Presses for Medical Device Assembly
As the following case histories show, medical device manufacturers are using presses to solve diverse assembly challenges.
Peak Pipette Performance
Indianapolis-based Cook Medical Inc. manufactures a wide range of products, including eight series of pipettes. Pipettes are long, slender tubes that attach to or incorporate a rubber bulb. By squeezing the bulb, lab technicians or medical personnel can suction small quantities of liquid into the tube for transference or measuring out.
Nearly 20 assemblers at Cook Medical use a manual VK750 toggle press from BalTec Corp. to precisely press small O-rings or bushings into the bulb so that the pipette-bulb interface is leak-free with maximum suction. The assemblers work in a lean-manufacturing environment.
Cook has used the VK750 presses for several years. The company prefers them because they have a square ram rather than a round one and produce the full rated force at the end of a stroke. The VK750 has a force capacity of 7.5 kilonewtons and a 40-millmeter working stroke.
“This press is ideal for the production of high-precision tiny components in small and medium batches,” says Charles Rupprecht, executive vice president of BalTec Corp.
Plunging Into the Syringe Market
Many people hate syringes, but that feeling isn’t shared by one U.S.-based manufacturer of medical devices and press supplier Promess Inc. For the past three years, these two companies have worked together to improve the quantity and quality of syringes produced.
Each syringe consists of a preassembled plunger that is pressed into a glass or plastic tube. The medical-device manufacturer uses the Promess EMAP01 electromechanical press to insert the plunger into the tube.
After that, the press ram pulls the plunger up and pushes it back down through the complete range of motion twice. The first time is to make sure the plunger moves smoothly; the second time to collect force-distance data, as the press contains an integrated force transducer. Assembled plungers are then conveyed to another workstation for packaging.
“The transducer monitors the force-distance curve so the company can spot failed parts, which are generally plunger faults,” says Glenn Nausley, president of Promess. “The three primary faults are mismatched components, bad piston and plunger rod assemblies, and defective pistons.”
A high-volume, fully automated application, syringe assembly takes place in a clean room and is done using five presses. Each press uses only about 3 pounds of force to insert the plunger and completes an assembly cycle every 4 seconds. The presses run continuously two shifts per day, five or six days per week.
“Previously, the manufacturer used pneumatic presses,” says Nausley. “Unfortunately, the plunger often got hung up during testing and didn’t move correctly, resulting in many unusable syringes.”
Since 2007, an upper Midwest medical-device manufacturer has been using several JP054-CL servo-driven electric presses to join wire leads to 100,000 pacemakers annually. The manufacturer operates 12 of the presses, made by Janome Industrial Equipment USA Inc., two shifts per day, five days per week.
Previously, the manufacturer used pneumatic presses, but they often produced poor crimping and broken wires, says Phil Cohen, national sales manager for Janome Industrial. The pneumatic presses also offered little control of ram force or distance.
Before assembly begins, a worker scans the bar code of the correct fixture and attaches it to the press. The PLC automatically calls up the associated program, and Janome’s SPC software collects ram force and distance data.
Next, the assembler retrieves a wire lead and pacemaker from separate bins. Each wire lead consists of two wires, 3 to 4 inches long. The pacemaker is about the size of a quarter.
The assembler places the two components in the fixture, then activates the press using its two-hand switchbox. Both parts must be correctly placed in the fixture for the press to activate. The press joins the wire to the pacemaker in 1 second. The worker removes the assembly, which is conveyed to the next workcell for continuity testing.
Regardless of where a medical-device manufacturer is located, it faces the constant challenge of reducing rework. One United Kingdom manufacturer of bandages and various medical products has significantly reduced rework on its catheters by using a pneumatic press.
The manufacturer produces 200,000 to 300,000 catheters annually. Until recently, the company used ultrasonic welding to join one end of a catheter tube to a valve and cut the other end. Unfortunately, this process often created burrs at the cut end.
Earlier this year, the manufacturer replaced the ultrasonic welding system with a Toggle-Aire 1030 pneumatic press and 17 fixtures made by AIM-Joraco. Some fixtures contain a blade, which cuts the catheter tube cleanly.
“The press eliminates the need for someone to further clean the parts,” says Andy Lewis, president of AIM-Joraco. “This saves money and increases productivity.”
The 17 fixtures sit on a wheeled cart next to the stationary press. The worker retrieves the correct fixture and installs it in the press.
Catheter tubes and valves are automatically fed into the press, which joins the two components. The crimping process takes 1 second and requires 100 pounds of force.
After the operator changes the fixture, the tube-valve assemblies are re-fed into the press, which cuts the open tube end on each catheter and conveys the finished catheters to the packing area.
From its Cork, Ireland, headquarters, Millipore produces advanced products for the biopharmaceutical manufacturing sector. Among its core products are specialized filtration equipment and filter membranes for purifying water for blood and cell analysis applications.
In 2004, Millipore automated its filter membrane-cutting process—replacing its existing multistage press tool with eight Model 415 servo presses from Schmidt Technology.
Vincent Smith, senior project engineer for Millipore, says the 415 servo presses have increased productivity and decreased maintenance. He says the presses have completed more than 40 million cycles with no downtime apart from routine maintenance.
Dave Zabrosky, North American sales manager for Schmidt Technology, says the presses provide accuracy and repeatability to within ±0.01 millimeter, and cut membranes from 150 to 320 millimeters wide.
Millipore has integrated some presses into robotic handling systems, enabling the company to further increase production and reduce scrap material. A specially designed blade mounted on the press ram cuts individual discs from a roll of filter membrane. Each disc is then retrieved by a pick-and-place robot, placed on a conveyor, and moved to another workstation for placement in fabrication equipment.
Pin ’Em Together
For the past two years, a Pennsylvania-based prosthesis manufacturer has been using the 5000L-10 pneumatic press by Fancort Industries Inc. to pin together joints used in artificial legs and arms. Several types of joints are made at the plant. Volume is several thousand joints per week.
The company had tried a hydraulic press and another supplier’s pneumatic press, but neither performed consistently. Often times, the output force went beyond the “sweet spot,” which is 50 percent to 75 percent of press capacity, says Robert Antonelli, vice president of Fancort Industries.
Each joint type requires a unique fixture that the worker attaches to the press. The worker then retrieves one pin and two joint pieces from separate bins. The pin is about ½-inch long and made of titanium or stainless steel. Joint pieces vary in size and are made of durable plastic.
The worker places the pin between the joint pieces, sets the components into the fixture and activates the press by using a two-hand anti-tie down switch. Cycle time is 1 to 2 seconds.
The press swages the joint pieces and creates a hinged joint, which the worker removes and places in a bin. These joints are later used to attach upper and lower sections of prosthetic limbs.
Clean Machine for Surgical Tools
Miniature pins are difficult to accurately insert into surgical-tool components during assembly. This reality has led a major U.S. medical-device manufacturer to use an enhanced Model CR press to automatically insert these tiny pins, which are less than 2 millimeters OD and shorter than 10 millimeters.
Made by Spirol International Corp., the enhanced Model CR machine is mounted in a self-contained workstation specially designed for clean-room applications. Machine components that come in direct contact with the surgical tools are made of inert 300 stainless steel and Delrin polymer. Noncontact areas feature either electroless nickel plating or white epoxy paint.
A load cell is installed between the insertion cylinder and the insertion punch to measure the force required to install each pin. This data is registered on the interface display, and can be transferred to a flash drive, PC or PLC for further analysis.
When assembling a surgical tool, the worker loads one or more components in a fixture located just below the pin insertion device. The fixture keeps the component in perfect alignment with the pin or pins to be inserted.
Upon machine activation, the insertion head advances, installs one or more pins, retracts and resets, says Christie Jones, market development manager for Spirol International Corp. Cycle time is about 3 seconds. The worker removes the assembled tool (or tool section) and places it in a bin.
The Lifeblood of Assembly
Haemonetics, based in Braintree, MA, has been making blood-processing equipment for more than 40 years. This automated equipment is used to collect, wash, and return a patient’s blood during and after orthopedic surgery to help prevent infection.
Although assembly takes place in Braintree, fabrication of the aluminum components used in the equipment is done by many shops throughout North America. Many of these fabricators use the Pemserter Series 4 or Series 2000 press to attach self-clinching nuts or studs to components. Some fabricators have used as many as nine presses for the past 20 years, says John McLaughlin, North America sales manager for the Pemserter division of Penn Engineering. Volume varies for each fabricator, but averages several thousand fasteners annually.
Aluminum components with holes in them are brought to each assembly workstation. The components include flat panels, chassis, brackets with right-angle bends and control boxes. They range from 2 by 4 inches to 4 by 12 by 24 inches.
To install a self-clinching nut with a Series 4 press, a worker inserts the fastener into a counterbore in the anvil of the press. He then inserts an aluminum sheet into the press, centering the hole over the nut shank, and activates the press with a foot pedal. The process is similar for a self-clinching stud. The assembler inserts the threaded section of the fastener into a hollow in the anvil. He then inserts the sheet into the press, centering the hole over the base of the stud, and activates the press. Cycle time is 2 seconds.
Fasteners are automatically bowl fed into the Series 2000 press. In this case, the worker places the hole in the sheet over a pin in the anvil before activating the press.
Depending on the application, press force is 1,500 to 6,000 pounds. The Series 2000 press has an inline transducer that immediately displays press force on a touch screen.
Sealed With a Press
Although Medtronics does not use a press to assemble its implantable defibrillators, the company has used many HyperCyl HD2G-10 hydropneumatic presses the past 12 years to seal the device’s packaging. Medtronics tried hydraulic presses, but they often contaminated the defibrillators. Packaging is done in a clean room.
Currently, Medtronics uses 20 HD2G-10 presses, says Todd Brieschke, president of Aries Engineering Co. Inc. All of the presses are nickel plated and feature stainless steel construction. In addition, the press has a bolster plate that holds a heating element.
The packaging process begins with workers placing one defibrillator into each pocket of a thick plastic container. This container has 12 pockets for large defibrillators, 24 pockets for small defibrillators.
Each container is then covered with heat-shrink material and conveyed to the press station. There, the container is placed within the press fixture so that the edge of the heat-shrink material is aligned with the heating element.
The worker activates the HD2G-10 press, which creates a seal by pressing the heat-shrink material against the heating element for 5 to 10 seconds. The finished container is removed from the press and conveyed to the shipping department.