What should I do if the injection molding machine is broken?

As we all know, the pull rod (Golden column) of the general toggle type (machine hinge) injection molding machine is easier to break than the full hydraulic type tie rod. What is the reason? In the design of the toggle lever type, since the rigidity of the system is considered, since the toggle lever type generates a clamping force by rigidity, the diameter of the general drawbar is large. But the strange thing is that its tie rods are easy to break, especially in some industries, such as the production of video cassettes, plastic fast food, forks and other industries, due to thin product walls, good material flow, large molding area, fast production speed Therefore, the breakage of the tie rod link (hinge) is very common and may even cause the template to break.

First, the analysis of the cause of the tie rod fracture

1. Fatigue damage

The working process of the injection molding machine is a process of alternating stress, so any factor that causes stress concentration may cause fatigue damage. Such as: 1) The step where the shaft diameter changes greatly. 2) There is a lack of rounded corners, undercuts, etc. at the transition. 3) Surface scratches or machined threads inadvertently damage the surface of the optical axis. 4) The surface roughness of the thread is too large. 5) The thread is pressed for a long time, and the surface is crushed and damaged due to insufficient surface strength (at the mold nut). 6) Improper heat treatment of the thread surface causes stress concentration. 7) Material defects.

2, overload pull off

Since the toggle lever is deformed by the four tie rods to obtain the clamping force, if the length of the four tie rods is different, the deformation is different. If one of the four is shorter, the shorter tie rod may withstand much more than itself. Withstands a quarter of the clamping force, which causes the break.

3, temperature strain causes the pull off

If the length of the four tie rods is different, for example, one long and three short, the thermal stress caused by the sharp temperature rise or decrease of the longer tie rod is restrained by the other three rods and is in a static state, which will result in the The tie rod is broken.

4. Breakage caused by composite strain

If the mold is not flat, the combined error of the length of the connecting rod (hinge), the height of the bearing seat and the length of the tie rod is too large. When the connecting rod is straight, the two sides are unevenly stressed. Then 1) causing the rear template to oscillate, the tie rod is bent, and the tie rod is easily broken under the action of bending stress and tensile stress. 2) The product is caused by flashing. Generally, the operator who lacks experience will further increase the clamping force, which will cause the pull rod to be overloaded and the mold overload deformation.

5. Damage caused by transient impact stress

Since the toggle force can be released before the mold is opened, 1) the instantaneous impact during mold opening causes the machine to vibrate and damage the tie rod and other parts. 2) As the entire mold clamping part (including the mold) is kept under stress for a long time, it will lead to premature fatigue failure of the part.

Solution

1. In design, it is necessary to avoid abrupt changes in the shaft diameter. In the step or the undercut, try to use a large rounded corner transition to select a material with better comprehensive performance. The special treatment must solve the hardness of the thread surface (to be wear-resistant). Try to reduce the surface stress concentration, improve the surface finish, and minimize stress damage.

2, to ensure the processing accuracy, especially the length of the connecting rod, the height of the bearing seat, the accuracy of the crosshead, the positioning accuracy of the bearing seat in the template.

3. Pay special attention to the length of the four tie rods during assembly or after dismantling the mold clamping nut. The distance between the mold clamping nut and the rear template should also be adjusted.

4. When the product is produced, the reason should be analyzed. Do not improve the clamping force on one side. If the mold is found to be uneven, it should be smoothed. If the length of the connecting rod is uneven, it should be corrected, including pad copper, paper, etc., or correct the mold adjustment. Nut.

The above solutions can only play a certain role, and may not be solved fundamentally, and some measures will increase manufacturing costs, such as increasing the diameter of the tie rods and using good materials. Therefore, it depends to some extent on the trade-offs of the manufacturers. For the use of full hydraulic clamping structure, it is a better choice to solve the broken rod. However, due to the traditional hydraulic type, there are still problems such as slow speed and high energy consumption. Therefore, after the manufacturers weighed, the small and medium-sized machines were still mainly toggle-type, and until the emergence of the two-plate type, they were fundamentally solved.

Two-plate and four-cylinder straight lock two-plate type

The two-plate type is mainly divided into four-cylinder two-plate type and four-cylinder direct-locking two-plate type. The two-plate type is much better than the liquid-filled type from the clamping force, because the two-plate closed force line is only in the middle of the tie rod. , set the template, between the molds. Since the force length of the tie rod is reduced by nearly 50%, the rigidity of the entire mold clamping system is improved, and the force parts are also reduced a lot (such as the rear mold plate, the oil cylinder, etc.), so that the parts damaged by the fatigue of the whole machine are also reduced, thereby improving the life of the whole machine. The four-cylinder bag has two plates. Because it requires mechanical action conversion (such as nut hug), which affects the speed of opening and closing, it can only be used for mainframes. The four-cylinder direct-locking two-plate type does not require mechanical action conversion. It is convenient to use, such as direct pressure type, the speed is faster or faster than the toggle type, and the clamping force can be reduced with the end of the injection process, so that the parts (including the mold) are subjected to high pressure time. With nearly 80% reduction, the machine life will be more than doubled, so the four-cylinder direct-lock injection molding machine will be the best choice for solving the broken rod.