Introduction

In Vietnam’s manufacturing sector, advancements in electrification, high functionality, and shorter delivery times are raising the standards for corrosion resistance, anti-loosening, and traceability required of screws (fasteners).
This article provides a practical overview of the key points of the latest screw technology in Vietnam. It explains surface treatment and hydrogen embrittlement countermeasures, transverse vibration testing (Junker-type), torque and angle management with IoT, thread-forming screws, and preventive measures based on IATF/ISO, complete with implementation procedures and checklists.
This is intended for personnel in charge of quality, production engineering, and procurement. The goal is to achieve results verification, standardization, and mass production deployment within 90 days.

Basics of Standards/Environmental Compliance and Conformity

When mass-producing or procuring screws in Vietnam, it is crucial to distinguish between standards (the language of drawings) and conformity (the language of laws and certifications). This section outlines how to write specifications on drawings, key points for selecting environmentally friendly surface treatments, practical measures to avoid hydrogen embrittlement, and the essentials of local conformity procedures.

Organizing the Relationship Between TCVN/QCVN and ISO/JIS

TCVN (Vietnam Standards) are voluntary, while QCVN (National Technical Regulations) are mandatory. For screw design and manufacturing, descriptions based on ISO/JIS are mainstream from the perspective of international harmonization. Specifying the following three points on drawings can reduce differences in interpretation among suppliers:

• Size/Grade: e.g., M6×1-8g, Property Class 8.8 (ISO 898-1)
• Surface Treatment: e.g., Zn-Ni 8-12 µm, finish color, target friction coefficient
• Test Method: e.g., Friction/axial force correlation ISO 16047, plating requirements ISO 4042

Practical Tip: Use both English and Vietnamese on drawings and purchasing specifications, and operate them as a set with control charts (incoming inspection, plating lot traceability). Audits will check the three-way link of “Standard → Test → Record.”

Environmentally Friendly Surface Treatments and Hydrogen Embrittlement Countermeasures

For projects requiring RoHS/ELV compliance, hexavalent chromium-free Zn-Ni and zinc flake (non-electrolytic) are leading candidates. Since electrolytic plating increases the risk of hydrogen embrittlement in high-strength materials, the following controls are essential:

• Optimization of Pre-treatment: Minimize acid pickling time and concentration to suppress hydrogen absorption.
• Baking: Perform dehydrogenation treatment after plating, typically at 190 ± 10 °C for 2-4 hours.
• Hardness Threshold Management: Implement stricter controls for high-strength materials (目安 HV≧320 equivalent).
• Agreement on Friction Coefficient: Actually measure the friction coefficient μ (ISO 16047) before mass production, depending on the coating agent and film.

Specification Example (Excerpt):

Surface Treatment: Zn-Ni 10 µm, Trivalent Chromate Finish / Baking: 190 °C × 3 h / Target Friction Coefficient: 0.12-0.18 / Testing: Conforms to ISO 4042, ISO 16047

Non-electrolytic zinc flake coating has a low risk of hydrogen embrittlement and is effective for applications requiring high corrosion resistance, such as outdoor and automotive underbody parts (see, e.g., ISO 10683). However, requirements for dimensional increase, conductivity, and appearance color must be agreed upon in advance.

Key Points for Vietnamese Laws and Conformity

First, confirm if the target product falls within the scope of a QCVN. If it does, displaying the CR mark and preparing technical documentation is necessary. While many general machine parts are operated under voluntary application based on TCVN/ISO, the jurisdiction may change if they are incorporated into electrical, pressure, or safety-related equipment. The following steps are effective in practice:

1. Classification: Check the application, HS code, and whether any QCVN applies.
2. Declaration of Conformity: Select the required certification method (third-party certification / self-declaration).
3. Technical File: Store a complete set of drawings, material certificates, surface treatment specifications, test reports (ISO 16047, ISO 4042, etc.), and lot traceability records.
4. Marking and Labeling: As required, add Vietnamese language labels, the CR mark, and manufacturer information.
5. Audit Response: Link incoming inspection records and change management (for surface treatment conditions, plating supplier changes, etc.) with the QMS.

Checklist (Excerpt):

• TCVN/ISO drawing numbers and test methods are specified on the drawing.
• RoHS/ELV compliance certificates and baking conditions are written in the purchasing specifications.
• There is a flow to check the friction coefficient/axial force with lot samples during incoming inspection.
• The applicability of QCVN has been checked, and if necessary, the CR mark and technical documents are prepared.
• Vietnamese instruction manuals/labels and traceability ledgers are updated.

Fastening Reliability and Digital Quality Management

Most fastening failures stem from “unexpected loosening,” “friction variations,” and “missing records.” This section presents a three-pronged approach:
1) visualizing effective countermeasures with transverse vibration testing,
2) managing mass production with torque x angle and IoT
3) implementing preventive measures through a QMS.

Evaluation by Junker-type Transverse Vibration Test

Objective: To reproduce clamp load reduction under transverse vibration (Junker) and quantitatively compare combinations of washers, nuts, and coating agents.

Key Points for Test Design

• Use bolts and nuts from the same lot as mass production (matching material, heat treatment, and surface treatment).
• Match the bearing surface roughness, tightening force, and clamped part hardness to the actual machine.
• Define cycle conditions (amplitude, frequency, load) based on the operating environment (e.g., ±0.3 mm / 12.5 Hz / 10 kN).
• Set the initial clamp load to the center of the mass production target value and repeat the test at least 3 times.

Judgment Example (Guideline)

• A residual clamp load of ≥80% after N cycles is considered passing.
• Select the combination with a smaller initial sharp drop and subsequent stabilization in the curve.

Common Mistakes

• The bolt’s effective length is too short, making the spring constant inappropriate and causing the axial force drop to appear excessive.
• Testing with different lubrication or bearing surfaces than in mass production, leading to overestimation or underestimation.

On-site Tip: Store the results as “test curve + photo + condition table” in the component selection record and reflect them in the purchasing specifications (washer type, coating agent type).

Torque x Angle Management and IoT Traceability

Background: Torque-only management is susceptible to friction variations, causing axial force to vary even at the same torque. By combining torque and angle, pass/fail is determined by the work’s profile (signature).

Setup Steps

1. Preliminary Evaluation: Obtain the torque-axial force correlation using a standardized method and set the target value in the middle of the elastic region.
2. Gate Design: Define a “tightening window” with a four-fold gate of torque lower/upper limits and angle upper/lower limits.
3. Equipment: Assign a Tool ID and Program ID to wireless wrenches/electric screwdrivers and enable error-proofing (serial scanning, sequence control).
4. IoT Items: Record time, product/lot number, station, torque, angle, result (OK/NOK [Not OK]), number of retightenings, operator ID, and firmware version.
5. Analysis: Monitor histograms and control charts (mean, σ) daily and investigate outliers with physical checks before taking corrective action.

Example Operation Rules

• Tightening Audit: Check reproducibility with random sampling, such as 5 points per line per day.
• Definition of No Retightening: In case of NOK, replace the bolt or move to a re-evaluation flow.
• Calibration: Calibrate torque equipment at least once a year and inspect angle encoders semi-annually.

On-site Tip: Setting the abnormality detection threshold too strictly will cause frequent line stops. Start with a wider Warning zone and gradually tighten it while analyzing a Pareto chart of causes.

Preventive Measures with QMS (IATF 16949 / ISO 9001)

Goal: To identify sources of variation from design to mass production in advance and maintain stable quality even when changes occur.

Flow of Essential Documents

• FMEA (Design/Process): List the cause → phenomenon → countermeasure for loosening, corrosion, fracture, and tightening errors, and reflect high RPN items in Characteristic Management (CTQ).
• Control Plan: Define torque/angle gates, inspection frequency, and monitoring indicators for IoT data (first-pass yield, rework rate).
• MSA: Conduct Gage R&R (GRR) for torque wrenches/angle meters (target %GRR ≤ 10%, provisional operation up to ≤ 30%).
• Change Management (ECN: Engineering Change Notice): When changing surface treatment, coating agents, or tool programs, conduct re-evaluation tests (Junker-type/correlation) and obtain approval.
• PPAP (Production Part Approval Process): Store and submit a complete package including drawings, material certificates, heat treatment/surface treatment records, test reports, appearance standards, samples, and process capability data.

Example of Layered Process Audit (LPA)

• The tool ID and program are linked to the correct product number.
• Confirm adherence to the procedure for tightening sequence and from snug tightening to final tightening.
• The reaction plan for NOK (tagging, segregation, outflow prevention) is activated immediately.

On-site Tip: Prioritize a system that detects early and stops small rather than aiming for zero defects. The key to utilizing IoT data is to create a system that can cycle through alert, on-site confirmation, correction, and recurrence prevention “within 24 hours.”

Process Optimization and Implementation

The core of process optimization is “eliminating the source of rework in the preceding process.” For screw fastening, simultaneously advancing tap process reduction, error-proofing, and data acquisition can achieve both takt time reduction and defect reduction. This section focuses on going tapless (using thread-forming screws) and presents check points for implementation and a 90-day implementation plan.

Shortening Processes with Thread-forming Screws (Tapless)

Goal: To eliminate tapping (cutting threads) and fasten by plastically forming threads directly into a pilot hole. This process generates no chips, and the close contact of the threads tends to improve loosening resistance and fatigue resistance.

Applicable Scenarios

• Materials: Low-carbon steel, aluminum, magnesium, and some plastics (materials that can secure a plastic region).
• Shapes: Sheet metal / extruded enclosures / brackets. Both through-holes and blind holes are possible (depth allowance needs confirmation).
• Quality Requirements: No chips allowed (electrical components, sealing parts), takt time reduction, robust design.

Key Design and Process Points

• Pilot Hole Diameter: A certain ratio of the nominal diameter (the optimal value varies with material and plate thickness). Determine using the manufacturer’s recommendation chart and manage the tolerance at ±0.05 mm (guideline).
• Plate Thickness / Thread Engagement Length: A minimum of 2 to 2.5 pitches is a guideline. For thin plates, consider using bosses or collars.
• Chamfer: A small chamfer at the entrance (e.g., 0.2-0.4 mm × 45°) stabilizes the forming load.
• Lubrication: Select a suitable grease/coating to prevent seizing during initial forming.
• Evaluation Index: The safety factor between the driving torque (T_drive) and the stripping/thread-stripping torque (T_strip). An internal guideline example is T_strip / T_drive ≥ 1.25 to 1.40.

Example Effects (Trends)

• Eliminates tapping, cleaning, and chip removal, shortening the time by several seconds per point. Defects caused by chips are significantly reduced.
• Increased plastic contact of the threads improves vibration resistance, and the residual clamp load in Junker-type tests stabilizes.

Points to Note

• For materials with excessively high hardness or in weld heat-affected zones, the forming load increases sharply, so feasibility must be determined by testing.
• Variations in pilot hole and surface roughness are the main causes of driving torque fluctuations. SPC management of processing conditions and tool wear is effective.

On-site Checklist (Points to Check During Implementation)

• Drawings/Purchasing Specifications: Specify the type of thread-forming screw, pilot hole diameter and tolerance, chamfer, surface treatment, presence of lubrication, and T_drive/T_strip targets.
• Pilot Hole Machining: Drill diameter, rotation/feed, position, and procedure for removing burrs/weld spatter. Perform daily checks with gauges (pin/snap).
• Tools/Jigs: Ensure consistency of the screwdriver’s torque, speed, angle control, bit shape, pressing force, and screw feeder.
• Testing: Measure the driving torque curve and stripping torque with initial samples, and conduct Junker-type and ISO 16047 tests as necessary.
• IoT and Traceability: Automatically record Tool ID/Program ID, torque, angle, pass/fail, number of retightenings, and operator ID.
• Quality Rules: Establish a reaction plan for NOK (part replacement/segregation), criteria for allowing retightening, and appearance pass/fail samples.
• Training: Provide standard training to operators on the importance of pilot hole tolerance, bit pressing posture, and NOK response.

Implementation Roadmap (90-Day Plan)

• Weeks 0-2 | Diagnosis: Understand the current takt time, rework for tapping, cleaning, and chip handling, and the Pareto of fastening defects to select target areas.
• Weeks 3-6 | Technical Evaluation: Optimize pilot hole diameter, chamfer, and lubrication with samples. Measure T_drive/T_strip, and if necessary, obtain correlation with vibration tests and ISO 16047. Define target torque and angle gates.
• Weeks 7-9 | Standardization: Revise SOPs/inspection standards/control plans. Set up tool programs, screw feeding, and IoT items, and update FMEA/ECN.
• Weeks 10-12 | Mass Production Transition: Move from pilot production to initial flow. Monitor CT (Cycle Time), first-pass yield, rework rate, and tool life daily, and reflect improvements weekly.
• Week 13 | Audit/Stabilization: Conduct LPA and performance review. Finalize purchasing specifications and drawings, and provide supplier training. Judge full-line deployment based on KPI achievement.

Example KPIs: Takt time -10 to 20%, chip-related defects -90%, first-pass yield +2 to 5 pts, tool life +20%, line stops -20 to 30%.

Summary

This article has organized the latest screw technologies effective in Vietnamese manufacturing along three axes:
1) standards and environmental compliance
2) fastening reliability and digital quality
3) process optimization.
It proposes a path to evaluation, standardization, and mass production stabilization in 90 days, focusing on harmonizing ISO/JIS with TCVN/QCVN, comparing countermeasures with Junker tests, recording with torque x angle + IoT, and reducing takt time with thread-forming screws. Please start by specifying standards and test methods on drawings, agreeing on friction coefficients, and setting up IoT items.

Conclusion

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