Going on a Bender?
Want to bend some plate or sheet metal? Then you probably need a brake of some type, and if the metal is hard or thick enough, you will want a powered press brake for the job.
While some buyer somewhere might pick out a press brake based on a nice paint color, that’s probably not a realistic criterion for locating the right machine for your project at hand — not to mention anticipated future work. How do you find the perfect press brake? Let’s “brake” the process down into some essential points for consideration.
Not My Type
Before buying a press brake, you should become familiar with the different types of press brakes available.
- Mechanical press brakes are the original powered press brakes. They’ve been all but replaced by hydraulic press brakes, but buyers with minimal bending needs can still find used models available.
- Pneumatic press brakes are usually smaller brakes that run off of shop air and are used for extremely light work where accuracy isn’t as big of an issue.
- Hydraulic press brakes have been the mainstay of the metal fabrication world since the last quarter of the 20th century and remain so today since they are stronger and cheaper than most electric brakes. The ram is moved by a system of hydraulic cylinders and is perfect for the shop with heavy workloads.
- Electric press brakes are becoming more common in the industry and are equipped with servomotors instead of cylinders, making them quieter and more energy efficient than their hydraulic counterparts. They also require less maintenance and are often much more accurate.
- Hybrid press brakes are hydraulic brakes equipped with electric motors which minimize the used of the hydraulic system for greater cost savings while still having full hydraulic power.
An important thing to remember is that you want to buy a bigger machine than your biggest job. If you buy a press brake with a capacity that’s rated to handle your largest anticipated part (both for length and for tonnage), you need to realize that your machine isn’t built to maintain its full capacity day-in and day-out. The rated capacity is really a “you can bend this once-in-a-while if you absolutely have to” limit.
Decide what your largest job will be, find a press brake that will handle it, then go one “size” (20-30%) bigger from that manufacturer, as far as tonnage goes. It really wouldn’t hurt to go a couple extra feet in length as well, as you never know when a slightly longer part will need bending.
It May Take Two to Tango
Speaking of length, if you have really long but fairly lightweight parts, there’s no need to buy a huge brake just to meet your length requirement. Most good press brake manufacturers will build their CNC brakes in such a way that they can be combined into a tandem configuration of two side-by-side brakes of the same working height that can be run from a single control.
This same type of synchronous operation can often be used with brakes in a trio or even a quad configuration, so check with your press brake distributor to see if that’s available. Multiple smaller brakes can often be less expensive than a single massive one to achieve the same length. (This would be a good place to mention that you have to be sure to take into consideration your shop space, not only for the size of your new machine, but also how your workflow is going fit around it.)
Now You’re Just Deflecting
When you work with metal fabrication machines, understanding the concept of deflection is important. Deflection is the degree to which a structural element like a machine frame is temporarily deformed under a load. In the case of press brakes, it refers to the displacement or flexing of the ram and the bed while pressure is being directed through them into the work piece. This in turn can be transferred into the part being made, causing a slight arcing or bowing of the final product.
Knowing the deflection limits of the press brakes you are looking at will help you decide on the best one for your money. The amount of deflection a brake has increases exponentially when you move to longer models. Basic press brakes will require shimming to maintain a parallel bend in your finished part, while more sophisticated machines can have some sort of deflection compensation built in, such as a crowning system.
You Need to Apply Yourself
“What is my application?” is the single most important question you can ask yourself when buying a press brake. Regardless of cost, you need to match your machine to your projects, including your best guess at future jobs.
What parts will you be making? How accurate do they have to be? Will there be a lot of one-off parts, or will you be producing the same pieces over and over? How will the workpieces be loaded and unloaded? Knowing what you want to accomplish with your new press brake is critical in buying one.
Understanding not only what the finished part will look like, but what it is made from is essential. The metal fabricator needs to look at the types of material that will used in each of the bending jobs on the new press brake. What is the longest piece of each metal? The shortest? The thickest? The thinnest?
Any special characteristics of each metal — such as texture, elasticity, yield or increased tensile strength — also have to be factored in when calculating bends. Deflection figures into material as well as machines, so while you might know what type of press brake is required to bend a certain length and thickness of mild steel, the load requirement for stainless steel increases by about 50%, while soft aluminum might require 50% less.
A Ton to Know
Press brakes are a little different than leaf brakes in that they are measured in lengths and tons, rather than lengths and metal thickness. The nature of the bending process on a press brake —bending metal between a punch and a die under great pressure — differs from the simpler folding process of manual brakes.
Calculating the correct tonnage for your needs might sound like rocket science, but most manufacturers offer a press brake bending chart to figure it out fairly easily (side note: if your purchased brake doesn’t have such a chart mounted on it, be sure to affix one for the daily use of your operators). Most tonnage charts will be based on air bending mild steel, so they won’t be accurate for different materials or different bending processes, like bottom bending or coining.
A Bend to Die for
In order to read a press brake bending chart, you don’t just need to know the length and thickness of your specific material, you need to know the inside radius of your finished part, and you also have to look at what V-die will be needed. The wider the V-die opening, the less tonnage will be required to bend the same material.
For example, if you decide that you need a press brake that can bend 10 feet of 1/4″ mild steel, you would consult an air bending tonnage chart, which would show you that the standard for bending 1/4″ material is a 2″ V-die. It would also tell you that it’s going to take 15.5 tons per foot to bend it. Multiplying 15.5 by 10 for your length gives you 155 tons, which means you will need at least a 155-ton press brake with a minimum of 10′ of bed length for your metal bending job.
What the Flange?
Another factor in determining the correct press brake is knowing what the flange lengths will be in your finished parts, since V-die widths limit the sizes of the flanges that can be bent. If the part you are wanting to bend has a 1″ flange length, then the standard 2″ V-die won’t work, since the flange would fall into the die while being bent. Your press brake bending chart will show you what the minimum flange length has to be for each V-die.
In our example of air bending 10 feet of 1/4″ mild steel, if you determine that you need to use a 1-1/2″ V-die to accommodate your flange length, you will see that significantly more tonnage will now be required to make the bend. In this case, you’d have to increase from 15.5 to 22.8 tons per foot, meaning that you will now need a minimum of a 228-ton brake to bend your part.
Well, That’s Deep
Your flange length can also affect the required length of your press brake as well. If you have a 3′ long flange length, then you will be bending that length of material back into the press brake. If the width of the metal is 10′ then a 10′ wide brake won’t be wide enough to allow for that size of flange, since the distance between the side frames of a press brake is almost always less than the length of the bed.
The side frames on a 10′ press brake are usually around 8 feet apart and would prevent a 3′ flange on 10′ material from being bent back inside of the machine, as the throat (the C-shaped opening cut into both side frames) wouldn’t be anywhere close to that deep. So, you would probably need at least a 12′ press brake that has 10′ between the frames to bend that length of flange.
I’ve Seen the Light
Traditionally called “daylight,” the open height of the machine also needs to be looked at when determining the right press brake for your needs. While standard open height may work fine for you, you may want to consider ordering a brake that has a larger open height with a longer stroke depending on your jobs and the tooling you are using. If you will be bending large flanges, you may find that you can’t easily remove the part from a press brake with standard open height.
All of the dimensions of the working area of a press brake — open height, stroke length and throat depth — have to be taken into consideration when buying the right machine.
To CNC or Not to CNC — That Is the Question
Will you want to buy a CNC press brake? That depend on how many axes you will want to control on your brake, and how easily you want to do it. Your Y-axis is the up and down movement of the ram on your press brake, but with most CNC hydraulic press brakes you will be able to control each hydraulic cylinder (called Y1 and Y2) independent of each other.
A back gauge is important to have on a press brake, as it will measure the flange length, or the distance from the punch and die to the edge of the metal (X-axis), allowing you to place your bend at the correct spot. You can usually set the horizontal position of the back gauge (Z-axis) and even its height (R-axis). If you opt for separate fully powered, CNC-controlled back gauges on your press brake, then your operator can independently set the positions of the left (R1, Z1, X1) and the right (R2, Z2, X2) back gauges right at the control and have them adjust automatically during the bending process, vastly saving time. Functions like powered crowning or controlling a sheet following system can also be automated through a CNC control.
Beyond the ABCs
Understanding the different axes and why you would want to control them will help you pick out your best brake. Having a Y1 axis that is controlled separately from a Y2 axis allows both sides of the ram to come down exactly parallel to the die for an accurate bend angle on a long workpiece. Being able to raise a back gauge up and down (R-axis) is important if you are going to be making multiple bends, such as putting a 45° bend into a piece of material and then making another bend further into that same piece.
Will you be running small parts on your press brake? If, for example, you will be alternating between 2′ and 10′ wide pieces on your brake, you may want powered Z1 and Z2 fingers, so you won’t have to keep manually adjusting the width of the fingers for each different bend. Will you be bending on an angle? If, for example, you will be bending a flange that is 3″ deep on one side and 2-1/2″ on the other side, then you may want a Z-Prime axis — also known as a Delta X-axis — so that you can adjust your press brake on an angle with one fixed finger and a second one that can adjust plus or minus 5″ (separate Z1 and Z2 axes can accomplish the same thing).
The Right Tool for the Job
Without tooling, a press brake is just an oversized doorstop. Tooling is what does the job once the pressure is applied, so make sure you have the right tooling to complement your new press brake. Somewhat worn conventional tooling from your old manually operated brake probably won’t cut it with your brand-new CNC press brake, where precision-ground tooling is highly recommended.
You will probably want to get a press brake with a universal die rail. It has two C-flanges on it to hold a 4-way V-die, but it also has a groove down the center, which will allow you to also buy single tooling with an American-style tang that will sit down in the slot. If your operator is going to be bending the same thing all the time using standard tooling, then you probably only need a 4-way V-die on the bottom that can rotated when needed.
If your operator is going to be making many different bends in different material and will be changing tooling frequently, you need to consider whether you want them to take the time to use a wrench to put the tooling in the clamps (seating the tooling manually each time) or would it be more cost effective to order a tooling system for your new press brake? Some tooling systems have upper tooling clamps with a power pack that releases the tooling with a push of a button. The tooling can be pulled out, a new one inserted, and with another push of a button the new tooling is locked and seated and ready to go. The same type of option can be purchased for the bottom tooling as well.
All the Bells and Whistles
Once you’ve calculated your size and axis requirements for bending and picked out your tooling, there are still many options to look at in order to choose the right press brake for your needs, such as front sheet supports, extended length back gauges or robotic loading and unloading. Please keep in mind, however, that every upgrade to your brake comes at a cost that has to be weighed against the convenience and efficiency you will get from those optional accessories.
One important area to look at is the type of safety guarding systems you will want. A good press brake dealer will always provide at least the minimum equipment that is required for safety, but there are other factors you should look at, such as how automated and how user-friendly you want your machine to be. These choices have a bearing on the safety options that you need to consider. If you only want the most basic laser package that projects a beam across the bottom of the tooling, you have to realize that it can be somewhat cumbersome at times. While it is effective and works, it can get in the way during tooling changes. There are more sophisticated safety lasers that you can upgrade to, such as systems that are monitored through the control, making them much more user-friendly.
You’ve heard the saying, “A tool is only as good as the hands that wield it”? Well, that applies to really big and expensive tools like press brakes, too. If you are moving up from more basic equipment to your first CNC press brake, you will likely either need to provide extensive training to existing personnel or add a trained operator to the payroll. Either way, you should figure those costs into your overall budget for your new press brake.
Your operators have to know how to safely run a press brake and be dedicated to doing so. They also have to keep press brake maintenance clearly in mind and take daily steps to clean tooling and perform other preventative tasks. Shop costs can skyrocket when damage, accidents and injuries occur because a press brake operator doesn’t strictly following set procedures along with some common sense.
I Know a Guy Who Knows a Guy
Knowing everything there is to know about press brakes won’t do you much good if you don’t have a good supplier that you can trust. Get some recommendations for press brake dealers from people you know in the industry, check them out and find an experienced one that is knowledgeable and patient and offers quality machine, regardless of price tag. You will likely want to find a company that offers tooling, replacement parts, maintenance packages and repair services all under the same roof, so they can become your one-stop-shop for all things press brakes long after the sale is complete.
Once you find a good press brake provider, plan to stick with them, even if you are required to look elsewhere for bids on future machines. A good machinery salesman is like a good doctor or dentist — they will get to know you and your needs over the years and will be able to make recommendations specifically for you that keep your best interests in mind.