Precision grinding assures fast, compliant MRO repairs

Precision grinding plays an important role in the maintenance, repair, and overhaul (MRO) of critical components to achieve safety and compliance. At the top of the list is aircraft brake rotor resurfacing, a maintenance process to restore brake rotor surfaces, typically made of iron or steel. Crucial to an aircraft’s braking system, these rotors are subjected to significant wear due to extreme heat and friction during landing and braking.

When brake rotors show signs of wear, damage, or deformation, precision grinding can remove a thin layer from the surface of the rotor to eliminate irregularities such as scoring, uneven wear, corrosion, and brake pad deposits to restore the rotor to required specifications.

However, imprecise grinding can seriously compromise aircraft safety and performance, including uneven brake wear; increased heat, vibration, and noise; or lead to premature replacement while slow grinding can impede MRO turnaround time.

Advanced precision grinders can speed rotor resurfacing by leveling surface irregularities to improve performance, safety, and longevity. Grinders can also be used in repair and maintenance operations of other aerospace components, including landing gear parts.

Benefits of precise grinding

For aircraft MROs, there are numerous benefits in using extremely accurate, semi-automated grinders for brake rotor resurfacing.

Uneven rotor surfaces can cause wear on brake pads, which adversely affects braking performance and can lead to vibration and/or noise during braking. The high temperatures generated can cause the rotor to warp, a condition that must be corrected by restoring it to a true, flat state. Contaminants and debris accumulating on the rotor surface must also be removed.

To accomplish this, MROs are increasingly using more precise, semi-automated rotary surface grinders to resurface aircraft rotors (often referred to as Blanchard-style grinding but not exclusive to that brand of grinding machine). These grinders are designed to outperform conventional reciprocating surface grinders by efficiently removing larger amounts of material to tight tolerances in much less processing time. More advanced automated and semi-automated solutions allow less-skilled operators to run parts with less time, attention, and labor involved.

According to Mike Anderson, a technical specialist at DCM Tech Inc., a company that designs and builds industrial semi-automated rotary surface grinders, most aircraft rotors he receives from customers doing sample grinding arrive with deep scores.

“Because too much material would need to be removed to resurface to the depth of the deepest grooves, most MROs tend to grind the rotor surface at least 60% or until most of the imperfections are removed. This practice helps prolong rotor service life,” Anderson says.

Weight and balance considerations also factor in the grinding operation. Brake rotors that are thicker on one side of the aircraft landing gear and thinner on the other can create a weight imbalance affecting straight and level flight of the aircraft.

Conventional reciprocating surface grinders with a reciprocating table and a horizontal spindle spinning the grinding wheel have a slow material removal rate due to requiring multiple table passes across the workpiece and a skilled operator to continually monitor the grinding process.

Conventional rotary surface grinders (without technological enhancements) are a faster option than reciprocating surface grinders but can be problematic in the hands of less experienced operators. With limited control of spindle speeds as well as manual 3-axis traverse controls, the equipment requires sophisticated operators with considerable expertise in achieving optimal machine performance.

Today, rotary surface grinders are designed with much more advanced sensors and control technology that allow an easy-to-use touchscreen interface. These surface grinders outperform conventional surface grinders (both manual rotary and reciprocating) by more efficiently removing large amounts of material, maintaining close tolerances, and reducing process time.

“Features such as variable feed rate and spindle speed, single or multi-step grinding, and easily programmable grind processes make this machine an ideal platform for processing a wide range of materials,” Anderson says.

One machine often selected for aircraft brake rotor grinding is DCM Tech’s IG 080 M, which can handle large aircraft rotors. The grinder includes an 18" diameter variable strength electromagnetic chuck that quickly and securely holds brake rotors of various sizes during processing.

The surface grinder holds the workpiece firmly in place on a rotating table underneath a vertical spindle. Unlike conventional grinders, grinding isn’t performed by the peripheral edge of the wheel, but by the entire diameter of the abrasive surface.

“The 8" abrasive wheel more than covers the cross section of the rotor between its I.D. and O.D. for complete grinding of the rotor surface,” Anderson explains. “To expedite the maintenance or overhaul, the grinder provides an automatic feed system, so the machine can continue running without further operator oversight once it’s started.” A unique demagnetization (demag) function on the electromagnetic chuck ensures that before the brake rotor is released from the machine, any residual magnetism is dissipated.

“This can be valuable for MROs, because if any magnetism remains in the rotor, it might attract magnetic material that could have a negative effect on the brake pads once installed,” Anderson says.

The machine is available with a low open shroud or fully enclosed shroud. The full enclosure contributes to a cleaner shop environment by containing the debris and preventing it from entering the work area. The shroud, which is a sliding door with a built-in window for viewing the process, has the added benefit of reducing the noise produced by the machine. The enclosure also includes a safety door interlock, viewing window, work light, and mist collector unit.

In addition to aircraft brake rotor resurfacing, precision grinding can produce or maintain other aerospace components where flatness, height, or parallelism are critical, including complex engine seals.

Seals are involved in critical processes such as gas flow or temperature regulation, so the grinder must be able to hold very precise tolerances to achieve the desired results. Additionally, the coatings and treatments applied to engine seals tend to be hard and brittle, so grinding operations and handling must be performed with care. Similar coatings are applied to other aerospace components that must be corrosion-, wear-, and thermal-resistant.

MROs are tasked with efficiently repairing and maintaining aircraft fleets to help companies reliably meet their commitment to safety and service. Whether for fast and easy aircraft brake rotor resurfacing or other aerospace components, by opting for more efficient, precise grinding equipment, MROs can expedite necessary repairs and maintenance while facilitating safety and productivity.

DCM Tech Inc.
https://www.dcm-tech.com