Tolerances and accuracy in laser cutting

Tolerances in laser cutting: How to achieve the highest accuracies

As with any cutting process, minor deviations from the production data occur during laser cutting due to the production process. These are caused, for example, by minute inaccuracies in the movement of the laser system, irregularities in the material and in the beam shaping.

To ensure that the laser parts nevertheless meet their requirements, fit accurately and, above all, are interchangeable in series production or mass production, permissible tolerances to the nominal dimension are determined. By specifying suitable manufacturing tolerances, the desired accuracy of a cutting part can be clearly defined, necessary clearance or overfitting between two parts can be specified, and the economic efficiency of production can also be optimized. Here, the tolerance results from the difference between the maximum dimension and the minimum dimension.

 

The tolerance is therefore the permissible deviation of the blank from the nominal dimension, which the customer specifies to the manufacturer. The actual dimension of the laser-cut part must lie within the upper and lower limit dimensions. If no explicit specifications are determined by the customer, standards exist for general manufacturing tolerances.

 

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General manufacturing tolerances according to ISO 2768

DIN ISO 2768 summarizes generally applicable tolerance dimensions, which are used on many technical drawings for tolerancing dimensions and angles that are not separately toleranced. That is, for dimensions that do not have an explicit specification for the nominal dimension and the permissible tolerance.

 

Tolerance classes

Within DIN ISO 2768, there are so-called tolerance classes that define tolerances of varying closeness. The general tolerances are subdivided as follows:

• f (f) fine
• m (m) medium
• c (g) coarse
• v (sg) very coarse

At TEPROSA, all cutting parts are manufactured according to the standard DIN ISO 2768-1 m (general tolerances) for the geometric dimension, unless otherwise agreed with the customer. Through the four possible tolerance classes fine (f), medium (m), coarse (g) and very coarse (sg), the respective accuracy in manufacturing is defined and simplified by DIN ISO 2768-1.

 

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Limit for length according to DIN ISO 2768 m

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DIN ISO 2768-m: Limiting dimensions for rounding radius and chamfer height

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Straightness and flatness

In terms of straightness or flatness, DIN ISO 2768-2 recognizes the tolerance classes H, K and L.

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Standard tolerance thermal processes according to ISO 9013-1

DIN EN ISO 9013 defines standard tolerances for thermal processes. In addition to laser cutting, the plasma cutting and oxyfuel cutting processes are mentioned. DIN EN ISO 9013-1 is another standard that defines relevant specifications for laser cutting with regard to tolerances.

 

Dimensional tolerances for laser cutting according to ISO 9013-1, tolerance class 1:

As you can see in all dimensions the tables, the tolerance is strongly dependent on the thickness of the material. The thicker a material is, the more challenging it becomes to implement a tight geometric tolerance.

 

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Tolerances of the starting material

Eveness tolerances according to DIN EN 10259 – cold-rolled sheet

DIN EN 10259 defines limits regarding flatness in for cold rolled sheet. The following tolerances are already achieved in the starting material.

 

Eveness tolerances according to DIN EN 10029 – hot rolled sheet

DIN EN 10029 specifies limits with regard to flatness in 1,000 mm and 2,000 mm gauge lengths for hot-rolled sheet. The following tolerances are already achieved in the starting material.

 

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Thickness tolerance for precision and spring steel strip according to DIN EN 9445-1

Tolerances for spring and precision strip according to EN ISO 9445-1:2010-06

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General design guidelines

Although the laser processing method is already very precise, limits exist. The quality of cut edges, of the kerf, angular accuracy, cut quality and geometric accuracy in general depend on various influencing factors. In order to provide you with a perfect cut part, it is advisable that your design takes into account the following key points.

• Minimum component dimensions: 1 x 1 mm
• Maximum component dimensions: 1500 x 1000 mm
• Processable file formats: DXF, DWG, STEP, SLDPRT, CATPART, CATDRAWING, GEO, GERBER
• Send us only one part/cut per file at a time
• Contours should be closed and always have a connection (micro ridge) to the main part.
• Your design file should have no protruding or overlapping lines.
• Place registration marks such as circles or crosses with in your drawing. We can gladly apply these directly during the cutting process with (laser marking)
• The contour should be drawn, on a scale of 1:1, to the desired tolerance center.

 

General notes

We always strive to provide our customers with the best service and the highest quality at your target price. Here are a few more note that might be relevant to you.

• 2D laser cutting: we only produce two-dimensional parts.
• Micro-bars: it may be necessary in individual cases that we add micro-bars to your blanks. In this case, we coordinate the position in advance with you.
• Heat input and residual stress can lead to distortion of the blanks during laser processing. Depending on the cutting process used, this occurs in particular with laser-cut parts with many holes/openings.
• The processing of material thicknesses below 0.05 mm can, due to the cutting gas pressure and the resulting material vibration, lead to non-smooth cutting edges.