Thickened plastic storage boxes are mostly made of PP and HDPE with wall thickness 3.5-5mm, belonging to large-scale thick-walled injection molded products bearing high melt pressure during molding. Insufficient mold strength leads to mold expansion, flash, template deflection and dimensional deviation. Scientific strength calculation is the core basis for standardized mold design and stable long-term production.
Basic Design Reference ParametersUnify industry common standard parameters before calculation: cavity internal melt pressure 90-110MPa, 95MPa as standard calculation pressure; P20 pre-hardened mold steel with allowable stress 120MPa, steel elastic modulus fixed at 2.06×10⁵MPa; maximum allowable deflection deformation of large plastic products limited to 0.15mm, beyond which product flatness and demolding effect are affected. Conventional storage box specifications are taken as examples to verify calculated data rationality.
Cavity Side Wall Strength Calculation
The cavity side wall bears lateral melt pressure, using the simply supported beam stress model with formula S=L×√(P/(16×[σ]), where S is cavity side wall thickness, L effective span, P melt pressure, [σ] steel allowable stress. In actual design, when span reaches 450mm, theoretical wall thickness is about 100mm, with safety margin reserved. If ordinary carbon steel is used, wall thickness needs to be increased due to low allowable stress, so high-quality pre-hardened steel is preferred for thickened storage box molds to avoid long-term cavity deformation.
Mold Base Plate Deflection Deformation CalculationThe movable mold base plate middle part is prone to bending and sinking under pressure, directly affecting product bottom forming quality. Combine theoretical calculation formula with practical experience to determine plate thickness standard: storage boxes under 400mm length, base plate thickness 35-40mm; 400-600mm products, 45-50mm; oversized thickened products, minimum thickness 55mm. Equip with enough support pins to reduce base plate force span, effectively inhibiting deflection deformation and improving overall mold rigidity.
Parting Surface Clamping Force CheckCore formula for clamping force calculation is F=P×A, where F required clamping force, P average cavity pressure, A total projected area of products and runners. Unit conversion is carried out according to 1 ton force equal to 9800N. The average cavity pressure of thick-walled PP storage boxes is 35MPa, with 15% safety margin added on calculated basis. Reasonable matching of injection molding machine tonnage avoids mold opening and material overflow during high-pressure packing, reducing flash repair work.
Ejection System Strength Design Standard
Thick-walled products have strong wrapping force on the core after cooling and shaping. Thin thimbles are forbidden for ejection, with main thimble diameter not less than 6mm to prevent bending deformation and product top whitening/cracking. The ejection fixed plate and bottom plate thickness are increased by 20% compared with conventional molds to adapt to high-frequency reciprocating ejection. Equip with balanced ejection blocks to ensure uniform ejection force and prevent product tilting and deformation during demolding.
Overall Design SummaryThickened storage box mold strength design focuses on four core parts: cavity compression resistance, base plate deformation resistance, clamping force matching and ejection bearing capacity. All calculated data comply with mold design industry standards and actual production test values. Following the design principles of thickened wall, thickened base plate and multi-point support, with sufficient safety margin reserved, common production failures are solved, mold service life is extended, and storage box overall forming quality and dimensional accuracy are stably controlled.
