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STAMPING PRESSES

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1. Stamping with a Balance press

2. Introduction

From the 16th century onwards, jewelry and coins, then mechanical parts, were shaped, formed and/or cut using stamping presses. Stamping allows for identical reproducibility of complex shapes and patterns, at lower and decreasing production costs.

3. Stamp, die and punch

Stamping requires the manufacture of cutting tools specific to each part design: the stamp.
The stamp is made up of two elements: the die and the punch.
The die is a hard metal plate (usually steel) in which the outline of the component to be manufactured (negative) is cut and hollowed out. The punch is made from the same Metal as the Die and machined in positive according to the same contour. The material is punched (cut), stamped or bent by the pressure exerted by the punch through the Die.

4. Quality and durability at decreasing costs

The manufacturing of cutting tools (punch and Die) requires solid expertise and long hours of work, often of a craft-based nature. This technology therefore involves heavy tooling costs. These logically decrease as production progresses. All the more so since Stamping tools can have lifespans reaching decades, even centuries, and can reach almost unlimited production volumes.
Compared to other production methods (turning machines, machining centers, electrical discharge machining (EDM) machines), the machines require few adjustments and production start-up is significantly faster. Moreover, even automated machines, sometimes capable of producing several dozen components per minute, do not require digital programming.

5. Versatility

Most metals used in watchmaking can be stamped (gold, platinum, steels, brasses, aluminium, etc.). Stamping is used to produce Movement components (wheel plates, springs, pallets, etc.) and External parts (case, dial, hands) components (cases, dials, bracelets, etc.). The stress exerted on the Material during Stamping generates structural tensions. Stamping involves heat treatments (annealing) to eliminate these tensions.

6. An ancestral technology with future potential

Highly developed until 1980, the production of watchmaking components by Stamping saw, from then on, a marked decline with the emergence of the first machining centers and numerically controlled machines. Paradoxically, it is these same machines that now make it possible to manufacture more complex and cheaper stamping dies, thus revitalizing the Stamping industry.

7. Balance presses

Still present in many watchmaking workshops, the Balance press is a manually operated machine for cutting, stamping or mechanical bending. Depending on their construction and size, Balance presses can be placed on the floor or fixed to a Bench.

Elements and operation of a Balance press

The body of the machine is generally made of Smeltingsteel.
A table that is horizontal and flat occupies the center of its body. It is on this table that the die is positioned and fixed.
The table is surmounted by an arch vertically crossed by a worm screw.
The punch is fixed to the lower end of the worm screw.
It is positioned and guided by vertical slides.
A large lever horizontal is fixed by its center to the top of the worm screw and driven by a square fitting.
Weights are generally arranged at the ends of the two arms of the lever in order to increase its inertia.
The material to be stamped is positioned at the centre of the vertical axis. The craftsman sets the balance formed by the lever and its weights into rotation. Thanks to the action of the worm screw, the punch descends vertically to the desired depth (through the material and the die for cutting). Depending on the pitch of the worm screw, the angle required for the balance to perform a strike, as well as the speed of movement of the punch, can be adapted to the type of operations for which the press is intended.

Pressure forces

The pressure exerted on the material depends here on the inertia of the balance and the force exerted by the operator (craftsman).
Most balance presses used nowadays have powers ranging from a few hundred kilograms to a few tonnes.

8. Hydraulic presses

The operating principle of a hydraulic press is similar to that of a balance press.

Elements and operation of a hydraulic press

Instead of the worm screw, it is cylinders that drive the punch.
Hydraulic pistons make it possible to considerably multiply the energy supplied to the machine and to achieve high power levels.

Pressing forces

Hydraulic presses used in watchmaking exert pressures ranging from 1 to 200 tonnes.

Manual presses, automatic presses and progressive stamping

Some presses require manual handling between each stroke (removal of the stamped part, repositioning of the raw material for the next stroke). Other machines are automatic. In this case, an animation (generally hydraulic) allows the stamped component to be ejected and collected, and the strip of raw material or a magazine to be advanced (via perforations, in the manner of a film reel) to carry out the next stroke. This principle allows some presses to be fitted with dies that sequence several successive stamping operations. This is known as progressive stamping.