Statistical Quality Control
⭐ Meaning of Quality
| 1️⃣ Conformance to specifications |
| 2️⃣ Fitness for use |
| 3️⃣ Customer satisfaction |
| 4️⃣ Delighting the customer |
| 5️⃣ Enchanting the customer (modern view) |
🌟 Dimensions of Quality
| Attribute | Meaning |
|---|---|
| Performance | How well it works |
| Features | Additional characteristics |
| Reliability | Consistency |
| Conformance | Meeting standards |
| Durability | Life of the product |
| Serviceability | Ease of repair |
| Aesthetics | Look & feel |
| Reputation | Brand trust |
🔧 Quality Control
A procedure to measure quality, compare with standards, and correct deviations.
🔹 Quality must be planned → achieved → controlled → improved continuously
📊 Statistical Quality Control (SQC)
Applying statistical methods to control and improve product quality.
🎯 Purpose of SQC
✔ Reduce variation
✔ Improve quality
✔ Lower scrap & rework
✔ Better productivity & inspection
🖼 Seven Quality Control Tools (7-QC)
Below are simplified visual representations to help you post:
| Tool | Simple visual image |
|---|---|
| Flow Chart | 🔁 Start → Step → Step → End |
| Histogram | 📊 ▃▄▅▆█ distribution |
| Cause-Effect (Fishbone) | 🐟 Head (defect) ← Man / Machine / Material / Method |
| Check Sheet | ☑ Tally counts for defects |
| Scatter Diagram | 🔹 Points scattered on X-Y plane showing relationship |
| Control Chart | 📈 CL with UCL & LCL, points staying inside/outside |
| Pareto Chart | 🔶 Bars high → medium → low (80/20 rule) |
⚙ Process Control vs Product Control
| Type | Purpose | Example |
|---|---|---|
| Process Control | Keep production under control | Control Charts |
| Product Control | Accept/reject finished lots | Sampling Inspection Plans |
📍 Variation in Quality
| Type | Meaning |
|---|---|
| Chance Causes | Natural random variation — cannot be eliminated |
| Assignable Causes | Specific avoidable factors — must be identified & corrected |
📌 Control vs Specification vs Tolerance Limits
| Type | Used in | Meaning |
|---|---|---|
| Control Limits | Control Charts | Detect assignable causes |
| Specification Limits | Product design | Max & Min acceptable dimensions |
| Tolerance Limits | Statistical probability | Range expected to cover X% with confidence |
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