Today's hydraulic presses are faster and more reliable than ever, with technology undergoing constant change. Improvements in seals, more efficient pumps, and stronger hoses and couplings have virtually eliminated leaks and required maintenance has been minimized. Programmable logic controllers and other electronically-based controls have improved speed and flexibility. With new computer interfaces and monitoring, hydraulic presses are now widely used in advanced computer-integrated manufacturing systems.
Ideal for Hand-Fed Work
Mechanical presses are often faster in automatically fed, short-stroke and short-feed-length blanking operations. Despite the automation trend, a majority of jobs are still hand-fed, and the lot sizes of many jobs simply are too small to justify the expense of automatic feeding. With markets changing so rapidly, many manufacturers are reluctant to make large investments in automatic-feeding equipment. Just-In-Time (JIT) manufacturing has further increased the amount of short runs. With hand feeding remaining a primary feed method, hydraulic presses offer competitive advantages on this type of work.
Hydraulic-press users, especially those used to the highly critical job of setting the stroke for a mechanical press, are often amazed at how quickly they can change dies and start a new job. Hydraulic presses eliminate the difficult, time-consuming stroke-setting task. Because a hydraulic press maintains full tonnage throughout the entire length of a stroke, there is no need to determine the exact location of maximum tonnage.
Given such advantages, on hand-fed jobs, the floor-to-floor or bench-to-bench time often is the same for mechanical and hydraulic presses. As a result, their faster setups and increased uptime make hydraulic presses more productive than mechanical presses.
Making Inroads in High-Volume Work
Besides being ideal for lower-volume hand-fed stamping jobs, hydraulic-press lines also are finding increased use on high-volume work, inside and outside of the metal-stamping industry. Examples include:
- Electric-motor manufacturers assemble motor shafts to rotors, compress laminations and press cores into housing.
- Automotive manufacturers press tiny shafts into water pumps, assemble shock absorbers, blank and form diaphragms and stake disc brakes together.
- Jewelers coin Boy Scout and other organization pins.
- Frozen fish blocks are shaped for more efficient processing.
- Aircraft companies form tough titanium housings.
- Tuba bells and cymbals are shaped in huge forming presses.
- Hardened road-grader blades and machine ways are straightened.
- Hollow-ware manufacturers blank and draw brass bowls automatically from coiled stock.
Hydraulic presses are available for many types of applications. This triple-action model is used to draw sheetmetal for aerospace applications. Photo courtesy of Greenerd Press & Machine Co. Inc.
Full tonnage throughout stroke
Importantly, the full power of a hydraulic press can be delivered at any point in the stroke, not only at the very bottom as with mechanical presses. That means no allowances for reduced tonnage at the top of the stroke. In drawing operations, for example, the full power of the press is available at the top of the stroke. A stamper need not buy a 200-ton press to get 100 tons throughout the stroke, as may be necessary when specifying a mechanical press for such work.
Built-in overload protection
A 100-ton hydraulic press will exert only 100 tons of pressure (or less, if it is set to exert less). Stampers need not worry about overloading or breaking the press, or smashing a die. When a hydraulic press reaches its set pressure, that's all the pressure there is. The relief valve opens at that limit, eliminating any danger of overload.
Lower original costs and operating costs
Hydraulic presses feature relatively simple construction and components, and offer significant cost advantages over mechanical presses in comparable tonnages. The numbers of moving parts are few, and these are fully lubricated in a flow of pressurized oil. Breakdowns are usually minor—the operator and maintenance staff will not see for example, a broken crankshaft. Maintenance of hydraulic presses may include replacement of packing, solenoid coils and occasionally a valve. These parts, besides being inexpensive, are replaced easily without tearing the machine apart. These factors translate to increased uptime and decreased maintenance costs.
Hydraulic press power always remains under control. Ram force, direction, speed, release of force and duration of pressure dwell all can be adjusted to fit a particular job. Jobs with light dies can be accomplished with pressure decreased. The ram can set to approach the work rapidly, then shift to a slower speed before contacting the work, thus prolonging tool life. In addition, timers, feeders, heaters, coolers and a variety of auxiliary functions can be brought into the sequence to suit the job.
A single hydraulic press can perform a variety of jobs within its tonnage range. These include deep drawing, shell reduction, urethane bulging, forming, blanking and piercing, staking, punching, press fitting, straightening, and assembly. Hydraulic presses also find use in powdered-metal forming, abrasive-wheel forming, bonding, broaching, ball sizing, plastic and rubber compression, and transfer molding.
Fewer moving parts and the elimination of a flywheel reduce the overall noise level of hydraulic presses as compared to mechanical presses. Properly sized and properly mounted pumping units meet and exceed current federal standards for noise, even with the pumps operating under full pressure. Also, because each phase of ram movement can be controlled, noise levels also can be controlled. A hydraulic ram can be controlled to pass through the work slowly and quietly.
A typical 20-ton hydraulic press measures 8 ft. high, 6 ft. deep and 2 ft. wide. A 200-ton hydraulic press measures 10 ft. high, 9 ft. deep and a bit more than 3 ft. wide. At 10 times the capacity, the 200-ton press only takes up 50 percent more floor space.
Lower tool cost
Tools can be sized to withstand the load of a particular job, not a particular press, due to the fact that a hydraulic press can be set to provide pressure at a level needed for the job. The lack of impact, shock, and vibration that may result from excessive pressure promotes longer tool life.
Information for this article was supplied by Greenerd Press & Machine Co. Inc., Nashua, NH; www.greenerd.com.
Do you employ hydraulic presses in your stamping operations? Are there applications where a hydraulic press can provide an economic and productive alternative to mechanical presses at your plant?