Punching vs laser cutting

A CNC punching machine & an industrial laser. Both photos are published at Wikipedia & licensed under
the Creative Commons Attribution.

Because they cost less, because they can contour and form a variety of materials, and because they were faster for repetitive shapes, more turret punches than laser cutters were used for metal fabrication ten years ago. But new technology has changed the machine of choice for some processes, and this article explains why.

Although punching machines are still good at producing parts with numerous holes, fiber lasers, with its small spot size, can also rip through thick sheets of steel at incredible speed. Even though the laser cutter cannot be used for applications such as forming, the preference over what technology to use today is shifting towards lasers.

Of course, a combination machine,such as a punch/shear or a punch/laser can do much more without the need to move a part from one machine to another. But the shop may not have the right mix of parts or the volume to put these machines to maximum use.

Before reviewing any fabricating technology, you must realize that the mix of parts and the volume of production in the machine shop will ultimately influence the decision to buy a turret press or a laser cutter or a combination machine. The following are some questions to bear in mind as we review the technologies.

• How much additional capacity is needed?
• Which jobs and what volume will be given to the new machine?
• Will the new machine reduce work-in-process?
• Are you trying to reduce labor costs?
• Do you want to eliminate material handling by combining operations?

Dedicated Turret Punch Press

The turret punch press has been around for a long time. And the combined experience of both equipment manufacturers and tooling suppliers has made the machine adaptable and cost-effective. It can carry out many tasks to eliminate secondary operations, often performing these functions while the part remains on the same work area.

Innovation has improved the turret punch press considerably all these years. It may be capable of punching more than 1,000 strokes per minute. Its maximum feed rate has been boosted up to 150 m/min, its index tool speed raised to as much as 250 rpm. A servo-electric punching machine built today is expected to deliver punches more precisely than the the hydraulic driven system of yesterday, (or the clutch and brake technology built not so long ago.)

Servo-electric power enables the punch tools on the upper and lower turrets to index at different angular orientations. Flanges can be created from the rotation of these indexable tools. Contouring, marking, and even tapping can be performed with the right tools.

Of course, how adaptable the punching presses can be depends on the type of tooling available. We will focus on the 16-station CNC turret punch press, although there are machines with more tooling stations. These machines are capable of working with a variety of materials, such as mild steel, stainless steel, and aluminum. These punch presses typically work with material thickness up to 8 mm.

Secured with programmable and relocatable work clamps, the sheets are positioned to minimize the portion that cannot be punched (dead zone.) When production changes to smaller sheets, the clamp settings are automatically changed without the need for an operator to set it up. Lift tables have become a commonly equipment for loading. These minimize scratches that may result from dragging sheets across tools.

Much of a turret press operators’ work can now be automated. This includes automation for sheet loading, parts unloading and stacking. Less expensive solutions to minimize operator intervention include having a trapdoor in the table, allowing parts to be dropped onto conveyors for removal.

Dedicated laser cutters

The first laser cutting machines were produced in 1965, for drilling holes in diamond dies. With innovation and new applications over time, it is well accepted today. Since it can flat cut almost any shape, it is well suited for jobs with intricate features. Material thickness may not matter anymore today. Fiber lasers processes thin material very quickly. ven for thick plate, Nd:YAG lasers can cut 25cm mild steel at speeds of 900 mm/min. Improved software and control technology has also made these machines easier to use.

Fiber lasers has lately made tremendous strides into the market. These cutters can cut much faster CO2 lasers, cutting up to 254 m/min, piercing 15 holes per second. Nevertheless, if the job is hole-intensive, the turret press is more cost-effective.

Fiber lasers are used to cut thin materials because the size of the focused spot is small, and its intensity consistent. CO2 lasers are use to cut metals thicker than 5mm because the size of the focused spot is larger, creating a wider kerf for optimum ejection of molten metal.

A fiber laser cutter does not need additional optics. Its simplicity makes it easier to use than a CO2 cutter. However, it poses a greater risk to the operators eyes because of its shorter wavelength. It must be run in totally enclosed work areas. The 1-micron wavelength is absorbed by many metals, such as copper, brass, and aluminum. Fiber lasers can be used on reflective materials without fear of back reflections damaging the machine.

Cost of Operation

Since most turret punches uses servo-electric motors today, they do not need changes of oil or filters. These modern CNC presses also does not require as much electricity as hydraulic driven ones. Nevertheless, its parts, such as mechanical drives and shear blades, do wear out and require replacement. A matching punch and die set must also be made and maintained for each manufactured component. This is probably the most expensive operating cost of the machine because these tools cannot be amortized over large volume productions.

CO2 laser cutters needs a supply of gases, a mixture of carbon dioxide and other gases (helium, nitrogen, etc.) Fiber lasers require not only less maintenance but also less electricity for operation.

Conclusion

Although the global production of machine tools has tapered over the last few years, the sales of laser cutting machines is still strong over the same period. If improvements in laser cutters can be sustained, this trend is expected to continue.

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