Water Cutting Of Silicon Steel Sheet

The conventional production of silicon steel sheets used in motors and electrical appliances is produced by installing molds on mechanical presses.

mechanical presses

The cold stamping die of silicon steel sheet is mainly composed of male and female dies, which are installed on the press to punch the silicon steel sheet into motor stator and rotor or transformer iron chip.

When the silicon steel sheet die works, the edge part bears the impact force, shear force and bending force.

At the same time, the edge part is squeezed and rubbed by the silicon steel sheet. The special coating on the surface of the silicon steel sheet strengthens the friction and wear of the edge. The normal failure of the silicon steel sheet die is mainly the wear of the edge.

Therefore, the die wear is serious, and it is often necessary to sharpen before the ideal service life. The number of punched parts of a set of die is often less than its theoretical value.

Take the blanking of silicon steel sheet of a certain motor as an example. Seven kinds of dies are required to complete the blanking of silicon steel sheet of a motor, with a total cost of 190000 yuan.

The hardness of a stamping die for a rotor sheet is 60 ~ 62Hrc, which is installed on a 60t stamping machine tool. Under normal circumstances, the die can punch more than 200000 pieces.

However, when the die is used for less than 9000 times, the edge of the slot hole of the die collapses.

Grind the die (normally 50000 ~ 60000 times before grinding) and put it on the machine again. The collapse continues to occur and cracks appear on the outer edge of the die.

In the process of continuous stamping, the crack expands rapidly, and the die fails and cannot be used less than 20000 times;

Every time two motors are produced, three kinds of molds need to be sharpened, and the cost is 400 ~ 800 yuan/time, and the product manufacturing cost is relatively high.

Especially in the process of new product trial production, the cost of mold manufacturing is very high, and the production cycle is long, which makes the cost of new product development double.

Production and requirements of silicon steel sheet

Silicon steel sheet is the key component of motor and electrical appliances. Its performance is not only directly related to the loss of electric energy, but also related to the performance, volume and weight of motor, transformer and other products.

Therefore, the performance of silicon steel sheet should roughly meet the following requirements:

  • It has good shape and surface coating, high dimensional accuracy and very small thickness difference of the same plate;
  • It has good electromagnetic properties and grain orientation structure meeting the requirements of the application.

The blanking process of silicon steel sheet shall not only have the process and product characteristics of general metal shearing, but also meet the following special requirements.

Burr height

The height of the silicon steel sheet blanking burr is no more than 0.05mm. People pay more and more attention to the influence of burr on mechanical parts on the performance of the whole machine.

The burr on silicon steel sheet used in generator, motor and transformer has a significant impact on its electromagnetic characteristics.

Silicon steel sheets used in generators, motors and transformers are formed by die blanking.

Usually, the die manufacturing gap is too large, or the gap increases due to wear.

During blanking, the silicon steel sheet is extruded, resulting in slight plastic deformation, which remains on the edge of the sheet and forms burrs.

The rotor, stator and transformer core of generator and motor are stacked by a large number of blanking silicon steel sheets.

The burr on the silicon steel sheet reduces the stacking factor.

If you want to install the same number of sheets, the motor volume must increase.

In addition, the burr also affects the output power of the motor.

The practice shows that the output power of the generator with deburring silicon steel sheet can be increased by 0.1% ~ 0.2% compared with the generator without deburring silicon steel sheet.

The practice shows that the output power of the generator with deburring silicon steel sheet can be increased by 0.1% ~ 0.2% compared with the generator without deburring silicon steel sheet.

Impact on generator life

The existence of silicon steel sheet burr causes a large gap between laminations, which is easy to produce eddy current, increase magnetic loss, increase temperature rise and noise, and even short circuit, resulting in motor failure.

The average service life of the motor with deburring can be increased by more than 5% compared with that without deburring silicon steel sheets.

Processed silicon steel sheets can generally be stacked automatically or manually, and the gap at the joint shall be minimized.

This requires the equipment to maintain high accuracy (including spare parts accuracy) when reaching the maximum production capacity, so as to ensure that the products after shearing are basically free of burrs (the burr height after longitudinal shearing of silicon steel sheet shall not be greater than 0.05mm).

Otherwise, during lamination, the burr causes the lap short circuit between the laminations, increases the eddy current loss, and reduces the filling coefficient of the lamination.

China’s relevant standards clearly stipulate that the burr height of silicon steel sheet is no more than 0.05mm.

But in fact, many motor factories have not taken effective deburring measures. Even if the burr is as high as 0.07 ~ 0.1mm, they are still installed and used, which seriously affects the quality.

At the same time, the insulating paint film on the surface of silicon steel sheet shall not be obviously scratched during deburring.

Effect of stress

After cutting, stamping and stacking, silicon steel sheets will produce internal stress, which will deform the grains, reduce the permeability and increase the specific iron loss.

In order to avoid or minimize this, the cold-rolled oriented silicon steel sheet after shear processing is usually treated by nitrogen filling annealing at a temperature of about 800 ℃ to eliminate the stress generated during processing and ensure the original properties.

Although the test shows that the specific iron loss of cold-rolled oriented silicon steel sheet after annealing is reduced by about 30%, many manufacturers do not adopt this process because the cost increases.

Steel sheet sickle bending

Due to the special performance requirements of silicon steel sheet, it is necessary to have a high standard for silicon steel sheet.

This standard even exceeds the American Society for testing and materials (ASTM) side bending standard for general sheared metal (no more than 6mm / 3M long), which puts forward higher requirements for the shear process layout of silicon steel sheet.

Lotus leaf edge

The sheared silicon steel sheet shall be free from obvious waves (commonly known as lotus leaf edge).

Even if there are waves, the ratio of wave height to wave length shall not be greater than 2.5%. Otherwise, the silicon steel sheet will undergo severe plastic deformation, the domain structure will be damaged and the loss will increase significantly.

Insulation

Insulation damage is not allowed in the shear range and on the surface of the strip, and the edge of the sheet shall be free of extrusion damage, otherwise the quality of the iron core will be affected.

Application of water cutting technology

Water Cutting Of Silicon Steel Sheet

Ultra high-pressure water cutting, also known as water knife and water jet, is a high-energy water flow generated by multistage pressurization of ordinary water, and then through a very fine nozzle to spray cutting at a speed of nearly kilometers per second.

This cutting method is called ultra-high pressure water cutting.

The “discovery” of high-pressure water cutting originated in Scotland. After 100 years of experimental research, industrial high-pressure water cutting system appeared.

In fact, high-pressure water cutting is not a patent.

It was not until 1968 that the professor of Columbia University in the United States added abrasive in high-pressure water, which accelerated the completion of the cutting process through the high-pressure jet of water and the grinding of abrasive.

At present, the United States, Germany, Russia and Italy have broken through the technology of ultra-high pressure water cutting, with a maximum cutting pressure of 550MPa, and are widely used in the cutting of stone, metal, glass, ceramics, cement products, paper, food, plastics, cloth, polyurethane, wood, leather, rubber, ammunition and other materials.

There are three main uses of water cutting:

First, cutting non combustible materials, such as marble, ceramic tile, glass, cement products and other materials, which cannot be processed by thermal cutting;

Second, cutting combustible materials, such as steel plate, plastic, cloth, polyurethane, wood, leather, rubber, etc.

In the past, thermal cutting can also process these materials, but it is easy to produce combustion areas and burrs.

Water cutting will not produce those, and the physical and mechanical properties of the cut materials will not change, which is also a major advantage of water cutting;

Third, cutting flammable and explosive materials, such as ammunition and cutting in flammable and explosive environment, which can not be replaced by other processing methods.

In terms of water quality, ultra-high pressure water cutting has two forms: pure water cutting and abrasive cutting.

Water cutting test

In the water cutting test scheme of silicon steel sheet, the main equipment used is Altorf water knife.

The high voltage generator (apw38037z-09a) of the equipment adopts a complete set of original imported supercharger from accustream Inc. the control system adopts PLC instead of relay to realize communication and flexible control with computer;

The cutting platform (apw-2030ba) adopts gantry structure instead of cantilever structure to make the cutting platform more stable and accurate;

Industrial PC platform, special water cutting software based on windows, supported by genuine WindowsXP system;

Industrial PC platform, special water cutting software based on windows, supported by genuine WindowsXP system;

The process cutting speed is 800mm / min for the linear part and 300mm / min for the circular arc part; The thickness of silicon steel sheet is 0.5mm.

After the test, the product fell into the water tank of the cutting platform, fished out and dried, and then checked the size.

As a result, there was only an out of tolerance at the knife entry during round hole cutting, which obviously felt elliptical, which was mainly caused by too fast knife entry during programming.

During the retest, this phenomenon disappears, and the burr is less than 0.05mm. It can be stacked without grinding, and the rest meet the requirements of the drawing.

Conclusion

The water cutting process test of silicon steel sheet shows that the ideal product quality can be obtained by using the correct cutting process parameters, strictly controlling the water quality and sand particle size, and controlling the inlet speed and direction of the arc.

Water cutting has the advantages of high speed, good quality, cost saving and convenient product modification.

In particular, the trial production of new products is more convenient without mold, which greatly shortens the production preparation cycle and reduces the early investment of new products, and the effect is satisfactory.

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