Before reading this article, pls spend some time to watch below video which shows you various different bending methods. You will learn a lot from it.
In general, press brake dies can be divided into the upper die, the lower die, guide rail, lower die base etc.
These bending dies have a wide range of versatility, most of them can be fabricated.
Commonly Used Press Brake Dies
In order to extend the service life of mold, the press brake punch and dies are designed with rounded corners as far as possible. Commonly used brake press dies are as follows.
Generally, the height of flanged edge L≥3t (t=plate thickness). If the height of the flanged edge is too small, even use bending die is not conducive to forming.
The Classification of Press Brake Dies:
|Punch Type||Main Application|
|Straight Punch||Fabricated angles ≥90°|
|Goose Neck Punch||Fabricated angles ≥90°|
|Pointed Punch||Fabricated angles ≥30°|
|Punch Type||Main Application|
|Sing V Die||1. While V angle = 88°(ref), able to bend angles ≥ 90°|
|Double V Die||2. While V angle = 30°(ref), able to bend angles ≥ 30°|
Press brake segment die
Generally, the standard length of press brake punch and die set is 835mm. In order to bend workpiece in different length, the punch and die are separated into below size: 10+15+20+40+50+100+100+200+300=835
Press Brake Dies Materials
Generally, the materials of press brake die including T8 steel, T10 steel, 42CrMo, and Cr12MoV.
Cr12MoV is also good material. The using performance can be satisfied, the process performance is also good, but the price will be high.
42CrMo is a high strength alloy quenched and tempered steel with high strength and strong toughness. It can work under the temperature of -500℃.
It mainly requires high strength, high toughness, and good wear resistance.
How to Choose Press Brake Dies
The different die should be used for fabricating different workpiece. You need to know the fabrication parameters of the press brake machine as well as the die very well, then it is possible for you to choose the right press brake die to match each other.
The parameters of press brake including stroke, working ability, daylight (open height), middle plate type.
The parameters of the die including upper die shank type (match middle plate), max bending force etc.
A. How to choose press brake parameters
Press brake die height formula
— Stroke (mm)=daylight – middle plate height – upper die height – lower die height -(lower die height – 0.5V+t)
t = plate thickness（mm）
Given: daylight 370mm, max stroke 100mm
Reach: stroke = 370-120-70-75-(26-0.5*8+t) = (83-t)mm
Note: 0.5V < stroke < max stroke
Please note the lower die base also have many different heights, which is used for different fabrication purpose. So don’t forget this when choosing lower die base.
Different tool & die cluster can obtain different combined height for different fabrication purpose of parts.
B. How to choose press brake dies parameters
Upper die shank type
Upper die shank has three types to match different middle plate.
Upper die shape
Common standard upper die:
Upper die point radius & top angle
Common upper die point radius including:
（1）0.2R （2）0.6R （3）0.8R （4）1.5R （5）3.0R
How to choose proper press brake die point radius: choose 0.6R for plate thickness<3mm
Standard upper die point angle including: 90°, 88°, 86°, 60°, 45°, 30°, etc.
The dihedral angle of the die should less than fabrication angle.
For example, if the workpiece’s bending angle is 90°, you should choose the die with 88° point angle.
Lower die type
Generally, the lower die has a single V type and double V type, among which it is separated into the separated die and full-length die. The different die is applied to a different fabricating purpose.
However, the single-V die has a much wider application than double-V die, while the separated die is more widely used than full-length die.
Lower die V width, V groove angle
V groove choosing & plate thickness (T):
The V angle of the lower die is the same as upper die’s angle.
In order to choose small V die for bending purpose in some special case, the spread of every punch should increase 0.2mm
Min bending size
Normally min bending size:
— L-type: slot width/2 + plate thickness
— Z-type: slot width/2 + plate thickness * 2
Press Brake Toolings Drawings
Spring-back angle Δα=b-a
In the formula:
b—The actual angle of the workpiece after spring-back
Spring-back Angle for single 90 o free bending
|Steel||r/t||Plate Thickness t (mm)|
|Medium carbon steel σb=400-500MPa||<1||5°||2°||0°|
|Hard brass σb=350-400MPa||1-5||6°||3°||1°|
|Hard bronze σb=350-400MPa||>5||8°||5°||3°|
|High carbon steel σb>550MPa||<1||7°||4°||2°|
The factors that affect the resilience and the measures to reduce the spring back:
- Mechanical properties of the material
The spring back angle is proportional to the yield point of the material and is inversely proportional to the elastic modulus E. In order to reduce the spring back for those sheet metal which requires high precision, the low carbon steel should be the first consideration, do not choose high carbon steel and stainless steel.
- The larger the relative bending radius r / t, the smaller the degree of deformation, the greater the rebound angle Δα.
This is one very important concept. In the case of material properties permitting, the small bend radius should be chosen to improve accuracy. In particular, attention should be made to avoid designing large arcs as much as possible, as shown in the following figure. Such large arcs have a greater impact on production and quality control:
Press Brake Dies Installation and Commission
Press brake is a kind of forging machinery, mainly applied in the metal processing industry. The press brake toolings are composed of a lot of parts.
Therefore, when installation must check the status of the equipment, and carry out in strict accordance with the steps. At the same time, pay attention to safety in the installation and commissioning process.
Well, what are the precautions during press brake toolings installation and commissioning?
- CNC press brake adjustment, before the installation, first of all, to adjust the machine performance, the process must be patient and serious. Check the machine for dust and used iron debris, etc., to carry out the necessary cleanup to reduce the late trouble.
- CNC press brake slider stroke adjustment. Pay attention to check the thickness of the mold and the normalness of the upper and lower mold proportion. Normally, the mold should be controlled at the switching point of the stroke line.
- Stroke module adjustment, that is to adjust the upper limit point of the stroke. When the module up to the highest level, set the switch and set aside the stay position of the slider. At the same time, reduce the speed of the module when down moving, better protect the machines and molds.
- Gad adjustment. Mainly to measure the distance between the upper module and the lower module. The specific gap is set according to the folding plate.
- Angle adjustment. The angle adjustment has a certain relationship with the product. Generally, bending 90° molds, the middle angle must larger than the angle between the two sides. The tightness can be adjusted according to the screw. Adjust the pressure according to the pressure gauge to avoid mold chipping.
Determinants of Press Brake Dies Accuracy and Angle
Whether the press brake toolings production standards lies in the accuracy and angle?
Imagine that if the press brake toolings accuracy and angle cannot be guaranteed, then, it is likely to lead to the entire production into the non-standard road.
(A) Factors that affect the accuracy
- wear of the bending machine mold;
- eccentric of press brake upper mold and lower mold
- the back stopper is not set in the specified position, or the surface been blocked by the burr;
- the workpiece itself;
- processing steps.
(B) Factors that affect the accuracy of the angle
- bending machine mold deformation, wear;
- mold shape;
- work surface flatness;
- the degree of parallelism from the horizontal support plane close to the upper mold to the work surface;
- the verticality of the slider stroke to the work surface;
- bending position;
- cutting method.
Top 10 Considerations When Using Press Brake Toolings
How to use press brake toolings?
Press brake toolings including L-shape, R-shape, U-shape, Z-shape bending.
Press brake upper die mainly include 90°punch, 88°punch, 45°punch, 30°punch, 20°punch, 15°punch, etc, while the lower die includes dual-V die and single-V die with various slot width from 4V to 18V. Besides, there are R-lower die, acute angle lower die and hemming/flattening die.
The punch and die include separated and the whole length. The separated upper die include 300mm,200mm,100mm,100mm,50mm,40mm,20mm,15mm,10mm, while the whole length is 835mm.
The separated lower die include 400mm,200mm,100mm,50mm,40mm,20mm,15mm,10mm, while the whole length is 835mm.
① Press brake bending mold is made of high-quality steel products made by special heat treatment, with high hardness, not easy to wear and tear, able to bear great pressure, but each mold has its limits pressure: ton/meter, so choose the length of the mold when using the press brake toolings correctly, that is, how much pressure per meter to bear, must not exceed the marked limit pressure.
② In order not to damage the die, we stipulate that align with the original point, it is necessary to use the upper and lower modes with the length of 300mm to do the alignment. The upper mold lower mold of the same height only can be used after the alignment.
It is strictly forbidden to use the split small mold for the alignment, and the alignment must be based on the regulated pressure inside the press brake machine.
③ In the use of the mold, due to the various height of the molds, the mold can only be used in a press brake machine with the same height, which can not be used in different heights.
④ When using the press brake toolings, choose the right upper die and lower die according to the sheet metal hardness, thickness, and length. Generally, the slot width of the lower die should be 5-6 times the thickness of the metal plate, while the length should be longer than the sheet. The harder and the thickness of the sheet metal material, the wider of the lower die slot.
⑤ When bending an acute angle or a dead angle, 30° punch should be chosen. Bending the acute angle first, then flattening. When bending R angle, R punch and R die should be chosen.
⑥ In bending the long piece of work, it is better not to use a segmented mold in order to reduce the indentation at the mold connection position, and it is better to choose a single slot die, because the exterior angle R of lower die with single slot V is big, not easy to generate bending indentation.
⑦ When selecting the top punch, we should know the type of die and the parameters well, and then decide which punch should be used based on the shape of the product that needs to be formed.
⑧ When bending hard or too thick product, do not use press brake die to bend steel bar or other cylinder products.
⑨ When using the press brake mold, the operators should have a clear mind. The upper die and lower die of press brake machine should be locked after alignment, in case the punch fall down to hurt the workers or damage the die. Attention should be paid when adding pressure during operation process, do not add too much pressure and pay attention to the data changes on the display screen.
⑩ After finish using the press brake toolings, put the die back in the press brake die cabinet (press brake store) according to the marking, clean the dust on the mold regularly, and apply the anti-rust oil to prevent rust which will reduce the precision of the toolings.
U Bending with Press Brake Dies
U bending always use gooseneck die, we currently use three types: small, middle, large.
U bending size range
Note: A size do not include plate thickness
Press Brake Dies Cabinet
The cabinet will be convenient for you to store the press brake punches and dies.
20 Press Brake Toolings Application
Press Brake Dies Manufacturing Technique Analysis
The high precision press brake toolings occupy a very important position and function in the sheet metal processing system.
However, due to the differences in equipment, materials and technology of various manufacturers in the process of manufacturing bending die, the life and the precision gap of bending die are greatly caused.
Therefore, this article makes a brief analysis and expatiation on some related content in the production process of bending die and hopes to give some reference to sheet metal users when choosing bending molds.
Sheet metal processing industry is an important support force in the machinery manufacturing industry.
The bending process is an indispensable process in sheet metal fabrication, and the daily use frequency is relatively high.
However, in order to effectively improve the quality and production efficiency of the parts, it is very important to choose a good bending die.
The main content of this article is how to realize the good quality of bending die from production.
The Status of Press Brake Toolings
At present, there are several difficulties for sheet metal users in the demand of press brake toolings:
(1) There is a certain gap compared to the bending die made in Euro, for example, the mold brand is uneven, the mold quality is not stable, the precision is not good.
(2) Using imported bending die, the price is high and the delivery time is long.
(3) If the demand is non-standard mold, the communication channel with the mold manufacturer is less, and the timeliness is poor;
(4) The industry did not implement a set of mold standards, leading to the manufacturers of the mold cannot be exchanged. In turn, the user of sheet metal have no choices when using the mold. They can only purchase the bending from the press brake manufacturers.
Core Elements of Mold Quality
The press brake bending dies material should choose 42CrMo produced by regular steel enterprises.
Compared with other materials, 42CrMo materials have excellent mechanical properties.
It has the characteristics of high strength and hardenability, good toughness, small deformation during quenching, high creep strength and persistent strength at high temperature.
The bending die materials also have T7A and T8A on the market.
Although these materials can be treated by heat treatment to certain surface hardness, due to the shallow depth of the quenching layer, the tool core is soft and easily deformed.
Due to price constraints, many of the bending die materials are relatively inexpensive materials.
In order to obtain qualified and uniform hardness, the process of heat treatment is very important.
The hardness of the bending die is 47±2HRC, which means that the hardness of any position of the mold should be between 45~49HRC. And the depth of the hardness layer is over 10mm.
The approximate process of heat treatment is:
First weld the hoisting ring on the end face of the blank mold after rough milling, then put it into the heating furnace up to 880℃. When the whole mold reaches the temperature→discharge→quenching oil→cooling→check deformation→cold correction→tempering→hardness testing.
The tempering time is different according to the batch.
Complete the above steps and basically finish the heat treatment of rough milling blank mold.
The above steps have several key points:
- Suspend heating and suspend quenching oil cooling on end welding rings.
Due to the shape of the bending die is irregular geometry, when it is cooled, the cooling is uneven and varies speed, which will result in large deformation and uncontrollable.
Therefore, only the suspended combustion mode and suspended cooling can effectively minimize the deformation of the mold.
In the process of heating and cooling, the hoisting ring is welded together with bending die before put into the heating furnace.
If the mold is overweight, it is easy to cause the fracture between hoisting ring and mold under the temperature of 880 ℃.
Due to the heating restriction of heat treatment, the bending die factory insists on making the press brake bending die standard length 835mm.
If the mold has defective in heat treatment, the service life of the die will be greatly reduced.
- Cold correction.
After the product comes out of the oil furnace, due to the irregular shape of the mold itself, the deformation amount is not controllable.
Therefore, after the mold is out of the oil furnace, each product needs to detect deformation.
If the deformation is too large, cold correction is required.
Many manufacturers choose to use the old-fashioned method of flame gun burning to rectify the deformation.
The heavy burning position will cause local softening, and there are safety hazards in daily use.
The following service life of the bending die should be achieved after strict heat treatment process control:
When bending the stainless steel plate with the thickness of 2.0mm (including 2.0mm) and the cold plate under 3.0mm (including 3.0mm), adopting the lower die with V opening 6-8 times the thickness, The R angle of the bending edge can withstand the frequent bending of 2000000 times (convert into years, calculated based on the bending die can be used for 200,000 times within a year, and can be used for 10 years) and the abrasion of the cutting edge within 0.03mm.
Is the low price really cost-effective?
If calculated based on the number of uses, you will see that it’s not like that actually.
Only professional heat treatment technique and qualified material can ensure the bending die durable.
Precision CNC forming grinding
The mold material and heat treatment mentioned in the first two points are mainly concerned with the life of the bending die.
Then the processing method of the cutting edge and V groove are the key processes to ensure the precision of the die.
There are the traditional grinding method and CNC Precision Grinding.
In the whole manufacturing process The traditional grinding method, most are human intervention; however, for CNC grinding, the size formation and precision of the products are controlled by the equipment and CNC controller throughout the whole grinding process.
Therefore, the consistency and stability of the molds are fundamentally different.
It is also the difference between domestic and foreign manufacturers in the technique causing the bending die has no industry standard. Each manufacturer produces the mold with the size of their own.
If there is a uniform size standard, sheet metal users can be more independent when choosing the bending die manufacturer, without the need to accommodate a particular mold or manufacturer.
Currently, the most popular length of press brane bending die is 835mm, 500mm and 515mm.
Under the premise that the accuracy can be guaranteed, the lightweight mold can improve the production efficiency and reduce the labor intensity of the production personnel.
Fig.1 Commonly used top punch.
Fig.2 Different V slot ratios for the lower die