Successfully bending materials using a press brake requires a detailed understanding of how your machine functions and your role in operating it. If you’re new to working with press brakes, there are some important things you should know:
Types of Press Brakes
The most common type of press brake is hydraulic, though electronic press brakes are also available:
- Hydraulic press brakes have been around a long time and are relatively easy to use. They can be designed for the heaviest workloads. They have been manufactured in sizes of 3000 tons and 50 feet in length, but mostly are found in the 100-300 ton range. For very thick materials there is no other option.
- Electronic press brakes are relative newcomers, but they offer many attractive features. Since there is no hydraulic oil required there are no oil leaks, seals, and other issues to fix. They also use less electricity than conventional hydraulic machines since the motors are not running continuously. Generally these machines come in small sizes – under 50 tons – although they are available up to 300 tons. They tend to be more accurate and quicker than their hydraulic counterparts.
Press Brake Tooling
It’s important to check tooling tolerances each time you select a punch and die to use. It is the operator’s responsibility to ensure the tooling fits the manufacturer’s specifications and make adjustments when necessary.
Some of the most common dies available to you include:
- V-Dies: They vary in angle, depth, and width, but they will all create v-shaped bends. You can bend your material multiple times if that’s what your project requires.
- Acute-Angle Dies: These dies can create acute, obtuse, and 90-degree angles.
- Gooseneck Dies: This die is used to clear flanges, the rims that protrude from a workpiece.
- Offset Dies: These are combination punch and die sets, which produce two angles to create a “Z” shape.
- Seaming Dies: These produce seams in sheets and tubes.
- Curling Dies: These curl or coil the edges of sheets.
- Tube-and-Pipe-Forming Dies: These dies first roll the edges of a sheet upwards, and then form the rolled edges into a cylinder.
- Rocker-Type Dies: By moving side-to-side as well as up-and-down, these dies bend the material to which they are applied.
- Corrugating Dies: These dies are characterized by their wavy surfaces, which produces unique bends.
- Multiple-Bend Dies: These die sets are made to form specific shapes for individual projects. They are useful for forming several bends in one motion.
Bending using a Press Brake
Key terms to understand are air bending, bottom bending, and coining:
- Air Bending: With this method, the workpiece will only come into contact with the edge of the die and the tip of the punch, the punch being forced past the top of the die into the v opening without touching the bottom of the v. Since the punch tip does not penetrate the workpiece, the inside radius of the bend will be controlled almost entirely by the size of the v opening of the bottom die. The benefit of this is that the operator can compensate for mistakes or tweak the design by simply switching bottom dies. If the dies are not selected carefully and according to an air bend force chart, however, it becomes easy to produce bad parts.
A note of caution: if you’re working with an older, mechanical model, you should almost never air bend. More dated machines usually have greater margins or error, and even a few thousands of an inch difference can result in poor parts.
- Coining: This basic type of bending involves stamping a workpiece between a punch and die. By exerting the right amount of pressure, the punch tip will penetrate and start to flow into the material. The results are accurate, highly repeatable, and can be achieved with simpler machines than those needed for air bending.
The trade-off is that this method requires very large tonnages, often in excess of 50 tons per-square-inch versus 1 to 2 tons per-square-inch for air bending. The resulting wear-and-tear on the machines is greater and more robust tools are needed, which can limit tooling options.
- Bottom Bending: With this method, the die angle should match the intended angle of the workpiece, adjusting a few degrees to account for spring back. First, the workpiece should be bottomed against the die. Then, the radius of the punch is forced into the workpiece, which achieves the angle. The last step is to release and let the material spring back to meet the die again.
Because the pressure is not as intense as it is when coining, the operator must account for spring back. Always over-bend the material by a few degrees. Any larger and you risk damaging the tooling and the workpiece.
Like air bending, the results of bottom bending can be highly repeatable if properly set up. This method does, however, require heightened understandings of tooling, tonnage, materials, and timing of steps, giving more experienced operators a definite advantage.
Although there can be some overlap, each process will require its own set of tooling. Air bending is often the preferred method, but sometimes the angle tolerance and required inside radius necessitates bottom bending or coining.
Press Brake Tonnage
As the operator, you’ll need to understand concentrated load limits, as exceeding them can damage the machine, its tooling, or the formed part. You should familiarize yourself with concepts including forming tonnage, tooling load limits, sinking tonnage limits, and centreline load limits, and know how to calculate them.
Tonnage estimates are available from press brake manufacturers, and they are sometimes mounted on the machine. Remember that charts are for air bending only. If you are bottom bending you can exceed the estimate by four times. You can exceed it by eight times for coining. You can’t exceed it when air bending without risking damage to the machine, your tooling, and the material.
If the machine is designed for off-centre loading, it can sometimes be better to form the part off-centre. Do not attempt this method if the machine is not suited for it.
Maintaining Your Press Brake
Even if maintenance isn’t your responsibility, the press brake operator should remain up-to-date with the machine’s requirements and perform daily and weekly inspections. Always inspect punches and dies before use to ensure they’re free of dents or cracking. Corrupted pieces can produce poor work or damage the machine.
If you are working with a hydraulic model, the oil and filter will need to be periodically changed. A 2000-hour (or as per manufacturer instructions) maintenance check should be performed to check the oil, filters, and valves.
It is important to lubricate elements weekly, ensuring you use a lubricant consistent with the manufacturer’s specifications.
Pay attention to:
- Ball screws
- Gear segment
- Guide encoder and encoder guiding system
- Guides and rails
- Rack and pinion system
- Ram guiding system
It is necessary to inspect mechanical components at least twice a year and the electrical system at least once to ensure the machine’s optimal performance.
Optimizing Press Brake Production Runs
As the operator, your ultimate goal is to produce quality pieces while keeping setup times to a minimum, ensuring maximum efficiency.
Be conscious of the correlation between setup time and the number of parts being produced. Simple parts that require little setup can be made in small quantities, while complicated parts requiring more time beforehand should be made in larger volumes. As you become more familiar with the machine you’re working with, the expertize you gain will help you make the appropriate decisions about setup and production times.
Be familiar with reading drawings. They will include information on the dimensions of parts, bend angles, inside radii, and blank sizes, and should be based on the capabilities of the press brakes and tooling.
If information is omitted, the operator must take action to make the necessary changes. This not only consumes valuable production time, but also leads to more scrap metal being mistakenly produced. Making appropriate decisions in the face of faulty plans will become easier with more experience, but it is still not an ideal situation for any press brake operator.
Your company should provide you with the training necessary to operate the machines in your shop. That coaching coupled with first-hand experience working with a well-built, well-maintained machine will put you on the road to becoming an experienced, successful press brake operator.
Westway Machinery is the Canadian leader in press brakes. Contact us to find out more about our products and services.
For a complete guide to press brakes, click here.
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