DRAMATIC IMPROVEMENTS IN MACHINING SURGICAL TOOLS

Stryker Corporation (Kalamazoo, MI) is a global manufacturer of medical devices and equipment, ranging from orthopaedic implants to all types of surgical apparatus and patient care devices. Its products are found in medical care facilities around the world.

The Stryker Instruments Division operates five facilities that are located in Kalamazoo, Texas, Puerto Rico, Germany and Ireland. This division produces surgical tools, including cast cutters, inflow/outflow cannulae, burrs, drills, saws and microdebriders for surgeons and operating room equipment specifiers, as well as otolaryngologists (ear, nose and throat or ENT), emergency medical vehicle outfitters and others. These devices are used primarily for orthopaedic, spine, neurological and ENT procedures, plus minimally invasive interventional pain procedures.

Stryker has frequent requirements to manufacture low quantities of its high-precision System 6 power tools, which include highly specialized handheld devices such as oscillating bone saws. This scenario presents an ongoing challenge for the Production Group management team at the main manufacturing location in Kalamazoo, which is also home to the Experimental Group that investigates new technologies, advanced materials and various manufacturing protocols in an effort to maintain optimal productivity for the company. Production Part Approval Process (PPAP) protocols are also strategized here.

The company uses a variety of substrates in its tool production, including 300 and 400 series stainless steels, 6061 aluminum and titanium, plus specialty materials such as Inconel, Nitinol, ALG alloys and others. Assorted thermoplastics such as Delrin, ABS and Teflon, plus thermoplastic elastomers, are also machined here. Production processes are strictly monitored for compliance to FDA standards.

The Experimental Group provides components to Stryker research and development engineers for testing and evaluation, including prototyping surgical tools for field evaluation and aesthetic feedback by surgeons, though not for formal trials or surgical use. As a result, the company maintains a variety of machine tools and other metalworking equipment at its Kalamazoo facility. Basic milling and drilling equipment is here, alongside three- and five-axis CNC machining centers and EDMs.

Among the newest advanced CNC machines in the Experimental Group is a DMG Model DMC 635 V eco, a powerful three-axis vertical milling center with an 8000 rpm spindle and a 20-position tool changer, all run by the Siemens Sinumerik 810D CNC and ShopMill software onboard. Rich Mitchell, supervisor of the Experimental Group, explains how ?We typically store a few programs on the CNC and keep our backlog of programs on a network drive for easy recall. Our group supports about 60 engineers, so the communication between departments is constant and quite fluid. We take IGES or PRT 3D files and can program directly from the digital content, using MasterCAM and now the ShopMill program that is right on the machine.?

Mitchell added that ?The Sinumerik 810D control receives excellent ratings from our operators and has fast become their control of choice, especially on this very fast and flexible three-axis ECO milling machine from DMG.? He detailed how the part and tool set-up pages are quite intuitive and incorporate graphic depictions for specific data inputs, thereby reducing the learning curve for the operators. ?Most of our guys had never used a Siemens control previously, so it is ironic that this CNC is now their favorite. They literally line up to use it,? says Mitchell.

He further noted that program transfer from the Stryker network back to the CNC is fast and simple. This is very advantageous in the Experimental Group, where most jobs are one-offs or very small quantities. Operators can write and run multiple programs through each CNC daily, saving time on entering and editing set-up data onto the machine.

The very nature of this department, as it conducts various experimental trials to seek out the best production methods and machining strategies, mandates extremely fast turnarounds and Mitchell credits the CNC for facilitating this process. ?We currently have four other controls in our milling department, so it?s easy to imagine the challenges our guys face daily. This numerical control has worked quite well for us with a manual touch probe and manual Z-axis presetter for tooling. As we expand or replace current milling technology in our production, we will most likely transition to an 840D with a Renishaw touch probe and tool presetter to expedite set-ups.?

The seven operators in the Experimental Group were all given training on the programming of the CNC by machine tool builder DMG America, represented by Nate Buck, a sales engineer operating from the OEM?s North American headquarters in Itasca, Illinois, just outside Chicago.

This machine joins multiple TWIN 65 and TWIN 42 machining centers, each with an upper B-axis to complement the Y-axis and driven tools and create the contours and sophisticated geometries needed at Stryker. These turning machines have the Sinumerik 840D onboard to enable precise and transferable control of spindle and axis movement variations via compile cycles, so the Experimental engineers can make more rapid changes in their production scheduling, according to Randy Carpenter, a senior project engineer for Stryker Instrument?s Production Group.

In one manufacturing example, Carpenter details how ?We run families of parts most often. We have one set of parts, run in grades 416 and 17-4 stainless steel with 38 Rockwell hardness. We?re typically running dimensional tolerances down to the ten-thousandths, so it is very precise work. Compared to the older machines and controls, we have tracked our cycle times in relation to our target Cpks and found that we are getting better than 20 percent reductions, as a result of the DMG machines with Siemens CNC onboard.?

That?s not all. ?Plus, we already see the improvements in surface finish, owing to the smoother translations line-to-line in the milling and turning programs,? adds Carpenter, who also noted his production department has been able to achieve considerably higher changeover efficiencies that allow more jobs to run per shift. ?System 6 has become a big seller for us and our ability to ramp up production on these machine tools with these numerical controls has been a big plus.?

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DMG America, Inc., 265 Spring Lake Drive, Itasca, IL 60143, 630-227-3900, Fax: 630-227-3975; contact Julian Seume, marketing manager, at info@dmgamerica.com, www.dmgamerica.com.

Siemens Industry, Inc. Drives Technologies-Motion Control, 390 Kent Avenue, Elk Grove Village, IL 60007, 847-640-1595, Fax: 847-437-0784; contact John Meyer, manager, marketing communications, at SiemensMTBUMarCom.sea@siemens.com, www.usa.siemens.com/cnc.