16 Jul 2019
July 16, 2019
From mechanical to hydraulic, and then on to hybrid and electric, press brakes have evolved significantly over the last 100 years. “Accuracy is all that matters,” and “more tonnage for your money” are just a few sales slogans you will hear when shopping for a new brake for your job shop or production floor. Use this “How To Buying a Press Brake” guide to know what you’re looking for before you begin shopping for your next press brake.
Important factors to consider when purchasing your next press brake include the material you wish to bend, the flanges and other bends you wish to make, your operator experience and braking knowledge, operating costs, speed, and how much you are able to invest in your new machine.
There are three main brake styles in the market today. The press brake most commonly found on production floors is that which utilizes hydraulic power exclusively, via large hydraulic pistons, to provide the pressing power. Next you will find electric press brakes, which utilize ball-screw or pulley systems to drive the ram. Finally, hybrid press brakes combine the hydraulic pistons with electric (servo) motors.
It is important to ensure that your new press brake will be wide enough to fit the materials you wish to bend. Do you need a 10’ brake, or do you need 10’ between the columns? The main support columns, located on either end of the press, are typically C-shaped and have a throat for inserting materials into the entire length of the brake, but this throat depth can vary by machine and manufacturer. See Fig. 1. Here at KAAST, we offer brakes 3 – 20’ wide. Typically, it is better to invest in a machine which allows the majority of your materials to fit between these columns unencumbered by the throat’s max depth of insertion. Once you know what length of brake you need, you can go on to determine what tonnage machine you will need.
The tonnage necessary to bend your material is based on its inherent properties including elasticity, yield, and thickness. The thicker or harder your material is the more tonnage you will need to form it. Standard tonnage charts, see Fig. 2, can be used to simply match your material thickness with the size of your die (typically a V) to determine the tonnage needed per linear foot of material based on the desired bend radius. Multiply this number by the width of your material in feet and you will get to total tonnage needed.
The tonnage necessary to bend your material is based on its inherent properties including elasticity, yield, and thickness. The thicker or harder your material is the more tonnage you will need to form it. Standard tonnage charts, see Fig. 2, can be used to simply match your material thickness with the size of your die (typically a V) to determine the tonnage needed per linear foot of material based on the desired bend radius. Multiply this number by the width of your material in feet and you will get to total tonnage needed. When braking harder materials, such as stainless steel, add 50% of additional tonnage; and when braking softer materials, such as aluminum, deduct 50% of the total. See Fig. 3. KAAST offers brakes with tonnage ranging from 44 to 440 tons of pressure.
When buying a press brake, you will also want to ensure you will have enough daylight to allow the material to be maneuvered between the upper and lower tooling, between bends or at the end of the bend cycle. However, as the daylight increases, so can your cycle times. Most brakes increase the speed at which the ram travels toward the material, and then slows the travel speed during the actual braking.
The most basic style of brake has only one axis control, the vertical, known as Y, which controls how deeply the ram pushes the top tooling into the bottom die. The KAAST HPA-P hydraulic workshop press brakes offer this single axis control, which is manually adjusted on the side of the machine column. The KAAST HPB CNC press brakes are available with up to 10 axis CNC control, see Fig. 4.
Adding a back-gauge when buying a press brake, controls the length of your bend leg or flange. The most basic back-gauges are manually adjusted while CNC back-gauges are powered and adjust according to the requirements determined by the bending program. How many axes you will need to control (and how they are adjusted) depends on the complexity of your desired final product and the skill of your operator. Control over the X axis (flat, horizontal), see Fig. 5, allows the operator to control the flange length by setting the depth at which the material is inserted into the brake. This can also be split into X1 and X2, allowing one end of the material to be inserted farther than the other resulting in an asymmetrical flange.
Control over the height of the back-gauge, is realized by adding an R axis control, see Fig. 6. This allows the backgauge to be aligned to the edge of the material for a second bend.
The amount of variation in your material width determines if you need Z axis control, allowing horizontal adjustment of the width between the touch points of the back-gauge, also known as the fingers, see Fig. 7. If bending one specific width of material, you probably don’t need powered Z axis control, but if your material widths vary greatly, powering these fingers will greatly reduce operator set-up time.
Your control system will also determine the speed at which your brake will be able to produce accurate parts. CNC controls allow for much quicker adjustments to back-gauge and tonnage settings than manually controlled machines, but they also allow the machine to do the work of bending faster and more accurately as well. For shops utilizing their press brake for one-off bends and ad-hock production, a manual control system is probably sufficient. However, for production lines a CNC control is going to be needed.
When selecting a CNC control as you are buying a press brake, consider the operator’s programming knowledge and the complexity of your projects. The KAAST HPB series of press brakes, utilizing the Delem touchscreen CNC control, are hydraulic CNC press brakes which allow operators with no G-Code experience to program easily right at the brake. The operator draws the desired bends on the touch screen and the control sets the required tonnage and back-gauge settings. These settings are based on the material selected from the library (which comes with several per-programed materials and the option to add more as needed) and the desired bends in the material. See Fig. 8. For expert operators with extensive G-Code knowledge a more basic CNC control which only takes G-Code programming may be the most cost-effective option as your investment is based with your operator. But once your expert retires or moves on, what happens then? Investing in a conversational CNC control allows your machine to continue producing parts no matter who is running it. A good CNC control system will also allow operators to walk through the bend program step-by-step before the material is inserted into the machine. This allows for any issues to be corrected without wasting materials.
Other costs to consider when shopping for your next press-brake include operator salary, consumables (such as hydraulic fluid and tooling), and commodity (electrical) costs, as well as downtime. Better, more experienced operators cost more than their counterparts, but typically result in increased production rates. Hydraulic fluid will need to be changed based on the number of hours a machine is run. Investing in high-quality long-life fluids will help to keep this cost down. Tooling costs can be kept low by choosing tools made from hardened metals and ensuring that the tooling is matched to the job. Energy efficient machines may seem like moneysavers on paper, but they typically run slower than other brakes, lowering your production rates. With this trade-off of energy savings for speed most manufactures place lower priority on this cost, but it is important to consider your electric bill when determining running costs of any machine.
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The most expensive unexpected cost for many shops is the cost of downtime. When your machine is not working you are still paying your operator and you lose the income generated by the parts output. How do you keep downtime to a minimum? Ask for references from customers running the machine you are interested in; inquire about after-sales support, spare parts availability, and estimated machine life; consider the brands of the electrical and mechanical components to ensure aftermarket availability; review the suggested maintenance schedule; finish with researching the style of tooling for the brake you are considering. Also, consider the country of origin of for any machine you are considering. Europe has distinguished itself as a premiere manufacturing hub in the last decade. With an educated workforce, low cost of living, and a culture of entrepreneurial spirit, the region is thriving. It was these attributions that drew KAAST to the region when deciding between production factories for our fabrication machines. “Our [fabrication] machines are like the people who build them. They are sturdy, hard-working, easy to work with, and reliable,” KAAST USA President Angus Catterson explains. The HPA-P and HPB series are produced in a factory that specializes in building brakes. You frequently see machines that are painted a different color and stickered with a different brand, but the same in all other ways to their competitors. KAAST machines are different. They are built to our exacting specifications following our unique designs. It is this factory’s attention to detail and commitment to quality that sets our machines apart, and ahead, of the competition. Only name brand, easily accessible components are used, and spare parts are readily available.
Press brakes typically take one of three styles of tooling. American Traditional Precision-Planed tooling is an affordable and functional general use option. These pieces are produced in lengths up to 20’, then cut down according to end-user requirements. These tools are subject to the inherent error of planning anything of that length and are the least precise and least expensive option. European Precision Ground tooling is precision ground from short lengths of pre-shaped tool blanks which have been through-hardened. This through-hardening provides extra wear protection. The precision grinding of this tooling type allows CNC controls to produce exact bends quickly with tolerances as close as ±0.0005 in. in profile accuracy and in height, while holding a consistent centerline. With their high level of precision and long life, these tools tend to be on the more expensive end of the tooling price range. New Standard (aka New American) press brake tooling has all of the precision of the European style, but is designed for use in specialty clamping systems, like those offered on the KAAST HBP series. These specialty clamping systems allow for quick tooling changes in a production environment, reducing the amount of time the operator spends setting up. Like the European style, the New Standard style has a center that is fixed and consistent allowing it to operate seamlessly with CNC controls. New Standard style tooling falls in the middle of the price spectrum, with the precision of the European style, making it an easy choice for CNC brake operators. Generally speaking, it is a good investment to have a complete duplicate set of tooling on the shelf available for swapping in on-demand in case of tooling damage. This helps to keep downtime (waiting for new tooling to arrive from the supplier) to a minimum.
The running costs for press brakes can be calculated by adding the costs of the machine, operator, and maintenance for one year. Then divide by the number of hours the machine will run during that year. (Don’t forget to account for scheduled downtime for routine maintenance!) This will give you your cost per hour (CPH) for your brake during its first year of operation.
Typically, the CPH will be a deciding factor when a customer is torn between two otherwise equal (equal in length, tonnage, and control system) machines. When this number is combined with brand reputation buying a press brake becomes much simpler!
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