How to ensure the dimensional accuracy of electronic injection molds?

一, Design phase: Building a precision controlled digital base
1. Deep integration of 3D modeling and model flow analysis
The digital simulation of mold structure through CAD/CAE technology can identify potential risks such as melt flow and cooling shrinkage in advance. For example, in the development of the Xiaomi 14 Ultra ceramic frame mold, engineers used Moldflow software to simulate the temperature distribution of the melt in the mold cavity and found a local shrinkage deviation of 0.03mm in the original design. By optimizing the gate position and cooling water circuit layout, the actual shrinkage rate fluctuation was ultimately controlled within ± 0.005mm.
2. The "three-level progressive" strategy for tolerance allocation
Electronic injection molds must follow the progressive principle of "mold part tolerance<plastic part tolerance<assembly tolerance". Taking the Apple Watch Ultra strap mold as an example, the plastic part tolerance requirement is ± 0.05mm, and the mold core tolerance needs to be compressed to ± 0.01mm. At the same time, dynamic compression technology is used to compensate for a material shrinkage rate of 0.03%, ensuring that the final product meets the sealing requirements of IP68 waterproof certification.
3. Innovative design of conformal cooling water circuit
For complex structural components such as curved screens, traditional linear cooling water circuits are prone to local overheating and deformation. The Samsung Galaxy Z Fold series folding screen hinge mold adopts 3D printing technology to manufacture a conformal cooling water circuit, which improves cooling efficiency by 40%, reduces product warpage from 0.15mm to 0.03mm, and significantly improves the pass rate of opening and closing life tests.
二, Material selection: laying the physical foundation for stable accuracy
1. Directional application of high-strength wear-resistant steel
Electronic molds need to withstand high-frequency injection pressure impacts. Cr12MoV mold steel, after quenching and tempering treatment, can achieve a hardness of HRC58-62 and resist the erosion and wear of plastic melts. The Lenovo Moto razr 50 Ultra folding screen hinge mold uses this material, and after 2 million opening and closing tests, the wear of key dimensions is still controlled within 0.005mm.
2. Optimization of the proportion of thermally stable materials
H13 steel has become the preferred substrate for electronic molds due to its excellent thermal fatigue performance. In the OPPO Find X7 Ultra periscope telephoto lens mold, by adding 0.3% molybdenum element, the mold can work continuously for 500 hours at a high temperature of 150 ℃, reducing the occurrence of hot cracks by 70% and improving dimensional stability by three times.
3. Electric slag remelting process with purity control
Impurities can cause defects such as pitting and porosity in injection molded parts. The back cover mold of Huawei P70 Art Edition is made of SKD61 steel purified by electroslag remelting. The content of harmful elements such as sulfur and phosphorus is controlled below 0.005%, resulting in a surface roughness of Ra0.08 μ m and meeting high gloss requirements.
三, Processing technology: achieve micrometer level manufacturing accuracy
1. Five axis linkage high-speed milling technology
In the manufacturing of curved glass molds for vivo X100 Pro, a micro tool path strategy with a step size of 0.01mm is adopted, combined with a tool compensation of 0.005mm, to achieve a surface roughness of Ra0.1 μ m on the mold cavity, which is three precision levels higher than traditional machining.
2. Dynamic compensation of precision electric discharge molding machine
For the buckle structure of the mobile phone card holder mold, the fitting tolerance is controlled within ± 8 μ m by real-time monitoring of electrode loss and automatic adjustment of discharge parameters. This technology enables the product to pass 100000 insertion and extraction tests, increasing its lifespan by 5 times compared to traditional processes.
3. Intelligent control of laser cladding repair
When the wear of the mold core exceeds the tolerance, laser cladding technology is used for in-situ repair. The Xiaomi 14 series camera module mold uses this technology to increase the bonding strength between the repair layer and the substrate to 450MPa, with a size recovery accuracy of ± 2 μ m, which is 80% more efficient than traditional welding processes.
四, Detection technology: Building a closed-loop quality system throughout the entire process
1. Full size scanning of coordinate measuring machine
In the acceptance stage of the Porsche design rear cover mold for Honor Magic6 RSR, a 0.001mm precision coordinate measuring machine was used to scan and detect 2000 key points on the mold frame. When the flatness error exceeds 0.015mm, the system automatically triggers the repair process to ensure the accuracy of mold assembly.
2. Real time monitoring of optical projectors
During the injection molding production process, the first product is subjected to full-size inspection through an optical projector, and the data is uploaded in real-time to the MES system. When the size deviation exceeds the warning value, the system automatically adjusts the parameters of the injection molding machine to stabilize the product qualification rate at above 99.2%.
3. Temperature field analysis of infrared thermography
For medical microfluidic chip molds, infrared thermal imaging is used to monitor the temperature distribution of the mold. When the local temperature difference exceeds 5 ℃, the system automatically adjusts the cooling water flow rate to ensure that the consistency of product shrinkage rate reaches 98.5%.
五, Maintenance Management: A Scientific Strategy for Extending Precision Life
1. Preventive maintenance based on PFMEA
Establish a Mold Failure Mode and Effects Analysis (PFMEA) database to predict the lifespan of vulnerable parts such as ejector pins and sliders. When the cumulative injection molding times reach 80% of the design life, the system automatically generates a replacement work order to avoid size deviation caused by sudden failures.
2. Wear resistance enhancement of nano coatings
Spray diamond-like carbon (DLC) nano coating on the surface of the mold cavity to reduce the friction coefficient to 0.05 and improve wear resistance by 10 times. After adopting this technology, the maintenance cycle of the metal frame mold for Samsung Galaxy S25 Ultra has been extended from every 50000 molds to 200000 molds.
3. Full lifecycle management of digital twins
Build a virtual model of the mold through digital twin technology, and collect real-time process parameters such as injection pressure and temperature. When the monitoring data deviates from the standard value, the system automatically generates an optimization plan to control the mold size accuracy attenuation rate within 0.001mm/year.