How to produce hex bolts by cold forged machine?

To produce hex bolts using a cold forging machine, the primary method is the cold heading process, a fast and cost-effective open-die forging technique used for the vast majority of commercial screws and bolts.

Here is the core production process, along with key machine types and quality considerations.

🔩 The Standard Production Process

Most hex bolts are produced in a multi-stage sequence. Here's how the typical flow works:

· 1. Cutting & Heading: Straight wire is cut to size and transferred to a die where the head is formed by high-pressure impact (heading).
· 2. Shaping (if needed): For certain bolts like hex washer heads, additional upsetting stations refine the head shape and form features like washers.
· 3. Trimming (if needed): An extra step to remove excess "flash" material from the formed head, sometimes required for near-net-shape forging.
· 4. Threading: The bolt blank (shank) is rolled between two threaded dies (thread rolling/forming) to create precise, strong threads.
· 5. Heat Treatment & Finishing: Bolts are hardened and tempered to meet required strength grades, then often coated (e.g., zinc plating, black oxide) for corrosion resistance.

⚙️ Key Equipment and Technology

Cold forging requires specialized, high-capacity machinery. Here's a breakdown of core equipment and its role:

Core Machine: Cold Heading/Bolt Former

· Purpose: Performs cutting, heading, and shaping.
· Key Feature: Multi-station design (e.g., 4 die 4 blow) allows progressive forming across several stations in one cycle.
· Capability: Machines are sized by the bolt diameter they can produce (e.g., from M4 up to M30).

Supporting Equipment

· Thread Rolling Machine: Dedicated machine for forming threads on bolt shanks after heading.
· Heat Treatment Furnaces: For hardening, tempering, and annealing to achieve mechanical properties.
· Tooling & Dies: Hardened steel dies and punches are critical. Special designs like split dies or angular hexagonal dies are used to forge sharp hex corners and extend die life.

✅ Advantages and Quality Considerations

Cold forging is favored for its high speed (tens of thousands of pieces per day) and material efficiency, as it shapes metal without removing chips. The process also improves the metal's grain structure, resulting in stronger bolts than those made by machining.

To achieve high quality, manufacturers focus on:

· Die Design and Maintenance: Proper die design is critical to ensure complete filling of the hexagonal head's corners and prevent defects.
· Process Optimization: Parameters like wire quality, lubrication, and force at each station are optimized for specific bolt sizes and standards.
· Secondary Operations: Additional steps like grinding, machining, or automatic optical inspection may be used for high-precision or special-purpose bolts.

📈 Comparing Cold Forging with CNC Machining

While over 95% of standard fasteners are cold forged, other methods like CNC machining are used for very small batches, prototypes, or extremely high-precision applications (e.g., luxury watches). Here's a quick comparison:

Cold Forging

· Volume: Mass production
· Speed: Very High (e.g., 80,000-100,000 pcs/day)
· Cost per Unit: Very Low
· Precision & Finish: Good for standard applications; may have minor flash
· Best For: Standard hex bolts for construction, automotive, general industry

CNC Machining

· Volume: Low-volume, prototypes
· Speed: Slow (e.g., 3,000-5,000 pcs/day)
· Cost per Unit: Very High
· Precision & Finish: Excellent, smooth
· Best For: Custom, non-standard, or ultra-high-precision parts

In summary, producing hex bolts by cold forging involves a sequence of cutting, cold heading, threading, and heat treatment on specialized, automated machines. It's a high-speed, efficient process ideal for mass production.

I hope this detailed overview is helpful. If you have a specific question about a particular stage of the process or the specifications of the bolts you're interested in, feel free to ask for more focused information.