Plastik enjeksiyon makinası için sayısal denetim sistemi tasarımı
Digital systems design for an injection molding machine
- Tez No: 39305
- Danışmanlar: Y.DOÇ.DR. TURGUT BERAT KARYOT
- Tez Türü: Yüksek Lisans
- Konular: Astronomi ve Uzay Bilimleri, Astronomy and Space Sciences
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1994
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 92
Özet
ÖZET Plastik Enjeksiyon Makinaları ülkemizde genellikle konvansiyonel sistemler ile çalıştırılmaktadır. Bu makinalarda bilgisayar ile denetim, konvansiyonel sistemlerin yetersiz kalması nedeni ile endüstrinin diğer dallarında olduğu gibi, bu dalda da önem kazanmaktadır. Çünkü bilgisayar vasıtası ile kumanda edilen bir makinadan daha yüksek oranlarda verim almak mümkündür. Dolayısı ile, eski kontrol sistemlerinin yeni imal edilen makinalarda kullanımı gittikçe azalmak durumundadır. Plastik Enjeksiyon Makinalan hız, basınç, pozisyon ve sıcaklık kontrolü gerektiren karmaşık sistemlerdir. Bu sistemlerin kumandasında bu zamana dek kullanılan konvansiyonel teknik (kontaktörler, röleler,“thumbwheel”anahtarlar ve“displayler), gelişen plastik teknolojisi karşısında yapabileceklerinin en üst limitine ulaşmışlardır. Plastik Enjeksiyon Makinaları Kapama ve Enjeksiyon üniteleri olmak üzere iki ana kısımda incelenebilirler. Sistemde kontrol edilen büyüklükler, sistemin basıncı ve farklı silindirlere gidecek debi miktarları, makinanın beş farklı bölgesinde yapılacak konum kontrolleri, plastik hammaddenin ergitilmesi esnasında kullanılan ısıtıcı rezistansların, hidrolik yağ, kalıp ve su çemberi sıcaklıklarının kontrolü ve hidrolik akışkanın gideceği silindirlere ve hidrolik motora kumanda eden valflerin kontrolüdür. Bu araştırmanın amacı, yukarıda belirtilen kontrolleri sağlamak üzre bir sayısal denetim sistemi tasarımıdır. Denetim sisteminde AT tabanlı 80486 SX-25 bilgisayar, bir adet PCL-812 A/S Çevirici - S/A Çevirici -Sayısal giriş - Sayıal çıkış ve bir adet de PCL-830 Sayıcı kartı kullanılmıştır. Bilgisayar dışında pano üzerinde montaj edilmiş, araştırmacı tarafından dizayn edilen kartlar; bir adet Sıcaklık Kontrol Kartı, Kodlayıcı kartı, Sayısal giriş kartı, Sayısal çıkışl kartı, Sayısal çıkış 2 - Solid kartı, Sayısal çıkış 2 kartı, Analog Çıkış kartı ve Besleme kartı ayrıca Oransal Valf kartı, Oransal Valf giriş kartı ve diğer devre elemanları bulunmaktadır. Kontrol sistemi programlamasında C dili kullanılmış olup, yapı itibariyle bir ana program ve birçok ”header" dosyalardan oluşmaktadır. Plastik Enjeksiyon Makinasının çalışması çok basit olarak, kısaca şöyledir: Kapama sistemi, kapama silindiri vasıtası ile kapatılarak kalıptan ergiyik hammadde sızması önlenir. Enjeksiyon potasına alınıp, ısıtıcı rezistanslar tarafından ergitilen hammadde, Enjeksiyon silindiri tarafından metal kalıp içerisindeki boşluğa basınçlı olarak püskürtülür. Kapama sistemi açılarak, kalıp içerisinde soğuyan mamul madde itici silindiri tarafından kalıp dışına itilir. Kapama sistemi tekrar kapatılarak süreç başa döner. vi
Özet (Çeviri)
SUMMARY DIGITAL SYSTEM DESIGN FOR AN INJECTION MOLDING MACHINE An injection molding machine is a machine that discontinuously produces formed articles, primarily from polymeric materials. The conversion is done by plasticating the molding material and injecting it under pressure into the mold, where it solidifies in the shape of the cavity. The two essential components of an injection molding machine are the injection unit and the clamping unit. The complete molding equipment consists of an injection molding machine, an injection mold and a mold temperature control unit (heat exchanger). These three components exercise a direct influence on the fabricating process and determine its success or failure. They also interact with one another. The raw material is supplied to the injection molding machine through the feed hopper, which is located on the top of the injection unit. This is done by manually or automatically charging a cylinder with a piston that compresses the material and conveys it into the flights of the screw. For processing thermoplastic pellets, the connecting channel between feed hopper and barrel, the feed chute, usually is of the same diameter or has the same width as the screw. The screw takes in the material and conveys it to the screw tip. On its way, the plastic passes through heated barrel zones, while the rotation of the screw results in a continuous rearrangement of the plastic particles in the flights of the screw. Share and heat transfer from the barrel wall cause a largely homogeneous heating of the material. The conveying action of the screw builds up pressure in front of the tip. This pressure pushes back the screw. As soon as there is enough supply of melt in the space between screw tip and nozzle for one shot, the nozzle is thrust against the spur bushing of the mold. At this time the mold should already be clamped. A sudden pressure surge in the hydraulic cylinder pushes the screw forward and pumps the melt into the mold cavity. There, the plastic cools under temporary, usually decreasing, pressure. The molding produced can consist of one or more individual parts and the runner system. When the molded part is sufficiently solidified and cooled, the clamping unit opens. The mold usually is designed in such a way that, during opening, the molded part is kept in the mold half that is mounted on the movable pattern. It is ejected by an ejector at an adjustable distance from stationary platen. Figure 1 depicts the stages of a typical full cycle. viiFigure 1 The three stages of injection molding a) Meld preparation phase b) Injection phase c) Ejection phase 1- Front mold 4- Rear Mold 2- Molded material 5- Nozzle 3- Mold cavity 6- Heater band 7- Melt 8- Screw 9- Raw material The control system of injection molding machine in this project comprises all that equipment that controls oil pressure and flow rates by Proportional solenoid valve. This system also controls nozzle and barrel temperatures, hydraulic oil temperatures, another most influential parameter in the injection molding process; the mold temperatures and water cooling circle around the feed chute by thermocouples as temperature sensors. This system also comprises position controls with the data came from rotary encoders. Hydraulic oil direction controls are done by solenoid valves. This system is uses to get the temperature and keeps it as constant as needed. The process of keeping temperatures constant, works independent from main process, by PID control logic with interrupts. vmTemperature Control System works like that; The Analog data in 0-40 mV levels came from thermocouples located different 4 points on barrel and nozzle, heated by heating bands, amplifies 100 times with an amplifier circuit up to 4V levels. Because of analog input of the controller is set to -2 / +2V level, this analog level turns with a difference amplifier to -2 / +2V level. This range is equivalent to 0- 4096 digital bits and the reading sensitivity is 0.1 (°C/bits) if the maximum material temperature supposes 400 °C. To keep the temperature constant, the PID control system turn on and off the heating bands. This system works by itself independent of the main program. Main system operation is briefly like that; At the beginning of the program, the variable parameters should be read from the mold register. These are; - Temperature instructions : The temperatures are used by temperature control system to keep them constant at a desired value. - Position instructions : Position instructions are used five different place on the machine. These are clamping unit opening distance, injection volume, group system movement distance, ejector movement distance and moid adjusting distance. - Pressure and flow rate instructions : When a cylinder or hydromotor works the Proportional solenoid valve adjusts these desired pressure and flow rate knowledges. After having the variable instructions of the mold, the mechanism have to reset itself for position control. It begins by clamping unit. So the software asks if the clamping unit is open? If the answer is No, than it sets the desired pressure and flow rates for clamping on the Proportional solenoid valve and pumps the oil to the opening side of clamping cylinder. When the unit opens, it stops to pump the oil. Otherwise if the answer is Yes, there is nothing to do for opening. The software sets desired pressure and flow rates for clamping on the Proportional solenoid valve and pumps the oil to the closing side of clamping cylinder. When the encoder gives reference output signal, it stops to pump the oil and than resets the clamping unit counter. The second position control is applied to group unit. The software asks if the group unit is at the back? If the answer is No, than it sets the desired pressure and flow rates for group on the Proportional solenoid valve and pumps the oil to the back side of group cylinder. When the unit opens, it stops to pump the oil. Or if the answer is Yes, there is nothing to do for moving back. The software sets the desired pressure and flow rates for group on Proportional solenoid valve and pumps the oil to the forward side of group cylinder. When the encoder gives reference output signal, it stops to pump the oil and than resets the group unit counter. IXThe third position control system is at the ejection unit. The software asks if the ejection unit is at the back? If the answer is No, than it sets the desired pressure and flow rates for ejection on the Proportional solenoid valve and pumps the oil to the back side of ejection cylinder. When the unit opens, it stops to pump the oil. In the other case if the answer is Yes, there is nothing to do for moving back. The software sets the desired pressure and flow rates for ejection on the Proportional solenoid valve and pumps the oil to the forward side of ejection cylinder. When the encoder gives reference output signal, it stops to pump the oil and than resets the ejection unit counter. The fourth and the most important resetting operation is at the injection unit. The software asks if there is any melt in the barrel? If the answer is Yes, than asks if the mold security door is closed? and waits for its closing. After it sets the desired pressure and flow rates for clamping on the Proportional solenoid valve and pumps the oil to the closing side of clamping cylinder. When the clamping unit counter reaches the desired value, it stops to pump the oil. The software sets the desired pressure and flow rates for group on the Proportional solenoid valve and pumps the oil to the forward side of group cylinder. When the group unit counter reaches the desired it stops to pump the oil. The software sets the desired pressure and flow rates for injection on the Proportional solenoid valve and pumps the oil to the injection cylinder. When the injection unit reaches to the top, it stops to pump the oil. The software sets the desired pressure and flow rates for group on the Proportional solenoid valve and pumps the oil to the back side of group cylinder. When the group unit counter resets, it stops to pump the oil. Than waits for cooling the material in the mold about 4-5 sec. It sets the desired pressure and flow rates for clamping on the Proportional solenoid valve and pumps the oil to the opening side of clamping cylinder. When the clamping counter resets, it stops to pump the oil. The software sets the desired pressure and flow rates for ejection on the Proportional solenoid valve and pumps the oil to the forward side of ejection cylinder. When the ejection counter reaches the desired value, it stops to pump the oil. Than sets the desired pressure and flow rates also for ejection on the Proportional solenoid valve and pumps the oil to the back side of ejection cylinder. When the ejection counter resets, it stops to pump the oil. The fourth and the most important resetting operation was at the injection unit and the software asks if there is any melt in the barrel? In the other case If the answer is No, it continues also from here and sets the desired pressure and flow rates also for injection on the Proportional solenoid valve and pumps the oil to the sucking back side of injection cylinder. When the encoder gives reference output signal, it stops to pump the oil and than resets the injection unit counter and resetting operations finishes. Now the injection process begins for one shot. The software sets the desired pressure and flow rates for preparing the material for injection on the Proportional solenoid valve and pumps the oil to the hydraulic motor. When the injection counter reaches the desired value, it stops to pump the oil. Than asks if the mold securitydoor is closed? and waits for its closing. After it sets the desired pressure and flow rates for clamping on the Proportional solenoid valve and pumps the oil to the closing side of clamping cylinder. When the clamping unit counter reaches the desired value, it stops to pump the oil. The software sets the desired pressure and flow rates for group on the Proportional solenoid valve and pumps the oil to the forward side of group cylinder. When the group unit counter reaches the desired value it stops to pump the oil. The software sets the desired pressure and flow rates for injection on the Proportional solenoid valve and pumps the oil to the injection cylinder. When the injection unit counter reaches the desired value, it stops to pump the oil. The software sets the desired pressure and flow rates for group on the Proportional solenoid valve and pumps the oil to the back side of group cylinder. When the group unit counter resets, it stops to pump the oil. Than sets the desired pressure and flow rates also for injection on the Proportional solenoid valve and pumps the oil to the sucking back side of injection cylinder. When the injection unit counter reaches the desired value, it stops to pump the oil. Than waits for cooling the material in the mold about 4-5 sec. It sets the desired pressure and flow rates for clamping on the Proportional solenoid valve and pumps the oil to the opening side of clamping cylinder. When the clamping counter resets, it stops to pump the oil. The software sets the desired pressure and flow rates for ejection on the Proportional solenoid valve and pumps the oil to the forward side of ejection cylinder. When the ejection counter reaches the desired value, it stops to pump the oil. Than sets the desired pressure and flow rates also for ejection on the Proportional solenoid valve and pumps the oil to the back side of ejection cylinder. When the ejection counter resets, it stops to pump the oil. So in this way, the injection process finishes for one shot. If the process will continue, it works without resetting. XI
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