Blow molding machine is a kind of equipment that uses the principle of "extrusion blow molding" to form hollow products. Rotary blow molding machine has higher production efficiency than linear blow molding machine due to its continuous movement performance. The cam profile curve design is one of the key technologies to realize the movement of the bottle blowing machine, which is directly related to the smoothness of the mold opening and closing movement, the smoothness of the equipment movement and the service life.
The blow molding machine realizes the opening and closing of the mold in the rotating head part, and the design of the cam curve directly affects the dynamic performance of the mechanism. If the cam curve is not well designed, in the production process, when the rotation speed increases, the contact force between the roller and the cam will increase rapidly, resulting in a greater impact. On the one hand, its service life will be greatly reduced; on the other hand, its required driving power requirements are high, and energy consumption will increase accordingly. At the same time, in order to adapt to the production of different types and sizes of high-density polyethylene (HDPE) bottles, there are special displacement requirements for different positions of the cam curve, and its accuracy is critical to the overall performance. In response to the above problems, the research team established a mathematical model of the mold motion law based on the first-generation product of a company’s rotary bottle blowing machine, and used analytical methods to design and optimize its mold opening and closing cam mechanism to improve its dynamic performance.
1 Rotating head cam curve design
1.1 Design analysis
Rotary head cam mechanism The cam is a spatial cylindrical cam, and its motion is commonly used to meet the cam contour curve expansion diagram of "push, stop, and return" motion, in which the push stroke and return stroke meet the law of constant velocity motion. The lower mold seat of the rotating head is installed on the rear flange, and its position is relatively fixed. The upper mold seat is installed on the front flange, and the upper mold seat is moved by the cooperation between the upper mold seat and the cylindrical cam, so as to achieve the opening and closing of the mold. purpose.
1.2 Cam curve optimization of clamping section
The curve design method of the mold clamping section of the original bottle blowing machine is the same as that of the mold opening section. The impact is obvious when the mold is clamped during the production process, which generates a lot of noise. The average moving speed of the mold in the closing section is higher than that in the opening section, which requires smooth movement and low impact. On this basis, due to the needs of flexible production, the shear adjustment area of a certain angle range from θ2 to θ3 is controlled for displacement, so there are additional position requirements for the beginning and the end of the shear adjustment interval. The mold clamping is derived from the above. In the case of high-speed motion, the above motion law theoretically only has no impact on the cycloid motion, but its displacement curve is determined and cannot be adjusted, so it cannot meet the design requirements. High-order polynomials will introduce constraints such as displacement, velocity and acceleration when solving the coefficient matrix, so the rigid and flexible impact can be directly eliminated in the theoretical design. The high-order polynomial motion law curve can meet the requirement of smooth connection between the beginning and end positions of this section and the front and rear sections. At the same time, increasing the power can better control the movement position, and realize the displacement control of the remaining points in the curve section except for the beginning and end position requirements.