Choosing the right EDM process isn’t just about what’s technically possible—it’s about matching your design requirements to the most cost-effective manufacturing approach. With extensive experience machining precision components for aerospace, medical, and industrial applications, a smart EDM choice can save both time and money while ensuring your tolerances are achievable.
Wire EDM excels at complex external profiles and through-cuts, Sinker EDM handles internal cavities and 3D shapes, while Hole Drilling EDM creates precision holes in hard materials. Each process has distinct capabilities, cost structures, and geometric limitations that directly impact your design decisions.
Learn how to match your part geometry to the right EDM method, plus design optimization tips to minimize cost without compromising precision.
Table of Contents
Which EDM Process Should I Choose for My Part Geometry?
Wire EDM: through-cuts and external profiles. Sinker EDM: internal cavities and blind features. Hole Drilling EDM: precision holes only. Choose based on your part’s most complex feature that conventional machining cannot handle.
Quick Decision Tool:
- Through-cuts needed? → Wire EDM
- Internal pockets/cavities? → Sinker EDM
- Precision holes only? → Hole Drilling EDM
- Multiple complex features? → Hybrid approach
Most parts combine geometries, so identify your limiting factor first. A housing needing external slots (Wire EDM) plus internal channels (Sinker EDM) requires hybrid manufacturing rather than forcing everything through expensive Sinker EDM. We’ve seen 60% cost reductions when developers separate simple features for conventional machining instead of over-specifying EDM for the entire part.
Design Takeaway: Match your most complex, unmachineable feature to the right EDM process, then use conventional methods for simpler geometries to minimize cost.
Can Sinker EDM Machine Internal Cavities Wire EDM Cannot Reach?
Sinker EDM machines internal cavities that Wire EDM cannot reach, but first test: can you access your feature from two sides? Wire EDM needs through-access, Sinker EDM creates enclosed cavities. The access test determines both feasibility and cost—custom Sinker EDM electrodes typically add $800-2000 vs. $200-400 for Wire EDM setup.
Part Assessment Method:
- Through-hole possible without compromising function? → Wire EDM (cheaper)
- Must remain completely enclosed? → Sinker EDM required
- Multiple disconnected internal features? → Consider part splitting strategy
Real examples help clarify: Medical housings with internal fluid channels need Sinker EDM because through-holes would cause leakage. However, structural brackets with internal lightening pockets could be redesigned with through-access to use Wire EDM instead. We’ve helped aerospace clients save 60% on bracket costs by adding strategic through-holes that didn’t affect structural performance.
For hybrid parts with both internal cavities and through-cuts, use Sinker EDM only for truly enclosed features and Wire EDM for accessible geometries—this minimizes electrode costs while maintaining design intent.
Design Takeaway: Before committing to expensive Sinker EDM, validate with your assembly team whether through-access modifications would compromise functionality. Often, creative design changes enable much cheaper Wire EDM manufacturing.
When Is Wire EDM Required for Tight Tolerance Features?
Wire EDM is required when standard ±0.005″ CNC tolerances cause functional problems like poor fits, binding, or leakage. The key question: will your assembly still work properly if this feature varies by ±0.005″? If yes, standard CNC saves significant cost.
Application-Based Tolerance Guide:
- Bearing surfaces/rotating shafts: ±0.0005″ often required for proper fit
- Sealing surfaces/O-ring grooves: ±0.001″ prevents leakage
- Mounting holes/fasteners: ±0.005″ typically sufficient
- Hardened materials (HRC 45+): Wire EDM needed for any tight tolerance
Cost Reality Check: Tightening tolerances from ±0.005″ to ±0.001″ typically doubles machining cost, while ±0.0005″ can triple it. For a $500 CNC part, Wire EDM precision might cost $1500. Medical device housings often justify this for sealing performance, but mounting brackets rarely need this precision.
For mixed-tolerance parts, specify tight tolerances only on critical features and use standard ±0.005″ elsewhere—this optimizes cost while maintaining assembly requirements.
Design Takeaway: Start your tolerance analysis at ±0.005″ and justify tighter specs only where function demands it. Reserve Wire EDM precision for features that directly affect product performance, not aesthetic preferences.
What Design Features Make EDM Machining Most Expensive?
Look at your CAD model: count internal pockets (each needs a $500-2000 electrode) and complex external curves (add programming time). Most cost explosions come from unnecessary internal cavities that could be simplified or eliminated without affecting function.
Design Cost Assessment:
- Count internal cavities: 1 cavity = +$800, 3 cavities = +$3000
- Evaluate external complexity: Simple profiles = $1200, intricate details = $4000+
- Check functional necessity: Does each feature affect performance or just aesthetics?
Real Cost Reduction Examples: Medical housing original design: 3 separate cooling channels requiring 3 electrodes = $3500 in tooling. Redesigned version: 1 larger channel with internal ribs = $800 electrode cost. Aerospace bracket: Complex external profile with decorative details = $4200. Simplified functional profile = $1400, saving $2800 without performance impact.
Practical Redesign Strategies: Instead of multiple small internal pockets, use one larger cavity with internal walls. Replace complex external curves with straight lines and standard radii where possible. Remove decorative features that don’t affect assembly or function—these often account for 40% of EDM programming time.
Cost Validation Method: Before finalizing your design, ask: “What happens if we eliminate this feature?” If the answer is “nothing functionally changes,” consider removing it. We’ve helped clients achieve 50-60% cost reductions using this simple evaluation.
Design Takeaway: Challenge every internal cavity and complex external detail before submitting for quotes. Often, minor functional compromises enable major cost savings.
What Tolerances and Finishes Require Secondary Processing After EDM?
Check your assembly requirements: if parts mate properly with ±0.0005″ and Ra 32 μin, use standard EDM specs. Tighter requirements trigger expensive grinding or polishing that adds 50-100% to part cost. Most developers over-specify without functional justification.
Function-Based Specification Strategy: Start with standard EDM capabilities and test with prototypes before specifying expensive secondary work. Bearing surfaces in rotating assemblies typically need grinding to ±0.0001″ and Ra 8 μin for proper clearances. Sealing surfaces may require Ra 16 μin or better to prevent leakage. However, mounting holes, structural bosses, and most assembly interfaces work fine with standard EDM finish.
Application Examples: Medical fluid channels often need Ra 16 μin for cleanability, but housing walls work perfectly at Ra 32 μin. Aerospace brackets requiring ±0.0005″ on mounting holes but only ±0.002″ on structural features save 40% by avoiding unnecessary precision on non-critical surfaces.
Specification Testing Approach: Build prototypes with standard EDM specs first. Test assembly fit, sealing performance, and functional requirements. Add secondary processing only where standard specs cause actual problems—not just because tighter seems “better.”
Drawing Specification Tips: Note “Ra 32 μin unless noted” and call out tighter specs only on critical features. This prevents manufacturers from over-processing the entire part.
Design Takeaway: Validate specification requirements with prototypes before committing to expensive secondary operations. Reserve tight tolerances and fine finishes for surfaces where function demands them.
Can I Combine EDM with Conventional Machining to Save Cost?
Use conventional machining for 70-80% of features and EDM only for complex geometries—this hybrid approach typically saves 30-50% compared to all-EDM manufacturing. Success depends on finding suppliers who can coordinate both processes or managing handoffs between specialized shops.
Supplier Selection Strategy:
- Best option: Find shops offering both CNC and EDM in-house
- Alternative: Coordinate between separate vendors using shared fixture standards
- RFQ approach: Request quotes for both all-EDM and hybrid manufacturing to compare costs
Practical Coordination Steps: When requesting quotes, specify which features need EDM precision and which can use conventional methods. Provide clear handoff requirements and stock allowances (0.010-0.020″ on EDM surfaces). Ask suppliers to propose optimal manufacturing sequences—they often identify additional cost-saving opportunities.
Communication with Your Team: Tell purchasing to prioritize suppliers with both capabilities. Expect 2-3 extra days for hybrid processes but significant cost reductions. A $3500 all-EDM part typically costs $1800 with hybrid manufacturing, justifying the coordination effort.
Design Takeaway: During vendor selection, evaluate both single-source capabilities and multi-vendor coordination options. The supplier relationship often determines hybrid manufacturing success more than design complexity.
How Can I Redesign Parts to Minimize EDM Requirements?
Identify blind internal pockets, spline curves, and radii smaller than 0.125″ in your CAD model—these features drive EDM costs that design changes can often eliminate. Converting internal features to external access or simplifying complex curves enables conventional machining.
CAD Feature Analysis Method:
- Blind pockets: Internal cavities with no exit path
- Complex curves: Splines instead of standard arc segments
- Tight radii: Smaller than 0.125″ requiring specialized tooling
- Multi-level steps: Internal geometry requiring multiple electrodes
Redesign Strategy Examples: Replace internal cooling channels with external fittings—eliminates $2500 Sinker EDM electrode costs. Convert spline profiles to arc segments with standard radii for conventional milling. Split complex parts into two simpler components that avoid EDM entirely.
Trade-Off Validation: Evaluate functional impact before redesigning. External cooling adds assembly steps but eliminates EDM costs. Simplified profiles maintain performance while reducing manufacturing complexity.
Design Takeaway: Use CAD analysis to systematically identify EDM-driving features, then explore external access, simplified geometries, or part splitting to enable conventional manufacturing methods.
How Does Choosing EDM Affect My Production Timeline and Cost?
EDM adds 2-4 weeks to timelines and costs 150-300% more than conventional machining, but enables precision and geometries impossible with other methods. Timeline and cost impact varies by EDM type and part complexity.
Quick Timeline Assessment:
- Wire EDM: 1-2 weeks (programming + cutting)
- Sinker EDM: 3-4 weeks (electrode manufacturing + operations)
- Hole Drilling EDM: 3-5 days (fastest EDM option)
- Hybrid approach: 2-3 weeks (reduces pure EDM time)
Cost Planning Guide: A $500 conventional part costs $1200-2000 with Wire EDM, $2000-3500 with Sinker EDM. For prototypes (1-50 parts), setup costs dominate. Above 100 parts, electrode costs amortize better, improving economics.
Project Planning Checklist: Can your launch timeline accommodate 3-4 weeks additional lead time? Does your budget support 2-3x cost increases? Are EDM capabilities actually required for your design functionality? Consider these factors during initial design phases, not during manufacturing quotes.
Schedule Risk Mitigation: Build EDM time into project timelines early—rushing compromises quality and increases costs. For tight deadlines, explore hybrid manufacturing or parallel EDM operations on multiple features.
Design Takeaway: Factor EDM timeline and cost constraints into design decisions from project start. Early planning enables optimization for both performance requirements and production realities.
Conclusion
EDM selection depends on your part geometry, tolerance requirements, and cost constraints. Wire EDM handles external profiles, Sinker EDM creates internal cavities, while hybrid approaches optimize costs. Reserve tight tolerances and complex features only where functionally required to balance precision with budget realities.
Contact us to explore EDM manufacturing solutions tailored to your product design requirements.
Frequently Asked Questions
EDM only works on electrically conductive materials like metals and carbon fiber composites. Plastics cannot be EDM machined since they don’t conduct electricity. Consider conventional machining or molding for plastic components requiring precision features.
Wire EDM can cut external threads, but internal threads typically require conventional tapping after EDM hole creation. Sinker EDM can form threads using specially shaped electrodes, but this is expensive and usually limited to special applications requiring threads in very hard materials.
EDM creates minimal mechanical stress since it uses electrical discharge rather than cutting forces. However, the process can create a thin recast layer that may require removal for critical applications. Discuss stress relief requirements with your supplier based on part function.
Most EDM shops handle single prototypes to low-volume production runs. Setup costs make single parts expensive, but there’s typically no minimum quantity requirement. Economics improve significantly above 25-50 parts due to setup cost amortization.
Most shops work with standard CAD formats (STEP, IGES) and accept DXF files for 2D profiles. Provide 3D models when possible, as they help programmers optimize toolpaths and identify potential machining issues before production begins.
EDM holes maintain ±0.0005″ positional accuracy even in hardened materials, while conventional drilling in hard materials often drifts ±0.002″ or more. EDM eliminates drill wandering and produces perfectly round holes regardless of material hardness.
