Core Benefits of Round Design for Plastic Products

1.Mold Machining and Injection Molding Process

（1）Relieve Stress Concentration to Prevent Mold Cracking and Edge Chipping
Sharp right-angle corners impose extreme stress on mold steel, causing microcracks and edge chipping under long-term repeated injection impact. Fillets disperse clamping and injection pressure, extend mold service life and reduce mold maintenance costs.

（2）Optimize Melt Flow to Reduce Short Shots, Weld Lines and Air Bubbles
Plastic melt generates eddy currents and trapped air when flowing through right angles. Smooth fillet transition ensures uniform cavity filling, effectively eliminating defects such as air burn, short shots and obvious weld lines, and improving appearance yield.

（3）Reduce Demolding Resistance to Avoid Product Scratches and Whitening
Right-angle inner walls cause vacuum adsorption and high friction resistance. Products with fillets can be ejected smoothly without sharp corners, preventing surface whitening, scratches and deformation.

（4）Simplify Polishing to Improve Glossy and Matte Appearance
Sharp mold corners are difficult to polish and prone to tool marks and pitting. Curved fillets feature excellent machinability for polishing, delivering uniform high-gloss or matte surface effect.

2.Structural Strength of Plastic Products

（1）Eliminate Internal Stress to Prevent Cracking and Warpage
Abrupt wall thickness changes at right-angle corners cause uneven shrinkage and huge internal stress during cooling, leading to cracking under storage, low-temperature or assembly stress. Gradual fillet transition stabilizes wall thickness and greatly reduces internal stress.

（2）Enhance Impact and Drop Resistance
Sharp corners are structural weak points where impact stress concentrates completely during dropping. Fillets disperse impact force, improve product toughness, and are widely applied to casings, handheld devices and children’s products.

（3）Reduce Edge Chipping During Assembly
Right-angle edges are easy to break during assembly, screw tightening and buckle fitting. Fillet transition avoids collision damage and lowers assembly defect rate.

3.Appearance and Operational Safety

（1）Prevent Scratches and Comply with Safety Standards
Sharp corners may hurt human skin and damage clothes. Fillet design is mandatory for children’s products, home appliance casings and handheld devices to meet 3C, toy and kitchenware safety regulations.

（2）Optimize Visual Texture and Product Aesthetics
Smooth fillet lines deliver softer visual effects than rigid right angles, which has become the mainstream design style for consumer electronics and home products.

（3）Reduce Dirt Residue and Facilitate Cleaning
Right-angle gaps trap dust, water and oil stains easily. Curved fillets leave no sanitary dead corners for easy wiping, suitable for kitchenware, bathroom and medical plastic parts.

4.Post-processing and Assembly Advantages

（1）Prevent Coating and Electroplating Peeling
Edge coatings on right-angle corners are thin and prone to peeling under stress during spraying, UV coating and electroplating. Fillets ensure uniform coating thickness and enhance adhesion.

（2）Improve Assembly Compatibility and Protect Matching Parts
When matched with metal, sheet metal and other plastic parts, filleted edges will not scratch mating components and reduce assembly wear.

Supplementary Design Tips

• Minimum inner fillet of regular casing: R≥0.5mm; Appearance fillet: R1.0~3.0mm;
• Uniform wall thickness principle: Outer fillet radius R ≥ 0.5 times of product wall thickness to avoid sink marks caused by local glue accumulation.