The plasma cutting process has been around for many years and is proving to be a very flexible and cost effective method of manufacture. Systems are available that can cut 1mm thick parts right the way through to 60mm thick parts. The process is being used to cut aluminium, mild steel, stainless steel and the toughest wear resistant material.
Manufacturers from around the globe make great claims for their plasma units being the “best available” and “market leading”, however, many of the issues that might allow them to reach such a high accolade are out of their control.
Plasma units form a key part of the cutting process, however, it’s the sum of the complimentary parts that controls, holds and moves the plasma cutting torch that will ultimately define the cut quality.
Historically early CNC profiling machines were fitted with single or multiple oxy-fuel cutting heads.
These machines were built using large heavy castings and/or structural beams and driven around at relatively slow speeds using gearboxes with large motors. Machines are still available to this day that still utilise this type of design.
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. To achieve this requires a more refined machine design that includes the following features.
Key COMPONENTS FOR ULTIMATE MACHINE DESIGN
The key components that would form the “ultimate” machine design would include ……..
- A rigid bridge assembly that is strong but not overweight. The task of the bridge is to move the torch assembly and associated cabling and hoses to the correct position on the cutting table and then follow a predefined NC toolpath.
- 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. The controller should be able to provide feedback to the user and communicate with the plasma unit to set power settings, speeds, feeds and gas pressures where appropriate.
- Precision electronic torch height control that can maintain the exact pierce and cut height for the plasma process. This needs to be vibration free as any movement or vibration in the torch will transmit into similar marks on the cut profile.
- Safety breakaway device for the torch. This needs to be “rigid” but also able to protect the torch over the life of the machine. These are typically either magnetic or maintenance free pneumatic style. Whichever style is selected the torch needs to maintain its rigidity as it operates during the cutting process.
- Independent downdraft cutting tables that are not connected in any way to the motion system. By remaining stand alone, the tables will ensure that vibrations are not introduced into the motion control system whilst cutting.
- Advanced CAM software that can take base CAD geometry and apply appropriate technology to the part to ensure consistent high quality profiles are cut. This should include intelligent selection of cutting speeds for holes, slots and other internal features together with intelligent strategies to pierce and lead-in and lead out of cut profiles. Failure to do so will impact consumable life and subsequent cut quality.
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. A well designed machine that is serviced on a regular basis and fitted with the manufacturers’ original parts and consumables will reward you with years of reliable operation.
All you need do now is find a manufacturer who can deliver a machine and plasma unit to the above specification and who has a reputation for providing you with the quality of service and support that this type of technology requires!
The key to the success of Kerf is Independence
Kerf Developments and its team of experienced engineers have developed a wide range of profile cutting machines. These include solutions for oxy-fuel, plasma and waterjet cutting applications.
The company remains owned and managed by the original founder of the Company. Key to the success has been the belief that equipment should be selected on merit. We believe that all of our machines utilise best in class elements that offer excellent performance and reliability.
Being completely independent brings significant benefits for our design team and indeed our customers. We are able to evaluate new products as and when they are launched and establish if they are suitable, reliable and cost-effective for our customers. We will only offer new products to our customers when our engineers are completely satisfied that they meet our in-house standards.
When applying these standards and beliefs to the specification for the “ultimate” plasma machine we have highlighted what we would recommend and the reason for the choice.
The key components that would form the “ultimate” machine design would include ……..
- A rigid bridge assembly that is strong but not overweight. The task of the bridge is to move the torch assembly and associated cabling and hoses to the correct position on the cutting table and then follow a predefined NC toolpath.
The bridge on Kerf plasma machines are strong portal frames manufactured from steel. They are fully welded, stress relieved and subsequently machined. They provide an excellent solid base onto which we mount the drive systems. The design of the RUR and RUM machines are such that other aspects (such as control system) 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. The controller should be able to provide feedback to the user and communicate with the plasma unit to set power settings, speeds, feeds and gas pressures where appropriate.
Burny controller systems
Over the years Kerf have supplied a range of BURNY controller and drive systems. Our reason for opting for this unit goes back to the formative years of the Company where at the time we only offered service and repair for third party machines. It was clear at the time 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. Furthermore for an OEM they provide Kerf with the highest possible levels of support which is something that we value greatly. There are lower cost options out there in the market; however, for our new oxy-fuel, plasma and waterjet machines Kerf specify a BURNY control system
The spring loaded EasyGlide drive system that we use in conjunction with the Burny systems eliminate 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. This needs to be vibration free as any movement or vibration in the torch will transmit into similar marks on the cut profile.
Our 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.
These are typically either magnetic or maintenance free pneumatic style. Whichever style is selected the torch needs to maintain its rigidity as it operates during the cutting process.
Kerf can provide either a magnetic or pneumatic torch protection system.
Given the environment in which plasma machines operate our preference is for the maintenance free sealed pneumatic type.
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. By remaining stand alone, the tables will ensure that vibrations are not introduced into the motion control system whilst cutting.
The heavy duty tables that Kerf supply have been designed to efficiently collect the 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 the fumes from the area immediately under the cutting torch and immediate 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.
This should include intelligent selection of cutting speeds for holes, slots and other internal features together with intelligent strategies to pierce and lead-in and lead out of cut profiles. Failure to do so will impact consumable life and subsequent cut quality.
The strategy of some machine suppliers is to offer their own dedicated software system. It is often seen as an easy option. Longer term however it does tie you as a user to one particular style of machine.
Kerf’s strategy is to work with leading independent global suppliers whose systems are not tied to any particular process or machine type.
This then allows our customers the freedom to invest in new equipment at a later date without having to compromise on selecting the most suitable machine manufacturer or scrap their previous investment in CAD and CAM databases.
The value of your production database should not be underestimated. It is worth significantly more than the initial cost of the software.
Kerf has worked with several independent CADCAM 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 are happy to work with customers and their suppliers for the creation of a machine efficient post processor.
For new installations or where UltraSharp cut quality is required our most popular system is the Lantek Expert system.
In addition to industry leading nesting algorithms the software offers fully automatic nesting, remnant and material management, automatic tool path selection, intelligent lead-in and lead-out strategies and strong data import facilities.
The software produces UltraSharp quality programs irrespective of the origin of the base geometry.
In addition Lantek offer a range of complimentary software products that streamline the production process together with support for other machine tool types such as punching machines, laser cutting machines, press brakes etc)
Plasma Units
As a supplier investing in numerous plasma systems we need the confidence that our supplier is offering reliable products and have the infrastructure to support us. As the World’s largest supplier of welding and cutting systems Lincoln Electric have delivered excellent products to us and have been there to support Kerf and its customer base. As a key strategic partner we could not ask more from them.
The team at Kerf have no doubt that the Lincoln Electric Spirit II based systems fitted to our machines offer unrivalled price performance and have proven reliable operation. They offer excellent cut quality, consumable life and cost of operation.
Summary
When investing in this type of CNC technology you are doing so with a view to decreasing your costs and increasing your profits. This can be by possibly bringing work back in house or perhaps to offer a cutting service to others. Therefore the machine needs to be fit for purpose, reliable and when things go wrong, as they sometimes do; you need the backing of a team of service and support engineers who know what they are talking about.
A high performance plasma cutting machine can reward you with returns in excess of a hundred pounds an hour if you are able to 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 the downstream disruption causes. Furthermore the knock on effect it has with your customers and possibly their customers is potentially even more costly and damaging to your business.
The true value of a good quality machine, serviced in line with the manufacturers guidelines, backed up by a team of service and support engineers (with the availability of spare parts from stock!) should not be underestimated.
