Starting from a customer complaint about 20MnB4 oil pipe nuts
"This batch of material is hard to work with; let's try another piece."
When cold heading results in surface scratches, the first reaction on-site is often to change the material. But if the problem persists after switching materials, what should be done next?
During an on-site investigation at the customer’s facility, 20MnB4 hexagonal oil pipe nuts exhibited surface scratches, accompanied by unusual noises from the equipment. With no changes made to the equipment or die, the customer switched to using No. 35 steel for trial production.
The noise decreased slightly, but every part produced still showed surface scratches.
This outcome doesn’t immediately point to one party being right or wrong, but it does remind us that we shouldn’t just keep swapping materials.
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Does changing socks solve the problem when shoes pinch your feet?
If a particular spot in your shoe pinches, changing socks might make walking a bit more comfortable, but the pressure point itself hasn’t disappeared.
Cold heading surface scratches can sometimes follow the same logic.
We collected samples from each station and compared them, discovering insufficient clearance in the die gap. After re-measuring, the customer also confirmed this issue.
To put it plainly: as the material passes through certain areas, it should flow smoothly, but instead experiences unwanted squeezing and rubbing. Once the protective lubrication layer on the surface is damaged, subsequent friction can scratch the surface, resulting in surface defects.
Therefore, a thicker coating isn’t always better. Just like when your shoes pinch—you can’t expect simply changing socks to fix the problem.
Original site photo 17 Original site photo 15
Having oil doesn’t necessarily mean lubrication is fine
Another noteworthy detail observed on-site: the machine’s lubricating fluid had become quite thick, and operators reported that it hadn’t been changed for a long time. The product’s hexagonal faces also showed signs of blackening.
The thickening of lubricating fluid can have multiple causes and shouldn’t be simply attributed to “not having changed the oil in a long time.” Besides usage duration, it’s important to check what contaminants have entered the fluid and whether impurities are being effectively removed.
During machining, metal chips and residues from surface coatings can enter the lubricant. Without effective filtration, metallic particles may circulate within the system, re-entering between the die and workpiece, exacerbating surface abrasion and die wear.
It’s like using a cloth with grit to clean a lens—intended to protect the surface, it ends up making it even more scratched.
Thus, “having oil” does not automatically mean “lubrication is effective.” Both the condition of the lubricant and the effectiveness of filtration must be evaluated. The thickened and blackened appearance observed in this case serves as a clue for further inspection, but does not yet confirm contamination by metal debris.
When machining clearances are inadequate and lubrication conditions are problematic, simply asking for a thicker coating on the material won’t solve all issues.
What customers need goes beyond just “trying another piece”
In this investigation, insufficient die clearance was identified as one cause of surface scratches, and recommendations were made to address both fit and lubrication issues. However, the effectiveness of these improvements still requires confirmation through production trials.
For the customer, the losses extend beyond just a few defective parts—they include downtime, material changes, and repeated attempts without a clear direction.
We supply materials while also paying attention to why they perform well—or poorly—once installed in the customer’s machines. We directly address issues related to the material itself and collaboratively analyze problems involving machining fit. Helping customers understand where to look next is far more valuable than simply stating, “The material is fine.”
If you’re also experiencing cold heading surface scratches, difficulty working with new materials, or inconsistent performance with the same material, don’t jump to conclusions. Send us photos of the defective parts, the material grade, and details of the affected processes, and we can help determine the best troubleshooting path, conducting deeper analysis with samples if necessary.