Press Brake: The Ultimate Guide (2019 Updated)

What Is A Press Brake

If you read the term “press brake” for the first time, I believe most of you don’t know what exactly does it mean. You will never connect this term with one machine for sheet metal bending.

After doing some research you finally know it refers to the bending machine specially used for sheet metal. But why call it “press brake”? Why not directly call it “bending machine”?

We’ve written one article to explain the reason. You can read the following blog post to get the details.

• Why the machine for sheet metal bending is been called press brake

Now let’s started from the definition of the press brake.

Press Brake Definition

“A press brake is a machine tool for bending sheet and plate material, most commonly sheet metal. It forms predetermined bends by clamping the workpiece between a matching punch and die.”

 

 

Press Brake Types

According to the source of bending force, the brake is divided into:

• mechanical press brake
• pneumatic press brake
• hydraulic press brake
• servo-electric press brake

For the mechanical press brake, the vertical movement of the ram is driven by a crank mechanism which is powered by the flywheel.

And the pneumatic press brake makes use of air pressure to move the ram.

Hydraulic press brake utilizes the two synchronized hydraulic cylinders to move the ram.

Servo-electric brakes use a servo-motor to drive a ball screw or belt drive to exert force on the ram to make it move vertically.

Until the 1950s, mechanical brakes dominated the world market. With the development of hydraulics and computer controls, the hydraulic type press brake becomes the most popular all over the world.

From another point of view, the press brake can be divided into:

• Manual press brake
• Hydraulic press brake
• CNC press brake

Manual Press Brake

It is the most common type among various press brakes, also been called sheet metal brake.

Manual press brakes are required to adjust the bending dimensions and angles manually when used. It contains worktable, supporters, and the clamping plate. The worktable is mounted on the supporters, which consists of a base and a pressure plate.

Manual press brakes are much more complex in operation than other types of press brakes, therefore, it is necessary to make mass production after confirming bending size and bending angles. When finished one batch of mass production, adjusting bending size and bending angles for continued production.

Hydraulic Press Brake

Classified by synchronization, the hydraulic press brake can be divided into:

• Torsion Synchronization Press Brake
• Hybrid Press Brake
• Electric Hydraulic Synchronization Press Brake

Classified by movement, the hydraulic press brake can be divided into:

• Up Moving Press Brake
• Down Moving Press Brake

CNC Press Brake

Electro-hydraulic servo press brake, which is a kind of sheet metal processing equipment with high precision and efficiency.

It consists of:

• machine frame
• ram (slider)
• workbench
• oil cylinder
• hydraulic proportional servo system
• position detection system
• CNC controller
• electrical control system

CNC press brake realizes bending function by controlling slider stroke and back gauge.

When using CNC press brake, you only need to input the number of the pieces which required for bending as well as bending angle for each step, the CNC press brake will finish bending according to the steps you just set in the controller.

Advanced CNC press brake mainly adopts hydro-electric servo system and grating ruler to form closed-loop control.

It features high control accuracy, as well as bending accuracy and repositioning accuracy.

Advantages and Performance Features of CNC Press Brakes

With the progress of science and technology, electro-hydraulic servo synchronization technology is been adopted to complete the upgrade. It mainly has the following advantages:

• CNC press brake using electro-hydraulic servo system to control the two-cylinder synchronization. With the international standard grating ruler realize the full closed-loop control. It featured high precision synchronization, high bending accuracy, high repeat positioning accuracy.
• Equipped with a hydraulic automatic clamp or fast clamp for the upper die, and socket lower die based on customer’s requirement to reduce the labor intensity and improve production efficiency.
• The back gauge of CNC press brakes can be extended to six axis. The crowning is automatically adjusted by the controller, which is convenient and accurate.
• Equipped with Germany Bosch-Rexroth valve block, linear motion guide and ball screw manufactured by BLIS, Taiwan HIWIN or other international companies to ensure that the positioning accuracy.
• The separated upper die which is in different lengths can be assembled into a certain width according to the requirements of the workpiece in order to meet the special needs of the fabrication.
• Automatic cylinder crowning system overcomes the impact on the workpiece quality caused by ram deformation, to ensure the good straightness and bending angle of the final products.

Working Principle of the Press Brake

Fix the top punch and bottom die on the upper and lower worktable, utilize the relative motion of the worktable driven by hydraulic transmission as well as the shape of the punch and die, to achieve the bending formation for sheet metal materials.

Hydraulic Press Brake Working Principle Diagram

Press Brake Composition

Generally, the press brake machine including four main parts:

• Mechanical parts
• Electrical parts
• Hydraulic part
• NC/CNC controller

Frame

The frame of press brake is welded by the left and right upright plate, worktable, supporting bodies and fuel tanks. The worktable is under the left and right uprights. The fuel tank is welded with the uprights, which can improve the rigidity and strength of the frame, as well as increase the heat dissipation area of the hydraulic oil.

Features of Press Brake Structure:

• Adopt a fully welded structure, with sufficient strength and rigidity;
• Up transmission of hydraulic oil, the cylinders on both ends of press brake are installed on the slider, directly drive the sliding work;
• Slider adopt torsion to force synchronization;
• Adopt mechanical stopper, stable and reliable;
• Slider stroke is adjusted by the controller, fine adjustment manually, counter display;
• Wedge-shaped crowning, to ensure a higher bending accuracy.

Ram

The ram is made from the whole steel plate and is connected with the piston rod in the center of the left and right oil cylinder. The cylinder is fixed on the connecting plate of the left and right wall plate, and the piston rod is driven by the hydraulic drive to move the slider up and down.

In order to ensure the accurate positioning of the ram in the upper dead point, a grating ruler is arranged on both sides of the ram to transfer the position information back to NC controller, and the position is adjusted by the controller. At the same time to ensure the synchronous operation of the ram.

The ram adopts hydraulic transmission and the ram system consists of the slider, oil cylinder and mechanical stopper for fine adjustment.

The left and right cylinders are fixed on the frame, and the piston (rod) is driven by the hydraulic pressure to move the ram up and down.

The mechanical stopper is controlled by the numerical control system.

Workbench

The forward and backward movement of the back stopper is driven by the motor, and the moving distance of back stopper is controlled by CNC controller, with minimum reading 0.01mm (there is stroke limit switch both at the front and back position).

Synchronization System

The mechanical synchronization mechanism consists of torsion, swing arm, joint bearings etc. It has a simple structure, stable and reliable performance, as well as high precision synchronization.

The position of the mechanical press brake stops is adjusted by the motor, while the data is controlled by the CNC controller.

Back Gauge

The backgauge of the CNC press brake adopt motor driving transmission, to realize synchronous movement of two ball screw timing belt.

The backgauge distance is controlled by the CNC controller.

 

Axis Diagram

Press Brake coordinates

X, Y, Z directions of press brake are as follows, the arrow in the figure is positive.

Press brake axis can be classified as follows:

Y1, Y2-axis: control the upward and downward movement of the ram

V-axis: control press brake crowning

X1, X2, R, Z1, Z2-axis: all is backgauge control axis to control backgauge positioning

Exploded View

Front Support Arms

The front supporter arms of press brake are fixed on the T-groove or linear guide in front of the machine and are designed with a manually adjusted back position claw.

Foot Pedal Switch

The pedal switch of the press brake is mainly used to control the up and down of the top punch during bending operation. There is also one emergency button on top of the pedal switch for emergencies.

Top Punch Clamps

Press Brake clamps including normal standard clamps and fast clamping tools for quick change of the top punch.

Clearly, fast clamping tools will make it much easier for change punch die, not only convenient but also time-saving.

Kits and Accessories (Parts)

Guarding

Generally, the press brake will be equipped with a steel fence to protect the workers from injury. If you want to have better safety assurance, then you can consider using a light curtain safety device and laser protection device.  As I know, the safety of the machine must reach a certain degree, otherwise, it’s forbidden to use it. So I suggest you equip the press brake with at least light curtain device for safety consideration.

Press Brake Safety Guards

 

Press Brake Light Curtains

 

Press Brake Laser Guard

Electrical System

CNC Bending Machine power supply using three-phase AC 50HZ 380V power, can not only be directly used for the main motor operation, but also for the rear gear servo and equipment lighting use after output AC voltage through the system internal transformer. The other group form into two sets of DC 24V after rectification, one way for CNC controller use, the other for the use of controlling loop.

Hydraulic System

Press Brake Hydraulic System Working Principle

The motor, oil pump, valve are connected with the fuel tank, in order to ensure that the oil tank is filled with oil when the ram is rapidly falling, the structure of filling valve is adopted, which will not only improve the travel speed of the ram but also save energy.

The hydraulic control of CNC press brakes requires a high degree of automation and standardization rate in manufacturing. Therefore, the press brakes must integrate the hydraulic system into it.

The frame of the press brake becomes the basis for the installation of hydraulic parts and integrate the oil tank into the stamping frame.

Three control block style

It has three control blocks.

Two with the middle plate filling valve and the main control block directly installed in the hydraulic cylinder in order to achieve the pipe-free connection between the main control block and the hydraulic cylinder.

The back pressure assembly consists of a reversing seat valve and two relief valves, corresponding to the customer’s requirement as a non-leaking type.

The main installation here is the proportional relief valve and a maximum pressure shut off valve, as well as monitor the reversal valve at the position of the pilot valve.

Central control block

The central control block combined three control blocks into one which is mainly used in some special structure due to control reasons.

The control block and the connection between the two-hydraulic cylinder must in the symmetrical layout.

It uses an SFA series of oil filling valve.

The valve is in flange structure, directly installed in the hydraulic cylinder, and connected to the tank by a suction pipe.

Sensor and axis interface distributor

All the solenoid valves are concentrated in a control block. Similarly, the electrical connections of the valves are also concentrated on a single cable to achieve a common connection.

For this purpose, an interface distributor is provided on the central control block.

See also:

• How Does the Press Brake Hydraulic System Work?
• Open Loop v.s Close Loop: Machine Tools Hydraulic Control Analysis

Hydraulic Oil Cylinder

Clean the Hydraulic Oil

The hydraulic system has a high requirement for the cleanliness of hydraulic oil. The clean of the oil tank is very important.

When replacing the hydraulic oil, you must discharge the cover of the oil tank. Use the towel to clean the bottom of the tank (do not use cotton yarn), then wash with cleaning coal oil gasoline. For the limitation of tank cover, the arm cannot reach the end of the tank; you can wrap the towel on the bamboo or stick to wipe each corner. Loosen the leaking plug or brake valve to leak out the dirty oil.

Use the cleaning towel to dry the sides and bottom of the tank until it’s clean. If necessary, roll the dough at the welding seam or difficult cleaning places to cling the dirt, and then put on the cover.

Choose the hydraulic oil

The mark value of hydraulic oil is equal to the average value of viscosity when the temperature is 40℃.

If the working pressure and temperature of the hydraulic system are higher, and the working speeds slower, the chose hydraulic oil mark is higher.

It is recommended to use antiwar hydraulic oil ISO VG46# (the average value of viscosity is46mm2/s, when the temperature is 40℃.). If the machine operates under 5℃ for a long period, you can choose hydraulic oil ISO VG32#.

It is also recommended not to use the machine at very low temperatures (below -5°). However, should this occur, and then let the machine run idle for a while. An oil heater can be fitted in the circuit if required.

Under normal working conditions, the oil temperature must not exceed 70C. Under special conditions, oil cooler can be fitted necessary.

Fill the oil

The using oil must clean. Screw the nut of air filter, filling through the air filter. If using the filling equipment with filter, you can open the cover of the oil tank and fill directly. Observe oil gauge, when ram stops at Top Dead Spot, the hydraulic oil fills at 80~90% of interspaces.

Make the machine work, first idling then at the maximum stroke to expel any air bubbles in the hydraulic circuit.

See also:

• The Commissioning of CNC Press Brakes Hydraulic System

Oil Seal Ring

Weight

The weight of press brake ranges from 5T to 300T, this is much depending on the size of the machine. For example, for 80T/2000mm press brake, the weight is around 6T, however, the weight for 2000Tx12000mm press brake is over 300T.

Crowing (Deflection)

The press brake is pressurized by two working cylinders at both ends of the ram. The deformation force of the bending workpiece is in the middle, so the sliding block and the worktable are deformed together with the upper and lower die. It causes the sheet material to be uneven along the length of the die edge, which directly affects the accuracy and straightness of the bending workpiece.

Therefore, it is necessary to take corresponding measures to reduce or eliminate the deflection caused by the deformation.

The so-called deflection compensation device has preset a deformation in the direction of the opposite force-deformation in the sliding block and the upper die or the worktable and the lower die working table, and the deformation has the same amount of deformation generated in the actual work.

Therefore, to realize the compensation of the relative deformation of the ram to the worktable, the pressure distribution between the dies is more uniform and the bending quality of the sheet material is improved.

At present, the press brake crowning mainly has three types:

• geometric crowning
• hydraulic crowning
• mechanical crowning

Geometric crowning

Generally, the press brake manufacturer will not adopt this type of crowning method.

Working table fixed convex, that is, at the time of manufacture, the worktable was machined into arc shape with a slightly convex in the middle to compensate for the deflection caused by bending.

To make the appropriate correction for the upper mold, the middle part of the mold slightly curved, so when the slider occurs upward deflection deformation, the upper die edge basically tends to be straight, therefore it keeps each bending point along the bend line generate the same bending force for the plate.

The advantages of the geometrical compensation method are low cost and easy to manufacture, but there are some disadvantages which can only realize the compensation of fixed deformation and small compensation flexibility.

In addition, the compensation block arc correction quantity needs to pass through the precise calculation. The calculation method which based on the mechanics’ theory and the finite element calculation all has the certain error, therefore, even this kind of crowning method can achieve the deflection compensation effect, but it is very difficult to realize.

Hydraulic Crowning

Mainly used on the electro-hydraulic synchronous CNC press brake, because the amount of compensation needs to be controlled by the controller, such as DA52S, DA66T controller etc.

In addition, install two hydraulic cylinders at two sides of the press brake frame and install another two-auxiliary hydraulic cylinder in the middle of the machine. When the ram down, the auxiliary cylinder filled with liquid oil and go downward. During the bending process, hydraulic oil inlet into the auxiliary cylinder, so that the slider generate downward deflection for compensation.

Install the auxiliary hydraulic cylinder in the lower part of the worktable. During the bending process, it generates an upward force on the worktable, which forms the automatic crowning system.

The pressure compensation device is composed of several small oil cylinders, comprising an oil cylinder, a motherboard, an auxiliary plate and a pin shaft, and a compensating cylinder is placed on the worktable. The pressure compensation system is formed with a proportional relief valve.

During working, the auxiliary plate supports the oil cylinder, the oil cylinder holds up the motherboard up, just overcomes the deformation of the slider and the worktable. The convex device is controlled by a numerical control system, so that the preload can be determined according to the thickness of the plate, the opening of the die and the tensile strength of the material when bending different sheet materials.

The advantage of hydraulic crowning is that it can realize the deflection compensation for continuous variable deformation with large compensation flexibility, but there are also some disadvantages of complex structure and in relatively high cost.

Mechanical Crowning

Most widely used crowning method for the ordinary press brake, with good compensation effect and low cost. In real operation, it is very convenient and easy for operators.

Mechanical crowning is a kind of new deflection compensation method, which generally uses a triangular oblique wedge structure.

The principle is that the two-triangle wedge block with α angles, the upper wedge moving is fixed at x-direction and can only move in Y-direction. When the wedge moves the △x distance along the X-direction, the upper wedge moves up the H distance under the lower wedge force.

Regarding existing mechanical compensation structure, two bolster plates are placed in full length on the worktable, the upper and lower plates are connected through the disc spring and bolts. The upper and lower plates are consist of a number of oblique wedges with different slopes, through the motor drive to make them relatively moving and forming an ideal curve for a set of convex position.

Press Brake Application

Press brakes are widely used in energy, transportation, automobile, machinery, metallurgy, shipbuilding, aviation, military, agricultural machinery, petroleum machinery, power generation industries.

 

Press Brake Toolings

Press brake standard toolings including the punch and die, for the stamping and separation of sheet metal. The die for forming has a cavity, while for separation it has a blade edge.

See also:

• Press Brake Dies: The Ultimate Guide

Press Brake Gauge

The commonly used press brake gauge including angle gauge, angle ruler and venier.

 

TOP Press Brake Manufacturer List

The following two lists will definitely help you sort out the ideal press brake manufacturers for you.

• Top 10 Press Brake Manufacturers
• The list of world top 100 machine tools manufacturer

 

Press Brake Training

The best training provides you with the manuals, you can learn wherever you are, and anytime you want. Here I collect some of the most popular manuals for your reference:

• Press Brake Estun E21 Operation Manual
• Press Brake Estun E200P Operation Manual
• Press Brake Estun E300 Operation Manual
• Press Brake Delem DA41 Operation Manual
• Press Brake Delem DA52s Operation Manual
• Press Brake Delem DA-66T Operation Manual

You can also check out the definitive guide to press brake bending basics to learn more information about sheet metal bending.

Press Brake Safety

I believe here I don’t need to explain how it is important to take note of the safe operation of the press brake. You can check out the press brake safety tips to know more.

If you press brake operators, you should read below press brake common failure analysis carefully, probably it will help you solve big problems.

• 56 Press Brake Bending Problems (With Analysis and Proved Solutions)

 

Press Brake Maintenance Checklist

Before the press brake maintenance or cleaning of the machine, align the top punch with the bottom die before drop it, then shut down the press brake until the completion of the work. If required to start the machine or other operations, select the jog mode, and ensure safety.

The maintenance content is as follows:

Hydraulic oil circuit

• Weekly inspection of the oil levels in oil tanks, it should also be checked for hydraulic system maintenance. If oil level below the oil window, the oil tank should be filled with hydraulic oil;
• The hydraulic oil used in press brake is ISO HM46 or Mobil DTE25;
• The new press brake should change the oil after 2000 hours running, after that change oil for every 4,000-6,000 hours operation. Clean the fuel tank for every oil changing;
• System oil temperature should be between 35℃~60℃, no more than 70 ℃, the too high temperature will lead to deterioration of oily and accessory damage.

Filter

• Each time during the oil change, the filter should be replaced or thoroughly cleaned;
• If the press brake has the related alarm or the oil is not clean, or some other unusual things for the filter, the filter should be replaced;
• Clean the air filter on the tank every 3 months, preferably change it every year.

Hydraulic Parts

• Monthly cleaning of hydraulic components (substrates, valves, motors, pumps, tubing, etc.), to prevent dirt from entering the system, cannot use detergent;
• One month after the use of the new press brake machine, check whether the bending point of the tubing has deformation, if yes then it should be replaced. After the use of two months, should be fastened to all parts of the connection, the press brake should be shut down to ensure that there was no pressure of the system when doing this work.

 

Press Brake Inspection Checklist

Brief Description

• Standard test order does not mean the actual test order, it is changeable
• Adjusting the mechanism and parts which may affect the precision is prohibited during the test process.
• Workpiece precision inspection conditions:
• Requirements on workpiece
• If the workpiece is made by an A3 steel plate, it’s tensile strength Qb≤ 450MPa
• The number of workpieces shall not less than 3 pieces
• The opening size of lower die shall be 8-10 times as large as workpiece thickness
• The workpiece should be put on the worktable middle position
• Bending angle is 90°
• Measure from end 100mm

The inspection method and accuracy range shall be based on GBT-14349-2011-Metal Press Brake- Precision

Note: the worktable is floated, inspection G2, G3 shall refer worktable vertical plate as a benchmark.

 

Press Brake Bending Radius

There should have a bending radius for sheet metal bending, it should not be too large or too small, and should be chosen appropriately. If the bending radius is too small, it will cause cracking at the bend position; if the bending radius is too large, it is easy to rebound.

The optimum bending radius of different thickness of various materials (bend inner RADIUS) see table below:

The data in the table above is the preferred data for reference only. In fact, the rounded corners of press brake are usually 0.3, and a small number of the rounded corners of the press brake punch is 0.5.

For ordinary low carbon steel plate, anti-rust aluminum plate, yellow copper, purple copper etc, the inner radius 0.2 is no problem, but for some high carbon steel, hard aluminum, super-hard aluminum, the use of 0.2 radius will lead to bending fracture or the outer radius crack.

 

Press Brake Tonnage Calculation

• How to Calculate Press Brake Tonnage (By Chart, Formula & Calculator)
• Press Brake Tonnage Calculator

 

DIY Press Brake

Sometimes, the workshop owners need to bend steel, just for several pieces of steel, so buy a completely new press brake is not the best way. That’s why they want to build a press brake on their own, just to diy some simple press brake for bending purpose.

Therefore, the homemade metal brake press is what they want.

Here I collect some videos for the home build press brake, hope you can make one with the tutorials been provided.

Press Brake Wiring Diagram

Different manufacturers will design different press brake wiring diagram. When you purchase it, the suppliers will send you the wiring diagram together with the hydraulic diagram as well as the installation and operation manuals. If you did not see it when you receive the machine, please contact your supplier immediately.

The following press brake wiring diagram is from us, just for your reference.

 

Press Brake Controller

There are two popular press brake controllers, one is from China’s Estun, which is the sole agent of DELEM control in China, the other one is DELEM from Holland.

See also:

• How to Choose Press Brake Controller, NC or CNC?
• Press Brake Controller: E21 V.S E200P

The key factor for press brake including two parts, one is the machine itself, such as the quality, accuracy, etc, the other one is the control system.

The installation manual and operation manual of press brake controllers in PDF form can be downloaded from below link.

Operation Manual:

• Press Brake Estun E21 Operation Manual
• Press Brake Estun E200P Operation Manual
• Press Brake Estun E300 Operation Manual
• Press Brake Delem DA41 Operation Manual
• Press Brake Delem DA52s Operation Manual
• Press Brake Delem DA-66T Operation Manual

Installation Manual:

• Press Brake Estun E21 Installation Manual
• Press Brake Estun E200P Installation Manual
• Press Brake Estun E300 Installation Manual

 

Press Brake Programming and Setup

The above operation manual and installation manual of press brake controllers have explained the programming and setup very clear, please download it from above and read it carefully.

 

Press Brake User Manual

How to use the press brake

According to fabricate Q235 mild steel with hydraulic press brake to do a simple introduction:

• First, connect the power, turn on the key switch on the control panel, and then press the pump to start, then you can hear the oil pump rotating sound. (The machine does not run at the current time)
• Stroke adjustment. You must pay attention to stroke adjustment for press brake operation, it must be tested before bending. Must ensure that there is clearance which equals the thickness of the plate when the top punch down to the bottom of the lower die. Otherwise, the mold and press brake will be damaged. The adjustment of the stroke also has the electric quick adjustment and the manual fine adjusts.
• Regarding V-width choosing, generally, the width of the V opening should be 8 times the thickness of the plate. For example, for bending 4mm plate, you should choose 32mm V-opening die.
• Back gauge adjustment generally has electric fast adjustment and manual fine-adjustment.
• Step down the pedal switch to start bending, you can loosen at any time. If loosen the foot, the bending machine will stop, step again to continue bending.

Here we provide press brake operation manuals to guide you operating press brake. Download the press brake operating instructions here.

See also:

• Precautions for Sheet Metal Z-bending and N-bending

 

Press Brake Forming Process Technology

 

Press Brake Tips

If you read the articles on our bending category, you will see various different types of articles writing about press brake and sheet metal bending. So take your time to read it carefully for learning. You will benefit a lot from it.

A quick calculation method of sheet metal bend expansion

For sheet metal bending and expansion, one side of the sheet will be elongated, the other side will be compressed. The affecting factors including material type, material thickness, heat treatment and bending angle.

 

Expand Calculation Principle:

• During the bending process, the outer layer is subjected to tensile stress, and the inner layers are subjected to compressive stress. There is a transition layer which is neither tensile nor pressure from pull to pressure, which is called the neutral layer. The length of the neutral layer remains unchanged in the bending process, the same as the length before the bending, so the neutral layer is the basis for calculating the expansion length of the bending piece.
• The position of the neutral layer is related to the degree of deformation.

When the bending radius is larger and the bending angle is small, the deformation degree is small, and the neutral layer is near the center of the sheet thickness; When the bending radius becomes smaller and the bending angle increases, the degree of deformation increases, and the position of the neutral layer moves toward the inner part of the bending center gradually. The distance from the neutral layer to the inside of the sheet is expressed in λ.

 

Basic Formula for Expansion Calculation:

Expansion length = inner layer + inner layer + compensation amount

Calculation of minimum bending edge of one bend

The starting state of the L-bend is shown in the following illustration:

Reference table for bending inner R and minimum bending height of the cold rolled sheet

The starting state of the Z-bend is shown in the following illustration:

The minimum bending size (L) of the sheet metal corresponding to Z-bend for materials with different thickness is shown in the following table:

See also:

• How to Calculate the Min Bending Edge of Sheet Metal

Press Brake Bending Allowance (Tolerances)

1) Tolerance Standards for Common Bending

2) Tolerance Standards for Z Bending

3) Tolerance Standards for V Bending

4) Tolerance Standards for U Bending

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