CNC machining is a highly accurate and efficient method of manufacturing parts. It has revolutionized the manufacturing industry and made the production process faster and more cost-effective. However, for small businesses or individuals who require only limited production runs, it can be challenging to leverage CNC machining effectively. In this article, we will discuss how to design parts for small batch CNC machining to help you get the most out of this manufacturing process.
What Is Small Batch CNC Machining?
Small Batch CNC (Computer Numerical Control) Machining is a manufacturing process that creates precise parts in smaller quantities, typically ranging from one to several hundred units. It’s a popular choice for prototypes, custom orders, or small production runs where high precision is needed.
The process uses pre-programmed computer software to control the movement of machinery and tools. The computer controls can operate complex machinery such as grinders, mills, routers, and lathes, allowing for high accuracy and repeatability in manufacturing parts.
Small Batch CNC Machining contrasts with mass production that makes thousands or millions of identical parts. It provides a cost-effective solution for low-volume businesses needing high-quality, custom parts. The high customization, rapid prototyping, and reduced inventory costs make Small Batch CNC Machining an attractive option for many businesses.
What Are the Different Types of Small Batch Machining Processes and their advantages?
CNC milling is a manufacturing process that uses a cutting tool mounted on a rotating spindle to selectively remove material from a block of raw substrate. The workpiece is rigidly mounted to a table, and this table moves or rotates on different planes so the tool can work at many angles. Sophisticated CNC milling machines can have 5 or more axes of independent motion to make more complex shapes or to avoid having to move the workpiece to a separate machine.
CNC drilling is a precise CNC machining method that employs computer numerical control (CNC) where drill bits are utilized to bore holes into a material.
Unlike manual drilling, CNC drilling harnesses the power of computers to control the drill bits’ movements, ensuring accuracy and consistency that manual operations can’t match. This method is beneficial for industries requiring high precision, such as aerospace, automotive, and electronics, where even a minor discrepancy can lead to significant issues.
Electrical discharge machining (EDM), also known as spark machining, spark eroding, die sinking, wire burning or wire erosion, is a metal fabrication process whereby a desired shape is obtained by using electrical discharges (sparks). Material is removed from the work piece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid and subject to an electric voltage.
Surface grinding is a manufacturing process which moves or grinding wheel relative a surface in a plane while a grinding wheel contacts the surface and removes a minute amount of material,such that a flat surface is created.The term surface grinding designates any process which accurately processes or grind a surface.
| CNC Miliing | CNC Drilling | EDM Machining (Sinker and Wire) | Surface Grinding |
|---|---|---|---|
| Complex Geometries | Accurate Hole Placement | Complex Shapes and Fine Details | Superior Surface Finish |
| Rapid Prototyping | Depth Control | Hard Material Machining | Tight Tolerance Achievement |
| High Customizability | Material Compatibility | Minimal Surface Impact | Material Versatility |
| Efficient Production | Customization Flexibility | Precision Slots and Cavities | Custom Tooling and Fixtures |
Why CNC Machining for Small Batch Production?
Manual machining can be acceptable for manufacturing small numbers of parts. However, manual machining has several drawbacks, including labor costs, lead times, and potential accuracy issues. On the other hand, CNC machining provides high accuracy and repeatability, which makes it an efficient and cost-effective option for small batch production. It can be an excellent choice for small businesses, startups, or individuals who need to manufacture a limited run of parts.
CNC machining originated in the mass production era and has a long history. As technology progressed and the complexities in manufacturing amplified, there’s been a notable shift to smaller, more customized batches. This transition is primarily fueled by the escalating demand for precision and adaptability in manufacturing.
Driven by evolving market trends and the call for tailored so
lutions, the manufacturing sector has seen a considerable pivot from large-scale to agile, small batch production. The smaller batches enable manufacturers to adjust to market fluctuations nimbly, curbing inventory expenses and waste. This approach also facilitates speedy prototyping and customization, catering effectively to niche markets. With technological advancements, the uptake of small batch CNC machining has surged, resulting in efficient, precision-focused manufacturing and ensuring quick delivery of products that align with unique customer specifications.
Applications of Small Batch CNC Machining
Listed below are a few applications in which small-batch CNC machining can be used:
- Electronic Enclosures:Small batch CNC machining is useful for the fabrication of electronic enclosures, especially one-off or special enclosures with small physical volumes. Milling and drilling are all applicable machining processes for electronic enclosures.
- Electronic Component Racks:Electronic component racks are another application where small batch CNC machining is useful. Electronic component racks are storage solutions that hold sensitive electronic equipment.
- Custom Storage Racks:Small batch CNC machining is also good for the fabrication of custom storage racks designed to accommodate specific tools, equipment, and various other items. Since these racks are tailor-made for specific items which may also be custom-made, manufacturing volumes of these racks will be small.
- Mounting Brackets:Mounting brackets are another application where small batch CNC machining shines. Mounting brackets are relatively simple to produce. As such, manufacturers can create and alternate between many different types of mounting brackets with ease and efficiency.
main restrictions of CNC design
CNC offers great design flexibility, but there are a few restrictions. These limitations relate to the basic mechanics of the cutting process and mainly concern tool geometry and tool access.
Tool geometry
Most common CNC cutting tools (end mill tools and drills) have a cylindrical shape and a limited cutting length.
As material is removed from the workpiece, the geometry of the tool is transferred to a machined part. This means, for example, that the internal corners of a CNC part always have a radius, no matter how small a cutting tool was used.
tool access
To remove material, the cutting tool approaches the workpiece directly from above. Features that cannot be accessed in this way cannot be CNC machined.
Recommending aligning all your model’s features (holes, cavities, vertical walls, etc.) to one of the six principal directions. However, see this rule as a recommendation and not a restriction, as 5-axis CNC systems offer advanced workpiece-holding capabilities.
Tool access is also an issue when machining features with a large depth-to-width ratio. To reach the bottom of a deep cavity, for example, you need tools with extended reach. This means a wider range of motion for the end effector, which increases the machine chatter and lowers the achievable accuracy.
It will simplify production if you design parts that can be CNC machined with the tool that has the largest possible diameter and the shortest possible length.
small batch CNC part design guiderlines
Certain features, such as minimum wall thickness and achievable tolerances, in CNC designs can be tricky and should be examined on a case-by-case basis, but staying within a set of geometric recommendations can help ensure better results and a successful machining process.
1.Tolerances
Longsheng ensures the quality of CNC machined parts with ISO 9001:2015, ISO 9001:14001 and IATF16949 certified quality management systems.
Tolerances down to +/- 0.005mm
2.Cavities and Pockets
The recommended depth of any cavity in your design is four times its width because end mill tools have a limit to their cutting length. This limit typically three to four times the diameter of the tool. Lower depth-to-width ratios lead to increased vibration, tool deflection and chip evacuation.
If you need larger depths for design, you can use variable cavity depth to get around this problem. It is possible to have a 30:1 ratio for tool diameter to cavity depth if using a specialized tool.
3.internal edges
When designing inner edges, the recommended vertical corner radius is one-third of the cavity depth or greater. If you use the recommended corner radii, you will be able to use a diameter tool that follows the suggested cavity depth guidelines. Corner radii slightly higher than the recommended amount enables you to cut along a circular path, rather than a 90-degree angle, which creates a surface finish that is of a higher quality. If you instead need a 90-degree angle, it is recommended that you use a T-bone undercut rather than decreasing the corner radius.
The recommended floor radius is 0.5 millimeters, one millimeter or no radius, although any radius is technically feasible.
4.Thin Walls
The walls of your CNC-machined part should ideally be at least 0.8 millimeters thick for metals or 1.5 millimeters thick for plastics, although thicknesses of 0.5 millimeters for metals and one millimeter for plastics are technically feasible.
Thinner walls increase the vibrations that occur during machining and reduce the degree of accuracy you can achieve. Thinner plastic walls may also warp because of residual stress or soften because of temperatures increases.
5.Holes
Machinists use either drill bits or end mill tools to machine holes. When deciding on the diameters of the holes in your design, use standard drill bit sizes, which are measured in either metric or imperial units, as a guide. Any diameter above one millimeter is technically possible. If holes require tight tolerances, machinists use reamers and boring tools to finish. It’s recommended to use a standard diameter for holes smaller than about 20 millimeters that need a high accuracy.
The maximum suggested depth of any hole is four times the nominal diameter, and 40 times this number is feasible. A typical ratio is around 10 times the nominal diameter.
6.Threads
When designing CNC-machined parts, the recommended thread size is M6 or above, but the minimum you can use is M2. For cutting threads down to M6, machinists use CNC threading tools, which reduce tap breakage risk. Taps and dies can cut down to M2.
The recommended thread length is three times the nominal diameter, and the minimum is 1.5 times the nominal diameter. For all threads that are below M6, you will need to add at the bottom of the hole an unthreaded length equaling 1.5 times the nominal diameter. For threads larger than M6, you can thread the hole throughout its length.
7.Small Features
You can include some small features in your design, but there are some best practices to help make sure they turn out the way you want them to. The recommended minimum diameter of any hole in a design is 2.5 millimeters. The majority of machine shops should be able to accurately machine holes of this diameter with standard tools.
With specialty tools called micro-drills, machinists with the necessary expertise can cut holes down 0.5 millimeters.
8.Text and lettering
Engraved text is preferred over embossed text, as less material is removed. Using a minimum size of -20 sans -serif font (e.g. Arial or Verdana) is recommended. Many CNC machines have pre-programmed routines for these fonts.
Recommended: font size 20 (or larger), 5 mm engraved
considerations for small batch CNC part design
When undertaking small batch CNC machining, specific design guidelines must be considered. These considerations include the materials used, the intricacies of the design, tolerances, and finishing processes. Remember, these guidelines can vary based on the specific requirements of each project.
- Understand Material Properties: Different materials behave differently during machining. It’s crucial to understand the properties of the material you’re working with, such as hardness, brittleness, and heat resistance, as these can influence the design and CNC machining process.
- Specify Tolerances Only When Necessary: Over-specifying tolerances can increase costs and production time. Use standard tolerances where possible and only specify tighter tolerances for critical features.
- Consider Tool Accessibility: Ensure that standard CNC tools can access all areas of your design. Complex internal features or undercuts may require specialized tools, which can increase costs.
- Simplify Your Design: Aim for simplicity in your design while maintaining functionality and aesthetics. Strive to eliminate undue complexity, which could make the CNC machining process more challenging and potentially inflate costs.
- Avoid Thin Walls and Fine Features: Thin walls and fine features can be difficult to machine and may lack durability. If your design requires such features, it’s essential to consider the limitations of your chosen material and the capabilities of the CNC machine.
- Avoid sharp internal corners: Radiusing internal corners strengthens the part and increases tool life.
- Optimize for Multi-Axis Machining: If you’re using a multi-axis CNC machine, design your part to take full advantage of the machine’s capabilities. This can help reduce the need for repositioning the part, saving time and reducing errors.
General Rules to Follow
Keep these rules of thumb in mind when completing your part design for CNC machining:
- Design your parts so that tools of the largest diameters possible can machine them.
- Add large fillets of at least a third the size of the cavity depth to interior vertical corners.
- Don’t design cavities that are more than four times deeper than their width.
- Make sure the features of the design align with one of the six principal directions. If this is not feasible, you can use five-axis CNC machining.
- If your design includes specifications for things like tolerances, threads and surface finish, include a technical drawing with your design.
CNC machine setups and parts orientation
One of the primary design constraints in CNC machining is tool access. The workpiece needs to be turned several times to access all surfaces of the model.
The machine must be recalibrated each time the workpiece is rotated, and a new coordinate system must be established.
Machine installations should be taken into account when planning for two reasons:
- The total number of machine sets influences the cost. The item must be manually rotated and realigned, which extends the machining process.
- Two features must be machined in the same arrangement for the relative positional precision to be at its highest. This is due to a slight inaccuracy introduced by the new calibration step.
CNC machining undercuts
Undercuts are features that cannot be machined using standard cutting tools, as some of their surfaces are not accessible directly from above.
There are two main types of undercuts: T-slots and dovetails. Undercuts can be one-sided or double-sided and are machined using special tools.
T-slot cutting tools are made of a horizontal cutting blade attached to a vertical shaft. The width of an undercut can vary between 3mm and 40mm. We recommend using standard sizes for the width (i.e. whole millimeter increments or standard inch fractions), as it is more likely that an appropriate tool is already available.
For dovetail cutting tools, the angle is the defining feature size. Both 45- and 60-degree dovetail tools are considered standard. Tools with an angle of 5-, 10- and up to 120-degree (at 10 degree increments) also exist but are less commonly used.
Drafting a technical drawing
Technical drawings are sometimes used by engineers to communicate specific manufacturing requirements to the machinist.
Here are some tips of drafting a technical drawing
- Orthographic views should be placed in the drawing’s center after determining which views are most crucial for your component.
- Add segment views or more in-depth views.
- All of the views should include building lines.
- Your drawing should have dimensions.
- List each thread’s position, dimensions, and length.
- Add additional tolerance information for any features requiring a higher level of accuracy than the default tolerances.
Conclusion
Small batch CNC machining can be an efficient and cost-effective option for manufacturing parts. However, it requires careful consideration of the design process to optimize the production process. Keeping it simple, optimizing tooling, selecting the right material, designing for manufacturability, and quality control are critical factors in designing parts for CNC machining. Following these tips will ensure that you get the most out of small batch CNC machining and improve your bottom line.
In conclusion, CNC machining provides small businesses and individuals with an affordable and efficient production process. By following the design tips outlined in this article, you can optimize your CNC machining process and produce high-quality parts with maximum efficiency and minimal cost.
FAQs
What types of materials can be machined in small batch CNC machining?
In small batch CNC machining, versatility reigns supreme. This process tackles a variety of materials:
- Metals: Durable alloys such as aluminum, steel, and titanium are known for their strength and wear resistance.Plastics: High-density types, like ABS and nylon, are admired for their lightweight, corrosion resistance, and insulation traits.
- Ceramics: Non-metallic, inorganic variants like alumina, preferred for their heat resistance and insulation capabilities.
- Composites: Enhanced strength materials like carbon fiber-reinforced plastics (CFRP), a mix of two or more distinct materials. This adaptability underscores the power and flexibility of small batch CNC machining.
What types of parts are suitable for small batch CNC?
Small complex parts requiring accuracy and repeatability are ideal. This includes components for machines, fixtures, prototypes, and consumer products. Simple shapes like brackets and mounts also work well.
what are the tips of cNC cost reduction?
CNC machining is widely employed across various industries for its precision, speed, and efficiency. However, it can be more costly when compared to other manufacturing methods such as 3D printing. This section outlines several design tips that can help reduce the overall cost of your CNC parts.
- Eliminate Deep Pockets: Deep pockets involve the removal of more material. Special tools may also be used to reach a specific depth. This translates to more machining time and higher costs. Therefore, limit the depth of pocket designs.
- Limit Tight Tolerances: The tighter the tolerance, the higher the cost. Specify tolerances only when necessary (such as for critical features); leave the rest of the model within a standard tolerance range.
- Choose Engraved Over Embossed: Engraved details often require less material removal than embossed and overall, less costs.
