Discussion on Dimension Error of Steel Plate Flame Cutting Parts

1. Main causes of dimensional error of parts caused by flame cutting

The main causes of errors in NC cutting and blanking are the thermal deformation of steel plate, operator technology, flatness of the support platform, equipment accuracy, corrosion degree of the steel plate surface, etc.

2. Dimensional error analysis of parts produced by flame cutting and targeted measures

The hot deformation of steel plate always exists in flame cutting.

Reducing the dimensional error of hot deformation parts can be greatly improved.

Operator technology affects cutting speed and part quality.

The flatness of the support platform and the accuracy of the equipment have the greatest impact on the size of the parts, which often directly leads to the scrapping of the parts.

The corrosion of the steel plate surface affects the cutting quality and cutting speed.

2.1 Dimensional error of parts caused by thermal deformation of steel plate

The thermal deformation of steel plate is mainly obvious on slender parts.

Through years of cutting practice and summary, it is analyzed that the dimensional error of parts caused by thermal deformation can be reduced from the following three aspects:

2.1.1 Drawing part graphics

When drawing part graphics, add a thermal expansion compensation amount in the length direction of the part (select different compensation amounts according to different parts).

Advantages: it directly compensates for the dimensional error of parts caused by thermal expansion;

Disadvantages: it is only applicable to square parts, and other shapes are not easy to compensate for.

2.1.2 Detailed discharge process

Starting from the discharge aspect, refine the discharge process, and formulate a special discharge process for volatile parts.

2.1.2 Use of common edge

Using the common edge can reduce the cutting time, the heat intake of the steel plate will be reduced, the expansion of the steel plate will be relatively reduced, and the dimensional error of the parts will be reduced accordingly.

As shown in Fig. 1, when the common edge is not made, AB and CD on two adjacent sides of two parts need to be cut once respectively.

After using the common edge, only AB edge needs to be cut, while CD edge does not need to be cut.

While reducing the error of parts, it also improves the cutting efficiency and plate utilization.

Discussion on Dimension Error of Steel Plate Flame Cutting Parts 1

2.1.2 Reasonable cutting direction

Determine the reasonable cutting direction of the part according to the actual situation, first cut the hole, then cut the shape, and first cut the edge close to the edge of the steel plate.

Try to ensure that there must be sufficient connection stiffness between the part and the steel plate before the part is cut close to the completion point, so as to ensure the cutting size and accuracy of the part.

For example, in Fig. 2, cut the inner hole (1-6) first, and then cut the outer contour in the order of A, B, C, D and A.

Reasonable cutting direction

2.1.3 Reasonable part layout and cutting path

The part error caused by steel plate deformation can be reduced by a reasonable part layout and adjusting the part cutting path.

As shown in Fig. 3, match the easily deformed T-shaped parts with small parts that are not easy to deform, so as to reduce local excessive heating, reduce thermal deformation and ensure the size of parts.

When the slender parts are centrally discharged, the dislocation cutting is adopted to reduce the deformation of the parts.

As shown in Fig. 4, after cutting part 2, cut part 3 in the second column.

When part 2 is cooled for a certain time, turn around and cut part 4.

As far as possible, avoid excessive local heating of the steel plate, reduce thermal deformation and ensure the size of the part.

Discussion on Dimension Error of Steel Plate Flame Cutting Parts 2
Discussion on Dimension Error of Steel Plate Flame Cutting Parts 3

2.1.2 Setting interval

Set intervals to reduce the part error caused by steel plate deformation (as shown in Fig. 5).

A. B, C and D will not be cut temporarily but will be cut during platform cleaning.

Advantages: directly and effectively reduce part deformation;

Disadvantages: the setting of the interval increases the number of cutting perforations, increases the cutting time, and increases the consumption of the cutting nozzle.

The platform cleaning personnel will leave scars when cutting the interval (as shown in Fig. 6).

Repair welding and grinding are required in the later stage.

Setting interval
control the deformation of steel plate

According to different situations, choosing and using appropriate methods or a combination of several methods to control the deformation of steel plate can play an obvious role.

2.2. Dimensional error of parts caused by NC operator technology

Theoretically, in the same equipment, the parts cut by the same NC program should be the same.

But this is not the case in reality.

The parts cut by different operators are not exactly the same, there are differences in the size of errors, and even the scrapped parts are cut with the correct procedure.

According to the thickness of the steel plate, select the corresponding cutting nozzle, adjust the appropriate flame and set the corresponding slit compensation, so as to cut qualified parts.

The following table is the table of gas cutting process parameters for reference.

Cutting process parameters

Cutting nozzle number

Cut oxygen hole diameter /mm

Cutting thickness

/mm

Cutting speed mm / min

Preheating time /s

Oxygen pressure Mpa

Gas pressure Mpa

Slit compensation value /mm

1

1.0

5-10

700-500

5-12

0.6-0.7

>0.03

2

2

1.2

10-20

600-380

15-25

0.6-0.7

>0.03

2.5

3

1.4

20-40

500-350

25-30

0.6~0.7

>0.03

3

4

1.6

40~60

420-300

35-50

0.6-0.7

>0.03

3.5

5

1.8

60-100

320-200

50-80

0.6-0.7

>0.03

3.5

6

2.0

100-150

260~140

80-120

0.7-0.8

>0.04

3.5

Note: the purity of oxygen is above 99.5%.

2.3. Dimensional error of parts caused by supporting platform

The main reason for the dimensional error of parts caused by the support platform is that the plane of the support platform is not parallel to the guide rail surface of the NC cutting machine.  

Because the working platform of the supporting steel plate is often impacted and bumped on the loading and unloading platform, the plane of the working platform of the supporting steel plate is easy to form and is not parallel to the guide rail surface of the NC cutting machine.

When the unevenness is serious, it will also cause the cutting torch of the cutting machine not perpendicular to the steel plate, resulting in the inclination of the thickness direction of the whole part.

Due to the perennial flame cutting, the insert plate of the support platform will appear cutting damage and slag adhesion, resulting in the local unevenness of the support platform.

During the part cutting process, the part is partially suspended, resulting in the partial inclination of the part thickness direction.

When the steel plate thickness is relatively large, the part size will have a large error.

2.4. Dimensional error of parts caused by equipment accuracy

The accuracy of equipment guide rail directly affects the accuracy of cutting parts.

Regularly maintain the equipment and regularly check the parallelism and flatness of the guide rail to minimize the error caused by guide rail accuracy.

Protection of equipment parameters.

Once the vertical and horizontal parameters of equipment are changed, the direct consequence is the scrapping of a large number of parts.

The operator shall do a good job in the self-inspection of parts, especially the self-inspection of large parts, and timely reflect the problems found, so as to effectively find such problems.

3. Conclusion

According to the causes of different parts’ errors, various methods can be used together to effectively reduce the errors and improve the product quality.

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