A shop swaps to a "harder" coating color and the same aluminum built-up edge or steel flank wear returns on the next shift. An RFQ names AlCrN or DLC while the alloy, coolant route and current wear photographs are still missing. Reground drills come back uncoated, hole quality drifts, and the team debates recoating without checking whether land and margin can be restored.
Choose the carbide substrate and drill geometry first. Use the coating to control the remaining wear, heat or adhesion mechanism at the chip-contact surface. Do not choose a drill by coating color, and do not assume one coating family works across steel, stainless steel, cast iron and aluminum. Match the surface to the observed failure mode, then confirm alloy, hardness, hole depth, coolant delivery and current wear pattern before release.
What the Carbide Substrate and Coating Each Control
A solid carbide drill is a system: substrate supports the edge; geometry controls entry, chip formation and evacuation; coating changes friction, adhesion and heat at the chip-contact surface. These layers are not interchangeable. Two drills that share a coating name can diverge when architecture, thickness, edge prep, finish or flute design differ.
| Decision layer | What it mainly controls | Typical questions |
|---|---|---|
| Carbide substrate | Edge support, toughness, stiffness and resistance to bulk fracture or plastic deformation. | Tough enough for interrupted entry? Wear-resistant enough for planned volume? |
| Drill geometry | Centering, thrust, chip formation, flute capacity, margin contact, entry/exit and coolant access. | Point suitable? Can chips leave a blind or deep hole? Edge prep too heavy? |
| Coating / surface condition | Friction, adhesion, abrasive wear, oxidation resistance and chip-contact thermal or chemical load. | Is BUE, flank wear, crater wear or heat-driven edge breakdown the limit? |
| Machine and process | Runout, rigidity, cutting data, coolant delivery and thermal cycling. | Coolant at the edge? Recutting chips? Runout loading one lip? |
TiN, TiCN, TiAlN, AlCrN, DLC and Uncoated Carbide Compared
The table is a selection aid. Commercial grades within one family vary by generation and process, so confirm the exact coating before release. XRZ publishes uncoated/polished carbide and TiAlN/AlTiN-class routes on its custom solid carbide drills page. TiN, TiCN, AlCrN and DLC are industry options; availability from XRZ requires quotation confirmation.
| Option | Useful starting conditions | Main limitation or caution | XRZ public capability status |
|---|---|---|---|
| Uncoated / polished carbide | Sharp edges; aluminum and sticky non-ferrous work where adhesion/BUE dominate; some short-chipping materials. | Less surface protection when abrasive or heat-driven wear dominates. Polish and flute design remain critical. | Confirmed published XRZ route (uncoated/polished). |
| TiN | General-purpose PVD in controlled, moderate-temperature cutting; can reduce friction versus uncoated in a suitable application. | Weaker default at higher thermal loads. Depends on substrate, thickness, edge condition and workpiece. | Industry option. Availability from XRZ requires quotation confirmation. |
| TiCN | Abrasion-focused option for stable cutting where hardness and wear behavior match the material and temperature window. | Weaker when heat and oxidation dominate. A hard layer cannot fix chipping or poor chip evacuation. | Industry option. Availability from XRZ requires quotation confirmation. |
| TiAlN / AlTiN class | Common candidate for steels and stainless when thermal load and abrasive wear rise; reviewed for dry or reduced-coolant ferrous cutting after process checks. | Weak default for sticky aluminum. Al/Ti ratio, architecture and finish matter; labels alone do not define performance. | Confirmed published XRZ route (TiAlN/AlTiN-class); exact grade is application-selected. |
| AlCrN | Candidate for high-temperature, wear-intensive or chemically demanding cutting, including selected ferrous wet or dry work. | Hardness or thermal stability does not guarantee the best hole finish in every test. Validate on the actual process. | Industry option. Availability from XRZ requires quotation confirmation. |
| DLC / ta-C | Low-friction option for aluminum and sticky non-ferrous work where sharpness, chip flow and adhesion control matter. | Best inside an appropriate thermal window. Distinct from CVD diamond and from a PCD cutting edge. | Industry option. Availability from XRZ requires quotation confirmation. |
Note: DLC/ta-C is a thin carbon-based coating; CVD diamond is crystalline diamond coating; PCD is a polycrystalline diamond cutting material. Edge construction, thermal limits, reconditioning and cost differ.
Choose the Coating by Workpiece Material
Material family is the first screen. Grade, hardness, heat treatment, silicon content and chip behavior can move the selection inside a group.
| Workpiece | First coating route to evaluate | Confirm before release |
|---|---|---|
| Steel / alloy steel | TiAlN/AlTiN class; AlCrN in selected heat- and wear-intensive cases; TiN/TiCN in controlled applications. | Grade and hardness, hole depth, interrupted entry, wet/dry mode, wear pattern. |
| Stainless steel | TiAlN/AlTiN or AlCrN candidate, with sharp enough geometry and reliable coolant and chip control. | Stainless grade, work-hardening risk, rigidity, feed, coolant pressure and delivery. |
| Cast iron | Uncoated fine-grain carbide or an application-matched wear-resistant nitride coating. | Grade, abrasiveness, dry/wet process, edge-chipping risk and dust management. |
| Wrought / low-Si aluminum | Polished uncoated carbide or DLC/ta-C when adhesion dominates. | Alloy and temper, silicon content, flute polish, coolant/MQL and BUE evidence. |
| High-Si cast aluminum | Specialized low-adhesion or abrasion-resistant route; diamond-coated carbide or PCD only after feasibility review. | Silicon %, volume, diameter, tolerance, entry/exit and reconditioning plan. |
Steel and alloy steel
Name the limit first: abrasive flank wear, heat, chipping or chip packing. TiAlN/AlTiN-class coatings are common candidates as heat and wear rise. AlCrN may be reviewed where thermal stability matters; TiN or TiCN can remain relevant in stable, less demanding conditions when justified. When hardness or thermal load drives steel selection, review carbide drills for hardened steel after grade and wear pattern are known. If the drill breaks before a normal wear land develops, check runout, point, feed, entry and chip evacuation before changing the coating.
Stainless steel
Stainless combines heat concentration, work hardening and long chips. TiAlN/AlTiN- or AlCrN-based systems may be candidates, but geometry, edge prep, feed and coolant come first. A coating cannot prevent work hardening if the drill rubs or dwells at the hole bottom. Align with carbide drills for stainless steel once the failure mode is named.
Cast iron
Selection depends on grade, graphite structure, abrasiveness and dry or wet process. Fine-grain uncoated carbide can work in suitable short-chipping conditions. A wear-resistant nitride coating may help when abrasion dominates. Validate dust control, hole depth and edge-chipping risk.
Aluminum alloys
Separate sticky wrought aluminum from abrasive cast aluminum. For many wrought and lower-silicon alloys, sharp polished uncoated carbide is a strong starting point because it limits BUE and preserves chip flow. DLC or ta-C may be considered when adhesion control is required. See carbide drills for aluminum for geometry and surface routes. Higher-silicon cast aluminum can shift toward abrasion; next steps may be specialized carbon-based coating, diamond-coated carbide or a PCD special tool. Treat each as a separate feasibility review.
Why Titanium-Containing Coatings Are a Poor Default for Sticky Aluminum
The rule is not that every titanium-containing coating is unsuitable for aluminum. TiN, TiCN and TiAlN are different chemistries, and products within each family behave differently. Avoid selecting by the word titanium or by coating color. Match the surface to the aluminum failure mechanism.
When sticky aluminum welds to the edge, prioritize a sharp edge, a smooth chip-contact surface, adequate flute space and a surface that limits adhesion. A polished uncoated drill or a suitable DLC/ta-C coating is often a better first comparison than an aluminum-bearing nitride coating selected for hot ferrous cutting. Alloy and process conditions can produce exceptions. Compare wear, BUE, hole size and finish under the same controlled conditions; do not judge by coating name alone.
Wet, MQL and Dry Drilling Change the Coating Decision
Cooling method is a system input. A heat-resistant coating does not make a deep hole safe to run dry if flute capacity is insufficient. Flood coolant does not solve chip packing when the jet never reaches the cutting zone.
| Process mode | What the coating must work with | Questions to ask |
|---|---|---|
| Wet / flood or internal coolant | Coolant access to the lips and flute; repeated heating and cooling; chip transport out of the hole. | Coolant at the edge? Pressure and flow adequate for diameter and depth? Chips still packing? |
| MQL | Small lubricant volume, controlled delivery and a drill or channel design that moves lubricant and chips through the engagement zone. | Holder and channel MQL-ready? Lubricant on both lips? Adhesion or temperature the dominant limit? |
| Dry | Higher thermal demand, stable chip evacuation and a coating, substrate and geometry combination designed for the material. | Dry appropriate for this alloy and depth? Chips leave without recutting? Guarding and dust control adequate? |
What a Coating Cannot Fix
Before changing the coating, determine whether the drill reaches a normal wear limit or fails from an unstable process. Coating changes have low value when the root cause sits elsewhere.
- Excessive spindle or holder runout that overloads one cutting lip.
- Point geometry or edge preparation that does not match the workpiece or entry condition.
- Insufficient flute space or poor chip shape in a blind, deep or interrupted hole.
- Inadequate coolant direction, pressure or flow at the cutting edge.
- Low rigidity, long unsupported tool length or unstable workholding.
- Cutting data that causes rubbing, work hardening, thermal overload or chip recutting.
- A worn or damaged margin that no longer guides the drill correctly.
Diagnosis sequence: inspect wear and chips, verify runout and setup, confirm geometry and coolant access, review speed and feed, then compare coating routes under controlled conditions.
Should a Reground Drill Be Recoated?
Regrinding restores cutting geometry and removes coating from the cutting edge. If original performance depended on that coating, leaving the reground edge uncoated changes the tool system. Do not assume equivalence. Recoating is appropriate only after the tool can be restored within dimensional and geometric limits.
- Inspect remaining diameter, margin condition, flute damage and available regrind allowance.
- Confirm that the original point, thinning, edge preparation and coolant exits can be restored.
- Determine whether the old coating must be stripped and whether stripping or recoating will affect critical dimensions.
- Match the replacement coating to the original application, or document why the process is being changed.
- Revalidate hole size, position, finish, chip form and tool behavior on critical production holes.
Do not recoat over rounded, chipped or geometrically incorrect edges. Solid carbide drills can often be reground and recoated when enough land and margin remain and the point can be restored; engineering inspection is required.
Information to Provide Before Requesting a Coated Drill
A useful quotation should identify the holemaking problem. The requested coating name alone is not enough. Send the data below so geometry, substrate and coating can be reviewed as one system. Unsupplied specs stay to your drawing or marked unknown. Application checks follow XRZ's sample validation process when a trial is required.
| Input | Minimum useful detail | Why it matters |
|---|---|---|
| Workpiece | Exact material grade, hardness or heat treatment, and aluminum silicon content when relevant. | Separates adhesion, abrasion, heat and chipping risks. |
| Hole | Diameter, tolerance, depth, L/D, through or blind, entry/exit angle, cross holes or interruptions. | Defines flute capacity, guidance, coolant need and edge loading. |
| Quality target | Hole size, cylindricity or straightness, surface finish, burr and positional requirements. | Keeps hole acceptance ahead of a tool-life preference. |
| Machine and holder | Machine type, spindle interface, holder, measured runout and available coolant pressure or flow. | Shows whether assumed stability and coolant conditions are real. |
| Process mode | Flood, through-coolant, MQL or dry; current speed, feed, peck cycle and cycle-time target. | Sets heat path, lubrication and chip-removal conditions. |
| Current tool evidence | Tool code, substrate or coating if known, wear photos, chips, failure position and holes per tool. | Connects coating selection to the observed limiting mechanism. |
| Commercial context | Annual volume, trial quantity, target tool life, regrind or recoat expectation and delivery requirement. | Supports an economical validation and lifecycle plan. |
Drill Bit Coatings FAQ
Which drill coating is best for stainless steel?
There is no single best coating for every stainless grade and hole. TiAlN/AlTiN- or AlCrN-based systems are common candidates, but the answer also depends on work-hardening risk, edge geometry, feed, hole depth, coolant access and the current failure mode.
Is TiAlN good for drilling aluminum?
It should not be the default answer for sticky aluminum. When built-up edge and adhesion dominate, polished uncoated carbide or a suitable DLC/ta-C route is often the better first comparison. Test results can vary with alloy, silicon content, geometry and coolant, so validate under the same controlled conditions.
Is DLC the same as a diamond-coated or PCD drill?
No. DLC/ta-C is a thin carbon-based coating; CVD diamond is a crystalline diamond coating; PCD is a polycrystalline diamond cutting material. Their edge structures, application windows, service routes and costs are different.
Can an uncoated carbide drill machine steel?
It can in some controlled conditions, but the decision should be based on wear, heat, hole depth and production economics. For sustained production in steel, an application-matched coating is often evaluated because the uncoated edge may reach its wear limit sooner.
Does every reground drill need recoating?
Not automatically. Recoating depends on whether the original coating was essential, whether geometry can be restored, the remaining diameter and margin condition, the tolerance target and the economics of the reconditioning cycle. Critical holes should be revalidated after regrinding and recoating.
Request a Quote
Send the hole drawing, exact material, current drill data and wear photographs. XRZ reviews point geometry, carbide grade, coating route, coolant strategy and validation plan together. Exact coating availability, including TiN, TiCN, AlCrN or DLC, must be confirmed in the quotation.