In the design of precision motor die casting molds, the selection and optimization of the parting surface is a crucial step in balancing sealing requirements and ease of demolding. As the core interface in contact when the mold closes, the parting surface directly affects the dimensional accuracy, surface quality, and mold life of the die casting. Insufficient sealing can allow molten metal to seep into the mold gaps, leading to flash, burrs, or even mold damage. An inadequate demolding design can cause die casting deformation, jamming, or mold wear. Therefore, a dynamic balance between these two aspects must be achieved through structural innovation and process synergy.
The sealing design of the parting surface must begin with ensuring the rigidity of the mold during closure. The mold parting surface must have sufficient contact area and flatness to withstand the impact of high-pressure molten metal. A monolithic parting surface structure is typically used, with high-precision machining (such as grinding and polishing) ensuring a surface roughness below Ra0.8μm to reduce micro-gaps. For complex curved die castings (such as motor end caps), a localized insert design can be used to decompose the parting surface into multiple small planes. Precise closure is achieved through locating pins and guide pillars, preventing leakage due to poor surface fit. Furthermore, adding sealing grooves or flange structures at the parting surface edges can further prevent molten metal overflow and improve sealing reliability.
Ease of demolding is achieved through a reasonable draft angle and guiding mechanism. Precision motor die castings often contain thin walls, deep cavities, or complex core structures. If the draft angle is too small, the die casting may become stuck due to excessive friction; if the draft angle is too large, it will affect the uniformity of wall thickness and dimensional accuracy. During design, the draft angle must be determined comprehensively based on the material shrinkage rate (e.g., approximately 0.5%-0.8% for aluminum alloys) and surface roughness requirements, typically ranging from 0.5° to 3°. Simultaneously, adding inclined guide pillars, sliders, or other core-pulling mechanisms to the mold can solve the demolding challenges of lateral parting. For example, in die-casting of motor rotors, the side core is driven to eject before the moving mold by inclined guide pillars, preventing deformation of the die-casting due to lateral tension.
The coordinated design of the parting surface and gating system has a significant impact on both sealing and demolding. The gate position should be as close as possible to the parting surface to shorten the length of the molten metal flow channel and reduce incomplete filling due to pressure loss. Simultaneously, the cross-sectional area of the ingate must match the sealing strength of the parting surface to prevent excessive flow velocity from impacting the parting surface. For multi-cavity molds, the parting surface must independently separate each cavity to prevent cross-seepage of molten metal leading to cross-cavity defects. For example, in a multi-cavity mold for a motor stator, isolating the gating system of each cavity through the parting surface, combined with local cooling channels to control the solidification sequence, ensures synchronous demolding of die-castings from all cavities without flash.
Mold materials and surface treatments significantly improve the performance of the parting surface. The parting surface contact area requires the use of high-hardness, wear-resistant materials (such as H13 steel), and surface treatments such as nitriding and chrome plating are used to enhance its anti-adhesion and anti-corrosion properties. For example, nitriding can form a 0.1-0.3mm hardened layer on the parting surface, with a hardness of HV1000 or higher, effectively reducing the erosion of the mold by molten metal. For high-precision die castings, PVD coating technology (such as TiN coating) can also be used to further reduce the coefficient of friction and improve demolding smoothness.
Dynamic sealing and demolding compensation mechanisms are innovative solutions for handling complex working conditions. During high-pressure die casting, the mold parting surface may develop tiny gaps due to thermal expansion or mechanical vibration. By adding elastic sealing elements (such as spring sheets or rubber sealing rings) to the parting surface, dynamic compensation can be achieved to maintain sealing pressure. Simultaneously, introducing hydraulic or pneumatic auxiliary devices into the demolding mechanism can provide additional demolding force, solving the problem of jamming caused by excessive core clamping force. For example, in die-casting of motor housings, a hydraulic cylinder drives the ejector rod and slide block in tandem, enabling the smooth ejection of complex cores.
Maintenance and upkeep of the parting surface are crucial for ensuring long-term performance. During mold service, the parting surface may experience wear due to molten metal erosion, ejector rod friction, or cooling water corrosion. Regular polishing and repair of the parting surface are necessary to remove adhering metal residues and oxide layers, and recoating with a release agent to reduce the coefficient of friction. For locally damaged areas, precision can be restored through welding repairs or insert replacement, preventing batch scrap due to seal failure.
The design of the parting surface in precision motor die casting molds must balance the dual requirements of static sealing and dynamic demolding. Through structural optimization, material upgrades, process coordination, and intelligent maintenance, comprehensive improvements in sealing performance, demolding convenience, and mold life can be achieved, providing a reliable guarantee for the high-precision and high-efficiency production of motor die castings.
