing screw. It is heated by the electric heater bands. III. The reciprocating screw It is used to compress, melt, and convey the material. While the outside diameter of the screw remains constant, the depth of the flights on the reciprocating screw decreases from the feed zone to the beginning of the metering zone. These flights compress the material against the inside diameter of the barrel, which creates viscous heat. This shear heat is mainly responsible for melting the material. The heater bands outside the barrel help maintain the material in the molten state. Typically, a molding machine can have three or more heater bands or zones with different temperature settings. IV. The reciprocating screw consist of three zones which are:  the feeding zone  the compressing or transition zone  the metering zone Figure 1.3: A reciprocating screw V. The nozzle It connects the barrel to the spure busing of the mold and forms a seal between the barrel and the mold. The temperature of the nozzle should be set to the material’s melt temperature or just below it, depending on the recommendation of the material supplier. When the barrel is in its full forward processing position, the radius of the nozzle should nest and seal in the concave radius in the supre busing with a locating ring. During purging of the barrel, the barrel backs out from 5 the spure, so the purging compounds can free fall from the nozzle. These two barrel positions are illustrated below. Figure 1.4: Nozzle with barrel in processing position (a) and nozzle with barrel backed out for purging (b). 1.2.2 Mold system The mold system consists of tie bars, stationary and moving platens, as well as molding plates that house the cavity, spure and runner systems, ejector pins, and cooling channels, as shown in Figure 1.5. The mold is essentially a heat exchanger in which the molten thermoplastic solidifies to the desired shape and dimensional details define by the cavity. A mold system is an assembly of platens and molding plates typically made of tool steel. The mold system shapes the plastics inside the mold cavity (or matrix of cavities) and ejects the molded part. The stationary platen is attached to the barrel side of the machine and is connected to the moving platen by the tie bars. The cavity plate is generally mounted on the stationary platen and houses the injection nozzle. The core plate moves with the moving platen guided by the tie bars. Occasionally, the cavity plate is mounted to the moving platen and the core plate and a hydraulic knock-out (ejector) system is mounted to the stationary platen. Figure 1.5: A typical (three-plate) molding system 6 I. Two plate mold The vast majority of molds consist essentially of two halves, as shown below. This kind of mold is used for parts that are typically gated on or around their edge, with the runner in the same mold plate as cavity. II. Three plate mold The three-plate mold is typically used for parts that are gated away from their edge. The runner is in two plates, separate from the cavity and core. 1.2.3 Clamping system The actual required tonnage depends on a number of factors, including part design, polymer viscosity, polymer flow length, mating mold surface condition, and mold construction. The mold should occupy approximately 2/3 of the platen area between the tie bars to prevent possible damage to the mold from “platen wrap-around” Using the minimum clamp force required to produce acceptable parts will reduce the center deflection of the mold. Figure 1.6 indicates mold cavity pressure with in thin walled parts and long flow paths for low to medium viscosity materials. Figure 1.6 7 1.3 Parameters in injection molding machine The quality of molded part is greatly influenced by the conditions under which it is processed. See, for example, the process window shown in figure 1.7. As you lower the temperature, higher the pressure is needed to deliver the polymer melt into the cavity. If the temperature is too high, you risk causing material degradation. If the injection pressure is too low, a short shot could result. If the pressure is too high, you will flash the mold. Figure1.7: Process window shows the influence of temperature versus pressure 1.3.1 Temperature Range: 370 to 390°F (190 to 200°C) The optimum temperature profile depends on many variables, including machine capacity to shot size ratio, screw design, mold and part design, and cycle time. Generally, barrel temperature controllers should be of PID type, and set so the material melts gradually, with cooler rear zone and hotter front zone temperature. For vented barrel machines, a relatively flat temperature profile is recommended to ensure the polymer is melted by the time it reaches the vent zone reverse temperature profiles are used occasionally to compensate for improper screw design, to reduce machine amperage or torque requirements, and to compensate for machines with short L/D ratios. 1.3.2 Pressure The injection pressure is the pressure of the melt in front of the screw. The injection pressure should be low as possible to reduce the part internal stress. On machine, set the injection pressure to the machine maximum. The purpose is completely exploit the injection velocity of the machine, 8 so that the pressure setting valve does not limit the velocity. Because the switch-over to holding pressure occurs before the mold is completely filled, no damage will be done to the mold. Figure 1.8 Resin/hydraulic pressure ration for a 30 mm screw 1.3.3 Injection volume When the process has stabilized (when the same parts are produced each time), adjust the switch-over position to 99 percent of filling. This will exploit the maximum injection speed in as large a part of the injection as possible. 1.4 Material used Many plastics are derived from fractions of petroleum or gases that are recovered during the refining process. For example: ethylene monomer, one of the more important feedstocks, or starting materials for plastics, is derived in a gaseous form from petroleum refinery, gas, liquefied petroleum gases, or liquid hydrocarbons. Although petroleum gas derivatives are not the only basic source used in making feedstocks for plastics, they are among the most popular and economical in use today. Coal is another excellent source in the manufacturing of feedstocks for plastics. From these basic sources come the feedstocks we call monomers. The monomer is subjected to a chemical reaction known as polymerization; it causes the small molecules to link together into ever increasingly long molecules. Chemically, the polymerization reaction gas turns the monomer into a polymer, and thus a given type of plastic resin. 9 Table 1.1 Origin of plastics 10 CHAPTER 2 Production Automation - Injection Molding There is no need to dwell on the challenges facing today’s injection molding industry, in the last couple of years, injection molders have made sizable capital investments to improve quality and efficiency in an effort to counter competitive pressures as well as rising material and labor costs. Now injection machines, advanced automation and inspection devices, to automated assembly machinery and sophisticated materials handling equipment have enabled molding plants to significantly increase output with a lower operation cost basis. As a result, they now enjoy the highest historical productivity rates. However, in spite of all these advances, the injection molding industry faces its biggest challenge yet. To further optimize efficiency, there is a need for an integrated approach that guarantees flawless execution from the conceptual stage of part design, to its high volume production, to its ultimate delivery to the customer. Unfortunately, the injection molding manufacturing process is a patchwork of disparate systems with which it is difficult to intelligently exchange data, making the planning, setup and ramp-up of new production lines time consuming and plagued by inefficient trial and error and fine tuning methods. 2.1 Set up, Optimize, Control and Monitor Once the part and the mold designs are optimized and the effects of the molding processes have been taken into account, the logical next step is to deliver optimal processing parameters to the primary equipment and other process controls in the manufacturing cell. Automating the setup process enables production to start more quickly and shortens the time required to determine and achieve the ideal process parameters such as shot size, injection speed, temperature and pressure settings. Used intelligently, design analysis simulation (DOE) results can provide appropriate initial conditions from which to begin the manufacturing process setup and downstream optimization and control tasks. The more complex the part, the material or the mold, the narrower is the processing window and the higher is the need for continuous [...]... delivered worldwide aare equipped with the servohydraulic eco drive which – depending on the machine type and application – bundling business In particular with the automotive industry and the significantly increased demand for all-electric e-motion injection molding machines, 3.1.1 Plastic processing goes Milacron LLC is the argest manufacturer of injection molding machines in the western Hemisphere, particularly... process and increases overall productivity for injection molding production 3.1 Growth Asia has made a significant contribution of this growth in revenue A further reason is the successful launch of the energy-saving ecodrive option which has boosted the market share of tie=bar=less injection molding machines and of big two=platen machines Today, half of the 20 hydraulic injection molding machines delivered... between the robot and the injectionmolding machine Since, work with both SPI and all Euromap protocols and provide a line of robots that integrate well with machines generating 50 to 5,000 tons of clamp force For machines of 1,000 tons and up, also offer solutions with shelf-mounted robots situated on top of the molding machines for optimal parts handling 3.8.4 How does more automation affect quality?... of automation is continuing Fig 3.2.2 robo controlor 25 3.4.3 3-Axis Robots Are used for automation on horizontal plastic injection molding machines(top entry applications) and operations requiring higher spped 3-Axis robots can be used for part picking, in mold decorating (IMD) and-mold labelling (IML), insert loading, stacking, palletizing inspection 3-Axiz robots are simple to operate and maintain... process or production monitoring system as it is the mechanism for providing access to critical information in real time so that informed business decisions can be made 2.7.2 Production scheduling As an injection molder increases the number of machines and molds that are scheduled to run in production, an automated production scheduling systems becomes a necessity Without a production scheduling system,... ease of use shile maintaining infinite positioning Servo sprue pickers allow for pre-staging above the mold, which minimizes action time in and out of the mold They are flexible allowing for deposit on both sides of the injection molding machines – runners out on one side and parts out on the other Robotic Automation Systems integrates Hahn Automation (GHS Automation / Geiger Handling) servo sprue pickers... robots and peripheral unit equipment for handling molded parts on the injection molding machine It also has feed systems for insert parts, robots for inserting and removing, as well as downstream equipment for processing, loading or storing Process specific automation concepts for back injection of textiles or films, for over molding glass or for production in a cleanroom environment supplement the range... by matching glue glow with robot speed for perfect bead consistency This naturally saves money for customers in terms of programming time and waste reduction 3.9 Reasons Why Automation is Vital for Injection Molding Today Precision and consistency in plastic injection molding are important quality considerations Without having both, you cannot produce high quality injection molded parts Measuring quality... technology particularly in combination with tie-bar-less injection molding machines and filter-fan units, all benefits are combined in compact production cell In addition to the linear robots, the multi-axis industrial robots can also be fully integrated into the system philosophy – without a Euromap 67 interface This is made possible by Engel easix With this innovation the Engel RC 200 or CC 200 control... the automation does not only think linear It always see the injection molding process as the whole.That’s why we can always expect complete system solutions Highly integreated system cells Turn key In which the individual system components such as the machine Multiaxis industrial robots Linear devices, camera tech-nology, tracing solutions and much more are perfectly coordinated All this is in the interest . 1994) Am injection molding machine, also known as an injection press, is a machine for manufacturing plastic products by the injection molding process. It consists of two main parts, an injection. thermoplastics, the injection molding machine converts granular or pelleted raw plastic into final molded parts via a melt, inject, pack, and cool cycle. A typical injection molding machine consists. confines and transports the plastic as it progresses through the feeding, compressing, degassing, melting, injection, and packing stages. Figure 1.2: A single screw injection molding machine