The accuracy and tolerances of laser cutting (sheet metal) 

The metal parts we laser cut from sheet metal are used for many different applications. As our customer, you can be sure that we will deliver the most accurate dimensions possible and that these will be within our tolerances.

But how accurately can we laser cut sheet metal, actually? Which factors affect the accuracy? And which tolerances can you expect from us?

In this blog post, we discuss the effects of the laser cutting head, the machine and other factors on the accuracy.

Precision of the laser cutting head

The laser cutting head itself has little effect on the accuracy. However, it does determine the width of the laser beam, and thus the width of the kerf that is cut out of the metal. The laser cutting head contains a lens, which narrows the laser beam. This results in a beam with a diameter of ± 0.1 mm. The kerf that is cut out of the metal is wider. There are several reasons for this, not all of which are related to the laser. It is also important to realise that a cut line can never be narrower than the kerf created by the laser.

Accuracy of the machine

The laser beam only determines the width of the kerf. It is the machine that actually determines the accuracy, or in other words, the final shape of the cut part. The machine moves the head across the metal to create the correct shape based on the supplied technical drawing. These movements can affect the accuracy.

What else affects the accuracy?

As well as the machine, several other factors can affect the accuracy:

• Metal type and thickness
• Stress in the sheet
• Outline size of the part
• Shapes of the part

The effects of the metal type and thickness are related to heat and the coefficient of expansion. During laser cutting, some of the heat radiated by the laser may be absorbed by the metal. This can cause it to expand. Once the part has been cut out and cools down, it will shrink again, which can cause it to be slightly smaller than the drawing.

Most sheet metal types have a certain stress in the sheet. Many metals are delivered to metal suppliers as large coils and subsequently decoiled and rolled flat. However, stress remains in the flat sheet, which can cause it to become distorted. This stress can lead to minor distortion during laser cutting of long and/or thin strips in particular, which has a negative effect on the accuracy.

There are two types of outline: outlines that determine the size of the product and small outlines (such as holes) inside a product. These are known as exterior and interior outlines respectively. There is always one exterior outline, but there may be multiple interior outlines. The same rule applies for both outline types: the larger the outline, the greater the risk of deviations. After all, the laser must travel a greater distance and must work for longer, which means there is more opportunity for deviations to arise. 

Finally, the shape of the part has an effect. This is actually a combination of the previous points. Imagine you have designed a part as shown below:

It has a long exterior outline and multiple narrow strips. The long exterior outline means the laser must travel a greater distance. The narrow strips may distort due to stress in the metal. Finally, narrower strips will heat up more readily, which can lead to expansion during cutting and contraction when the metal cools.

Tolerances: what can you expect?

Despite the fact that laser cutting is a relatively accurate metalworking process, deviations may still arise. The tolerances we guarantee are shown below. The maximum deviations that we tolerate are indicated. These take account of the effect of the machine and other factors.

Needless to say, we do our best to minimise deviations.

Do you have any questions about the accuracy of laser cutting?

Please  contact our Customer Service centre. We will be happy to assist you!