Laser Cutting in 3-D

Complex parts have increased the need for laser cutting systems capable of complex movements

September 1, 2010

Laser trimming of parts, as well as the laser cutting of stamped and hydroformed sheet metal parts, are poularizing because of the speed and repeatability of the systems.

As North America’s automotive sector continues to see an increase in vehicle sales, an increase in five-axis laser cutting will become necessary.

According to industry experts, trimming applications, as well as the laser cutting of stamped and hydroformed sheet metal parts, will popularize because of several factors, including the speed at which a laser can cut and the repeatability of its movement.

However, when compared to 2-D laser cutting, five-axis work is more complicated because of the additional axes being moved and more springback in the material being cut. The additional movement affects the entire cutting process - programming, fixturing, piercing, gas usage, and maintenance.

Mitsubishi Laser currently has two machines for the five-axis laser cutting market. The VZ1 is a nonoffset-head laser cutter, which means that the head is not offset from the center of the Z axis and has the same centerline. In this way more of the work envelope is used because the head can be tilted outside the envelope. Typically a 2-kW laser, this system is suitable for trimming 3-D parts. The other laser, the VZ2, has an offset head. The head on this laser cutter is offset a few inches from the center of the Z axis.

Programming and Fixturing

Today’s offline multiaxis programming software automatically creates code for a sheet metal workholding fixture, the 3-D part to be cut, and also performs a simulation to prove out the process. While most programming should be done offline, some machines have a teaching ability that allows the operator to reteach the program if necessary.

“Fixturing is very important in 3-D cutting,” explained Mitsubishi Laser National Laser Product Manager Jeff Hahn. “If fixturing is attached to the table properly and programmed correctly, then the operator should have a very easy time of loading the part and hitting the start button.”

Conversely, if a program is not correct, it can take some time for the operator to prove out the program.

Piercing

While piercing can be performed at any angle, it is usually recommended that it be done while the head is perpendicular to the material.

“As long as you have a quality machine, there should never be any problems that occur from tilting the axis,” said Hahn.

“There is no degradation in the cut whatsoever during any axis movement in five-axis laser cutting,” explained Mitsubishi 3-D Specialist Hank White. “It doesn’t matter how you tilt the head, the beam length is always the same.”

In certain applications, however, such as beveling, you do need to cut toward the material and not away from it. This acute angle cutting ensures that there is gas flow at the cutting location.

“You need to push into the cut, not pull away from it,” said White.

Gas Usage

As the cut proceeds and the laser cutter head tilts, it also slows down. For example, if 4.5-mm-thick material is being cut at a 45-degree angle, it becomes 6 mm thick. Inevitably the machine cuts slower and therefore uses more gas.

Most 3-D laser cutting applications involve angled cutting as well as flat cutting. This means that material thickness will change within the same part.

“You may have a set material thickness for that type of part, but due to the approach angle that you are hitting it from, and in the movement around corners, the material thickness will change,” said White. “You can adapt the cutting conditions to change with this, though.”

To compensate for changes in the material thickness, it is recommended that a larger gap be used between the head and the material.

Mitsubishi Laser’s VZ1, for example, also has a sixth axis for height compensation of +/- 10 mm.

“By adding this sixth axis we don’t have to lift the entire Z axis to make a change in the height of the head. You can react quicker to the springback of the 3-D shape, which also speeds up the cutting,” said White.

Maintenance

Typically, however, 3-D machines operate fewer hours than 2-D machines because they are not as suitable for production-style work. According to Hahn, five-axis machines are more suited to prototype work and lower-volume part runs, which means maintenance cycles are extended.

For more information, visit www.mitsubishi-world.com.