The Importance of Crowning Configuration
As technology continues to progress, updated componentry and features are becoming more and more commonly used industry wide. From touch screen controls, to servo driven back gauges, hydraulic and pneumatic clamping devices, are just a few common features offered by your precision press brake manufacturers. Through all of these implementations, accuracy and repeatability tolerances continue to become more and more impressive. However, there is paramount technology that varies across the press brake community. The implementation of this technology alone, has forever changed bending and offered a greater production rate of an overall more accurate part. You are probably asking “What is it that could be so influential?” the answer to that, crowning.
Crowning is the counter to the natural reaction of the bending process that is deflection. Deflection occurs as tonnage is exerted, from the cylinders that are mounted on your ram, to the bed or bolster plate of the machine. Deflection causes both the Ram and Bed of the machine, to flex in the center, in turn, resulting in under-bent or canoe shaped parts. Crowning is then implemented to counteract that deflection curve. How this is accomplished is done in various methods, that we will discuss in greater detail as we continue. Essentially all of which are trying to mirror the curve of deflection, helping create an equal distribution of tonnage to the entirety of the machine, resulting in an accurate part from end to end.
There are arguably three main methods used in today’s crowning applications; Centralized Hydraulic crowning, hydraulic cylinders (pucks) spaced throughout the bed, and bed mounted wedge “wave” style. While all of which are considered CNC crowning and help eliminate the time and guess work that is faced when manually compensating for deflection, all of these methods are not created equal. In respects to many aspects in production and even life in general, a unit is only as strong as its weakest component. Meaning a press brake can only be as accurate as its greatest variable allows. In this equation it can be argued that variable is crowning methodology.
By most industry leaders, the bed mounted wedge “wave” style crowning is seen as the precision crowning method. At Moore Machine Tools we share the same view and have taken such measures to implement this crowning methodology on our Accurl USA press brakes. There are several reasons that so many reputable industry leaders use this methodology. Some of which are; the simplicity of maintaining such a system, the ability to accurately manipulate the workpiece, eliminating unnecessary variables that influence the accuracy of the product. Being that the wedge style system is mounted on the bed, it is extremely easy to access the entire system for maintenance. In turn, helping provided reassurance when addressing reliability. An immense benefit to the crowning device’s location, is the ability to directly manipulate the work piece. This is accomplished by limiting the variables that have to manipulated in addition to the work piece. In this methodology the only variables in the crowning equation, aside from deviation, are what sits atop of the crowning device, the die rail, the die, and the material. The reason this important is by having less variables in your equation, you now introduce a more controllable and predictable bending environment.
The advantages of bed mounted wedge style crowning and the inability to match those are the disadvantages of other crowning methods. Being located within the bed/bolster area of the brake presents numerous negatives. From a maintenance standpoint, one of the most commonly serviceable components of a press brake is its cylinders. As a natural by-product of their composition, seals will eventually need to be replaced, and possibly even rebuilt. So now instead of having two cylinders to maintain, you now have one to sometimes six or more in addition. Each one of these cylinders added not only presents a maintenance concern, but also a reliability concern. There are hoses and other hydraulic elements that are involved in making each cylinder function, each one of those presents an opportunity for fault. In turn requiring a repair that is not only costly from a monetary standpoint, but from perspective of time as well.
An additional aspect beyond maintenance and reliability is the number of variables involved in the bending equation. A hydraulic system obviously utilizes hydraulic oil in order to function. A common variable that is overlooked, especially in non-climate-controlled environments is the temperature of your hydraulic oil. At the beginning of your shift your hydraulic oil is going to be a different temperature than it is at the middle of your shift, which directly correlates to the viscosity of your oil. In turn this can dramatically influence how that hydraulic system preforms. Another factor that has to come into consideration is the amount of steel you have to manipulate, essentially is 30% of the bolster area. Which is also subject to varying temperatures in relation to is rigidity. Thus, providing just another example to the volatility when dealing with this methodology of crowning. A common question that is asked is, "If hydraulic crowning is not a precision crowning style, why do other manufacturers use it?". The simple answer to that is that is cheaper than other styles. It offers a savings in manufactuering cost, in turn making it an attractive way to be competitive from a price perspective, hence why it is an offered and often times "pushed" configuration.
If you are dealing with a precision bending application, the only truly suitable crowning methodology is the bed mounted wedge style crowning. Anything other than that is easy to determine as a limitation on your press brake and over all precision capabilities. Don't limit yourself by utilizing antiquated technology in precision based applications.
Reach out to our team at Moore Machine Tools, where we will take the time to learn about your application and needs and formulate a solution that is dedicated to your immediate and long term success.