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Servo vs Variable Injection Molding Machine: What You Must Know

Mar 30.2022

servo injection molding machine

Are you looking for a servo injection molding machine? Servo injection molding machine is an important piece of equipment for the injection molding industry. We will answer several common questions regarding their nature, composition, and use.

However, we will provide detailed and high-quality answers to your questions through this article.


Comparison of motor current in the standby state of injection molding machine

Standby state: The state when the motor of the injection molding machine is started and the injection molding machine does not operate is called standby state. In the following cases, the injection molding machine is in standby mode.

1. When the cooling time is longer than the plasticizing time, the injection molding machine is in standby mode during the extra cooling time. The thicker the product is, the longer the standby time is. 2.

2. When the robot takes out the finished product/water outlet.

3. When the operator opens the safety door to take out the finished product/spout or insert during semi-automatic operation. The asynchronous motor-driven variable pump is rotating at constant speed without flow rate in standby mode, but the motor current is 7 A measured on an 11 kW injection molding machine, which is a large ratio (29%) compared to the rated current of 24 A for an 11 kW motor. The servo motor driving the variable pump is not rotating in standby mode. The only energy consumed is that of the servomotor (electronic) drive. In the case of an 11 kW servo motor, the current is less than 1 A.


Servo injection molding machine oil temperature for indication

servo injection molding machine

The energy saving effect of servo motor driven oil pump can be seen from the pressure oil oil temperature. Using a 50-ton injection molding machine to inject a single-cavity airline cup, the oil temperature is only 37 degrees Celsius on a hot summer day and without pressure oil cooling. The temperature rise of the pressure oil is an indication of energy saving, which is difficult to achieve even with asynchronous motor driven variable pumps.


Motor efficiency of injection molding machine

Efficiency is the ratio of output power divided by input power. Efficiency = Output power / Input power The input power of the motor is the power used for electricity. The output power of the motor is the power used to rotate. In an ideal situation with no losses, the output power equals the input power and the efficiency equals 100%. The power lost becomes the power of heat. Asynchronous motors are about 90% efficient at rated load, but when the load is below 50%, the efficiency drops dramatically, which is the reason for the aforementioned standby state consuming 29% of the rated current. Some British companies provide "Energy Saver" to reduce the supply voltage when the asynchronous motor is under low load, thus reducing the excess flux generated by the copper coil, reducing losses and achieving the effect of energy saving. The speed of the motor remains the same, so it does not affect the injection cycle.


Standards and other advantages of servo motors for injection molding machines

Servo motors are equipped with encoders on the rotating shaft to provide closed-loop control of rotational speed together with the drive. Since the injection speed of the screw is the target of closed-loop control and the oil pump speed is only proportional to the injection speed, the servo motor only achieves semi-closed-loop control of speed, but it is certainly more accurate than open-loop control. The servo motor driven oil pump is equipped with a pressure sensor at the outlet to provide closed-loop control of the pressure together with the drive. In this way, the servo motor driven oil pump can provide 3/4 closed loop control (3/4=1/2*1/2+1/2*1). Accurate speed and pressure control is a prerequisite for stable productivity. Since the oil temperature is not high, the fluctuation of oil temperature is also low, which further improves the stability. The low oil temperature also saves or even eliminates the need for pressure oil cooling. Other advantages are low noise (especially in standby mode), small size and light weight, etc.


How much energy can the servo motor of injection molding machine save?

The amount of energy saving depends on the wall thickness of the product, whether the mold uses cold runner, holding time, standby time, etc. It is not possible to make a generalization. Generally speaking, the larger the wall thickness, the more energy saving of servo motor. When the wall thickness is large, the holding time is longer and the standby time is also longer, so it can be more economical. The injection molding of bottle blanks belongs to this category. If the diameter of the cold runner is larger than the wall thickness, the cooling time is governed by the runner diameter. On the contrary, for thin-walled products (hot runner molds), the holding time is short and the energy saving of the servo motor is limited. Damien recommends that thin-walled lunch boxes (wall thickness 0.5mm) with a cycle time of 5 seconds or less be produced on an asynchronous motor-driven dosing pump injection molding machine, as most of the cycle is performed at full speed and full pressure, the waste savings are limited. Even the acceleration and deceleration of the servo motor will lengthen the injection cycle. Products with a cycle time of 5-8 seconds can be produced with an asynchronous motor-driven variable pump injection molding machine. Products with a cycle time of more than 8 seconds, cooling time longer than plasticizing time, injection time more than 3 seconds, screw speed below 70%, using robot to take out, using semi-automatic operation are recommended to use servo motor injection molding machine to produce. Of course, servo motor has its limitations. The counter emf of servo motor at "low speed" is lower than that at "high speed", and the current increase makes the coil overheat. This can happen when holding pressure for a long time. The company uses a variable pump to reduce the displacement and maintain the motor at a high speed to alleviate this problem. When selecting an injection molding machine, also pay attention to whether the servo motor power is too small. A large injection molding machine requires a large motor/oil pump to drive it, but a large servo motor has a large rotor inertia and cannot achieve 0.05 seconds from 0 to 2000 rpm.


The difference between servo injection molding machine than variable pump

servo injection molding machine

  • Servo Drive System Principle

    Flow control principle:When the pressure detected by the pressure sensor is less than the pressure set value, the servo drive controls the speed of the servo motor to keep the output flow of the pump at the set value.

    Pressure control principle: When the pressure detected by the pressure sensor reaches the set value, the servo drive controls the torque of the servo motor to keep the output pressure of the pump at the set value.

  • Variable displacement pump system principle

    Variable displacement pumps are pumps with variable displacement. Variable displacement pumps can be single acting vane pumps, radial piston pumps or axial piston pumps, widely used in metallurgy, mining, construction machinery, ships, civil aviation ground equipment and other hydraulic transmission fields.

    Variable displacement pump radial piston pump including piston eccentric and shaft eccentric type, axial piston type including swash plate type and tilt shaft type.

    Variable displacement pump working principle

    Two-way variable pump refers to a pump, in the case of the direction of rotation of the prime mover remains unchanged, by changing the variable mechanism such as the swash plate of the axial piston pump tilt direction or compression ratio to change the method of displacement.

  • Servo vs variable pump injection molding machine

    Variable pump injection molding machines usually have a constant speed motor and a variable pump with a swash plate that can be controlled to adjust the flow of oil from the pump to suit the current demand of the hydraulic system. If the machine does not move at all, the pump will still idle and waste energy.

    In general, servo-driven injection molding machines are considered hydraulic machines with servo motors (adjustable to variable speed) driving high quality, low noise pumps. For larger machines, more combinations of servo motors and pump units are deployed. That is, all-electric machines also use servo motors, but they do not drive hydraulic pumps. Servo motor injection molding machines are close to all-electric to improve energy efficiency, but offer a wider range of performance in terms of speed and power.

    Standard injection molding machines have the speed and power to use AC motors and various types of pumps, which are always variable capacity pumps on newer machines. While still cheaper than servo motors or all-electric, they consume a lot of power and therefore cost more to run. Standard IMMs can be modified to provide variable speed control of the motor, resulting in increased energy efficiency.

    Servo motors offer many advantages over ordinary AC motors. They can be controlled more precisely, consume less power, are lighter in weight, and are quieter. On the other hand, they are quite costly.


The essence of energy saving is to reduce waste. If you are looking for the right servo injection molding machine, welcome to check out LOG Machine's servo injection molding machine products!

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