Starting Point: Micron Tolerance Trained on Phone Precision Screws

In 2008, YF Zhichengjia entered a leading customer's phone business and thereby fully integrated into the top-tier phone supply chain. Phone internal space is extremely compact, and the screws used are mostly M0.5~M2 miniature precision screws, with extremely high requirements for thread tolerance, head coaxiality, and surface quality. A head offset of just 0.05mm on one screw can disrupt the assembly of an entire unit. It was in this "high-frequency, high-precision, high-yield" training ground of consumer electronics that the company built its mass production and inspection capability for precision small screws.

This experience left two key assets: first, process control experience for micro-dimensional tolerances, and second, a production line layout paired with automated inspection and optical sorting. These capabilities later became the underlying foundation for the company's upgrade into higher-requirement fields. The discipline of 100% optical inspection on every M0.6 screw, developed to keep SMT lines running, is the same discipline that now governs automotive-grade fastener output.

2017 Turning Point: Aluminum Sleeve from CNC to Cold Heading

2017 was the watershed in the company's process route. Before that, products like aluminum sleeves relied mainly on CNC machining: a bar of aluminum goes on a lathe, and the outer diameter, inner bore, and threads are turned one cut at a time, with low material utilization, slow takt, and high unit cost. Through process optimization, the company switched this product category to cold heading (cold forging): steel or aluminum wire is forged in a multi-station die at room temperature into a near-net shape in one stroke, followed by thread rolling and secondary machining.

The direct result of this transition was that the company smoothly entered the NEV supply chain. Cold-headed parts have continuous metal flow lines and dense grain structure, giving them better fatigue strength and impact resistance than cut parts. At the same time, material utilization improved dramatically and unit takt shortened, significantly reducing cost. The company has continued to extend and deepen this route on products such as aluminum lifting sleeves and high-strength aluminum bolts.

Cold Heading vs CNC: Cost, Strength, Efficiency

Cold heading and CNC machining are not mutually exclusive replacements but have different applicable boundaries. Understanding the differences is key to understanding why the company made this switch in 2017.

For parts like EV battery pack lifting sleeves - which are rotary symmetric, medium-high volume, and demand high fatigue strength - cold heading is almost always the better solution. For multi-variety, low-volume, irregular-shaped samples, CNC and rapid prototyping remain irreplaceable. The company's production lines retain both cold heading and CNC capability, choosing the process route based on order characteristics. This dual-process flexibility is important because new customers often start with low-volume CNC samples to validate a design, then ramp to cold-heading production once the design is frozen. The supplier that can support both stages without forcing the customer to change vendors is the one that keeps the program through mass production.

From Consumer Electronics to Automotive Grade: Quality Logic Upgrade

Moving from phone screws to NEV joining, what changed was not just product size but the entire quality logic. A phone screw failure usually means "rework," while an automotive fastener failure can mean "safety incident." This required the company to upgrade its systems and process control:

• System upgrade: The company obtained IATF 16949 automotive quality management certification in 2013, paving the way for later entry into automotive and NEV supply chains.
• Process control: Introduced automotive core tools APQP, FMEA, SPC, MSA, PPAP, with statistical process control monitoring variation on critical dimensions.
• Inspection capability: Equipped with metallographic microscope, hardness tester, vision measuring machine, universal tester, salt spray chamber, friction coefficient tester, covering material composition, dimensions, mechanicals, and environmental durability.
• Traceability: Full-process records from furnace heat number to delivery batch, meeting automotive customers' lot traceability requirements.

It is this capability - built on consumer electronics precision manufacturing and upgraded to automotive-grade systems - that has supported the company's subsequent expansion into NEV, AI servers, humanoid robots, and other mid-to-high-end markets.

The Next Stop for Cold-Heading Evolution

Cold heading at YF Zhichengjia has not stopped at aluminum sleeves. Along the route of "cold heading + material upgrade + surface treatment," the company is extending toward higher strength, smaller sizes, and more complex structures:

• Ultra-high-strength fine-thread bolts: Cold-headed 14.9+ class fine-thread bolts for automotive, generators, motorcycles, and aero engines.
• M1~M4 high-strength maintenance-free joints: For humanoid robot joints, coreless motors, reducers, and dexterous hands, pushing cold-heading precision into miniature scale.
• Multi-material galvanic corrosion protection: Combining special adhesives with 8.8-class aluminum bolts to solve dissimilar-metal joining corrosion in automotive, motorcycle, and communications applications.