The evolution of the plasma cutting process

Plasma cutting has long proven to be a flexible and cost-effective method of processing parts. The plasma process can cut aluminium, mild steel, stainless steel and the toughest wear-resistant materials from as little as 1mm thick, right through to 60mm. According to Craig Walsh, sales director at Kerf Developments however, choosing the right supplier is the key to success. 

Whilst there is an abundance of plasma equipment manufacturers staking claims as ‘market leading’, there are many issues that prevent validity to such claims. Whilst the plasma unit is central to the cutting process, it's the sum of the complementary parts that control, hold and move the plasma cutting torch that will ultimately define cut quality.

Early CNC profiling machines were fitted with single or multiple oxy-fuel cutting heads. These were built using large heavy castings and/or structural beams and driven around at relatively slow speeds using gearboxes with large motors – and such machine designs are still available today.

Modern high-speed precision plasma cutting machines need to be able to accelerate, decelerate and change direction in a smooth controlled and vibration-free manner. This requires a more refined machine design that includes a collective of features.

As the saying goes, a chain is only as strong as its weakest link, and that is very much the case with a plasma cutting machine installation. Now, all you need do is find a manufacturer to deliver a solution that incorporates all of the above.

Selected on merit 

Kerf Developments has developed a wide range of profile cutting machines that include solutions for oxy-fuel, plasma and waterjet cutting applications. The key to success has been the belief that equipment should be selected on merit. Kerf believes that all of its machines utilise best in class elements that offer excellent performance and reliability.

Being independent brings significant benefits as the team can evaluate new products and establish if they are suitable, reliable and cost-effective for the industry. Kerf offers new products when its engineers are completely satisfied that they meet in-house standards. When applying these standards to the specification for the ‘ultimate’ plasma machine, Kerf has highlighted the reasons for recommending a specific solution.

Better by design

The key components that form the ‘ultimate’ machine design would include:

• A rigid bridge assembly that is strong but not overweight

The bridges on Kerf plasma machines are strong portal frames manufactured from steel that are fully welded, stress relieved and machined. The bridge provides an excellent solid base for mounting the drive systems. The design of the RUR and RUM machines are such that other aspects can be replaced or upgraded if required to support new technology as and when it is available – a good example of this being the development of the UltraSharp precision plasma cutting technology.

• A reliable and predictable CNC control and motion system that can position the cutting torch exactly where it needs to be in a smooth and controlled manner

Kerf has supplied a range of Burny controller and drive systems. It was clear that the Burny units were very reliable even in the most hostile of environments.

The modern Burny systems provide reliable control and drive systems that feature ease of use and reliability. There are lower-cost options out there in the market; however, for the new Kerf oxy-fuel, plasma and waterjet machines – Burny control systems lead the way in our opinion.

The spring-loaded EasyGlide drive system used in conjunction with the Burny system eliminates backlash and reduces power consumption throughout the motion control system.

• Precision electronic torch height control that can maintain the exact pierce and cut height for the plasma process

The Kerf choice of electronic torch height control is the Inova. The unit is extremely stable and provides precision height control. The unit lowers the torch assembly down to the workpiece and sets the initial pierce height. Having pierced the material, the Inova unit then maintains the correct cut height above the plate and is constantly being adjusted as the head moves over the plate.

• Safety breakaway device for the torch. This needs to be rigid but also able to protect the torch over the life of the machine

Kerf offers both a magnetic or pneumatic torch protection system. Given the environment in which plasma machines operate, a maintenance-free sealed pneumatic type is advised. The unit is linked to the e-stop system and once activated stops the machine immediately should the torch come into contact with anything on the machine cutting bed.

• Independent downdraft cutting tables that are not connected in any way to the motion system

The heavy-duty Kerf tables have been designed to efficiently collect dross in bins and at the same time extract the fumes generated by the cutting process.

The bins are approximately 500mm wide and controlled by pneumatic rams that open and shut baffle plates. By extracting fumes from the area immediately under the cutting torch and surrounding area, the tables are highly efficient.

• Advanced CAM software that can take base CAD geometry and apply appropriate technology to the part to ensure consistent high-quality profiles are cut

The strategy of some machine suppliers is to offer their dedicated software system. Longer-term this ties the user to one particular style of machine.

Kerf works with leading independent global suppliers whose systems are not tied to any particular process or machine type. This allows customers the freedom to invest in new equipment at a later date without having to compromise on selecting a specific machine manufacturer or scrap their previous investment in CAD and CAM databases.

The value of a production database should not be underestimated. It is worth significantly more than the initial cost of the software.

Kerf has worked with several independent CAD/CAM suppliers over the years. There are systems on the market that offer differing levels of user control and automation. For installations where customers already have a CAM installation, Kerf works with customers and their suppliers to create a machine efficient post-processor.

For new installations or where UltraSharp cut quality is required, the most popular option is the Lantek Expert system. In addition to industry-leading nesting algorithms, the software offers fully automatic nesting, remnant and material management, automatic toolpath selection, intelligent lead-in and lead-out strategies and strong data import facilities.

Plasma units

Kerf has installed over 500 machines with a range of different plasma units. Early high definition systems included products from Hypertherm, Inner Logic and Kaliburn. More recently, the leading system for high-performance plasma cutting machines to Kerf Developments has been Lincoln Electric. These are our system of choice.

As the world’s largest supplier of welding and cutting systems, Lincoln Electric has delivered excellent products and support to Kerf and its customers. The team at Kerf does not doubt that the Lincoln Electric Spirit II systems fitted to its machines offer unrivalled price to performance ratios and have proven reliable operation.

Summary

When investing in this type of CNC technology you are doing so to decrease your costs and increase your profits. A high-performance plasma cutting machine can reward you with returns of over £100/hour if you can produce high-quality parts.

To counter that, a machine that lays idle waiting for spare parts, an engineer to arrive or simply for a call back from the supplier to resolve an issue will be costing you a similar figure plus the additional costs that downstream disruption causes. Furthermore, the knock-on effect with customers and the supply chain can be even more costly to your business.

Kerf Developments
www.kerfdevelopments.com