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What Does CAD Machining Mean?
CAD (computer-aided design) machining involves using computer software to design various parts and components manufactured with CNC machines for various applications, including aerospace, electronics, and automotive. This approach helps visualize simple or complex parts from different angles, allows necessary modifications, and ensures the design meets customers’ specific requirements. CNC programmers use CAD software like CATIA, AutoCAD, Siemens NX, SolidWorks, and Autodesk Fusion 360 to meet design requirements.
Importance of Integrating CAD in CNC Machining
Incorporating CAD in CNC processes has transformed production runs because of its digital nature. In the absence of CAD, product designers would have to manually produce specifications, which could extend production time and increase the risk of errors.
With the advent of CNC technology, product designers rely heavily on CAD and CAM software to create intricate representations of products for prototyping and optimization. CAD machining streamlines the production timeline by optimizing product design, while CAM ensures the efficiency and accuracy of CNC machines in fabricating the workpiece according to design specifications.
Working Principles of CAD in CNC Machining
Even though every CNC machining operation begins with a prototype in CAD software, how does the digital design get on a CNC machine? Here are basic steps that explain how CAD works in CNC machining, even though the process slightly differs based on the machine.
Design Creation
You must make a 2D or 3D design using your preferred CAD software each time you plan to design for CNC machining. CAD programs feature standard tools for creating shapes and forms so you can design preferred models. These digital designs represent what the final part would look like after completing the machining process.
Exporting to CAM Software
You can import the finalized design to CAM software. However, some modern CAD/CAM software possess internal CAM (Computer-Aided Manufacturing) features; hence, exporting the file into another software would be unnecessary. CAM software can automatically change the design into a CNC program but may require particular tweaks. Then, prompt the CAM software to create a toolpath for the machining operation.
Tool Paths Simulation
The next step is running simulations to verify the toolpaths and assess if the machine instructions will work as intended. The cutting tool can remove material erroneously, or machine components can crash into each other machine when you fail to simulate the toolpath before the first run. Hence, you can optimize the paths with this opportunity and avoid wasting time and resources.
Uploading the Code
After verifying and confirming the paths and code, you can import the command code to the CNC machine. Modern CNC systems allow the operator to input the CNC programming language over a local network.
Standard Formats of CAD File
With various CAD model formats available in CNC machining, choosing the right fit for your project is essential to reduce errors and frustration. Here are the typical categories of CAD software files:
Neutral File Formats
These are the most universal file formats for CAD users since they are compatible with any software. Interoperability is a major advantage of neutral file formats, enabling flexibility when working with a client using different software. STEP, QIF, IGES, and STL are typical neutral file formats.
Although these file formats exhibit exceptional compatibility, some CAD software possesses unique and advanced features that prevent neutral files from storing all the critical data from this software in some cases. Hence, the geometry of the design may become inaccurate or have errors when you attempt to assess them in other software. As such, you might have to spend more time fixing the design for it to function again, even though the file fails to open at all in some cases.
Native File Formats
A native file is an exclusive format compatible with a specific CAD software. SOLIDWORKS, for instance, uses .sldasm and .sldprt file extensions, meaning these files contain necessary data and work best with the related software.
Some neutral formats cannot hold all the essential information from a specific software. Hence, they may fail to interpret the file appropriately, and you may end up with erroneous data and inaccurate measurements. Thus, it is advisable to use native file formats if you don’t need to use them in another software or transfer files to anyone.
Helpful Tips for Improving CAD Design for CNC Machining
CNC machining operations can cost more than other manufacturing processes, considering the initial capital investments, skilled labor requirements, volume, and significant energy required. Making a cost- and time-saving design requires careful consideration of several factors. Here are the best practices for improving CAD designs for CNC machining operations:
Utilize Appropriate Software
Use 3D modeling packages like Solid Edge, SolidWorks, NX, or Autodesk Inventor when designing CNC machined parts. These packages possess various features to streamline the CNC design procedure. Most also feature cloud-based computations and optional CNC machining add-ons that enable seamless transitions from CAD (Computer-Aided Design) to CNC without changing the file into a different file type.
AutoCAD is one of the standard 2D CAD packages suitable for creating designs for CNC machining. Besides, some CAM (computer-aided manufacturing) packages have limited 3D modeling capabilities that are best suited for simple designs.
Use Standard Material Sizes
An ideal practice is to keep an updated list of common raw material stock sizes for reference. Product designers should create CAD design models based on common stock sizes to reduce machining cost and durations. For example, assume you will design a shaft with an outer diameter of 33mm. While 33mm may be the ideal thickness for certain applications, it’s unsuitable for manufacturability since the closest typical size is 40mm. As such, you would have to cut 7 mm off the shaft to achieve the final dimensions.
However, it would be best to design the shaft with an outer diameter of 28 mm so that you can use and fabricate a standard 30 mm rod at a lower cost. Besides, the thinner shaft will meet your design requirements in most cases, and if not, a simple material grade change is advisable to maintain the required parameters.
Reduce the Amount of Fixturing Steps
Reducing the number of fixturing setups is another key consideration when making CAD designs for CNC machining. A fixturing setup holds the workpiece in place so the cutter can remove material or add relevant features. Sometimes, it may be difficult for the CNC tool to reach the necessary areas to add specific features.
For instance, the cutting tool cannot drill a hole with an axis parallel to the machine bed on a 3-axis CNC machine. As such, the partially machined part must be re-fixtured, resulting in additional fixtures and expenses. Therefore, it would be best to design parts requiring less repositioning whenever possible.
Employ Standard Tooling
Understanding the standard tooling available when adding features to a design is key to achieving optimal results. It becomes easier to program a part and reduce machining time when you design a part with features achievable with the standard tool sizes.
For instance, you should consider making holes with a diameter the same as the standard drill sizes or adding internal fillets with a radius equivalent to a standard ball nose mill. AT Machining experts recommend using standard threads since they typically need readily available, standard tooling.
Tool Reach
When CNC machining parts with deep pockets, the machining accuracy of a hole becomes more difficult to maintain as the hole gets deeper. Besides, the machine tools may not add certain features since the collet or chuck may collide with the workpiece. Although it may be difficult to identify these pitfalls during the design stage, it is generally advisable to avoid deep, narrow features when designing CNC parts unless necessary and maintain a depth-to-diameter ratio of less than 10:1.
Surface Finishes
Cosmetic surface finishing treatments may boost CNC parts’ functionality, aesthetic appeal, and longevity. However, they are sometimes unrequired since the part may be embedded inside a larger assembly. Applying finishing treatments on CNC parts may be time-consuming and costly. Therefore, it would help to design parts with 63 µin or 1.6 µm as the standard machining surface roughness for most applications.
Tolerances
Deciding when to add tolerance to a feature or not is crucial in making CAD models for CNC machining. Over-tolerancing a part can increase production costs significantly because machinists need to prepare machining operations more carefully to achieve tight tolerances. Consequently, it requires longer programming and machining time.
After machining, you must measure these features to confirm they are within specified tolerances. However, it may be difficult for machinists to meet all the requirements, and a higher crap rate is likely if you add tolerance to every feature. Tolerances are typically necessary when other machined parts must fit in an assembly or on features that need to meet with high-precision parts, including bearing grooves.
Avoid Deep Features
Deep features and sharp internal corners are typical features to avoid when designing for CNC machining. Deep features require longer machine tools to cut the bottom of the hole without damaging the chuck or collet. The side load on the tool increases as the depth increases because of a moment force that the cutting load produces.
Tools deflection or breakage can sometimes occur, causing poor surface finishes due to vibration/chatter. Besides, deep holes are easier to create than deep slots because hole cutting exerts an axial load on the tool.
Getting the CAD File Ready for CNC Machining
After the CAD design is ready, the next step is to prepare it for CNC machining. Usually, CNC operators need a neutral CAD format like a step (.stp). You can directly import native CNC file formats from typical CAD packages like Solidworks and Inventor in some situations. However, experts advise confirming the required file format with the customers. There are no special steps required to export a file for CNC machining. Moreover, there are three major step formats commonly used in CNC machining. These are:
- AP203: This is the commonly used CAD file format containing geometric and limited model data, including approval status and security classification.
- AP214: It possesses characteristics of AP203 with colors, annotations, tolerance data, and GD&T (Geometric Dimensioning and Tolerancing).
- AP242: This step format comprises PMI 9Product Manufacturing Information) and is used in cases where a model must retain MBD (Model-Based Definition) annotation and notes.
Although AP214 and AP 242 are ideal for CNC machining in most cases, experts recommend using AP242 only if MBD functionality is implemented. You may also add a technical drawing to the step file to confirm features, dimensions, and special requirements.
The operator can then import the CAD file into any CAM software package once the file is ready. Then, the CNC programmers translate the CAD file into G-code (machine-readable instructions) for the CNC machine to follow.
Choose AT-Machining for Reliable CNC Machining Service
Precision and accuracy are vital in achieving quality and manufacturable designs when designing parts for CNC machining. CAD machining provides flexibility and cost-saving solutions that help reduce manufacturing complexity and prevent costly errors and reworks that are time-consuming. These 2D or 3D designs ensure the finished product meets the tolerance demands and industry standards.
AT-Machining is a distinguished CNC company with modern manufacturing facilities in China. We boast exceptional customer service, fast turnaround times, and competitive pricing. We deliver quality and precise parts with complex organic shapes to clients in the military, electrical, automotive, medical, and aerospace industries. Our skilled machinists and operations manager have years of experience and training catering to the most complex requirements. Upload your CAD models for an instant quote for your CNC machining projects!
