Making Life-Changing Devices

Modern medical machine shops are constantly striving to meet the demands of acute precision and complexity. An account of how a tool and die shop came up with innovative solutions in the face of challenges.

Complexus Medical, located in Mishawaka, Indiana, has evolved from a small tool and die shop
to a supplier of complex components and assemblies to the medical market. The bulk of its business is dedicated to producing complex orthopaedic instruments, although it also provides metallic and non-metallic implantable components for knee replacement and related medical procedures.

Since medical device OEMs are looking for suppliers that offer competitive cost advantages for the parts and assemblies, price pressure becomes a challenge. However, that is just one of the challenges that shops serving the medical industry, face today. And those challenges impact not only the equipment that this company has purchased over the years, but also the shop
floor practices and business strategies it has adopted to become more competitive.

Given below are a handful of challenges that the company faced as well as the actions the shop has taken to address them.

Challenge: Increasing part complexity; tighter part tolerances.

Solution: Increased adoption of multi-axis, multifunction equipment.

Complexus has a number of conventional CNC machines, including VMCs, turning centers, and wire and sinker EDM units. That said, it seems that the shop’s multifunction turn-mills and Swiss-type lathes are essential these days to efficiently produce some of the complex, contoured medical work that runs through the shop.

For instance, Complexus has three turn-mills from DMG MORI that operate virtually 24/7: two 12,000-rpm NT1000 models and one 20,000-rpm NXT1000. Each of these offers a B-axis milling head, a lower turret with live tooling and a subspindle.

One example of an ideal part to be produced on these machines, a component for a medical device for a femoral procedure, is indicated in image 2. Previously, the shop ran the part across seven machines (saw, lathe, another lathe, gun drill, mill, lathe and another mill). Today, it can be completed in one setup on one of these turn-mills. The parts are produced in batches of 100 to satisfy monthly customer demands. The previous method required 25 hours of total setup time (per 100-piece lot) and about 200 minutes of machining time per part. This has been reduced to four hours of total setup time per batch and 90 minutes of cycle time per part using the turn-mills.

The shop also performs gundrilling on these machines, minimizing bore runout by using relatively slow 250-rpm spindle counter rotation that opposes the gundrill’s rotation. The part shown above has a critical central bore produced via gundrilling on one of these machines. In this case, the turn-mill’s subspindle pulls the part out of the main spindle in three stages, and the part’s bore is gundrilled to 0.0002-inch runout.

The company also has four Star CNC Swiss-type lathes. Although these bar-fed, sliding-headstock machines are effective for producing long parts with relatively small diameters (thanks to their guide-bushing design that offers support very near the cut), the shop also uses these machines to produce relatively short parts that require multiple turning, milling and drilling operations. Machining these parts complete in one setup helps ensure feature-to-feature accuracy while minimizing setup time, work-in-process (WIP) and the number of times a part must be touched.

In fact, complete machining using equipment like this has also impacted the shop’s toolroom. Michael says this area isn’t nearly as large as it once was, because the shop doesn’t need as much custom fixturing as it previously did when it ran parts across multiple machines.

For the medical-grade plastics implant work, Complexus has established a high-speed, non-metallic cell consisting of two four-axis FANUC Robodrills. These 24,000-rpm machines run sans coolant to produce families of knee-replacement parts from ultra-high-molecular-weight (UHMW) polyethylene and other medical-grade plastics. They have fast-indexing rotary tables with four-sided fixtures to enable multiple parts to be installed for longer stretches of unattended machining.

Challenge : More than machining is needed.

Solution : Secondary processes in-house; use of trusted vendors.

The company is selective as to what non-conventional processes to have in-house. The two processes it recently added are laser welding and laser marking. Although the shop had outsourced these laser processes, extended delivery times spurred it to add these capabilities, especially because they are among the last operations to be performed on medical components prior to customer delivery. The shop can perform these operations in a matter of hours, rather than waiting a day or more for an outside vendor to complete them. This also enables components to be sent to the shop’s assembly department for quicker turnaround of completed devices to its customers.

However, it continues to outsource processes like anodizing, passivation, heat treating and electropolishing to trusted vendors, rather than dealing with nitric acid and other chemicals commonly used in those processes. The shop can send parts out for heat treating in the afternoon and have them back the following morning. By not bringing all these secondary processes in-house, the shop can concentrate more on its core capability of precisely machining complex components.

Challenge:Design for manufacturability advice sought by customers.

Solution:Increased engineering capacity.

Complexus strives to work closely with its customers’ design engineers to develop an effective strategy for component and assembly manufacturing, proactively eliminating potential machining problems at that early stage. By taking this critical early step, the company has the capability of helping refine new-product designs so that complex components can be produced at a more competitive cost. In fact, the shop has become deft at identifying obscure machining problems early on in the process through its design for manufacturability (DFM) capability.

In some cases, customers consult Complexus fairly early in the new product design stage. In other cases, customers approach the shop with a 3D CAD model or a prototype (often produced via additive manufacturing), asking for design-improvement advice that will simplify production.

Clean Operation

The facility is clean, organized and well-lit. Recently it increased its floor space to 40,000 sq ft. As part of the expansion, it added more windows to allow more natural light to shine through and upgraded its lighting system. The previous lighting system provided 40 ft candles of light intensity, but the new system provides 175 ft candles. Improved lighting enables employees to more easily see burrs or recognize signs of machining chatter on parts. This type of manufacturing environment is also attractive to the shop’s medical customers because cleanliness and organization is the nature of their business, too.

Author

Derek Korn
Executive Editor
Modern Machine Shop
dkorn@ mmsonline.com