FAQ

Shot peening is a controlled surface treatment that induces residual compressive stresses through calibrated media impacts. Apply it whenever the part sees cyclic fatigue loading — landing gear, engine shafts, blades, springs — per AMS 2430 and AMS 2432.

Conventional shot peening uses calibrated media in a cabinet or through a nozzle on removed parts. Flapper peening is performed in-situ with a handheld rotary tool — ideal for localized work on a fitted aircraft without disassembly, per AMS 2590.

HFMI (High Frequency Mechanical Impact) specifically targets weld toes and is qualified by IIW 2016. For equivalent strength, it improves weld fatigue life much more than shot peening — use HFMI on welded joints, shot peening on machined surfaces.

Cold working mechanically expands a hole (rivet, bolt) with a mandrel to create a compressive ring around the bore. Following BACC 5060 / FTI ForceMate / Split-Sleeve Cold Expansion, it multiplies fatigue life of a structural hole by 3 to 10.

Laser peening (LSP) delivers deeper compressive stresses (1 to 2 mm vs 0.2 to 0.4 mm for shot peening) but with significantly higher cost and cycle time. LSP is justified on high-value engine blades or thick critical parts; for volume production and structures, AMS 2430 shot peening remains the cost-effective reference.

Needle peening uses a bundle of high-frequency needles to induce compressive stresses on complex geometries or hard-to-reach areas. It fits naval repair, tank welds and heavy structures where media blasting is less practical.

Not directly. CFRP / GFRP composites are not peened; however we intervene on the surrounding metallic fittings, inserts, lugs and metal-composite interfaces where fatigue concentrates.

Depending on size and zones covered by the OEM spec: 6 to 12 hours of effective processing for a single-aisle landing gear (A320, B737), 24 to 48 hours for a widebody. Add preparation, masking and Almen strip control.

We master ultrasonic peening and flapper peening technologies from the main market players with no manufacturer bias. Depending on the client spec and part accessibility, we recommend the most relevant technology — including STRESSONIC when mandated by the package.

Yes, very often: cold working a hole followed by localized shot peening, or shot peening an area then flapper peening a post-repair touch-up. Each sequence is validated by the Process Engineer per the NADCAP file.

These are two distinct processes that use the same type of machine. Shot peening is a mechanical treatment: it introduces residual compressive stresses below the surface to delay fatigue crack initiation. It is driven by a measured Almen intensity and coverage rate, and documented in a qualification file. Shot blasting is surface preparation: it removes scale, oxides or paint, with no mechanical objective and no Almen control. Confusing the two on a structural part is a classic audit non-conformity.

Yes. « Shot peening » is the standard term; « shot peen » and « shotpeening » are common variants, the latter written as one word. In French the normalised term is « grenaillage de précontrainte », in German « Kugelstrahlen » or « Verfestigungsstrahlen ». All refer to the same process, governed by the same standards — AMS 2430 for aerospace, SAE J442 and J443 for Almen strips and saturation curves. Do not confuse it with plain « blasting », which usually means cleaning.

Through three elements, not merely a machine setting. First the Almen saturation curve: arc height is plotted against exposure time, and saturation is reached when doubling the time increases arc height by no more than 10 % (SAE J443 criterion). Then coverage, checked visually or with a fluorescent tracer, typically required at 100 % or 200 %. Finally traceability: media used and its condition, parameters, qualified operator, records. Our engineering office supplies the complete file, and our online saturation curve calculator lets you check your own measurements.

Yes, in many cases. That is precisely what flapper peening and roto peening are for: they are applied with portable tooling on assembled parts or on the aircraft, with masking of the areas not concerned. Bore cold working can also be done in place where access allows. The decision rests on three criteria: actual accessibility of the area, the applicable specification, and the ability to verify intensity on site. Our teams travel with the tooling and the inspection equipment; describe the configuration and we reply within 12 working hours.

None in substance: both refer to the cold expansion of a hole, in which an oversized mandrel is drawn through the bore to create a residual compressive zone around it. « Cold expansion » emphasises the mechanism, « cold working » the resulting work hardening. « Cold hole expansion » is also used. The typical fatigue life gain is three to five times the original life. Reference specifications are BACC 5060, ABP 1-4100 and customers' internal specifications.

Both produce the same mechanical effect through different kinematics. Split sleeve places a disposable split sleeve between the mandrel and the bore: expansion is very uniform, the sleeve protects the bore wall, and access is needed from one side only. Split mandrel needs no consumable — the mandrel itself is split and retractable, which lowers recurring cost but generally requires access from both sides. The choice rests on bore accessibility, thickness, volume to be processed and above all the specification imposed by your customer. Kronos Engineering is an official FTI partner and applies both approaches.

Both are viable, and the criterion is volume. Below a few hundred holes a year, buying the tooling and qualifying it costs more than subcontracting: we then work on your site with the tooling, the operators and the inspection equipment, and hand over the compliance file. Above that, bringing it in house pays off: we supply the tooling, train your operators, write the work instructions and support you through qualification. Many customers start with the first option and switch later.

That is one of its main uses. In life-extension programmes, cold expansion is applied to fastener holes in fatigue-critical areas — spars, fuselage frames, fittings — to postpone crack initiation. It applies to new production as well as maintenance returns, and is often prescribed by a service bulletin or a structural repair manual. Our structure engineers produce the supporting justification notes when the repair falls outside the manual.

No, these are two names for the same process. You will find « flapper peening », « flap peening » and occasionally « flap peen ». It is peening performed with an abrasive flap mounted on a mandrel and driven by a pneumatic grinder: the flap strikes the surface and introduces compressive stresses, with no media projection. Its value lies in manual application, on assembled parts or on the aircraft, where a blast cabinet is impossible. The applicable aerospace standard is AMS 2432.

When the part cannot go into a cabinet. Cabinet shot peening remains preferable for series production: it is faster, more repeatable and easier to instrument. Flapper peening takes over as soon as removal is impossible or too costly: on-aircraft repair, a localised area of a large structure, a part mounted in a sub-assembly, an AOG emergency. It also allows a precise area to be treated without exposing the rest of the part. In return it requires a qualified operator, since consistency depends on technique, and on-site intensity verification with Almen strips.

Yes, it is one of our routine AOG uses. The tooling fits in a case, needs neither a cabinet nor media recovery, and intensity is verified on the spot with Almen strips. The conditions are physical access to the area, careful masking of adjacent zones, and an applicable repair instruction — from the structural repair manual, a service bulletin, or drawn up by our structure engineering office when the case falls outside the manual. Our emergency line answers within two hours, around the clock.

Yes. HFMI is used both in new fabrication and to upgrade existing structures, provided the weld toe is sound to begin with. The process delays crack initiation but does not repair an existing crack, so each weld is first inspected by magnetic particle or dye penetrant testing, and any indication is ground out or repaired before treatment. The coating has to be removed locally and reinstated after inspection. The benefit applies to the remaining life, which is why early treatment pays off. We work on site with our own tooling and inspection equipment; a weld list and the drawings are enough for us to quote.

Yes, provided the justification method is accepted by the project's certification body. The IIW 2016 recommendations allow the fatigue class (FAT) of a treated joint to be raised, and the higher the steel's yield strength, the greater the gain. On monopiles, transition pieces and jackets, two conditions decide whether the calculation holds: corrosion protection must be maintained, since the benefit drops under free corrosion, and quality assurance must be documented weld by weld. Our structural engineering office can produce the justification note, and our teams can carry out the treatment in the fabrication yard or on site.

They set the conditions under which a fatigue improvement can be claimed for an HFMI-treated weld. The document covers structural steels with yield strengths from 235 to 960 MPa and plate thicknesses from 5 to 50 mm. It defines the FAT class increase as a function of yield strength, restrictions for high stress ratios and high peak loads, and quality assurance requirements: procedure, operator training, groove inspection and records. It only addresses failures initiating at the weld toe, not at the root. We train your staff and apply these recommendations on your projects.

Acceptance rests on examining the treated groove, not on a mere statement that the tool has passed. Visual inspection covers 100 % of the treated length: a continuous, even groove along the weld toe, with no trace of the original toe and no folded material. Groove width and depth are measured on a sampling basis, with gauges or on surface replicas, against the ranges of the qualified procedure (typically 3 to 5 mm wide, 0.1 to 0.3 mm deep). The file should include the procedure, operator qualifications, parameters, a map of treated welds, photographs and a signed report. That is the standard content of our job reports.

The choice depends first on the part and the working environment, then on the specification. Roto peening uses a portable rotary tool with carbide elements to treat local areas on machined metal parts, bores or zones reworked after repair, with Almen intensity verification; in aerospace it falls under AMS 2590. Needle peening applies a pneumatic bundle of needles to welds and heavy structures with confined geometry, in shipbuilding, rail or offshore. Ultrasonic peening, which projects no media, is reserved for environments where any contamination is ruled out, such as nuclear components or turbine internals. Where no specification is imposed, our technology benchmark settles your case.

Not by default: any process substitution must be approved by the design authority, meaning the OEM or the engineering office that owns the definition. In practice, structural repair manuals often allow rotary peening to re-treat a local area after rework machining, at an equivalent Almen intensity and specified coverage. Intensity is verified on Almen strips per SAE J443, with a saturation curve. We operate within the NADCAP Surface Enhancement (AC7117) and PART-145 frameworks, either directly or as a subcontractor to approved organisations. Send us the drawing or manual reference and we will prepare the technical content of the request.

Its limitations lie in controlling the result rather than in its effectiveness. Intensity is not measured by a standardised method comparable to the Almen strip, and consistency depends heavily on operator technique. The resulting surface is heavily marked, which rules the process out for finished surfaces and thin light-alloy parts. Noise and vibration call for protective measures and limited exposure times. Finally, recognition in construction codes is less formalised than for HFMI, so qualification is done case by case on test pieces. We can support you through that qualification ahead of the on-site job.

When media projection is impossible or prohibited. Balls set vibrating by a piezoelectric transducer strike the surface inside a closed chamber: no shot to recover, no contamination of neighbouring areas, and residual roughness often lower than with shot peening. That makes sense for nuclear components, turbine internals, assemblies with cavities and parts with tight roughness requirements. On the other hand, cost is noticeably higher and the tooling often has to be adapted to the geometry. Intensity is verified on Almen strips, with a saturation curve. We recommend the technology case by case, with no manufacturer bias.

Before, yes; after, only if the specification explicitly allows it. Shot blasting can prepare the part by removing scale or oxides, provided all machining, grinding and heat treatment are completed before shot peening. Once the part has been peened, any abrasive blasting may remove or alter the compressive layer and cancel the benefit. Media matters too: steel shot used on aluminium or titanium leaves ferrous contamination, a classic audit finding. Send us your routing sheet and we will check the sequence of operations before quoting.

Cleanliness is specified to ISO 8501-1: Sa 2½ for most paint systems in corrosive environments, generally Sa 3 for thermal spray metallising. The Sa grade alone is not enough: the roughness profile must also be specified and checked with a comparator per ISO 8503, along with residual dust per ISO 8502-3. In US terms, SSPC-SP 10 roughly corresponds to Sa 2½ and SSPC-SP 5 to Sa 3. The time between blasting and coating must be kept short to prevent flash rusting. We quote on-site blasting based on surface area, target grade, coating system and access conditions.

Yes, in most cases: expansion leaves an axial ridge from the split sleeve and a slight upset at the hole edge, and precision reaming brings the bore to the fastener fit size. The final diameter and the maximum allowable removal are set by the applicable specification (BACC 5060, OEM specification or structural repair manual), because excessive reaming eats into the compressive zone. On structures the operation is done with portable tooling, commonly to H7 to H8 tolerance, followed by spot facing where required. We carry out expansion, reaming and dimensional inspection in the same on-site intervention.

It allows the surface of a part to be examined under a microscope without removing it, often avoiding disassembly. The area is prepared locally, then its imprint is taken with a specialised film or polymer and analysed in a laboratory by optical or electron microscopy, following the method described in ASTM E1351. Microcracks, intergranular corrosion, wear or post-treatment microstructure can be read from it. Limitations: the information is confined to the surface, and prior polishing or etching must be authorised on flight parts. It complements volumetric inspection such as ultrasonic or eddy current testing but does not replace it. We take replicas on site.

Kronos Engineering does not hold these approvals in its own name. We work within their technical framework — NADCAP Surface Enhancement (AC7117 criteria) for shot peening and flapper peening, EN 9100 / AS9100, PART-145 — either directly for manufacturers and airlines, or as a subcontractor and embedded team for prime contractors and approved organisations. We apply AMS 2430, AMS 2432, BACC 5060 and the specifications of the main OEMs (Airbus, Boeing, Safran, Dassault). The right contractual set-up for your project is defined at quotation stage.

Yes. Our teams apply the AC7117 checklist requirements every day: Almen intensity and saturation curves, coverage, masking, media control, process control and traceability. That is what allows us to work inside an accredited facility without putting its accreditation at risk, and to prepare a NADCAP audit.

EN 9100 is the European version, AS9100 the American — content is identical (ISO 9001 + IAQG aerospace requirements). An EN 9100 certificate is recognized by AS9100 customers and vice versa.

Yes. We apply the RCC-M (design and construction rules for mechanical components of nuclear islands) for stress-relief and fatigue-enhancement processes, to the operator's or manufacturer's specification.

Yes. MIL-S-13165 (shot peening for vehicles and weapon systems), MIL-STD-2154 and MIL-HDBK-516 are applied for our land, naval and aerial defense clients.

IIW 2016 recommendation (Document XIII-2617-16) published by the International Institute of Welding, plus DNV rules, Eurocode 3 Annex B and client specifications (Vestas, Siemens Gamesa, Enercon in wind energy).

Yes, AS9102 FAI report signed by the Quality Manager, including Almen strip, saturation curve, visual, metrology and media traceability — delivered with the first lot of any new part.

End-to-end traceability: media lot number, Almen curve per shift, qualified Level I/II/III operator, machine, parameters, masking, post-process control and digital record archived for 15 years per OEM and PART-145 requirements.

Phone response guaranteed within 2 hours, 365 days/year. Qualified technician + tooling takeoff within 24 h for major aerospace hubs (Europe, Middle East, Southeast Asia, Americas), within 48 h for secondary destinations. AOG line: +33 7 69 51 61 26.

An AOG intervention is billed on a mobilization lump sum (on-call, travel, tooling) + technician days. No weekend or night surcharge — on-call is included. Firm quotation sent within one hour of need qualification.

Yes. This is precisely what our AOG line is built for: shot peening, flapper peening, cold working or structural rework performed on a grounded aircraft, at an FBO, third-party MRO or on the apron subject to operator authorization.

Yes. Our technicians hold clearances suited to military zones and operational bases. ITAR / French national defense clearances on file. Confidential intervention under STANAG 4671, MIL-HDBK-516.

Handheld flapper peening, needle peening, split-sleeve cold working, bushing expansion, HFMI weld rework, Almen strip checks. Cabinet shot peening is not performed in AOG (workshop return required).

Yes. A qualified Process Engineer can be dispatched to your MRO partner to oversee execution, sign conformity statements and clear a process issue — with no commercial overlap with your MRO.

Yes. Short, medium and long-haul fleets — A320 / A321neo / A330 / A350 / A380 / B737 / B747 / B777 / B787 / ATR / Embraer E-Jets. Direct intervention or through MRO partners (Lufthansa Technik, AFI KLM E&M, ST Engineering, AAR, HAECO, SR Technics).

Yes. Falcon, Gulfstream, Bombardier Global, Embraer Executive, HondaJet, Pilatus. Confidential intervention at FBO or OEM facility — shot peening, flapper peening, cold working on landing gear, wings, flight controls and engine components.

Yes. Dedicated cargo fleets (FedEx, UPS, DHL, Cargolux, Atlas Air, Turkish Cargo) and Passenger-to-Freighter (P2F) converted aircraft. Structural reinforcement, post-conversion rework, fatigue maintenance on zones exposed to the more severe cargo cycles.

Yes. Tactical platforms, MALE (Medium Altitude Long Endurance) and HALE (High Altitude Long Endurance). Shot peening of wings/fuselage, cold working of landing gear, on-site flapper peening on operational base, AOG on grounded drones. Qualifications STANAG 4671 / 4703, MIL-HDBK-516.

Yes. Joby Aviation, Volocopter, Lilium, Archer, EHang, Wingcopter programs. HFMI on motor boom welds, shot peening on structures, flapper peening on critical zones. Support towards EASA Special Condition VTOL qualification.

Yes. Airbus Helicopters (H125, H135, H145, H160, H175, H215, H225, Tiger, NH90), Bell, Leonardo (AW139, AW169), Sikorsky, MD Helicopters. Shot peening on shafts, gearboxes, blades, rotor heads and landing gear.

Yes. HFMI of weld toes on monopiles, transition pieces, jackets, tubular towers, nacelle hubs and frames for Vestas, Siemens Gamesa, GE, Nordex, Enercon. Compliance with IIW 2016, DNV, Eurocode 3.

Yes. Primary and secondary components for EDF / Framatome, vessels and steam generators, de-tensioning of maintenance welds per RCC-M. Nuclear-grade traceability enforced.

Yes. Civil shipyards (Chantiers de l'Atlantique, Fincantieri) and defense (Naval Group, TKMS) — HFMI on hull welds, needle peening for repairs, shot peening on fatigued structures.

Yes. Bogies, axles, springs, suspensions for Alstom, Siemens Mobility, Stadler, Bombardier Transport. Shot peening compliant with SNCF, DB, RATP and OEM specifications.

Yes. Armored vehicles (Leclerc, Jaguar, Griffon, Serval, VBMR), artillery (CAESAR), gun cradles and gearboxes. Shot peening per MIL-S-13165, Nexter / KNDS, Arquus, Thales.

Yes. Blades, disks, shafts, gears and casings — Safran, GE Aviation, Pratt & Whitney, Rolls-Royce, MTU, Solar Turbines, MAN Energy Solutions, Wärtsilä programs.

Yes. Regular interventions in Bavaria (Munich, Augsburg, Donauwörth — Airbus Helicopters), Hamburg (Airbus, Lufthansa Technik) and Baden-Württemberg. Mobilization within 24 h from Bordeaux or long-term secondment.

Yes. Singapore (ST Engineering, SIA Engineering, Seletar), Malaysia (Subang, Kuala Lumpur), Indonesia, Vietnam, Thailand, Philippines. Technicians deployable within 48 h from Bordeaux, multi-month secondment available.

Yes. Interventions in the USA (Texas, Florida, California, Wichita, Seattle) and Canada (Montreal, Toronto, Mirabel — Bombardier, Pratt & Whitney Canada). Operational B1 business visas, ITAR-compliant.

Yes. Dubai (Emirates Engineering), Abu Dhabi, Doha (Qatar Airways), Riyadh, Dammam, Istanbul (Turkish Technic). Intervention on wide-body, business jet and defense fleets.

Yes. Morocco (Casablanca, Royal Air Maroc, Bombardier), Egypt (EgyptAir), South Africa (Johannesburg, Cape Town), Kenya, Nigeria, Ethiopia. Scheduled interventions with anticipated visa and logistics.

Yes. Brazil (Embraer São José dos Campos, GOL, LATAM), Argentina, Mexico (Querétaro aerospace cluster), Chile, Colombia. Technical support and AOG interventions.

Yes. Sydney, Melbourne, Brisbane, Adelaide (ASC Pty Ltd, BAE Systems Australia). Defense and civil aviation interventions, AOG lead times of 48 to 72 h from Bordeaux.

Yes. Secondments from 1 to 12 months — resident technician at OEM or MRO, production line supervision, process transfer. Contract and visa tailored to the country.

Level I (operator), Level II (inspector), Level III (process engineer) per the NADCAP / NAS 410 pyramid for shot peening, flapper peening, HFMI and cold working. Initial, refresh and recycling training.

5 days in classroom + workshop in Bordeaux or at client site, including theory (AMS 2430/2432), hands-on Almen strip, saturation, masking, written exam and practical test. Kronos certificate recognized by NADCAP auditors.

Our training is designed to meet the operator qualification requirements expected during NADCAP AC7117 audits. The operator certificate itself is issued by the employer per their internal qualification procedure, using our materials.

Yes, worldwide. Training is often paired with an intervention or process transfer to maximize the value of the trip. Support in French, English, German, Spanish.

Yes. Dedicated 3-day HFMI training covering weld fatigue theory, IIW 2016 recommendation, use of PIT / UIT / HiFIT tools, groove shape quality control and saturation. For design offices and field operators.

Yes. 2 to 3-day internal auditor training with an AC7117 audit simulation, checklist by checklist, analysis of common non-conformities and action plans. Before initial audit or renewal.

Price depends on level, duration, number of attendees and location. From €1,200 / day / group at Bordeaux site, custom quote for in-house training at client site. Volume negotiable for multi-year programs.

Yes. 2-day 'Fatigue & surface treatments for engineers' module — sizing, process selection, writing specs, reading Almen strip and saturation curve. For design, quality and methods teams.

Yes. Kronos Engineering designs and sells its own shot peening cabinets, flapper peening machines, control instrumentation, consumables (steel, ceramic, glass media) and custom tooling.

No. Kronos Engineering is independent, with no manufacturer bias. We master the processes across the technologies of the main market players and recommend the most relevant solution — with no commercial stake in any specific brand.

Yes. Certified A, N, C Almen strips, support blocks, calibrated media per AMS 2431, ceramic abrasive, conditioned steel shot and masking tooling. Delivery across Europe within 5 to 10 working days.

Yes. Upgrade of legacy cabinets: digital instrumentation, media flow control, nozzle actuation, CNC programming, lot traceability. Retrofit project framed after a preliminary technical audit.

Yes, we distribute and integrate PIT (Pneumatic Impact Treatment), UIT (Ultrasonic Impact Treatment) and HiFIT tools per client spec and applicable IIW 2016 standard.

Yes. FTI mandrels, split-sleeves, bushings and installation tooling per BACC 5060 and Boeing / Airbus specs. Standard sizes in stock, special sizes on order.

Yes. Almen gauges, saturators, coverage measurement systems, surface profilometers, media flow sensors. Traceable calibration and annual maintenance.

12 months parts and labor, contractual extension up to 36 months. Phone technical support included, on-site intervention within 72 h in Europe (excluding wear consumables).

Call or quotation form, needs qualification within 24 h by a Process Engineer, firm quote sent within 48 working hours for a standard intervention, within 1 h for an AOG emergency.

Price depends on process, volume, part, location and urgency. From €1,800 / day / technician in Europe + consumables + tooling. Tailored quote within 48 h of receiving the technical package.

Yes. Systematic NDA offered before exchanging technical packages, specs or drawings. We routinely work under client, OEM and defense NDAs. Interventions on sensitive programs without any marketing communication commitment.

No. We operate as Tech Rep, process subcontractor or trainer embedded in your organization — no competition on your core activity. Our client orders, we execute the specialized process under their label if required.

Yes. Intervention under the principal's brand, documentation matching their quality template, operators under client instructions. Common practice for MROs, OEMs and engineering firms wanting to broaden their offer without hiring the special-process skills.

Drawings, specs and production data remain client property. Stored in our quality archives for 15 years (PART-145 / EN 9100 requirement) on French servers, with attested destruction at program end on request.

Kronos Engineering positions on quality, AOG responsiveness and technological independence rather than rock-bottom pricing. Our value lies in low rejection rates, on-time delivery and a long-term trust relationship with principals.

Yes. One-off orders, simple purchase orders, emergency interventions outside any framework — our commercial process is sized for agility. Master contract recommended above 3 to 4 yearly interventions to optimize rates and lead times.

Four items are enough for a firm answer: the part and its material, the process and applicable specification (AMS 2430, AMS 2432, BACC 5060 or your customer's internal specification), the quantity and expected rate, and the location — your premises, our Bordeaux workshop, or an on-site job abroad. A drawing or a photograph of the area always speeds up the analysis. If the specification seems ambiguous, simply describe the functional need: our engineering office identifies the applicable standard. We reply within 12 working hours.