In modern injection mold manufacturing, precision machining plays a critical role in determining mold quality, production efficiency, and final plastic part performance.
Two of the most important machining technologies used in mold production are CNC machining and EDM machining.
Both processes are widely used for manufacturing mold components such as:
Mold inserts
Core and cavity blocks
Sliders
Lifters
Precision mold parts
However, CNC and EDM machining have different advantages and applications.
Understanding the difference between EDM machining vs CNC machining helps engineers select the right manufacturing process for achieving the best balance between accuracy, surface finish, cost, and production time.
At Fentormold, we use CNC machining, EDM, wire EDM, and precision grinding together to manufacture high-quality injection molds for automotive, electronics, medical, and industrial applications.
What Is CNC Machining for Injection Molds?
CNC machining (Computer Numerical Control machining) is a subtractive manufacturing process that uses computer-controlled cutting tools to remove material from metal blocks.
The CNC machine follows CAD/CAM programming instructions to create precise mold components.
Common CNC machining operations include:
Milling
Drilling
Pocket machining
Contour machining
High-speed finishing
CNC machining is commonly used for:
Mold bases
Electrode manufacturing
Core blocks
Cavity blocks
Mold inserts
Precision mechanical components
What Is EDM Machining for Injection Molds?
EDM (Electrical Discharge Machining) is a machining process that removes material using controlled electrical sparks between an electrode and the workpiece.
Unlike CNC machining, EDM does not use physical cutting tools.
Instead, the electrical discharge generates heat that melts and removes small amounts of metal.
The two main types of EDM used in mold manufacturing are:
- Sink EDM
Sink EDM uses a shaped electrode to create complex cavities and features.
It is commonly used for:
Deep ribs
Sharp corners
Narrow slots
Complex cavity details
- Wire EDM
Wire EDM uses a thin electrically charged wire to cut through metal.
It is mainly used for:
Precision inserts
Mold plates
Slides
Complex profiles
Wire EDM can achieve extremely high accuracy for precision mold components.
EDM Machining vs CNC Machining: Main Differences
Feature CNC Machining EDM Machining
Machining method Mechanical cutting Electrical discharge
Cutting tool Milling cutter Electrode or wire
Material hardness Limited by cutting tools Can machine hardened steel
Speed Generally faster Usually slower
Surface finish Good Excellent for fine details
Complex cavities Limited Excellent
Sharp corners Difficult Excellent
Cost Lower for many operations Higher for complex work
Accuracy Comparison Between CNC and EDM
Both CNC and EDM can achieve high precision, but their strengths are different.
CNC Machining Accuracy
Modern CNC machines can typically achieve:
±0.02 mm standard tolerance
±0.005–0.01 mm for precision machining
CNC is ideal for:
Large mold components
Flat surfaces
Structural parts
General precision machining
EDM Machining Accuracy
EDM is especially suitable for extremely detailed features.
Advantages include:
Excellent dimensional accuracy
Stable machining of hardened steel
Ability to create sharp internal corners
EDM is often selected for mold components where traditional cutting tools cannot achieve the required geometry.
When Should You Use CNC Machining for Injection Molds?
CNC machining is usually the preferred choice when:
- Machining Large Mold Components
CNC machines efficiently process:
Mold plates
Large inserts
Aluminum molds
Steel blocks
The high material removal rate makes CNC cost-effective for larger components.
- Fast Material Removal Is Required
For rough machining, CNC is significantly faster than EDM.
Typical applications:
Removing excess steel
Creating basic cavity shapes
Preparing components before EDM finishing
- Surface Quality and Efficiency Are Important
High-speed CNC machining can provide excellent surface finishes while maintaining production efficiency.
When Should You Use EDM Machining for Injection Molds?
EDM becomes the better choice when mold geometry is difficult or impossible to achieve with CNC.
- Deep and Narrow Features
Some injection mold designs include:
Deep ribs
Small slots
Thin walls
These features can be difficult for CNC tools because of tool access limitations.
EDM can machine these areas accurately.
- Hardened Tool Steel Machining
After heat treatment, mold steel becomes extremely hard.
Materials such as:
S136 stainless steel
H13 steel
Hardened tool steel
can be difficult to machine using traditional cutting tools.
EDM can process these materials without reducing hardness.
- Complex Cavity Details
EDM is widely used for:
Textured surfaces
Logo details
Fine ribs
Complex shapes
This makes EDM essential for cosmetic plastic parts.
CNC and EDM Work Together in Injection Mold Manufacturing
In professional mold manufacturing, CNC and EDM are not competing technologies.
They are complementary processes.
A typical mold manufacturing workflow may include:
Step 1: CNC Rough Machining
Remove most of the material quickly.
↓
Step 2: Heat Treatment
Increase steel hardness and durability.
↓
Step 3: CNC Finishing
Machine accurate reference surfaces.
↓
Step 4: EDM Machining
Create complex details and precision features.
↓
Step 5: Grinding and Polishing
Achieve final surface requirements.
This combination provides the best balance between:
Accuracy
Efficiency
Cost
Mold lifespan
Advantages of Combining CNC and EDM Machining
Higher Mold Accuracy
Using the right process for each feature reduces machining errors.
Better Surface Finish
EDM can produce detailed surfaces that improve plastic part appearance.
Longer Mold Life
Precision components reduce:
Wear
Misalignment
Maintenance requirements
Faster Mold Development
A combined machining approach reduces unnecessary processing time.
Applications of CNC and EDM in Injection Mold Manufacturing
Automotive Injection Molds
Used for:
Interior components
Exterior trim
Lighting parts
Functional assemblies
Electronics Injection Molds
Used for:
Connector housings
Consumer electronics parts
Precision plastic components
Medical Injection Molds
Used for:
Medical device components
Laboratory products
Disposable plastic parts
How Fentormold Uses CNC and EDM Technology
At Fentormold, we understand that different mold components require different machining solutions.
Our manufacturing capabilities include:
CNC machining
EDM machining
Wire EDM
Surface grinding
Injection mold assembly
Plastic injection molding
By combining advanced machining technology with experienced mold engineering, we help customers produce accurate, reliable injection molds.
Learn more:
Internal Links:
Injection Mold Manufacturing Service
https://fentormold.com/injection-mold-manufacturing/
CNC Machining Service
https://fentormold.com/cnc-machining/
Prototype Injection Molding
https://fentormold.com/prototype-injection-molding/
Conclusion
Both EDM machining and CNC machining are essential technologies in modern injection mold manufacturing.
CNC machining provides speed, efficiency, and excellent accuracy for most mold components.
EDM machining provides unique advantages for complex geometries, hardened steel, and precision details.
The best injection molds usually require both technologies working together.
Choosing a mold manufacturer with strong CNC and EDM capabilities ensures better mold quality, shorter development time, and more stable plastic part production.
www.fentormold.com