Appearance
An industrial robot manufacturer was producing 12,000 robotic arm joint housings per year from 7075-T6 aluminium. The housings required a 25 mm × 300 mm through-bore for cable routing and harmonic drive integration. After switching from conventional drilling on a CNC machining centre (which required peck cycles, frequent tool changes, and produced inconsistent surface finish) to a dedicated gun drilling machine with 0.05 mm/rev feed and 8,000 rpm spindle speed, cycle time dropped from 18 minutes to 4 minutes per housing, surface finish improved from Ra 3.2 µm to Ra 0.8 µm, and drill breakage was eliminated. The result was a straight-through bore that allowed the robot cabling to pass freely without snagging, and the reduced cycle time freed up CNC capacity for other critical operations.
Robotics Components Requiring Deep Hole Drilling
As robots become more compact, lightweight, and precise, deep hole drilling has found increasing application in the manufacturing of robotic components. Unlike traditional heavy-equipment applications, robotics components demand high precision in lightweight materials with complex geometries.
Robotic arm joint housings: Each robot joint — from the base to the wrist — contains a housing that must accommodate wiring, cabling, and the harmonic drive or RV reducer. These housings feature through-bores for cable routing (typically 15–60 mm diameter, 100–500 mm length) that must be smooth and burr-free to prevent cable chafing during robot articulation.
Actuator components: Robot actuators integrate motors, gearboxes, and encoders into compact packages. The actuator housings contain precision bores for bearing seats, oil passages for lubrication, and cooling channels for high-torque applications. Bore diameters range from 6–40 mm with moderate depth-to-diameter ratios of 5:1 to 20:1.
Sensor housings: Force-torque sensors, vision system housings, and proximity sensor mounts require precision-drilled bores for sensor element installation and cable routing. These are typically small-diameter holes (3–15 mm) in compact housings.
Structural components: Robot base plates, arm segments, and wrist housings contain weight-reduction bores and cable passages. While many of these are simple through-holes, some require gun-drilled straightness for wiring conduits or hydraulic/ pneumatic passages in heavy-payload robots.
Collaborative robot (cobot) components: Cobot joints are typically smaller and more compact than industrial robot joints. The harmonic drive housings and output shaft bores require gun drilling for cable routing through the centre of the joint.
End-effector and gripper components: Robot grippers and end-effectors often contain internal air passages and sensor wiring channels that are created by gun drilling. These components are typically manufactured from aluminium or stainless steel.
Materials for Robotics Components
Robotics components use materials selected for high strength-to-weight ratio, corrosion resistance, and dimensional stability.
Aluminium alloys (primary material for robotics):
| Alloy | Condition | Tensile strength (MPa) | Applications | Drillability |
|---|---|---|---|---|
| 6061-T6 | Wrought | 310 | General structural, housings | Excellent |
| 7075-T6 | Wrought | 570 | High-load joints, arms | Good (abrasive) |
| 2024-T4 | Wrought | 470 | Aerospace-style arms | Good |
| AlSi10Mg | Cast | 350 | Complex housings (cast then drill) | Good |
Stainless steels (corrosion-resistant applications):
| Alloy | Condition | Tensile strength (MPa) | Applications | Drillability |
|---|---|---|---|---|
| 304L | Annealed | 585 | Sensor housings, food-grade robots | Good (work-hardens) |
| 316L | Annealed | 585 | Medical robots, marine | Good (work-hardens) |
| 17-4PH | H900 | 1,300 | High-strength grippers | Moderate |
Titanium alloys (lightweight high-performance):
| Alloy | Condition | Tensile strength (MPa) | Applications | Drillability |
|---|---|---|---|---|
| Ti-6Al-4V | Annealed | 950 | High-performance robot arms, aerospace-grade robots | Challenging |
| Ti-6Al-4V ELI | Annealed | 900 | Medical robotics | Challenging |
Engineering plastics (light-duty robotics):
| Material | Tensile strength (MPa) | Applications | Drillability |
|---|---|---|---|
| PEEK | 100 | Medical robots, lightweight components | Excellent (low force) |
| PA66 (Nylon) | 80 | Cable guides, bushing housings | Good |
| POM (Acetal) | 70 | Sensor mounts, lightweight parts | Excellent |
Tip: For aluminium alloy gun drilling in robotics components, use uncoated or TiN-coated carbide drills with polished flutes to prevent aluminium build-up on the cutting edge. Coolant pressure of 20–40 bar is sufficient for diameters above 10 mm. For smaller diameters, increase pressure to 50–70 bar.
Gun Drilling Parameters for Robotics Materials
Aluminium alloys (6061-T6, 7075-T6):
| Bore diameter | Cutting speed (m/min) | Feed (mm/rev) | RPM | Coolant pressure (bar) |
|---|---|---|---|---|
| 6 mm | 120–200 | 0.04–0.10 | 6,400–10,600 | 30–60 |
| 10 mm | 100–180 | 0.06–0.14 | 3,200–5,700 | 25–50 |
| 20 mm | 80–150 | 0.08–0.18 | 1,300–2,400 | 20–40 |
| 30 mm | 70–120 | 0.10–0.22 | 740–1,300 | 15–35 |
| 40 mm | 60–100 | 0.12–0.25 | 480–800 | 15–30 |
Stainless steels (304L, 316L):
| Bore diameter | Cutting speed (m/min) | Feed (mm/rev) | RPM | Coolant pressure (bar) |
|---|---|---|---|---|
| 6 mm | 40–70 | 0.02–0.05 | 2,100–3,700 | 60–100 |
| 10 mm | 35–60 | 0.03–0.06 | 1,100–1,900 | 50–80 |
| 20 mm | 30–50 | 0.04–0.08 | 480–800 | 40–70 |
| 30 mm | 25–45 | 0.05–0.10 | 260–480 | 35–60 |
Ti-6Al-4V titanium:
| Bore diameter | Cutting speed (m/min) | Feed (mm/rev) | RPM | Coolant pressure (bar) |
|---|---|---|---|---|
| 6 mm | 25–45 | 0.015–0.04 | 1,300–2,400 | 80–120 |
| 10 mm | 20–40 | 0.02–0.05 | 640–1,300 | 70–100 |
| 20 mm | 18–35 | 0.025–0.06 | 280–560 | 60–90 |
| 30 mm | 15–30 | 0.03–0.07 | 160–320 | 50–80 |
Engineering plastics (PEEK, PA66):
| Bore diameter | Cutting speed (m/min) | Feed (mm/rev) | RPM | Coolant pressure (bar) |
|---|---|---|---|---|
| 6 mm | 80–150 | 0.05–0.15 | 4,200–8,000 | 10–20 |
| 20 mm | 60–120 | 0.08–0.25 | 950–1,900 | 10–20 |
Warning: When gun drilling engineering plastics for robotics components, coolant pressure should be limited to 20 bar maximum. Higher pressure can cause the plastic to swell from coolant absorption or delaminate at the hole exit. Use oil-based coolant rather than emulsion to minimise moisture absorption in the material.
BTA Drilling for Large Robot Components
For heavy-payload robots (> 100 kg capacity), the base and arm structural components may require BTA drilling for large-diameter bores.
| Bore diameter | Material | Cutting speed (m/min) | Feed (mm/rev) | Coolant flow (L/min) |
|---|---|---|---|---|
| 40–60 mm | 6061-T6 Al | 80–150 | 0.12–0.25 | 150–300 |
| 60–80 mm | 7075-T6 Al | 70–120 | 0.14–0.28 | 250–450 |
| 40–60 mm | 17-4PH SS | 40–60 | 0.10–0.18 | 200–350 |
BTA drilling for robotics components is less common than gun drilling because most robotic bores are under 40 mm diameter. However, large-payload robots (200 kg+ class) increasingly use BTA-drilled components for the main structural bores.
Machine Configurations for Robotics Components
Robotics component drilling requires different machine configurations than traditional heavy-equipment drilling. The emphasis is on precision, small-diameter capability, and rapid changeover.
Compact gun drilling machines (UNISIG UNE series):
The UNISIG UNE series is well-suited for robotics components due to its compact footprint and high spindle speeds:
- Drilling diameter: 0.8–12 mm (UNE-12) or up to 40 mm (other models)
- Spindle speed: up to 12,000–28,000 rpm
- Coolant pressure: up to 150–207 bar
- Counter-rotation: available for improved straightness
- Compact footprint: suitable for floor space-constrained facilities
Inverted vertical machines (SHIN-IL):
Inverted vertical deep hole drilling machines offer advantages for complex robotic housing components where multiple bores at different angles are required:
- Gravity-assisted chip evacuation — important for small-diameter bores in aluminium
- 5–15 minute setup time for frequent changeovers
- Positioning accuracy: 0.008 mm
- Suitable for short-to-medium length components (50–350 mm)
Multi-spindle configurations:
For high-volume production of standardised robotic joints (common in collaborative robot manufacturing), 2–4 spindle gundrilling machines significantly increase throughput. Each spindle operates independently with individual coolant control, allowing simultaneous drilling of different-sized bores in the same component.
CNC machining centres with deep hole drilling capability:
Many robotics components are produced on 5-axis CNC machining centres rather than dedicated deep hole drilling machines. Gun drilling attachments (through-coolant adaptors with high-pressure coolant boosters) enable deep hole drilling on conventional CNC machines. This approach is common for low-to-medium volume production where the cost of a dedicated deep hole drilling machine cannot be justified.
Quality Requirements for Robotics Components
Robotics components require precision deep hole drilling that meets the demands of high-cycle, high-precision robotic articulation.
Bore quality specifications:
| Component | Diameter tolerance | Straightness | Surface finish Ra |
|---|---|---|---|
| Joint housing cable bore | ±0.05 mm | < 0.15 mm overall | < 1.6 µm |
| Harmonic drive housing bore | H7 (±0.015 mm) | < 0.02 mm | < 0.4 µm |
| Actuator housing oil passage | ±0.05 mm | N/A (short bore) | < 3.2 µm |
| Sensor housing bore | H7–H8 | < 0.01 mm per 25 mm | < 0.4 µm |
| End-effector air passage | ±0.1 mm | N/A | < 3.2 µm |
| Structural weight-reduction bore | ±0.2 mm | < 0.5 mm overall | < 6.3 µm |
Inspection methods for robotics components:
- Air gauging: Bore diameter measurement (±0.002 mm resolution)
- Go/no-go plug gauges: Quick verification of diameter limits
- Surface profilometer: Ra, Rz measurement
- Borescope inspection: Visual check for burrs and surface defects in cable bores
- CMM: Position and orientation verification for multi-bore housings
Cleanliness requirements:
Robotics components, particularly joint housings with cable routing bores, require:
- No sharp edges or burrs that could damage cables during articulation
- Deburring of all entry, exit, and intersection edges
- Cleanliness level ISO 4406 class 18/15/13 or better for oil-lubricated joints
- Verification by swab test or particle count
Tip: For robotic arm cable routing bores, specify a chamfer at both ends of the bore (0.5–1.0 mm × 45°) to prevent cable chafing during robot movement. This chamfer is typically added as a secondary operation after gun drilling, using a chamfering tool or countersink in the same setup.
Troubleshooting Robotics Component Drilling
| Symptom | Likely cause | Correction |
|---|---|---|
| Built-up edge in 7075 aluminium | Coolant pressure too low or lubricity inadequate | Increase coolant pressure to 40+ bar; use oil-based coolant; check AlTiN coating |
| Cable chafing in robot joint bore | Burr at bore exit not removed | Add exit deburring step; increase chamfer size; verify with borescope |
| Harmonic drive housing bore eccentric | Insufficient clamping rigidity | Improve fixture design; add clamp near bore; reduce feed by 20 % |
| Oversized bore in thin-walled aluminium housing | Clamp distortion during drilling | Reduce clamping force; use distributed clamping; sequence drilling before final OD machining |
| Drill breakage in small-diameter stainless steel bore | Chip packing in flute | Increase coolant pressure; add peck cycle; check chip form |
| Poor surface finish in Ti-6Al-4V | Cutting speed too high causing work hardening | Reduce speed to 20–30 m/min; maintain constant feed; use sharp drill |
| Plastic bore surface melting | Coolant pressure causing frictional heating | Reduce coolant pressure to 10–15 bar; increase feed; use compressed air cooling |
| Chip welding in aluminium bore | Insufficient chip clearance in flute | Use polished flute drill; increase coolant flow; check coolant concentration |
Frequently Asked Questions
Why is deep hole drilling used for robot joint housings? Robot joint housings require smooth, straight through-bores for cable routing, harmonic drive integration, and weight reduction. Gun drilling produces these bores in a single pass with superior straightness and surface finish compared to conventional drilling on CNC machining centres.
What materials are most common in robotic components that require deep hole drilling? Aluminium alloys (6061-T6, 7075-T6) are the most common, followed by stainless steels (304L, 316L) for corrosion-resistant applications, and Ti-6Al-4V for high-performance lightweight robots. Engineering plastics (PEEK, PA66) are used in medical and food-grade robotics.
What are the typical cycle time savings from dedicated gun drilling vs CNC machining centre drilling? Dedicated gun drilling reduces cycle time by 60–80 % for robotic components. For a 25 mm × 300 mm aluminium joint housing bore, gun drilling takes approximately 4 minutes compared to 18 minutes on a CNC machining centre with peck cycles.
What coolant pressure is needed for gun drilling aluminium robotics components? 15–60 bar depending on bore diameter. Larger bores (30–40 mm) require 15–35 bar; smaller bores (6–10 mm) require 30–60 bar. Unlike steel drilling, aluminium drilling benefits from higher coolant flow rather than higher pressure.
Can deep hole drilling be performed on a 5-axis CNC machining centre? Yes, using through-coolant adaptors with high-pressure coolant boosters. This approach is common for low-to-medium volume robotics component production but is typically slower than dedicated gun drilling machines for high volumes.
How does robotic component deep hole drilling differ from traditional applications? Robotics components are typically made from lightweight materials (aluminium, titanium, plastics) rather than steel. The bores are shorter (100–500 mm), tolerances are tighter (H7 for bearing seats), and surface finish requirements are higher for cable routing bores. Production volumes are medium-to-high (5,000–50,000 units per year for popular robot models).
What is the typical bore diameter for a collaborative robot joint housing? Collaborative robot (cobot) joint housing cable bores typically range from 10–30 mm diameter with lengths of 100–300 mm. The bore must be large enough to pass power, communication, and pneumatic cables while maintaining sufficient wall thickness for structural integrity.
Is BTA drilling used in robotics manufacturing? BTA drilling is used for larger robotic components — typically base and structural elements for heavy-payload robots (100 kg+ capacity) where bore diameters exceed 40 mm. For the majority of robotic components (under 40 mm bore), gun drilling is the standard method.
What quality issues are specific to deep hole drilling of robotic components? Cable chafing from unremoved burrs, harmonic drive housing eccentricity, thin-wall distortion from clamping forces, and built-up edge in aluminium alloys are the most common quality issues specific to robotic component drilling.
How is the robotics industry expected to affect deep hole drilling demand? The International Federation of Robotics projects 10–14 % annual growth in robot installations through 2028. Each robot contains 4–8 joint housings with cable bores, plus actuator components and structural parts requiring deep hole drilling. This creates growing demand for compact gun drilling machines capable of high-precision drilling in lightweight materials.
Summary
| Aspect | Joint housing cable bores | Harmonic drive housings | Sensor/actuator bores |
|---|---|---|---|
| Typical bore diameter | 10–40 mm | 15–60 mm | 3–15 mm |
| Typical length | 100–500 mm | 50–200 mm | 20–100 mm |
| Drilling method | Gun drilling | Gun drilling | Gun drilling |
| Typical material | 6061-T6, 7075-T6 Al | 7075-T6 Al, 17-4PH SS | 304L, 316L SS |
| Cutting speed | 60–200 m/min | 60–150 m/min | 30–70 m/min |
| Feed | 0.04–0.25 mm/rev | 0.04–0.22 mm/rev | 0.02–0.06 mm/rev |
| Coolant pressure | 15–60 bar | 15–50 bar | 50–100 bar |
| Straightness requirement | < 0.15 mm overall | < 0.02 mm | < 0.01 mm |
| Surface finish Ra | < 1.6 µm | < 0.4 µm | < 0.4 µm |
| Cycle time (typical) | 2–8 min | 2–6 min | 0.5–3 min |
| Production volume | 5,000–50,000/yr | 5,000–50,000/yr | 5,000–50,000/yr |
Deep hole drilling for robotics and automation components represents a growing application area that differs significantly from traditional deep hole drilling. The emphasis on lightweight materials (aluminium, titanium, engineering plastics), moderate bore diameters, high precision requirements, cable routing bores that must be smooth and burr-free, and the need for rapid changeover between different component types makes robotics component drilling a distinct specialization. Compact gun drilling machines with high spindle speeds and advanced coolant systems are the preferred equipment, while multi-spindle configurations serve high-volume collaborative robot production. As the global robotics market continues to expand at 10–14 % annually, driven by labour shortages, e-commerce fulfilment automation, and the growth of collaborative robots in small-to-medium enterprises, deep hole drilling for robotic components will become an increasingly important segment of the deep hole drilling industry.