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A New Paradigm in Crimping Press Design

A New Paradigm in Crimping Press Design
06/22/2015
By Rob Boyd, Senior Product Manager, Schleuniger, Inc.

“Over 100 million cycles with no maintenance.” This statement probably seems unbelievable, yet it is true. Schleuniger developed a new crimping press and wanted to ensure that the new design was superior compared to the current state of the art. The newly designed press was life-cycle tested and ran more than 120 million cycles with a 2-ton load. During the test period, no preventive maintenance was performed and not a single part was replaced.

When the Schleuniger UniCrimp 220 was introduced to the market, it was a radical design change with regards to automatic crimping presses. Conventional designs use thick, steel side-plates or a cast frame in conjunction with a motor and gear box combination. These proven designs work very well, however manufacturing costs (and therefore enduser pricing) are higher than desired. These high manufacturing costs are due to very high tolerance requirements for many of the components used in conventional crimping presses. The performance of conventional presses degrades over time due to the design of the motor and gearbox combination. Schleuniger embarked on a project to build a better, yet more cost effective press.

The goal was to create a compact, efficient, cost-effective, 20 kN (2 ton) press with high process capability and durability. The design had to be simple, easy to manufacture and easy to maintain. Of course ease of set-up, application flexibility and integrated crimp force monitoring were also a must.

The frame of the UniCrimp 220 press is made of formed sheet metal rather than solid pieces of heavy steel or a cast frame. Instead of the conventional motor and gearbox combination, a direct belt-drive system was used. A patented ram spring mechanism was incorporated into the press ram, providing excellent consistency and durability. The press stroke is adjustable between 30 mm (1.18”) and 40 mm (1.57”) to easily accommodate the wide range of crimping applicators on the market. Finally, Schleuniger’s CFM 20 crimp force monitor, with its patented Dynamic Tolerance capability, was integrated as a standard feature on all UniCrimp 22X presses.

Frame Design

Comparing the different frame designs further explains why the formed sheet metal design was chosen. Cast frames are very low cost and very rugged; however, volumes must be very high for the initial investment costs to be justified. Welded frame constructions are also very durable but the manufacturing process is relatively expensive. Similarly, using heavy, solid steel side plates, such as those used on the UniCrimp’s predecessor, has also been proven as a very durable design. Unfortunately, the manufacturing process has proven to be too expensive due to the required milling and plating processes. Furthermore, it was determined that the solid steel side plate construction is overkill for forces up to 20 kN (2 tons). The force load distribution over the side plates does not require the same thickness throughout the entire width to achieve the desired results for the target applications.

The forces exerted by the crimping process on the side plates are opposing from front to back. High, outward forces are exerted on the front of the side plates (closest to the applicator). In contrast, lower inward forces are exerted on the back of the side plates. Between the front and the back, the forces cancel. Therefore, it is not necessary to have the same support structure, e.g. side plate thickness, throughout the entire side plate. The formed steel side plates of the UniCrimp 220 press support these forces where it is exerted, in the front and the back.

At first, building a crimping press out of formed sheet metal seemed to be a radical concept; however, it has been used successfully in other industries. One example is truck frames. Truck frames are made of formed sheet metal that support forces far greater than realized on a 20 kN crimping press.

The Schleuniger UC 2XX crimping presses have 6 mm thick side plates that are laser cut for precision and galvanized for durability. The back edges are formed to provide added rigidity. The strength on the front edge is provided by a 10 mm square bar. It’s a very simple concept yet it is very effective.

Drive Design

The traditional gear motor drive design is effective, yet expensive. The gearbox, shaft and ram coupling must be aligned perfectly to prevent premature bearing wear. Tolerances need to be very tight and these tighter tolerances mean higher prices. Furthermore, if parts are installed incorrectly, components will wear prematurely. Finally, as we all know, mechanical parts inevitably wear over time. After millions of cycles, excess play begins to degrade performance. The challenge was to design a crimping press that could achieve the same or better durability and precision with a simpler, lower cost design.

The implementation of a belt drive makes the design much simpler and, as a result, much easier to manufacture and assemble. Tolerances are less critical because the flexible timing belt will compensate. Because of the looser tolerances, parts are less expensive. An added benefit of this design is that servicing is much easier as well

A simple spring was the key

So how do you get precision from a system that has relaxed tolerances? It is true that relaxed tolerances inherently mean that there is more play in the system. However, the answer was quite simple: a spring. Schleuniger developed and implemented a patented spring mechanism that compresses all of the excess play at the bottom of the crimping stroke; where the precision is needed most. This simple spring assembly provides considerably better process capability results. Throughout the life of the press, the spring mechanism continues to remove excess play as parts wear. Machine capability and precision remain consistent for a much longer period of time, therefore extending the lifetime of the machine.

Life Cycle Testing & Independent Study

Life cycle testing of the UC 220 began in September, 2010. A new UC 220 crimping press was set up and initial capability testing revealed a shut height Cmk of 16.146 and a force shut height of 3.19. An aluminium block was installed to provide a 2-ton crimping load and it was left to run at approximately 5,000 cycles per hour, 24 hours a day, 7 days a week.

After 40 million cycles, the test press and a new press were sent to the Frauenhofer Institute to conduct an independent study. The Frauenhofer Institute is “Europe’s largest application-oriented research organization. “ The task was to compare the UC 220 test press, with its 40 million cycles, to a newly manufactured UC 220 press. The objective was to determine if there were any significant differences between a new press and an old press either due to wear or any other reason. Before the press was shipped to Frauenhofer, another capability study revealed a shut height Cmk of 14.837 and a force shut height of 3.08; still extremely good results.

Using very sophisticated test instruments, Frauenhofer set up multiple test scenarios to compare press ram forces and shut height, press ram acceleration, and side plate strain distribution. After numerous tests, the conclusion was that the test press, after 40 million cycles, exhibited only slight differences in press ram acceleration; however these differences were not due to wear or fatigue. Otherwise there were no measurable differences between a new press and a press with 40 million cycles on it, thereby proving the stability of the press over an extended period. An important fact is that throughout the 40 million test cycles, no parts were exchanged and no maintenance was performed; yet the press consistency and stability was still maintained.

Testing was resumed back at Schleuniger; approximately 5,000 cycles per hour under a 2-ton load, 24 hours a day, 7 days a week. In March of 2013, the test press had seen over 120 million cycles.

Conclusion

Through external and long-term testing, the design concepts of the Schleuniger UniCrimp presses have proven to provide world-class performance and durability over an extended period of time.

The latest press models, the UniCrimp 221 and UniCrimp 222 are based on the UniCrimp 220 design but with some improvements. The motor is more energy efficient, metal covers were added to improve appearance, application flexibility has been enhanced and LED lighting was added to improve visibility. However, the basic concepts of the test press detailed above remain the same, meaning customers can expect the same results from the UniCrimp 221 and 222 as was achieved with the UniCrimp 220.

Today, over 1,000 UniCrimp 22X presses have been delivered to customers, providing long-lasting performance and durability for years of precision, trouble-free crimp terminations.