Tips to simplify designs
CNC machining is the automated and programmable derivative of traditional manual machining, evolved out of a long development process that began with the Jacquard looms of the early 18th century. CNC machine tools are diverse and range from the simplest 3 axis part motion, spinning cutter to intricate and flexible 12 or more axis machines that can function as both mill, lathe and even automatic welder and cutter.
Their role is primarily in single part and low volume traditionally, but as capabilities and automation improve, the creep of CNC services into mass production is developing fast. This transition massively increases the pressure towards effective use of DFM throughout the design process, to be volume ready.
Advantages of CNC machining in manufacture
Using CNC machined components in a design delivers various pivotal design and product wins that make effective design for CNC machining a central capability in the designers arsenal;
- CNC machines can produce highly accurate and repeatable parts with tight tolerances, ensuring consistency and compliance in every part. Repeatable and identical parts with low errors and high quality are maintainable across large production runs.
- Machining parts on CNC equipment allows low labor, 24/7 operation, with minimal human intervention, delivering high productivity and fast turnaround times.
- CNC machines can work with an astonishing range of materials – metals, plastics, composites, ceramics and even natural materials like wood, stone etc., making the capability central to many production environments.
- These processes can deliver intricate and complex geometry, within certain limitations. Equivalent outcomes are difficult or impossible to achieve repeatably with manual machining.
- Although the initial setup cost can be relatively high and often involves custom fixtures and programming, CNC machining removes considerable downstream and inflexible labor costs, relative to manual machining. Typically material waste and scrap rates are improved, moving the errors into virtual and simulated operations..
- CNC machines can be readily programmed to produce divergent components in quickly changed materials, rendering the method suitable for both prototyping and full-scale production runs.
- Automated control of the process minimizes the risk of human error, once setup and programming are validated, delivering repeatable quality in manufactured parts.
- CNC machines operate with enclosed/interlocked cutting environments and automated processes, reducing, presenting low risk of accidents and injuries in the workplace.
- CNC machining can seamlessly scale from prototypes to high-volume production runs without sacrificing quality or efficiency.
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Mechanical Engineer
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DFM Principles
The guidelines that must drive the part design process to be CNC ready result in easier setup and manufacture of lower cost parts. The design limitations imposed by machine-readiness are not extensive, but there are rules that must not be broken.
Select materials with care
Consider machinability when selecting materials – harder materials means slower cuts and lower throughput.
Where post hardening is required, after machining, allow for distortions that may result by stress relieving before machining and my post processing using grinding or EDM approaches to reimpose precision.
Simplicity is key
Minimize complexity by simplifying designs helps to reduce and moderate intricate details that otherwise increase machining time and cost. Use simple geometries and avoid deep cavities or sharp internal corners.
Design holes to standard sizes that match readily available drill bits and limit the variety of diameters in a part to reduce tool changes. This speeds up throughput considerably.
Use minimalist tolerancing
Specify tolerances that are as tight as absolutely necessary for function and fit. Overly tight tolerances dramatically increase machining time, programming complexity and component cost.
Take care with geometry
Maintain consistent wall thickness to reduce stress concentrations, reduce warp risk, and improve part strength. This is highly relevant in some materials, but the rule is far from universal as many materials can be stress relieved before machining to improve the tolerance of variations in section weight.
Design parts to avoid deep pockets, which are often challenging and time-consuming to machine. Where deep pockets are necessary, consider making them stepped in profile or open and cut through allowing two-sides cutting.
Add filets to internal corners to distribute stress and reduce the likelihood of cracking, and allow cutting tools to navigate the part more smoothly in transitions. Aim for filets that use a tool that is suitable for.
Plan the approaches to part clamping and machining order in the early design phase, to avoid later difficulties and extended machining times
Plan for secondary operations, such as deburring or surface finishing, and design parts to minimize these processes whenever possible.
Toolpath efficiency
Plan tool-paths in the design to minimize the number of tool changes required. Try to design so that you cluster similar features, to allow for continuous machining with the same tool, improving toolpath efficiency.
Make hole sizes and internal radii consistent to reduce tool changes
Conclusion
Incorporating DFM principles in parts prepared for CNC machining can greatly enhance the efficiency, quality, and cost-effectiveness of the manufacture. By optimizing material selection, part geometry, design-planned toolpaths and machining strategies, you can minimize production time and reduce material waste.
Effective use of DFM ensures that the designs are compatible with CNC capabilities, allowing for precise, repeatable, and high-quality production. On that basis, it is important to plan according to the axis-count of the expected supplier/machine, to minimize the required setups and repositioning error sources. Additionally, adhering to DFM guidelines facilitates smoother transitions from prototyping to full-scale production, ensuring that parts are not only manufacturable but also economically viable.
CNC machining bridges the gap between design intent and practical manufacturing, leading to superior product outcomes and a competitive edge in the market. Effective application of the core principles of DFM can greatly improve machinability and cost effectiveness.
Benjamin S
