How Are Steel Doors Made? – The Complete Manufacturing Process

What Is a Steel Door?

Steel doors are an essential component in modern architecture and industrial applications. Known for their durability, security, and fire resistance, steel doors are commonly used in commercial, residential, and institutional buildings. But how exactly are these doors made?

At Zonle Doors, we specialize in manufacturing high-quality steel doors for global clients. In this article, we’ll walk you through the step-by-step production process of steel doors—backed by advanced technology, strict quality control, and industry expertise.

1. Material Selection: Choosing the Right Steel

The production process starts with selecting premium-grade galvanized or cold-rolled steel. Depending on the door's application—whether for fireproof, soundproof, or high-security environments—we choose the appropriate thickness and coating.

• Galvanized steel for rust resistance

• Cold-rolled steel for high precision and smooth finish

• Stainless steel for corrosion-sensitive environments

Zonle Tip: We use only certified steel that meets international standards (e.g., ISO, ASTM).

2. Sheet Cutting and Blanking

Large steel coils are flattened and cut into sheets using high-precision machines. This ensures all steel door panels are consistently shaped with minimal deviation.

• CNC-controlled cutting ensures ±0.2 mm accuracy

• Efficient layout planning reduces material waste

3. Bending and Forming

Using press brake machines, steel sheets are bent to form the door frame, leaf, and reinforcements. Reinforcement areas for locks, hinges, or vision panels are also pre-formed at this stage.

• Edge folding enhances structural integrity

• Robotic forming for consistent angles and weld points

4. Welding and Assembly

The cut and bent steel parts are now welded together using MIG or spot welding. Internal reinforcements are added for hinges, lock boxes, and hardware mounting.

• Seamless welding minimizes air gaps

• Every weld is checked for strength and alignment

5. Surface Treatment: Cleaning and Coating

Before painting, the door undergoes surface treatment to remove oil, dust, and rust. This improves adhesion and corrosion resistance.

• Phosphate treatment for better primer bonding

• Electrostatic powder coating or baked painting for surface protection

At Zonle Doors, our coating process complies with RoHS and REACH environmental standards.

6. Insulation and Core Filling

Depending on the design, steel doors are filled with core materials to improve fire resistance, soundproofing, or thermal insulation:

• Honeycomb paper for lightweight durability

• Rock wool or mineral wool for fire-rated doors

• Polyurethane foam for thermal insulation

All materials are eco-friendly and tested according to EN and UL standards.

7. Final Assembly and Hardware Installation

After the core filling, the doors are pressed, sealed, and equipped with hardware:

• Locks, hinges, peepholes, and closers

• Custom hardware upon client request (e.g., smart locks, panic bars)

8. Quality Control & Testing

Every Zonle steel door undergoes a series of inspections:

• Dimension check and surface inspection

• Opening/closing cycle tests

• Fire resistance or impact testing (if applicable)

9. Packaging and Shipping

After final cleaning, the doors are packed using:

• PE film + foam protection

• Strong export-grade wooden pallets

• Moisture-proof packaging for overseas shipping

Why Choose Zonle for Your Steel Doors?

• Over 20 years of manufacturing experience

• OEM & ODM service available

• Certified by ISO9001, CE, and UL standards

• Exported to 190+ countries

Frequently Asked Questions (FAQs)

Q: How long does production take?
A: Standard steel doors take 7–15 days depending on order quantity and specifications.

Q: Can I request custom designs or hardware?
A: Yes, we offer full customization including size, finish, glass inserts, and locksets.

Q: Do your steel doors meet fire rating standards?
A: Yes. We offer fire-rated doors tested according to UL and BS standards.

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