What is press brake and how does it work?

What is Press Brake and How Does It Work

Press brake is an important equipment for bending and forming workpieces in sheet metal industry, it uses a simple and general mold, and sheet metal can be pressed into certain geometric shapes. A press brake is mainly composed of left and right columns, worktables and beams. These three major parts are the key parts of press brake. Its strength and ease of use directly determine the running accuracy, service life, and workpiece accuracy of the machine tool.

Table of Contents

Introduction of CNC Press Brake Working Methods

1. Set the pressure holding time, the pressure relief time, the advance and retreat distance of the horizontal stopper, and adjust the horizontal stopper position of the CNC press brake.

2. Set the number of steps of the CNC press brake, the position of the stopper and the number of bending sheets for each step.

3. Select the continuous operation position, the pressing and bending mechanism is not in the up-travel switch position and first automatically returns to the up-travel switch position; step on the pedal to move slowly, and press down the bending mechanism to automatically press down;

4. when the lower travel switch is touched, the horizontal stopper mechanism retreats by the set distance, and at the same time automatically maintains pressure; automatic pressure relief, the pressure relief time is down and the bending mechanism automatically returns, and the horizontal stopper mechanism automatically advances the set distance; when it hits the travel switch, one bending action ends, and the next bending is performed.

5. The bending times of the current step are completed, and the stroke switch is hit, the horizontal stopper position is automatically adjusted, and the CNC press brake enters the next step bending action.

6. After all the steps are completed, the stroke switch is hit, and the continuous bending action of the CNC sheet metal bending machine ends.

What is Press Brake?

1) Main functions of press brake (principles)

Press brake uses the equipped mold (general or special mold) to bend the metal sheet in the cold state into workpieces with various geometric cross-sectional shapes. Press brake generally adopts the special numerical control system. The coordinate axis of press brake has been developed from a single axis to 12 axes. The numerical control system can automatically realize the control of the running depth of the slider, the left and right tilt adjustment of the slider, and the front and rear adjustment of the rear stopper, left and right adjustment, pressure tonnage adjustment and slider approaching working speed adjustment and so on. Press brake can easily realize the actions of the slider downward, jog, continuous, pressure holding, return and stop in the middle, and complete the bending of multiple elbows at the same angle or different angles at one time.

2) Structural components of press brake

Press brake is an important equipment for bending and forming workpieces in the sheet metal industry. Its function is to press the steel plate into parts of various shapes according to the needs of the process. The frame is mainly composed of left and right columns, worktables and beams. The left and right oil cylinders are fixed on the columns. The slider is connected with the pistons of the oil cylinders and moves up and down along the guide rails fixed on the columns. The lower die is fixed on the workbench and the upper die is installed on the lower end of the slider, the hydraulic system provides power, and the electrical system gives instructions. 

Under the action of the oil cylinder, the slider drives the upper die down and the lower die is closed to realize the bending of the sheet. The left and right uprights, the worktable and the slider (hereinafter referred to as the three major pieces) are the key parts of the bending machine, and the sum of the weight of the three pieces accounts for 70% to 80% of the total weight of a bending machine. Its strength and rigidity directly determine the running accuracy and service life of the machine tool, as well as the accuracy of the workpiece.

1. Slider part

hydraulic transmission is adopted, and the slider part is composed of a slider, an oil cylinder and a mechanical stopper fine-tuning structure. The left and right oil cylinders are fixed on the frame, and the piston (rod) drives the slider to move up and down through hydraulic pressure, and the mechanical stop is controlled by the numerical control system to adjust the value;

2. Worktable part

Operated by the button box, the motor drives the material stopper to move back and forth, and the distance of movement is controlled by the numerical control system. The minimum reading is 0.01 mm (there are limit switches at the front and rear positions);

3. Synchronization system

The machine is composed of a mechanical synchronizing mechanism composed of a torsion shaft, a swing arm, a joint bearing, etc., with a simple structure, stable and reliable performance, and high synchronization accuracy. The mechanical stop is adjusted by the motor, and the numerical control system controls the value;

4. Material stopper mechanism

The material stopper is driven by a motor, which drives the two screw rods to move synchronously through chain operation, and the numerical control system controls the stopper size.

3)Structural features of press brake

1. All-steel welded structure with sufficient strength and rigidity;

2. Hydraulic upper transmission, the oil cylinders at both ends of the machine tool are placed on the slider to directly drive the sliding work;

3. The slider synchronization mechanism adopts torsion shaft forced synchronization;

4. Adopt mechanical block structure, stable and reliable;

5. The slider stroke is motorized and quickly adjusted, manual fine-tuning, and counter display;

6. Wedge-type deflection compensation mechanism to ensure a higher bending precision.

Structural features of press brake​

Types of Press Brake?

According to the driving method, the commonly used bending presses are as follows:

What are the types of bending machines

1. NC press brake:

NC press brake adopts the torsion axis synchronization rod structure for forced synchronization. When one cylinder goes down, it will drive the slider to move down at the same time, the torsion axis synchronization rod starts to work, and forces the other side of the cylinder to descend to achieve the cylinder synchronization. This is the working principle of NC press brake. Press brake relies on the pressure of the die on the slider to force the plate to bend and deform, but the slider is very long, and the bending angles of the left and right ends are often different. How to synchronize the two oil cylinders on the slider is the key point. Therefore, compared with CNC press brake, NC press brake brings a worse customer experience. The accuracy is worse and  the employee requirement is higher.

2. CNC press brake:

CNC press brake is equipped with a grating ruler on the slider and the fuselage. The CNC system of press brake can analyze the synchronization on both sides of the slider through the real-time feedback information of the grating ruler. If there is an error, the numerical control system will adjust it through the proportional valve (Y1, Y2 axis), so that the strokes on both sides of the slider are synchronized. CNC system, hydraulic control valve and the grating ruler together constitute the feedback closed-loop control of the CNC press brake. In a word, CNC press brake is a sheet metal processing equipment with more optimized design principles, more complete functions, and guaranteed accuracy and speed.

3. Oil-electric hybrid press brake.

It is the same as CNC press brake, except that the main motor is replaced by a servo motor, which reduces the consumption of oil and electricity, the noise of the machine, and achieves the effect of energy saving.

Capability and Structural Features of CNC Press Brake?

Advantages of CNC Press Brake​

1. The performance of the machine tool

Using a new rigid design and finite element optimization analysis, it has good rigidity and stability, minimizes the impact of bending deformation on the quality of the workpiece, and ensures the machining accuracy of the workpiece.

Adopt Germany Rexroth imported fully closed-loop electro-hydraulic servo synchronous control system, feedback synchronization.

It adopts simple style new process design and appearance. The machine tool is sandblasted to remove rust, and sprayed with anti-rust paint.

Speed: CNC press brake set and save each process through the computer, which can be operated continuously and uninterruptedly, effectively improving the speed of the bending steps, thereby improving work efficiency. At the same time, when the slider goes down, the speed has the function of fast down and slow down, and the transition between fast and slow is smooth, which can greatly improve the production efficiency. 

2.Structural features of machine tool

The steel plate is wholly welded, the welding process, pre-weld preparation, workpiece orthopedic, post-weld heat treatment, weld quality inspection, weld, repair and other technical requirements of all workpieces conform to the requirements of the process documents; welding materials and base metals Matching; for large structural parts, a large annealing furnace is used for overall annealing, and the seismic performance is strong.

After the large tempering furnace is adopted, the stress is eliminated by vibration, the stability is good, and the frame is not deformed;

The frame is formed by a precision floor boring machine or a multi-faceted machining center at one time, which ensures the parallelism and verticality of each installation surface;

There is a “C”-shaped plate mechanism at the throat of the frame, which directly detects the distance between the upper and lower molds to ensure the accuracy of the parts.

3. Advantages of CNC press brake

1. Operation

CNC press brake is controlled by a professional and advanced CNC system and is equipped with a deflection compensation device. The operation is very simple and the experience requirements of the operator are very low. There is no need for manual lofting, and the correct step size is input in the drawing, and the bending can be performed, and it can also be automatically calculated. Compared with NC press brake, it liberates a lot of manpower and relieves the excessive dependence on manual experience of bending work.

2. Strength

The Y1, Y2 axes on the left and right side of CNC press brake run independently and can perform eccentric bending. This advantage is a good solution to the problem which NC press brake cannot achieve.

3. Straightness

Take our 4m CNC press brake as an example, the straightness of the processed product is very high. The 201 stainless steel plate does not bend the small U-groove of 10*15*10 without slotting.

4. Efficiency

CNC press brake is controlled by CNC system, which realizes automatic calculation, storage and conversion of various processes, and saves a lot of labor costs. The positioning of the back gauge is more accurate and the size of the front gauge is accurate. When used together, many special-shaped products can be folded. Expand the processing range of the equipment, faster and more efficient. In addition, CNC press brake supports multiple axes and multiple types, and can be customized according to the needs of the industry. In addition to the conventional Y1 and Y2 axes (the left and right oil cylinders that drive the slider to move up and down), the X axis (the back and forth movement of the back gauge), there are also the R axis (the up and down movement of the back gauge), Z1 axis, Z2 axis ( The left and right movement of the finger), etc., can reach more than 18 axes at most.

5. Deflection compensation

CNC press brake install a deflection compensation device, its function includes:angle compensation, length compensation, gap error compensation and so on. The device ensures the accuracy of the workpiece, reduces the error, and greatly improves the phenomenon of large error and rework of NC press brake.

Using Methods of Press Brake?

Make a brief introduction of common hydraulic press brake processing Q235:

1. First turn on the power, turn on the key switch on the control panel, and then press the oil pump to start.

2. Stroke adjustment. It is necessary to adjust stroke and test before bending. When the upper die of the bending machine goes down to the bottom, there must be a gap of plate thickness. Otherwise, it will cause damage to the mold and the machine. Stroke adjustment includes quick electric adjustment and manual fine adjustment.

3. The bending notch is generally selected with 8 times the thickness of the plate. For bending 4mm sheet, you need to choose a notch of about 32.

4. Back gauge adjustment generally have quick electric adjustment and manual fine adjustment, the same as shearing machine.

5. Step on the foot switch to start bending. Press brake is different from the shearing machine. When your foot stops, the machine stops.

Using Methods of Press Brake?

1. Strictly obey safe operating procedure, wear labor protection equipment as required.

2. Before starting, carefully check whether the motor, switch, circuit and grounding are normal and firm, and check that the operating parts and buttons of the equipment are in the correct position.

3. Check the coincidence and firmness of the upper and lower molds; check whether each positioning device meets the requirements of being processed.

4. When the upper slide plate and each positioning axis are not at the origin, run the back-to-origin program.

5. After the equipment is started, it should run idly for 1-2 minutes, and the upper sliding plate will move 2-3 times in full stroke. If any abnormal sound or fault is found, it should be stopped immediately, the fault should be eliminated, and it can work only after everything is normal.

6. The work should be under the unified command of one person, so that the operator closely cooperates with the feeding and pressing personnel to ensure that the cooperating personnel are all in a safe position before issuing the bending signal.

7. The sheet must be compacted when bending, to prevent the sheet from lifting and hurting people during bending.

8. The power supply must be cut off when the plate material is pressed, and the operation must be stopped.

9. Any material cannot touch the lower die when change the alternative notch of the lower die.

10. When working, no one is allowed to stand behind the machine.

11. It is strictly forbidden to fold the sheet at one end alone.

12. If the workpiece or mold is found to be incorrect during operation, it should be stopped for correction. It is strictly forbidden to correct by hand during operation to prevent hand injury.

13. It is forbidden to fold super-thick iron plates or quenched steel plates, high-grade alloy steel, square steel and plates that exceed the performance of the plate bending machine, so as not to damage the machine tool.

14. Often check the coincidence degree of upper and lower die and whether the indication of the pressure gauge complies with the regulations.

15. Immediately shut down when an abnormality occurs, check the cause and eliminate it in time.

16. Before shutting down, place a wooden block on the lower die under the oil cylinders on both sides and lower the upper sliding plate to the wooden block.

17. Exit the control system program first, and then cut off the power.

Tips for Purchasing a Press Brake?

1. Workpiece

The first thing you should consider is your workpiece, the key is to buy a machine that can do the job with the shortest table and the smallest tonnage.

Carefully consider material grades and maximum thickness and length. If most of the work is mild steel with a thickness of 16 gauge and a maximum length of 10 feet, the free bending force need not be greater than 50 tons. However, if you are doing a lot of bottomed die forming, maybe a 150-ton machine should be considered. Assuming the thickest material is 1/4 inch, a 10-foot free bend requires 165 tons, and a bottomed die bend (corrected bend) requires at least 600 tons. If the majority of workpieces are 5 feet or less, the tonnage is almost halved, greatly reducing the acquisition cost. Part length is very important in sizing new machines.

2. Deflection

Under the same load, the deflection of the table and slider of the 10-foot machine is 4 times that of the 5-foot machine. That said, shorter machines require less shim adjustment to produce acceptable parts. Reduced shim adjustment in turn reduces setup time. Material grade is also a key factor. Compared to mild steel, stainless steel typically requires around 50% more load, while most grades of soft aluminium require around 50% less. You can always get a machine tonnage table from the press brake manufacturer that shows an estimate of the tonnage required per foot of length for different thicknesses and materials.

3. Bending radius of workpiece

When free bending, the bending radius is 0.156 times the opening distance of the die. During the free bending process, the opening distance of the die should be 8 times the thickness of the metal material. For example, when forming mild steel with a 1/2 inch opening distance, the part has a bend radius of about 0.078 inch. If the bending radius is almost as small as the material thickness, a bottomed die forming is required. However, the pressure required for forming a bottomed die is about 4 times greater than that of free bending.

If bending radius is shorter than the material thickness, it is necessary to use a punch with a front-end fillet radius smaller than the material thickness, and resort to the imprint bending method. In this way, 10 times the pressure of free bending is required.

For free bending, punches and dies are machined at 85° or less. When using this set of dies, pay attention to the gap between the punch and die at the bottom of the stroke, and the overbending enough to compensate for springback to keep the material around 90°.

Generally, The springback angle produced by the free bending die on the new bending machine is ≤2°, and the bending radius is equal to 0.156 times the opening distance of the die.

For bottomed die bending, the die angle is generally 86 to 90°. At the bottom end of the stroke, there should be a gap slightly larger than the material thickness between the male and female dies. The forming angle is improved due to the higher tonnage of the bottomed die bending (approximately 4 times that of the free bending), reducing the stress that normally causes springback within the bending radius.

Imprint bending is the same as bottomed die bending, except that the front end of the punch is processed to the required bending radius, and the punch and die gap at the bottom of the stroke is smaller than the material thickness. Springback is essentially avoided by applying enough pressure (about 10 times the free bend) to force the front end of the punch into contact with the material.

In order to select the lowest tonnage specification, it is best to plan for a bend radius greater than the material thickness and use the free bending method whenever possible. When the bending radius is large, it often does not affect the quality of the finished part and its future use.

4. Precision

Bending precision factor requires careful consideration. Whether you should buy a CNC press brake or manual press brake depends on the bending precision. If bending accuracy requires ±1°and keep remaining, you must choose a CNC press brake.

The repeatability of the CNC bending machine slider is ±0.0004 inches, and the precise angle must be formed with such precision and a good mold. The repeatability of the slider of the manual bending machine is ±0.002 inches, and the deviation of ±2~3° will generally occur under the condition of using a suitable mold. In addition to that, CNC press brakes are ready for quick die set-up, which is an unquestionable reason to consider when you need to bend many small batches of parts.

5. Mold

Even if you have a rack full of molds, don’t assume these molds are suitable for a new machine. Each piece of die must be checked for wear by measuring the length from the front of the punch to the shoulder and the length between the shoulders of the die.

For conventional molds, the deviation per foot should be around ±0.001 inches, and the total length deviation should be no more than ±0.005 inches. For fine grinding dies, the accuracy should be ±0.0004 inches per foot, and the total accuracy should not be greater than ±0.002 inches. It is best to use fine ground dies for CNC press brakes and regular dies for manual press brakes.

6. Side length of workpiece

Assuming a 90° bend along a 5-by-10-foot mild steel sheet, the press brake would have to apply an additional 7.5 tons of pressure to lift the sheet, and the operator would have to prepare for a 280-pound straight-edge drop. Making that part can take several able-bodied workers or even a crane, and press brake operators often need to bend long-side parts without realizing how strenuous their work is.

There is now a feeding device suitable for workshops doing this kind of work. This device can be modified according to the needs of new and old machines. With this device, only one person needs to operate the forming long-side parts.

7. Precision of press brake:

The repeatability of the CNC bending machine slider is ±0.0004 inches, and the precise angle must be formed with such precision and a good mold. The repeatability of the slider of the manual bending machine is ±0.002 inches, and the deviation of ±2~3° will generally occur under the condition of using a suitable mold. In addition, CNC press brakes are ready for rapid die set-up, which is an undeniable reason to consider when you need to bend many low-volume parts.

Advantages of CNC Press Brake

Advantages of CNC Press Brake​

1. High flexibility

CNC press brake has good flexibility after processing, no need for tools and molds, combined with CAD/CAM technology, can cut plates of any shape and size, especially suitable for the cutting of multi-variety, small-batch, and complex-shaped parts.

2. High efficiency

Bending and cutting are non-contact processing, there is no impact force during mechanical punching, there is no wear and tear of tools and molds, and there is no need to lap edges during mechanical punching and blanking. The workpieces are closely arranged, which can save 20%-30% of materials. , cutting once and forming without subsequent processing.

3. High precision

The bending and cutting incision is narrow and smooth, without rounded corners and burrs that are common in mechanical blanking; the heat-affected zone, thermal stress and thermal deformation are all small.

Main Application of Press Brake?

Application of bending machine

1. In the decoration industry, high-speed shearing machines are widely used, generally used in conjunction with bending machine equipment, to complete the production of stainless steel plates, doors and windows, and the decoration of some special places;

2. In the electrical and power industry, the shearing machine can cut the plates into different sizes, and then re-process them through the press brake, such as computer cases, electrical cabinets, refrigerator air conditioning shells, etc. are all made in this way;

3. In the kitchen and catering industry, various varieties and specifications of stainless steel kitchen utensils are used for secondary processing, such as welding, bending, etc.;

4. In the wind communication industry, wind power poles, road light poles, communication tower poles, traffic light poles, traffic signal poles, monitoring poles, etc. are bent;

5. In the automobile and shipbuilding industry, large-scale CNC hydraulic shears are generally used, mainly to complete the shearing of the plate, and then perform secondary processing, such as welding, bending, etc.;

6. In the aerospace industry, high precision is generally required, and a high-precision CNC shearing machine can be selected, which is accurate and efficient.

As small as non-ferrous metals, ferrous metal sheets, automobiles and ships, electrical appliances, decoration, kitchenware sheets, chassis cabinets, elevator cabinet doors, shearing and bending; as large as the aerospace field, CNC shearing machines and press brakes are play an increasingly important role.

Conclusion

When buying a press brake, users should not only look at the price. First consider the thickness and size of each piece of material. The rigidity of the machine is the foundation of the machine’s life, and then consider whether all accessories are authentic brands, and understand all accessories. Functions and models, if you need to know more about press brake, please contact us.

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Please learn about the production of Press Brake through the video