2025/11/18

Ultrasonic CMC Machining Playbook: Higher MRR, Better Holes, Longer Tool Life

Using a #80 Φ120mm electroplated diamond wheel with HIT HBT-40 ultrasonic grinding wheel module, we achieved 3.3 times higher MRR (Material Removal Rate) and 3 times longer wheel life versus the baseline CCB (Carbon-Ceramic Brake Disc) rough-grind. With HIT HBT-40 ultrasonic toolholder module and a Φ5mm diamond drill, we saw 5 times faster cycle time, ≤0.1mm crack size, and 4 times longer tool life. Test conditions and parameters are listed in Tables A-D.

Why are CMCs hard to machine?

🔘 What material properties drive chipping, fraying, and heat?

Low fracture toughness and limited plasticity

CMCs (Ceramic Matrix Composites) have low fracture toughness and virtually no plasticity that cause cracks to initiate at small defects instead of forming a continuous shear chip.

(Figure 1. fragment of sports car carbon-ceramic discs brakes)

High hardness and abrasive ceramic phases

Their very hard, abrasive phases (e.g., SiC, Al2O3) intensify tool wear and frictions, which concentrates heat at the tool-workpiece interface.

Heterogeneous and anisotropic architecture

The heterogeneous fiber structure indicates unstable cutting force during processing; weak fiber-matrix interfaces bring potential interfacial debonding, so edges fuzz and fray rather than cut cleanly.

Thermal properties that localize heat

Many matrices have modest thermal conductivity, which easily builds up cutting heat in within. Heat concentrates at the tool-workpiece interface, raising wear and burn risk.

Oxidation sensitivity

At temperature, oxidative embrittlement of carbon-containing phases further reduces toughness and accelerate edge chipping.

🔘 Where do conventional grinding and drilling fail on CMCs?

Long process time with heat generation that seriously consumes wheels

Grinding of CMCs runs slow and eats wheels because the ceramic phases are very hard and abrasive, so diamond grains dull and pull out quickly. As a result, the depth of cut and feed should remain low to avoid brittle fracture and heat. Hardness of the material brings excessive heat generation during processing. The wheels wear out quickly and force more dress cycles, so material removal rate stays low, while wheel consumption stays high.

Long process time, poor hole quality, and serious tool wear

Drilling of CMCs takes long, cracks the hole edges, and burns tools mainly because of its high hardness and heterogeneous structure. The cutting lips see continuous hard-abrasive contact that strips diamond coatings fast. To prevent cracks around the drilling holes, efficiency usually must be sacrificed, which extends cycle time further.

How does HIT Ultrasonic improve CMC machining?

🔘 What is the ultrasonic mechanism in grinding and drilling?

Ultrasonic mechanism in grinding process

Ultrasonic provides high frequency micro-scale vibrations (over 20,000 times per second in axial direction) to the grinding wheel. The vibration periodically separates wheel and workpiece during processing, turning conventional rubbing into micro-impacts, which facilitates in massive material removal. The periodic separation also pumps cutting fluid into the interface, which helps with wheel cooling and cutting chip evacuation.

(Figure 2. HIT ultrasonic-assisted surface grinding of carbon-ceramic brake disc)

Ultrasonic mechanism in drilling process

The percussive micro-cutting from ultrasonic micro-vibrations initiates micro-fracture in brittle phases, so material removal shifts from crushing to controlled chip or powder formation. Short contact times and better fracture mechanics reduce frictional heating, which allows coolant for easier inflow to the interface.

🔘 Methods and results in HIT ultrasonic grinding of CMC

Table A. Ultrasonic Grinding of CMC: Machining Information
Material	Carbon-ceramic (C/SiC) brake disc
Feature	Surface grinding (roughing)
Toolholder	HBT-40-W01 ultrasonic grinding wheel toolholder
Wheel Selection	#80 Φ120mm electroplated diamond wheel

[Surface Grinding of Carbon-Ceramic Brake Disc (CCB)] Machining Methods

Table B. Parameters (Conventional vs. Ultrasonic)
	Spindle Speed (S: rpm)	Feed Rate (mm/min)	Radial Depth of Cut (Ae: mm)	Axial Depth of Cut (Ap: mm)	UltrasonicPower Level (%)
HIT Ultrasonic	5,952	1,200	20	0.020	100
Original Process	5,952	900	20	0.008	-

HIT ultrasonic provides high frequency micro-vibrations to the grinding wheel, which intermittently impacts the workpiece during processing, creating space for cooling and chip removal, helping to reduce grinding force.
The reduction in grinding force allows for increased feed rate and depth of cut per pass, achieving an overall 3.3 times improvement in material removal rate (MRR). Along with effective cooling and improved chip removal of the grinding wheel, HIT ultrasonic helps to extend the wheel life by 3 times.

[Surface Grinding of Carbon-Ceramic Brake Disc (CCB)] Machining Results

Table C. Results - Higher MRR & Longer Wheel Life with Ultrasonic
	Material Removal Rate (mm³/min)	Wheel Life (pcs/per wheel)
HIT Ultrasonic	480	3
Original Process	144	1

(Figure 3. HIT ultrasonic-assisted surface grinding of carbon-ceramic brake disc brought 3.3x higher material removal rate)

(Figure 4. HIT ultrasonic-assisted surface grinding of carbon-ceramic brake disc brought 3x longer wheel life)

🧠 Learn more about this case study at Surface Grinding of Carbon Ceramic Brake Disc (CCB)

🔘 Methods and results in HIT ultrasonic drilling of CMC

Table D. Ultrasonic Drilling of CMC: Machining Information
Material	Carbon-ceramic (C/SiC) brake disc
Feature	*Φ5 x 5mm (blind holes) aspect ratio: 1x**
Toolholder	HBT-40 ultrasonic toolholder
Tool Selection	Φ5mm diamond drill

[Drilling of Carbon-Ceramic Brake Disc (CCB)] Machining Methods

Table E. Parameters (Conventional vs. Ultrasonic)
	Spindle Speed (S: rpm)	Feed Rate (mm/min)	Q-peck drilling (mm)	Axial Depth of Cut (Ap: mm)	Ultrasonic Power Level (%)
HIT Ultrasonic	4,000~6,500	2~8	0.16~1.00	2.5~5	50
Original Process	4,000	1	0.04	5	-

During HIT ultrasonic machining, the tool intermittently impacts the workpiece, creating space for cooling and chip evacuation, which helps reduce drilling force.
The reduction in drilling force allows for optimization of machining parameters, effectively shortening the process time per hole and achieving 5 times higher machining efficiency.
The tool’s impact on the workpiece became smaller yet more frequent, significantly decreasing the size of edge-cracks around the drilled holes. This led to 5 times better hole quality.
Compared with the process without ultrasonic (using the same optimized parameters), the number of drilling holes completed per tool increases, and the overall tool life is extended by 4 times.

[Drilling of Carbon-Ceramic Brake Disc (CCB)] Machining Results

Table F. Results - Higher Efficiency, Cleaner Holes, Longer Tool Life with Ultrasonic
	Process Time (min/per hole)	Size of Edge-Cracks (mm)	Number of Drilling Holes (holes/per tool)
HIT Ultrasonic	3	0.1	12
Original Process	15	0.5	3

(Figure 5. HIT ultrasonic-assisted drilling of carbon-ceramic brake disc brought 5x higher machining efficiency)

(Figure 6. HIT ultrasonic-assisted drilling of carbon-ceramic brake disc brought 5x better hole quality)

(Figure 7. HIT ultrasonic-assisted drilling of carbon-ceramic brake disc brought 4x longer tool life)

🧠 Learn more about this case study at Drilling of Carbon Ceramic Brake Disc (CCB)

Where is ultrasonic CMC machining used in industry?

🔘 Carbon-Ceramic Brake Disc (CCB) in Motorsports Industry

(Figure 8. carbon-ceramic brake discs are widely used in motorsports industry, photo by Gemanis Industries LLC)

Carbon-ceramic (C/SiC) brake discs (CCB) are used in GT and endurance racing for their low mass, high stiffness, and exceptional fade resistance at sustained temperatures beyond iron rotors. Less mass means better turn-in, quicker response, and steadier pedal over long stints. Their ceramic matrix resists oxidation and wear far better than carbon-carbon in wet or mixed conditions. However, they need proper warm-up and pad bedding, are sensitive to impact and thermal shock, and can carry high cost. Teams use them when durability and consistency matter more than upfront price.

🔘 Aircraft Brackets in Aerospace Industry

(Figure 9. generated image by AI shows simulation of aircraft brackets made of CMC used in aerospace industry)

Ceramic matrix composites are used for aircraft brackets that sit near hot zones—engine nacelles, exhaust ducts, thermal shielding—where metal brackets creep or oxidize. CMC brackets cut weight, keep stiffness at high temperatures, and hold shape due to low thermal expansion and good oxidation resistance. They also isolate heat into the stack, reducing thermal growth loads on fasteners and skins. However, they bear higher cost, notch sensitivity, and tight machining tolerances.

FAQs on Ultrasonic CMC Machining

🔘 Q1. What diamond grits and bonds suit CMC grinding for high MRR?

Use coarse diamond with the grits size ranging from #60~#120 wheel for massive material removal roughing process. Start at #80 for roughing and move finer only if edge quality demands it. The electroplated diamond grinding wheel is recommended for maximum bite and short-to-medium runs. Pair it with ultrasonic grinding technology to reduce grinding force and improve cooling and chip evacuation. The parameters can be further optimized with higher material removal rate (MRR).

🔘 Q2. What amplitude works for CMC drilling?

For CMC drilling process, 100% ultrasonic power level (approximately 15µm amplitude) is often too aggressive and raises micro-chipping and cracks around drilling holes. With HIT ultrasonic drilling technology, it delivers intermittent contact and fracture-assisted cutting without over-impact. It also keeps thrust and torque low, which limits the edge damage. It is suggested to use around 50% ultrasonic power level on carbon-ceramic brake disc (CCB) for drillings holes in heterogeneous CMCs.

💡 Learn more about HIT Ultrasonic Process Solution for machining of advanced-materials (ceramics, quartz, glass, ceramic matrix composites, etc.):

📖 References:

Machining of ceramic matrix composites: Challenges in surface integrity by Venkata Kanaka Srivani Maddala and others from Materials Today: Proceedings Journal
The new challenges of machining Ceramic Matrix Composites (CMCs): Review of surface integrity by Oriol Gavalda Diaz and others from International Journal of Machine Tools and Manufacture
The Pros & Cons of Advanced Ceramics by Julie Sullivan from MSC Industrial Direct Co., Inc.
Ceramic Matrix Composites by BCC Publishing from BCC Research
Ceramic Matrix Composites Offer Lighter, More Durable Engine Parts by Pratt & Whitney (P&W) from SAE Media Group
Arris Composites, Airbus collaborate on composites research for lightweighting cabin brackets by Grace Nehls from CompositesWorld
Brake Designs For Cars, What Do They Mean? by Mike G from Gemanis Industries LLC
Study of the machining quality of CMC ceramic composite during high-speed grinding by D.S. Rechenko and R. U. Kamenov from Journal of Physics: Conference Series

-
Hantop Intelligence Tech.
✨Ultrasonic Process Solution for Advanced Materials✨
☎️ +886-4-2285-0838
📧 sales@hit-tw.com