CNC CNC Quality Control and Inspection 2 — Questions and Answers
Question 1: In GD&T, what does the 'flatness' callout control?
- How parallel a surface is to a reference datum
- The variation of all points on a surface lying within two parallel planes (Correct answer)
- The squareness of a surface relative to a datum axis
- The profile of a curved surface relative to true position
Correct answer: The variation of all points on a surface lying within two parallel planes
Flatness controls how much a surface can deviate from a theoretically perfect flat plane, defined by a tolerance zone between two parallel planes.
Question 2: What does 'true position' (⊕) tolerance in GD&T define?
- The maximum allowed angle deviation of a hole axis
- The allowed zone within which the center axis or point of a feature must lie (Correct answer)
- The minimum material condition for a bore
- The allowable run-out of a circular feature
Correct answer: The allowed zone within which the center axis or point of a feature must lie
True position defines a cylindrical (or 2D) tolerance zone centered on the theoretically exact position within which the feature's center must fall.
Question 3: What is Statistical Process Control (SPC) primarily used for in CNC machining?
- Programming tool path compensation automatically
- Monitoring production processes to detect trends before defects occur (Correct answer)
- Calculating optimal cutting speeds and feeds
- Scheduling preventive maintenance intervals
Correct answer: Monitoring production processes to detect trends before defects occur
SPC uses control charts and statistical methods to monitor process output over time, identifying when a process is trending out of control before it produces scrap.
Question 4: In precision measurement, what does 'gauge R&R' study evaluate?
- The repeatability and reproducibility of a measurement system (Correct answer)
- The gauge's range and resolution for a given application
- The calibration interval needed for a measuring instrument
- The gauge's resistance to thermal expansion
Correct answer: The repeatability and reproducibility of a measurement system
Gauge R&R (Repeatability and Reproducibility) studies determine how much of the measurement variation comes from the gauge itself versus the parts being measured.
Question 5: What does 'MMC' (Maximum Material Condition) mean in GD&T?
- The condition when the material has the highest hardness value
- The condition where the feature contains the maximum amount of material (smallest hole, largest shaft) (Correct answer)
- The maximum allowed material removal during machining
- The minimum clearance between mating parts
Correct answer: The condition where the feature contains the maximum amount of material (smallest hole, largest shaft)
MMC is the condition where a feature contains the most material: for a hole, this is its smallest allowable diameter; for a shaft, it is its largest allowable diameter.
Question 6: What is the primary purpose of a control chart's Upper Control Limit (UCL) and Lower Control Limit (LCL)?
- They define the engineering tolerance for the machined feature
- They define the bounds of normal process variation (typically ±3 sigma) to detect out-of-control conditions (Correct answer)
- They set the alarm limits for the CNC machine's servo drives
- They establish the maximum and minimum tool offset values allowed
Correct answer: They define the bounds of normal process variation (typically ±3 sigma) to detect out-of-control conditions
UCL and LCL are set at ±3 standard deviations from the process mean, and any point outside these limits signals that a special cause of variation is present.
CNC CNC Quality Control and Inspection 2
In GD&T, what does the 'flatness' callout control?