How To Optimize CNC Plasma Cutting Process?

With the continuous development of plasma cutting technology, the use of CNC plasma cutting machine is becoming more and more common.

CNC plasma cutting machine

As one of the main cutting and blanking equipment for medium and small thickness plates, the CNC plasma cutting machine has the advantages of simple operation, high accuracy, high work efficiency and low labor intensity.

It is widely used in many industries, such as the chemical industry, automobile industry, machinery industry, rail transit industry and so on.

For materials that are difficult to cut by traditional cutting methods, a CNC plasma cutting machine can be used;

In terms of cutting speed, when cutting medium and small thickness carbon steel plate, the CNC plasma cutting speed is faster than the traditional flame cutting speed, and the cutting surface remains smooth and hot deformation is good;

In terms of cutting costs, the cost of CNC plasma cutting is far lower than that of laser cutting.

Optimization of the cutting table

The cutting table of the cutting machine is supported by many diaphragms. As shown in Figure 1, the spacing between the two diaphragms is 110mm.

CNC plasma cutting machine with cutting table

Fig. 1 CNC plasma cutting machine with cutting table

When cutting small parts, the workpiece often falls between the diaphragms and cannot be taken out. And the diaphragm is 8mm × 190mm × 4600mm straight flat steel plate, due to frequent cutting, there are too many oxide slags on the lower diaphragm, which affects the normal cutting and needs to be cleaned or replaced frequently.

Optimization scheme and implementation of cutting worktable

Since the product structure and product batch of the industry are not fixed, in order to save materials, nesting is often used (i.e. matching typesetting of large materials and small materials).

How to improve the utilization rate of plasma cutting machine and the service life of cutting bench through the process innovation of plasma bench is the problem we need to solve at present.

To solve this problem, the existing blanking products are analyzed and classified.

Select the smallest cutting part, determine the size of the smallest part, and design a new set of workbench according to the site conditions, as shown in Fig. 2.

Table model after optimization of CNC plasma cutting machine

Fig. 2 Table model after optimization of CNC plasma cutting machine

(1) Specific scheme.

1) The platform is 1500mm × 3000mm size, which can be combined with multiple platforms;

2) The outer frame of the platform is folded into U-shaped parts from 4mm plates and welded into a rectangular frame structure to ensure the stiffness of the frame and prevent deformation during hoisting;

3) There are 2 ~ 3 V-shaped parts folded by 4mm plates inside the frame, which are buckled in the frame longitudinally, and a 3.5mm wide notch is opened on the longitudinal beam to facilitate the insertion of the diaphragm;

4) The diaphragm consists of 1500mm × Made of 200mm plate with one side cut into serrated structure.

(2) Specific implementation process.

1) Design the length, width, height and partition spacing of the cutting workbench according to the equipment parameters and the size of the required cutting parts;

2) Make cutting workbench according to the design drawing;

3) All cutting table parts are cut out at one time by CNC cutting machine, with accurate size and convenient replacement of diaphragm;

4) The cutting table frame adopts CNC bending machine for programming bending, with accurate positioning size and good formability;

5) Assembly, welding and cutting workbench frame;

6) Insert the diaphragm into the cutting table;

7) Place the cutting table on the original cutting table. When cutting, put the material on the movable cutting table for cutting, as shown in Fig. 3.

Physical drawing of worktable after optimization of CNC plasma cutting machine

Fig. 3 Physical drawing of worktable after optimization of CNC plasma cutting machine

Path optimization in the cutting process

Due to the thermal expansion and cold contraction effect of the plate, there will be relative movement between the machined part and the remaining material during the cutting process.

According to the difference between the weight of the machined part and the weight of the remaining material, the relative movement can be divided into the following three situations:

(1) when the weight of the machined part is greater than the weight of the remaining material, the machined part does not move, and the remaining material moves relative to the platform, which does not affect the size of the machined part;

(2) when the weight of the machined part is less than the weight of the remaining material, the machined part moves relative to the platform, the remaining material does not move, and the machined part has a certain deviation;

(3) when the weight of the machined part is equal to the weight of the surplus material, the machined part and the surplus material may move relative to the platform, affecting the size of the machined part.

Practice shows that the dimensional error of machined parts is generally between 0.3 ~ 4mm due to the movement of machined parts or surplus materials relative to the platform.

The cutting path on one side of the workpiece

In the process of CNC plasma cutting, the deformation will be different if a reasonable cutting process is selected.

When cutting the plate shown in Fig. 4, if point A is selected as the arc starting point, the cutting direction and sequence are: A → D → C → B → A (Fig. 4a).

Cutting path and deformation of one side of the workpiece

Fig. 4 Cutting path and deformation of one side of the workpiece

When the AD section is cut and the DC section is processed, due to the narrow residual material in the DC section, the residual material in the DC section is linearly elongated due to the high temperature during cutting, and the CB section deflects outward.

After cutting, the size of the DC section is reduced δ (Fig. 4b),   The size ofδ  is proportional to the size of the DC section.

If the cutting sequence of A → B → C → D → A is selected, the workpiece is finally separated from the motherboard through DA, which can effectively reduce the cutting deformation.

Deformation control of slender parts

For the cutting of slender parts in Figure 5, if A→ B → C → D → A is followed, when cutting DA section, the expansion of BC section can prevent the expansion of CD section.

Cutting of slender parts

Fig. 5 Cutting of slender parts

After overall cutting and cooling, the shrinkage of DA section shall be greater than that of BC section, so as to bend the workpiece to DA side.

The side bending amount δ depends on the length-width ratio Y / X of the machined part. The greater the length width ratio, the greater the side bending amount δ.

If two pairs are used for cutting, as shown in Fig. 6, select point A as the arc starting point, and the cutting direction and sequence: A → B → C → D → E → A → F.

Paired cutting of two slender parts

Fig. 6 Paired cutting of two slender parts

When completing the DE section, separating from the motherboard is equivalent to reducing the length-width ratio of the workpiece by half, so as to reduce the side bending amount.

When cutting the AF section, the expansion and contraction on both sides of the workpiece are equal, and the side bending δ deformation of slender parts can be significantly reduced.

Cutting technology of special-shaped parts

For the cutting of special parts (Fig. 7), the following cutting processes can be selected according to the above processing methods and different special-shaped parts.

Cutting of special parts

Fig. 7 Cutting of special parts

(1) For concave parts, two paired cutting methods are adopted.

First cutting the inner edge, then cutting the outer edge, and finally separating the two parts from the outside to the inside.

The cutting sequence is shown in Fig. 8.

The inner edge: A1 → B1 → C1 → D1 → A1;

Outside: A → B → C → D → A, and finally E → F, H → G.

Paired cutting of two concave parts

Fig. 8 Paired cutting of two concave parts

(2) For offset hollow parts, two pieces shall be cut in pairs, and finally the two pieces shall be separated.

The cutting sequence is shown in Fig. 9.

The inner side: A1 → B1 → C1 → D1 → A1, A2 → B2 → C2 → D2 → A2

The outer side: A → B → C → D → A, and finally E → F.

Paired cutting of two offset hollow parts

Fig. 9 Paired cutting of two offset hollow parts

Conclusion

The beneficial effects of this process innovation are as follows: through the process innovation, the utilization rate of plasma cutting machine is greatly improved, the replacement of worktable diaphragm is convenient, the replacement rate is reduced by half, and the replacement cost is reduced.

The cutting of small parts has been met.

At present, this process innovation has been widely used in the blanking of steel structure of railway passenger cars.

Many small parts need to be cut and blanking in each car, which improves the work efficiency and saves a lot of costs.

The following problems should be paid attention to when using plasma cutting: analyze the deformation law and influence of cutting parts of CNC plasma cutting machine;

Before cutting, carry out appropriate plate leveling treatment and reasonably fix the plate to prevent the movement of machined parts during cutting;

When compiling the cutting program, select a reasonable cutting process to separate the maximum size surface of the workpiece from the motherboard;

When cutting slender parts or special-shaped parts, the control methods such as two-piece paired cutting can effectively prevent or reduce the deformation of the cutting parts.

CNC plasma cutting is superior to flame cutting in terms of cutting quality and cutting benefits in the processing industry.

It can cut all kinds of metals with different working gases, especially non-ferrous metals.

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