BOCHU laser cutting head for a fiber laser cutting machine — autofocus, height sensor, and collision protection

The laser cutting head is one of the most important components of a fiber laser cutter. It is through this component that the laser beam is guided, focused, and directed onto the material being processed—and the stability of the process, edge quality, part repeatability, and the safety of components in the cutting zone all depend on its proper operation.

In STIGAL laser cutters, we use BOCHU laser cutting heads, which—depending on the configuration—are equipped with features that support the automation of laser cutting: automatic focal length adjustment (autofocus), height measurement, and collision protection. These features reduce the need for manual operator intervention, help maintain proper process parameters, and protect the cutting head from the effects of contact with the material. In this article, we explain how they work and how they interact in practice.

What is the function of a laser cutting head?

The laser cutting head is responsible for guiding the beam from the laser source to the cutting site and focusing it properly. Inside, there are optical components that give the beam the correct geometry and position the focal point relative to the material’s surface. During operation, the head works in conjunction with a nozzle that supplies an assist gas, which removes molten material from the cut and protects the optics from spatter.

Proper cutting requires controlling several interrelated parameters:

• location of the fire,
• the distance between the nozzle and the steel plate,
• alignment of the jet relative to the nozzle,
• the condition of the optical components,
• the type and pressure of the auxiliary gas,
• machine motion parameters.

A modern fiber laser cutting machine automates some of these tasks, so the operator does not have to manually adjust the laser cutting head every time the material or cutting method changes.

Autofocus — automatic adjustment of the focus point

Autofocus allows the focusing lens inside the head to be repositioned automatically. This enables the control system to set the beam’s focal point at a specific height relative to the surface or cross-section of the material being cut. The focal position determines how energy is transferred to the steel plate—one setting works best for piercing, another for the actual cutting process, and yet another when the type of steel plate, its thickness, or the assist gas is changed. In a head with autofocus, this value is determined by the cutting technology and is set automatically by the machine system.

What are the benefits of autofocus in everyday production?

• faster transitions between technologies and materials,
• fewer manual tasks for the operator,
• greater consistency in settings,
• separate optimization of the piercing and cutting processes,
• a lower risk of error when changing parameters,
• more efficient processing of orders involving steel plates of various thicknesses.

Autofocus becomes particularly important when a laser cutter is processing short runs, frequently changing orders, or parts made from materials with varying properties. However, this does not mean that autofocus selects the technology on its own—its settings should be based on properly configured parameters, tailored to factors such as the material, steel plate thickness, laser source power, and the gas used.

Height sensor — maintaining the distance between the nozzle and the steel plate

During laser cutting, the nozzle must move at a precisely defined distance from the material’s surface. A gap that is too large or too small affects gas flow, beam geometry, process stability, and edge quality. However, the surface of a steel plate is rarely perfectly flat—the plate may warp, corrugate, or become stressed, and small components may lift due to heat.

The height sensor measures the distance between the nozzle and the material, and the control system uses this signal to continuously adjust the Z-axis position, guiding the head along the actual contour of the steel plate surface. In fiber lasers, the measurement is typically based on changes in electrical capacitance between the nozzle and the conductive material; specific functions depend on the head model and control configuration.

Why is a constant head height so important?

• a steady flow of gas through the nozzle,
• proper conditions in the kerf,
• consistent part quality across the entire sheet,
• repeatable piercing conditions,
• a lower risk of the nozzle coming into contact with the steel plate surface,
• greater process stability when working with materials that are not perfectly flat.

The height sensor is particularly important when cutting thin steel plates at high speeds, when even slight changes in the surface position must be detected and compensated for instantly. However, it does not replace proper material preparation—a severely warped steel plate or floating cut-out pieces can still disrupt the process.

Laser Cutting Head Collision Protection

During cutting, there is a risk that the cutting head may come into contact with a component that has risen above the surface of the sheet. This can happen when:

• the cut-out piece will tilt in the slot in the table,
• a small piece of waste will remain standing upright,
• the steel plate will deform under stress or due to temperature,
• the material will be placed incorrectly,
• The path of travel runs over the protruding part.

Without protection, such a collision could damage the nozzle, its mount, the head mechanisms, the optical system, or components of the Z-axis. Collision protection is designed to limit the effects of such an event — the design may allow the head’s working part to deflect or disengage upon impact, rather than transferring the entire force to precision components, and detection of an incorrect position may stop the machine’s movement. The scope of protection depends on the type of head, mounting, and machine configuration; however, the system does not eliminate the need to monitor the condition of the material and the table—its purpose is to reduce the risk of more serious damage in an emergency situation.

How does collision protection affect machine operation?

• minimizes the effects of accidental contact with the part,
• protects the expensive components of the optical system,
• reduces the risk of prolonged machine downtime,
• makes it easier to return the cylinder head to its proper position,
• improves workplace safety when working with a variety of parts,
• reduces the risk of damage to the Z-axis.

However, after each collision, you should check the condition of the head, nozzle, ceramic components, optical shields, and mounting, and often also recheck the beam alignment and working height.

How do the autofocus, altitude sensor, and collision avoidance system work together?

Each of these functions is responsible for a different area of the print head’s operation:

• Autofocus sets the focal point of the beam inside the head,
• The height sensor controls the Z-axis so that the nozzle moves at a set distance from the steel plate,
• Collision protection limits the effects of physical contact with material or a workpiece.

It is worth noting that the autofocus does not adjust the height of the entire head above the steel plate—it only changes the position of the optical element inside it. A height sensor controls the distance between the nozzle and the material, and the collision protection system kicks in when standard adjustment is insufficient—for example, when a workpiece suddenly rises right in front of the head. Only when all three systems work together can a stable and as safe as possible laser cutting process be achieved.

What affects the proper operation of the BOCHU printhead?

Even an advanced laser cutting head requires proper operation and maintenance. Process stability is influenced by, among other things:

Doesn’t the autofocus head require operator control?

Autofocus reduces the number of manual adjustments, but it does not eliminate the need for head control. The operator should still:

• check the condition of the nozzle and the ceramic element,
• check the cleanliness of the protective glass,
• perform a beam alignment test,
• respond to unusual sounds and alarms,
• monitor the quality of the piercing and the edges,
• Check the cylinder head after every collision,
• Follow the procedures for replacing consumable parts.

Automation improves process consistency, but it yields the best results when combined with proper operation and regular inspections of the machine’s technical condition.

The BOCHU cutting head as part of a complete cutting system

The quality of the cut is not determined by a single component. The BOCHU cutting head works in conjunction with the laser source, the CNC control system, the servo drives, the axis guidance system, the gas supply system, the cooler, and the process software. Therefore, when selecting a laser cutter, the entire system should be evaluated, not just the brand of the laser cutting head. The following factors are also important:

• matching the laser cutting head to the power of the laser source,
• compatibility with the control system,
• Z-axis speed and precision,
• availability of diagnostic services,
• ease of replacing consumable parts,
• the ability to develop processes for various materials,
• technical support from the machine manufacturer.

In STIGAL laser cutters, the laser cutting head, drives, machine design, and control system are selected as components of a single manufacturing solution—and the specific configuration depends on the materials being processed, the required productivity, the thickness range, and the production setup. We cover related topics in more detail in our guides on selecting fiber laser power and on selecting assist gas for laser cutting.

A laser cutting head designed to fit the entire cutting machine

Autofocus, a height sensor, and collision protection improve the performance of a fiber laser cutter, but their effectiveness depends on proper integration with the machine’s overall system. STIGAL designs and manufactures CNC metal-cutting machines, selecting the laser cutting head, laser source, CNC control, and structure to meet the actual needs of the facility—whether for flexible production with frequent material changes or for efficient batch cutting. Our product lineup includes fiber laser cutters and machines configured as laser cutters for steel plates.

Frequently Asked Questions — BOCHU Head