Crimping dies: why the surface decides everything

Three surfaces meet in a crimped joint: the fitting ferrule, the hose braid and the working face of the die. The ferrule and the hose are consumables, while the die works for years and survives tens of thousands of cycles. The quality of every joint leaving the machine depends on its condition. That is why the choice and condition of the dies deserve as much attention as the machine itself.

What happens to the ferrule during crimping

Crimping is a controlled plastic flow of metal. The dies compress the ferrule and its material spreads: it stretches along the axis, flows into the relief of the braid and redistributes around the circumference. All this time the ferrule slides over the working face of the die under enormous contact pressure.

While the face is smooth, the metal flows freely, and after crimping the ferrule remains even with its protective coating intact. A rough or worn face acts as an abrasive: it scratches and damages the zinc layer of the ferrule. Such damage is more than cosmetic: corrosion of the finished fitting starts from the scores, and uneven friction adds scatter to the crimp diameter.

How a Link Technology die is built: three layers of protection

Our dies go through a complete process in which each operation solves its own task:

1. Through hardening. The core of the part gains strength and toughness — the die withstands impact cyclic loads without chipping or cracking.
2. Plasma nitriding of the surface. In a glow-discharge plasma, nitrogen diffuses into the surface layer of the steel, forming nitrides with a hardness above 1000 HV — twice that of ordinary hardened steel. The process runs at a relatively low temperature, so the part does not warp: the exact geometry of the working face is preserved without finish grinding. The nitrided layer hardly wears and keeps its original smoothness for years.
3. Zinc-nickel plating with chromium passivation. The finishing barrier: more than 900 hours in neutral salt spray before red rust (tested to ISO 9227) — against 100–300 hours for conventional zinc plating with passivation. Plus a low coefficient of friction: the ferrule slides over the die even more easily.

In practice the combination works simply: the die stays smooth longer, ferrules come out without scores and with their coating intact, and the crimp diameter stays stable from the first cycle to the ten-thousandth. For serial production this is a tangible saving — less scrap and fewer set replacements.

Any shape of working surface

The working face of the die acts as a mould: the part takes the shape cut into the face. The standard profile is a smooth cylinder for hydraulic hoses, but we manufacture dies with any geometry to customer drawings.

Wave profile: air-conditioning hoses

Automotive A/C and refrigeration lines are crimped with dies that have annular ridges perpendicular to the hose axis. The ridges press the ferrule into the grooves of the barbed nipple, creating a labyrinth seal that holds the volatile refrigerant under pressure and vibration. Smoothness matters twice as much here: the aluminium ferrules of A/C fittings are softer than steel and score first.

Stepped profile: tube reducing

A press with dies can reduce the diameter of a tube end — evenly, all around, without folds. This is how telescopic joints are made: the reduced end of one tube fits tightly into the next. It is a mass technology in tubular structures — roof snow guards for country houses, playground frames, railings, flagpoles: the joint is assembled without welding and looks like a single tube.

A separate case is an oval tube after cutting or bending: a stepped or smooth die both calibrates the section and forms the seating diameter in one stroke.

What else special dies do

• Wire rope slings and cables — crimping aluminium and copper ferrules with extended smooth dies: the joint holds in tension as well as the rope itself.
• Large cable lugs — uniform radial crimping without pinching the strands.
• Bead stop on a tube — a grooved die raises an annular bead that acts as a stop for a hose or spring.
• Silent blocks and rubber-metal bushings — calibrated press-fitting with diameter control.
• Marking while crimping — engraving on the working face leaves a batch stamp or logo on the ferrule: marking and crimping in one cycle.
• Delicate surfaces — dies with soft inserts crimp polished and chrome-plated tubes without marks.