A seemingly simple subcutaneous injection needle embodies the pinnacle of modern precision manufacturing technology. From special stainless‑steel raw materials to final sterile‑packaged finished products, it undergoes dozens of rigorous precision processes. This procedure is not merely metalworking, but an ultimate test of material science, mechanical engineering and quality control systems.

Step 1: Raw Material and Tube Fabrication

Tubing for medical injection needles is typically made of austenitic stainless steel such as 304 or 316L, which features excellent biocompatibility, corrosion resistance and suitable mechanical properties (strength and toughness). Manufacturing begins with multiple cold rolling and drawing of stainless‑steel strips via precision dies to continuously reduce outer diameter and wall thickness, while enhancing material hardness and tensile strength. The strips are then curled and welded into seamless or micro‑seam ultra‑fine tube blanks using laser welding technology. Known as the floating process, this stage requires repeated iterations to produce tubing close to final specifications. The formed tube blanks further undergo annealing to eliminate processing stress, adjust hardness and optimise performance for subsequent precision machining.

Step 2: Precision Shaping and Cutting

Preliminarily processed tube blanks are fed into drawing machines, where dies precisely regulate outer and inner diameters to meet specific injection needle gauges (e.g., 27G, 30G). Straighteners straighten the slender steel tubes, which are then cut to preset lengths to form individual needle cannulas ready for further fabrication. Dimensional accuracy is critical at this stage; batch sampling is regularly conducted with precision instruments to measure outer diameter, inner diameter and wall thickness.

Step 3: Needle Tip Grinding – The Core of All Processes

Needle‑tip geometry determines injection‑related pain and tissue damage severity. Cannulas are secured on high‑precision CNC grinders and ground by high‑speed rotating diamond or cubic boron nitride (CBN) grinding wheels. Modern processes commonly adopt multi‑facet grinding (three‑facet or five‑facet) to form sharp, symmetrical bevel angles (typically 12–18°). Grinding parameters including wheel rotation speed, feed rate and coolant flow must be precisely controlled. Studies show that optimising these parameters maintains the tip chamfer angle within the optimal range, lowering penetration force by more than 0.18 N and significantly reducing the risk of tip fracture.

Step 4: Surface Treatment and Cleaning

Ground needle tips and cannula surfaces may bear micro‑burrs or rough spots. Electropolishing smooths metal surfaces at the microscopic level, reducing surface roughness below 0.2 μm and cutting penetration friction resistance by up to 60% compared with conventional mechanical polishing. Cannulas then undergo multiple strict cleaning procedures to remove residual metal particles, oil stains and contaminants from manufacturing. Cleaned cannulas are transferred to cleanrooms for siliconisation: an ultra‑thin layer of medical‑grade silicone oil is evenly coated on the outer cannula surface to further lubricate the needle for smoother penetration.

Step 5: Assembly, Sterilisation and Final Quality Inspection

Processed stainless‑steel cannulas are precisely assembled with plastic hubs (usually polypropylene or ABS) via adhesive bonding or hot‑melt technology. After 100% preliminary inspection, assembled injection needles are sealed in special breathable packaging and sterilised using ethylene oxide (EO) or gamma radiation to ensure sterility. Prior to release, a series of destructive and non‑destructive tests are conducted, including but not limited to:

Penetration force test: Professional instruments (e.g., NPT‑01) simulate skin penetration to ensure penetration force complies with standards (e.g., below 0.7 N).

Toughness test: Bending tests evaluate the cannula's fracture resistance.

Flow‑rate test: Verifies smooth passage of medicinal solution through the cannula.

Biocompatibility test: Confirms materials are safe and non‑toxic to the human body.

Only injection needles passing all these stringent assessments are approved for market distribution, serving healthcare institutions and patients worldwide. Behind this tiny needle lies a vast industrial chain integrating material science, precision machinery, automation and digital quality management.