In-Depth Analysis Of Chiba Needle Tip Manufacturing Processes

The Full Precision Machining Workflow from Stainless Steel Tube to Sharp Cutting Edge

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The Chiba needle may appear to be a simple hollow thin needle, but the manufacturing of its tip involves precision tube machining, multi-stage grinding, electrochemical treatment, and stringent quality control - a quintessential high-precision medical device manufacturing process. The following details the entire tip manufacturing process step by step.

1. Raw Material Selection and Tube Pretreatment

The Chiba needle body is mostly made of medical-grade stainless steel 304 or 316L (some high-end products use nickel-titanium alloy NiTi for flexible needle bodies). The raw material is cold-drawn seamless capillary tubing, with outer diameter tolerance within ±0.02 mm and wall thickness uniformity deviation <5%. Incoming materials undergo spectroscopic analysis and hardness testing to ensure compliance with ISO 10993 biocompatibility requirements.

2. Fixed-Length Cutting and Pre-Forming of Tube End

Using a high-precision tube cutter, the material is cut to the target length (usually 15/18/20 cm), with end-face perpendicularity error <0.05 mm. The tube end is given a preliminary chamfer to remove shear burrs, preparing for subsequent tip forming. At this stage, the tube end is still flat, without a bevel.

3. Needle Tip Bevel Grinding

This is the most critical process determining tip quality. A CNC grinding machine with a diamond wheel or CBN (cubic boron nitride) wheel grinds the tube end to the specified bevel angle (standard 25°±2°). Key process points include:

Feed speed control: Too fast causes burn discoloration and micro-cracks; too slow reduces efficiency and may dull the edge.

Cooling and lubrication: Water-soluble cutting fluid is used throughout to prevent the heat-affected zone (HAZ) from altering stainless steel hardness.

Symmetry assurance: The left and right cutting edges must be symmetrical about the needle tube axis, with equal edge lengths; otherwise, puncture deflection increases.

4. Edge Fine Grinding and Tip Honing

After rough grinding, the edge has a sharp angle but may have micro-chipping. Fine grinding (honing) with a wool felt wheel and diamond paste eliminates micron-level burrs, making the edge sharp and smooth. Some manufacturers apply a very slight tip rounding (about 1–2 μm) at the very apex to prevent micro-chipping when first contacting hard tissue, without affecting the subjective puncture feel.

5. Inner Wall Polishing and Deburring (Electropolishing)

The inner lumen of the tip and the tube inner wall undergo electropolishing to remove machining marks and reduce surface roughness Ra to below 0.2 μm, minimizing cell adhesion and lumen clogging risk. The outer wall is simultaneously electropolished to thin the passive layer and enhance corrosion resistance.

6. Microscopic Inspection and QC of the Tip

Optical projector/tool microscope: Measures bevel angle, edge length, tip diameter, and symmetry.

Puncture force tester: Penetrates a standard PU membrane or excised pig liver capsule at a constant rate, recording peak force; batches exceeding limits are rejected wholesale.

SEM sampling: Scanning electron microscopy observes whether the edge has micro-cracks or rolled edges.

100% visual inspection: Each tip is visually examined under 40× magnification.

7. Cleaning, Assembly, and Sterilization

After ultrasonic cleaning, pure water rinsing, and vacuum drying, the stylet is inserted, the hub attached, and the unit is packaged for ethylene oxide (EO) or irradiation sterilization, completing finished product release.

The manufacturing difficulty of a quality Chiba needle tip does not lie in "grinding a bevel," but in batch consistency - controlling bevel angle deviation within ±1° and maintaining uniform micro-quality of the edge across tens of thousands of needles of the same model. This is the core yardstick distinguishing ordinary from high-end Chiba needle manufacturing.