Today, self-contained hydraulic workholding systems offer the designer and machine operator many advantages. The following are important benefits to consider when planning a system. Though covered separately here, in practice the advantages of power workholding are interdependent. Each benefit may actually lead to several other production advantages.
Increased clamping speed is one of the more-obvious advantages of power workholding. Rather than taking several minutes to manually tighten and loosen the clamps on a workholder, a machine operator can activate the complete clamping system from a single point in a matter of seconds. The increased clamping speed thereby reduces the non-productive time which characterizes the loading and unloading cycles. But reduced loading time is only one reason to select power workholding. There are other less-obvious reasons that are even more important.
In addition to the reduction of clamping time, power-workholding systems allow much-faster machining cycles. Power clamps offer added security. Instead of relying on the operator to properly tighten the clamps, power-operated clamping systems provide consistent clamping forces. Holding forces can also be adjusted to suit the specific requirements of the workpiece. This permits clamping forces to be increased, allowing heavier feeds and faster speeds.
Improved Part Quality
Improved part quality is perhaps the greatest benefit of power-workholding systems. These systems improve overall quality and reduce rejected or scrapped parts by providing consistent, controllable clamping forces and self-adjusting work supports.
Consistent and Repeatable Operation. A major feature of power-workholding systems is consistent and repeatable clamping forces. Manually operated clamps rely solely on the strength and diligence of the operator. Power clamps, however, are controlled by a power source, so the strength and fatigue level of the operator have no effect on the clamping force.
Control of clamping force increases both the safety and efficiency of the machining operation. Likewise, with swing clamps, extending clamps, or other forms of self-positioning clamps, the position of the clamp on the workpiece is established by the clamp. Once properly set and positioned, power clamps perform the same way, part after part, throughout the production run. The amount of operator interaction is reduced, while consistency and repeatability are enhanced.
Controlled Clamping Force. Power-workholding systems are adjustable to provide exactly the right amount of clamping force. When either light or heavy clamping forces are required for a workpiece, the clamping force can be adjusted for those specific conditions. A controlled clamping force is important for parts with varying thicknesses, brittle materials, odd shapes, or similar characteristics. Reduced clamping forces can be applied if the workpiece is delicate or has thin cross sections, as with some cast parts. Conversely, if the workpiece requires greater holding forces, power clamps can also be adjusted for additional pressure.
Automatically Adjusting Work Supports. Many workpieces require additional support to prevent deflection or vibration during the machining cycle. In these cases, self-adjusting work supports are quite useful. These supports are placed under the workpiece and either advance to meet the workpiece, or are depressed by loading the part in the fixture. Once the required height is achieved, work supports are locked in position by hydraulic pressure and act as additional fixed locators throughout the machining cycle. At the time of unloading, the work supports return to the free position and are repositioned with the loading and clamping of a new part. So, virtually any differences in the supported surface, such as steps or irregular features, are easily accommodated.
Power-workholding systems offer several other advantages over manual clamping. These advantages include remote clamp operation, reduced operator fatigue, automatic sequencing, fixture compactness, and increased machine-tool capacity.
Remote Clamp Operation. Most fixturing operations require more than one clamp to hold the workpiece. Of these clamps, some may be hard to reach, and present a safety hazard to the operator. A large workpiece, for example, may require six or more clamps to completely hold the part. Power clamps are typically operated together, from a single point. By simply positioning the clamping valve away from the cutters, the hazard of the operator reaching over the part to tighten a clamp close to a cutter is eliminated. The single remote operating point greatly reduces the time and expense of manually positioning and tightening each clamp, while enhancing operator safety and eliminating hard-to-reach clamps.
Reduced Operator Fatigue. Operator fatigue is a design consideration often overlooked. Most operators over-tighten clamps in the morning and under-tighten clamps in the afternoon. Power clamping systems reduce operator fatigue by replacing the strenuous activity of clamping and unclamping manually with the consistent and controllable functioning of hydraulically actuated clamps. This consistency and control results in higher production.
Automatic Sequencing. Automatic sequencing is the ability of a power-workholding system to operate clamps and other devices in a specific order. In many clamping situations, this feature is important. Power-workholding systems handle sequencing with one or more sequence valves in the hydraulic circuit. These valves activate the clamps and other devices at the proper time.
To reduce the chance of deformed parts, it may be necessary to activate clamps in a specific order. Self-adjusting work supports often reduce the chance of part deflection. When supports are used, the first operation in the sequence locks the supports under the part. Once the supports are in fixed position against the workpiece, the clamps are brought into contact with the part.
The sequence of operation is also important when a clamp must be moved out of the way during a machining operation. A clamping valve moves the clamp out of the way as the cutter passes. When the cutter is clear, the valve then re-clamps the part. In almost every case, a power sequencing arrangement is much faster and more reliable than its manual counterpart.
Fixture Compactness. The high holding force of small power clamps often allows loading more workpieces on a fixture, in many cases, because the clamps can be positioned closer together. One result of this change is increased productivity when the chip-cutting time is lengthened and the percentage of time operator attention is required decreases.
Increased Machine-Tool Capacity. The consistent holding force of power clamps allows for faster machining rates. The increased production rates translate into greater capacity, especially important on expensive machine tools.