In the injection molding or die casting process, insufficient venting performance in steel ferrule head molds can easily lead to porosity inside the part, affecting product strength and sealing. Porosity primarily stems from the inability to timely expel gases from the mold cavity, including moisture evaporation from raw materials, gases from high-temperature decomposition, and pre-existing air within the cavity. Improving venting performance requires a comprehensive approach encompassing mold design, process optimization, and material control.
During the mold design phase, the proper placement of venting grooves is crucial. Venting grooves are typically located at the parting line, the end of the gating system, or around the ejector pins, and their depth and width must be adjusted according to material flowability. For example, parting line venting grooves should avoid the product's surface to prevent flash; gating system end venting grooves prevent gas from being trapped by the melt; ejector pin gap venting is achieved by controlling the fit precision. For complex structures, vent plugs can be added in dead corners or an interlocking structure can be used to vent through the gaps between the joints. Additionally, vacuum pump venting systems can actively extract gases from the cavity, particularly suitable for high-precision applications, but careful attention must be paid to maintaining a tight seal.
Process parameter optimization is a direct means of improving venting effectiveness. Excessive injection or die-casting speed can easily trap gas. A "slow-fast-slow" pouring rhythm needs to be adjusted according to the part structure: rapid filling in the initial stage to build pressure and prevent gas intrusion; appropriate acceleration in the middle stage to reduce melt cooling; and slow reduction of pressure at the end stage to allow gas to rise and escape. Holding time and pressure must be matched to material properties; too short a time will lead to shrinkage and porosity, while too long a time may cause flash. Mold temperature control is equally important; too high a temperature will exacerbate raw material decomposition, while too low a temperature will reduce fluidity, both of which are detrimental to gas venting.
Material pretreatment is a fundamental step in preventing porosity. Steel molds must ensure that the raw materials are dry and free of impurities, especially alloys containing easily oxidized elements such as titanium and aluminum, which require strict screening. Rusty, oily, or damp raw materials will release a large amount of gas at high temperatures, requiring pretreatment such as baking and rust removal to reduce moisture content. Furthermore, the quality of molding sand has a significant impact on cast steel parts; molding sand with uniform particles and good permeability can reduce gas retention. When reusing old sand, thorough dust removal is necessary to prevent impurities from clogging venting channels.
Mold surface treatment can indirectly improve venting performance. Increasing surface roughness through sandblasting or chemical polishing can create microgrooves that serve as auxiliary venting channels, especially suitable for areas where venting channels are difficult to create. However, it's crucial to control the roughness to avoid affecting the product's appearance or causing demolding difficulties. For precision parts, electrical discharge machining (EDM) can be used to create uniform micropores on the cavity surface, effectively venting without damaging surface quality.
Maintaining the venting system is key to ensuring long-term stability. Regularly clean residue from the venting channels to prevent blockages; check for wear on vent plugs and replace them promptly; conduct leak tests on the vacuum pump system to ensure pumping efficiency. Furthermore, molds must be thoroughly dried and stored after use to prevent corrosion caused by humid environments, which can affect venting performance.
Trial molding and iterative optimization are essential steps in improving venting performance. After the initial trial molding, X-ray inspection or cross-sectional analysis of the part's internal porosity distribution is necessary to pinpoint areas with insufficient venting. Based on the inspection results, adjust the size and position of the venting channels or add auxiliary venting structures until the porosity meets requirements. For mass production molds, regular re-inspection of venting performance is also necessary to address the impact of material changes or process fluctuations.
Improving the venting performance of steel ferrule head molds requires a comprehensive approach encompassing design, manufacturing processes, materials, and maintenance. By scientifically designing the venting structure, precisely controlling process parameters, rigorously pre-treating raw materials, and establishing a maintenance system, porosity defects can be effectively reduced, thereby improving product quality and production efficiency.
