In the injection molding process of disposable knife, fork, and spoon parts, optimizing the mold structure is crucial for reducing product burrs. Burrs primarily originate from the overflow of molten plastic at the mold parting surface, insert gaps, or ejector pin holes, and their formation is closely related to mold design, machining accuracy, and injection parameters. Targeted optimization of the mold structure can reduce burr risk at its source and improve product yield.
The design of the mold parting surface is the primary optimization direction. The parting surface should be located at the smallest contour of the product and its structure should be simplified as much as possible to avoid complex shapes that could lead to poor mold closing. For thin-walled parts like disposable knife, fork, and spoon parts, the parting surface must be smooth and flat, avoiding steps or unevenness, otherwise uneven pressure distribution during mold closing can easily cause plastic overflow. Furthermore, a slight draft angle can be designed into the parting surface, facilitating demolding and reducing friction during mold closing, thus lowering the likelihood of burr formation.
The mold inserts and core structure must be strictly matched. Inserts are critical components in molds prone to burr formation, and their clearance with the core must be controlled to a minimum. During design, adding insert locating pins or using interference fits can ensure that the insert does not shift under high-pressure injection molding. Simultaneously, the edges and corners of the insert must be rounded to prevent stress concentration and plastic from squeezing into gaps. For details such as the fork teeth of a disposable knife, fork, or spoon, or the edge of a spoon, the insert design must perfectly fit the product shape to reduce splicing marks.
The design of the ejection system directly affects the burr situation during product demolding. Ejector pins or blocks should be positioned away from product edges, preferably on flat surfaces or reinforcing ribs, to prevent tearing of product edges during ejection. The clearance between the ejector pins and the core must be precisely controlled to prevent plastic from squeezing in and forming burrs. For deep-cavity products, pneumatic ejection or delayed ejection methods can be used to reduce the impact of ejection force on the product edges. Furthermore, the ejection system's reset mechanism must be reliable to ensure that the ejector pins fully retract each time the mold closes, avoiding interference with the core.
The design of the mold's gating system must balance filling efficiency and burr control. The gate location should be chosen at the thickest part of the product, avoiding direct contact with the parting line or edges to reduce the impact of molten plastic on the parting line. For disposable knife, fork, and spoon parts, point gates or submarine gates can be used to facilitate post-processing of gate marks. The runner design should have smooth transitions, avoiding right angles or sharp bends that could obstruct plastic flow and increase injection pressure. The placement of the cold slug well is also crucial; its capacity must be sufficient to accommodate the cold slug at the front, preventing burrs caused by uneven shrinkage after the cold slug enters the cavity.
The mold's venting system is an often overlooked but significantly impactful aspect. Venting channels should be located at the end of the cavity filling, with a minimal depth, to both expel air from the cavity and prevent plastic overflow. For thin-walled parts like disposable knife, fork, and spoon parts, the width of the venting channels should be appropriately reduced to avoid burrs caused by excessive venting. In addition, the parting surface and insert gaps of the mold can be improved by adding vents or permeable steel to enhance venting and reduce scorching or burrs caused by trapped air.
The machining precision and surface treatment of the mold are fundamental guarantees for reducing burrs. The mold cavity and core must be machined using high-precision equipment, achieving a mirror-like surface roughness to reduce frictional resistance during plastic flow. Parting surfaces, inserts, and other critical areas require polishing to eliminate machining marks and ensure a perfect fit during mold closing. For food-grade disposable knives, forks, and spoons, the mold surface requires special treatment, such as chrome plating or nitriding, to improve wear resistance and corrosion resistance, extending mold life while reducing burr formation.
Mold maintenance and upkeep are key to long-term burr reduction. Regularly clean plastic residue from the parting surface and ejector pin holes to prevent foreign objects from causing improper mold closing. Replace or repair worn inserts or ejector pins promptly to prevent burrs caused by increased gaps. Furthermore, the mold must be stored dry and clean to prevent rust or deformation from affecting mold closing accuracy. Through systematic mold maintenance, it can be ensured that the mold is in optimal condition for a long time, and that disposable knives, forks and spoons with few burrs and stable quality can be continuously produced.
