Injection mold and solution
Injection mold damage, also known as mold crush, is a common and serious defect in injection molding production. It occurs when, for some reason, the movable mold and fixed mold, or mold components, come into abnormal contact during the mold closing or injection process. This damages the mold surface or damages components. It can also lead to indentations, deformation, and material shortages on plastic parts, seriously impacting production schedules and mold life. The occurrence of mold crush not only increases mold repair costs but can also lead to the scrapping of batches of products. Therefore, it is important to identify the causes of mold crush and implement effective solutions to prevent its occurrence.
There are many reasons why injection molding can cause mold compression, primarily due to factors such as poor mold design, improper mold installation and commissioning, incorrect process parameter settings, and non-standard production operations. Improper mold design, such as the presence of protrusions or ribs on the parting surface without adequate clearance, can easily cause these parts to collide with each other during mold closing, resulting in crushing. Excessive clearance between mold guide pins and sleeves, or severe wear, can lead to inaccurate mold positioning during mold closing, causing the movable and fixed molds to shift, resulting in localized extrusion and mold compression. Improper mold installation and commissioning, such as failure to level the mold during installation, resulting in uneven force during mold closing, or the ejector mechanism failing to fully return to its original position, causing parts such as ejectors and lifters to collide with the fixed mold during mold closing, can also cause mold compression. Incorrect process parameter settings, such as excessive clamping force exceeding the mold ‘s capacity, can cause mold deformation or even crushing. Excessive injection pressure, resulting in excessive melt impact on the mold cavity, can also cause mold compression.
To prevent compression caused by unreasonable mold structure design, optimization should be carried out from the mold design stage to ensure sufficient clearance and positioning accuracy between the various parts of the mold. When designing the parting surface, reasonable clearance should be set for parts prone to collision, such as protrusions and ribs. The clearance amount is usually 0.1-0.5mm, which is determined according to the specific size of the parts to avoid mutual squeezing during mold closing. Strengthen the mold’s guiding and positioning system, select high-precision guide pins and guide sleeves, control the matching clearance to 0.01-0.03mm, and set locating pins at the four corners of the mold to improve positioning accuracy during mold closing and prevent mold offset. For the ejection mechanism, a reliable reset device, such as a reset spring and a return rod, must be designed to ensure that parts such as the ejector pin and the inclined ejector are fully reset before mold closing to avoid collision with the fixed mold. In addition, the mold should be equipped with sufficient support columns to enhance the rigidity of the mold and prevent mold deformation under the action of the clamping force and compression.
Improper mold installation and debugging is an important cause of mold compression, so the mold installation and debugging process must be standardized to ensure that the mold is installed accurately and debugged reasonably. Before installing the mold, it is necessary to clean the oil and impurities on the injection molding machine’s tie rods and the surface of the template, check the parallelism and verticality of the injection molding machine, and ensure that it meets the installation requirements. When installing the mold, it is necessary to use a spirit level to correct the level of the mold to ensure that the mold is evenly stressed when the mold is closed; when tightening the mold bolts, they should be tightened evenly diagonally to avoid the mold from shifting due to uneven stress. When debugging the mold, you should first perform slow empty mold closing, observe the movement of each part of the mold, check for interference or collision, and then gradually increase the mold closing speed after confirming that it is correct. For the ejector mechanism, its reset condition needs to be tested to ensure that parts such as the ejector pin and bevel ejector can be completely reset. This can be monitored by installing a travel switch. Once it is found that the reset is not in place, stop the mold closing immediately to avoid mold compression.
Incorrect process parameter settings and non-standard production operations are also common causes of mold compression, which can be prevented through optimized process parameters and standardized operations. The clamping force should be set appropriately based on the projected area of the part and the viscosity of the plastic, generally 1.2-1.5 times the calculated value, to avoid damage to the mold caused by excessive clamping force. The clamping speed should also be increased gradually to prevent the impact of rapid mold closing, which can cause mold collisions. Control the injection and holding pressures. Based on the part’s structure and material properties, set the injection pressure appropriately to avoid excessive pressure that places excessive stress on the mold cavity. The holding pressure should also be kept low to prevent overfilling the mold with melt, which can cause localized compression and deformation. During production, operators should strictly follow operating procedures and regularly check the mold’s operating status. If any unusual noises or indentations are detected, the machine should be stopped immediately for inspection and troubleshooting. Production can only resume after the problem is resolved. Regular mold maintenance, including replacement of worn guide pins and bushings, can also effectively prevent mold compression. By taking the above measures in combination, the occurrence of injection molding failure can be effectively reduced, ensuring the smooth progress of production and the service life of the mold.
