Case Study / Die Casting and Plating Quality
Zinc Alloy Die-Cast Plated Keychain Defect Analysis Case Study
A quality case study based on 379-piece final inspection data for zinc alloy die-cast pearl chrome plated keychains, with Pareto analysis and improvement priorities.
Inspection Data
| Defect Type | Qty | Rate vs Total | Share of Defects | Initial Cause Direction |
|---|---|---|---|---|
| Bubbles | 59 | 15.56% | 40.14% | Die casting porosity, pretreatment residue, plating adhesion or trapped gas after finishing. |
| Impact / handling damage | 46 | 12.13% | 31.29% | Demolding, trimming, polishing, rack handling, transfer boxes or final packing contact. |
| Carbon marks | 15 | 3.95% | 10.20% | Mold release residue, polishing compound, incomplete cleaning or surface contamination before plating. |
| Imprint marks | 10 | 2.63% | 6.80% | Fixture contact, rack marks, inspection handling or pressure during stacking. |
| Rolled edge | 10 | 2.63% | 6.80% | Trimming, deburring, polishing edge control or local thin-wall deformation. |
| Plating defects | 7 | 1.84% | 4.76% | Pretreatment, bath stability, rack conductivity, current density or coating thickness variation. |
Pareto Finding
The top two defects, bubbles and impact or handling damage, account for 105 rejected pieces, equal to 71.43% of all defects. Improvement resources should therefore focus first on separating plating bubbles from die casting substrate defects, and then on controlling handling damage across demolding, polishing, plating racks and packing.
Priority 1: Bubble Defect Investigation
Bubble defects must be split into at least two categories: substrate-related bubbles and plating-process bubbles. Without this split, the team may adjust the plating line while the real cause is porosity, or adjust die casting parameters while the real cause is cleaning or adhesion.
- Cut and inspect selected bubble samples to determine whether the defect starts from the zinc alloy substrate or the coating interface.
- Review die casting parameters, venting, melt temperature, shot stability and mold release usage for trapped gas risk.
- Check polishing residue, degreasing, activation, rinsing and drying before plating.
- Confirm rack position, current density and coating thickness distribution for the pearl chrome finish.
Priority 2: Handling Damage Control
Impact and compression damage is the second largest issue. It is often created after the part is already acceptable, so the improvement path should include physical separation, fixture protection and process ownership, not only operator reminders.
- Separate parts in trays or soft partitions after demolding, polishing and plating.
- Review contact points on trimming tools, polishing fixtures, plating racks and inspection tables.
- Define a no-stacking rule for cosmetic surfaces before final packing.
- Add in-process checks after polishing and after plating to locate the exact damage step.
Process Improvement Route
- Run a second inspection batch after bubble root-cause classification and handling-control actions.
- Track the same six defect categories so the before-and-after result can be compared directly.
- Use a target of reducing bubbles and handling damage by at least 50% before discussing scale-up.
- For regulated automotive or export programs, confirm whether the plating chemistry and finish route meet RoHS, ELV and customer-specific compliance requirements.
The value of this data is not the 38.78% defect rate itself. The value is that the defect structure points clearly to the first improvement actions before mass production.
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Send Quality Data案例学习 / 压铸电镀质量分析
锌合金压铸电镀钥匙扣小批量全检不良分析案例
基于 379 件锌合金压铸电镀钥匙扣小批量全检数据，建立缺陷 Pareto、主因判断和改善优先级。
全检数据
| 不良项目 | 数量 | 占总数 | 占不良品 | 初步归因方向 |
|---|---|---|---|---|
| 汽泡 | 59 | 15.56% | 40.14% | 需区分压铸基材气孔、前处理残留、电镀附着力和镀后起泡。 |
| 压碰伤 | 46 | 12.13% | 31.29% | 重点排查脱模、修边、抛光、电镀挂具、周转盒和包装接触。 |
| 积碳印 | 15 | 3.95% | 10.20% | 可能来自脱模剂残留、抛光蜡、清洗不足或电镀前表面污染。 |
| 印痕 | 10 | 2.63% | 6.80% | 重点检查治具接触、挂具印、检验周转和堆叠压力。 |
| 卷边 | 10 | 2.63% | 6.80% | 可能来自修边、去毛刺、抛光边缘控制或局部薄壁变形。 |
| 电镀不良 | 7 | 1.84% | 4.76% | 排查前处理、槽液稳定性、挂具导电、电流密度和镀层厚度波动。 |
Pareto 结论
汽泡和压碰伤是最主要的两个不良项目，合计 105 件，占全部不良品的 71.43%。因此改善资源不应该平均分散，而应优先判断汽泡到底来自压铸基材还是电镀过程，并同步控制脱模、抛光、电镀挂具、周转和包装造成的压碰伤。
优先事项一：汽泡不良分层分析
汽泡必须先分成至少两类：基材相关汽泡和电镀过程汽泡。如果不做分层，团队可能会在真正问题是压铸气孔时反复调整电镀线，也可能在真正问题是清洗和附着力时错误调整压铸参数。
- 选取典型汽泡样品切开或剥离检查，判断缺陷起点在锌合金基材内部还是镀层界面。
- 复核压铸参数、排气、熔汤温度、射出稳定性和脱模剂用量，判断卷气与气孔风险。
- 检查抛光蜡残留、除油、活化、水洗和烘干等电镀前处理条件。
- 确认珍珠铬效果下的挂具位置、电流密度和镀层厚度分布。
优先事项二：压碰伤过程控制
压碰伤是第二大问题，而且常常发生在产品已经合格之后。改善不能只靠提醒员工小心，而要把防护治具、周转方式和责任工序定义清楚。
- 脱模、抛光、电镀和检验后使用托盘或软隔断，避免外观面直接接触。
- 检查修边工具、抛光治具、电镀挂具和检验台面的接触点。
- 对外观面建立禁止堆叠规则，包装前保持单件隔离或受控周转。
- 在抛光后、电镀后分别增加过程检查，用数据定位压碰伤发生工序。
改善路线建议
- 先完成汽泡归因分层和压碰伤防护动作，再做第二轮小批量复检。
- 复检仍沿用相同六类不良项目，保证前后数据可以直接对比。
- 建议以汽泡和压碰伤各下降 50% 以上作为下一阶段放量前的改善目标。
- 如果用于汽车、出口或合规要求较高项目，应同步确认电镀化学体系和表面处理路线是否满足 RoHS、ELV 及客户指定要求。
这组数据的价值不在于 38.78% 这个不良率本身，而在于它清楚指出了量产前最应该优先改善的两个方向。