Metal stamping vs laser cutting: volume, cost and edge quality

Two routes to a flat part

Laser cutting is a thermal process. A focused beam melts and vaporises the material along a path, and the assist gas blows the molten metal out of the kerf. The part is cut from a nested sheet, one contour at a time. There is no forming die, and the cut path is set by a program.

Stamping is a mechanical process. A die cuts the outline and the holes in one or more strokes, and the part is formed if the design needs it. The tool is a fixed cost, and the piece price falls as the volume rises. The two processes are often compared on a flat part, but they are not interchangeable for every geometry.

Where the cost sits in each route

In laser cutting, most of the cost is machine time and material. The laser runs at a speed set by the thickness, the material and the contour length. A part with a long perimeter and many holes takes longer than a simple outline. Nesting decides how much of the sheet is used, and the scrap value is recovered only at scrap rates.

In stamping, most of the cost is the die and the material. The press time per part is short, and the labour is mostly setup and inspection. The die is a fixed cost that has to be amortised, and the strip layout decides the material utilisation. A part that nests well on a laser sheet may not nest well on a strip, and the reverse is also true.

The laser hourly rate is not a single number. It depends on the machine, the power, the assist gas and the thickness. A fibre laser cutting thin steel runs fast; the same machine cutting thick stainless runs slowly and uses more gas. Ask for the cut speed and the gas cost in the quote, not just an hourly rate. That is what makes the comparison with a die traceable.

Finding the crossover

The crossover is the volume at which the total cost of the two routes is equal. Below it, laser cutting is usually cheaper. Above it, stamping is usually cheaper. The exact number depends on the die cost, the laser hourly rate, the part area, the material and the scrap value.

A simple model is enough to find the range. Take the die cost and divide it by the saving per part. If a die costs a certain amount and stamping saves a small amount per part, the payback volume is the die cost divided by the saving. Add the trial parts and the maintenance reserve to the die cost, and use the good parts, not the parts ordered. The result is illustrative, but it shows whether the crossover is at 2,000 pieces or 200,000.

Edge quality and what it means for the part

A laser cut edge has a narrow kerf, a slight taper and a heat affected zone. On mild steel the edge is usually clean enough to use, but on thick material there can be dross at the bottom and a rougher surface. The heat affected zone is hard and can crack if the part is bent sharply along the cut edge. On stainless, the cut edge may need pickling or passivation to restore corrosion resistance.

A stamped edge has a rollover, a shear zone, a fracture zone and a burr. The burr side is set by the die, and the edge is work-hardened. That is usually fine for a part that is not highly stressed, but a fatigue-critical part may need a deburr or a shave. The burr direction has to be called out if it sits against a mating face or a seal.

The assist gas changes the edge as well. Oxygen cutting leaves an oxidised edge on mild steel that is harder and less suitable for a painted or plated finish without cleaning. Nitrogen cutting gives a cleaner, brighter edge on stainless and aluminium but costs more gas. If the part is to be plated, say so, because the edge condition and the cleaning route both change.

Tolerance, flatness and repeatability

Laser cutting can hold a position tolerance that is tight for a flat part, because the machine positions the head and the sheet. The limiting factors are the sheet flatness, the material stress and the heat input. Thin sheet can bow, and a large part can move as the material is cut. The first part and the last part from a sheet may not measure the same.

Stamping holds a tolerance through the die, so the repeatability is high once the tool is set. The limiting factors are the die wear, the material thickness variation and the strip location. A progressive die can hold a tight tolerance on a feature near the datum and a looser one far from it. For both processes, the drawing should use a functional datum and a realistic general tolerance.

Repeatability is the number to ask for, not just the tolerance band. A laser can hit a tight band on a good sheet and lose it when the material is stressed. A die can hold a band across a long run, but it drifts as the punches wear. Ask how the supplier will monitor the drift and when the tool will be serviced.

Material utilisation and scrap

Laser cutting nests parts on a sheet, so the material utilisation depends on the part shape and the nest. A circular part can nest tightly. An irregular part may leave a lot of scrap. The scrap is sold at scrap value, which recovers some of the cost but not all of it.

Stamping uses a strip, and the carrier and the bridge take material that the part does not use. A well-designed strip can be efficient, but a part that is wide relative to its length may waste more than a laser nest. The material cost per part should be calculated from the actual strip layout or nest, not from the part area alone.

What to check in a trial

For a laser route, check the first part and the last part from the same nest. The sheet can move as the cut releases stress, so a part cut early may not match one cut late. Measure the kerf, the taper and the dross on the bottom edge. Check the heat affected zone if the part will be bent or plated.

For a stamping route, check the first, middle and last part from a coil and the first part after a tool regrind. Measure the burr height, the bend angle and the critical hole positions. Check the strip for marks and the scrap for slugs that have not cleared. The trial should use the production material and the production speed, not a bench sample.

The hybrid route

Many programmes use both processes. Laser cutting makes the prototype and the first build, so the design can be tested without a die. Once the design is stable, a die is built for production. The same drawing can be used for both if the part is designed for stamping from the start.

That last point is the trap. A part designed only for laser cutting may have a narrow web, a sharp corner or a hole too close to an edge for a die. If the production route is stamping, design for the die and use the laser for the samples. If the production route is laser, do not add a die-friendly feature that the function does not need.

• Laser for prototypes, first build and bridge volume
• Stamping for stable designs at production volume
• Keep one drawing and one datum scheme across both routes
• Check the edge and burr requirement before choosing
• Price both routes at the first-year and programme volumes