Spanish automation equipment manufacturer breaks through the difficulties of high-precision screw technology

Core process difficulties

Balance between strong magnetism and corrosion resistance

• Challenge: Traditional stainless steel (such as 304 series) is corrosion-resistant but non-magnetic, while carbon steel is magnetic but easy to rust. The customer requires the screw tip to have both strong magnetism (Gauss value <000000>ge; 800) and salt spray resistance test <000000>ge; 500 hours.
• Solution:
  • Material innovation: Use 430 stainless steel (ferrite) + 410 stainless steel (martensite) composite formula, control the ratio of ferrite and martensite through heat treatment, and achieve the best balance between magnetism and corrosion resistance.
  • Process optimization: Use vacuum quenching process to avoid the oxide layer from destroying magnetism, while increasing the hardness to above HV300.

Precision molding of micro screws

• Challenge: The head size error of micro screws such as M1.6*3 needs to be controlled within ± 0.02mm, and the tip needs to form a cone angle of 20 °± 1° to ensure magnetic attraction stability.
• Solution:
  • Multi-station cold heading technology: Use a high-speed cold heading machine imported from Switzerland, through 5-station progressive forming, reduce material stress concentration, and achieve 0.01mm level accuracy.
  • Laser calibration: 3D laser scanning is performed on each batch of samples to detect the head shape and tip angle, and the qualified rate is increased to 99.8%.

Synergistic effect of double surface treatment

• Challenge: Passivation and black oxidation need to be implemented step by step, and the thickness of the oxide layer needs to be controlled at 8-12 μ m to avoid affecting the magnetism.
• Solution:
  • Step-by-step processing flow:
    • Passivation pretreatment: Use a mixed solution of nitric acid + hydrofluoric acid to remove surface impurities and activate the metal surface.
    • Black oxidation: Use a high-temperature alkaline solution (NaOH+NaNO2) to form a uniform oxide film by controlling the temperature (140 ± 5 ℃ ) and time (25-30 minutes).
  • Film thickness detection: Use an eddy current thickness gauge online for real-time monitoring to ensure the uniformity of the oxide layer thickness.

EU CBAM certified low-carbon process

• Challenges: Carbon emissions in the production process need to be quantified, involving full-chain data tracking such as raw material procurement, heat treatment, and surface treatment.
• Solution:
  • Digital carbon footprint management:
    • Use blockchain technology to record the carbon emissions of each batch of steel (such as CO ₂ equivalent in the steelmaking process).
    • Optimize the energy structure of the heat treatment furnace, use natural gas instead of coal, and reduce the energy consumption of a single furnace by 35%.
  • Third-party verification: Pass SGS certification to ensure compliance with the EU CBAM transition period reporting requirements.

Manufacturing process and key parameters

Cold heading

• Equipment: Swiss cold heading machine
• Speed: 200 times/minute
• Precision: dimensional tolerance ± 0.015mm

Vacuum quenching

• Temperatura: 1050 ℃± 10 ℃
• Time: 90 minutes
• Cooling medium: nitrogen

Tratamiento de superficies

• Passivation: nitric acid concentration 15-20%, processing time 5-8 minutes
• Black oxidation: solution pH 13.5-14, processing time 25 minutes

Magnetic detection

• Equipment: Tesla meter (range 0-2000mT)
• Standard: tip magnetic field strength <000000>ge; 800mt

Project Achievements

Technology breakthrough:

• The magnetic uniformity of micro screws has been improved by 40%, and the mis-absorption rate has been reduced from the industry average of 5% to 0.5%.
• The salt spray test has met the standard (no red rust for 500 hours), and the service life is 3 times longer than that of carbon steel screws.

Efficiency and cost:

• The cold heading efficiency has been increased by 25%, and the production cost of a single screw has been reduced by 18%.

Environmental compliance:

• Carbon emissions have been reduced by 42% compared with traditional processes, and CBAM certification has been successfully passed.

This case successfully broke through multiple manufacturing difficulties of screws for automation equipment through material formula optimization, precision molding technology, surface treatment collaborative process and low-carbon production management. In particular, it provides a replicable solution for the industry in terms of the balance between strong magnetism and corrosion resistance, precision control of micro screws and EU environmental certification.