How a Progressive Stamping Die Shop Cut Costs 48% by Switching to Gas Springs

In high-volume progressive stamping operations, tool reliability is the primary driver of profitability. Unscheduled press stops to replace fractured components quickly erase thin manufacturing margins. This case study details how a Tier-1 automotive stamper upgraded a problematic structural bracket die from mechanical coil springs to nitrogen gas springs, reducing total annual tooling operating costs by 48% and eliminating chronic press downtime.

Challenge: High Fatigue and Unscheduled Stops

An automotive bracket stamping manufacturer was running a high-speed progressive die to produce structural HVAC brackets from 2.5 mm thick SAE 1010 hot-rolled steel. The 4-stage tool performed heavy piercing, blanking, and forming operations at a press speed of 80 strokes per minute (SPM).

To strip the thick material from the punches, the stripper plate required 12,000 daN of force. The tool was originally designed with sixteen 50 mm diameter, 102 mm free-length mechanical coil springs (ISO 10243 red series).

Under these operating conditions, the coil springs experienced severe fatigue. Running at 80 SPM generated significant internal friction and heat within the chrome silicon wire coils. Compressing the springs close to their maximum deflection limit accelerated microscopic micro-cracking, resulting in sudden fatigue fractures every 150,000 to 200,000 cycles.

These spring failures caused three major problems:

• Unscheduled Press Stops: Every spring fracture required stopping the press, clearing metal fragments from the tool, and replacing the entire set of springs to ensure balanced load. Each stop resulted in an average of 1.5 hours of downtime, costing $$1,200$ per hour in lost capacity.
• Tooling Damage: When a coil spring broke, the stripper plate tilted under load. This misalignment caused a major punch to jam and fracture, resulting in $$8,500$ in toolroom repairs.
• High Part Scrap: Worn coil springs suffered from force decay, resulting in insufficient holding force at the start of the stroke. This allowed the metal strip to shift, producing out-of-tolerance parts and a $2.4%$ scrap rate.

Solution: Upgrading to Nitrogen Gas Springs

To solve these chronic issues, the tooling engineering team decided to replace the mechanical coil springs with a modern nitrogen gas spring system.

The team selected four MISUMI GSK-1000 Series Gas Springs, each providing 1000 daN of initial contact force. Because nitrogen gas springs have high force density, four cylinders replaced all sixteen coil springs, simplifying the die layout.

The conversion process involved:

1. Pocket Modification: The existing 50 mm coil spring pockets were deepened to accommodate the taller gas cylinders.
2. Groove Mounting: The gas cylinders were secured using MSGP-1000 Lower Groove Brackets, anchoring the springs rigidly to the stripper backing plate to prevent rotation or lateral movement.
3. Manifold Connection: The four cylinders were linked together using high-pressure micro-hoses connected to a control panel mounted on the outside of the die shoe. This linked configuration ensured that nitrogen pressure remained identical in all four cylinders, keeping the stripper plate perfectly balanced.

Results and Cost Savings

The progressive die was put back into production with the new gas spring system. Over the following 12 months, the tool ran 3.5 million cycles. The table below compares the tool's performance and operating costs before and after the gas spring upgrade.

"Switching to the GSK gas springs completely changed how this tool runs. We used to keep two backup sets of coil springs in the toolroom at all times and expected tool stops every week. Now, the die runs for months without a single maintenance stop, and our part dimensions have never been more consistent."

— Stamping Toolroom Superintendent

Engineering Discussion: Physical Principles

The dramatic reduction in operating costs is explained by the physical performance differences between tool steel coils and pressurized nitrogen gas.

First, the rate of force decay in mechanical springs is high under cyclic loading. As a steel coil spring is compressed, it undergoes shear stress. Over hundreds of thousands of cycles, these stresses cause tool steel fatigue, leading to a loss of free length—a phenomenon known as "setting." This loss of length reduces the preload force. In this case, the stripping force dropped by over 25% after 150,000 cycles, allowing the sheet metal strip to shift during cutting and resulting in large burrs on the stamped parts.

The nitrogen gas springs, however, maintain their force profile. Because the force is generated by the pressure of nitrogen gas acting on a piston rod, there is no mechanical fatigue. The force profile remains constant throughout the spring's life:

Unless nitrogen gas escapes, the force does not decay. The manifold connection allowed the maintenance team to monitor pressure from an external control panel, ensuring any minor pressure loss was detected and corrected before it could affect part quality.