Quality Case / Zinc Die Casting Finishing
Zinc Die Casting Over-Polishing Quality Problem Case Study
How excessive polishing removes edges and contour lines on zinc alloy die cast parts, and how to control the finishing process.
Problem Description
The defect shown in the production photos is typical over-polishing: the operator removes too much material around the edge and contour area. The original crisp edge, step line or parting-line visual reference becomes rounded and unclear.
For decorative zinc die cast parts, polishing is not only a surface cleaning process. It directly affects product geometry, edge definition and customer-perceived quality.
Why Over-Polishing Happens
| Cause | What Happens | Quality Risk |
|---|---|---|
| Casting defect covered by polishing | Flow marks, parting flash, dents or carbon marks are removed by grinding instead of solving the upstream cause | Edges and lines are consumed while the real casting problem remains |
| No limit sample | Operators judge by experience without a clear OK/NG boundary | Different workers create different edge shapes |
| Wrong abrasive tool | Coarse belt, hard wheel or high-speed hand tool removes material too quickly | Local flat spots, rounded corners and uneven gloss appear |
| Uncontrolled pressure and time | Polishing force and contact time are not standardized | Good parts become NG parts during finishing |
| No protected edge design | Critical edge or decorative line has no fixture protection | Feature line disappears after repeated polishing |
How to Judge the Defect
Control Plan
- Create OK, warning and NG limit samples for edge definition, contour line and surface gloss.
- Define no-polish or light-polish protected zones around decorative edges, parting lines and assembly references.
- Replace free-hand heavy grinding with fixture-guided polishing where the edge must be preserved.
- Use finer abrasive sequence and reduce single-step material removal instead of one aggressive grinding operation.
- Record abrasive type, tool speed, contact pressure and polishing time for production repeatability.
- Fix upstream casting causes such as flash, flow mark, shrinkage or carbon mark instead of relying on polishing to hide them.
Engineering Recommendation
| Stage | Required Action | Acceptance Evidence |
|---|---|---|
| Mold trial | Confirm whether the edge and parting line are already clean before polishing | Trial samples and cavity-separated photos |
| Polishing setup | Lock abrasive grade, fixture, motion direction and maximum polishing time | Process instruction and operator training record |
| First article | Compare with limit sample before batch production | Approved first article photos and measurement data |
| Mass production | Inspect contour line, edge radius, mating gap and appearance consistency | Sampling record and defect Pareto |
Conclusion: over-polishing is a process-control failure. The right solution is to reduce upstream defects, protect critical edges, define limit samples and control polishing parameters. Do not use grinding as an unlimited repair method.
Need help reviewing polishing defects?
Send photos, drawings, finishing route, limit samples and inspection data. XSD can help separate casting defects, polishing defects and surface-treatment risks.
Send Defect Data质量案例 / 锌合金压铸后处理
锌合金压铸打磨过度质量问题案例
说明锌合金压铸件打磨过度如何导致棱角和线条消失，以及如何建立后处理过程控制。
问题现象
图片里的缺陷是典型的打磨过度：操作员在端部、棱边和轮廓线附近去除材料太多，原本应该保留的尖角、台阶线、分型线或装饰线变圆、变钝，甚至完全看不清。
对装饰类锌合金压铸件来说，打磨不是简单的清理表面。它会直接影响产品几何形状、边界清晰度和客户看到的品质感。
打磨过度的根因
| 原因 | 现场表现 | 质量风险 |
|---|---|---|
| 用打磨掩盖压铸缺陷 | 流痕、飞边、压伤、积碳印靠打磨处理，而不是解决前端原因 | 棱角和线条被磨掉，真实压铸问题仍然存在 |
| 没有限度样 | 员工凭经验判断，没有清楚的 OK/NG 边界 | 不同员工打出来的棱角和线条不一致 |
| 砂带或工具选择错误 | 砂带太粗、砂轮太硬、手持工具速度过高 | 局部平面、圆角变大、光泽不均 |
| 压力和时间不受控 | 打磨力度、接触时间没有标准 | 良品在后处理过程中被打成不良品 |
| 关键边没有保护 | 装饰线、分型线、装配边没有工装保护 | 重复打磨后特征线消失 |
如何判断是否 NG
过程控制方法
- 建立 OK、警戒、NG 限度样，明确棱角、轮廓线和表面光泽的接受边界。
- 对装饰边、分型线、装配基准边设定禁止重磨或轻磨保护区。
- 关键外观边不要完全自由手打磨，应使用工装限位或导向打磨。
- 采用更细的砂带顺序，减少单次去除量，不要用一次重磨解决所有问题。
- 记录砂带型号、工具转速、接触压力和打磨时间，保证批量可重复。
- 前端压铸的飞边、流痕、缩水、积碳印要从模具和工艺解决，不能长期依赖打磨遮盖。
工程改善建议
| 阶段 | 必须动作 | 验收证据 |
|---|---|---|
| 试模阶段 | 确认打磨前棱边和分型线是否已经足够干净 | 试模样件和按穴号拍摄的照片 |
| 打磨设定 | 锁定砂带目数、工装、运动方向和最大打磨时间 | 作业指导书和员工培训记录 |
| 首件确认 | 批量前必须和限度样对比 | 首件照片和尺寸数据 |
| 量产检查 | 检查轮廓线、圆角、装配间隙和外观一致性 | 抽检记录和不良 Pareto |
结论：打磨过度不是单纯员工手法问题，而是过程控制失效。正确做法是减少前端压铸缺陷、保护关键棱边、建立限度样并控制打磨参数。打磨不能作为无限制的返修手段。