THE ‘GREENING’ OF FASTENER-INSTALLATION PRESSES
Roger Patton of PennEngineering explains how advances in automated fastener-installation press technology are contributing significantly toward resolving traditional equipment-related issues and promoting both “green” and cost-effective operations.
Advances in automated fastener-installation press technology are contributing significantly toward resolving traditional equipment-related issues and promoting both “green” and cost-effective operations.
Among the processes performed by sheet-metal fabricators, the efficient installation of fasteners can be one of the most challenging. The work typically can be labor intensive, often requires time-consuming tooling changeovers to install different types of fasteners, may be handled with equipment for which energy efficiency was an afterthought, and can jeopardize goals for “green” and sustainable operations.
The growth in applications for self-clinching fasteners over the years has helped to mitigate labor concerns by reducing the amount of required hardware to handle and install in thin-metal assemblies. Along the way, advances in automated fastener-installation press technology have contributed significantly toward resolving traditional equipment-related issues and promoting both “green” and cost-effective operations.
INSTALLING SELF-CLINCHING FASTENERS
Self-clinching fasteners offer reliable attachment solutions for thin-metal assemblies by providing permanent and reusable load-bearing threads. Generally, they will be specified for applications where good pullout and torque loads are required in sheet metal too thin to provide secure fastening by any other method. More often than not, they are installed during fabrication.
These types of fasteners (in dozens of types and thousands of variations) often will dramatically reduce or eliminate the amount of attachment hardware (such as loose washers, lock washers, and nuts) and usually require only a single mating piece to complete final component attachment. Fewer parts to install enable quicker assembly and lower production costs and, when installed properly, the fasteners will not loosen or fall out and never have to be handled again.
Fabricators install self-clinching fasteners permanently in thin ductile metal sheets by pressing them into place in a properly sized mounting hole and applying sufficient squeezing force. This causes displaced sheet material to cold flow into a specially designed annular recess in the shank or pilot of the fastener, permanently locking the fastener in place. A serrated clinching ring, knurl, ribs, or hex head prevents the fastener from rotating in the metal when tightening torque is applied to mating hardware.
While all presses to install self-clinching fasteners will provide necessary squeezing force to allow the fastener to become an integral part of an assembly, press similarities end there. Some of the considerations in deciding which type of press to utilize include overall job volume, fastener sizes and how many different types of fasteners will be installed, and work piece size and configuration.
For high-volume applications, press options in the marketplace historically have been limited to hydraulic, air over oil, oil over oil, air over air, or mechanical versions to deliver the necessary force generation. All have comparative advantages, depending on the job, but all tend to fall short in the areas of efficiency, energy costs, and potentially adverse environmental impact. The engineering behind the world’s first automated electro-mechanical press to install multiple types of self-clinching fasteners has introduced a practical and cost-effective alternative to competing technologies, especially for high-volume and multiple fastener installations.
A GREEN ‘MACHINE’
The heart of the unique PEMSERTER® Series 3000™ press system is a custom-built, full servo controlled dual axis electro-mechanical actuator integrating advanced technologies and optimized for efficiency. The system operates without hydraulic oil and is sealed and lubricated for life, which eliminates environmental issues and the maintenance costs associated with oil leaks, spills, changes, and disposal fees. In addition, the system has recently undergone independent testing for energy efficiency and earned unprecedented flying colors compared with conventional hydraulic presses.
Overall, the Series 3000 stands as a one-of-a-kind “green machine.” Key innovations offer distinct benefits for fabricators, particularly in energy efficiencies and improved productivity on the shop floor. Among the system’s highlights:
• Dual axis actuator promotes fast ram travel and high pressing forces using minimal energy.
• Proprietary clutch system utilizing optimal acceleration and deceleration profiles enables a smooth, energy-efficient transition between servo axes.
• High torque (high force) axis has a 10:1 gear ratio to achieve high pressing forces with minimal energy consumption.
• Roller screw technology carries larger loads and higher speeds more efficiently.
• Optimized coil construction allows for high-density coil packs without extraneous magnetic field generation to reduce the physical size of the actuator and increase motor efficiency.
• Regenerative/dynamic braking captures inertial energy and applies it to deceleration for substantial reduction in the system’s external energy requirements.
• PC control utilizes only the hard drive for machine setup. During a run, all logic is maintained by solid-state memory in the system’s servo controllers. This is inherently energy-efficient, because the PC moves into idle, or “sleep,” mode after setup.
TYPICAL PRESS CYCLE
Here’s a step-by-step look at how the press system works in practice to conserve energy during the fastener installation process:
The operator sets up the press via the PC, which passes the setup instructions to solid-state servo drive memory modules and then reverts to a “standby,” totally idle condition (consuming less energy).
The operator next initiates the press cycle using a foot pedal and the ram begins to travel down. Because of low internal friction, low initial load, and the effects of gravity, very little energy is required to accelerate the downward movement of the ram.
As the ram approaches the pressing position, it begins to decelerate and the high torque motor (high force pressing motor) begins to accelerate. Due to the design and function of the unique clutching system, the high torque motor seamlessly takes control of the ram travel and presses with high force. Very little energy is required for the pressing, given the 10:1 gear ratio and short pressing distance.
When the preset force is achieved, the high torque motor is reversed and the high-speed motor begins to accelerate. The high-speed motor takes control and the ram begins upward movement. The low inertial load minimizes energy required to move the ram up.
As the ram approaches the top home position, the regenerative/dynamic brake is applied, which halts travel of the ram. No external energy is required to stop the ram, because the regenerative braking creates its own energy from the motion of the high-speed motor.
NUMBERS TELL THE STORY
The inherent efficiencies of this servo-driven system deliver a cost-effective solution for sheet-metal fabricators striving to “go green.” An added benefit is that multiple types of self-clinching fasteners can be installed automatically without any need for tooling changeovers.
In an effort to decisively quantify energy savings compared with “non-green” hydraulic press equipment, a reputable testing house was recently selected to conduct an independent study of the Series 3000 press. The study’s report card:
Running at 40 spm, the Series 3000 press system was documented to consume less than $40 of energy annually in producing 4.9 million fastener insertions. In contrast, a typical 8-ton hydraulic press running at only 15 spm uses more than $860 of energy to produce 1.4 million fastener insertions.
These numbers tell a compelling story. The electro-mechanical press effectively was shown to consume 20 times less energy while producing 3.5 times the insertions, compared with hydraulic systems. In short, the conclusion is that it would cost more than $3,060 annually for energy alone to run a conventional 8-ton hydraulic press and produce the same amount of strokes delivered by the more efficient Series 3000 system, according to the study.
Footnote: The energy usage reported here was based on straight-line calculations from the independent study and grounded in a relatively low energy cost of $0.10 per kW/hour. Even better news: Higher electricity costs would bolster the outcome by equating to even greater energy cost savings for fabricators seeking to relieve headaches and advance “green” objectives on the shop floor.