CAD File Formats for CNC Machining
CNC (Computer Numerical Control) machines have been a game changer in the manufacturing realm. They are a beacon of efficiency and accuracy, allowing manufacturers to achieve precision and speed that would be otherwise impossible using manual machining methods. CNC machining has proven vital in various manufacturing processes including prototyping and product development.
An IGES file, which has the .igs file extension, is used to save vector image data for transferring 2D and 3D information between various CAD applications.
We cannot talk about CNC machining without mentioning CNC files — the digital blueprints that CNC machines utilize when cutting parts. This comprehensive article discusses the different CAD file formats used in CNC machining operations as well as their pros and cons. I will also guide you through the process of converting CAD files.
What Is CNC Machining?
CNC machining is a precision manufacturing process that uses computer-generated instructions and machine tools to remove material from a workpiece creating the desired shapes. Modern CNC machines are fully automated. They rely on digital files that contain specific instructions that guide the movements of the physical machine. For example, these instructions control the movement of the cutting tool and workpiece, spindle speed, RPMs, and more.
The general CNC machining process can be broken down into four steps.
Step 1: Designing a 3D CAD model
The first step in the CNC machining process involves designing the part using Computer-Aided Design (CAD) software to create geometric models. The 3D CAD model represents the dimensions and characteristics of the physical object.
Step 2: Conversion of CAD to a CNC-readable format
Next, the CAD design is fed into Computer-Aided Manufacturing (CAM) software. The software prepares the CAD model for manufacturing by converting the digital design into codes that can be understood by CNC machines. This conversion process involves creating a mathematical representation of the design. Often, an STP file is used in this process due to its ability to transfer 3D modeling data efficiently. The STP file format is essential for interoperability within CAD and CAM environments, and it can be opened using various software such as AutoCAD, SolidWorks, and Fusion 360. These codes — G-code and M-code — are saved to the machine. They contain machine-readable instructions that are used during part production.
Step 3: CNC machine preparation
In this step, the operator prepares the CNC machine for its upcoming task. This involves cleaning and maintenance, securing the workpiece, choosing and attaching the right tooling, loading the CNC codes into the computer numerical controller, and ensuring that all CNC machining accessories are functioning optimally.
Step 4: CNC production
Once everything is set up, the actual machining operation can begin. The G-code guides the CNC machine’s motion and function, such as moving the spindle or cutting at a particular speed. The M-code commands non-cutting actions such as turning on the coolant and starting or stopping a program. The CNC machine will execute a series of actions to produce the final desired part.
What is the most common CNC software?
CNC machines rely on software for optimal function. There are different types of CNC software, with CAD and CAM being the most common.
Computer-Aided Design (CAD) software: Designers and engineers use CAD software to create 2D and 3D designs. It serves as a replacement for manual drafting, increasing the speed and precision of the process. The output of CAD software is engineering drawings and solid models. CAD programs use different entity types, such as line font pattern entity, to simplify feature type specification.
Computer-Aided Manufacturing (CAM) software: CAM software analyzes CAD designs and converts them into CNC code. Further, it communicates this code to a CNC machine that fabricates the physical part using the instructions in the code.
CAD/ CAM software: As the name suggests, this software package integrates CAM and CAD. Therefore, it is used to create geometric models of products and to generate machine-understandable instructions that guide CNC machining operations.
There are many CNC software options on the market, and picking the right fit can be overwhelming. If you’re looking for a starting point, here are some examples of the best software for CNC applications.
AutoCAD – It is a powerful CAD program developed by Autodesk.
PTC Creo (Formerly known as Pro/ENGINEER) – This is an integrated CAD/ CAM software developed by PTC.
NX (Formerly known as Unigraphics) – Like Creo, NX has CAD/ CAM capabilities. It is owned by Siemens Digital Industries Software.
SolidWorks – This is a CAD software from Dassault Systèmes
What are Native and Neutral CAD Files?
As we’ve mentioned, part production begins with a CAD file. CAD files are usually stored in one of two formats — native CAD or neutral CAD. Let’s take a closer look at each of these CAD file formats.
Native CAD formats
Native file formats are specially designed and optimized for a specific CAD system. They are only usable on the specific software used to create them. For example, AutoCAD is a native file format. Therefore, it is challenging to open this file type using Creo or other CAD software. CATIA, Solidworks, and NX are also native file types. The main advantage of native files is that they contain a more detailed representation of 3D CAD models.
Neutral CAD formats
Unlike native files, neutral file formats offer compatibility with different CAD software. In other words, these file types can be read by many CAD systems. This is especially beneficial when you need to transfer 3D data from one program/ to another. Neutral CAD formats are generally less detailed than native files.
Types Of CNC Machining Files
CNC machines follow precise instructions during manufacturing, and the files provided to them need to accurately communicate these directions. It is critical that product engineers use file formats that match the machine’s capabilities and requirements. Using the wrong file type may lead to errors and defective products.
A transformation matrix entity is crucial in defining geometric shapes, specifically circular arcs and conic arcs, and plays a significant role in the mathematical representation of these curves.
Let’s discuss the different file types used with CNC machines.
STEP Format
STEP format, or STP format, is an abbreviation for Standard for the Exchange of Product Data. STEP files are a neutral CAD format, and are widely regarded as the best and most common file type for sharing 3D models.
Most CAD programs are compatible with STEP format. Therefore, it’s always recommended that you include this file format when sharing 3D models with a third party. The standard gets frequent updates, with the most recent one being in 2016. There are three main variations of STEP files — AP203, AP214, and AP242.
AP203 – AP203 is an older STEP standard that is still commonly used to date. It supports a range of features including basic geometries, topology, and assemblies. However, AP203 does not define advanced features such as color and layers. Therefore, if you want to convey these details with your 3D model you can opt for AP214 or AP242.
AP214 – This format supports all the features in AP203. It also has advanced capabilities including layers, color information, and GD&T (Geometric Dimensioning and Tolerance). AP214 was primarily developed for the aerospace and automotive industries.
AP242 – AP242 is the latest variation of the STEP standard and it merges AP203 and AP214. In addition to the features found in the previous versions, this format also supports kinematic information, mechatronics, and access & digital rights management (DRM). AP242 is also an MBD-ready format.
Type: Neutral
Geometry representation: B-rep
Standard: ISO 10303
Creation year: 1980s
Creator: ISO
Pros:
Compatibility: The STEP format is compatible with various CAD/ CAM programs. This minimizes the need for multiple file conversions reducing the likelihood of errors and saving time.
Precision: The STEP standard is highly reliable since it accurately conveys the dimensions and features of the design.
Efficiency: You can use STEP files to share 3D models across different platforms quickly. This can facilitate workflow optimization and reduce lead times.
Cons:
File size: STEP files tend to be large, especially for complex product models with extensive entity data. This can affect storage and the duration needed to transfer files.
Incompatibility: This format is generally compatible with a wide range of software. However, errors may occur due to discrepancies in how different CAD systems translate STEP files.
IGES Format
Extensions: .igs, .iges
Type: Neutral
Geometry representation: B-rep, meshes
Standard: ANSI
Creation year: 1980s
Creator: U.S. National Bureau of Standards
IGES is an abbreviation for Initial graphics exchange specification, a standard that stores information in the ASCII format, including encoded curves. This file format was developed in the 1980s and hasn’t been updated since 1996. Although IGES is an older standard, many people still use it today. It supports different types of CAD data including wireframe designs, circuit diagrams, free-form surfaces, and solid models.
Pros
Software compatibility: IGES files are neutral and can be opened across multiple CAD and CAM applications.
Accuracy: The IGES file format processes product designs as encoded curves and surfaces. This results in manufactured products that are very similar to their digital designs.
Cons:
Older format: IGES was last updated in 1996. This means this file type is not as up-to-date as other, newer formats.
File conversion: Due to its ASCII format, converting IGES files to another file type and back again typically leads to a decline in quality.
STL Format
Extensions: .stl
Type: Neutral
Geometry representation: meshes
Creation year: 1987
Creator: Albert Consulting Group for 3D Systems
STL is an abbreviation for stereolithography. It is also referred to as Standard Tessellation Language. This file format is mainly used for 3D printing and CAD. One of the unique features of STL is how it stores entities’ data. It utilizes a series of interlocking triangles to define the surface of a 3D model. These tiny triangles combine to form the final design. The number of triangles tends to increase with the complexity of the design.
Pros:
Compatibility: STL files are generally regarded as the standard format for 3D printing. Therefore, virtually all 3D modeling applications are compatible with this file type.
File size: STL files tend to be smaller than other formats due to their simplicity. This makes them very easy to publish and share.
Cons
Texture and color data: One of the main limitations of STL is that it does not contain texture and color data.
Metadata: It does not store metadata, including location, authorship, and copyright.
DXF Format
Extensions: .dxf
Type: Native and Neutral
Geometry representation: meshes
Creation year: 1982
Creator: Autodesk
Drawing Exchange Format (DXF) files are a type of open-source, vector file. They are typically used when sharing digital designs across different CAD applications. DXF files support a wide range of features including layers, colors, line types, and other visual attributes
Pros:
Compatibility: DXF has exceptional compatibility. Users can view and edit this file type using a range of CAD and CNC software.
Open format: DXF files are built to support extensive third-party access. Hence, they are popular with developers creating CAD programs.
Cons:
File size: Complex DXF drawings tend to have large file sizes which may impact storage and transfers.
Limited support for 3D elements: DXF allows you to work with 3D elements though it does not fully support them. This standard fully supports 2D elements only.
DWG Format
Extensions: .dwg
Type: native
Geometry representation: meshes
Creation year: 1982
Creator: Autodesk
DWG stands for drawing, and this format is closely linked to CAD programs. It is written with a binary makeup and is primarily used for designing and storing 2D and 3D data. DWG is a proprietary CAD format that supports a variety of parameter data including surfaces, meshes, and surfaces.
Pros:
Compact file size: DWG files have a binary makeup which helps keep file size to a minimum. This compactness is highly beneficial for storage and transfer purposes.
2D and 3D capabilities: DWG format can map both 2D and 3D images. This facilitates the smooth integration of 2D and 3D geometry at different stages of design.
Cons
Limited to CAD software: You can open DWGs using CAD software. Therefore, collaboration without CAD tools can be challenging.
Subject to versioning: DWG has evolved over time leading to several versions of this format. Older software may not be compatible with new features built into later versions of DWG causing access challenges.
How to convert CAD files?
At some point, you may need to convert CAD files into different formats. Fortunately, there are a host of online tools that you can use for this purpose. Some conversion software is free while others are paid. For example, OnShape Personal is a free file conversion tool making it ideal for individuals and hobbyists.
If you’re part of a large company, it’s likely that your CAD package allows you to import and export to a range of CAD formats. You can verify the supported file formats by checking the CAD package documentation.
Author
Gavin Leo is a technical writer at Aria with 8 years of experience in Engineering, He proficient in machining characteristics and surface finish process of various materials. and participated in the development of more than 100complex injection molding and CNC machining projects. He is passionate about sharing his knowledge and experience.