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By: Matthew Danford 18. May 2015

Engineering the Micro

The Kern Micro in this shot, taken at the company’s contract manufacturing operation in Murnau, is set up with an Erowa robot compact for a particularly challenging application: completely unattended production of customer parts made from material that’s 23-percent cobalt.

Featuring multiple technical demonstrations, presentations from customers, and tours of two separate facilities, Kern Microtechnik’s April 23-24 “Precision Days” open house packed a lot of information into two short days in Southern Germany. The stars of all these proceedings, of course, were the machines themselves—machines with a number of design characteristics that struck me as a bit unusual. (Notably, the company’s technology development is heavily informed by real-world applications).

That’s particularly true of the company’s latest offering, the Kern Micro, which is also the machine with perhaps the broadest appeal for U.S. mold manufacturers. Capable of running with water-based coolants, oil mist or completely dry, the machine is said to be well-suited for cutting both steel and graphite electrodes (vacuum systems and other options are available for the latter). Like all Kern machines, it’s designed for nano-level precision (According to the company, positional tolerances of +/-0.5 µm enable achieving part accuracy to +/- 2 µm.) Meanwhile, a high-capacity toolchanger, workpiece palletization and both three- and five-axis configurations ensure plenty of options. Here are just a few of the ways Kern has achieved its goals for precision and versatility with this particular model:  

Automated workpiece handling. Like many other models on the market, the left side of the machine’s workzone is open to accommodate a robot. However, workpiece handling doesn’t have to be limited to external systems. It can actually be built into the toolchanger. 

The upper stations are for tools; the lower stations are for workpieces. 

Rather than the carousel common to many other machine designs, that toolchanger incorporates rows of cutters that are retrieved and brought to the workzone by a pneumatic arm. Total capacity is 209 tools, but customers have the option of sacrificing 90 of those slots to instead accommodate as many as 30 workpieces instead (maximum part size for these 30 stations is 75 × 75 × 150 mm). After all, for the pneumatic arm, retrieving raw material is essentially no different from retrieving cutting tools. With no additional software, components or training required, this configuration adds versatility without adding to costs or floorspace requirements (although some customers opt for both this option and an external robot). However, it’s only available with the machine’s five-axis configuration because the table has to tilt 90 degrees to interface with the pneumatic arm. 

Flexible tool selection. The Micro’s toolchanger is also notable in that the rows of cutters are sub-divided into separate, quick-change pallets with 8 stations each. This enables operators to store complete sets of tools for any given job or application separately and retrieve them as-needed to minimize setup time. So long as the program doesn’t call for a tool in the pallet being swapped, this task can be performed while the machine runs. 

Removable toolchanger pallets add to the machine’s flexibility. 

Aluminum Axis Construction. That’s right: the axes of the Kern Micro aren’t made of steel. They’re 100-percent aluminum. This construction is said to enable smoother machining because aluminum is both stiffer and lighter than steel. That said, aluminum also has a higher thermal expansion coefficient, so making this design work required an intensive focus on temperature control. 

Intelligent temperature management. All machine components, including the aforementioned aluminum axis structure, the spindle, the electrical cabinet and coolants, are kept at a constant temperature of 20°C (which can be raised or lowered as desired). In essence, the company’s patented temperature management system relies on dissipating heat by pumping cold water through critical areas of the machine and the entire periphery.

A look at the machine’s internals reveals no chiller within the enclosure. This configuration eliminates a common source of heat, which can adversely affect machining accuracy. 

Two aspects of this system struck me as particularly unusual. First, a look inside the machine reveals no obvious mechanism to chill the aforementioned water. That’s because chillers produce heat—heat that would otherwise radiate throughout the machine and even into the wider shop. Given the potential effect of this heat on machining accuracy, the company opted instead to employ a system relying on an external chiller, a water-to-water heat exchanger and two, independent cooling circuits. Cold water pumped into the machine on one circuit absorbs the heat of warm water on its way out of the machine on the other circuit  (thus, only heat is exchanged, not water). The result is a constant, stable temperature. And with the chiller located outside the machine enclosure, any excess heat it creates can be pumped away from the machining environment or used to heat the facility. 

The second aspect of the system that caught my eye is the fact that the temperature control system doesn’t stop with the machine. It also extends to the workpiece. Underneath the table is a system that employs both water (for cooling) and oil (for heating) to keep parts at a constant temperature.

Matthias Fritz, head of product development and primary designer of the Micro, shows attendees the workpiece cooling system located beneath the workzone. 

According to the company, this temperature control system is responsible for much of the machine’s nano-level precision. To demonstrate that precision, Kern conducted a “step test” that involved machining three separate faces from a bar inserted into the collet chuck on a five-axis Micro. 

First, the machine cut five “steps” into one face, leaving a height difference of exactly 2µm between each. Next, it cut a slot, visible on the top face running perpendicular to the steps, to a depth of 5 µm when measured from the top of the block. Measured from the second step down, the groove is 3 µm-deep. From the third step, the depth is 1µm. Thus, the floor of the groove is also exactly 1 µm higher than the top of the fourth step, which the cutting tool didn’t touch. The machine then repeated these operations on two more adjacent faces, first by indexing the table 90 degrees and then by tilting it 90 degrees. (Diagram below courtesy of  U.K.-based Kern supplier Rainford Precision).   

For specifications and other information on the Micro, visit Kern’s website, where you’ll also find overviews of the company’s other equipment. 


By: Randy Kerkstra 15. May 2015

The Designer's Edge: Venting

Burn at end of fill knit line from inadequate venting.

If you have been reading my Plastics Technology column or MMT blogs, you know that I spent the first half of my career building and designing injection molds. During this time I was focused on building the highest quality mold to produce a clean part. However, at that time I had no idea how the tool could affect the process window on the molding side, which later exposed some big gaps in my tool standards. All of this experience has lead me to speak with tool shops and moldmakers about their opinions on venting and how some of the tool standards they use can cause issues on the molding side.

Venting is a daily challenge when it comes to part quality and processing. Inadequate venting can cause weak knit lines, gloss issues, bubbles, splay, burns, erosion, increased cycle times, excessive cleaning of the parting lines and very small process windows when lack of venting is processed around.

So, what is adequate venting? There are various thoughts on venting and many are based on opinion without true knowledge or experience. Despite the varied opinions, one thing is for sure: tool shops impact tool standards. For example, a tool can be sent out to have vents added or deepened. Then it comes back and the part now has flash, so the mold is sent back out again. This time it returns with burns on the part from welding up the vent. Varied opinions on venting and indiviual moldmaker work quality can complicate matters when it comes to mold standards.

My next blog on Friday, May 29th, will review a few old standards and how they do not provide adequate venting. It will also examine how parting line bearing surface plays a critical role with keeping vents open.

For more on this and other Designer's Edge topics, catch up with Randy the Amerimold Expo on June 17 for his talk on "Overcoming Repair and Part Quality Challenges with Design." Click here to register to attend.


By: Christina M. Fuges 14. May 2015

WEBINAR:The Evolution of Pre-Hardened Mold Steels

Mold material selection has been a hot topic this year. MMT has hosted webinars, published articles and even secured speakers for the upcoming Amerimold Expo on the subject. 

Our next mold material webinar will take a look at global advances in pre-hardened mold steels on Tuesday, June 9 at 2:00PM EST. International Mold Steel will review the evolution of pre-hardened mold steels from past to present, discussing the differences and advantages among pre-hardened materials.

Attendess will learn how choosing the right material can lower the cost of a mold, how to take advantage of using a pre-hard material versus a harden-able material, how Europe and Asia have evolved in different directions and how the United States began Euro-centric and has evolved into a globalized view.

Register today!


By: Matthew Danford 13. May 2015

Real-World Experience Guides Machine Development

 

Nestled among the Alpine foothills in Bavaria, southern Germany, the building depicted above looks more like a home or a ski lodge than an advanced manufacturing plant. In fact, it’s the primary production facility of a company that claims to be Europe’s largest supplier of micro parts (loosely defined as those measuring less than 50 square mm). Although the components machined here are small, the facility’s outward appearance belies its size. Production occurs mostly underground on machinery that’s capable of achieving tolerances measured not in millimeters, but in microns.

Notably, the majority of that machinery was manufactured at this very same plant. The company, Kern Microtechnik, isn’t just a producer of discrete parts. It’s also a machine tool builder—a machine tool builder that’s ready and eager to apply its manufacturing expertise toward making further inroads with you, the U.S. mold manufacturer.

The company’s Marnau location is dedicated not just to building its own machines, but using those same machines to produce customer parts. 

This focus on the U.S. mold and die sector is evidenced by more than just the invitation of MoldMaking Technology to the company’s April 23-24 “Precision Days” open house event.  Recent years have seen European mold manufacturers purchase Kern machines in increasing numbers, and the company hopes to duplicate that success here in the States. So says Toni Mangold, who recently moved from Murnau to Webster, Massachusetts to serve as sales director for U.S. arm Kern Precision. Beyond personnel shifts, the operation recently expanded its U.S. presence through a partnership with Michigan-based machine tool supplier Merrifield Machinery Solutions.

Like those in Europe, U.S. mold shops potentially have much to gain from technology informed by real-world experience in manufacturing some of the most intricate parts on the globe, Mangold says. The company’s experiences with its own machines in actual contract applications, which account for 80 percent of the Murnau plant’s business, better prepares it to help other users with their own production challenges, he explains. Likewise, lessons learned in contract manufacturing help engineers design better machines at the headquarters and assembly facility in nearby Eschenlohe.

The company’s most precise machine is the Pyramid Nano, which features hydrostatic drives and guides in all linear axes. This model is an ideal fit for shops with a niche in parts that with exceptionally stringent accuracy and surface finish requirements, Mangold says. 

The Pyramid Nano, shown on the left cutting hard ceramic dental implants at the contract manufacturing operation in Murnau, incorporates all hydrostatic axes. The company invited attendees to “feel” the benefits for themselves with the functional model of the axis structure on the right. 

However, he says the latest offering, the Kern Micro, is more accessible for the vast majority of even the most demanding mold manufacturing applications. Building on the success of the earlier Evo model, the Micro’s positional accuracy of +/- 0.5 µm in both three- and five-axis configurations places it firmly within the company’s historical niche: Complex, intricate machining to extremely tight tolerances.  

The Micro in this shot is set up with an Erowa robot compact for a particularly challenging application: completely unattended production of customer parts made from material that’s 23-percent cobalt. The machine’s temperature stability, CBN cutting tools and in-machine laser from Blum are just a few critical aspects of manufacturing these parts effectively, not to mention careful process engineering. 

Although the Micro was the machine I focused on most during my time at Kern, the machine’s broad moldmaking appeal wasn’t the only reason. For me at least, the design concepts behind the machine’s flexibility and precision seemed just as noteworthy as its raw capability. Highlights include an aluminum axis structure, a different type of travel system, a proprietary temperature-control concept, and a particularly versatile toolchanger design, all of which are covered in more detail here


By: Christina M. Fuges 12. May 2015

MMT's May Digital Edition Is Now Available

This month we look at how simulation of both the induction heating and injection molding processes can optimize cycle time and final part results; how normal vectors are not always the best choice for milling complex mold surfaces; how hard-coating provides benefits that make aluminum tooling an attractive alternative to steel, how tool center point management streamlines five-axis programming and setup, and much more.

Other topics include: social media, cost management, profile of Superior Tooling, a software case study, a repair case study, Pellet to Part (P2P) on mold cooling, speical Amerimold Expo Exhibitor Product Focus, MoldMaking Business Index, Automotive/Transportation and Consumer Products end market reports and our tip on 3D machining with demo video.

Click here for our digital edition.



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