Press Brake

How to Choose The Hydraulic Press Brake

CNC press brake

The hydraulic press brake feature is different in its processing field and process, so it is used as a comprehensive consideration when buying the hydraulic press brake as a purchaser.

DA66T CNC Press Brake
DA66T CNC Press Brake

It is best to carefully consider which model to buy in terms of the end-use of the machine, the amount of deflection that may occur in the known machine, and the bending radius of the part. Of course, as a decision-maker, you have the responsibility to understand the equipment’s performance, processing range, processing function, processing accuracy, etc. in detail. This responsibility is actually no small matter. Once you choose an improper choice, your production cost will rise, and the hydraulic press brake cannot expect to recover the cost. Therefore, there are several factors that must be weighed when purchasing!

DA41T Press Brake
DA41T Press Brake

Workpiece

The first important thing to consider is the parts you want to produce. The point is to buy a machine that can complete the processing task with the shortest workbench and the smallest tonnage.

Carefully consider the material grade and the maximum processing thickness and length. If most of the products produced are mild steel with a thickness of 3mm and a maximum length of 2500mm, then the free bending force does not need to be greater than 80 tons. However, if you are engaged in a large number of bottomed die forming, perhaps you should consider a machine tool of about 150 tonnages.

Bending Workpieces
Bending Workpieces

If the thickest material to be bent in production is 6mm, and the length of 2500mm is free to bend low-carbon steel, then it is necessary to consider the need for a bending machine of more than 100 tons.

If you bend some with a bottom concave die (correction bending), then a larger tonnage bending machine is needed. If most of the workpieces to be bent are 1250mm or shorter, then considering that the tonnage of the bending machine is almost halved, thereby greatly reducing the purchase cost. Therefore, the length of the processed parts is very important to determine the specifications and models of the new models.

Torsion

In the bending process of the bending machine, especially when bending long-size workpieces, the bending will occur. The longer the workpiece, the greater the degree of deflection. Under the same load, the deflection of the 2500mm model table and the slider is 4 times that of the 1250mm model.

This means that a shorter machine requires fewer shim adjustments to produce qualified parts, reducing shim adjustments and shortening preparation time. However, the current numerical control hydraulic bending machine has added hydraulic deflection compensation function in the production design, which reduces the adjustment of the equipment by the production operator, and at the same time improves the bending accuracy and production efficiency.

The hydraulic deflection compensation function is controlled by the numerical control system. The hydraulic oil enters the compensation cylinder through the magnetic servo valve to lift the worktable upward. At the same time, the deflection compensation force increases with the increase of the bending force, which plays a role in deflection compensation.

The quality of the processed material is also a key factor. Compared with low-carbon steel, the load required for stainless steel is usually increased by about 50%, while most of the material made of soft aluminum is reduced by about 50%. The relevant standard bending pressure parameters can be obtained from the bending machine manufacturer. The table shows the required bending force per 1000mm length under different thicknesses and different materials.

Bending Parts
Bending Parts

Part Bending Radius

In the process of bending products, the bending angle radius of the workpiece is also a factor to be considered. When using free bending, the bending radius is 0.156 times the opening size of the V groove.

During the free bending process, the opening size of the V-groove should be 8 times the thickness of the metal material. For example, when using a 12mm V-groove opening size to bend 1.5mm mild steel, the bending radius of the part is about R=1.9mm. If the bending radius is close to the thickness of the material or smaller than the thickness of the plate, the bottom die must be used for forming. However, the pressure required for forming with a bottom die is about 4 times greater than that of free bending.

Bending Radius
Bending Radius

When performing free bending, pay attention to the gap between the upper mold and the lower mold at the bottom of the stroke, and the excessive bending that is sufficient to compensate for the spring back and keep the material at about 90°. Generally, the spring-back angle of 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 lower die.

Therefore, it is generally free to bend the upper and lower molds, and the mold angle is generally 86 ~ 90°. At the bottom of the stroke, there should be a gap slightly larger than the thickness of the material between the upper and lower molds.

The forming angle is improved because the tonnage of bending with the bottom die is larger (about 4 times free bending), which reduces the stress that usually causes spring back in the bending radius. Imprint bending is the same as bending with a bottom concave die, except that the front end of the upper die is processed to the required bending radius, and the gap between the upper and lower die at the bottom of the stroke is smaller than the material thickness. Since enough pressure (approximately 10 times free bending) is applied to force the front end of the upper die to contact the material, it is basically avoided.

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

Bending Process
Bending Process

The Hydraulic Press Brake Precision

Bending accuracy requirements are a factor that needs to be carefully considered. It is this factor that determines whether you need to consider a CNC bending machine or an ordinary NC bending machine. If the bending accuracy is within ±0.5° and cannot be changed, you must focus on the CNC bending machine. The repeatability of the slider of the CNC bending machine is generally guaranteed to be within ±0.01mm, and the precise angle of forming must use such precision and a good mold.

The repeatability of the slide block of the NC bending machine is ±0.5mm, and the deviation of ±2~3° will generally occur under the condition of using a suitable mold. In addition, CNC bending machines are equipped with a rapid die-loading CNC system and die-loading fixtures. When you need to bend many small batches of parts, this is an indisputable reason for consideration.

DA66T Controller
DA66T Controller

The Hydraulic Press Brake Tooling

Bending molds also directly affect the accuracy of bending. Therefore, it is necessary to check the wear of the mold by measuring the length from the front end of the upper mold to the shoulder and the length between the shoulder of the lower mold.

For conventional molds, the deviation per 10mm should be about ±0.01mm, and the total length deviation should not be greater than ±0.15mm. As for the precision grinding mold, the accuracy per 100mm should be ±0.005mm, and the total accuracy should not be greater than ±0.05mm. It is best to use fine grinding molds for CNC bending machines, and conventional molds for NC bending machines.

WILA Quick Clamp
WILA Quick Clamp

Electro-Hydraulic Control System

  • Closed-Loop

Closed-loop is also called a feedback control system. The system compares the measured value of the system output with the expected given value to generate a deviation signal and then uses the signal deviation to control and adjust, so that the output value can be close to the desired value. For example, when driving, people first have a preliminary perception of the driving direction of the car in the brain. During the driving process, people observe the driving direction of the car with eyes, and compare the driving direction of the car with the expected direction. In this process, the direction is continuously adjusted, and finally, the driving direction of the car is continuously approached to the target direction, thereby forming a closed-loop control.

Closed-loop control is based on the operating conditions of each part of the machine tool, with high accuracy and response speed. Since the closed-loop control system involves many elements, compared with the open-loop system, the structure of the whole system is more complicated and the price is higher.

Hydraulic Valve
Hydraulic Valve
  • Open-Loop

Open-loop is compared to closed-loop, that is, open-loop control does not feedback the current system control results. For example, throw things. Once something is thrown out, people cannot control what is thrown out. Because once things leave the hands of people, people’s control over things stops immediately.

Therefore, in the open-loop system of the bending machine, the accuracy of bending depends on the accuracy of each part of the machine tool. The system cannot control and compensate for the parameter changes produced during the bending process, resulting in low bending accuracy. Once the outside of the machine tool is disturbed, the internal parameters of the machine tool will change. However, in terms of system design, the open-loop design is simpler and more stable. Whether it is the installation of the machine tool in the early stage, or the maintenance of the subsequent machine tool, it is easier.

Mini CNC Press Brake In Sale

Estimated reading time: 9 minutes

Related Posts

2 thoughts on “How to Choose The Hydraulic Press Brake

  1. Carlosjulio Pedrozahurtado says:

    I have one machine , it has some question, could you help me ?

    1. Ivy Zhang says:

      do you buy the machine from our company?
      if possible, could you send me the video to show the question?
      My mail is ivy@harsle.com

Leave a Reply

Your email address will not be published.