Flame cutting, plasma cutting or laser cutting? Which technology is best? Let us rephrase the question, because technology suitability regardless our specific needs does nor really make much sense. The right question to ask is: Which cutting technology is most suitable for me?

   Now we can address the issue examining the parametres involved in each specific case. The more we think about it, the more complex the answer to this question gets: Which are these parametres? We could roughly classify them into four categories:

• A. Those associated with the material to be cut
• B. The ones related to the cut characteristics we want to achieve
• C. The cost of implementing the technology in question
• D. The nature and the volume of the work to be done, of the one we expect to knock our door

   Before we go any further, we must make sure we distinguish between two confusing terms:

a) “Cut Surface” and

b) “Cutting Surface”.

   Cut Surface is the actual cut surface, what we get when the cutting tool has severed the material, that is the surface we get as a result of the very cutting process.

   Cuttting Surface is the surface of the sheet of the material to be cut, the surface of the sheet we place in the cutting bed of our machine, what is there before the cutting process starts. We distinguish between the upper and the lower cutting surface.

   Now we can go further: We shall try to distinguish the categories already mentioned into sub-categories and comment on some individual parametres within each sub-category:

• A. Factors associated with the material to be cut
  • Α1. Material properties
  • Α2. Sheet thickness
  • Α3. Condition of the cutting surface

• B. Factors associated with the characteristics of the cutting job
  • Β1. Cut quality
  • Β2. Cutting velocity
  • Β3. Characteristics of the specific profiles we want to cut

• C. The cost of implementing the technology in question
  • C1. Cost for purchase and installation of this technology
  • C2. Operating costs
    • C2a. Maintenance,
    • C2b. Consumables
    • C2c. Power
    • C2d. Labour

• D. Workload expected to enter our business
  • D1. Volume of workload
  • D2. Type of work we usually undertake
  • D3. Potential penetration into other markets

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   Let's go through some facts related to each subcategory:

A. Factors associated with the material to be cut

    Α1. Material type, composition and properties.
    The materials can be divided into metallic and nonmetallic; the metalic ones into ferrous (steel and black iron) and non-ferrous (aluminium, copper, brass, silver, gold, various other alloys, such as bronze). The non-metallic ones can be devided into natural organic (wood, leather, paper, pressed cardboard, textile, fabric), artificial organic (synthetic, acrylic, Plexiglas, PVC, polyurethane, other such materials as rubber, vinyl, foam, nylon) and inorganic (ceramic, glass). The type and composition of the materials directly affect their properties. Thermal conductivity, absorption, combustibility, positive or negative thermal expansion, and more, play a decisive role. Different materials are cut by different technologies.

    Α2. Material Sheet Thickness.
    The thickness of the sheet of material to be cut may be a few tenths of a millimeter to several centimeters. Cutting thicknesses of 150-300 mm is daily routine for a great number of applications. We must have in mind that there is no technology offering quality cuts for materials of a very wide range of thicknesses.

   Α3. Properties and Condition of the cutting surface
    Factors to be taken into consideration are : The reflectivity of the surface, which affects the laser. Spray finishes, paint and plastic coatings also affect the cutting results; so does pickling or not of the surface of hot-rolled sheet. Residues from grains of sand blasting, rolling marks and grooves, stamps and mechanical damage, roughness, are important, sometimes decisive, factors.

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Β. Factors associated with the characteristics of the cutting process

   The second category of parameters which play a role in the choice of technology are related to the cutting process itself. More specifically:

   Β1. Cut quality
   It is often the most important of all factors influencing our choice of technology and is measured by specialised methods, according to specific industry standards (for lasers, DIN 2310 Part 5 and ISO-9013). Cutting must be precise, exactly reproducing all drawing details of the profile to cut. It must be vertical, or deviation from verticality should not exceed a maximum tolerance (cut angle, top edge undercut and cut flatness are relevant parametres). It should be free of dross or spatter, so it does not require post-processing, which costs time and money. It should show little or no change of color or of the chemical composition of the cut surface (oxidation) or any such change should be acceptable. Excessive thermal material stresses are not allowed, which may affect longevity and the ability of further processing the cut part or its being part of an assembly. Kerf width should allow cutting complex shapes. Cut surface smoothness is analysed into all possible contributing factors each of which is separately measured to get a precise final rating of how rough the cut surface is: We measure the general roughness and go into parametres like cut surface finish, dragging and scoring, and cratering. All these factors form a general picture as far as cut quality is concerned, which may or may not be decisive for product suitability, but should, by all means, be taken into account.

    B2. Material Sheet Thickness.
   The higher Cutting velocity is, the better for the business: productivity mainly depends on quick processing of any order coming in, but there are many reasons to make some compromises. Cutting velocity must always conform to the rest of the cutting characteristics; it depends on the cutting technology, the specific machining characteristics as well as the specific material. For example, a  100 A plasma cutting machine cuts faster than a 50 A one material of the same type and thickness. The same machine cuts material of smaller thickness faster than it cuts a thicker sheet of the same material. Specific material characteristics also play an important role. Final cut quality itself depends on cutting velocity, so we should  always proceed with careful steps. Our purpose should always be to achieve the best cut quality considering all the other parametres of the cutting procedure.

   B3. Specific characteristics of the profile we wish to cut
   Cutting parts of very small dimensions or high complexity (e.g. the necklace by etsy in our photo at the top of this page) put a lot of strain to our system. Kerf must be very narrow (to the right please see the kerf width differences with the three cutting technologies while cutting 19 mm / 0.75 in. thick mild steel). Generally, all thermal cutting of metallic materials results in the development of thermal stresses around the cut edges. Depending on the cutting speed, power intensity, and material properties, stress levels reaching and exceeding the yielding limit of the material in the cutting bed can result. This is especially true when the material sheet is very thin; we must pay special attention while configuring the cutting parametres to avoid the material getting destroyed by a too high energy transfer. Special attention should be paid also while piercing, because energy transfer takes place in a very limited space and for a longer time, risking unwanted results. If we also have bevel cuts, our CNC driver should be suitable to do the job.

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C. Cost for the relevant technology
     Here we shall deal with the most important of the factors to consider before we decide which technology is best for us: it is the costs of the technology we wish to go in to.

    C1. Acquisition and establishment costs
    The rule has it that the older the technology is, the cheaper it is to buy. Oxyfuel cutting is relatively cheap, Plasma cutting is somewhat more expensive but generally affordable, Laser is considerably more expensive than Oxy and Plasma. There are cost variations also within each technology: for example, the latest development of High Definition plasma is substancially more expensive than simple plasma and, as automation gains ground, the cost gets higher, as is the case with the new automatic cutting-gas mixture control 'Plasmagas FlowControl' by Kjellberg. All these facts should be examined before the purchase, because they influence the height of our investment and determine the selling cost of our final products, as it must include the amortisation of our capital. We must also take into account the cost for any infrastructure necessary for our machines' operation (plumbing, electrical installations, smoke/dust exhaustion, filtering) not necessarily present at our premises prior to machinery purchase.

    C2. Running Costs
    We do not always pay much attention to running costs, as we think of them as a small percentage on our gross income. We often underestimate fixed costs and end up economising on our machines' running costs, mainly maintenance costs, usually with unpleasant results.

        C2a. Maintenance – Damages
        It makes good sense to expect that unattended machines will not operate for long. More details here. We cannot overstress the fact that failures are less frequent and of minor importance with regular maintenance, consequently our production is rarely interrupted, our machines' longevity gets higher and our product quality is better when it comes from a well serviced machine; working environment protection and natural environment preservation are also better. We should know that maintenance costs depend on the kind of technology: Oxyfuel, as well as plasma cutting machines, are easier and cheaper to service, in contrast with laser cutting machine maintenance, which requires highly skilled personnel.

        C2b. Consumables
        Consumables are different in each technology: combustion gases for oxyfuel cutting, electrodes, nozzles and gases for plasma, lenses and mirrors for lasers. The “tricky point” has to do with using not genuine consumables: Buying them is usually cheaper, but if you think they are also cost-effective, well, you may be wrong! Both longevity of the genuine consumables and cut quality are higher, so we end up "penny wise, pound foolish”.  We should also mention that we risk ourselves out of warranty coverage, since the use of non genuine consumables is, for many manufacturers, good reason to terminate the guarantee; we also risk spoiling our good relations with the manufacturer / supplier of our system, because they are obliged to face more frequent, and  more difficult to remedy, damages; we cause their machines to behave less reliably than they actually could, and  this may indirectly prove defamatory for their business.

        C2c. Power
        Cutting technologies are generally energy intensive. Plasma is more energy consuming than Oxy, likewise Laser compared to Plasma.

        C2d. Labour
        The truth is that, with automation technology evolving, the need for trained personnel to operate it diminishes. We could, generally speaking, say that Oxyfuel cutting should be entrusted to very experienced personnel; Plasma cutting is less demanding. Laser technology is the most demanding. While highly trained operators seem to be redundant, it is also true that experienced eyes will see something going wrong at a much earlier stage, one that gives the operator time to intervene and protect the machine from some serious damage and our personnel from eventual risks. An experienced operator can better describe to servicing technicians what the problem seems to be, and most of the times proceed to all necessary maintenance or repair work without getting any help from outsiders, permitting the continuation of production without any unnecessary delays. The choice is yours.

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   The outcome of the whole venture depends on the work that will knock at our door: We must, last but not least, deal with the last category of the factors involved in this issue.

D. Volume and Type of our workload
How many orders and what type of jobs do we usually get? How does our work vary over time? In some cases buying (and amortisation of) a machine may be based solely on some big contract we have undertaken, in which case all other arguments are out of the question but, most of the times, all factors involved must be taken into account, the kind of the job we usually undertake being one of them.

    D1. Volume of workload
   In case our workload is below some easily calculated level, resorting to expensive technologies is not justified; an occasional order cannot pay for the purchase of this type of machines, outsourcing is more profitable. Purchase of a laser sheet cutting machine is only justified when the total workload and/or special cutting needs are not covered to our satisfaction by plasma technology. If work inflow is constant and we seldom need to accelerate our production we are allowed to use machines of lower power than we would if work was streaming in with high seasonal variation.

    D2. The type of job we usually have
   The technology we will need depends directly on the kind of our cutting needs. Tiny parts or complicated profiles, very narrow tabs or acute angles, very thin sheets, or simply most non metallic materials require laser, thick metal sheets are better cut by plasma, sheets of a wide range of thickness require high definition plasma equipped with state-of-the-art torches (to avoid constant and time-wasting changes of traditional torches), large parts require large cutting beds (otherwise we will have to preform metal sheets into ones of smaller dimensions), cutting of acrylic materials exclusively justifies smaller source wattage but obliges us to equip the cutting bed with some elaborate smoke exhaust system, cutting many different types of material of various thickness may dictate the purchase of the latest technology in automatic gas-flow control like Plasmagas FlowControl by Kjellberg we have already mentioned, etc.

    D3. Potential penetration into other markets
   Establishing a new machine often results into our better chance to get new orders which we may or may not know of beforehand. Sometimes the results come as a pleasant surprise to the business. In the following we shall go into a business sector very little spoken of: Transfer from designing heavy welded metal constructions e.g. using metal tubing (less expensive and quicker design in the developing stage) to implementing bent sheet metal technology, which is more time consuming to engineer and therefore more expensive in the developing stage but with lower manufacturing cost of the final product, nevertheless achieving the same of strength and functionality values. This way of manufacturing requires more careful and innovative design, but it also requires the use of CNC Laser or Plasma cutting machines, which, in its turn, enables a wider use for the machinery we contemplate purchasing!

   In the past, whenever equipment with high strength values was needed, heavy metal welded profiles were used. Such constructions, compared to bent metal sheet ones, require more expensive raw materials, are heavier and more voluminous to manage and transport, and with higher cost of production, since the welding process is a manual operation done by highly skilled professionals with relatively higher wages. It also takes much longer than preformed parts assembled at the final stages, after being painted and shipped. We should also mention that welding causes deterioration of some initial properties of the material, such as strength. The only less expensive stage is the design: it is much easier to design a construction made of bent and welded metal tubing than its substitute of bent metal sheet. Designing the latter takes imagination, ingenuity and precision, which is possible with the state-of-the-art technologies (laser cutting and piercing is possible with precision higher than 0.5 mm).

   We could also look into constructions assembled of many small parts. With CNC cutting and forming, it is easy to redesign the product so that it consists of less parts. The total cost diminishes, on the basis of having less parts to manage and  to assemble, paint or apply coating to. There are also less screws or fasteners and better precision, because less joined parts show less tolerance accumulation. We could also manufacture many different products using some identical parts as the basis of their manufacture, differentiating others specifically required for individual final products, thus achieving even lower manufacturing costs.

   Concluding, if we decide to allocate more funds to the designing stage, we get final products cheaper to manufacture and with better quality values. And, let us say once more, this way we provide the machines we have purchased or plan to with more workload, since we can address ourselves to manufacturing sectors we have had no access so far.

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   We hope this article has been of some help! If you have more queries, our specialised personnel will be only happy to listen to you and answer any questions you might have. There are innumerable possible situations, yours is one of them. Please ring us or send us an e-mail. Twenty five years in research, design and manufacture of cutting machines have taught us much more than can be included in one article, no matter how long it is!