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Application of SUNFAR Inverters in Injection Molding Machines

Abstract:

This article describes successful application of SUNFAR V260 series inverters in injection molding machines.

Keywords: Injection molding machine, dedicated expansion cards for injection molding machines, V60, energy saving and variable frequency.

Preface
  With wider and wider applications of plastic products, the injection molding industry is witnessing rapid development and competition among injection molding machine manufacturers is also getting increasingly intense. Known from the technology process of injection molding machines, reducing electricity consumption of injection and molding is the best way to increase competitiveness of injection molding machines and plastic products. This article describes a kind of variable-frequency control application solution dedicated for injection molding machines.
I. Process introduction
      Ordinary injection molding machines generally adopt hydraulic transmission, with its structure as shown in Figure 1 and mainly consist of injection device, opening-closing mould device, hydraulic transmission device and electrical control device


    The moulding process of the injection molding machine is a predefined cycling process, which is to form a piece of product by the processing procedures including die assembly – mould locking – nozzle forwarding - pressure maintaining – cooling- preplasticizing – injection platform backward – mould opening -taking out finished product.

The losses of ordinary injection and molding process mainly come from following aspects: 

    1.Overflow loss. Each procedure needs different hydraulic pressure, flow and pressure according to different products and processing procedures. Therefore, with respect to the oil pump motor, the load during the process of injection and molding is always changing and the pump’s flow is designed according to the maximum flow required. The hydraulic flow is provided at constant revolution when the oil pump is running. So, when the flow required for the injection molding machine is less than the maximum flow, redundant hydraulic pressure will flow back via the overflow valve, and this part of energy is then wasted.

    2.Throttling loss. When the hydraulic oil flows through the valve’s throttle, the pressure will be reduced at a certain degree, which is called the throttling loss. Owing to large throttling area of the direction valve, most throttling loss occurs at the proportional valve. In addition, due to long-term full-speed circulation of hydraulic oil and intense friction with hydraulic elements, adverse phonemes are caused such as excessive high oil temperature, loud noise and short service life of machineries. 

     3.Design margin loss. Generally the design takes account of universal characteristics. The design is based on maximum capacity, so the design capacity of users’oil pump motor is much higher than that actually required, causing the phenomenon of driving small vehicle with high capacity of motor. As a result, a large quantity of electricity energy is wasted.

II. Control scheme
   SUNFAR V260 series inverter with dedicated expansion card is designed to match with forming procedures and process characteristics of the injection molding machine. The system is shown in Figure 1, with details as below:
1.Dedicated expansion card, integrated four-circuit analog quantity input channel, two-circuit voltage, two-circuit current, providing input port for different types of flow and pressure commands;
2.Integrated multi-speed control, allowing for setting inverter’s running frequency after superposition with flow and pressure setting signals;
3.Allowing for setting of bottom flow, improving system response speed and stability.

III. System wiring
   The system wiring diagram is shown in Figure 2.

 

IV. Scheme advantages
1.Having running frequency setting channel dedicated for injection molding machines, short acceleration and deceleration time and rapid system response;
2.Strong current suppression capability to effectively avoid overcurrent and other fault and make system run stably;
3.Multi-speed overlaying with flow and pressure commands, convenient for meeting requirements of running frequency for different procedures.
4.The temperature rise of hydraulic oil of the injection molding machine decreases dramatically, effectively prolonging service life of hydraulic oil.
5.Significant energy-saving effect by 30%~50% generally. 

Conclusion
       This article describes a kind of injection molding machine driving scheme based on SUNFAR inverters. V260 high-performance vector inverter with dedicated adaptor enables rapid and precise control over oil pump motors. Featuring high efficiency and rapid response, it can effectively optimize use of oil pump motor and is now widely used in the control system of injection molding machines nationwide.

References:
User Manual of V260 Series High-performance Vector Inverters of Shenzhen SUNFAR Electric Technologies Co., Ltd
User Manual of Dedicated Expansion Cards for Injection Molding Machines of Shenzhen SUNFAR Electric Technologies Co., Ltd