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On the road to energy saving and precision, Ge electric-plus plastics injection moulding machines have taken the lead.
On the road to energy saving and precision, Ge electric-plus plastics injection moulding machines have taken the lead.

The toggle-type clamping mechanism is composed of mould displace hydraulic cylinder and toggle connecting rod. It can use a small hydraulic cylinder, through the leverage of toggle to reach enough clamping force. In the opening and closing process, this mechanism can achieve slow - fast - slow motion, improve clamping speed, save energy and improve efficiency. In the case of the same input power, the kinematic of the toggle-type clamping mechanism is superior to other types of clamping mechanism. For example, If the same size machine at the same speed of movement, toggle-type clamping mechanism is saving about 10% -20% input power more than full hydraulic. However, this mechanism also has obvious shortcomings:

1. Force situation is not satisfactory. As the toggle-type mechanism achieves its clamping force by the rod deformation, rod can not be too strong. If the rod is too strong, its rigidity will be too high, the force increasing the curve will rise rapidly when clamping, and too sensitive to changes. It will result in difficult to adjust the mould, the clamping force may be not enough, or too high and lead to damage on the rod, tie rod nuts, toggle pin or mould plate. Due to manufacturing or assembly adjustment deviation, force may be uneven on some parts or components, increasing the possibility of damage.

2. Clamping force instability. Processing accuracy, assembly accuracy, mechanical wear and other factors will cause the clamping force changes. Changes in lever length caused by temperature changes can also cause changes in the clamping force.

3. Impact is big when the mould is opened. Since the toggle-type mechanism mainly obtains the clamping force by the deformation of the rod.  When the mold is opened and the toggle rod is turned out of the lock range, the system deformation force of the toggle clamping mechanism is recovered, and reverse push the mould cylinder rapidly, cause the mechanical and hydraulic impact.

Although the hydraulic toggle-type clamping mechanism has the above shortcomings, but still its energy-saving, Anti mould expansion and other excellent features occupy the current mainstream of the IMM market. In the above three major clamping mechanisms of IMM, the toggle-type clamping mechanism is most widely used. However, the design of its mechanism is also the most complicated. The quality of the design will largely affect the performance of the clamping mechanism. A good toggle mechanism should have a high mould moving speed, a smooth speed change and a suitable magnification ratio. As shown in the above picture, these requirements are closely related to the geometry of the mechanism. Through motion and mechanics analysis of this mechanism, it is not hard to come out with the following points:

1. Hc and Hd are related to the size and stress state of the board. When the value of Hc and Hd are small, the weight and force of the board are favorable, but it is difficult to draw a good motion curve (smooth speed change); on the contrary, larger value are not conducive to the cost control of the board.

2. When critical angle (α0) value is too large, the system rigidity will be not enough; when the value is too small, it will make the operator difficult to adjust.

3. Different pursue on speed ratio and force magnification ratio. When you pursue speed ratio, you get bigger movement stroke and higher speed for mould-plate, and shorten the axial size of the clamping mechanism, it is suitable for small and middle size IMM. When you pursue force magnification ratio, you can get enough clamping force by smaller Cylinder thrust, but the axial size will be lengthened, this is suitable for middle and big size IMM.

In a conclusion, we think that it is virtually impossible to obtain the optimal solution on all the parameters. There is a contradiction or mutual restriction between them. Therefore, how to coordinate different parameters and performance is the most important question for the design of the toggle mechanism.

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