Ultrasonic drilling is an abrasive process, not a cutting one. A tool vibrating at high frequency drives abrasive particles into the glass and removes material in tiny fractures. It suits small, deep or tightly positioned holes in brittle, non-conductive material, where conventional drilling tends to chip, crack or heat-stress the part. It is not a finish-free process, though, and the quality of the hole depends on tool, slurry, feed rate and how the exit side is supported. This guide is for engineers and buyers who need to decide whether to specify it and how to write the requirement.
TL;DR
- Ultrasonic machining (and its rotary variant) removes glass through micro-fracture at roughly 20 to 40 kHz, avoiding the thermal and chemical damage associated with other routes.
- Feed rate is the dominant parameter for material removal rate. Faster feeds raise productivity but cost you chipping and surface roughness.
- Exit-side chipping and poorer exit circularity are the usual defects. Backing plates, reduced feed at breakthrough and tool-path control are the standard remedies.
- Specify the hole diameter, depth, tolerance, chamfer, exit-side quality and inspection method on the drawing, not just “drilled”.
- Send us the drawing and glass type early. We will advise on the best machining route for the part.
Table of Contents
- What ultrasonic drilling of glass actually is
- Why glass needs a different approach
- What hole sizes and aspect ratios are realistic
- The parameters that decide hole quality
- Exit chipping: the defect to design around
- How ultrasonic drilling compares with other routes
- What to put on the drawing and in the RFQ
- Our perspective
- Who benefits most from ultrasonic hole making
- Working with us on drilled and machined glass
- FAQ
- Sources
What ultrasonic drilling of glass actually is
The name is slightly misleading. The tool, often a tungsten carbide pin or a diamond-coated sonotrode, does not shear through the glass the way a twist drill does. It vibrates, and in slurry-based set-ups it hammers abrasive particles into the surface so that the glass fractures at micro level. Each impact removes a very small amount of material. Because the energy is delivered locally and in small pulses, heat build-up and large cracks are far less likely than with conventional rotary drilling.
There are three variants you will meet in practice:
| Variant | How material is removed | Typical use |
|---|---|---|
| Slurry-based ultrasonic machining | Vibrating tool drives loose abrasive slurry into the glass | Shaped holes, arrays of holes, thin substrates |
| Rotary ultrasonic drilling | Rotating diamond tool with superimposed axial vibration | Round holes in optical glass, borosilicate, quartz |
| Ultrasonic vibration-assisted grinding | Grinding with small-amplitude vibration added | Micro-holes, where grinding force and edge chipping must be reduced |
A review of ultrasonic, chemical-assisted and rotary ultrasonic machining of glass covers the working principles and mechanisms of each in detail, and is a good starting point if you want the engineering background.
Why glass needs a different approach
Glass is hard, brittle and electrically non-conductive. That combination rules out several processes outright. Electrical discharge machining and electrochemical machining both depend on conductivity, so they are not options for glass. Ultrasonic machining does not need conductivity, which is why it is regarded as a foundational capability for precision glass components such as optical windows and sensor covers.
Conventional mechanical drilling, by contrast, often causes excessive chipping, micro-cracks and localised heat stress. Heat stress matters most when the part is in service. Residual stress left in a hole edge can drive delayed failure months later, under thermal cycling or vibration, which is exactly the situation in aerospace, defence and medical assemblies.
What hole sizes and aspect ratios are realistic
Capability depends on the glass, the tool and the machine, so treat published figures as indications rather than guarantees for your part.
- Micro-holes: a review of micro-hole drilling on glass substrates reports micro-ultrasonic machining achieving holes as small as 5 to 10 μm, with aspect ratios up to about 10:1. These are specialist results, using force-feedback control and diamond-bonded tool pins to manage tool wear.
- Quartz micro-holes: one study of ultrasonic vibration-assisted grinding reported a minimum hole diameter of 112 μm with a depth-to-diameter ratio above 10 in quartz glass, with lower grinding force and less edge chipping than conventional grinding.
- Everyday engineering holes: for typical optical windows, display cover glass and sensor covers, holes of around a millimetre and above are the normal working range, and the controlling issue is edge quality and position tolerance rather than minimum size.
For deep holes, ask about the aspect ratio early. As depth-to-diameter ratio climbs, slurry exchange, tool wear and taper all become harder to control.
The parameters that decide hole quality
Feed rate
In experimental models of ultrasonic machining of float glass, feed rate is the most influential parameter for material removal rate, contributing over 97% of the variance in the reported analysis. Higher feed rates raise throughput but have to be balanced against chipping area and surface roughness. The same study reports that settings of 75% power and a 0.6 mm/min feed rate cut overcut error by up to 36.7% for that float glass set-up. Those numbers belong to that experiment, not to every glass and tool, but the lesson transfers: the fastest cycle is rarely the best hole.
Grit size and staged finishing
Abrasive grit controls both speed and subsurface damage. Ultrasonic drilling reduces damage compared with conventional methods, but subsurface micro-cracking can still occur depending on grit size. Reaching a fine bore finish, down to around 1 μm Ra, normally means a multi-stage cycle: a faster, coarser first pass followed by finer tooling. If your drawing asks for a polished bore, say so, because it changes the route and the cost.
Slurry control
In slurry-based processes the abrasive suspension matters as much as the vibration. Slurry degrades over time, fluid evaporates and the ultrasonic action creates mist, all of which can make hole quality inconsistent. Research on micro ultrasonic machining notes the need for adaptive control of cutting force for process stability, and in practice that means controlling slurry concentration and replacing it on a schedule rather than when holes start to drift.
Glass type
Borosilicate, fused quartz, float glass and optical glasses such as BK7 respond differently. Work on rotary ultrasonic drilling of borosilicate glass focused on reducing edge chipping and taper, and optimisation work on quartz found that process settings need to be tuned to the material. Our guide to selecting glass for industrial applications explains how the choice of glass affects what you can machine and at what cost.
Exit chipping: the defect to design around
The most common failure in glass drilling is chipping where the tool breaks through the back surface. The glass is unsupported at that point, and the last thin layer fails in a brittle way. Manufacturers tackle it in three main ways:
- Sacrificial backing plate. Supporting the exit side stops the last layer flexing and spalling.
- Reduced feed before breakthrough. Slowing the tool as it approaches the exit lowers the load on the final layer.
- Pecking cycles and tool-path control. Retracting and re-entering clears debris and slurry, and specialised tool paths improve exit circularity.
As a rule, the entry side of a hole shows better circularity than the exit side unless the tool path is controlled. If the exit face is a sealing, optical or bonding surface, put a requirement on it. If both faces are critical, tell your supplier, because the answer may be to drill from both sides or to add a finishing step.
How ultrasonic drilling compares with other routes
| Route | Strengths | Limits |
|---|---|---|
| Conventional diamond core drilling | Quick for larger, non-critical holes | More chipping, higher forces, heat |
| Ultrasonic or rotary ultrasonic drilling | Lower forces, less thermal damage, works on non-conductive glass | Slower, tooling wear, finishing may be needed |
| Waterjet | No heat, good for larger apertures and profiles | Larger minimum feature size, taper |
| Laser-based methods | Very small features, no tool contact | Heat effects and micro-cracking depend on process |
| CNC grinding and milling | Flexible profiles, slots and pockets | Needs rigid fixturing and careful coolant control |
No single route wins on every part. Our pages on waterjet cutting of glass, slot machining and CNC glass machining set out where each process earns its place.
What to put on the drawing and in the RFQ
A drawing that just says “hole, 3 mm” invites a wide range of outcomes. For a drilled hole in technical glass, specify:
- Nominal diameter and tolerance, with the glass type and thickness
- Hole position tolerance relative to datums
- Depth, and whether the hole is through or blind
- Entry and exit edge condition: maximum chip size, chamfer or radius
- Bore finish, as Ra if it matters
- Any coatings, ceramic printing or toughening that follow, since these affect when holes must be made
- Inspection method and sampling plan, plus traceability requirements
Sequence matters. Thermally toughened glass cannot normally be drilled after toughening, so holes have to be made first. Chemically strengthened glass has its own constraints on machining after strengthening. Raise the order of operations at quotation stage, not after the first batch fails.
For inspection, hole edges can be checked visually under magnification and by dimensional measurement. If your quality plan also includes non-destructive evaluation of the finished assembly, this overview of industrial NDT methods explains the main techniques and where each is used. For cut and ground edges, our article on edge finishing and fracture testing argues for requiring fracture evidence, not just a finish name.
Our perspective
We see the same pattern again and again: the hole is the last thing an engineer thinks about and the first thing that causes scrap. A glass part can have a flawless polished face and still fail at a drilled edge, because the hole is where stress concentrates.
Our view is that three habits prevent most problems. First, decide the order of operations with the glass type in mind, before the drawing is frozen. Second, define edge quality in measurable terms, not adjectives. Third, treat inspection and traceability as part of the process, not an afterthought. We work to ISO 9001, keep batch-level traceability and apply advanced inspection to our output, so that a part made in a prototype run can be repeated at volume and shown to be the same.
We would rather discuss a difficult drawing before quotation than rescue it afterwards. If a hole is close to an edge, deep for its diameter or sits on an optical surface, send it to us and we will tell you honestly what the process can and cannot deliver.
— Alexandra
Who benefits most from ultrasonic hole making
The process earns its keep where the consequence of a damaged hole is high:
- Medical devices: fluidic and sensor windows where cleanliness and edge integrity matter.
- Aerospace and defence: optical windows and instrument covers exposed to vibration and temperature cycling. Research at Loughborough University on ultrasonically assisted drilling in aerospace materials reports reduced drilling force and torque, though that work concerns composites, not glass.
- Electronics and displays: cover glass and scanner glass with apertures for sensors, buttons or cameras.
- Automotive dashboards and lighting: panels with openings that need consistent edges before ceramic printing or coating.
- Marine technology: instrument glass where sealing faces must be dependable.
Working with us on drilled and machined glass
We design, fabricate and deliver custom glass components for defence, aerospace, medical, automotive, lighting, electronics and marine customers. Our services include glass cutting, CNC glass machining, edge finishing, toughened and laminated glass, coated glass, display glass, optical windows and custom components, and we can support your project from prototype to volume. Our optical components range covers lenses, beam splitters and filters.
If you have a drawing with holes, slots or apertures, share it with us through the Precision Glasses site along with the glass type, quantities and inspection requirements. We will come back with a view on the route and the points on the drawing worth tightening.
FAQ
Does ultrasonic work through glass?
In manufacturing the question is usually whether ultrasonic vibration can machine glass, and it can. The vibrating tool drives abrasive into the glass and removes material by micro-fracture. Ultrasonic waves also travel through glass, but that is a separate matter from drilling it.
What is the best way to drill glass without breaking it?
For precision parts, use a low-force process such as ultrasonic or rotary ultrasonic drilling, support the exit side with a backing plate and slow the feed before breakthrough. Keep the tool and slurry in good condition and cool the work. For a one-off household job, a different approach applies, and that is outside what we do.
Is ultrasonic drilling completely free of chipping?
No. It significantly reduces damage compared with conventional drilling, but subsurface micro-cracking can still occur depending on grit size, and the exit side is more prone to chipping than the entry side. Specify maximum chip size and edge condition on the drawing so the process is set up to meet them.
What is the difference between ultrasonic drilling and ultrasonic machining?
Ultrasonic drilling is the hole-making application of ultrasonic machining. The wider process can also produce shaped cavities, arrays of holes and profiles. Rotary ultrasonic drilling adds tool rotation to the vibration, using a diamond-bonded tool in place of loose slurry.
Sources
- Ultrasonic machining of glass substrates
- Micro-Hole Drilling on Glass Substrates: A Review
- Ultrasonic, chemical-assisted ultrasonic and rotary ultrasonic machining of glass: a review
- Experimental investigation of float glass in ultrasonic machining
- Adaptive Cutting Force Control for Process Stability of Micro Ultrasonic Machining
- Ultrasonic vibration-assisted grinding of quartz glass micro-hole
- Investigation of hole quality in rotary ultrasonic drilling of borosilicate glass
- Optimization of process parameters in rotary ultrasonic-assisted drilling of quartz
- Anish Roy, Loughborough University
