Prototype machining is an efficient method of creating high-quality prototypes in small batches using CNC machines. Product designers and engineers often create prototypes with the intention of future production runs. The CNC machining process helps to create a physical and functional representation of the final parts. As such, prototype machining shows how a digital design would come out physically.
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Manufacturers can easily detect and eliminate design flaws with prototype machining before large-volume manufacturing begins. Moreover, production becomes more cost-effective when you eliminate design defects at the prototyping stage.
There are various reasons why CNC machining is the ideal prototyping process with the most reliable results. First of all, Computer Numerical Control (CNC) machines use high-end technology that allows them to deliver high accuracy and precision.
Thus, the computer program controls the cutting tools&#; and workpiece&#;s movement and interaction. These CNC machines consider each angle on your prototype design, ensuring they meet the final product specifications.
Moreover, the machining process offers adequate speed, unlike most traditional methods. For instance, manufacturers and product engineers must wait some time to prepare the tolerances and mold for injection molding prototypes.
CNC Turning & MillingCNC machining prototyping begins with drafting the final product&#;s 3D CAM model, which you must convert to a CAD file. The Computer-Aided Manufacturing (CAM) files consist of the G-Code and M-code. These codes guide the operation of the CNC machines when machining prototypes. However, these machines understand the CAD file directly since it contains machining commands.
Engineers in different industries use various types of CNC prototyping processes to achieve desired results. However, factors like the material used and design specifications determine the ideal machining operation for your model. Below are the common CNC prototyping operations:
The multi-axis machining is an efficient rapid prototyping operation suitable for producing prototypes with intricate specifications. This machined tooling uses more axes than traditional machining operations. It uses modern CNC machines with 4-axis, 5-axis, and as many as 9-axis to 12-axis.
Besides, the machining centers can deliver tighter tolerances depending on the number of axes involved. The higher the axes, the higher the machining capabilities.
The CNC milling process is a subtractive manufacturing process that uses milling machines with multipoint cutting tools to create prototypes. Each cutting point delivers sharp cuts, consistently removing material from a workpiece to make CNC machine prototypes of varying shapes and sizes.
However, the prototype complexity dictates the depth and type of cut that the cutting tool makes on the workpiece material. However, the CNC milling machine features additional axes that improve its cutting for high precision machining.
The CNC turning process uses a turning machine with a lathe tool to create prototypes that meet specifications. This machine tool is perfect for creating CNC machined prototypes and end-products with round or cylindrical properties. The workpiece material rotates close to the stationary lathe&#;s cutting tool in this operation.
The turning machine removes material from the rotating workpiece with a single-point cutting tool to produce cylindrical components. The CNC turning technique makes linear features on a prototype&#;s exterior. Likewise, it is suitable for creating threads, slots, and tapers on the internal edges.
This section discusses the benefits of CNC prototype machining, which may help you decide whether to make your prototypes using CNC machining processes. Below are these advantages:
Manufacturers often machine CNC prototypes in small or single batches to access the parts&#; visually and functionally. Small batch production is a fail-safe that prevents financial losses in manufacturing. As a result, any loss would be minimal if you detect any design flaws during these assessments rather than after mass production.
CNC machining offers the high precision, accuracy, and tight tolerances that your prototypes require. This manufacturing process uses computerized controls to determine the cutting tools&#; movement, ensuring high precision and accuracy. However, defects or errors in CNC machined prototypes are often traceable to the design since the machining process is precise and accurate.
Prototype machining is more compatible with extensive materials than other manufacturing methods like 3D printing. Although not all machining methods are compatible with sheet metal forming, CNC prototyping machining allows you to use various types of metals and even other materials like wood, plastics, or any other material.
Typical plastic materials suitable for CNC prototype machining include ABS, PS, POM, PCGF, LDPE, PAGF, PP, HDPE, PMMA, PC, and Teflon. On the other hand, common metals and metal alloys suitable for this process include aluminum, brass, bronze, copper, stainless steel, steel, magnesium, zinc, and titanium.
CNC prototype machining allows higher levels of repeatability. As a result, you can use the same design and process used to develop a specific finished product to create a replica of the product with exact specifications.
Moreover, CNC prototyping machines use cutting tools that deliver consistent cuts, offering replicas of the original design regardless of the amount produced. This procedure is unlike other prototyping strategies like injection molding, where the mold depreciates after several repetitions. These discrepancies result in unavoidable changes to the design of injection-molded prototypes.
Making CNC-machined prototypes saves time. You don&#;t have to consider factors like mold creation or other time-consuming conditions. More so, you can modify your designs easily by making changes to the CAM and CAD files and creating the prototypes again using the CNC machine.
There are various setbacks to prototyping with CNC machining, despite its enormous benefits as one of the best strategies for producing prototypes. These limitations include:
Before you can produce CNC machining prototypes, it would be best to have the technical know-how of designing CAD files and how to generate a CAM file from them. Installing and programming CNC machines require certain technical expertise.
More importantly, the knowledge of testing procedures, innovative approaches, creative vision, and experience is essential in CNC prototyping. In addition, it would help to know that not all CNC machining service providers can create CNC prototypes without prior training.
CNC prototype machining is a subtractive process that cuts material from a bar stock during prototyping or manufacturing. As a result, the material cost increases due to increased material usage during the prototyping operation.
Moreover, you will likely incur additional costs and waste more material since it is not certain that a prototype will be perfect on the first attempt. Likewise, even if the small batch of prototypes meets all technical requirements, there is little-to-no likelihood of selling them. Hence, they increase the amount of material wasted.
The inability of the CNC prototyping process to machine interior geometries is one of its major setbacks. CNC machines primarily work only on the exterior of a workpiece. As a result, developing prototypes with internal components may be challenging using CNC prototype machining.
However, you may choose alternative prototyping processes like 3D printing to make prototypes with internal components. 3D printing is ideal for manufacturing internal geometries of prototypes since it can work from the interior to the exterior area of a workpiece.
The CNC prototype machining costs more than SLS 3D printing process due to the incurred material costs. Besides, the cost of prototyping increases significantly sometimes because the focus is usually on the details instead of cost optimization. However, prototype machining makes up for its price with microscopic precision, high accuracy, and material versatility.
CNC prototype machining is a widely utilized prototyping method across all manufacturing industries. Here are some of the industries that use CNC machining prototypes:
The aerospace industry is one of the industries with high use for CNC prototype technology. Machinists in the aerospace sector use this process to develop functional prototypes with high levels of precision and accuracy.
Additionally, engineers use this prototyping technology to test the functionality of the machined components and other innovations within the aerospace industry. It helps to ensure the dependability of these parts, preventing malfunction when the aircraft is airborne. Typical components of aircraft made with the CNC prototyping technology are airfoils, bushings, manifolds, etc.
The medical sector has a high demand for parts and medical equipment with tight tolerances and precision. The medical industry benefits from CNC prototype machining as it is compatible with various CNC machining materials.
Besides, there are demands for medical components with the tightest tolerances, such as prosthetics, implant holders, surgical scissors, biopsy tubes, etc., following medical technology&#;s evolution. The CNC machines produce superior quality functional prototypes with excellent precision and accuracy for the medical industry.
Manufacturers use CNC machining extensively in the architectural and construction sector to create interior and exterior elements. Although injection molding is the common process used in the early days, it takes longer and incurs higher costs.
However, CNC prototype machining has made manufacturing functional prototypes for this sector much cheaper and faster.
This sector is one of the top industries with high use for CNC machining prototypes with tighter tolerances and high precision. Gears, wheels, brakes, and suspension components are typical examples of CNC parts machined with CNC prototype machining. Besides, these auto parts require the tightest tolerances to ensure vehicles&#; peak performance and safety.
The automotive industry develops prototypes and tests their functionality by fitting them in vehicles to ensure they meet the intended purposes. However, creating automotive prototypes that serve the intended purposes and specifications may be challenging without CNC prototype machining.
The oil sector has a high demand for parts with excellent strength capable of mining great depths in the earth&#;s surface to extract resources. Engineers often use CNC milling prototyping or other custom CNC machining processes to create these parts to meet the requirements.
Likewise, the energy industries use CNC prototypes to explore green energy resources that mitigate environmental impact.
The research and development department benefits from using the CNC prototype machining process in the military sector. Military R&D utilizes this fabrication technique in developing aircraft, warfare vehicles, and other CNC machined parts.
Engineers and product developers in this industry depend on prototype CNC machining since it allows rapid prototyping and part manufacturing irrespective of the material&#;s hardness.
Since manufacturers depend on CNC prototype machining to produce parts according to specifications and requirements, there are certain pivotal factors that you must consider for successful CNC prototyping. Here are some of them:
The extensive application of CAD in machining various parts has resulted in the development of several CAD software for custom prototypes across industries. However, some are good for specific applications, while others are too limited or unnecessarily complex. Therefore, choosing the perfect CAD application for your intended applications or industry is best.
Tighter tolerances cause significant increases in production costs since it often requires specialized cutting tools and extra fixtures. Therefore, using default tolerances is arguably the best machining practice. However, it would be best to seek professional assistance from the CNC services expert handling your parts design to determine the ideal tolerance level for your prototypes.
The complexity of your prototype is another critical factor to consider in CNC prototype machining. It would help to note that the CNC machining cost increases depending on the complexity of your prototype design.
Besides, setting up the machine for a model that requires various angles and undercuts takes longer, resulting in extended development time. Therefore, reducing your prototype complexity is advisable since the complexity hikes production costs and increases time to market.
Examine the cutting tools&#; axial properties during prototype CNC machining since the cutting process is rotary. Most cutting tools used in this process are round and have restricted cutting lengths. Thus, the tools&#; geometry influences the cutting operations.
Consider the minimum wall thickness for your prototype when drafting your design. This is because your CNC machined prototype or part may exhibit poor mechanical stability and fail due to thin wall thickness.
However, maintain a minimum wall thickness of 0.8mm in your metal parts as a general rule of thumb. On the other hand, the ideal wall thickness for plastic components should be more than 1.5mm.
Partnering with a seasoned CNC machining expert is essential to the success of your CNC prototyping project. Manufacturing specialists focus on making the machining processes more efficient to produce superior-quality prototypes.
Your manufacturing specialist considers the geometric restrictions of the machining method required to create the preferred prototype design. However, it would be challenging to benefit from the vast benefits of machining prototypes with CNC machines without the assistance of a seasoned prototype manufacturer.
Prototypes contribute significantly to the manufacturing process in different industries. CNC machining prototype for your project helps to prevent long-term issues while saving costs. CNC machining is perfect for producing parts in the prototyping stages. It is fast and offers precise prototypes.
Meanwhile, this guide has discussed everything you need to know about CNC prototype machining. Therefore, you can produce high-quality prototypes for your products. However, if you need quality prototypes that meet the intended purpose without spending too much, AT Machining is your best partner!
AT Machining is your one-stop machine shop for reliable CNC machining services and production runs. We rely on our advanced CNC technology and good years of CNC prototyping expertise as we bring your CAD models to life.
Our team of engineering specialists has adequate industry machining experience that enables us to create high-quality prototypes that meet stringent quality standards for various industries. We offer competitive pricing as we provide finished products with the highest quality. Kindly upload your CAD files on our platform today; we offer reliable DfM and quotations.
CNC prototype machining is the best choice when material versatility, fast production, or precision are primary factors in producing your prototypes.
The choice of material, tolerances, and design complexity of your prototype are various factors that can affect your CNC machined prototype cost. Additionally, CNC machines and surface finishing options are other factors that may affect the cost of your project.
The injection molding process is more expensive for making prototypes, even though you can divide the mold cost over a large volume. However, prototypes are produced in small batches, rendering injection molding unsuitable for prototyping. Therefore, CNC prototype machining is cost-effective because it makes recyclable waste material.
There are a few easy steps you can take to optimize your designs for computer numerical control (CNC) machining. By following design-for-manufacturing (DFM) rules, you can get more out of CNC machining's broad capabilities. This can be challenging though, as industry-wide specific standards do not exist.
In this article, we offer a comprehensive guide to the best design practices for CNC machining. To compile this extensive up-to-date information, we asked for feedback from industry experts and CNC machining service providers. If you are optimizing for costs, check out this guide to designing cost-effective parts for CNC.
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CNC machining is a subtractive manufacturing technology. In CNC, material is removed from a solid block using a variety of cutting tools that rotate at high speed&#;thousands of RPM&#;to produce a part based on a CAD model. Both metals and plastics can be CNC machined.
CNC-machined parts have high dimensional accuracy and tight tolerances. CNC is suitable for both high-volume production and one-off jobs. In fact, CNC machining is currently the most cost-effective way of producing metal prototypes, even compared to 3D printing.
Read our introduction to the basic principle of CNC machining.
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.
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.
To remove material, the cutting tool approaches the workpiece directly from above. Features that cannot be accessed in this way cannot be CNC machined.
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There is an exception to this rule: undercuts. There&#;s a section on undercuts towards the end of this article.
We recommend 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.
A challenge that frequently comes up while designing a part for CNC machining is that no industry-wide specific standards exist. CNC machine and tool manufacturers continuously improve the technology&#;s capabilities, expanding the limits of what is possible. The table below summarizes recommended and feasible values for the most common features encountered in CNC machined parts.
Recommended cavity depth: 4 times cavity width
End mill tools have a limited cutting length (typically 3&#;4 times their diameter). Tool deflection, chip evacuation and vibrations become more prominent when cavities have a smaller depth-to-width ratio.
Limiting the depth of the cavity to four times its width ensures good results.
If larger depths are required, consider designing parts with a variable cavity depth.
Deep cavity milling: Cavities with depths greater than six times the tool diameter are considered deep. A tool diameter-to-cavity depth ratio of up to 30:1 is possible using specialized tooling (maximum depth: 35 cm with a 1-inch diameter end mill tool).
Vertical corner radius
Recommended: &#; times cavity depth (or larger)
Using the recommended value for internal corner radii ensures that a suitable diameter tool can be used and aligns with guidelines for the recommended cavity depth.
Increasing the corner radii slightly above the recommended value (e.g. by 1 mm), allows the tool to cut following a circular path instead of a 90 angle. This is preferred as it results in a higher quality surface finish. If sharp 90-degree internal corners are required, consider adding a T-bone undercut instead of reducing the corner radius.
Floor radius
Recommended: 0.5 mm, 1 mm or no radius
Feasible: any radius
End mill tools have a flat or slightly rounded lower cutting edge. Other floor radii can be machined using ball end tools. It is good design practice to use the recommended values, as it is preferred by the machinists.
Minimum wall thickness
Recommended: 0.8 mm (metals), 1.5 mm (plastics)
Feasible: 0.5 mm (metals), 1.0 mm (plastics)
Decreasing the wall thickness reduces the stiffness of the material, which increases vibrations during machining and lowers the achievable accuracy. Plastics are prone to warping (due to residual stresses) and softening (due to temperature increase), so a larger minimum wall thickness is recommended. The feasible values stated above should be examined on a case-by-case basis.
Diameter
Recommended: standard drill bit
Feasible: any diameter larger than 1 mm
Holes are machined using either a drill bit or an end mill tool. The size of the drill bits is standardized (in metric and imperial units). Reamers and boring tools are used to finish holes that require tight tolerances. For high-accuracy holes with a diameter smaller than 20 mm, using a standard diameter is recommended.
Maximum depth
Recommended: 4 times nominal diameter
Typical: 10 times nominal diameter
Feasible: 40 times nominal diameter
Holes with a non-standard diameter must be machined with an end mill tool. In this case, the maximum cavity depth restrictions apply and the recommended maximum depth value should be used. Holes deeper than the typical value are machined using specialized drill bits (with a minimum diameter of 3mm). Blind holes machined with a drill have a conical floor (135-degree angle), while holes machined with an end mill tool are flat.
There is no particular preference between through holes or blind holes in CNC machining.
Thread size
Minimum: M1 (and lower, in some cases)
Recommended: M6 or larger
Threads are cut with taps and external threads with dies. Taps and dies can be used to cut threads down to M2. CNC threading tools are common and are preferred by machinists, as they limit the risk of tap breakage. CNC threading tools can be used to cut threads down to M6.
Thread length
Minimum: 1.5 times nominal diameter
Recommended: 3 times nominal diameter
The majority of the load applied to a thread is taken by the few first teeth (up to 1.5 times the nominal diameter). Threads longer than 3 times the nominal diameter are thus unnecessary.
For threads in blind holes cut with taps (i.e. all threads smaller than M6), add an unthreaded length equal to 1.5 times the nominal diameter at the bottom of the hole. When a CNC threading tool can be used (i.e. threads larger than M6), the hole can be threaded throughout its length.
Minimum hole diameter
Recommended: 2.5 mm (0.1 inches.'')
Feasible: 0.05 mm (0.005 inches.'')
Most machine shops can accurately machine cavities and holes using tools down to 2.5 mm (0.1 inches) in diameter. Anything below this limit is considered micro-machining. Specialty tools (micro-drills) and expert knowledge are required to machine such features because the physics of the cutting process change with this scale. Unless absolutely necessary, the recommendation is therefore to avoid them.
Typical: +-0.1 mm
Feasible: +-0.02 mm
Our tolerances are either medium or fine. If tolerances are not specified, manufacturing partners will use the selected grade.
Tolerances define the boundaries for an acceptable dimension. The achievable tolerances vary according to the base dimension and the geometry of the part. The values above are reasonable guidelines.
Recommended: font size 20 (or larger), 5 mm engraved
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.
Tool access is one of the main design limitations in CNC machining. To reach all surfaces of the model, the workpiece has to be rotated multiple times.
Whenever the workpiece is rotated, the machine has to be recalibrated and a new coordinate system has to be defined.
While designing, it is important to consider machine setups for two reasons:
The total number of machine setups affects the cost. Rotating and realigning the part requires manual work and increases total machining time. This is often acceptable if the part needs to be rotated up to three or four times, but anything above this limit is excessive.
To achieve maximum relative positional accuracy, two features must be machined in the same setup. This is because the new calibration step introduces a small (but non-negligible) error.
A 5-axis CNC machine moves cutting tools or parts along five axes at the same time. Multi-axis CNC machines can manufacture parts with complex geometries, as they offer two additional rotational axes. These machines eliminate the need for multiple machine setups.
Five-axis CNC machining allows the tool to remain constantly tangential to the cutting surface. The tool paths can be more intricate and efficient, resulting in parts with better surface finish and lower machining times.
That said, 5-axis CNC has its limitations. Basic tool geometry and tool access limitations still apply (for example, parts with internal geometries cannot be machined). Moreover, the cost of using such systems is higher.
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.
A T-slot (left), a dovetail undercut (middle), and a one-sided undercut on an internal wall (right).When designing parts with undercuts on internal walls, remember to add enough clearance for the tool. A good rule of thumb is to add space equal to at least four times the depth of the undercut between the machined wall and any other internal wall.
For standard tools, the typical ratio between the cutting diameter and the diameter of the shaft is 2:1, thereby limiting the cutting depth. When a non-standard undercut is required, it is common practice for machine shops to manufacture their own custom undercut tools. This can add to lead time and cost, so avoid it if possible.
Technical drawings are sometimes used by engineers to communicate specific manufacturing requirements to the machinist. If you are interested in the topic, read this article about how, when and why to use technical drawings.
We don&#;t usually require a technical drawing for orders on our platform, but in some cases, they can add valuable context to a quote request. Certain design specifications cannot be included in a STEP or IGES file. For example, you&#;ll have to include a 2D technical drawing if your model includes threaded holes or shafts and/or dimensions with tolerances tighter than the selected grade.
If you add a technical drawing, please make sure it matches the specifications of the files uploaded. If the technical drawings do not match the files uploaded or the quote specifications:
The quote specifications are considered the point of reference for the technology, material and surface finishes.
The technical drawings are considered the point of reference for the thread specifications, tolerance specifications, surface finish details, part marking requests and heat treatment specifications.
The CAD file is considered the point of reference for the part design, geometry, dimension and feature locations.
For further details, read our specifications policy.
Design parts that can be machined using the tool with the largest possible diameter.
Add the large fillets (at least &#; times the cavity depth) to all internal vertical corners.
Limit the depth of cavities to 4 times their width.
Align the main features of your design with one of the six principal directions. If that is not possible, 5-axis CNC machining is an option.
Submit a technical drawing with your drawing if your design includes threads, tolerances, surface finish specifications or other notes for the machine operator.
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