Plastic Tooling : Design and Manufacturing of Plastic Drawer Molds for Home Appliance Refrigerators-Case Studies

Plastic tooling is the core equipment for plastic product molding, and its design rationality and manufacturing precision directly determine product quality, production efficiency, and cost control. In the home appliance industry, plastic drawers for refrigerators, as core storage components, have extremely high requirements for dimensional accuracy, surface finish, low-temperature impact resistance, and food contact safety. The performance of plastic tooling directly affects the assembly adaptability and service life of the drawers. Taking the plastic drawer for the refrigerating compartment of a 600L refrigerator as the target product, this article elaborates on the design points, manufacturing process, technical control, and application value of special plastic tooling, providing a reference for the mold development of similar home appliance plastic products.

I. Product Characteristics and Core Mold Requirements

The plastic drawer for the refrigerating compartment of a 600L refrigerator has a shallow cavity box structure with an overall size of 480mm×320mm×120mm and a box wall thickness of 1.5mm. It is equipped with snap-fit卡槽 (adapting to refrigerator guide rails) at the edges. The inner wall must be smooth and texture-free for easy cleaning, and the appearance surface must be free of bubbles, scratches, flash, shrinkage marks, and other defects. The product is made of food-grade PP/ABS alloy material, complying with GB/T 23332-2022 "Plastic Components for Household Refrigerators". It has excellent low-temperature impact resistance (no cracking at -20℃), aging resistance, and food contact safety, with no odor or harmful substances released after molding.

The corresponding core requirements for the mold are strict: cavity dimensional tolerance ±0.02mm to ensure the consistency of the drawer's length, width, height, and slot dimensions, adapting to the guide rail assembly gap (0.1-0.2mm); the mold's appearance cavity requires mirror polishing (Ra≤0.2μm) to avoid residual processing textures on the drawer surface; multi-cavity design is adopted to improve production capacity while ensuring uniform product precision of each cavity; an efficient cooling system must be equipped to adapt to the shrinkage characteristics of PP/ABS alloy, reduce molding cycle, and avoid shrinkage marks and deformation; the mold material must be corrosion-resistant, easy to polish, meet food contact hygiene requirements, and have no risk of impurity precipitation.

II. Design Points of Refrigerator Drawer Mold

The mold adopts an overall two-plate structure suitable for horizontal injection molding machines, designed with a 4-cavity layout (symmetrically distributed) to balance melt distribution and cooling efficiency, adapting to the large external size of the drawer. Each mold cycle can produce 4 drawers, meeting the mass production needs of the home appliance industry. The core design links are as follows:

Cavity and core design: The cavity adopts a modular structure, made of S136 stainless steel, which is solution-treated to improve hardness (HRC 48-52), featuring excellent polishing performance, corrosion resistance, and wear resistance, suitable for food-grade material molding. The core surface is rounded (R2mm) to avoid stress concentration and cracking at the drawer corners, and a slot molding structure is reserved. The dimensional accuracy of the slot is guaranteed by Electrical Discharge Machining (EDM). The fit gap between the cavity and core is controlled at 0.01-0.015mm to prevent flash and adapt to material shrinkage.

Gating and cooling system: A hot runner + submarine gate gating system is adopted, with a main sprue diameter of 10mm and a branch sprue diameter of 5mm. Each cavity is equipped with an independent hot runner nozzle, with a temperature control accuracy of ±1℃, reducing gate waste and avoiding gate marks on the drawer surface. The cooling system adopts a zoned water channel design, fitting different structural areas such as the drawer box wall and slot, with a water channel spacing of 6-8mm. The mold temperature is controlled at 50℃ and precisely regulated by a constant temperature machine to ensure consistent cooling rate of each cavity, avoid drawer deformation due to uneven cooling, and shorten the molding cycle to 18s.

Ejection and venting system: A combined ejection mechanism of ejector pins and ejector plates is adopted. Ejector pins are evenly distributed at the drawer bottom and slot positions, and the ejector plate is attached to the drawer edge, ensuring uniform ejection force distribution and avoiding ejection marks or deformation on the drawer surface. Micro vent grooves (width 0.02mm, depth 0.01mm) are set at the cavity corners and slot roots to quickly discharge air and melt volatiles in the cavity, preventing bubbles, burning, and material shortage defects, and ensuring the integrity of the drawer appearance.

III. Mold Manufacturing Process and Precision Control

Mold manufacturing follows the principle of "high-precision machining + multi-process inspection", with the process flow: mold material pretreatment → CNC milling → EDM/wire cutting → mirror polishing → assembly and debugging → mold testing and optimization → finished product acceptance. The whole process is controlled around the dual cores of food-grade safety and dimensional accuracy.

High-precision machining link: After quenching and tempering treatment, S136 steel is processed into cavity and core blanks by 5-axis CNC milling, with a machining accuracy of ±0.003mm, focusing on ensuring the key structural dimensions such as the drawer slot and edge fillets. The cavity surface is finished by EDM, using copper electrodes for electrical discharge machining of complex slot structures and corner areas, reducing the surface roughness to Ra≤0.1μm. Wire cutting is used to process precision parts such as ejector pins, positioning pins, and ejector plates to ensure the fit accuracy of each component and avoid assembly jamming.

Mirror polishing and assembly: A composite process of "mechanical polishing + chemical polishing" is adopted, grinding from 800# abrasive wheel to 10000# polishing paste step by step, finally achieving a mirror effect of Ra≤0.2μm on the cavity inner wall with no residual polishing texture, ensuring the drawer surface finish. During assembly, a dial gauge and optical projector are used to calibrate the coaxiality and parallelism of each component, ensuring the ejection mechanism moves smoothly without jamming. Food-grade rubber is selected for seals to prevent hydraulic oil leakage and product contamination, meeting food contact safety requirements.

Mold testing and optimization: A Haitian MA3200/1100 injection molding machine is selected for mold testing, adapting to the large molding area of the drawer. The plasticizing temperature is set at 200-230℃, injection pressure at 80-100MPa, holding pressure at 60-70MPa, and cooling time at 18s. After mold testing, a coordinate measuring machine is used to detect the drawer dimensions and slot gap, and an optical projector is used to check the surface quality. The holding time and zoned mold temperature are adjusted to solve slight shrinkage marks at the corners. After optimization, the product qualification rate reaches 99.7% and the assembly adaptability is 100%.

IV. Mold Application Value and Maintenance Points

After the mold is put into production, the single-shift output reaches 19,200 drawers, doubling the efficiency compared with traditional 2-cavity molds, and reducing the unit product mold sharing cost by 30%, adapting to the mass production needs of the home appliance industry. The mold has excellent stability, with a service life of up to 5 million cycles under normal production conditions, far exceeding the 3 million cycles of ordinary molds, greatly reducing mold replacement frequency and production costs. At the same time, the mold is suitable for food-grade material molding, and the products can directly meet the refrigerator assembly standards without additional grinding, shortening the production chain.

Daily mold maintenance should focus on precision maintenance and food-grade hygiene control: regularly polish and maintain the cavity every 100,000 cycles to remove slight surface wear marks and maintain the mirror effect; clean the hot runner nozzle and gate area after each shutdown to avoid residual material accumulation affecting the next molding; regularly inspect the ejection mechanism and seals, and replace aging components in time to prevent hydraulic oil leakage; clean the cavity and apply food-grade anti-rust oil before mold storage to avoid rust and contamination, ensuring product safety.

Conclusion: The design and manufacturing of plastic drawer molds for refrigerators accurately meet the core needs of the home appliance industry for mass production, precision, and safety. Through scientific cavity structure design, efficient cooling system configuration, and full-process precision control, the mold not only achieves dual improvements in product quality and production efficiency but also provides a replicable technical idea for the mold development of similar plastic components in the home appliance industry (such as storage boxes and door liners). With the upgrading of the home appliance industry towards lightweight and environmental protection, plastic tooling will further optimize material selection and structural design, helping home appliance products improve quality and efficiency.