How to achieve automatic demolding of electronic product injection molding?

1, The technical principles and core challenges of automatic demolding
Scientific calculation of demolding force
The core formula for demolding force is:
F = A × P × μ + F₀
Among them, A is the surface area of the product side, P is the cavity pressure, μ is the friction coefficient, and F ₀ is the vacuum adsorption force. Taking the middle frame of a mobile phone as an example, if the product size is 150mm × 70mm × 8mm, using PC/ABS material (μ ≈ 0.3), and the cavity pressure is usually 30-50MPa, the theoretical demolding force needs to reach 800-1200N. In actual production, CAE software (such as Moldflow) needs to simulate the melt filling process, optimize the gate position and cooling water circuit layout to reduce demolding resistance.
Key contradictions during demolding process
Product deformation control: Thin walled parts (thickness<1mm) are prone to warping during ejection due to stress concentration. For example, a smartwatch case had a yield rate of less than 80% for a long time due to an unreasonable pin layout. Later, by adopting a multi-stage ejector design (initial speed<10mm/s, later accelerated to 50mm/s), combined with silicone assisted ejector pins, the yield rate was increased to 95%.
Inverted structure treatment: Products with threads or buckles need to be demolded through a lateral core pulling mechanism. A certain laptop shaft mold uses a slanted needle to drive the shaft core to rotate and demold. Through the cooperation of the slanted needle travel hole and the precision positioning wedge, the demolding stroke error is controlled within ± 0.02mm.
Extended mold life: The sprue area is prone to wear due to high-frequency shear. A certain auto parts factory has increased the mold life from 100000 times to 300000 times by using powder metallurgy steel (ASP-23, hardness HRC60-62) sprue inserts, combined with titanium (TiN) coating.
2, Design points of automatic demolding system
Selection of driving mode
Pneumatic demolding: suitable for deep cavity thin-walled parts (such as medical test tubes), directly blow out the product through 0.4-0.6MPa compressed air. A certain medical device supplier adopts a pneumatic dual demolding mechanism, which sets air inlets in the fixed and moving molds respectively to achieve non-destructive demolding of complex structural products.
Hydraulic demolding: used for large structural components (such as automotive instrument panels), providing stable ejection force through hydraulic cylinders. A certain new energy vehicle company adopts a servo hydraulic system, combined with pressure sensor feedback, to control the fluctuation of the top out force within ± 5N.
Mechanical demolding: The traditional combination of top pins and push plates is still mainstream, but the top pin holes need to be processed through slow wire cutting (accuracy ± 0.003mm) to avoid motion jamming. A certain mobile phone mold factory reduced the depth of the ejector mark from 0.1mm to 0.03mm by optimizing the arrangement of the ejector pins (spacing ≤ 15mm).
Intelligent Control Strategy
Multi stage ejection control: A certain electronic cigarette shell mold adopts a three-stage ejection design: the first stage releases internal stress at a speed of 5mm/s, the second stage accelerates to 20mm/s to complete preliminary separation, and the third stage slowly ejects at 10mm/s to the endpoint. This plan reduces the deformation rate of the product from 12% to 1.5%.
Vacuum adsorption assistance: A vacuum chamber is integrated on the back of the mold, and a negative pressure of -80kPa is generated by a vacuum generator to adsorb the surface of the product. After adopting this technology, the number of top pins in a certain AR eyeglass frame mold decreased by 60%, and the surface smoothness (Ra) of the product increased from 0.8 μ m to 0.3 μ m.
Real time monitoring of sensors: Install pressure sensors and displacement sensors on the top plate, and monitor the demolding process in real time through PLC. A certain precision connector mold automatically shuts down when the demolding force is abnormal through this system to avoid mold damage.
3, Typical application case analysis
Automatic demolding mold for mobile phone protective case
A certain utility model patent uses elastic components to drive the top rod for demolding: when the mold is closed, the L-shaped pressure rod is subjected to the pressure of the upper mold, causing the lifting plate to descend, and the top block is flush with the surface of the mold cavity; When opening the mold, the elastic component (limit spring+support rod) pushes the lifting plate up, and the top rod pushes the product out. This design reduces the demolding time from 3 seconds to 0.8 seconds without the need for manual intervention.
Laptop shaft rotation demolding
A certain shaft mold adopts a diagonal needle shaft core linkage mechanism: after injection molding is completed, an external driving device pushes the diagonal needle to move downward along the diagonal hole, and drives the shaft core to make circular motion through the shaft travel slot, separating the toothed inverted buckle structure from the product. This plan controls the demolding stroke error within ± 0.05mm to avoid damage to the internal threads of the product.
Pneumatic demolding of smart watch strap
A certain watch strap mold adopts pneumatic rotary demolding technology: the threaded core is driven to rotate by a cylinder, and the product is blown out with compressed air. This design shortens the demolding cycle from 15 seconds to 8 seconds, and the product surface has no protruding marks, meeting the high requirements of the high-end market for appearance.