What issues should be paid attention to when molding Bluetooth earphones?

1, Die Design: Double Challenges of Precision and Complexity
The design of Bluetooth earphone molds needs to break through the precision boundaries of traditional consumer electronics molds to achieve precise molding of millimeter level structures. For example, the wall thickness of a TWS earphone shell from a certain brand is only 0.6mm, and it requires the integration of micro structures such as charging contacts and microphone holes, which places extremely high demands on the mold's parting surface design, gate layout, and exhaust system.
Optimization of parting surface and gate
The parting surface should avoid the appearance of the product and prevent the mold line from affecting the integrity of the high gloss surface. For the thin-walled characteristics of the earphone casing, it is recommended to use point gates or hidden gates to reduce the impact of gate marks on the appearance. A certain enterprise reduced the diameter of the gate to 0.3mm, resulting in a 60% decrease in the diameter of the gate marks on the black glossy shell, significantly improving product yield.
Refinement of exhaust system
The exhaust slot design of Bluetooth earphone molds needs to balance exhaust efficiency and flash control. For high viscosity materials such as PC/ABS, the depth of the exhaust groove should be controlled between 0.02-0.03mm and the width should not exceed 1.5mm. In a certain case, by adding a 0.02mm deep exhaust groove at the edge of the core, the problem of bubbles at the edge of the earphone shell was successfully solved, and the product qualification rate increased from 82% to 95%.
Balancing of cooling system
The mold cooling water channel needs to adopt a conformal design to ensure that the cooling rate difference between different parts of the product is less than 15%. A certain enterprise has developed a "spiral+straight through" composite cooling water channel for earphone charging case molds, which shortens the cooling time to 18 seconds, improves efficiency by 40% compared to traditional designs, and controls product warpage deformation within 0.05mm.
2, Material Selection: The Art of Balancing Performance and Cost
The mold material for Bluetooth earphones needs to balance wear resistance, corrosion resistance, and processing performance. The mainstream choices include:
Mold steel material
NAK80: Suitable for small and medium-sized molds, with excellent polishing performance, capable of achieving a # 12000 mirror effect, but moderate wear resistance, suitable for molds with an annual output of less than 500000 times.
S136H: Pre hardened treatment, with a hardness of HRC32-35 and strong corrosion resistance, suitable for producing acidic materials such as PC and ABS. A certain headphone brand has extended the mold life to 800000 times by using S136H mold steel.
H13: Hot work mold steel, suitable for processing high-temperature materials such as PPS and PEEK, but requires nitriding treatment to improve surface hardness.
Surface treatment technology
PVD coating: Deposition of TiN or CrN coating on the surface of the mold cavity can improve wear resistance by 3-5 times. A certain enterprise has extended the polishing cycle of the earphone shell mold from every 20000 times to 80000 times through PVD treatment.
Laser cladding: For the easily worn areas on the edge of the mold core, laser cladding technology is used for repair, which can restore the dimensional accuracy to ± 0.002mm, and the repair cost is only 30% of that of newly made molds.
3, Process Control: Parameter Optimization and Defect Prevention
The injection molding process for Bluetooth earphones needs to achieve "three lows and one high": low injection pressure, low mold temperature, low locking force, and high filling speed. Typical process parameters are as follows:
Parameters: PC/ABS material, LCP material
Melt temperature 260-280 ℃ 320-340 ℃
Mold temperature 80-90 ℃ 120-130 ℃
Injection pressure 80-100MPa 120-150MPa
Holding pressure 60-70MPa 90-110MPa
Cooling time 15-20 seconds 8-12 seconds
Flying edge and shrinkage control
Flying edges are often caused by insufficient locking force or wear on the parting surface of the mold. They can be solved by increasing the locking force to 1.2 times the theoretical value or using a hydraulic clamping system. Shrinkage marks require optimization of product design to ensure uniform wall thickness, and compensation for material shrinkage by increasing the holding pressure to 70% -80% of the injection pressure.
Prevention of high gloss surface defects
In response to the white fog phenomenon of the black highlight shell, optimization is needed from two aspects: mold exhaust and process parameters:
Mold exhaust: Adding a 0.02mm deep exhaust groove at the edge of the mold cavity, combined with a vacuum pump for pumping, can reduce the trapped gas rate by 80%.
Process adjustment: Adopting the "low pressure slow speed" filling strategy, the injection speed is controlled at 30-50mm/s, and the mold temperature is raised to 90 ℃, which can effectively reduce material degradation caused by melt shear heat generation.
4, Defect Prevention: Closed loop Management from Design to Production
The prevention of defects in Bluetooth earphone molds requires the establishment of a three-level control system of "design trial production":
design phase
Use Moldflow software for mold flow analysis to predict the filling path, pressure distribution, and warpage deformation of the melt. A certain enterprise optimized the gate position of the earphone charging case mold through simulation, reducing the product warpage from 0.12mm to 0.03mm.
Trial stage
Using DOE (Design of Experiments) method to optimize process parameters, with a focus on the interactive effects of injection speed, holding pressure, and cooling time. In a certain case, the optimal process combination was determined through orthogonal experiments to reduce the short emissivity of the earphone shell from 15% to 2%.
Mass production stage
Establish an SPC (Statistical Process Control) system to monitor in real-time the fluctuation range of key parameters such as injection pressure and mold temperature. A certain enterprise increased the product size CPK value from 1.0 to 1.67 by setting a process parameter control limit of ± 5%.
5, Maintenance and upkeep: a key measure to extend the lifespan of molds
The maintenance of Bluetooth earphone molds should follow the principle of "prevention first, repair as a supplement":
Daily maintenance
Cleaning: Clean the mold cavity with a copper brush after each production, and do not use iron wire to prevent scratching the surface.
Lubrication: Apply high-temperature grease to moving parts such as guide columns and top pins every week to reduce wear.
Rust prevention: When production is stopped for more than 48 hours, rust prevention oil should be sprayed on the surface of the mold and stored in a constant temperature and humidity warehouse.
Regular maintenance
Mold cavity testing: Use a coordinate measuring instrument to test the size of the mold cavity every 50000 production cycles. If the deviation exceeds 0.02mm, it needs to be repaired.
Hot runner maintenance: Check the resistance value of the hot runner heating coil every 3 months, and replace it if the deviation exceeds 10%.
Cooling system cleaning: Clean the cooling water channel with a high-pressure water gun every six months to prevent scale blockage.