Minneapolis, Minnesota: Swiss machine technology has proven itself to the medical device community where larger quantities of precision machined cylindrical parts are required with consistent quality.
Swiss machining is not a new concept, but it is ideally suited to the growing field of medical device manufacturing. The Swiss process originated and got its name in the 1800's when Swiss watch manufacturers developed a modification to then current lathe technology. This was done in order to make very small, precise parts for watches that required long, small diameter machining turns. Today's Swiss technology has come a long way from that era and now includes computer numeric control (CNC).
This article describes the latest trends in automated Swiss machining and offers a manufacturing approach for the medical device industry that enhances quality, speeds shipments and lowers costs. (Photo One And Photo Two)
The number of patients that require surgery continues to grow as the population ages. New devices are developed while demand increases despite a troubled economy. Precision machined medical devices span an increasingly wider range of medical conditions and treatment. For example, tools like medical introducers and trocars are common, but there are many more: interventional cardiology devices (catheters and surgical tools), urological devices (surgical needles), orthopedic devices (bone screws, implants and joint replacements), minimally invasive surgical devices (laparoscopic instruments), diagnostic devices (point-of-care testing instruments), wound-care devices (staples, suture anchors and clips), and dental devices (implants and instruments).
The need therefore for this new automated Swiss technology is broad-based and growing at an estimated 8 percent annual rate. Figuring a $100 billion medical manufacturing device market in the U.S. alone, the opportunities for application of this new automated Swiss technology appear limitless for those embracing this new technology.
Today's Swiss machines are very precise and allow for a wide range of feature generating techniques. Along with standard milling and turning, a CNC Swiss machine can perform broaching, polygon milling, honing, knurling, burnishing, hobbing (gear cutting), and threading (including thread whirling and thread rolling), as well as other complex machining processes. In many cases, a CNC Swiss machine can produce parts complete, burr free and without additional finishing in a single manufacturing operation. (Photo Three)
The latest Swiss machines such as the Citizen Cincom L20 model are extremely fast, performing multi-axis machining operations simultaneously. Each machine has two spindles, a main spindle and a secondary spindle, whereby the machining is shared and handed off between the two spindles. Primary spindle speeds up to 10,000 rpm, secondary spindle speeds up to 8,000 rpm and gang rotary tool speeds up to 5,000 rpm are the highest for this type of machine. While these machines are extremely fast, their output is multiplied many times when configured into an automated cell. (Photo Four and Photo Five)
The cell's lifeblood is a gantry robot on an elevated 30-foot long track. The gantry robot transfers parts from all four Swiss machines – the workhorses of the cell – to the secondary operation stations in the cell. Programming logic for the robot ensures that parts are removed from the Swiss machine that finishes first (not necessarily in sequential order). This minimizes delays and keeps parts moving efficiently through the cell. (Illustration One )
Each Swiss machine is equipped with its own bar feeder. The bar feeder's purpose is to supply the Swiss machine with raw material. Each bar is twelve feet in length, and the diameter of the bar is dictated by the required diameter of the finished part. Depending upon the diameter of the raw material required for a specific project, anywhere from four to 50 bars of raw material can be placed into the bar feeder, ranging in diameter (respectively) from .750" to .060". The bar feeder "feeds" one bar at a time into the Swiss machine, and as it extracts the last remnant of the current bar it has been machining, it indexes a new bar into the feed channel. This allows less operator intervention.
A three-station cleaning is performed after each part is machined. This subcell includes its own small robot, which takes each part through the three separate ultrasonic baths to remove chips and cutting fluids. This station also contains a rinse tank. After the cleaning and rinse cycles are completed, parts are blown dry. The gantry robot jaws are also cleaned and blown dry prior to delivering finished parts into the gauging system for final inspection. (Photo Six)
The inspection station is the final stage of the cell. Here again the system shines for its capability and flexibility. Every part can be inspected, or if the process capability warrants, a specified percentage of parts can be inspected (for example, 1 part in 20 from each of the four Swiss machines). (Photo Seven)
Parts are inspected using a TESA Scan 50 non-contact measuring system. The system gauge measures length, diameter, angles, radii and other features on cylindrically symmetric components. Runout and other dynamic measurements are also possible. In many cases, no other inspections are needed.
If an out-of-tolerance part is found, the system will shut down only the Swiss machine that machined the non-conforming part. The rest of the cell will continue to operate uninterrupted. The operator is alerted, and can identify the problem and attend to the affected machine while the rest of the cell continues to run.
The inspection gauge is tied in with Q-C Calc software which automatically downloads each measurement taken in order to generate SPC data and other process control information. This information is displayed at the cell so the status of the process can be viewed at a glance in real time.
Finished parts are palletized by the gantry robot in order to maintain lot integrity and part traceability. Each part can be traced not only to when it was made, but which specific machine each part came from, as needed. If there is a problem, non-conforming parts can be easily identified and segregated, without significant operator sorting. This is a cost-saving benefit to both customer and supplier. (Photo Eight)
Not all medical device components are ideally suited to run in this type of cell, but when there is a match, customer benefits are substantial. The cell is designed to create specific manufacturing processes for longer running jobs for the most cost-effective per unit cost. Designed as a low cost solution, the cell optimizes processes and provides a flexible delivery schedule in medium to high volumes (20,000 to 500,000 pieces annually). The automated cell is a very cost-effective choice for producing families of similar parts.
Once a process is created, the cell is designed to minimize changeover between parts. Process standardization (pre-set cutting tools, custom designed pick-off and ejection tooling, CAM program generation and programming adaptations utilizing macros, etc.) allows seamless changeover from one part to the next.
In addition, the ability to switch over quickly between different longer running jobs allows lower inventory levels while providing delivery schedule flexibility.
Substantial efficiencies are achieved when families of parts are manufactured using the automated cell. Within this particular family machined from 17-4 PH stainless steel, there are 13 different components with a combined annual production run of 65,000 parts. The hex and the shank for all 13 components are identical. The length (38mm) for all 13 parts is also identical. The difference between each family part member is the outer angle of the flare, the step diameter dimensions at the end of the flare and inner angle of the flare. (Photo Nine)
All 13 parts within this family are machined from the same raw bar stock size (based on the largest diameter). Because these parts require a common bar size, changeover times is eliminated (cutting tools, guide bushings, collets and bar feeder tooling remain constant). By designing 13 different programs to produce the 13 different sizes, changeover time is virtually eliminated from running one size to another. Machines continue to operate during changeover.
In addition, the automated cell has sufficient flexibility to run a different part in each of the four machines when required. The palletization process keeps parts separated while running to ensure lot integrity and traceability. Each part can be inspected according to its own program and can be called up when the gantry robot delivers it for viewing at the inspection station.
These three similar components are machined from 17-4 PH stainless steel in the cell. With many of the benefits of the first "family of parts" example, this part project shows a range of features that can be machined in the cell. (Photo Ten)
Single use surgical needles for implanting medical devices into the body can be contoured to the desired shape in the automated cell. Machined of 17-4 stainless rod in custom lengths, these instruments have diameter ranges from .06 to .200 inch. The needle pictured has two cross holes centered on the rod diameter and with holes connected with an EDM produced slot. Hole diameters have .0005 inch tolerance and ± .002 inch positioning accuracy.
The EDM produced feature is an example of additional machining operations and finishing processes that are available for one-stop, single sourcing. Additional outside services provided by Marshall include texturing, passivation, electro-polishing, Teflon coating, overmolding, and many types of plating. (Photo Eleven)
The parts pictured provide a typical range of medical device components suitable for production in the new automated Swiss screw machine systems. To recap, they include: (1) families of parts, large and miniature, (2) multiple component assemblies, (3) surgical needle devices. Cost effective part runs range from 20,000 to 500,000 and beyond depending on factors such as material and design complexity. (Photo Twelve)
(Marshall Manufacturing is an ISO certified medical manufacturer of components - and a Twin Cities market pioneer in precision bending, 3D bending, and medical laser tube cutting - that recently
incorporated cellular automated Swiss machining into its precision machining operations.)