An Italian manufacturer of precision micro-fluidic valves for laboratory automation needed a set of custom compression springs that could deliver identical return force across an 8-channel valve block. Any variation in spring force between channels would cause uneven flow rates, affecting test accuracy.
The Specification
Wire Diameter: 0.4mm Stainless Steel 302.
Outer Diameter: 3.2mm, free length 14mm.
Critical Requirement: Force of 4.2N ±3% at 10mm compressed height.
Quantity: Only 400 springs for a prototype instrument build.
Why Tight Force Tolerance Was Difficult
Achieving ±3% force tolerance on a small compression spring requires exceptional control over every manufacturing variable. Wire tensile strength, coiling pitch, stress relief parameters, and end grinding all affect the final force. Loose control in any one area would push the variation beyond the narrow window.
Tingfeng’s Controlled Process
We selected a single certified wire coil to ensure uniform tensile properties. The CNC coiling program was adjusted after a statistical trial run of 20 pieces, centering the force distribution exactly on 4.2N. After coiling, the springs were stress-relieved at 260°C, then both ends were ground flat to ensure square seating. Every one of the 400 springs was tested at 10mm compressed height on a calibrated force gauge. The entire batch showed a standard deviation of only 0.06N, comfortably within the ±3% window.
Result
The Italian client installed the springs and verified identical flow rates across all eight valve channels. The prototype instrument passed its performance qualification, and the client has ordered a follow-on batch of 2,000 springs for the next development phase.