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1. Customer Background and Project Overview
In mid-2024, a well-known automotive component manufacturer from Italy contacted our engineering team with a critical sourcing requirement:They needed custom stainless steel fasteners for high-performance automatic transmissions used in electric vehicles (EVs).
These fasteners had to perform reliably under extreme vibration, high torque, and elevated temperatures, where standard off-the-shelf bolts could not maintain structural integrity.
The customer’s main challenge was finding a CNC machining supplier capable of producing tight-tolerance fasteners with controlled surface finishes and consistent mechanical performance across large batches.
With over a decade of experience in precision CNC machining and custom fasteners manufacturing, our company — [Your Company Name] — became their trusted partner for developing, testing, and mass-producing these critical components.
2. Project Requirements and Challenges
After the first technical meeting and review of the CAD drawings, several key challenges were identified:
High material performance:The fasteners required AISI 304 and 316 stainless steel, each with specific mechanical and corrosion-resistance properties.
Dimensional accuracy:The hex socket head and threaded section required tolerance control within ±0.01 mm for accurate torque application.
Surface finish quality:The automotive client specified a Ra ≤ 0.8 µm finish to prevent micro-cracks under vibration stress.
Thread precision:The M8 x 1.25 thread had to pass both GO/NOGO and 3D scanning validation to meet ISO 965-2 standard.
Corrosion and fatigue resistance:The parts were used near the transmission casing, where oil, heat, and moisture exposure were constant.
These strict requirements made the project highly technical and demanding — a challenge our CNC and materials engineering teams were well-prepared to handle.
3. Engineering & Production Solution
Our team proposed a multi-phase engineering solution, beginning from DFM analysis to pilot production and quality validation.
a. Material Selection and Testing
We selected AISI 316 stainless steel for its superior corrosion resistance in high-temperature automotive environments.Before production, we performed spectrochemical analysis and mechanical property testing (tensile strength, hardness, elongation) to ensure material conformity.
Material hardness was maintained at HV 230–260, providing the perfect balance between machinability and strength.
b. DFM & Process Optimization
Our engineers reviewed the part geometry and optimized the manufacturing process:
Recommended slight adjustments to undercut depths for better tool reach.
Simulated machining using MasterCAM to reduce unnecessary tool changes.
Implemented a two-step threading process (turning + thread rolling) to improve thread fatigue life by 20%.
This stage reduced production cycle time by 18%, improving both cost efficiency and throughput.
c. Precision Machining Process
The custom fasteners were produced using CNC turning centers (Tsugami TMA8F) combined with Swiss-type lathes for high accuracy.
Machining Step
Process Details
Turning
Achieved outer diameter precision within ±0.005 mm
Thread Rolling
ISO M8 × 1.25 pitch, after heat treatment
Drilling
Depth tolerance ±0.02 mm
Head Milling
Controlled with live tooling spindle
Deburring
Automatic chamfering tool for edge consistency
Each machine was programmed and monitored by skilled technicians to ensure stable output over long runs.
4. Heat Treatment and Surface Finishing
After machining, the fasteners underwent controlled heat treatment to relieve residual stress and enhance tensile strength.
Heat treatment condition: 420°C for 2 hours, air-cooled.
Surface treatment: Passivation per ASTM A967, improving corrosion resistance in oil-contact environments.
Optional coating: Nickel plating for aesthetic appeal (per client request on secondary batch).
Surface roughness after treatment remained at Ra 0.7 µm, and the coating adhesion was tested via ASTM D3359 (Grade 5B).
5. Quality Control and Inspection
Quality assurance is the backbone of our CNC machining operations.For this project, every stage of production followed a documented PPAP (Production Part Approval Process) and SPC (Statistical Process Control) procedure.
Key Inspection Procedures:
Incoming Material Verification
Spectrometer analysis and mechanical certification from supplier.
In-Process Control (IPQC)
Thread pitch and concentricity inspected every 20 pcs.
Automatic optical measurement for head diameter and undercut.
Final Inspection
100% visual inspection for surface defects and burrs.
CMM measurement for random samples (batch size 200 pcs).
Salt spray corrosion test for 48 hours (passed without rust).
Torque and tensile testing with digital torque gauge.
Each inspection record was logged into our MES (Manufacturing Execution System) for traceability and shared with the client during shipment.
6. Project Results and Customer Feedback
The first batch of 5,000 custom stainless steel fasteners was delivered within four weeks — two weeks ahead of schedule.After testing and validation, the client reported outstanding performance metrics:
Torque consistency: ±2% variance across samples.
Zero defects: No burrs or thread failures reported during assembly.
Corrosion resistance: Maintained integrity after 96-hour exposure test.
Dimensional accuracy: 100% parts within drawing specification.
Batch repeatability: Consistent results across 5 consecutive shipments.
“We have worked with several suppliers before, but none provided the level of precision and communication your team did. Your CNC fasteners exceeded our expectations in both performance and reliability.”— Procurement Director, Italian EV Transmission Manufacturer
Encouraged by these results, the client extended the partnership for additional custom threaded inserts and titanium bolts for their next EV platform.
7. Technical Achievements and Capabilities Demonstrated
This project fully utilized our company’s advanced CNC machining capabilities and strict quality management system.
Capability
Specification
Tolerance
Up to ±0.005 mm
Thread Standard
ISO 965-2 / DIN 13
Material Used
AISI 304, 316, 17-4PH
Surface Finish
Passivation, Nickel Plating, Black Oxide
Inspection Tools
Mitutoyo CMM, Profile Projector, Thread Gauge, Torque Tester
Certifications
ISO 9001:2015, IATF 16949, RoHS, PPAP Available
We also implemented a digital inspection workflow using barcode tracking, ensuring full visibility of every production stage — from raw material to packaging.
8. Packaging and Logistics
Given the sensitivity of surface finishes and thread quality, our packaging process was designed with care:
Each fastener was separated by anti-scratch foam dividers.
Vacuum-sealed in groups of 50 pcs with silica gel packets.
Export-grade cartons labeled with QR codes for batch traceability.
All shipments were handled via DHL Express and sea freight, depending on customer urgency.
Lead time for standard reorders: 10–12 working days.
9. Broader Application and Industry Value
Following this successful project, similar custom stainless steel fasteners have been applied to:
EV Powertrain Systems(Battery case bolts, inverter housing screws)
Heavy-Duty Machinery(Vibration-resistant locking bolts)
Marine Equipment(Anti-corrosion threaded connectors)
Industrial Robotics(Precision alignment pins and torque fasteners)
This showcases how our CNC machining expertise and material knowledge allow us to support various industries where strength, reliability, and precision are essential.
10. Why Choose [Lock Technology(shenzhen)Co.,LTD]
Expert in Custom Machined Fasteners
17+ years of experience manufacturing stainless steel, titanium, and alloy fasteners.
Advanced Equipment Fleet
Swiss-type lathes, 5-axis centers, automatic thread rollers.
Quality Without Compromise
Certified ISO 9001 / IATF 16949 with full inspection documentation.
Flexible Order Volume
Prototype to mass production, no MOQ limit.
Global Customer Trust
Clients in Europe, USA, Japan, and Australia across automotive and robotics sectors.
11. Conclusion
This Custom Stainless Steel Fasteners Case Study exemplifies how a technical partnership and precision machining expertise can transform complex engineering requirements into reliable, production-ready solutions.
Through the integration of CNC precision, quality control, and customer-focused engineering, [Lock Technology(shenzhen)Co.,LTD] successfully helped the client improve transmission reliability, reduce production time, and strengthen their EV product competitiveness.
Whether you require custom bolts, nuts, shafts, or non-standard precision fasteners, our engineering team can deliver tailored CNC machining solutions that meet your toughest requirements — every time.
[Lock Technology(shenzhen)Co.,LTD] — Precision You Can Trust, Performance You Can Measure.
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Om de normale werking van de apparatuur te waarborgen, is regelmatig onderhoud van speciale schroeven, die onbelangrijke kleine onderdelen van de apparatuur zijn, zeer noodzakelijk.Gezien het belang van speciale schroeven, is het belangrijk om tijdens het onderhoud aandacht te schenken aan dit aspect om problemen met speciale schroeven te voorkomen.
Speciale schroeven
1、 Verwijder puin
Speciale schroeven moeten na het afdoen met silicaten worden gereinigd en na het reinigen ook met water worden gewassen.het is belangrijk om heel voorzichtig te zijn bij het wassen.
2Speciale schroeven gestapeld en beschadigd
Soms komen we situaties tegen waarin speciale schroeven van kleur veranderen na verwarming, en na het weken in ether, wordt er een olierig residu gevonden,die aangeeft dat het oppervlak van de speciale schroef niet schoon isNa analyse bleek dat dit te wijten was aan een onjuiste stapeling van speciale schroeven tijdens het verwarmen, wat resulteerde in een lichte oxidatie in de blus olie.
3Oppervlaktelijke residuen
Als hoogsterke schroeven niet met een zuurreinigingsmachine worden gereinigd en de spoeltank onvoldoende wordt gecontroleerd, kunnen er witte residuen op de schroeven zitten.waarvan na de eerste fase van de inspectie is vastgesteld dat het fosfyde is.
4Alkalibrand
Als een speciale stalen schroef de blus-olie binnendringt zonder de alkalische stoffen van het oppervlak te verwijderen,wordt geconstateerd dat de schroef zwart wordt als gevolg van het doven van de restwarmte en een gelijkmatig en vlak oliezwart buitenste oppervlak heeftOmdat de schroeven die niet schoongemaakt werden verbrand op het oppervlak bij hoge temperaturen, en de schade verergerd tijdens het temperen.het is noodzakelijk om de alkalische residuen die brandwonden kunnen veroorzaken op speciale schroeven grondig te reinigen.
5Onjuist spoelen
Soms blijkt dat bij het gebruik van een waterige oplossing van polymeren voor het blussen van grote speciale schroeven, bij het gebruik van een alkalische reinigingsmachine voor spoelen,de speciale schroeven zijn al roestig tijdens de interne testOm ervoor te zorgen dat bij het spoelen speciale schroeven niet roesten, is het dus noodzakelijk het spoelwater regelmatig te vervangen.
6. Overmatige corrosie
De overmatige veroudering van de blus-olie laat bij het drogen van hoge sterkte speciale schroeven zwarte strepen achter, wat een rest is van oppervlakterrest,die de evolutie van de gasfase tijdens het blusproces isDaarom wordt aanbevolen nieuwe olie toe te voegen.
Voor
