Constant Chip Loads Let Your Micro Machining Tools Live Longer

As part features get smaller, the challenges loom large for manufacturers, particularly those in the mold and die industry. After all, when the cutting tools can be as small as a tenth of a millimeter in diameter, a stiff breeze might cause them to break. But even when micro machining processes are perfectly stable, they may be suboptimal in terms of tool life.

Advancements in coatings, carbide substrates and cutting geometries, such as those Seco and Niagara Cutter have incorporated into its latest solid end mills, have resulted in up to 40 to 50 percent longer tool life, but even the best tool will run into problems with dirty collet bores, ambient temperature changes or unstable machine foundations. Even a perfectly balanced tool will instantly run out of balance if its temperature drops a single degree. But perhaps the most important aspect of the micro-milling process to consider is chip load consistency.

It’s far less easy to measure chip load in micro machining, given that average chip thickness will likely be tenths of a thousandth of an inch. Unfortunately, many manufacturers approach micro machining as something best solved with high-rpm spindle speeds, a cutting strategy that can actually impact chip formation in a bad way.

Good chip formation requires a balance between speeds and feeds, but this can be deceptive at the micro level. Even the fastest machines fail to accelerate or decelerate fast enough to keep up with spindle speeds. The results are poorly formed chips, a subpar surface finish and sharply diminished tool life. The solution? Speed up to slow down.

It may sound like an oxymoron – how can you go fast by machining slower? – but after figuring out the average functional feedrate, a shop can then adjust the spindle speed down to the appropriate rpm. Even when depths of cut are as small as 0.001", the same mechanical actions, the same heat and pressure, is required to cut the chip instead of just pushing it around.

For example, a cutting program set to 40,000 rpm at 50 ipm is well within the range of advanced machine tools, but because of the short micro-milling cutting paths, it simply can’t feed that fast. Instead, the actual average speed is 25 ipm, and a reduction in spindle speed to 20,000 rpm reestablishes equilibrium and a constant chip load.

In developing these processes, trial and error is one option, but naturally, tooling OEMs are best equipped to help with these calculations. Given the huge range of materials and tools in use in today’s manufacturing industry, manufacturers will typically be the best resource for cutting data for unfamiliar materials.

Whether it’s components for lifesaving medical devices or the scored grip on the bottom of a tube of lip balm, manufacturers now need to generate the smallest of part features, often with molds. And as these molds continue to shrink in size, tooling manufacturers like Seco and Niagara Cutter will provide the techniques and tool geometries needed for the smallest cuts – and the biggest productivity boosts.