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Down to the bone: Using EDM in medical device manufacturing

Say “medical device manufacturing” and most people think of investment cast hip joints and replacement patellas. The reality is, medical devices range from, as the FDA says, “…tongue depressors and bedpans to … pacemakers … and laser surgical devices.” Some of these devices need electro-discharge machining (EDM) for their manufacture while many more need EDM machining to make the tooling that produces the devices. Here we’ll look at the role played by EDM in both these fields.

The Materials Challenge

Implantable devices like screws and replacement joints, as well as orthodontic braces and other dental pieces, are usually made from extremely tough materials. Not only is biocompatibility essential, but repair options are limited, so they have to survive years of use. For replacement joints titanium, cobalt chrome and stainless steel are favored while nitinol, an alloy of nickel and titanium, is used for catheters and stents as well as in orthodontics. All these metals are hard to machine with conventional removal processes.

Complex Machining Challenges

Medical tools like clamps, saws and knives must endure rigorous sterilization routines, so durability and corrosion-resistance are essential. Stainless steel is used extensively, formed into complex shapes for ease-of-use. Such geometries are hard to produce by conventional machining methods. In addition, some components have sub-millimeter features and distortion during cutting is a significant issue.

Precise, Repeatable Tooling

Many devices used outside the body are molded from plastics. Syringes are one example. These need accurate mold tools with high repeatability between individual cavities. Surface finish requirements are usually demanding and lifetimes of millions of cycles are expected.

Tool steel is commonly used for its low wear rates but machining, especially of flowing curves, is slow and expensive. It’s not uncommon for a tool to need hours of hand polishing to arrive at the final shape and finish, which also increases intra-cavity variation.

Advantages of EDM

As an erosion process, EDM is non-contact, so there are no cutting forces and consequently no distortion. Benefits include:

  • Machining speed independent of workpiece hardness.
  • Ability to make holes in curved surfaces where a drill would slip.
  • Thin walls are possible.
  • Long, deep holes (high L:D ratio,) are possible without fear of tool breakage or wander

Unlike most conventional machining processes, there is no need to rotate either tool or workpiece. This allows machining of sharp internal corners, even for blind pockets. EDM can produce complex forms and do so repeatedly and with high accuracy. It can save time compared to multiple conventional machining processes and achieve smooth blends from one radius to another.

Wire EDM

This uses a thin conductive wire to cut a path through the metal workpiece. The wire is held vertically, but can be angled, giving wire EDM machines a 3D capability.

Wire EDM is useful for putting complex serrations on the jaws of grippers, enabling them to hold in a particular way. It’s used to create precise cutting edges and also for miniature implantable devices like tiny gerotor pumps.

RAM/Sinker EDM

This uses a tool, usually machined from graphite, shaped as a mirror image of the cavity to be cut. (If the finished form is considered negative, the RAM/Sinker EDM tool is the positive.)

RAM/Sinker EDM is used to produce cavities. These could be the hex form on the end of a bone screw (where the surgeon inserts an Allen wrench to tighten the screw,) or to put a cavity in a mold tool.

Hole Cutting

Small hole EDM uses a spinning tubular EDM tool to erode holes. It’s especially useful with curved workpiece surfaces where a conventional drill would wander and likely break. It’s also used in small but deep holes and to create a start location for wire EDM.

Answering The Challenges

As a non-contact process EDM is an essential tool for medical device manufacturing. Parts don’t distort, the designer can have the complex shapes needed, and accuracy and repeatability are high. That’s why it’s used for surgical tools, production of medical device tooling and implantable devices like bone screws

About Micropulse West

Since 1994, Micropulse West has been proudly offering Precision Manufacturing Services such as EDM, CNC and Manual Machining to companies within highly regulated industries like Aerospace/Defense, Energy, Medical, High Tech as well as the Automotive and Firearms Industry. Our skilled and experienced machinists use the latest and most accurate Precision Machining technologies in order to deliver the highest quality precision machined parts.  From small prototyping projects to high volume machining projects, Micropulse West is the Precision Machine Shop you can trust.

If you would like to learn more about what makes Micropulse West different and how we can help with your precision machining needs, call 1- 480-966-2300.