Injection molds often have deep cavities, contoured surfaces, tight radii, complex parting lines, and other features that are difficult to machine with conventional equipment. Multi-axis CNC milling gives toolmakers greater access to these challenging geometries while helping improve accuracy, surface finish, and lead times.
Although traditional 3-axis CNC machining is still important in mold making, adding rotary axes can reduce setups, permit shorter cutting tools, and sometimes eliminate electrical discharge machining (EDM). True simultaneous 5-axis CNC milling takes this capability even further by continuously controlling all five axes during a cut.
For injection molders and OEMs sourcing tooling, knowing these differences helps determine which process is right for a particular mold, insert, core, or cavity.
A conventional 3-axis CNC milling machine moves along three linear axes: X, Y, and Z. This arrangement works well for plates, mold bases, pockets, holes, and relatively straightforward surfaces.
A 5-axis machine adds two rotary axes, allowing the machine to change the angle between the cutter and workpiece. This added freedom can access surfaces that otherwise require repositioning, longer cutting tools, or another manufacturing process.
Mold components can include sculpted surfaces, steep walls, deep pockets, undercuts, draft angles, complex shutoffs, and small internal radii.
3-axis machining restricts the cutter to an orientation parallel to the machine’s Z-axis, while multi-axis machining positions the cutter at an angle that provides better access.
Benefits can include:
Although 3+2 and simultaneous 5-axis machining can both use a 5-axis machine, they use those axes differently.
In 3+2 machining, the two rotary axes position the workpiece or cutter at a specific angle. The rotary axes then remain stationary while conventional 3-axis cutting takes place. The machine can reposition to another angle for the next operation.
Also called positional or indexed 5-axis machining, this approach works well for:
It provides some of the setup-reduction advantages of 5-axis machining without requiring continuous coordinated movement of all five axes.
With simultaneous 5-axis milling, the machine can move the X, Y, and Z axes while also moving both rotary axes during cutting. The cutter orientation can therefore change continuously as it travels across the workpiece.
This is particularly valuable on complex 3D mold surfaces. Instead of approaching a contoured surface from one fixed direction, the CNC system continuously adjusts the cutter to maintain an advantageous relationship between the cutting edge and mold surface.
The process requires sophisticated controls, computer-aided machining (CAM) programming, collision avoidance and accurate simultaneous machine movement. But it enables capabilities that 3+2 machining cannot efficiently replicate.
Not every mold component needs simultaneous 5-axis machining. A simple mold plate, for example, may be produced more economically on a 3-axis machining center. The advantages increase as geometry becomes more complex.
It’s not unusual for mold cavities and cores to have compound curves and sculpted surfaces. Simultaneous 5-axis CNC milling allows the cutting tool to follow these surfaces while continuously changing its angle.
This makes it possible to machine tooling that produces housings, complex consumer products, automotive parts, medical products and other molded parts with complex 3D geometry.
Deep cavities present another challenge. A 3-axis machine may require a long tool to reach the bottom while clearing surrounding walls.
Long tools are less rigid and more susceptible to vibration, deflection, and breakage. A 5-axis machine can tilt the cutter or workpiece to improve access, often permitting a shorter cutter.
Greater rigidity allows for more aggressive cutting while reducing chatter and deflection, improving accuracy and surface quality.
Multi-axis machining can also simplify angled features, parting surfaces, shutoffs, and other areas that are difficult to reach from one direction.
Machining more features in a single setup saves time and reduces positioning errors that can happen when a workpiece is repeatedly removed and reclamped.
Surface quality is critical in mold making because tooling marks on the mold’s surface are transferred to the molded part.
With a ball-nose end mill, cutting conditions vary across the tool. At the very center of the cutter, effective cutting speed is low.
A 3-axis strategy may force portions of a contoured surface to be machined near this inefficient center region. By tilting the tool, 5-axis machining can position a more effective portion of the cutting edge against the workpiece and maintain that relationship over complex geometry.
The result can be a smoother and more consistent machined surface.
A better machined finish can reduce hand polishing, bench work, and other secondary operations.
Reducing manual finishing can also help preserve dimensional accuracy. Every hand-finishing operation introduces some potential for unintended changes to critical mold geometry.
EDM is still needed for sharp internal corners, deep narrow ribs, and features that CNC cutting tools cannot machine. However, advanced multi-axis milling can eliminate or reduce EDM on some mold components.
A combination of 5-axis movement, high-speed machining, small-diameter tools, and efficient toolpaths can directly machine features that once might have been assigned to EDM.
Where geometry permits, direct milling can eliminate electrode design, electrode manufacturing, EDM setup, and the time-consuming burn cycle.
EDM also produces a characteristic recast layer and surface texture that may require additional finishing. When a feature can instead be finish-milled with an optimized 5-axis toolpath, the toolmaker may achieve a smooth surface directly from machining.
The objective is not to replace EDM entirely, but to use it only where the geometry or required detail makes it advantageous.
More axes do not automatically make a machining process better. The appropriate approach depends on the mold design.
Traditional 3-axis machining remains cost-effective for mold bases, plates, straightforward pockets, holes, and components with relatively simple geometry.
3+2 machining is ideal when a component requires machining from several orientations but does not need continuous changes in tool angle.
Toolmakers can machine several faces or angled features in one clamping while benefiting from shorter, more rigid tools.
True simultaneous 5-axis CNC milling offers its greatest advantages on difficult geometry, including:
The important question is not merely whether a part can be 5-axis machined, but whether 5-axis machining provides a meaningful manufacturing advantage.
The advantage of multi-axis CNC milling is not that the machine moves in more directions but that it offers toolmakers greater control over manufacturing complex mold components.
For suitable tooling, 3+2 or simultaneous 5-axis machining can reduce setups, improve access, allow shorter, more rigid cutting tools, improve dimensional consistency, and produce better surface finishes. In some applications, it can also reduce hand polishing and eliminate EDM operations.
For molders and OEMs, however, specifying “5-axis” should not be the goal itself. Straightforward mold components may be produced most economically with 3-axis CNC milling. Components with multiple faces and fixed-angle features are often good candidates for 3+2 machining. Complex cores, cavities, and contoured surfaces are where true simultaneous 5-axis CNC milling provides its greatest advantages.
A good toolmaker can look at the geometry, tolerances, surface finish, material, production requirements and downstream operations to determine the best combination of conventional milling, multi-axis machining, EDM and finishing.
When applied in the right tooling applications, multi-axis CNC milling can reduce manufacturing steps and lead times while delivering the accuracy, surface quality and the reliability that injection molders and OEMs demand.
We’ve been making over 9000 molds and counting. Using the 5-axis CNC milling is part of our process for several mold inserts.
Need help with a tooling project? Contact us.