Precision grinding assures fast, compliant MRO repairs

For aircraft MROs, precision grinding plays an important role in the maintenance, repair, and overhaul of various critical components to achieve safety and compliance.

At the top of the list is aircraft brake rotor resurfacing, a maintenance process used to restore the surface of the brake rotors, typically made of iron or steel. As critical components of an aircraft's braking system, these rotors are subjected to significant wear and tear due to extreme conditions of 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 lead to serious issues that can compromise the safety and performance of the aircraft, including uneven brake wear, increased heat, vibration, and noise, or lead to premature replacement. Slow grinding can also impede the MRO turnaround time.

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

The Benefits of Precise Grinding Operations

For aircraft MROs, there are numerous benefits to utilizing 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 that accumulate 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.

There are also weight and balance considerations that factor into the grinding operation. If the brake rotors are thicker on one side of the aircraft landing gear and thinner on the other, this can create a weight imbalance that can affect straight and level flight of the aircraft.

Conventional reciprocating surface grinders with a reciprocating table and a horizontal spindle that spins the grinding wheel have a slow material removal rate due to multiple table passes across the work piece being required to complete the work and a skilled operator to continually monitor the grind 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 that can sense optimal machine performance.

Today, rotary surface grinders are designed with much more advanced sensors and control technology that allows for an interface with easy-to-use touchscreen HMI’s. 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,” says Anderson.

According to Anderson, the machine most often selected for aircraft brake rotor grinding is DCM Tech’s IG 080 M, which is economical and ideally sized to 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, the grinding is not performed by the peripheral edge of the wheel, but by the entire diameter of the abrasive surface. Anderson says this is similar to a lawn mower blade that can cut a wide swath of grass versus a blade run on its end, which will only cut a narrow strip.

“The eight-inch abrasive wheel more than covers the cross section of the rotor between its ID and OD for complete grinding of the rotor surface,” says Anderson.

“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 is started,” adds Anderson.

A unique demag (demagnetization) 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,” says Anderson.

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.

Besides aircraft brake rotor resurfacing, precision grinding can also be used to produce or maintain various 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. In addition, 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.

Anderson says the alternatives to the IG 080 M for aerospace components include the larger IG 282 SD, which includes advanced features that automate the initial contact between the abrasive wheel and the part.

On the DCM SD series grinders, this option detects vibration as the abrasive wheel makes contact with the work piece. When the machine senses the abrasive wheel has contacted the part, it automatically transitions to the grind cycle parameters. Automatic part detection eliminates the need for the operator to do time-consuming, error-prone ‘manual touch offs,’ where they would manually feed the abrasive wheel down until it makes contact with the surface of the part, setting that z axis position as the zero set point, backing the abrasive off the work piece and cycle starting the grinder.

The IG 382 SD and IG 482 SD with 36” and 48” diameter tables respectively, can process single large parts or batches of smaller parts, including aircraft brake rotors.

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 for other aerospace components, by opting to utilize more efficient, precise grinding equipment, MROs can expedite necessary repairs and maintenance while facilitating safety and productivity.

For more information, call (800) 533-5339, email info@dcm-tech.com, visit www.dcm-tech.com, or write to DCM Tech at 4455 Theurer Blvd, Winona, MN 55987.