Achieve Desired CNC Machined Parts Surface Finish

Whether the parts you machine are highly polished (0.05 – 0.2 µm Ra) or fall within the standard 0.8 – 3.2 µm Ra range, ultimately the goal is to protect your bottom line by eliminating scrap and rework and, whenever possible, meeting Ra requirements in one operation.

This necessitates careful planning and the recognition that, regardless of a CNC machine tool’s accuracy and repeatability, there are other factors affecting the average roughness, or Ra, of a workpiece. These include using the appropriate cutting tools for the material being machined, programming optimum speed and feed rates, minimizing tool chatter and deflection, and efficiently removing chips.

That last issue – chip removal – is sometimes under evaluated. We assume that the coolant simply washes away debris into a chip conveyor that dumps various shapes and sizes into a hopper. Unfortunately, the process is far more complex given the variety of materials machined today. Too often errant chips find there way back into the cutting zone to mar the workpiece, damage the cutting tool so it wears prematurely and no longer machines as smoothly as before.

Two significant ways to prevent this scenario are (1) employing precisely delivered high-pressure coolant to the workpiece and (2) fitting the machine tool with a filtering chip conveyor.

The High-Pressure Coolant Difference

By enhancing chip evacuation, high-pressure coolant delivery prevents marring of the workpiece surface and premature degradation of tooling to reduce cut marks.

Here’s how:

Coolant applied to the cutting zone at low pressure can be counterproductive as much of its cooling capacity vaporizes on contact with the workpiece. However, coolant applied at high pressure (1,000 psi or greater) hits the workpiece at much greater force, thus eliminating super-heated steam vapors. This reduces workpiece and cutting tool temperatures to prolong tool life and maintain consistent surface finish.

Equally important, this action means chips are kept cooler, so they more easily break apart. These chips are not the long, stringy kind typically produced by low pressure coolant, but rather shorter, broken chips that are quickly evacuated.

There are 4 LNS Chipblaster brand high-pressure systems available to provide precise coolant volume and flow for any machining application. Including an LNS Cyclonic filter with the high-pressure system provides the added benefit of coolant filtration to 5 microns which reduces fines recirculation.

Filtering Chip Conveyors

While high-pressure coolant helps expedite chip removal, it’s the chip conveyor that must keep the process flowing by efficiently moving chips out of the way. A backup of chips into the cutting zone will not only degrade surface finish but can slow down or stop production.

In many applications, traditional, non-filtering conveyors may simply not be up to the task. Typically, such chip conveyors allow fine chip particles to recirculate through the coolant system, impacting the part surface finish and shortening both tooling and pump life. This is especially true when machining materials such as aluminum that produces very fine chips.

LNS Turbo filtering chip conveyors, on the other hand, filter coolant to 50 microns so only clean coolant recirculates throughout the system. These self-cleaning conveyors efficiently manage chip materials of all sizes and weights including fines, coarse, stringy, and bushy mixed metals. To match your specific application, choose from the LNS MH Series, MF4 or SF Compact filtering chip conveyors.

The Role of Bar Feeders

Achieving desired surface finish during the initial turning operation begins by reducing bar stock vibration that is transmitted through the spindle to the cutting area by high spindle speeds. The entire line of LNS bar feeders focuses on supporting bar stock to reduce vibrations using a variety of technologies developed by LNS more than 50 years ago.

Additionally, many LNS bar feeders use guiding channels that precisely fit the diameter range of an application, one-piece spindle liners that won’t scratch bar stock and non-marring front stabilizers.

Unloading Parts

After taking all precautions to produce a part with the required Ra surface finish, removing the part from the machine tool must be done carefully. One option is the LNS Blaze Air vacuum unloader that removes parts from the turning machine spindle onto a non-marring tray in 2 – 3 seconds. To protect even the most highly polished parts, the internal Blaze Air components are specially coated to prevent damage to the finished product.

More Than What’s on the Surface

LNS peripherals provide the means to achieve the manufacturing results you want and need, from ensuring consistent surface finishes to optimizing CNC productivity. To learn more, contact your LNS representative.

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