Cast Iron vs Welded Machine Bed: Which Lasts Longer for Your Fiber Laser?

When purchasing a fibre laser machine, the purchaser might get distracted by some “eye catching” specifications. When purchasing a laser cutter, you compare the power of the laser itself (6 kilowatts or 12 kilowatts), the brand of the laser cutter’s head or the speed of the machine’s motors.
While beneath the aluminium covers a glowing laser beam can be seen, the part of the machine that will last the longest is the bed itself.
The foundation of a laser engraver or laser cutter is the base it sits on. If the laser source becomes useless you can replace it. If your system is out of date then it is possible to update it. But if your machine bed warps, cracks, or loses its precision, the machine is essentially scrap metal. You cannot “fix” a warped foundation.
The age-old debate is machine tool component material: cast iron vs steel welded construction.
They preferred cast-iron engine blocks for many years. Fibres are now the standard material for the majority of high power lasers with welded plate frames. The most durable and long-lasting of the two is the induction brick. The induction brick has a long life of about 10 years, although this can vary greatly, depending on the application. In order to solve this, we must consider the metallurgical, vibrational physics and “thermal memory” aspects.

The Anatomy of the Welded Machine Bed

The fabricated machine bed is of welded construction and comprises steel tubes and steel plates of high grade. The components are welded into the specified size.
The Construction Process
ModernCNC laser cutters are not just simple welded boxes. Producers of high quality products make steel plates interlock in a ‘mortise and tenon’ joint before welding them together. The entire structure should be stress relieved after the welding process. As part of this process the components are subjected to high temperature annealing in a furnace. This involves heating to 600°C and then cooling slowly. The process helps to ‘relax’ the molecular structure.
Why It’s Popular

A welded bed frame is easily adjusted to the desired length. For the construction of a table that is 12 metres in length and 3 metres in width for cutting shipbuilding steel plates, the most cost-effective method to construct it would be through welding.

One of the important properties of steel as a material is its toughness. This is greater than that of the same metal in its pure form. Made without the danger of cracking, it can stand up to heavy metal plate cutting.

Welding processes can complete the production cycle for a welded bed in a faster period of time than a casting process at a foundry for a large iron piece.

The Anatomy of the Cast Iron Machine Bed

Cast iron machine beds are often produced by pouring molten grey iron, typically HT250 or HT200, into a mould. Made out of a single piece of metal it is.
The Construction Process
The machine tool industry prefers cast iron due to its internal microstructure. This material is known as grey cast iron because it contains graphite flakes. The flakes provide a microscopic insulation. The bed is put through a stress relieving process after manufacturing, known as seasoning. This seasoning process can be a simple one where the bed is left outside for several months. Alternatively, the manufacturer may use a vibration machine to age the bed.
Why It’s Prestigious

Precision is achievable only if the machine can maintain a consistent speed and feed while in operation. One of the more sought after technologies in laser cutting is vibration dampening. It is called the “Holy Grail” for laser cutting precision. Cast iron exhibits superior vibration dampening properties in comparison to steel. When operating at high acceleration levels, laser gantries can cause the bed to vibrate in a way that sounds like a ringing bell if the bed is not properly secured. A cast iron bed frame cuts much more smoothly than steel ones. This is because cast iron does not flex or vibrate as much when it is cutting through the material.

Iron has a lower coefficient of thermal expansion than steel. This gives castings a higher thermal stability than those made of steel. It does not move as much in varying shop temperatures, as for instance in the morning when it is 10 degrees C and in the afternoon when it is 30 degrees C.

The Showdown: Cast Iron vs Welded Machine Bed

When evaluating these two systems, it is essential to consider them under the four key factors of business sustainability.

Pillar 1: Vibration Dampening (The “Chatter” Test)

This advanced laser depends on the machine housing it being absolutely still. Vibration of the bed causes the beam to shiver resulting in serrated edges or ‘chatter marks’ on your finished parts.

Cast iron is a material that has a vibration dampening capacity which is between six and ten times greater than that of steel. Because cast iron is a material which is very good at dissipating heat, milling machines which are precision instruments and thus are generally run at high speeds, are usually constructed from this material.

Welded Bed: Steel is elastic. To reduce the vibrations that are often associated with them, many railcar manufacturers create railcar beds which are welded and include thick, heavy internal ribs. The use of hollow structures packed with sand or specialised concrete is another technique employed by railcar manufacturers to replicate the properties of iron, which is able to dampen vibrations.

Pillar 2: Long-Term Deformation (The “Memory” Factor)

The discussion can now become somewhat intense.

A welded bed that has not been heat treated can deform if subjected to high temperatures. As the seasons come and go and the machine continues to vibrate over the course of 2 or 3 years, the welds will attempt to return to their original shape. This results in a machine losing its balance and accuracy.

Cast iron remains stable in condition for very long periods. It does not require any joints to be pulled or stretched.

Pillar 3: Tensile Strength and Impact

A steel bed frame is very strong. It is welded together which gives it an advantage over one made from another type of metal which is held together with screws. Dropping a five-ton steel plate on to a welding bed would not cause it to break. This is due to the way the steel plate is made. It is fabricated from a lot of thin layers of steel which have been welded together in a process called ‘rolling’.

This material is brittle. It is cast iron. The metal is very dense but it is possible to crack it if it suffers a severe blow. Welded beds give some fabricators a secure sense of working with their machines.

Pillar 4: Maintenance and Repair

A bed with a frame welded together is not easily damaged because if you crash the machine or break the frame a welder can fix it.

As bed frames are made of cast iron, these can be prone to cracking. It is very difficult to fix cracks in cast iron as re-welding is impossible, as the weld area will lose its precise quality.

Is a Heavier Athlete Always Better Than a Lighter One?
These days CNC machines can be relatively small and still make excellent cuts. The size and weight of the machine has no direct effect on its cutting ability. If a small machine is properly used and maintained it can produce just as good cuts as a larger one.
The stability of an object is partly provided by its weight, however, the way the weight is distributed is more significant.
When comparing a welded machine bed with one made of cast iron, the cast iron machine bed is frequently observed to be heavier. In iron foundry production, a welded bed would weigh around 3 tons. An equivalent cast iron bed, by comparison, could weigh around 4.5 tons.

Adding weight to the four corners of the kart lowers its centre of mass. This has the effect of stabilising the kart when cornering at high speeds. The car is less likely to slide off in such conditions.

This is a drawback of the option of a slip-resistant resin finish over an industrial epoxy coating for your factory floor: a thicker layer of concrete is necessary. Additionally, transport costs for the product are significantly higher.

Which One Lasts Longer? ( The 10-Year Reality)

The 10 year stability of this pressure sensor is about ±0.03mm.

Cast iron is theoretically the metal likely to win the most medals. Made of stable high density stainless steel this material will withstand many years of use without wearing or decaying.

A welded bed made from steel plate 20mm thick and which has undergone high temperature annealing will easily last for 15 to 20 years in a production environment.

Cheap, thin-walled welded tanks are not the principal hazard; they are tanks which have been assembled by welding at very low cost. Low cost machines use 6 mm or 8 mm steel tubes which have been subjected to vibration ageing rather than the more expensive furnace ageing process. Within 24 months, these beds warp. Any software calibration will not correct a twisted frame.

Application Analysis: Matching the Bed to the Job

When to choose a Welded Bed:

In this case tables larger than 6 metres in length are usually required.

For very powerful machines (over 12 kW), 30 kW lasers in particular, the robustness of a heavily reinforced welded frame is often found necessary because the machine generates so much heat and processes thick plates.

A high-quality weld bed can be purchased for less money than a cast iron bed, enabling the use of a more powerful laser.

When to choose a Cast Iron Bed:

Precision Machining: Where precision and accuracy are of utmost importance – cutting high-end electronics, aerospace parts and medical devices which all require measurement in the micron.

High acceleration cutting involves a CNC machine moving rapidly, with jerky movements, back and forth, as it cuts out lots of tiny holes in a lighting fixture for example.

Machines with cast iron beds appear to retain their value more when they are resold because iron beds have a permanent base.

The Hybrid Solution: Why Many Choose “Heavy Plate Welding”

The trend within the industry is to move towards a middle ground which encompasses heavy plate welded structures.
The plates are cut into shapes of the required dimensions. They are then bent into circular shape to form the drum. The drum is then welded to the steel sheet to form the boiler. These plates feature designs with a hollow centre, allowing them to absorb iron with the strength of steel.
These welded steel tables with high-precision racks provide 98% of the performance of cast iron tables at a price lower than that of the cast iron tables.

What to Ask Your Supplier

Before you sign the contract, ask these three questions about the machine bed:

What is the total weight of the machine frame itself? Be wary of anything that measures 3 metres by 1.5 metres and weighs less than three tonnes.

How did the testing for stress in the bed take place? Insist on furnace annealing).

The main structural plates were 36mm thick. For high power applications (>3kW), look for a large heat sink of at least $12mm-16mm$ in thickness.

Conclusion: Foundation Over Flash

The choice between cast iron and welded steel machine bases is really about whether the benefits of one will outweigh the drawbacks in the final product.
When you need precision and money is no object, a boutique cast iron machine can provide exceptional stability. For the majority of modern metal fabrication shops, a steel bed treated with heat and welded professionally gives superior results. Its industrial grade construction provides the durability needed for heavy industrial applications, along with the versatility to process very large materials and a lifespan which is likely to exceed that of the laser’s electronic components.
We place great importance on our company foundation. Whatever the machine – be it a cast iron ultra precision machine or a heavy plate welded shipyard crane – the steel frame of the machine is subjected to a three day stress relief process. The machines we build will help drive your company’s progress for years to come.
Would you like to see a cross-section of our beds? Speak to Yihai Laser today to have your operation assessed technically and discover which laser foundation is most suitable for your business.

FAQ: Machine Bed Longevity

Q1: Does a cast iron bed make the machine cut faster?
Using a table or base with a vibration-dampening material will help reduce the vibration of the machine. As a result you can set your CNC laser cutter to higher acceleration settings. The higher acceleration of a vehicle enables it to traverse difficult sections of road more quickly.
Q2: Is “Welded Plate” better than “Welded Tube”?
In general thick plate welding has a larger mass and less tendency to ‘ring’ than square tubing with a thin wall. Because of the stress concentrations associated with welding thick material and the high stress levels due to the high power in a 3kW or greater fiber laser, a plate-welded structure is highly recommended.
Q3: Can a welded bed “relax” over time and become more accurate?
A commission is a form of warranty. If a bed relaxes after it has been commissioned, it is warping. This process is indispensable in furnace production. It is advantageous if the metal performs all of its movement before the final machining of the guide rails.
Q4: How do I check if my machine bed is warped?
The most frequent indication of an incorrectly set circular saw blade is uneven cutting. If the laser cuts perfectly on the left hand side but there is a burr on the right, then it is possible that the cutting bed has become uneven. Check that the frame which supports the cutting bed is level.