Chiba Needle Manufacturing Process And Core Machining Technology

From Medical Stainless Steel Tube to Sterile Finished Product

https://radiopaedia.org/articles/chiba-needle

The Chiba needle appears structurally simple - a hollow thin tube plus a plastic hub - yet its manufacturing process imposes stringent requirements on precision machining and clean production. A typical production flow at a reputable Chiba needle manufacturer is as follows:

Step 1: Raw Material Inspection & Tube Cutting​

Select seamless capillary tubing of SUS304, SUS316, or SUS316L conforming to ASTM F899 or ISO 7153-1, with OD tolerance within ±0.01 mm and wall thickness uniformity ≤±5%. IQC verifies chemical composition, hardness (typically HV300–380), straightness, and inner wall roughness (Ra < 0.4 μm). Cut to finished length + process allowance (usually +3–5 mm) using a CNC tube cutter; deburr both ends.

Step 2: Tube Sizing & Forming​

If special ID/OD combinations (thin-walled tube) are required, a pass of precision tube drawing or sizing roll may be performed. Some manufacturers apply micro-indentations or laser-marked centimeter scales on the mid-section - the scale depth must be strictly controlled to avoid weakening the tube or creating stress concentration points.

Step 3: Needle Tip Grinding (Grinding & Beveling)​

This is the most critical process for the Chiba needle. CNC micro-feed diamond wheel grinding produces the specified bevel angle (typically 20°–35°, classically 25°–30° short bevel). High-end lines perform secondary fine grinding to remove micro-burrs and slightly round the outer tip edge to prevent "fishmouth" deformation. Franseen tip variants require 3-axis simultaneous grinding to create three evenly distributed cutting facets. Post-grinding, 100% microscopic inspection is conducted to reject rolled edges, chipped tips, and asymmetric bevels.

Step 4: Inner Wall Polishing & Cleaning​

Electropolishing (ECP) or flexible mechanical polishing reduces inner wall Ra to below 0.2 μm, minimizing cell/blood adhesion and improving aspiration patency. This is followed by multi-stage purified water rinsing, ultrasonic degreasing, and deionized water flushing to thoroughly remove grinding debris and process fluid residues.

Step 5: Stylet Fabrication & Fit Testing​

The stylet outer diameter is slightly smaller than the cannula inner diameter (clearance approx. 5–15 μm). After insertion, it should slide smoothly without excessive play. Fit testing commonly uses go/no-go gauges or optical projection comparison. Some models have the stylet tip lightly chamfered to prevent seizing.

Step 6: Sub-Assembly - Hub Molding / Press-Fitting​

The needle tube tail is bonded or mechanically crimped to an ABS/PC/Luer Lock hub, ensuring a leak-free metal-to-plastic interface. A depth stop (sliding limiter ring made of PE or PP) is fitted onto the tube body. Assembly is performed in a Class 100,000 or Class 10,000 cleanroom, with operators wearing anti-static garments and finger cots.

Step 7: Final Cleaning, Drying & Packaging​

Post-assembly, the complete unit undergoes isopropanol/pure water spray wash → hot air or vacuum drying → full visual inspection → loaded into Tyvek/medical grade paper-plastic pouch or blister. After placing internal indicators, it is subjected to EO sterilization (or gamma irradiation), followed by sterile release testing (sterility, EO residue, endotoxin).

Step 8: Quality Control​

Key QC items include: dimensional (OD/ID/length/bevel angle) optical measurement, tip sharpness/puncture force testing (penetrating artificial membrane or silicone simulant), cannula-stylet fit (insertion/withdrawal force), inner lumen cleanliness (particulate count), leakage test at hub-tube junction, sterility and biocompatibility evaluation (cytotoxicity/sensitization/hemolysis per ISO 10993). The entire process is governed by an ISO 13485 system with batch-level traceability.

Excellent manufacturers also analyze the puncture force-penetration work curve of the needle tip, keeping puncture force below a benchmark referenced from industry standards (e.g., 22G Chiba needle penetrating a 0.25 mm silicone membrane with force ≤ X N, per enterprise standard), thereby quantifying the subjective "sharpness" feel into an objective metric that forms a differentiated competitive edge.