IMM's Plant Tour: Missiles, miracles, and extreme molding

Most of the products that we make violate the essential rules of molding and design." That's what Brian Evenson, president of McKechnie Plastic Components' Minneapolis operation, will tell you when asked how this facility is able to mold an impossibly thick nose cone for the Hellfire missile and incredibly small, insert molded parts for a life-saving medical device. These and other projects represent extreme molding, and the out-of-the-box thinking that goes along with it. 

Purchased in 1988 by McKechnie plc, a billion-dollar, multinational plastic and metal components group based in England, this facility concentrates on the medical, automotive, and military/aerospace markets. McKechnie Minneapolis has found a way to make demanding, unusual parts seem like everyday occurrences. Its approach relies on transforming itself into an extension of its customers' engineering and manufacturing efforts. "We combine early supplier involvement with our in-house expertise to seek least cost solutions to manufacturing challenges," Evenson says. "And we have also pared down our client list from 300 to 40. We are able to maintain close relationships with this smaller group." 

Market Masters 
Making the decision to serve fewer customers has changed the relationship, according to Mark Schaefer, vp business development. "We call them clients now, because the relationship is a professional one. We focus on industry leaders that have a clear strategy within their chosen markets, and keep that focus when developing new clients." 

According to Evenson and Schaefer, this strategy has strengthened McKechnie's business by fostering client confidence. Optimizing designs for manufacturability by consulting with OEMs early in the process has also produced stellar products. 

To better understand its clients, McKechnie sends employees directly to the OEM to observe its process and obtain feedback from its manufacturing and design people. "How can we take cost out if we've never seen the process?" says Schaefer. "By directly working with the OEM, we can bring back clear details that allow all of us to better understand the issues facing our clients." Conversely, McKechnie also offers office space to its clients and suppliers, and solicits their recommendations for improving its own operations. 

The markets served by this plant include medical (28 percent), automotive (30 percent), military/aerospace (19 percent), and an "other" category (23 percent) composed of industrial, IT, and agriculture. Each of the three main markets has different product life cycles, with medical at the low end and military/aerospace at the high end. "Designing our market mix this way means we are producing a range of products with varying life cycles for a more stable business climate," says Schaefer. 

Within the plant, shop-floor staff participate in a three-level training program. Each level requires mastery of different skill sets tied to wages. Manufacturing employees are segregated by molding volume—high, intermediate, or low. Medical molding operators are a fourth group, all certified in-house for cleanroom practices and procedures. Other employees are assigned to a specific market group, with the exception of senior management, which functions across all markets. By specializing in one market, employees are able to develop expertise in their own area—quality, engineering, or sales—as well as in that market. 

Medical Miracles 
First stop on the tour is the medical molding area, a Class 100,000 cleanroom (there also is a Class 10,000 cleanroom where Hellfire missile nose cone assembly is done). There are six presses in the Class 100,000 room and its extension; machines are Arburgs and Milacron Roboshots, ranging from 17 to 55 tons. The primary focus here is implantable devices. All of the machines have closed loop controls integrated with SPC, and most new molds have pressure transducers to do scientific molding. 

Materials processed range from the everyday to the exotic, so rather than being sent through the plant's Motan material handling system, they are handled at the press using modified dryer systems. (These were built by a supplier to meet McKechnie's proprietary design specs.) Because this is a dedicated medical molding room, raw material goes in, and packaged finished goods go out. Contract sterilization is the last segment of its process called MAPS—mold, assemble, package, sterilize. 

It is here that McKechnie produces and assembles a medical device that replaces conventional sutures, called a microvascular anastomic system, developed by 3M Medical Systems. Using this device rather than conventional sutures saves patients up to an hour on the operating table and reduces the potential for clotting. 

"It could be said that we are molding Velcro," says Schaefer, referring to the coupling rings in the product that interconnect to hold blood vessels together. To make it, McKechnie insert molds six stainless steel pins with a shaft diameter of .16 mm into a polyethylene ring. Operators use a 10x microscope to position the pins by hand for molding on a 35-ton vertical shuttle press. Injection speed and pressure are carefully controlled to prevent pins from moving in the tool. 

Other unusual products molded here include connectors for pacemakers and other electrical stimulation products. These are the parts that connect leads from the pacemaker to the heart and are implanted in the body. Many of them are insert molded, and require sterilization and packaging. McKechnie has relationships with all major OEMs in this industry. 

In the Class 100,000 cleanroom, operators mold parts for a maxillofacial surgical device from bioresorbable materials on a micromolding press. Bioresorbables are lactic-acid-based resins that are reabsorbed by the body in a specified amount of time. Reabsorption rates are based on geometry, design, and material chemistry, so it takes a high degree of manufacturing expertise to mold these parts in a consistent way. "These resins are sold by the gram," says Schaefer, "so we developed a system that ensures high-quality parts to minimize scrap." 

Molding by Volume 
McKechnie chose to organize its noncleanroom molding projects by volume—high, intermediate, and low—to improve plant efficiency. In the high-volume molding room, there are 14 presses, mostly Demags, ranging from 50 to 110 tons, with room for four more machines. Typically, each press runs no more than three molds per year, because higher-volume parts tend to run for an extended period of time. Many of these parts are for the automotive market. 

The average age of machines is three years. Each press is equipped with auxiliary equipment such as conveyors and automation, along with robots (Geiger and Conair) to pick parts and cut sprues and runners. "We work with various vendors to design workcells rather than stand-alone machines," says Schaefer. As a result of the automation, four to five presses can be operated by one staff member. 

An example of the challenging parts molded here is a fuel tank cap produced in a two-shot press. The substrate is nylon, but the overmold material is a blowmolding grade of HDPE. It has an extremely low melt flow and no resin-supplier data for the injection molding process. 

"Using our quality lab and manufacturing experts," says Schaefer, "we developed a method for overmolding this material onto nylon. It reminded one of our engineers of trying to push molasses, but we were able to make it work." 

Intermediate-volume molding presses range from 110 to 270 tons. In this area, products for IT, industrial durables, and agriculture markets are typically molded. Low-volume manufacturing is located near the CNC room, where some defense market products are machined after molding. 

Any press not located in a cleanroom receives material through a Motan centralized material handling system. It is capable of feeding 65 machines, and uses ceramic corner pipes for durability. McKechnie uses some filled materials, which can degrade metallic corner pipes. 

"The challenge in processing is to control the three Ms—material, mold, and machine," Schaefer adds. "We installed this system to control the material." It is a closed loop, sealed system that conveys with calibrated dryer air only. Material preparation and transport is pneumatic, and the dry air purges the line ahead of material flow as well as behind it. At each machine, a feeder hopper holds about 15 minutes' worth of material. 

For process control, McKechnie uses the same system as that found in the medical molding area—pressure transducers with closed loop controls tied directly to an SPC system. Molds are often produced at nearby McKechnie Tooling & Engineering (Staples, MN), allowing interaction between tool designers and manufacturing staff.