High-Precision Tooling Keeps Tolerances Tight for Multi-Axis Medical Work

In some instances, a part’s geometry also makes secure workholding difficult. This can be especially true toward the end of machining a five-axis part, when the shop must machine the features of the section that was held by the vise. At that point, the operator must flip the part and often secure it with workholding that grips the workpiece by its already-finished features, which means using less-than-optimal clamping force that likewise reduces rigidity.

Plus, some materials like titanium require greater cutting forces than aluminum or steel, which can further strain the rigidity of the system.

Certainly, high-quality workholding and the machine’s vibration damping capabilities will help overcome these workpiece feature challenges. However, medical part tolerances are often well under 0.001 inch, which means the machine, workholding, and tooling must all provide maximum rigidity and reduce runout as much as possible. Even the most rigid machine and stable workholding will fail to produce precision parts if subpar toolholders are used.

Run the right toolholders for rigidity

ER-collet type toolholding is common in high-precision machining applications. It provides rigidity by creating a uniform gripping force around the entire circumference of the cutting tool. This design dramatically reduces runout while also providing rigidity, precision, repeatability, and longer tool life.

However, there are more advanced collet designs that deliver even greater precision, one of which is the micRun super-precision collet system from REGO-FIX.

The micRun system is similar to the ER collet in design, but achieves a far greater degree of precision. When assembled, the super-precision system delivers a TIR of 3 micrometers (0.0001 inch) at tool lengths up to 3´D. Such low TIR is possible thanks to the system’s specially engineered nut that holds the collet together.

The nut is balanced by design and dramatically reduces friction along its inner threads and all mating surfaces, while increasing clamping forces. With performance at this level, shops medical components easily achieve excellent surface finishes and tight tolerances with a level of repeatability necessary for higher production volumes.

While solutions like the micRun system provide excellent clamping force and reduced runout, there are other types of toolholders equally as precise. Mechanically based, press-fit systems like powRgrip, also from REGO-FIX, is one example.

The powRgrip system uses pressure along with precision-mating tapers on the holder ID and the collet OD. In use, shops insert a cutting tool into the collet, then place the collet into the holder and load that assembly into a hydraulic press unit that pushes the collet into the toolholder body. As the collet slides in, its taper meshes with that of the holder’s to apply uniform clamping force to the cutting tool shank, locking it into place.

The process of pressing the collet into place takes less than 10 seconds and does not involve heating or cooling the holder assembly.

The design of the collet and holder provides higher clamping forces than shrink-fit tooling and runout that’s well under 0.0001 inch. The result is less vibration for improved tool life and superior surfaces finishes.

Even without multi-axis machining, medical manufacturing can require intense machining strategies to address the competing needs for complexity and precision, especially while trying to consistently keep parts in-tolerance at a profitable rate. The prevalence of difficult-to-machine materials like titanium or intricate features can exacerbate these challenges.

Fortunately, when the toolholder is as precise as these examples, precision machining at production levels can be much easier to achieve.