Reliability in Coating: Why SPC Matters More Than Sample Testing
1. Introduction
In the coating industry, the word reliability is often associated with good samples, passed tests, and acceptable coating weight results. But those indicators alone don’t always reveal whether a process is under true control. Many job coaters rely only on sampling methods to approve a coating lot, which may look compliant on paper but still hide significant variations inside the batch.
To achieve genuine and consistent reliability, manufacturers must go beyond basic testing. This is where Statistical Process Control (SPC) becomes the game-changer.
At Aum Dacro, we use SPC not as an optional tool, but as a core quality discipline to ensure every basket reflects real process stability — not just sample-based acceptability.
2. Why Sampling Alone Cannot Guarantee Reliability
Most coaters follow a simple sampling plan:
-
Pick 3–5 samples
-
Measure coating weight
-
Approve the lot if the numbers look okay
But here’s the flaw — samples do not represent the entire basket. A few parts may show acceptable coating thickness, while dozens or hundreds of other parts may still fall outside the required tolerance.
Sampling gives the illusion of reliability, but not the proof.
A coating lot may pass based on sample reports, yet fail in:
-
Corrosion resistance
-
Torque-tension behavior
-
Performance consistency during assembly
-
Long-term durability
If your quality assurance depends only on samples, you’re leaving too much to chance.
3. What SPC Really Reveals About Your Coating Process
Statistical Process Control provides a far deeper and more accurate view of the process. Instead of depending on a few pieces, SPC analyzes the entire distribution of coating weight across the full basket.
An SPC curve helps you understand:
-
Whether the process is stable
-
Whether variation is controlled
-
Whether the coating weight is evenly distributed
-
Whether the process naturally tends toward consistency
-
Whether the lot is genuinely reliable
The SPC curve does not just tell you “pass” or “fail.”
It tells you how healthy your process really is.
When the SPC curve is narrow, it indicates:
✔ Controlled variation
✔ Uniform coating
✔ Predictable results
✔ Strong process reliability
When the SPC curve is broad, it indicates:
✘ Inconsistent weights
✘ Hidden errors
✘ Poor coating spread
✘ Lack of control — even if the minimum coating weight is met
This is why SPC is essential for achieving real reliability.
4. The Hidden Risk of “Passing Samples”
A big misconception in the industry is believing that passing samples equals a good process. But this isn’t always true.
Consider this scenario:
A basket has both heavy-coated and lightly-coated components. If the sample happens to include only well-coated pieces, the report will look perfect.
But in the real batch, many pieces may still be undercoated or overcoated.
This leads to:
-
Inconsistent performance
-
Increased rejection at customer end
-
Torque-tension failures
-
Corrosion test failures
-
Warranty and service risks
Your paperwork may show “pass”, but your product may not show reliability.
5. How Loading Quantity Manipulates Coating Weight Results
This is an industry secret many do not talk about:
Increasing the loading quantity in a basket can artificially increase coating weight results.
More weight = more retained coating on the parts.
This can make the sample report look perfect.
But the SPC curve will expose the truth:
-
Broad distribution
-
High variability
-
Poor process stability
-
High-risk coating spread
So even though the samples show compliance, the coating process is not reliable.
This is why SPC is essential to break this illusion.
6. SPC Curves: The Real Indicator of Process Reliability
An SPC curve is like an ECG for the coating process.
-
A narrow curve means the process is stable, consistent, and operating predictably.
-
A broad curve means the process is unstable, inconsistent, and producing unreliable coating distribution.
This is why Aum Dacro analyzes SPC curves for each basket, not just for a few samples.
With SPC, we achieve:
✔ Predictable coating quality
✔ Uniform spread on every component
✔ Lower variation
✔ Minimum customer complaints
✔ Maximum long-term reliability
7. Why Aum Dacro Uses SPC for Every Basket
At Aum Dacro, we believe that reliability cannot be guessed — it must be measured.
That’s why we track coating weight using SPC for every lot.
Our approach ensures:
-
Every part is coated consistently
-
Variations are identified early
-
Trends are monitored continuously
-
Processes stay under control
-
Customers receive reliable performance, every time
This level of transparency and control protects your components from hidden risks that sample-based testing can never detect.
8. Conclusion
Don’t let your coating process rely on luck or limited samples.
True reliability comes only through Statistical Process Control, where every basket is analyzed, and every variation is exposed.
At Aum Dacro, we don’t settle for “paper-passing” reports.
We deliver real reliability, real consistency, and real performance — driven by SPC.
Don’t settle for sample-based quality.
Choose true process control.
Choose Aum Dacro.
CONTACT US TODAY FOR MORE DETAILS!
Visit us at aumdacro.com