The project was nothing new for Mikron; the company has built more than 3,800 assembly systems over the past 50 years. Every day, Mikron machines assemble some 150 million products, including inhalers, safety syringes, test cartridges, air bag parts, relays and connectors. The company employs more than 700 worldwide at offices in Boudry, Switzerland; Kaunas, Lithuania; Denver; Singapore; and Shanghai.

“Our assembly systems focus on small products—you can hold them in your hand. Our systems often involve complex processes, and data managementis becoming more and more important,” says Jean François Bauer, head of marketing and business development at Mikron.

The medical device industry has become particularly important to the company in the past 10 to 15 years. “That’s where we generate the lion’s share of our sales,” says Bauer. “In addition to high-volume systems with throughput rates of several hundred parts per minute, we also supply scalable systems for very low or medium production. This is because clinical studies and assembly tests have to be carried out in various stages before a medical device is launched on the market and mass production can really get going.”

To ensure maximum flexibility and efficiency, Mikron opts for a modular platform approach, following the example of the automotive industry. Standardized base machines are designed and specified to suit each customer’s requirements and application.

Precision Assembly and Process Documentation

Jörg Besold, who has been a project manager at Mikron for five years, was in charge of the auto-injector line. Together with a core team of 10 people, he was responsible for all the steps in the design and development process, from project kickoff through to final acceptance at the customer’s site.

“To assemble an autoinjector, several plastic parts and a syringe have to be assembled together in a process that must be accurate and controlled,” he says. “We’re using 12 servo presses from Kistler for one cell, and six more for the other cell. That allows us to triple the steps needed so we can achieve the desired volume of over 100 parts per minute.”

The NCFT joining module is an electromechanical servo press designed to apply small forces in a wide range, from 0.05 to 1.5 kilonewtons. Wireless, piezoelectricforce sensors precisely measure force. The sensors have high overload capacity. Very short cycle times are possible since the ram can move at to high velocity. The press is certified for use in ISO 14644-1 class 8 cleanrooms. (It can be used in class 7 clean rooms with some modifications.)

The press is available in two versions: a straight model with a stroke of 100 millimeters and a compact angular variant with strokeof 250 millimeters. Both versions can be combined with the maXYmos NC process monitoring system to achieve complete control of all movements and forces, including detailed process documentation based on piezoelectric force measurement.

“We already had some previous experience of using force-displacement sensor technology from Kistler combined with the maXYmos system,” Besold recalls. “But in view of the demanding requirements for this project, we opted for the high-end solution. It provides control of forces and positions at every point in time, as well as comprehensive process data for every product.

“Because the modules are integrated directly into the automation environment via OPC UA, we’re able to manufacture two product variants simultaneously. The machine control sends the different parameter sets to the maXYmos NC units that control the joining modules.”

All production data and quality parameters are stored in a database, and a matrix code engraved into every product guarantees 100 percent traceability for the customer. Mikron has also integrated quality testing for each step into both assembly cells.

“We’re highly satisfied not only with the equipment from Kistler, but also with the valuable support they give us. With project lead times of nine to 12 months or more, we need a reliable, professional partner who can support us throughout the various phases,” Besold points out.

As this was the first time that Mikron had used the NC joining systems, a joint workshop was staged at Kistler’s headquarters in Winterthur, Switzerland.

“Even though the maXYmos systems are simple to integrate, it was especially useful for our software engineers to learn how the entire joining process is synchronized with the machine and optimized,” says Besold.

Given that the presses would be used for medical device manufacturing, additional adaptations were implemented to meet industry requirements.

“First, we integrated functionality to track and back up all user changes to the system. This is what’s known as an audit trail, and it’s absolutely essential for med-tech applications,” explainsAndré Signer, sales engineer at Kistler. “Then, we prepared our NCFT system for production in class 7 cleanrooms. And finally, we had to replace the lubricants in all the modules to ensure compliance with medical requirements.”

Following a successful assembly test by the end customer, Mikron’s automated assembly system was delivered and mass production began.

“It’s not by chance that Kistler has a reputation for high precision,” says Besold. “These joining systems provide excellent process control for our complex assembly operations, and that’s why we’ll certainly continue using them in the future.”

For more information on servo pressesand process monitoring, call Kistler at 248-668-6900 or visit www.kistler.com.

For more information on automated assembly systems, call Mikron at 303-364-5222 or visit www.mikron.com.