A. THE BASIC USE CASE
1factory provides multiple fields: Operation, Inspection Type, Dimension Type, and Key (CTQ) to group and organize the required inspections for a part.
1. OPERATION:
An operation is any step in the manufacturing process where EITHER (1) a part is transformed i.e. some features change during the step. e.g. turning, grinding, deburring etc. OR (2) where the part undergoes an inspection e.g. Final Inspection in the QC Lab.
| Op # | Operation |
| 10 | Turn |
| 20 | Mill |
| 30 | Grind |
| 45 | Clean |
| 60 | Coat (Outside Processing) |
| 70 | Incoming QC |
| 100 | QC Final Inspection |
2. INSPECTION TYPE:
The Inspection Type field allows a further sub-grouping of features at each operation. These sub-groups allow us to define which features to check, and the associated inspection methods and sampling rules based on where and when the inspection is performed.
A feature may be assigned to more than one Inspection Type. The key assumption at this point is that there is no change to the feature between the various Inspection Types.
There are a few commonly used Inspection Types:
(1) Setup / First Piece:
Let's assume that we are at Op 10: Turn. Once the first part has been produced, the machinist measures certain important dimensions for the 1st piece. These measurements are then verified by the QC lab, and if all the first-piece dimensions are good, production can proceed.
To help the machinist easily identify which dimensions to check on the first-piece, we create the Inspection Type = First Piece.
(2) In Process:
Once production begins, we want the machinist to inspect certain features on every 10th or 20th part. We use this frequency based sampling to ensure that we can detect any drifts or shifts in the manufacturing process.
To help the machinist easily identify which features to check during the production run and at what frequency, we create the Inspection Type = In Process.
In the example below, only the Diameter is checked during the First Piece Inspection, but both the Diameter and the Linear Dimension are checked during the In Process Inspection at different sampling frequencies.
| Op # | Operation | Feature | First Piece | In Process | ||
| 10 | Turn | Dia 1.500 +/- .005 | Micrometer | 1 | Micrometer | 1 in 10 |
| Linear .545 - .547 | Micrometer | 1 in 20 | ||||
(3) Final Inspection:
Once all the machining and outside processing steps are complete, certain features (typically Critical to Quality features) from a subset of parts may need to be reinspected in the QC lab with more accurate instruments such as a touch-probe CMM or a Vision system.
To help the QC Lab team easily identify which features to check at Final Inspection, and how many parts to check, we create the Inspection Type = Final Inspection.
In the example below, the Diameter is rechecked during the Final Inspection, but using a different instrument (CMM), and with a different sampling rule.
| Op # | Operation | Feature | First Piece | In Process | Final | |||
| 10 | Turn | Dia 1.500 +/- .005 | Micrometer | 1 | Micrometer | 1 in 10 | CMM | C=0 AQL 1.0 |
| Linear .545 - .547 | Micrometer | 1 in 20 | ||||||
B. A MORE COMPLICATED USE CASE
AN IMPORTANT ASSUMPTION: When we assign a feature to more than one Inspection type, we make an important assumption: we assume that the feature does not change between those inspection types.
However, in many cases, the feature does change size from Op to Op. For example:
1. The feature may need to be checked at both Turning and Grinding. In this case, there is no change to the spec between Turning and Grinding, but additional material is removed during grinding resulting in a shift in the actual dimension.
2. The feature may need to be checked during Turning and then After Coating. In this case, the spec for feature at Turning is different (likely tighter) than the spec for the feature at Coating.
In this case, where a feature undergoes a further transformation between Ops (i.e. where either the measured value may change, or both the specification and the measured value may change), we must create two features (one for each Op) and classify the intermediate feature (in this case Turning) as a Manufacturing Dimension.
This is important to ensure that data sets are homogenous i.e. collected under the same conditions of 5M & 1E (man, machine, method, measurement, material, and environment) without which all data analysis is worthless.
The plan will then have two related features: a Manufacturing Dimension (the intermediate dimension achieved at Turning), and a Standard Dimension (the final dimension achieved after Grinding or Coating). In the example below, feature 4 is the Standard or Print Dimension, and fetaure 4.1 is the Manufacturing Dimension.
C. FINAL INSPECTION - BOTH AN OP AND AN INSPECTION TYPE
Final Inspections are a special case.
You may have noticed in the table above that Final Inspections are both an Operation (OP 60 FINAL), and an Inspection Type (FINAL).
While it would be sufficient to have Final Inspection as an Inspection Type, we also need to include Final Inspection as an Operation in a PPAP Process Flow diagram. Therefore, the Final Inspection is classified as both an Op and an Inspection Type.