Shot Peening LEAN manufacturing.
- Silvio Ruiu
- Jan 25
- 4 min read
Updated: Jan 26
MBA & Shot Peening.
Shot peening is a strictly controlled process, ruled by the norm SAE J443 with others and more restricted applications for example in aerospace; all these protocols are expensive to follow and are ruled by a “total quality” approach to avoid any possible discrepancy as well guaranteeing full compatibility in parts treated in different places, and in different moments too.
This field is grounded industrial production, so it is possible to apply LEAN manufacturing lenses to use norms as guidelines, making a shot peening process far cheaper yet effective for the targets decided – more info here.
Almen Strips.
These are the specimens used to measure the Almen intensity, which is the way to measure residual plastic deformations into the parts, ultimately the peening effect inducted, and to correlate to the fatigue life improvement.
Almen strips have 3 thickness measures: A – N – C. Detailed explanation is below; what is important to know is that this measuring system works by Almen effect, and thanks to it the strip under the media jet bends. This bend is exactly the peening intensity by definition, measured in inches and connected to millimeters by the chart below.
Using the Almen strips is possible to measure peening intensity of any part; orienting properly the strips under the media jet is possible to understand what is going on into the material. Orienting the strips is also related to the design of the part itself and where it has been decided to improve it. LEAN rule is to add value where needed, so sometimes is peened all around and sometimes is more oriented to the side more inclined to failure.
Saturation & Coverage.
Major part of metals, accordingly with type and microstructure, have a wide elastic field followed by the plastic one; it is mandatory to reach the plastic otherwise no residual stress so no peening effect. Saturation is when the elastic field has been left and we are moving on the plastic; coverage means that increasing the time of exposure (exactly doubling the time) peening effect increases less than 10%. This is by SAE norm; it is simple and works so great that is guideline “LEAN approved”.
Conclusion.
Shot peening is a great piece of engineering, can be intimidating due to the norms. Looking at it from a LEAN point of view, outside of strictly controlled fields of applications, it can be designed to increase profits within a reasonable cost. KPI is always the Almen strip result that can be easily “industrialized” to make quick and effective tests on a regular basis. See below.
This device allows to keep production going, runs 4 strips in parallel and it is done while production is ongoing.
To develop a shot peening process is not immediate and efforts free, for sure a support well inside the subject can make it faster and more effective, here if you wanna investigate.
Table of content:
3) Almen strips types and how them should be used to validate. this post.
Shot Peening Engineering Insights:
Almen Effect.
The Almen Effect is the measurable convex deformation of a standardized metal strip resulting from the residual compressive stresses induced by a high-velocity stream of abrasive media. When the media strikes the surface of the strip, it causes plastic deformation of the outer layer. Since the deeper layers resist this stretching, the strip bows toward the blast stream. This curvature, the arc height, is a direct proxy for the intensity of the process.
Almen Strips: Classification and Technical Specifications.
According to SAE J442, all Almen strips share the same footprint:
Length: 3.000 ± 0.015 inches (76.2 mm)
Width: 0.747 ± 0.003 inches (18.9 mm)
Material: SAE 1070 Cold Rolled Spring Steel
Hardness: 44 - 50 HRC
Strip Type | Nominal Thickness (in) | Nominal Thickness (mm) | Application Range (Arc Height) |
Type N (Normal) | 0.031" | 0.79 mm | Under 0.004" (0.10 mm) on 'A' strip |
Type A (Standard) | 0.051" | 1.30 mm | 0.004" to 0.024" (0.10 - 0.61 mm) |
Type C (Heavy) | 0.094" | 2.39 mm | Over 0.024" (0.61 mm) on 'A' strip |
Technical Conditions for Use (SAE J443)
Selection Rule: The Type A strip is the industry standard. If the arc height measured is less than 0.004", the Type N strip must be used. If it exceeds 0.024", the Type C strip is required.
Measurement Side: The arc height must always be measured on the unpeened (convex) side using a standardized Almen gage.
Nominal Parameters: To ensure process review accuracy, strips must be mounted on a standardized holder with four hardened screws to ensure the strip is perfectly flat before exposure.
