The whole strategy of multi-color/multi-material injection molding material switching of injection molding machine

At the moment when the injection molding process is constantly advancing, multi-color or multi-material injection molding gives products a higher added value of appearance and performance.However, the material switching link in this process is extremely important, and the slightest carelessness will cause difficult problems such as mixing and variegation, which will affect product quality.Mastering the correct switching steps and techniques is the key to achieving a perfect transition.
1. Adequate preparation before switching
First of all, the injection molding machine and surrounding auxiliary equipment must be thoroughly cleaned.The previous material remaining in the barrel, screw, nozzle, and connecting pipeline must be removed to avoid mixing with new materials and causing pollution.Special cleaning agents can be used to carry out cleaning operations in accordance with the prescribed procedures, such as high-temperature melt glue cleaning or chemical agent soaking cleaning, to ensure that there is no material residue on each component.
At the same time, according to the characteristics of the material to be switched, prepare the adapted screw and barrel components.Plastics of different materials have different properties such as melting viscosity and thermal stability. Choose the appropriate screw configuration, such as gradient screws for general plastics, mutant screws for high-viscosity engineering plastics, can optimize the plasticization effect of the material, and lay a solid foundation for the injection molding process after the switch.
In addition, carefully check the parameters of the new material, including drying requirements, processing temperature range, fluidity indicators, etc., and set the temperature control system of the injection molding machine in advance.Accurate temperature setting is a prerequisite for smooth melting and uniform mixing of materials, to ensure that the temperature of each section of the barrel and the hot runner (if any) is adapted to the new material.
2. The key steps of material switching
When the material switching is officially started, the injection molding machine is first switched to manual operation mode to facilitate fine control of each link.The first step is to empty the remaining material in the barrel, and slowly squeeze out the remaining old material through the rotation and retreat of the screw until the barrel is basically emptied.Pay attention to controlling the screw speed during the process to prevent the material from decomposing due to high-speed shear and heat generation, resulting in impurities mixed into subsequent materials.
Then, a small amount of new materials are introduced for “pre-filling”.At a lower screw speed, the new material is gradually filled into the front end of the barrel, allowing it to melt initially in a relatively low temperature environment. On the one hand, the smoothness of the new material can be detected, and on the other hand, the viscosity of the new material can be used to “blackmail” the old material that may remain to further clean the inside of the barrel.
After the pre-filling is completed, according to the processing temperature requirements of the new material, the barrel temperature is gradually increased to the set value, and the screw rotation is started again to make the new material fully plasticized and evenly mixed in the barrel.During this period, pay close attention to the temperature and pressure changes of the barrel to ensure that the material is in a good plasticized state and prepare for subsequent injection molding.
3. Skills to ensure a smooth transition
In order to eliminate the phenomenon of mixing and variegation, “transition materials” can be used in the process of switching materials.When switching from one color/material to another material with large differences, choose a transition material that is compatible with the two, such as a specific general-purpose plastic or a special compatible agent.First, between the emptying of the old material and the pre-filling of the new material, an appropriate amount of transition material is injected, and its “bridge” function is used to make the old and new materials smoothly connect at the interface to avoid uneven mixing due to mutations in the nature of the material.
Optimizing the injection program settings of the injection molding machine is also a key trick.In the first injection molding after switching materials, a low-speed and low-pressure injection strategy is adopted to allow the new materials to fill the mold cavity slowly and evenly, so as to avoid material turbulence caused by high-speed impact and cause mixing risks.At the same time, the holding time is appropriately extended to ensure that the corners of the cavity are filled with new materials, and the degree of compaction is uniform, so as to reduce the defects such as variegation and air bubbles caused by uneven local pressure.
Moreover, real-time monitoring of product quality feedback is essential.In the first few molds of the product after the material switching is completed, carefully check the appearance color, surface finish, internal structure integrity and other indicators. Once an abnormality is found, immediately stop work to investigate the cause and adjust the material switching steps or injection molding process parameters to prevent it before it happens.
In short, when operating an injection molding machine for multi-color or multi-material injection molding, material switching needs to be treated rigorously.From pre-preparation, implementation of key steps to the use of transition skills, every detail is related to success or failure. Only by working step by step can we ensure a smooth transition between different materials and create high-quality and high-value injection molded products.