CQI Free Practice Questions (Review Mode)

Free sample questions

3 questions from this set, shown in full with the correct answer and the reasoning behind it. Read them as a study resource.

1. Q1.The surface plate setup below is shown with the part ready to be turned by hand.
   
   What characteristic is being measured?

   

   • A.Hardness of the shaft
   • B.Runout of the shaft✓ Correct answer
   • C.Length of the shaft
   • D.Surface roughness of the shaft

   Explanation

   The indicator stays at one place while the shaft turns, so it reports how far the surface moves in and out as the part rotates. That change is runout. If the indicator were instead swept along the length while the shaft stayed still, the setup would be checking straightness or taper. Roughness needs a profilometer and hardness needs an indenter, so neither can come from this arrangement.

   Reference: CQI BoK II

2. Q2.The histogram below shows 120 measured diameters with the specification limits drawn on it.
   
   What does it show?

   

   • A.The process is off centre toward the upper limit✓ Correct answer
   • B.The process is centred with a comfortable margin
   • C.The process output follows two separate distributions
   • D.The measurement system is producing most of the spread

   Explanation

   The distribution has one peak, so it comes from a single process, and its shape is ordinary. What is wrong is where it sits: the peak lies well to the right of the middle of the specification, so there is spare room below the lower limit and almost none above the upper one. A small shift upward will immediately produce nonconforming parts. The fix is to recentre the process, which is usually far easier than reducing its variation.

   Reference: CQI BoK IV

3. Q3.Capability indices are calculated for three processes.
   
   $$\begin{array}{c|c|c} \textbf{Process} & \textbf{C}_p & \textbf{C}_{pk} \\ \hline \text{P1} & 1.50 & 1.48 \\ \text{P2} & 1.33 & 1.30 \\ \text{P3} & 1.80 & 0.90 \end{array}$$
   
   Which process is furthest off centre?

   • A.P2
   • B.P3✓ Correct answer
   • C.All three are equally centred
   • D.P1

   Explanation

   $C_p$ compares the specification width with the process spread and ignores where the process sits. $C_{pk}$ measures the distance to the nearer limit, so it falls as the process moves off centre. The gap between the two indices is therefore the measure of off centring, and P3 has by far the largest gap, $1.80$ against $0.90$. Note that P3 has the tightest spread of the three, so recentring it would make it the best performer.

   Reference: CQI BoK IV

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