Refrigerator drawers are load-bearing interior plastic parts for household appliances, mostly made of modified tough PP materials. Such products are featured with large volume, uniform wall thickness, dense reinforcing ribs and sliding rail undercut structures. They have strict requirements on appearance quality with no shrinkage, whitening, deformation and flash allowed. Traditional refrigerator drawer molds have many common defects in mass production, including uneven cooling, unsmooth demolding, poor exhaust effect and serious forming distortion. In order to reduce defective rate, improve mold operation stability and shorten molding cycle, targeted structural optimization is implemented on original molds to form complete technical improvement schemes.
1. Defect Analysis of Original MoldsIn terms of product forming, long melt flowing distance easily causes air trapping at terminal positions, resulting in air lines, burning marks and obvious welding lines. Thick rib positions are prone to surface shrinkage pits which damage overall appearance quality. Undercut sliding rail positions suffer large demolding resistance, leading to frequent surface pulling damage and whitening problems. In mold structure design, single-point feeding causes unbalanced material flow and obvious left-right temperature difference of drawers, triggering serious forming torsion deformation. Ordinary inclined pin core-pulling structures have large matching gaps and are easy to wear after long-term operation, generating continuous edge flash. Sparse layout of cooling pipelines leads to insufficient heat dissipation at key positions and prolonged forming cycle. In actual production, unreasonable ejector pin arrangement causes uneven stress and obvious ejection marks on product bottom. Insufficient exhaust groove setting fails to discharge internal air rapidly during high-pressure injection, while low mold guiding precision causes core position deviation and persistent burr problems.
2. Gating System Optimization
The traditional single large sprue structure is cancelled, and symmetrical double-side horn gates plus auxiliary submarine gates are adopted to balance melt flowing speed, shorten flowing paths and effectively control drawer torsion deformation. Transition positions of flow channels are designed with circular arc smooth connection to lower material shear heat and restrain air line defects of PP raw materials. Material collecting wells are added at corner thick material areas to intercept cold materials and avoid surface color spots and silver lines, greatly improving finished product appearance cleanliness.
3. Undercut Core-pulling Mechanism ImprovementThe thin original inclined pins are upgraded into thickened sliding bases combined with embedded split inserts, with sliding matching gaps strictly controlled within 0.01mm to completely eliminate flash at undercut positions. Wear-resistant plates are installed on all friction moving surfaces with overall nitriding hardening treatment to enhance surface hardness and avoid operational jamming and pulling damage in long-term continuous production. Split combined insert design is adopted for undercut structures, realizing independent replacement of worn parts without disassembling integral cores, effectively lowering later mold maintenance cost and shortening repair cycle.
4. Cooling Pipeline System UpgradeFully profile surrounding cooling circuits are arranged, with pipelines closely attached to cavity surfaces and controlled within 25mm spacing range to realize uniform and consistent mold temperature distribution. Independent water well strengthening cooling is added at four corner high-temperature dead zones to improve local shrinkage and stress concentration deformation. Quick-connect joints are uniformly used for pipeline interfaces with internal anti-rust treatment to prevent scale blockage, steadily shorten integral molding cycle by 15% to 20% and greatly boost production efficiency.
5. Exhaust Structure Optimization
Precision exhaust grooves with 0.015mm depth are opened at melt terminal positions, rib roots and corner dead zones to solve air trapping and product burning problems. Annular exhaust grooves are processed on parting surfaces to expand overall exhaust area and rapidly discharge compressed air inside cavities. Reserved exhaust gaps are set at inclined pin sliding contact surfaces to thoroughly eliminate whitening defects caused by air trapping at undercut positions.
6. Ejection System Structural AdjustmentCombined ejection mode of flat pins, round pins and local ejection blocks is applied, with ejection components densely arranged at drawer bottom, reinforcing rib areas and edge stress points. All ejector pins are made of SKD61 material with nitriding treatment to ensure smooth surface, good wear resistance and synchronous ejection action, fundamentally solving product surface whitening and deformation caused by unbalanced ejection force. Mechanical limit reset devices are installed to accurately control reset stroke and effectively prevent mold closing collision and insert crushing failures.
7. Mold Material Selection and Surface Treatment StandardHigh-rigidity 45# refined plates are selected for mold bases to keep overall structural stability and avoid shape changes after frequent mold opening and closing. 718H pre-hardened steel is used for cavities and cores, which has excellent polishing performance and is suitable for fine matte grain processing of household appliance interior parts. Inclined pins, sliding blocks and various wear-resistant inserts adopt high-performance SKD61 steel to improve comprehensive wear resistance. Uniform and delicate matte texture treatment is implemented on core surfaces to meet the comfortable touch and appearance standards of refrigerator interior accessories.
8. Practical Improvement Effects after Optimization
After overall structural optimization, common forming defects such as shrinkage, air lines, pulling damage and ejection whitening are completely eliminated, and qualified product rate is stably increased above 99%. Optimized cooling systems greatly shorten single-piece forming cycle and realize remarkable production capacity improvement. Wear-resistant structural design and overall nitriding treatment effectively extend comprehensive mold service life by 40%. The optimized mold runs stably in full-automatic production without sticking mold and operational jamming failures. Meanwhile, manual trimming work such as flash removal is reduced, effectively cutting down comprehensive production and processing costs.
9. Overall SummaryThis optimization work carries out comprehensive improvement covering gating system, core-pulling mechanism, cooling layout, exhaust design, ejection structure and mold material selection, thoroughly solving various persistent problems of traditional refrigerator drawer molds in actual production. The optimized molds feature compact structure, convenient daily maintenance and stable mass production performance, fully meeting the high-quality and large-scale production demands of household appliance industry. It also provides reliable practical reference for structural optimization of similar large thin-walled household plastic parts molds.
