Presses of all types—mechanical, pneumatic, servo, and hydraulic–have their place and offer unique advantages. However, over the past 50 years, hydraulic presses have trended toward greater utility. Today's hydraulic presses are faster and more reliable than ever, and the technology has gone through significant changes and refinements. Improvements in seals, pumps, hoses, and couplings have nearly eliminated leaks and minimized maintenance.
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An examination of hydraulic press technology and the press’s anatomy, as well as its benefits, limitations, tips for selection, and automation options, can net the best utility from a press.
Press Structure. These are the major components and features of the hydraulic press structure:
1. Cylinder. The cylinder assembly comprises a cylinder, piston, ram, packing, and seals. Piston diameter and oil pressure determine the force (tonnage) that a press can deliver.
2. Frame. The frame is the main structure of the press containing the cylinders and the working surfaces.
3. Stroke Control. Stroke length can be set for any distance within the stroke limits of the cylinder in the stroke control. Adjustments include the top of stroke, pre-slowdown point, and bottom of stroke.
4. Throat Clearance. The distance from the vertical centerline of the ram to the frame member behind the bed is called the throat clearance. This distance determines the maximum piece size that can be positioned with the part centerline under the center of the ram.4.The distance from the vertical centerline of the ram to the frame member behind the bed is called the throat clearance. This distance determines the maximum piece size that can be positioned with the part centerline under the center of the ram.
5. Daylight. This is the vertical clearance from the top of the bolster to the underside of the ram in its maximum up position. This term is sometimes confused with the mechanical press term shut height. Shut height is the clearance over the bed with the ram fully down. Daylight describes the maximum vertical die capacity of the press.
6. Bed. The bed is the flat, stationary machined surface that supports the bolster and dies.
7. Bolster. This is a plate or structure mounted on the bed that the tooling is mounted and attached to. Most hydraulic presses are constructed so that the bolster is removable.
8. Dual Palm Button Controls. This is a common method of actuating hydraulic presses. Both buttons must be depressed at the same time to bring the ram down, requiring the operator to use both hands. Control circuits include nonrepeat and anti-tiedown features.
9. Work Height. The distance from the floor to the top of the bolster is the work height.
Type of Frames. Many of these hydraulic frame types are common with mechanical press frames:
Four-post. This heavy-duty production press is built for continuous operation. It uses four heavy-duty, large-diameter, shouldered columns to tie the frame together. These large-diameter columns precision-guide the moving platen or press slide. This ensures exceptionally consistent upper and lower die alignment, minimizes deflection, and eliminates "lean-back." Any deflection that does occur in this style of press is straight up and down. It also enables loading of the press from any of the four sides, permitting easy integration into production lines and manufacturing cells.
Being familiar with these terms will enhance your understanding of a hydraulic press:
Also, programmable logic controllers (PLCs) and other electronic-based controls have improved a hydraulic press’s speed and flexibility. With new computer interfaces and monitoring, hydraulic presses can be used in advanced computer-integrated manufacturing systems.
The built-in overload protection applies to the tools too. If they are built to withstand a certain load, there is no danger of damaging them because of overloading. Tools can be sized to withstand the load of a particular job, not a particular press. The pressure of the press can be set to suit the job. The lack of impact, shock, and vibration promotes longer tool life.
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Open-gap presses provide easy access from three sides. Four-column presses ensure even pressure distribution. Straight-side presses offer the rigidity required for off-center loading in progressive die applications. One important thing to keep in mind is that the more critical the work and the more demanding the tolerances, the greater the reserve tonnage capacity should be.
Once the basics are determined, the next consideration is to select options. Most hydraulic press builders offer an array of accessories such as:
Note that the hydraulic circuit for a press is determined mainly by the application. In long-stroke applications such as deep-drawing, a dual-pump circuit with regeneration is typical. This allows the press ram to move quickly down to the work and out of the work while enabling a smooth draw speed.
However, when you are stamping on a hydraulic press, it is best to minimize how many valves you use during what is typically a very short stroke. Most presses used for stamping employ only a single hydraulic pump because of the short stroke required. This setup allows for fewer “valve shifts,” which reduces cycle time for a complete stroke and allows for many more strokes per minute.
Quality can vary greatly from press to press. Some light-duty presses are capable of "spanking" the work momentarily and reversing, and there are heavy-duty machines designed for general-purpose metalworking applications.
A few constructive points can be used to compare one machine with another:
Frame: Look at frame construction—rigidity, bolster thickness, dimensional capacity, and other factors. Cylinder: What diameter is it? How is it constructed? Who makes it? How serviceable is it? Maximum system pressure: At what PSI does the press develop full tonnage? The most common range for industrial presses is 1,000 to 3,000 PSI. Horsepower: The duration, length, and speed of the pressing stroke determine the horsepower required. Compare horsepower ratings.
Speed: Determine the speed each hydraulic press offers.
Press Tonnage. The tonnage required to do a job and the formulas to determine it is the same for hydraulic presses and mechanical presses. The tooling usually is interchangeable. There may be certain applications such as deep drawing in which the full power stroke characteristic of a hydraulic press reduces the tonnage, but there are no known instances of a hydraulic press requiring more tonnage.
Selecting press tonnage in the typical pressroom often is little more than guesswork.
For example, if a job is successful on a 100-ton mechanical press, tonnage tends to stay the same for the life of that job. The job may never have been tried at 75 or 50 tons. With a hydraulic press, however, you can adjust tonnage quickly and easily, tuning the press to precisely the right tonnage for each specific job.
How the Press Affects the Job. In most cases, the effect of stroke is the same on both hydraulic and mechanical presses. However, drop hammers and some mechanical presses seem to do a better job on soft jewelry pieces and impact jobs. The coining action seems sharper if the impact is there.
In deep drawing, however, the full power stroke of a hydraulic press produces significantly better results.
There are many ways and reasons to automate a hydraulic press, from simple to the very complex. Because press functionality is at the core of automation, it is advantageous to partner with a press manufacturer that is also an authorized system integrator and has a long history of providing integrated press automation systems for a range of applications.
Automation may be integrated during an initial press installation, or it can be added to an existing press setup. For the latter, most of the time automation is added not because the press is running slowly, but as a result of many other factors, some of them surprising:
The challenge is to identify the ”right size” for the automation system to address production needs for today and the future, while keeping within the project budget. As such, tailoring automation offerings to fit a range of applications is important. This includes everything from basic press automation (such as electrically integrating a material feeder to the press) to large multipress, multirobot autonomous working cells.
June 9, 2020
Hydraulic presses can help you complete tasks quickly and easily when you need to do some heavy lifting. The machines allow you to apply a relatively small force, with the device using a confined liquid to produce the large compressive force required to get work done. These presses are available in different styles and sizes and are widely used for a wide range of tasks where a large force is required.A press is a mechanical device that uses hydraulics to generate a compressive force that helps lift or compress large items. By generating this force, the machine increases the power of a standard mechanical level. Hydraulic presses are commonly used in manufacturing as they tend to be economical with materials and help to produce more intricate shapes. There are different types of presses available, each designed and made for different uses. These include arbor presses, laminating presses, C-frame presses, pneumatic presses, and H-frame presses. When choosing a variety, you may want to consider factors such as pressure, speed, and size. However, these machines can be modified to suit the need depending on the nature of work to be done. In addition to the different types, the devices come in a range of configurations. Automatic varieties are microprocessor controlled, power-assisted and programmable. There is also a manual option that is operated by hand. Other options that you can consider are power and motorized hydraulic presses. When looking for a machine to do some heavy lifting, you will have to figure out the right configuration for the task. One of the advantages of a hydraulic press is that it occupies less space than a mechanical counterpart of the same capacity. They are also cheaper, offer overload protection, and allow you to control the noise level. Some common applications of presses include packing food and consumables, making appliances, manufacturing electrical parts, making ceramics, and manufacturing automobile parts. The devices also come in handy in military applications, building aircraft and sword making.The mechanical function of these devices is quite straightforward . To understand how one works, it is important to look at the device's structure. The main components are cylinders, pipes, and pistons. These systems typically consist of two cylinders, the Ram and the Plunger, which are connected and are filled with fluid. One of the reasons why liquids are used in presses is because they do not compress easily. When you apply a small amount of force onto the Plunger, the cylinder will push the fluid below it. The pressure is distributed evenly throughout the liquid, making it raise the Ram. With the pressure between the Plunger and the Ram, you will be able to crush the item between these two cylinders. The hydrostatic system works based on Pascal's Law . Pascal's principle states that the larger cylinder's pressure will remain the same as the pressure in the smaller cylinder. In essence, a modest mechanical force applied to a small cross-sectional area on one part of the system results in a larger mechanical force in another part of the system. As much as the pressure on the second piston is the same as that of the first piston, the force on the second piston will be 10 times that of the first if the second one is 10 times larger than the first one. As such, the machine will convert a small force into a large force when a change of pressure is applied to an enclosed fluid.A hydrostatic mechanism can concentrate a force, allowing it to exert thousands of pounds of force. To determine how much force one exerts, you will need to look at the sizes of the cylinders. The first step is to measure the internal bore of the Ram in inches. Square the radius of the bore and multiply the product by Pi to give you the piston's surface area on which force is applied. The piston's surface area will give you the multiplication factor, with a surface area of 10 square inches, translating to a factor of 10. In case the pressure gauge reads 1000 PSI, the 1000 pounds per square inch is applied to 10 square inches. If every square inch of the surface area applies 1000 pounds of force, the 10 square inches will exert a total of 10,000 pounds of force. In short, the amount of force at each end of the system will depend on the area over which the pressure operates. Essentially, this means that varying the ratio of the areas will lead to a change in the ratio of the force. It is important to know how much force a given machine exerts before investing in one. Calculating the force will help you determine the kind of work that the machine can help you do. You will also be in a better position to pick the best device for your needs.Once you have bought one, you will want to keep the device working optimally. Sapphire Hydraulics provides quality and reliable services to help reduce your equipment downtime. Call us today to learn more about our hydraulic repair and maintenance services
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