Unlock Cost Savings: Smart strategies to reduce CNC Milling costs for your metal parts

To reduce the manufacturing cost of CNC-milled metal parts, it’s essential to address design, material choice, machining strategies, and collaboration with our engineering teams. We will explain you below the best practices to create cost-effective parts without compromising on quality or functionality:

1. Design simplification

Simplifying the design is one of the most effective ways to reduce costs in CNC milling. Complex features and intricate geometries require longer machining times, specialized tools, and often multiple setups, all of which add to the cost.

• Minimize complex geometries: Avoid unnecessary curves, complex internal features, and intricate contours. Simple shapes allow for more efficient machining and require less tool changes and repositioning, directly reducing cycle time and tool wear.

Example: Replace a complex, wavy surface with a flat plane or basic curve.

• Reduce the number of small features: Small holes, slots, or narrow channels require smaller, more delicate tools, which operate at slower speeds. Designing with larger, standard-size features allows for faster machining and extends tool life.

Example: Use a ?5 mm hole instead of a ?1 mm hole when functionality permits.

• Limit deep cavities: Deep cavities need longer tools and multiple tool passes, which can increase machining time and tool wear. When possible, use shallow pockets or adjust the design to reduce the depth. If deep cavities are essential, using a pocketing design instead of a solid block can help reduce both material and machining time.

Example: Design a 10 mm deep pocket instead of a 30 mm deep cavity, or hollow out a thick section.

• Use symmetrical features: Symmetry in design allows for more efficient fixturing and reduces the need for multiple orientations. This simplifies the machining process and reduces both time and error.

Example: A symmetrical housing can often be machined with fewer setups than an asymmetrical one.

• Avoid undercuts: Features that require undercuts often need specialized tooling or multiple setups. Replace them with features that can be machined using standard tools.

Example: Instead of a dovetail groove, use a stepped groove that can be machined with standard end mills.

2. Optimize wall thickness and pocket depth

Wall thickness and pocket depth significantly impact machining costs. Thin walls and deep pockets not only increase the machining time but also introduce challenges like vibration and tool deflection, which can lead to inaccuracies and tool breakage.

• Maintain uniform wall thickness: Thin walls are more prone to vibration and are difficult to machine quickly, as the tools need to operate at slower speeds to avoid damaging the part. Design with a wall thickness of at least 1.5 mm, and keep thickness uniform throughout the part to maintain structural integrity and improve machining speed.

Example: Instead of having a wall transition from 1 mm to 2 mm, maintain a uniform 2 mm thickness.

• Shallow pockets: Pockets that are too deep require additional passes and can result in slower machining speeds. Aim to keep pocket depths shallow (ideally no deeper than four times the diameter of the cutting tool). This approach allows for higher material removal rates and reduces the need for specialized tools.

Example: For a tool with a diameter of 10 mm, design pockets with a depth of no more than 40 mm.

3. Apply tolerances wisely

Applying the correct tolerances only where needed can save a lot in machining costs. Tight tolerances require slower speeds, precise tools, and additional inspection, which all add time and expense to production.

• Specify tight tolerances only for functional features: Critical features that interact with other parts may require close tolerances, but other areas of the part can have standard tolerances. Applying tight tolerances unnecessarily on non-critical areas increases machining time without adding value.

Example: A critical shaft diameter might need a tolerance of ±0.01 mm, but non-functional edges can use ±0.2 mm.

• Standardize tolerances: Aim to use industry-standard tolerances (such as ISO 2768 mK) wherever possible. This reduces the need for specialized inspection and minimizes the likelihood of part rejections or rework, lowering overall cost.

Example: A general ±0.1 mm tolerance for non-critical dimensions balances precision and efficiency.

4. Select cost-effective materials

Material choice directly affects both machining time and cost. Different metals have varying degrees of machinability, and selecting an easy-to-machine metal can save a significant amount of production time and reduce tooling costs.

• Use easily machinable metals: Aluminum (e.g., 6061 or 7075 alloys) and mild steel are both easy to machine and relatively inexpensive. Aluminum is often a preferred material because it is lightweight, strong, and machines quickly. Harder metals like stainless steel and titanium are more challenging to work with, requiring slower machining speeds and specialized tools, which increases costs.

Example: Choose aluminum for non-load-bearing parts to minimize machining time compared to using stainless steel.

• Consider material properties wisely: Avoid high-strength or corrosion-resistant alloys unless absolutely necessary. For instance, if corrosion resistance is only a minor concern, consider using mild steel with a protective coating rather than stainless steel.

Example: For parts in low-corrosion environments, avoid costly stainless steel and use a coated mild steel alternative.

5. Design for minimal setups

Each setup on a CNC mill requires time for fixturing and aligning the part, and excessive setups increase the risk of alignment errors, potentially resulting in rejected parts. Design the part to require as few setups as possible to save time and cost.

• Consolidate features into one or two setups: If possible, design parts that can be machined in one or two orientations. This reduces setup time, ensures better alignment, and minimizes the risk of part movement during machining.

Example: A part with features located on the top and one side can often be machined in two setups using a rotary table or multi-axis machine.

• Ensure accessibility: Place features on accessible faces so they can be reached from one or two orientations. Avoid placing critical features on multiple faces that would require flipping or re-fixturing the part.

Example: Place holes, pockets, or slots on the top face rather than scattered across different faces.

6. Use standard tool sizes and avoid custom tooling

Custom tooling and non-standard dimensions increase machining costs due to the need for specialized tools and more complex setups.

• Standardize Hole Sizes and Radii: Design holes with standard drill bit sizes, such as metric or fractional inch sizes, to avoid custom tools. For internal corners, use radii that match standard tool diameters, typically between 1/8” and 1/2”.

Example: Instead of designing a 3.2 mm hole, use a standard 3 mm or 3.5 mm size.

• Limit custom threads: Use standard thread sizes and pitches for tapped holes.

Example: Use M10 × 1.5 threads instead of a custom M10 × 1.25.

• Avoid Sharp Internal Corners: Sharp internal corners require smaller tools, which increase machining time. Instead, use filleted corners with a radius that matches a standard tool size. This speeds up machining and reduces tool wear.

Example: Instead of a sharp 90° internal corner, use a 6 mm fillet radius that aligns with a common 12 mm tool diameter.

7. Limit surface finish requirements

Surface finish requirements can add to machining costs if high-quality finishes are needed. Each additional pass required to improve surface finish adds time and increases the chance of tool wear.

• Use standard surface finishes when possible: Specify only the surface finish quality needed for functionality. For non-critical surfaces or hidden areas, a standard machined finish is sufficient (e.g., Ra 3.2 μm).

Example: Use a standard finish on structural components hidden inside an assembly, while applying a polished finish only to visible or sliding surfaces.

• Separate finishes by function: If certain areas require high polish while others don’t, specify these differences clearly. Only apply finishing steps to functional or visible areas.

Example: Indicate that sealing surfaces need Ra 0.8 μm while structural support surfaces can remain at Ra 3.2 μm.

8. Optimize toolpaths with CAM software

Efficient toolpaths can significantly reduce machining time by minimizing unnecessary tool movements and idle time.

• Optimize tool path strategies: Use CAM software to simulate and plan tool paths that minimize rapid movements and tool changes. High-speed machining strategies, which involve lighter and faster passes, can also help reduce cycle time and wear on tools.

Example: For contour milling, use continuous and smooth toolpaths instead of segmented ones, reducing start-stop motions and machining interruptions.

• Reduce tool changes: Consolidating features to require fewer tool changes can save time. CAM software can also help by automatically selecting efficient tool paths and minimizing redundant tool changes.

Example: Machine all holes of a similar diameter across the part with the same drill bit before switching to another tool.

9. Modularize complex parts & use interchangeable designs

For very complex parts, it may be more efficient to divide the design into simpler modules that can be assembled. This allows each part to be machined independently with simpler, faster processes, reducing both machining time and setup complexity.

Example: Instead of machining a one-piece housing with internal and external features, split it into two components bolted together.

• Design for assembly: Ensure modular parts can be easily assembled, possibly by using standard fasteners or snap-fit designs. This approach can reduce both machining and assembly costs.

Example: Use dowel pins or locating features to ensure accurate alignment during assembly.

• Separate non-critical features: Non-functional or aesthetic elements can sometimes be manufactured separately and attached, rather than requiring complex geometry to be machined in a single piece.

Example: A decorative faceplate can be machined independently and bolted onto a simpler base component.

• Reuse existing designs: Reuse or adapt existing part designs to avoid the cost of starting from scratch.

Example: Use a standardized motor mount design for multiple machine models instead of redesigning for each application.

10. Collaborate with our engineering team early

We have practical knowledge of machining limitations and cost-saving techniques. By consulting with us early in the design process, you can gain valuable feedback that helps avoid costly design features.

• Request design for manufacturing (DFM) feedback: Our engineering team can suggest design tweaks that simplify fixturing or tooling, streamline machining operations, and reduce production time.

Example: If the design includes an unnecessarily tight tolerance or complex feature, our engineering team can recommend an alternative that is easier to machine without compromising functionality.

• Leverage our capabilities: Our workshop is specialized in different metals, tool types, and machining processes. Adjusting the design to align with our capabilities can reduce machining time and reduce costs.

Example: Instead of designing a feature that requires custom tooling, modify it to use a standard cutter size available in our workshop to avoid ordering specific cutters.

11. Batch production and volume optimization

Producing parts in batches spreads setup costs over multiple units, reducing the per-part cost. Larger production volumes often lead to cost savings, as CNC shops may offer volume discounts.

Example: Instead of producing 10 parts in separate runs, machine all 10 in one batch to cut setup costs and time. A CNC shop might charge $50 per unit for a batch of 10 parts but drop to $30 per unit for a batch of 100

• Standardize parts across products: If similar parts are used across multiple products, consider standardizing dimensions and features. This reduces setup times, simplifies inventory management, and increases production efficiency.

Example: Design a common bracket size that fits multiple products, rather than creating unique brackets for each.

Examples of simplification

• Before: A part with deep pockets, sharp internal corners, and tight tolerances on non-critical features.
• After: Shallower pockets with fillets, relaxed tolerances, and simplified contours.

• Before: A component requiring multiple reorientations for machining.
• After: Features aligned for a single setup with tool access.

Conclusion

In brief, by implementing these design and manufacturing strategies, you can reduce CNC milling costs effectively.

Simplifying design, optimizing material selection, minimizing setups, and working closely with our engineering teams are key steps to achieve cost savings while maintaining the integrity and functionality of the final part.