CNC Turning Application Case: Manufacturing Process of Medical 304 Stainless Steel Hemostat Clip Body-Case Studies

As a core instrument for controlling bleeding in surgical operations, medical hemostat clips must possess extremely high structural precision, corrosion resistance, and mechanical stability. The body, as a key component bearing clamping force and positioning function, its processing technology directly determines the clinical safety of the instrument. This case takes the 304 stainless steel hemostat clip body as the processing object, adopting CNC turning technology to achieve batch precision processing. Centered on the core requirements of dimensional tolerance ±0.01mm and surface roughness Ra≤0.8μm, the product is manufactured through process planning, parameter optimization, and multi-process coordination. The following elaborates on the complete processing flow and technical key points in detail.

I. Product Specifications and Raw Material Preparation

The hemostat clip body processed this time has an arc-shaped symmetrical structure, with an overall length of 28mm, a maximum outer diameter of 5mm, and a minimum inner diameter of 2mm. The main body adopts an arc-shaped groove design to adapt to the clamping mechanism, with connecting holes and positioning steps reserved at both ends, which must withstand a clamping force of ≥50N without deformation. Considering that medical instruments need to contact human tissues and blood, the raw material selected is medical 304 stainless steel bar, which contains 18% chromium and 8% nickel, featuring excellent corrosion resistance, non-magnetism, and biocompatibility, complying with the GB/T 1220-2007 Medical Stainless Steel Standard. The bar diameter is 6mm (with 1mm machining allowance reserved) and the length is 1000mm, facilitating batch feeding and processing.

The raw material pretreatment process needs to remove oxide scale and oil stains on the surface of the bar. First, the outer circle of the bar is rough-ground by a centerless grinder to ensure the outer diameter tolerance is controlled within ±0.02mm, avoiding the influence of bar roundness deviation on subsequent turning precision. Then, it is ultrasonically cleaned with absolute ethanol for 20 minutes to remove surface impurities and grease, preventing increased tool wear caused by oil adhesion during processing, and avoiding the impact of residual pollutants on the finished product surface on biological safety.

II. CNC Turning Process Planning and Equipment Selection

Combined with product structure and precision requirements, a CK6150 CNC lathe is selected. Equipped with the FANUC 0i Mate-TD system, this equipment supports four-axis linkage control, with a spindle speed range of 0-3000r/min and a repeat positioning accuracy of ±0.005mm, which can meet the needs of precision turning. Cemented carbide coated tools are selected: the external turning tool model is CCMT09T304, the internal turning tool is S10K-STUPR09, and the drill bit is a solid cemented carbide twist drill (diameter 2mm). The coating material is TiAlN, which has high temperature resistance and strong wear resistance, suitable for the cutting needs of 304 stainless steel.

The process route is planned as a step-by-step flow of "rough turning - semi-finish turning - finish turning - drilling - chamfering - deburring". Layered cutting is adopted to reduce processing stress and avoid the problems of strong toughness and easy tool adhesion of 304 stainless steel. The rough turning stage removes most of the allowance, leaving 0.2mm for finish turning; the semi-finish turning optimizes the outer circle and end face precision, leaving 0.05mm for finish turning; the finish turning stage ensures the final dimension and surface quality; the subsequent drilling, chamfering, and deburring processes target the processing of detailed structures to ensure the product is suitable for assembly needs.

III. Step-by-Step Turning Process and Parameter Control

(I) Clamping, Positioning and Rough Turning

Clamping adopts a three-jaw self-centering chuck, matched with an end face positioning center, to ensure the bar coaxiality error is ≤0.01mm. Before clamping, a thin rubber sheet is padded at the contact between the chuck and the bar to prevent scratching the raw material surface; meanwhile, the chuck clamping force is adjusted to 3-5MPa to avoid bar deformation caused by excessive clamping force or loosening during processing due to insufficient clamping force.

In the rough turning stage, the spindle speed is set to 1500r/min, the feed rate is 0.2mm/r, and the cutting depth is 1mm. First, the bar end face is turned to ensure the end face flatness is ≤0.01mm, providing a benchmark for subsequent positioning; then the outer circle is turned to 5.2mm in diameter with a turning length of 28mm, and the arc-shaped groove is roughly processed with 0.2mm allowance reserved. During cutting, the cooling system is turned on, and 5% concentration emulsion is continuously sprayed on the cutting area to cool the tool and workpiece, reduce the cutting temperature (controlled below 600℃), and reduce tool wear and workpiece thermal deformation.

(II) Semi-Finish Turning and Finish Turning

In the semi-finish turning stage, the spindle speed is adjusted to 2200r/min, the feed rate is 0.1mm/r, and the cutting depth is 0.15mm. The outer circle is turned to 5.05mm in diameter, the arc-shaped groove contour is corrected, and the tool tip position is adjusted through the tool compensation function of the CNC system to compensate for the dimensional deviation in the rough turning stage. This link needs to focus on controlling the outer circle roundness, which is monitored in real time by the roundness detector equipped with the lathe to ensure the roundness error is ≤0.008mm.

Finish turning is the core process. The spindle speed is increased to 2800r/min, the feed rate is reduced to 0.05mm/r, and the cutting depth is 0.05mm, adopting layered micro-cutting. The outer circle is turned to the final dimension of 5mm, the arc-shaped groove is finished according to the drawing contour, and the surface roughness of the groove is ensured to be Ra≤0.8μm. During finish turning, the emulsion cooling is turned off and replaced with air cooling to avoid surface finish degradation caused by residual cooling fluid. For every 10 workpieces processed, the tool wear is inspected. If the tool tip wear exceeds 0.02mm, the tool is replaced immediately and the tool compensation parameters are reset to ensure processing consistency.

(III) Subsequent Process Processing

For the drilling process, a 2mm solid cemented carbide twist drill is selected, with a spindle speed of 2000r/min and a feed rate of 0.08mm/r. Positioning holes are drilled at both ends of the hemostat clip body, with a hole depth of 3mm and a hole position tolerance of ±0.01mm. Before drilling, a center hole (diameter 1mm, depth 1mm) is drilled at the hole position to prevent hole position deviation caused by drill bit deflection; during drilling, step-by-step retraction is performed for chip removal, retracting once every 1mm drilled to avoid chip winding around the drill bit affecting processing precision.

The chamfering process adopts a 45° cemented carbide chamfering tool, with a spindle speed of 2500r/min and a feed rate of 0.1mm/r. Chamfers (45° angle, 0.3mm size) are processed on the hole mouths and outer circle end faces to avoid sharp edges scratching assemblers and human tissues. Finally, manual deburring combined with ultrasonic cleaning is performed, residual burrs in holes and grooves are cleaned with a special fine brush, and secondary cleaning with absolute ethanol is conducted to remove residual cutting chips and oil stains from processing.

IV. Quality Inspection and Finished Product Acceptance

The finished product inspection adopts the mode of "100% inspection of key dimensions + sampling inspection of surface quality". Key dimensions are inspected by a coordinate measuring machine. 50 pieces are randomly sampled from each batch to inspect 12 key indicators such as outer circle diameter, hole position precision, and arc-shaped groove contour, with a qualification rate of over 99.5% required. Surface quality is inspected by a roughness meter, requiring Ra value ≤0.8μm, and the surface is observed with a 10x magnifying glass to ensure no scratches, tool adhesion marks, or oxidative discoloration.

For mechanical performance sampling inspection, 10 finished products are selected for clamping force test and corrosion resistance test. The clamping force must be ≥50N without plastic deformation, and no rusting occurs after a 48-hour neutral salt spray test, complying with medical instrument usage standards. Qualified finished products are packaged aseptically, with batch number and production date marked separately for quality traceability.

V. Case Summary

In this case, the medical 304 stainless steel hemostat clip body is processed by CNC turning technology. Through scientific process planning, precise parameter control, and strict quality inspection, batch precision production is realized, and the finished product's dimensional tolerance, surface quality, and mechanical performance all meet the requirements of the medical industry. During processing, by selecting suitable tools, optimizing cutting parameters, and adopting a step-by-step cutting strategy, the problems of tool adhesion and thermal deformation of 304 stainless steel are effectively solved. The processing efficiency reaches 80 pieces per hour, which is more than 40% higher than traditional ordinary turning. This case fully reflects the core advantages of CNC turning in the processing of precision medical parts and provides a replicable process plan for the batch processing of similar medical metal parts.