What is the best stainless steel laser cutting machine and how much does it cost?

What results can I expect from laser cutting stainless steel?

1.1 Cutting Speed

The cutting speed is dependent on the sheet thickness and the laser power. Cutting speed will increase as sheet thickness decreases and as laser power increases.

Figure 1 shows the cutting speed ranges for different powered lasers. The cutting speed must be balanced with other cutting parameters such as gas pressure and focal position to optimise the cut quality.  

If the cutting speed is correct, the cut edge will have a regular striation pattern and no dross (Figure 2).

If the cutting speed is too high, there is insufficient laser absorption into the material causing an increase in the melt viscosity and dross formation (Figure 3). The cut surface will have high frequency, fine striation lines.

If the cutting speed is too low, a large amount of dross will form on the underside of the cut (Figure 4) as well as the striation lines dragging towards the bottom of the cut.

1.2 Edge Quality

When cutting with nitrogen as the assist gas, there are two different regions of the cut surface. There is a distinct transition in edge quality called the Boundary Layer Separation point.

This is the point at which the melt velocity decreases and melt thickness increases and after which an irregular striation pattern appears on the cut edge. Improved edge quality can be achieved by optimising the following: assist gas pressure, nozzle diameter, focal point position, and cutting speed. 

The following parameters can improve the edge quality: 

• Focal point within material – this causes an increased spot size on the surface of the material and hence a wider kerf is produced so melt removal is easier and cut quality is improved. When cutting stainless steel, the focal position should be within the metal sheet (negative sign following standard practice). As the plate thickness increases, the focal position will decrease (i.e. further into the sheet) to provide the wider spot size.
• Adjust cutting speed – striation pattern can be optimised and dross reduced with careful adjustment of speed.
• Increase assist gas pressure – melt flow velocity increases so melt film thickness decreases and boundary layer separation occurs closer to the lower cut edge. Increasing the nozzle diameter also reduces surface roughness.  However, the gain in cut quality has to be balanced with the added cost of nitrogen.

1.3 Cutting Range

Fiber laser cutters can produce extremely precise and clean cuts very quickly for thin/medium thickness sheets.

In general, the higher the laser power, the wider the range of sheet thicknesses that can be cut, however, there may be a point at which for a set sheet thickness and laser power, cut quality will start to deteriorate and dross formation may become significant.

It is always important to consider what your priority is: productivity or edge quality. 

Table 1 provides the approximate sheet thickness ranges for different laser powers.

Table 1 Cutting range of different lasers

1.4 Thermal Impact

The heat affected zone increases down the cut edge because of the increase in melt temperature and thickness. The thermal impact of cutting can be reduced by increasing the assist gas pressure which provides additional cooling and ejects melt from the kerf.

1.5 High Burr Latitude

Burrs are produced when molten metal solidifies on the lower surface of the cut at a faster rate than it can be evacuated from the kerf by the auxiliary gas and is more prominent with increasing sheet thicknesses. Burrs can be minimised by: 

• Increasing the kerf width – this can be done by locating the focal position further within the workpiece (decreases the cutting speed). 
• Increasing the power intensity – this can be done by increasing the magnification of the laser beam (this can only be done on zoom cutting heads).
• Increasing assist gas pressure – melt ejection is more efficient. 

1.6 Does the assist gas matter for the results?

The assist gas is directed coaxially onto the workpiece alongside the laser beam and its principal purpose is to expel molten material from the kerf and prevent dross formation.

Typically, when cutting stainless steel nitrogen is used rather than oxygen to avoid the production of an oxidation layer which then needs further processing to remove. 

Cutting with nitrogen results in a narrow kerf width due to the lack of the exothermic oxidation reaction so higher nitrogen pressures are needed to expel the molten metal from the lower kerf.

Air can be used for cutting stainless steel. The oxygen will undergo an exothermic reaction, adding additional heat to the cutting surface which provides a smoother cut edge. However, the oxygen will cause a yellow tinge to the cut edge (Figure 5).

How to choose the best laser cutter for stainless steel?

2.1 CO2 vs. Fiber laser: Which is your best option?

CO₂ lasers have been used for sheet metal cutting since the 1970’s and have developed greatly over the years. However, the rapid development of fiber laser cutting has dramatically changed the process of sheet metal cutting. 

Table 2 Pro’s & Con’s of CO2 vs. Fiber Laser

Fiber lasers are able to achieve significantly smaller focus spot diameters (up to 300µm) compared to a CO₂ laser (450-600µm). The smaller spot diameter means the striations formed during cutting are much closer together, giving the appearance of a rougher cut edge.

Although, the smaller spot diameter allows for more detailed profiles to be cut with higher precision at much higher cutting speeds.

The principal advantage of a fiber laser however is its electrical efficiency. CO₂ lasers have an efficiency of approximately 10%, therefore to power a 6kW laser, a 60kW power supply is needed whereas, a fiber laser cutter is 45% efficient so only a 13kW supply is needed.

Maintenance costs of fiber lasers are also lower than CO₂ lasers due to their monolithic configuration.

Plastic coated stainless steel can be cut with both laser types. However, CO₂ laser beams are absorbed by both the plastic and the metal sheet meaning only one cut process is needed.

Whereas the fiber laser beam is not absorbed by the plastic therefore 2 processes are needed: one to melt the plastic and another to cut.

A single step process can be achieved with a fiber laser however, there will be a small amount of dross on the underside of the cut.

The increase in productivity from the faster cutting speeds, alongside the reduced power consumption of fiber lasers can significantly reduce the cost per part, providing a significant financial advantage. 

2.2 What difference does the cutting table make?

The cutting process can be severely affected by vibrations, whether from the motion system or from other machines in the vicinity, which can cause a rough-cut surface.

These vibrations can be minimised by making the cutting table independent to the motion system. The additional advantage is that the motion surfaces are protected from any thermal loading.

During the cutting process the laser will generate a large amount of heat which will be conducted through the machine. This heat could then cause the rack and pinion used for the machine motion to expand, reducing the movement precision and causing a deterioration in cut quality over time.

2.3 What difference does the laser source have?

The power of the laser is proportional to the cutting speeds (see Figure 1). Particularly when cutting stainless steel, increasing the power by 2kW can almost double the cutting speeds. This is applicable for any other metals (i.e. aluminium) which are cut with nitrogen as the assist gas.

Another factor related to the laser is the type of cutting head. Laser heads can be either zoom or non-zoom. A zoom head will allow you to adjust the focus spot diameter and hence the kerf. This means for the same power laser; thicker sheets can be cut.

2.4 Other factors to consider?

Ease of Use

Industry trained operators require years of training justifying a high salary. An intuitive HMI (Human Machine Interface) in the form of a CNC means that anyone, no matter their level of experience or training, can quickly learn to operate the machine.

This will significantly reduce operation costs as well as ensuring a smooth integration of the cutting system into an existing production line, allowing you to start obtaining the benefits of a fiber laser machine quickly.

Compact & Flexible Design

Often factory floor space is limited so it is important to have a machine that is compact and has handling flexibility as well as tailored software.

Service & Support

It is important to consider the support available to you as a customer should something go wrong. Things such as a deterioration in cut quality, damaged consumables or machine issues need to be solved quickly and efficiently to minimise the downtime of the machine.

Automation

Automation can be incorporated with a laser cutting machine to produce a “full lights out operation” (i.e. where operator simply has to switch the machine on and can then leave it run). This reduces the amount of human interaction needed with the machine, reducing the risk of human error as well as increasing productivity. 

Different materials and sheet thicknesses require a different sized nozzle to control the volume of assist gas. An auto-nozzle changer can be incorporated into a machine for an additional cost however, the full benefit is only realised with a load/unload system.

Plate loading and unloading can be fully automated. Here, the stainless steel sheets can be taken from stores, loaded into the machine, cut and then the profiles can be sorted and the scrap removed ready for the process to be repeated. 

This level of automation comes at a cost with extremely high acquisition prices; however, this must be balanced with the potential financial gain from increased productivity. 

Filtration

A filtration system is needed alongside any laser cutter to extract the harmful fumes and particles which result from the cutting process. The size of the filtration system required will increase firstly with the power of the laser and secondly with the size of the cutting table.

Software & Nesting

Positioning plates on the cutting bed and aligning them manually is time consuming and requires a skilled operator, both of which increase the cost per part.

LiveNest™ is an automatic plate detection system which visually projects the nest onto the detected plate and will move the cutting head to the optimal starting point and allow almost instantaneous cutting. This will significantly reduce the machine idle time and increase productivity.

Often, additional parts from a nest are needed, which typically requires the user to request a new CNC file which is a highly inefficient process. The ability to select historical nests at the touch of a button on the HMI reduces the impact of adding additional parts to a nest on the production flow.

Esprit’s LiveControl™ means the user can simply drop the part onto the sheet and optimally position it, even on offcuts, minimizing material wastage and again simplifying the cutting process.

Recent research into laser cutting in industrial settings estimates that 60% of downtime is caused by the cutting head colliding with tilted parts in the cutting process.

This can not only halt production but can also lead to significant damage to the laser head. Software such as LiveGuard™ means before cutting, the ProCut user is made aware of the collision risk and is given three options: 1) go ahead with cutting, 2) use a safer cutting path determined by the software or 3) add micro-tags to high risk zones to prevent parts tilting. The CNC file can then be output for the operator to cut.

Remote Monitoring & Industry 4.0

Industry 4.0 is focused on increasing interconnectivity and data exchange between manufacturing technologies with the aim of improving productivity and efficiency and reducing costs.

The ability to access real time data about both current and historical cutting processes, along with machine health and utilization can be key to minimise unnecessary downtime and maximise the machine output.

Esprit’s IRIS (Intelligent, Real-time Information System) allows the user to access all this data and displays it in a clear and concise manner. 

Safety Features

The wavelength of fiber lasers means they are invisible to the naked eye. This means that any direct or reflected rays will severely damage the retina, causing blindness and can cause significant damage to skin and the area below, therefore the enclosure should not allow a direct line of sight with the cut piece.

It is important when purchasing a fiber laser machine that both the laser source and the machine are fully CE (European Conformity) certified. 

What is the price of an industrial stainless steel laser cutting machine?

3.1 Acquisition Cost

It is estimated that a reasonably sized industrial fiber laser cutter can cost anywhere between £275,000 – £550,000 and sometimes higher.

The price will vary depending on the laser power (larger cooling system is required), bed size (larger extraction is hence needed) and level of automation.

Acquisition prices of a fiber laser cutter are significantly higher than that of a plasma equivalent.

3.2 Maintenance & Operation cost

Despite the high initial purchase price, the operating costs of a CNC fiber laser cutter are significantly lower than the alternatives due to increased electrical efficiency and the reduced number of consumables.

It is key to balance both the acquisition cost and operating costs with the potential increase in production capacity.

The high efficiency of fiber lasers compared to its alternatives results in reduced energy costs. However, this cost can be reduced even further through energy recovery systems. It is important to remember that when cutting, the machine spends most of its time accelerating/deceleration when changing cutting direction or during the traverse between profiles.

Esprit’s fiber laser cutters have extremely fast accelerations (5g) and very high vector speeds (325 m/min) increasing productivity. LiveRegen™ is a simple method to reduce energy costs.

This captures the kinetic energy lost as heat during the deceleration of the nozzle head, stores it and the energy is then utilised during the next acceleration of the nozzle head.

Maintenance costs for a fiber laser cutter are very low as there are less consumables than for plasma or CO₂ laser cutters. Service contracts can be arranged with the manufacturer and can vary in price.

A further operational cost when cutting stainless steel is the cost of nitrogen which is very expensive. The amount of gas used increases with sheet thickness.

Cutting 1 mm stainless steel can cost approximately £15/hour whereas cutting 15 mm can cost upwards of £150/hour. The exact cost of nitrogen will depend on the cutting parameters (specifically the nozzle size and gas pressure used).

Are there alternatives for cutting stainless steel?

4.1 HD Plasma

High Density (HD) plasma cutting is able to achieve clean cut edges for stainless steel at reasonable cutting speeds (although slower than lasers for material thicknesses less than 10 mm).

Cut edges are very smooth because of the large spot diameter (1 mm), however, because of this, plasma cutting has the lowest precision compared to both laser and waterjet cutting, as well as producing a larger heat affected zones which can cause hardening and deformation of the part. 

As with fiber laser machines, cutting speed and the assist gas can be adjusted to achieve the optimal cut quality and minimise burr production. 

HD plasma cutting machines have significantly lower purchase prices compared to laser cutting machines. For some applications, a plasma cutting machine may provide a cost-effective solution for certain volume and surface quality requirements.  

If you want to know more about the possibilities of cutting stainless steel with HD plasma, you can check out this article.

4.2 Waterjet

Waterjet cutting harnesses high pressure water to produce a cut in the workpiece and hence can be used to cut thicker stainless steel sheets without dross or burr formation when compared to laser cutting.

Additionally, it is a cold cutting process so there is no heat affected zone. It has high cutting precision (more than plasma but less than laser) and reduced surface roughness than laser cutting. These results become more pronounced as material thickness increases.

Waterjet cutting produces a high level of cutting waste requiring significant clean-up when compared to both plasma and laser cutting as well as high operating and maintenance costs. 

Additionally, cutting speeds are significantly slower than both laser and plasma therefore production capacity is reduced. Waterjet cutting also generates a significant level of noise. 

Conclusion

However, when comparing machines and suppliers it is important to consider a wider range of factors which allow you to get the most out of your machine, such as:

If you have any questions about fiber laser cutting stainless steel, please don’t hesitate to contact us.

Our team of expert engineers can help you to identify the right CNC cutting machine for you and they’d be delighted to talk through your specific requirements and how Esprit Automation could help you meet them.

If you want to learn more about the flagship laser cutting machines made by Esprit automation, you can have a look at the video below.