Surface cracks in textile machinery die castings are a common quality issue during production. Their causes involve multiple factors, including mold design, process parameters, and material properties. Improper mold ejection system design is a key factor contributing to these cracks. Optimizing the ejection system requires addressing three key dimensions: mechanical balance, structural adaptation, and process synergy. Systematic improvements should be made to reduce ejection stress and, therefore, mitigate the risk of cracks.
Ejection system design must adhere to the principle of "force balance." Textile machinery die castings often feature complex, thin-walled structures. Uneven ejection force distribution during ejection can lead to localized stress concentrations and cracks. For example, box-shaped die castings experience significant lateral resistance. Using only a single ejection point can easily lead to product deformation or cracking. Optimization should prioritize ejection zones based on the product shape, employing a symmetrical, multi-point layout for areas of concentrated resistance, such as at rib intersections or thicker wall sections. Furthermore, the ratio of ejector pin diameter to product projected area must be optimized to avoid excessive pressure per unit area due to excessively thin ejector pins. For deep-cavity molds, a combination of top and side ejection can be used to distribute ejection stress.
The selection and layout of ejector components directly impact demolding quality. Round ejectors are widely used due to their ease of manufacture, but slender ejectors are prone to bending, necessitating the design of stepped support pins for enhanced rigidity. For textile machinery die castings with annular or center holes, sleeve ejection ensures uniform force distribution around the entire circumference, preventing localized deformation. Plate ejection is suitable for thin parts such as containers. Its stable ejection force reduces the risk of cracking, but strict control of guide pin length and ejection stroke is required to prevent the ejector from falling off. Furthermore, the ejector position should avoid functional areas and exterior surfaces of the product. For example, avoid placing ejectors near the glue inlet, and prioritize placing ejector components below thin, deep ribs to minimize ejection marks and structural damage.
Mold structural compatibility is the foundation for optimizing the ejector system. The parting surface should be selected to ensure that the part remains on the side with the ejector mechanism, minimizing strain caused by forced demolding. For die castings with uneven wall thickness, increasing corner radius and adjusting the draft angle can reduce ejection resistance. For example, excessively small corner radius can exacerbate stress concentration. Optimizing this can improve metal flow and reduce the likelihood of cracks during ejection. Furthermore, the surface roughness of the mold cavity must be strictly controlled, as rough interfaces can increase demolding friction and indirectly increase the risk of cracks.
The coordination of process parameters and the ejection system is crucial. Mold temperature management directly affects metal solidification and demolding performance. Failure to provide cooling water channels in overheated areas of the mold can lead to localized coarse grains, reducing die-casting strength and making it more susceptible to cracking during ejection. Optimizing the cooling system and maintaining mold thermal balance can ensure more uniform metal solidification and reduce ejection stress. Furthermore, mold opening timing must be precisely controlled. Opening the mold too early can result in insufficient die-casting strength, leading to surface bulges and cracks caused by bubble expansion during ejection. Opening the mold too late can increase demolding resistance due to complete metal solidification.
The matching of material properties and the ejection system is crucial. Textile machinery die castings often use lightweight materials such as aluminum alloys, whose properties, such as linear shrinkage and the content of low-melting-point phases, can influence cracking susceptibility. For example, excessive magnesium content can reduce material toughness, necessitating composition adjustment by adding pure aluminum ingots or aluminum-silicon master alloys. Mold design should optimize ejection strategies based on material properties. For example, a more dispersed ejection layout can be adopted for brittle materials, while the number of ejection points can be appropriately reduced for tough materials.
Ejector system rigidity is key to ensuring balance. The ejector retaining plate must possess sufficient bending strength to prevent elastic deformation during ejection, leading to force displacement. Rib placement and support column positioning can enhance system rigidity, such as adding ribs to the back of the ejector plate or securing the ejector pins with locating pins. For multi-stage ejector systems, the stroke of each ejector pin must be precisely distributed to ensure synchronized movement and prevent product distortion due to stroke variations.
Optimizing cracks in textile machinery die castings focuses on the ejector system. A low-stress demolding environment can be created through force-balanced design, component selection and adaptation, mold structure optimization, process parameter coordination, material property matching, and increased system rigidity. In actual production, it is necessary to combine the specific structure of the product and the usage scenario, and gradually improve the ejection plan through trial mold verification and parameter adjustment, so as to ultimately achieve effective control of crack defects and improve the quality of die-casting parts and production efficiency.
