Zinc Die Casting Lock Body High Volume Case Study
Zinc die casting lock body high volume case study: SHG zinc purity checks and gate redesign eliminated 3.2% plating rejection on Zamak 5 padlock bodies.
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Finished Component
The completed die casting or machined component delivered for this project, demonstrating dimensional accuracy and surface quality.
Production & Inspection
In-process die casting operations, leak testing, machining, and quality inspection steps applied during this program.
Customer: Security hardware manufacturer, Taiwan Program: Padlock body, inner and outer components Annual volume: 2.4 million pieces/year (3-cavity die) Material: Zamak 5 zinc alloy Surface: Decorative chrome (electroplated by customer) Requirements: Zero plating rejection from casting defects; die life >=500,000 shots/cavity
The Challenge
Previous Chinese supplier had a 3.2% plating rejection rate -zinc pest-like blistering appearing after plating. Customer's plating partner confirmed blisters originated in the casting substrate. Cause: impurity-contaminated zinc ingot causing inter-granular corrosion, visible under chrome/nickel plating after exposure to plating bath chemistry.
Additionally, previous supplier's dies required major refurbishment at 400,000 shots -half the required service life. Gate erosion was the primary failure mode.
Solution
SHG Zinc with Spectrometer Verification Every Melt
KastMfg uses only Special High Grade (SHG) zinc at 99.99% minimum purity. Every production melt is verified by OES spectrometer: Pb <=0.005%, Cd <=0.004%, Sn <=0.003% -the critical purity limits below which zinc pest does not occur.
Previous supplier was using 99.95% commercial zinc with Pb averaging 0.012% -2.4x above the limit. KastMfg provided spectrometer certificates for all 14 production melts in year one.
Result: zero zinc pest-related plating rejections in 2.4 million pieces.
Gate Redesign: Reduced Velocity
Previous die: gates sized for maximum fill speed (52 m/s), sacrificing gate longevity. KastMfg redesigned gate geometry to maintain fill quality at 38 m/s -below zinc's soldering threshold, complete fill in 22 ms.
Die life: First die set reached 1,200,000 shots before scheduled gate insert replacement. Overall maintenance in 1.2M shots: two ejector pin replacements, one parting line refinish.
As-Cast Surface Quality
As-cast surface Ra on visible faces: 0.9-1.3 μm. No vibratory polishing required before plating -eliminating one pre-plating step and its cost.
Results
| Metric | Previous supplier | KastMfg |
|---|---|---|
| Plating rejection rate | 3.2% | 0.08% |
| Die life before major refurbishment | 400,000 shots | 1,200,000 shots |
| Melt spectrometer records | Not provided | Every melt, archived 3 years |
| As-cast Ra (visible faces) | 1.4-2.1 μm | 0.9-1.3 μm |
| Zinc pest incidents in 24 months | Multiple field returns | Zero |
Contact KastMfg: casting@kastdiecast.com | +86 138 1403 4409 | No.6, Rungu Road, Nanjing, China
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