Improving small medical part manufacturing

Since 1973, Micro-Matics of Fridley, Minnesota has been manufacturing CNC Swiss precision screw machine products including many kinds of contacts & pins, ground shafts, hardened bushings, rivets, screws, spacers, and other custom parts for the medical, dental, aerospace, commercial, defense, computer, telecommunications, and automotive industries.

According to Jason Wobig, operations manager, “Micro-Matics is primarily an aerospace and medical component Swiss machining job shop. We make components that are thousandths of an inch up to 1-1/4" in diameter. We started out with the old manual style, cam-driven Swiss machines, and we’re one of the largest Escomatic shops in the Midwest. As the company’s grown and evolved, we’ve turned into a Swiss house, mostly Citizen machines such as the M16, L12, and the M32, as well as Tsugami and Star brand machines that have a variety of capabilities.”

Medical part challenges

A while back, Micro-Matics was running a small medical catheter part, and they were struggling with it.

They had some custom collets made for pickoff and, according to Dave Thayer, department manager, “It was a constant struggle. This particular catheter part has very thin walls, it got crushed with a standard M16 collet system because you have very little accuracy in how much tension you’re putting on your collet. Too much force and parts started to collapse. If you don’t have enough tension on it, the part pushes back into the pickoff and you get varying part lengths and varying chamfer diameters. The parts would be out of round and they wouldn’t be on-center.”

Wobig had heard about Masa Tool’s Microconic systems through Todd Pakiz, president of High Tech Representation Inc. (High Tech) in New Prague, Minnesota. “Todd had told me about this system a couple years back. And we had been struggling with these parts. So, I reached out to Todd to see if he was still selling that system.”

High Tech is a manufacturer’s representative agency managing the territories of Minnesota, North Dakota, South Dakota, Iowa, and Nebraska. They represent industrial manufacturers whose products are focused on the machining industry and provide a high level of technical sales support. Pakiz brought in Masa’s F20M10 cartridge and the specific off-the-shelf Microconic collet for the catheter part.

“I wanted to try this system for the catheter part which is a small, thin-walled part approximately 0.040" in diameter and 0.040" in length, with a thickness of about 0.010",” Wobig says. “I wanted something that wasn’t crushing the part. It was really hard to adjust the machine’s pickoff spindle to any degree of accuracy without that happening.”

Wobig found the Masa Microconic system could set up the clamping with a gage pin and set the clamping tension with the Micrograd dial wrench, which sets collet clamping force so the most fragile parts can be held safely and firmly, according to Matt Saccomanno, CEO of Masa Tool.

Cartridge and collet solution

In 1996, Saccomanno was frustrated with the limitations of conventional collets and workholding systems when performing secondary machining operations, so he developed a high-precision, collet-type workholding device for small parts machining.

According to Saccomanno, “A collet system for any machine must be made large enough to fit the maximum workpiece diameter capacity of the machine, so the standard collet mechanism is designed to handle the largest workpieces, meaning it’s excessively forceful and bulky for the smaller workpieces. Smaller parts get sacrificed, because they typically require a higher degree of accuracy and the workholding is more critical.”

The Microconic system consists of a cartridge and collet, with the cartridge fitting in the machine like a standard legacy collet. The cartridge is a self-contained precision mechanism using the machine’s standard collet closing function, meaning the Microconic system can be used on any machine using 5C, TF20, TF25, or TF37 collets, and the Microconic collets fit into Masa’s unique cartridge. Every Microconic cartridge comes standard with extended nose for rigidity because of its single piece construction.

“In fact, the cartridge is so accurate it can be used as a gage to verify machine spindle accuracy,” Pakiz says.

Thayer explains how the Microconic system has worked for Micro-Matics. “With the Masa system we’re able to dial in a specific tension to hold that catheter part without crushing or deforming it and having it on center. We get better quality parts consistently with tighter tolerances. It’s led to a really significant improvement, it’s increased throughput, so we have more parts at the end of the day.” Wobig adds, “As a result of the implementation, the scrap rate on this part dropped by at least 30% once we added the new Masa system.”

According to Masa Tool, the Microconic cartridge concentricity is guaranteed to be within 5µm (0.0002") runout and the collets are hardened and precision ground to the highest quality standards. The regular UM10, 10mm collets Micro-Matics is using in their F20M10 cartridge are available from Ø0.2mm (0.008") to 10mm (0.394"). In addition to the TF 20 spindles, the same collets can be used in TF25, TF37, and 5C sub spindles.

Applying to other applications

Masa’s Microconic system has propagated to other machines and other jobs.

Micro-Matics has been running a collet for a couple of months straight on a distal coupler.

“The distal coupler part has a unique shape. It’s not perfectly round. It has some small flats milled on either side of the part. It’s like a cylindrical pill, like a capsule except with two sides of the long length milled in so there’re flats on it,” Thayer explains. “The part is 0.080" in length, 0.040" in diameter. We then mill the cylindrical diameters 180º from each other to a thickness of 0.030", so taking 0.10" off, then drilling and centering two holes on each end through the flats.”

“Our customer is extremely concerned about any collet indication marks or chip marks on the outside of that cylindrical diameter. The previous collets we were using were custom made that had the profile of the part basically machined into it,” Wobig says.

“It was a straight cylinder round collet, but it was split in half, so it was like two halves of a collet where we were trying to keep the flats in the spaces and then the round cylinder on the round collet part,” Thayer says. “The holding portion would move, and we didn’t have them pinned. Then we had the same issue as on the catheter part: If you squeeze it too tight, you’re starting to push the diameter into the flat so it would deform the OD into the flat and make deformed flats. If squeezed too hard, it would make the flat bump up. If it didn’t sit perfectly right in the custom collet, the split marks of the collet start interfering with the transition between the flat to the diameter and it would make lines on the diameter.”

Remedying the issues

“With the Microconic system, we didn’t need to buy special collets for specific profiles, we just got the actual diameter for the OD of the part and we’re running with that. The spaces in between on the collet are small enough they’re not distorting the round to flat portion if the part gets into there. So, there’s no timing issue at setup. We just put it in there, set our tension, and start picking them off,” Wobig explains.

Thayer notes that, “The extended nose pieces on the Microconic cartridge helps on the catheter tips because I can get closer to where I actually have a supporting back end. If I’m too far away from that supporting back, there’s more of a tendency to crush the front of that part. The Microconic gives me a better tension on the part. On the distal coupler, we have to use a boring bar, or a facing tool to create the back face, which is round. We’d have a lot of trouble trying to hold without nibs or anything on there. And this holds it so that the part stays a little squarer and we’re able to turn it better.”

Masa Tool Inc.: https://www.masatool.com; Micro-Matics Inc.: https://micro-matics.com; Marubeni Citizen-Cincom Inc.: http://www.marucit.com; Star CNC Machine Tool Corp.: https://starcnc.com; Tsugami Rem Sales LLC: https://www.remsales.com