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Abstract: If you or your company are considering purchasing a press brake to increase the processing capability of parts and improve production efficiency, please read the following information carefully. This could be of assistance to you or your company.
Many corporate decision-makers have experienced economic losses due to purchasing the wrong equipment.
I am not overstating when I say that this scenario occurs frequently.
Hycules has been manufacturing sheet metal processing equipment for several decades, and we have witnessed many such incidents.
However, suppose you are willing to take the time to conduct thorough research. In that case, you can clearly understand the type of press brake you or your company needs, the critical factors to consider when purchasing a press brake, and how to make the correct and practical decision.
For a company looking to purchase a press brake, the manufacturers will provide various pricing options with multiple configurations.
However, as a buyer, considering all factors can be challenging. Where should you start to decide which type of press brake to choose?
The best approach is to assess your or your company’s needs and use them as the core criteria when selecting a press brake.
Where should you start? The following press brake purchasing guide may be helpful to you or your company. Let’s delve into it together.
Contents
What is a press brake?
You may already know the definition of a press brake, but we still want to emphasize what it is.
Many first-time buyers of press brakes or those purchasing them for their companies may need to become more familiar with what it is.
Bending machines are used to bend sheet metal and consist of a table, ram, backstop, and hydraulic cylinders. Using simple punches and dies, we can easily bend sheet metal and shape it into a specific geometry.
The size of the opening in the V-groove of the lower die varies when turning different thicknesses of sheet metal and the required bending pressure varies. (The bending pressure required can be calculated from the bending pressure table.)
What are the commonly overlooked considerations when purchasing a press brake?
1. Market share
In today’s online ecosystem, when you search for a product online, you will likely see many manufacturers exaggerating their effects while discrediting their competitors. However, the most reliable product quality indicator is often its market share. You can determine which machines and equipment are widely used and well-received in different industries based on user feedback and which could be better and recommended. User feedback and reputation are essential because they offer primary perspectives and direct interaction with the product. We recommend paying attention to this feedback.
2. Enterprise scale
When considering a product purchase, it’s essential to feel the manufacturer’s reputation and the quality of their after-sales service. In today’s internet age, it can take time to discern a company’s trustworthy reputation from marketing claims. However, by examining the market share of a particular product brand in your industry, you can better understand its popularity and reliability.
It’s also essential to look for a reputable and healthy company, as this often indicates that they are trustworthy and can provide reliable after-sales service for users. To assess a company’s scale and strength, it’s recommended to personally visit their factory to understand their formalities and production strength. If a visit is not possible, online factory inspections can also be conducted through video or other online methods.
Hycules Machinery considers the different situations of users and provides online factory inspection services. Click here to start your online factory inspection journey.
3. Machine quality
The two points above are common sense terms that have nothing to do with the machine itself. Now let’s discuss the quality of the machine.
If you are not yet familiar with bending machines, comparing the quality of the machines may require a lot of work.
The size and weight of the machine are key factors to consider. As a rule, wider and heavier machines are stronger and of higher quality, as they use mainly steel in the machine.
Another key factor is precision. Ideally, you can bring (or ship) the parts to be machined to the factory to test the accuracy of the machine, but this is only sometimes possible. The accuracy of the machine is influenced by the backstop, the strength of the machine body and the tooling.
If the backstop is still chain driven, the accuracy of the machine cannot be guaranteed. Aluminium beams may look attractive, but they may warp after repeated impacts.
The third important factor is the screw and guide. The best companies often choose to use ball screws and linear guides.
Finally, the strength of the body strut is directly related to the thickness of the sheet chosen. If the container is too thin, the strength of the body will be significantly reduced.
4.Punches and dies
If we compare bending machines to soldiers, the tools are their weapons. If these weapons could be of better quality, it would be easier to defeat the enemy.
So, how do we evaluate the quality of the workpiece?
The most critical factor is the material used. Currently, 42CrMo is considered a good quality material for bending machine tooling, while other materials, such as Cr6W2Si, are also considered to be good choices. The average user may need to learn about this to differentiate between these materials.
In addition, most moulds are high-frequency hardened. Some manufacturers use moulds that are only heat treated at the cutting edge. However, high quality manufacturers will use moulds that have been heat treated throughout.
Fully heat treated moulds have a hole in the mould, which is a clear sign of a general heat treatment.
It is worth noting that a fully heat treated tool is much more expensive to manufacture than a tool with a heat treatment at the cutting edge only.
Four guidelines for choosing a bending machine
When selecting a bending machine, the following four principles must be considered:
Principle one: the accuracy of the operation of the mechanical system.
It is well known that certain physical errors in bending radius are unavoidable, but what is of concern is the degree of deviation that can be tolerated by the user. For relatively uncomplicated machined parts, small differences in accuracy are acceptable. Nevertheless, most machined parts usually require high accuracy, mainly when these parts are used in production after bending.
Principle 2: The flexibility required by the mechanical system.
The greater the variety of parts to be machined, the greater the flexibility required of the bending machine. In other words, the hardware and software components of the bending machine should be designed to be user-friendly. It should allow for easy expansion to ensure maximum cost-efficiency. In this way, the time required to adjust the bending machine parameters can be minimised even if the user’s processing instructions change frequently and are repeated very few times.
Principle 3: Determine the capacity and size of the bending machine.
When selecting a bending machine, it is necessary to consider the size of the part, the pressure, the bending length, the stroke and the height of the structure.
Principle 4: The potential customer should also carefully consider the end use of the machine, the potential known deformations and the bending radius of the parts to be processed.
Seven factors to consider when buying a bending machine.
Bending machines differ from other CNC machines in terms of processing and technology. As a user of a machine, you must consider all relevant factors such as application, deflection, bending radius and other machined parts before purchasing a bending machine.
As a decision maker for equipment procurement, you must understand a press brake’s performance, processing range, functions, and precision.
This is a matter of concern, as any wrong decision can increase production and possibly unrecoverable costs.
Therefore, before purchasing a press brake, consider the following seven factors, which may help you make the right choice.
1. What kind of parts do you want to produce?
Your goal in purchasing a press brake is to efficiently process your production tasks, not to buy the smallest and lightest machine possible. Most importantly, you need to consider the material type of the metal sheet and its maximum thickness and length.
For a stainless steel sheet with a maximum thickness of 3mm and length of 2500mm, an 80-ton press brake utilizing air bending would meet the requirements. However, if you need to use a bottom die, consider purchasing a press brake of about 150 tons.
If you use a low-carbon steel sheet with a maximum thickness of 6mm and a length of 2500mm, a 100-ton press brake is suitable for air bending. However, consider a more significant CNC press brake if you need to use a bottom die.
For metal sheets with a length of 1250mm or less, a smaller CNC press brake is sufficient to meet your needs. This can significantly reduce your purchasing costs. The metal sheet’s size is critical in choosing the most suitable press brake.
2. Compensation system
Deflection errors are inevitable in the bending process of CNC press brakes, especially for longer workpieces.
The deflection of the press brake increases proportionally with the length of the workpiece.
Under identical loads, a press brake processing a 2500mm plate will experience four times more deflection compared to processing a 1250mm plate.
In other words, shorter press brakes with fewer shim adjustments can produce higher precision products.
Reducing shim adjustments can also shorten the preparation time of the press brake.
Fortunately, most CNC hydraulic press brakes have added hydraulic deflection compensation during manufacturing, reducing the need for operator adjustments and dramatically improving bending accuracy and production efficiency.
The CNC system controls this function.
An electromagnetic servo valve allows hydraulic oil to flow into the compensation cylinder, which causes the worktable to move upwards. As the working pressure of the press brake increases, the deflection compensation force also increases, efficiently compensating for any deflection.
Automatic offset compensation is another less efficient compensation method.
3. Material type
Compared to regular carbon steel plates, the bending pressure required for stainless steel plates increases by around 50% during the bending process. However, the needed bending pressure decreases by 50% for softer aluminum plates.
The press brake manufacturer can acquire the bending pressure parameters as per the standard.
The following data table shows the bending pressures required for 1000mm metal plates of various thicknesses and materials.
There is also a quick way to calculate the required bending pressure for a press brake. You can use our online press brake pressure calculator to calculate the necessary press brake pressure in tons.
4. Bend radius
During air bending, the opening size of the lower die V-groove should be greater than eight times the thickness of the metal sheet.
For example, if a press brake with a lower die V-groove opening of 12 mm is used to bend a low-carbon steel plate with a thickness of 1.5 mm, the bending radius should be 1.9 mm.
If the bending radius is approximately equal to or smaller than the thickness of the metal sheet, then bottom bending is recommended.
However, in this case, the required bending pressure will be four times that of air bending. When performing air bending, it’s essential to take note of the clearance between the upper and lower molds at the punch and die’s base, as well as the spring-back force of the metal sheet after being bent to a 90° angle. Typically, the molds will cause the press brake to have a spring back angle of less than 2 degrees during air bending.
Therefore, for standard upper and lower mold bending processes, the angle of the upper mold punch should be between 86° and 90°.
At the bottom of the bending stroke, there should be a gap slightly larger than the thickness of the metal sheet.
5. Bend angle
The punch angle is improved because a larger bottom die is used, with a bending tonnage four times that of the blanking die. This helps reduce the spring back force within the specified bending radius.
Bottom die bending is similar to blanking, with the only difference being that the front end of the punch is converted to the required bending radius. Since the clearance between the top and bottom dies at the bottom of the bending stroke is smaller than the thickness of the metal sheet, and the bending pressure (which is ten times greater than the blanking pressure) is sufficient, this results in a reduction in the spring back force. The front end of the punch will fully contact the metal sheet.
To guarantee the durability of the press brake and ensure high-quality end products, selecting a bending machine that employs the blanking bending technique with a bending radius more significant than the metal sheet’s thickness is advisable. This approach ensures high-quality end products while promoting the press brake’s long-term use.
6. Bending accuracy
Choosing between a CNC press brake and a conventional press brake depends on the precision required.
A CNC press brake should be considered if a precision of ±0.5 degrees is required and cannot be changed. The repositioning accuracy of the slider can be controlled to within ±0.01 mm.
For high-precision bending workpieces, a high-precision and high-performance press brake is required.
However, the repositioning accuracy of a conventional CNC press brake slider is about ±0.5 mm, which can still produce a deviation of ±2-3 degrees under appropriate conditions.
In addition, CNC press brakes are usually equipped with a CNC controller and quick-change punch fixtures. This should be the primary consideration if you must process many small parts.
7. Punches and dies
The selection of the press brake’s die directly impacts the precision of the bending process for metal sheets.
Therefore, it is crucial to inspect the punch and die carefully.
The dies come in various shapes, and different punches and dies are used for other parts.
To achieve the ideal shape of the part, the material’s physical properties are mainly changed through the forming process.
Bending dies to process blank materials into parts with specific shapes and sizes under leaning pressure.
The dies used for press brakes are typically classified as either convex or concave, and they serve different purposes in sheet metal stamping and separation. A forming die has a cavity to create a specific shape, while a separation die has a blade to cut the sheet metal.
Bending dies are generally made of T8 or T10 steel, and some better dies may use 42CrMo material, which has higher strength, better toughness, and wear resistance.
Cr12MoV, a type of cold-rolled die steel, is also a highly suitable material for this purpose.
42CrMo is a type of high-strength alloy steel quenched and tempered. It possesses excellent strength and toughness and can operate effectively under temperatures below 500 degrees Celsius. To ensure the longevity of each die, it’s crucial to monitor wear and tear regularly. One way to check for wear on each die is to measure the die length directly from the front to the shoulder and the distance between the shoulders.
For standard dies, the allowable deviation per foot should be approximately ±0.001 inches, with a maximum total length deviation of ±0.005 inches.
For precision dies, the deviation per foot should be within ±0.0004 inches, and the total length deviation precision should not exceed ±0.002 inches.
It is best to use delicate dies for CNC press brakes and regular dies for manual and ordinary press brakes.
Final thoughts
Hycules has been serving the press brake manufacturing industry for decades, and we understand the importance of customers purchasing high-quality press brakes. “Good” refers to quality and includes reasonable prices and high-quality after-sales service.
We have seen too many examples where customers purchased press brakes from small factories, encountered problems without receiving technical support, and eventually contacted us to repurchase equipment. We have also witnessed agents losing a lot of money due to choosing the wrong press brake manufacturer brand.
To prevent these issues, it is highly recommended that you conduct extensive research on your options before making a final decision. Trust us; the time you invest will be worth it.
Learn more about shearing machines, bending machines, and other sheet metal equipment. For the best price, please contact us.
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