FMEA for Deep Hole Drilling — Failure Mode Effects Analysis

A precision machining shop producing 25 mm × 500 mm bores in 4340 steel using BTA drilling experiences a sudden drill breakage event that damages the workpiece and machine guide bushing, causing $12,000 in repair costs and 3 days of downtime. A subsequent process FMEA identifies that chip packing leading to torque overload was not detected because the machine lacked coolant pressure monitoring and the operator had no reaction plan for gradual pressure rise. Implementing the FMEA corrective actions — adding coolant pressure monitoring with alarm, establishing a chip packing reaction plan, and defining maximum tool life — eliminates drill breakage incidents over 18 months of subsequent production, saving $48,000 in repair costs.

FMEA Principles for Deep Hole Drilling ​

FMEA (Failure Mode and Effects Analysis) is a systematic method for identifying potential failure modes in a process, assessing their risks, and defining preventive and detection controls. For deep hole drilling, PFMEA (Process FMEA) is the applicable type.

The AIAG & VDA FMEA Handbook (1st Edition, 2019) defines a 7-step approach:

Deep Hole Drilling Process Structure ​

Process Flow for FMEA ​

Deep Hole Drilling Failure Modes ​

Primary Failure Modes ​

Failure Mode Descriptions and Mechanisms ​

Chip packing is the most critical failure mode in deep hole drilling. It occurs when chips fail to evacuate through the annular gap (BTA) or flute (gun drilling), accumulating and causing friction, torque increase, and eventually tool breakage. Research by Baumann & Eberhard (University of Stuttgart) using SPH simulation shows that chip packing creates a characteristic sawtooth pressure pattern and is the primary precursor to tool breakage.

Tool breakage has severity 9 because it can damage both the tool and the workpiece, may require machine repair (bushing, steady rest), and creates a safety hazard from flying carbide fragments.

Bore straightness deviation has severity 8 because it is difficult to detect without full-length measurement and cannot be corrected once the bore is complete.

AIAG VDA Rating Guidelines ​

Severity (S) ​

Occurrence (O) ​

Detection (D) ​

Complete PFMEA Example — BTA Drilling of Steel ​

Action Priority Determination ​

The AIAG VDA method uses Action Priority (AP) lookup tables rather than simple RPN multiplication. The AP level determines the urgency of corrective action.

Key AP Rules for Deep Hole Drilling ​

• Severity 9–10 always generates High AP regardless of occurrence and detection scores
• Severity 8 with Occurrence ≥ 4 generates High AP
• Severity 7 with Occurrence ≥ 6 and Detection ≥ 5 generates High AP
• Severity 5–6 with Occurrence ≥ 4 and Detection ≥ 5 generates Medium AP

Corrective Action Development ​

Control Plan Integration ​

The FMEA outputs feed directly into the control plan. For each failure mode with Medium or High AP, the control plan must specify:

Control Plan Example (derived from FMEA) ​

Maintaining the Living FMEA ​

Troubleshooting FMEA Implementation ​

FAQ ​

What is the difference between PFMEA and DFMEA for deep hole drilling? ​

PFMEA (Process FMEA) analyses the drilling process — focusing on how the bore is produced, including machine parameters, tooling, coolant, and inspection. DFMEA (Design FMEA) analyses the drill head or drill tube design — focusing on the product (the tool itself). For a deep hole drilling operation, PFMEA is the applicable method. DFMEA would be used by the tool manufacturer designing the drill head.

What are the most critical failure modes in deep hole drilling? ​

The most critical failure modes (highest risk) are tool breakage (severity 9), straightness deviation (severity 8), coolant system failure (severity 8), and burnished white layer/subsurface damage (severity 8). Chip packing is the most common precursor to tool breakage and should be carefully monitored through coolant pressure trend analysis. These failure modes typically generate Medium or High Action Priority under AIAG VDA methodology.

How does AIAG VDA FMEA differ from the previous RPN method? ​

The AIAG VDA method replaces the simple RPN multiplication (S × O × D) with Action Priority (AP) lookup tables that weight severity more heavily. Under the old RPN method, a failure with S=9, O=2, D=2 (RPN=36) might be ignored while a failure with S=4, O=7, D=7 (RPN=196) got attention. Under AIAG VDA, any failure with severity 9 or 10 automatically gets High AP regardless of occurrence or detection, correctly prioritising safety-critical failures. The new method also provides standardised tables rather than allowing arbitrary thresholds.

What is the recommended FMEA team composition for deep hole drilling? ​

The FMEA team should include the process engineer (deep hole drilling specialist), tooling engineer, quality engineer, machine operator (most familiar with day-to-day process behaviour), maintenance technician (familiar with coolant system and machine health), and a facilitator trained in AIAG VDA methodology. For suppliers to the automotive industry, the customer may also send a representative. The team should be 4–7 people.

How often should the deep hole drilling FMEA be updated? ​

The FMEA should be reviewed and updated annually at minimum. Updates are also triggered by any process change (new tool, new material, parameter change), customer complaint, internal nonconformance with root cause, or machine relocation. Major updates (new part family) require a full PFMEA review including new failure mode identification. The FMEA is a living document that should be continuously improved.

What severity rating should be assigned to tool breakage? ​

Tool breakage should be rated severity 9 (loss of primary function with safety impact) because it damages the workpiece, typically damages the machine guide bushing or steady rest, and can eject carbide fragments at high speed, creating a safety hazard. Under AIAG VDA rules, this automatically generates High Action Priority regardless of occurrence and detection ratings.

How do detection controls differ for deep hole drilling vs standard machining? ​

Detection is more challenging in deep hole drilling because the bore surface is not visible during cutting and the tool is hidden inside the bore. Direct measurement of diameter requires air gauging or in-process probes. Indirect detection methods — coolant pressure monitoring, spindle load trend analysis, and acoustic emission monitoring — provide earlier warning of developing problems than post-process inspection. A combination of direct and indirect detection controls is recommended.

What is the relationship between FMEA and control plan? ​

The FMEA identifies failure modes and defines prevention and detection controls. The control plan implements these controls on the production floor with specific parameters, methods, sample sizes, frequencies, and reaction plans. Every failure mode with Medium or High AP must have corresponding entries in the control plan. The control plan is essentially the production implementation of the FMEA. When the FMEA is updated, the control plan must be reviewed and updated accordingly.

How do you determine occurrence ratings for deep hole drilling processes? ​

Occurrence ratings should be based on historical data where available — scrap records, tool life data, nonconformance reports, and maintenance logs. For new processes without historical data, use engineering judgment based on experience with similar processes. The AIAG VDA occurrence scale ranges from 1 (< 1 in 1,500,000) to 10 (> 1 in 2). For a stable BTA drilling process with proper controls, typical occurrence ratings for diameter variation are 3–4 (1 in 2,000 to 1 in 15,000), while a process without coolant pressure monitoring might have occurrence 6–7 (1 in 20 to 1 in 80) for chip packing.

What corrective actions are most effective for reducing FMEA risk in deep hole drilling? ​

The most effective corrective actions address multiple failure modes simultaneously. Installing coolant pressure monitoring with alarm addresses chip packing, tool breakage, and coolant system failure. Implementing SPC for bore diameter addresses diameter oversize, undersize, and wear trends. Defining tool life limits and tracking tool usage addresses tool breakage and surface finish degradation. Annual machine alignment checks address straightness deviation and chatter. These actions typically reduce AP from High to Medium or Low across multiple failure modes.

Summary ​

Process FMEA for deep hole drilling systematically identifies and prioritises failure modes including chip packing, tool breakage, bore diameter variation, straightness deviation, surface finish degradation, and coolant system failure. The AIAG VDA FMEA methodology (2019) uses Action Priority determination that weights severity most heavily — tool breakage (severity 9) and straightness deviation (severity 8) typically generate High AP. The 7-step process moves from planning through structure analysis, function analysis, failure analysis, risk analysis, optimisation, and documentation. The FMEA outputs feed directly into the control plan, specifying controls, inspection methods, sample frequencies, and reaction plans for each medium and high priority failure mode. The most effective corrective actions — coolant pressure monitoring, SPC implementation, tool life tracking, and annual machine alignment — address multiple failure modes simultaneously. The FMEA must be maintained as a living document, updated annually and triggered by process changes, nonconformances, or customer feedback.