As the first step in the production process, quality control of the cutting process is particularly important for companies.
This article discusses the factors that affect the quality of flame cutting and addresses several common cutting problems by using process methods.
Flame cutting is still an important part of the production process as the main cutting method for small, medium and large companies.
Of course, it also faces various problems.
Flame cutting has been developed for many years, CNC cutting equipment has also been developed and mature, and some of the corresponding process methods and ways to achieve them have also been developed.
In this article, we combine the automatic nesting software XSuperNEST to investigate the factors affecting the quality of parts cut in flame cutting and how to improve the yield.
Influencing factors of cutting equipment
At present, the market emerged from the laser, plasma, water cutting and a variety of cutting methods and equipment, cutting quality and production efficiency are better than flame cutting.
But because the flame cutting cost is cheaper, so it still occupies an important position, and flame cutting machine is also still the mainstream equipment.
CNC flame cutting machines are being used more and more widely in the cutting down production process.
CNC cutting has the feature of non-interference after programming, this feature makes it impossible for workers to compensate for the parts in the cutting process to repair the dimensions affected by thermal deformation, which eventually leads to deviations in the dimensional accuracy of the parts.
And some factors of the CNC cutting machine itself will also have some impact on the cutting quality.
Factors affecting the quality of cutting
(1) Cutting gas selection
For flame cutting machines, the choice of cutting gas also has a great impact on the quality of the cut.
At present, the gas available are acetylene, propylene, propane and MPS.
Different gas combustion characteristics are different, so the cutting scenario is different, the appropriate choice of gas, to give full play to the advantages of gas cutting, to achieve high efficiency and low-cost cutting, has a certain significance.
Acetylene flame has the characteristics of concentrated heat, high temperature, short preheating time, low oxygen consumption, high cutting efficiency, small component deformation, etc., which is suitable for thin plates and the introduction of shorter parts cutting.
while propane flame has dispersed heat, low temperature, longer preheating time than acetylene, smooth and flat upper edge of cutting edge, less slag hanging on the lower edge, easy to remove, its relative cost is also low, so the cutting of large parts for thick plates is more economical than acetylene.
Propylene flame temperature is higher, preheating time is shorter compared to propane, slightly more than acetylene, and due to the high heat content of the outer flame, it is suitable for cutting large parts of thick plates.
(2) Oxygen concentration, speed and cutting nozzle height selection
In addition to the selection of the appropriate gas, cutting oxygen pressure, cutting speed, cutting nozzle height setting is also an important factor affecting the quality of flame cutting.
It has been shown that with the same oxygen pressure, the cutting time decreases as the oxygen concentration increases, while the oxygen demand decreases.
The choice of cutting speed is also particularly important.
If the speed is too high, although the yield is high, it is prone to quality defects, easy to ” flameout “, rough kerf, cutting machine speed is too slow, low yield, resulting in oxidation slag adhesion, kerf surface unevenness and other problems.
After a lot of practical experience, the best cutting speed should be in the rated speed of the cutting nozzle between the middle-upper and upper-middle level.
Such as the use of No. 5 nozzle to cut 40mm steel plate, rated speed range of 250 ~ 380mm / min, medium speed of 315 mm/min, divided into 10 levels of this range, using the sixth to the eighth level, between 336.6 ~ 358mm / min, 340mm / min is the best.
The choice of cutting nozzle height also has an impact on the cutting quality, too low flame center may contact the surface of the part, resulting in the collapse of the cut, slag splash blocking the cutting nozzle or even the occurrence of tempering;.
Too high makes the flame can not fully heat the kerf, resulting in reduced cutting capacity, slag removal difficulties.
Generally speaking, let the center of the flame and the work surface to maintain the best in 3 ~ 5 mm.
(3) Cutting order and lead application
Reasonable cutting order is conducive to the uniform heating of the steel plate, internal stresses offset each other, and thus reduce the thermal deformation of the parts.
Therefore, when cutting parts contour should comply with the principle of first inside then outside, first small then large, first round then square, cross jump, first complicated then simple, in order to avoid the phenomenon of displacement, deformation and size deviation of the parts.
Reasonable lead position and form are conducive to the integrity of the part notch, cutting stability to ensure the quality of the contour.
According to the actual production situation, the outer contour introduction position is generally placed on the right side of the bottom of the contour, and the inner contour lead form is appropriate to use the form of circular arc.
After the flame cutting equipment itself parameters are set up and debugged perfectly, it is not guaranteed that the parts will be cut without fail.
The shape of the part, the thickness of the plate, the position of the nesting material, the way of cutting, etc. may have an impact on the quality of the part cutting.
We will introduce you with the following production examples.
Usually, flame cut plates can be divided into thin plates (thickness <20mm), medium-thick plates and thick plates.
Thin plates are simple to perforate during the cutting process but easy to produce thermal deformation, so in the actual production should not be cut from the edge position of the steel plate, but should be perforated inside the steel plate cutting.
This practice can ensure the closure of the outer frame of the steel plate, and to a certain extent reduce the thermal deformation and arching of the parts.
In addition, the appropriate use of the “continuous cutting” process can effectively reduce the number of parts perforation, the use of the “stay cut” process can be more effective in reducing thermal deformation.
Medium-thick plate and thick plate in the cutting process of thermal deformation is smaller, but due to perforation prone to slagging phenomenon leading to damage to the cutting nozzle, so it is desirable to reduce perforation by using parts cutting edge preheating start cutting.
Figure 1 shows the conventional edge preheating cutting method.
Figure 1 Conventional edge preheating lead cutting method
(1) Reduction of preheat perforation by using “I perforation” process
The use of conventional edge preheating lead cutting method can solve the perforation problem of medium-thick plate and thick plate cutting to a certain extent, but the method requires a lot of human adjustment in the discharge, which requires high quality of nesting personnel and high precision of the cutting machine.
In this study, XSuperNEST software provides a new “I-piercing process” to optimize the cutting and piercing path.
Description of I perforation edge preheating lead cutting: I perforation cutting is to automatically find a suitable location to cut a lower circular hole based on the outer contour of the cut part, and the next part is introduced in this circular hole to preheat the cut to achieve the purpose of reducing perforation.
Figure 2 I Perforated edge preheating lead cutting method
(2) Using the “continuous cutting” process to improve cutting efficiency
To improve material utilization, small parts are usually nested in the inner contour of large parts, and the cutting path is usually to first cut the part in the inner contour, then jump to cut the part in the next inner contour, and finally cut the two inner contours separately.
This makes the cutting machine lift the gun several times, pierce the hole several times, and the cutting efficiency is low.
In view of the above problems, the cutting path can be optimized by using the “continuous cutting” process to reduce the perforation and emptying process, Figure 3 shows the cutting sequence after the optimization of the “continuous cutting” process.
Figure 3 shows the cutting sequence after the optimization of “continuous cutting” process. In Figure 3, each part in the inner contour is cut in a row, and then the inner contour lead is cut in a row, so that the parts in the inner contour and the inner contour can be cut out by only one perforation, which greatly improves the cutting efficiency.
Figure 3 Cutting sequence after optimization of “continuous cutting” process
(3) Using the “stay cut” process to reduce thermal deformation of parts
In the process of cutting the inner contour of the part, there is a problem that the actual size between the inner contour and the outer contour does not match the theoretical size.
Take the part with a thickness of 50 mm in Figure 4 as an example: the theoretical dimensions marked in the figure are 610 mm, but the actual dimensions after cutting are 3~5 mm smaller.
This is because the part cutting in the inner contour makes the heat accumulate, and then the heat increases when cutting the inner contour.
When cutting the outer contour above the part, the influence of heat further increases, and at this time there is no support in the inner contour, the outer contour is extruded inward by heat, and the part is deformed.
Figure 4 Part nesting diagram
In this case, the solution is to add a “stay cut” process.
As shown in Figure 5, the “stay cut” is added around the inner contour so that the frame contour of the inner contour is not detached from the part and plays a supporting role.
This method can effectively reduce the cutting error and improve the cutting accuracy, but the disadvantage is that the inner contour needs to be polished.
Figure 5 Cutting path after optimization of “stay cut” process
(4) The use of arc introduction to reduce the internal round hole start overburning
The traditional introduction method uses a straight line to cut into the contour of the part, along the straight edge of the contour, and then along the straight edge of the introduction, which does not affect the quality of cutting at the start of the part for the introduction of the contour of the lead section is straight.
However, in the cutting process of the inner circular hole, the traditional introduction method is used because there is no smooth transition when cutting directly into the contour, so the contour overburning often occurs, affecting the cutting quality, as shown in Figure 6.
Figure 6 Inner round hole overburning
In the research process, XSuperNEST provides an arc introduction method, which effectively avoids the overburning of the arc, makes the inner circular hole smooth and flat, and improves the quality of cutting the inner circular hole of the part.
The arc introduction cutting method is shown in Figure 7, using an arc tangent to the inner circular hole to form a smooth transition, leaving a gap with the introduction starting point and also a smooth introduction with a circular arc.
We have verified this method and confirmed that it is effective and has been used in actual production, as shown in Figure 8.
Figure 7 Circular arc leading to cutting
Figure 8 Using circular arcs to lead to cut parts
Blanking, as the first process of production, is crucial to enterprise production. Flame cutting, as the mainstream cutting method, the cutting quality directly affects production quality and productivity.
Therefore, effective control of flame cutting quality is very important to the control of production quality.
There are various factors affecting the cutting quality, from the equipment itself, the gas used, cutting speed, nozzle height, cutting sequence, etc. are all factors affecting the cutting quality.
According to the actual production situation to use the appropriate parameters in order to improve the cutting quality, improve the parts qualified rate.
In addition, according to the thickness of the parts, contour shape and other characteristics of their own, the use of the corresponding cutting process to optimize the cutting path can reduce the production error of the parts, improve the efficiency and quality of parts cutting, and ultimately improve the efficiency of enterprise production.
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