13.2 Mechanical and manufacturing design
6 min read•august 13, 2024
Mechanical and manufacturing design in CAD is all about creating precise digital models of parts and assemblies. It's like building with virtual Lego, but way more detailed. You'll learn to make drawings that show every angle and dimension of a part.
This topic dives into the nitty-gritty of using CAD software for mechanical design. You'll discover how to create 3D models, apply tolerances, and even simulate how parts will behave under stress. It's the backbone of modern engineering design.
CAD for Mechanical Components
Creating Detailed Part and Assembly Drawings
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- CAD software (, , ) is used to create precise 2D and 3D digital models and drawings of mechanical parts and assemblies
- Part drawings depict individual components of a mechanical system
- Include dimensions, tolerances, materials, and manufacturing processes
- Assembly drawings show the arrangement and relationship of multiple parts in a mechanical system
- Include exploded views, bill of materials (BOM), and assembly instructions
- Detailed drawings include various views to fully represent the geometry and features of a part or assembly
- Orthographic views (front, top, side)
- Section views
- Detail views
- Isometric views
- Drawings should adhere to industry standards (ASME Y14.5, ISO 128) for line types, dimensioning, tolerancing, and annotation
Utilizing CAD Software Features
- CAD software provides tools for creating and editing geometry, applying dimensions and tolerances, and generating standard drawing views and layouts
- Parametric modeling techniques allow for the creation of flexible, editable models that can be easily modified and updated
- Models are defined by features, dimensions, and constraints
- Changes to parameters automatically update the model geometry
- CAD software enables the creation of design tables, configurations, and part families
- Efficiently generate multiple variations of a part or assembly based on different parameter values
- CAD models serve as the basis for downstream applications
- Detailed drawing creation
- (FEA)
- Manufacturing process planning
- Computer-aided manufacturing (CAM)
GD&T for Drawings
GD&T Principles and Symbols
- (Geometric Dimensioning and Tolerancing) is a system for specifying the geometric requirements of parts and assemblies
- Ensures proper fit, function, and interchangeability
- GD&T symbols are used to define allowable variations in size, form, orientation, and location of part features
- Datums: theoretically exact points, lines, or planes used as references for dimensioning and tolerancing
- : consist of geometric characteristics symbols, tolerance values, datum references, and
- Tolerance zones: define the allowable variation in size, form, orientation, or location of a feature
- Specified as bilateral (±) or unilateral (+ or -)
- Geometric characteristics include:
- Form (flatness, straightness, circularity, cylindricity)
- Orientation (perpendicularity, angularity, parallelism)
- Location (position, concentricity, symmetry)
- Runout (circular runout, total runout)
Applying GD&T to Mechanical Drawings
- are physical features on a part that are used to establish datums
- Example: a flat surface used as a primary datum for dimensioning and tolerancing other features
- Material condition modifiers ( MMC, LMC) are used to control the relationship between size and geometry tolerances
- MMC: the condition where a feature contains the maximum amount of material within its specified size tolerance
- LMC: the condition where a feature contains the minimum amount of material within its specified size tolerance
- GD&T principles are applied to ensure proper assembly, interchangeability, and functionality of mating parts in a mechanical system
- Example: specifying a position tolerance with MMC for a hole to ensure proper fit with a mating pin
- GD&T callouts are added to mechanical drawings using feature control frames and datum references
- Callouts specify the geometric characteristics, tolerance values, and datum references for each feature
- Proper application of GD&T reduces ambiguity in mechanical drawings and improves communication between design, manufacturing, and inspection teams
Parametric Modeling of Parts
Parametric Modeling Techniques
- 3D parametric modeling is a technique for creating digital models of mechanical parts and assemblies using CAD software (SolidWorks, Inventor, CATIA)
- Parametric models are defined by features, dimensions, and constraints that can be easily modified and updated
- Allows for flexible design iterations and variations
- Sketches are the foundation of parametric modeling
- Consist of 2D profiles and constraints that define the basic shape and geometry of a part
- Features are the building blocks of parametric models
- Created by applying operations (extrude, revolve, sweep, loft) to sketches
- Standard features (holes, fillets, chamfers) can also be added
- Dimensions and constraints control the size, position, and relationships of features in a parametric model
- Dimensional constraints specify the size of features
- Geometric constraints (parallel, perpendicular, tangent, concentric) define the relationships between features
Creating Assembly Models
- Part models can be combined into assembly models
- Define the spatial relationships and interactions between multiple parts
- Mating constraints (coincident, parallel, perpendicular, tangent, concentric) are used to position and align parts in an assembly
- Example: using a concentric mate to align a hole in one part with a shaft in another part
- Assembly models can include additional features and components
- Fasteners (bolts, nuts, screws)
- Bearings, gears, and other standard mechanical components
- Weldments and structural frames
- Assembly models enable the creation of exploded views, bill of materials (BOM), and assembly instructions
- Exploded views show the individual parts of an assembly separated and arranged in a logical sequence
- BOM lists all the parts, quantities, and materials required for an assembly
- Assembly instructions provide step-by-step guidance for putting the parts together
FEA Simulation in CAD
Finite Element Analysis (FEA) Basics
- Finite element analysis (FEA) is a numerical method for predicting the behavior of mechanical parts and assemblies under various loading and boundary conditions
- CAD software (SolidWorks Simulation, Autodesk Inventor Stress Analysis, ANSYS) provides integrated tools for performing FEA on 3D parametric models
- FEA involves discretizing a continuous model into smaller, simpler elements (mesh)
- Element types (beam, shell, solid) are selected based on the geometry and behavior of the model
- and quality affect the accuracy and convergence of FEA results
- Material properties (, Poisson's ratio, yield strength) must be assigned to the model to define its mechanical behavior
- Loads (forces, pressures, moments) are applied to the model to simulate the external conditions acting on the part or assembly
- Boundary conditions (fixed supports, symmetry constraints) are used to define the model's interaction with its environment
Analyzing and Interpreting FEA Results
- FEA solvers use numerical methods (finite element method FEM, boundary element method BEM) to compute the model's response to the applied loads and constraints
- Results of an FEA include:
- Displacement plots: show the deformation of the model under load
- Stress and strain distributions: indicate the intensity and location of stresses and strains in the model
- Factor of safety (FOS) contours: show the ratio of the material's strength to the applied stress
- Reaction forces: represent the forces and moments required to maintain equilibrium at the supports
- FEA results are used to evaluate the strength, stiffness, and durability of a mechanical design
- Identify areas of high stress or deformation
- Optimize the design by modifying geometry, materials, or loading conditions
- Validate the design against performance requirements and industry standards
- CAD-integrated simulation tools also allow for the analysis of dynamic behavior
- Modal analysis: determines the natural frequencies and mode shapes of a structure
- Transient response: simulates the time-dependent behavior of a model under varying loads
- Harmonic response: predicts the steady-state response of a model to sinusoidal loads
- FEA results are used to reduce the need for physical prototypes and testing, saving time and cost in the product development process
Key Terms to Review (27)
Additive manufacturing: Additive manufacturing is a process that builds three-dimensional objects layer by layer, typically using materials like plastics, metals, or ceramics. This innovative technology allows for rapid prototyping and the creation of complex geometries that would be difficult or impossible to achieve with traditional manufacturing methods. By utilizing computer-aided design (CAD) software, designs can be translated into physical objects with high precision and minimal waste.
ASME Standards: ASME Standards refer to a set of technical standards developed by the American Society of Mechanical Engineers (ASME) that provide guidelines for the design, manufacturing, and performance of mechanical systems and components. These standards ensure safety, reliability, and efficiency in mechanical and manufacturing design, making them essential for engineers and designers to follow.
Assembly Drawing: An assembly drawing is a detailed representation that shows how various components fit together to create a complete product or system. It typically includes information about assembly sequences, the relationship between parts, and any necessary constraints or mates that dictate how the components interact. This drawing serves as a crucial tool in both mechanical design and manufacturing processes, ensuring that parts are assembled correctly and function as intended.
AutoCAD: AutoCAD is a computer-aided design (CAD) software application used for creating 2D and 3D designs, drafting, modeling, and documentation. It serves a wide range of industries, allowing users to produce detailed drawings and plans with precision, while its capabilities extend to various features that enhance design efficiency and collaboration.
Bearing selection: Bearing selection is the process of choosing the appropriate bearing type and size for a specific application, ensuring optimal performance and longevity. This involves evaluating factors such as load capacity, speed, operating environment, and maintenance needs, which are critical in mechanical and manufacturing design to ensure efficiency and reliability in machinery.
CNC Machining: CNC machining refers to a computer-controlled manufacturing process that uses programmed software to automate the movement of machinery and tools. This technology enables high precision and efficiency in producing complex shapes and designs, making it a critical aspect of mechanical and manufacturing design. The use of CNC machining allows for repeatable production, reduced human error, and the ability to create intricate parts that would be challenging or impossible to achieve through manual processes.
Computational fluid dynamics: Computational fluid dynamics (CFD) is a branch of fluid mechanics that uses numerical analysis and algorithms to solve and analyze problems involving fluid flows. This technology allows for the simulation of fluid behavior in various systems, making it essential in mechanical and manufacturing design for optimizing performance, predicting behaviors, and reducing costs through better design processes.
Conceptual design: Conceptual design is the initial phase of the design process where ideas are generated and visualized to address specific problems or requirements. This stage focuses on the overall structure and functionality of a product, emphasizing creativity and innovation before any detailed specifications or technical drawings are developed. Conceptual design serves as a bridge between abstract ideas and tangible designs, paving the way for further development and refinement in mechanical and manufacturing contexts.
Concurrent engineering: Concurrent engineering is an approach to product development that emphasizes the parallelization of tasks and collaborative efforts among different teams. By integrating various functions such as design, engineering, manufacturing, and marketing from the onset, this method aims to reduce time-to-market and improve product quality. It encourages open communication and collaboration, leading to more innovative solutions and fewer errors in the design process.
Datum Features: Datum features are reference points or surfaces used in engineering and design to establish a consistent frame of reference for measurements and dimensions. They provide a standard against which the rest of the part or assembly can be defined, ensuring accuracy and consistency throughout the manufacturing process. These features are critical for maintaining tolerances and ensuring that parts fit together as intended during assembly.
Design for Manufacturability: Design for manufacturability (DFM) is a design approach that focuses on simplifying and optimizing products to make them easier and more cost-effective to manufacture. This concept emphasizes the collaboration between design engineers and manufacturing teams to ensure that the design aligns with the production processes, materials, and technologies available. By integrating DFM principles, designers can reduce production costs, minimize waste, and improve product quality, which is crucial in various applications including CAD systems, rapid prototyping methods, assembly processes, and mechanical engineering.
Design iteration: Design iteration is the process of repeatedly refining and improving a design based on feedback and testing results. This approach emphasizes incremental changes, allowing designers to explore various possibilities and address issues as they arise. By integrating user feedback and performance data, design iteration fosters innovation and enhances the overall quality of mechanical and manufacturing designs.
Detail drawing: A detail drawing is a specific type of technical illustration that provides a clear and comprehensive representation of a particular part or component of a larger system. It emphasizes critical features such as dimensions, materials, and finishes, ensuring that all relevant information is conveyed for accurate manufacturing and assembly. These drawings play a vital role in the design process, allowing engineers and manufacturers to visualize and construct intricate parts with precision.
Elastic Modulus: Elastic modulus is a measure of a material's ability to deform elastically (i.e., non-permanently) when a force is applied. It quantifies the relationship between stress (force per unit area) and strain (deformation) in a material, reflecting its stiffness. A higher elastic modulus indicates a stiffer material that deforms less under the same load, making it crucial in mechanical and manufacturing design for selecting appropriate materials that can withstand various forces without permanent deformation.
Feature Control Frames: Feature control frames are specific geometric tolerancing symbols used in technical drawings to define the permissible limits of variation for the size, form, orientation, and location of features on a part. They provide a standardized way to communicate the design intent and manufacturing requirements for parts, ensuring that components fit and function together correctly in mechanical and manufacturing designs.
Finite Element Analysis: Finite Element Analysis (FEA) is a numerical method used to predict how structures and materials will behave under various conditions, such as forces, heat, and vibrations. This technique breaks down complex objects into smaller, simpler parts called finite elements, allowing for detailed simulations of physical phenomena. It’s crucial in assessing the performance and safety of designs in engineering fields, particularly in mechanical and manufacturing design.
Fusion 360: Fusion 360 is a cloud-based 3D CAD, CAM, and CAE tool that allows users to create, collaborate, and manage product designs in a single platform. This software integrates various aspects of mechanical design, including simulation, rendering, and machining, making it an essential resource for engineers and designers in the mechanical and manufacturing fields.
GD&T: GD&T, or Geometric Dimensioning and Tolerancing, is a system for defining and communicating engineering tolerances using symbols on technical drawings. This method allows for precise specifications of a part's geometry, ensuring it can be manufactured and assembled correctly while meeting functional requirements. GD&T enhances clarity in communication among engineers, designers, and manufacturers, contributing to improved product quality and consistency in the design process.
Gear train: A gear train is a series of gears connected together to transmit power and motion from one part of a machine to another. Gear trains are essential in mechanical systems as they allow for the adjustment of speed and torque, making them vital in various applications like vehicles, machinery, and tools.
ISO 9001: ISO 9001 is an international standard that specifies requirements for a quality management system (QMS), ensuring organizations consistently provide products and services that meet customer and regulatory requirements. It focuses on continual improvement, customer satisfaction, and the involvement of top management, which makes it crucial for various processes such as design automation, technical documentation, product data management, and manufacturing design.
Least Material Condition: Least material condition (LMC) refers to a state of a part where it contains the least amount of material while still fulfilling the design specifications. This concept is important because it defines the minimum physical size for a feature, which is essential in ensuring proper assembly and function of mechanical parts. LMC also plays a key role in establishing tolerances, influencing how parts fit together in an assembly and aiding in quality control processes during manufacturing.
Material Condition Modifiers: Material condition modifiers are symbols used in technical drawings and specifications to describe the allowable variation of features based on the actual material condition of a part. These modifiers help in defining tolerances and fit requirements in mechanical and manufacturing design, ensuring that parts will function correctly together even when they are produced with slight variations. They play a crucial role in the communication of engineering requirements and contribute to the overall quality and interoperability of components in assemblies.
Maximum Material Condition: Maximum Material Condition (MMC) is a crucial concept in engineering and design that refers to the condition of a part when it contains the largest amount of material within its specified limits. This concept is key in determining how parts fit together and function, as it helps in defining tolerances that ensure parts can be assembled correctly and function as intended, especially in relation to their mating components.
Mesh density: Mesh density refers to the number of polygons or vertices per unit area in a mesh model, which directly affects the level of detail and accuracy in 3D representations. A higher mesh density means more polygons are used, allowing for finer details and smoother surfaces, while a lower density can result in blocky or less realistic models. This concept is crucial in both modeling and editing meshes, as well as in the design and manufacturing processes, where precise representations are necessary for functionality and aesthetics.
Preliminary design: Preliminary design refers to the early phase in the design process where initial concepts are developed and evaluated before finalizing the specifications. This stage is crucial as it lays the foundation for further detailed design work, allowing designers to explore ideas, make decisions about materials, dimensions, and functions, and assess feasibility before moving forward.
SolidWorks: SolidWorks is a computer-aided design (CAD) software program used for 3D modeling, simulation, and product data management. This software is widely utilized in engineering and product design to create detailed models and assemblies that help visualize how components will fit and work together in real-world applications.
Tolerance analysis: Tolerance analysis is the process of evaluating the effects of manufacturing tolerances on the overall performance and functionality of a mechanical assembly. This involves understanding how variations in part dimensions can impact fit, function, and assembly processes, ensuring that products meet required specifications while maintaining quality and minimizing costs. Tolerance analysis is crucial in mechanical and manufacturing design because it helps predict potential issues during production and guides designers in making informed decisions about tolerances to optimize designs.