Mechanical Design: Process, Principles, Tools & Applications

Mechanical design concerns an array of products, machines, tools, and industrial equipment used in day-to-day human life. Regardless of being cars, engines, industrial robots, pumps and machines or industrial equipment, every product requires profound engineering expertise to design it correctly.

At the most basic level, it is defined as the skill or knowledge needed for the production of mechanically functional parts, products, and systems, as well as devices and installations made up of them. However, the work goes far beyond a few calculations and engineering a functional and visually pleasing product. Engineers should thoroughly consider loads, materials, manufacturing methods, tolerances, assemblies, costs, as well as the environment the product will be exposed to.

McGill University defines mechanical design as “a process of designing mechanically functional components, products, and systems by recognizing that engineering design is iterative and often requires multiple design cycles”.

Meanwhile, modern design widely makes use, among other tools, of computer-aided design and manufacturing, where product development is driven by simulation, CAD detailing and documentation, prototyping, and manufacturing tests. ISO defines a CAD model as design structure data concerning the representation of some object.

This article will discuss the basis, guidelines, tools, and practices that make a mechanical product fully functional and production-ready.

Table of Contents

1. What Is Mechanical Design?

2. Why Mechanical Design Matters

3. The Fundamental Principles of Mechanical Design

4. The Mechanical Design Process

5. CAD and 3D Modeling

6. Engineering Calculations and Simulation

7. Materials Selection

8. Design for Manufacturing and Assembly

9. Tolerances and GD&T

10. Prototyping and Testing

11. Safety and Reliability

12. Common Applications

13. Essential Software and Tools

14. Common Mechanical Design Challenges

15. Skills Required for Mechanical Designers

16. How to Improve the Design Process

17. Frequently Asked Questions

18. Conclusion

19. Key Takeaway

What Is Mechanical Design?

Mechanical design, at its core, is the engineering skill of designing components, machines, mechanisms, or mechanical products that will fulfill specific functions and needs.

Essentially, it aims to apply engineering to the creation of products and devices by considering their theoretical and practical aspects in manufacturing. One designer can imagine and work on how a certain mechanism will sustain certain forces, how it will be assembled, which materials to choose, and how these parts will affect the product’s functionality and service life.

It also goes by the name of machine design. The term engineering design defines the process of designing mechanical components, parts, products, and/or systems, according to Dassault Systèmes, a software development company.

One project generally involves steps from concept definition, requirement definition, 3D CAD modeling, production and material definition, engineering analysis and calculations, simulation, tolerance analysis, cost estimation, production and tooling documentation, prototype development, test specification, and test validation. In the end, it not only produces a beautiful-looking model but also a functional and valid product that fulfills all production and cost requirements.

Why Mechanical Design Matters

The essence of good design lies in creating and bringing new ideas to life in the form of a functional product.

Take, for instance, a simple shaft: A designer cannot decide its diameter and dimensions by its intended location and use alone. It also concerns its anticipated torsion, bending, fatigue – its environment and the forces applied to it, which materials will suit its manufacturing, finishing, its keyways, tolerance, fabrication method and how it will fit and work with other parts, and its maintenance and service. The same reasoning applies to more complex machine elements.

A great idea, therefore, does not always mean a working product. Not considering every aspect leads to a product that cannot be assembled or does not fulfill certain needs. For instance, a chosen material for a given part may be weaker than required, or a certain dimension may not be taken into consideration during assembly. This can result not only in extra costs during production but also in the product failing due to fatigue.

Other considerations can also define why the functional and reliable product is not achieved – e.g.:

• A part may need to be changed as it cannot be manufactured using a given method or requires specific and scarce resources and components.

• A designed system needs rework due to an incorrect assumption.

That is why, when looking at the broader picture, engineering design should also consider a product’s full life cycle, rather than only its geometrical features.

Another point to highlight is that nowadays, the engineering design process involves multiple disciplines. According to Autodesk, “machine design activities can cut across multiple functions including mechanical, electrical and electronics, industrial design, manufacturing, procurement, servicing, and project management”.

The Fundamental Principles of Mechanical Design

The process of successful design is built around a set of several key principles and steps. Among them are:

Function

The main principle dictates that every part and product is created with a defined use and function in mind. Simply put, a designer works with an idea of how this mechanism will serve a particular need or purpose.

Strength

A product should be created with required strength parameters in mind. It means that a designer should know what forces the mechanism will resist and how it will do that.

Stiffness

Not only strength, but also stiffness, is essential in designing. A certain structure and material might withstand stresses and forces efficiently but will experience major losses due to deflections.

Reliability

The functional product should also be reliable, with the designer considering factors such as stress, vibration, and others.

Manufacturability

It is crucial that a designer’s idea is not only good on paper but can also be manufactured using available tools and methods. The designer’s experience and knowledge play an essential role here, with different materials, methods, and technologies having different capabilities.

Cost

Cost is a significant factor, and designers will have to consider manufacturing costs, materials, assemblies, transport, maintenance, tooling, and others.

Generally speaking, the design and manufacturing process aims to achieve not only the lowest cost but overall the most beneficial and profitable approach.

The Mechanical Design Process

Designing mechanical components or products is an iterative process that requires returning to prior steps and constantly updating and refining them. The first step is to understand and define requirements and expectations.

Generally, it should define what the created product should actually do, how and with which elements and materials, what its size and service life should be, and under what conditions it will operate, among other criteria. It will also define certain limitations, such as manufacturing ones. All of these aspects are interconnected, and a wrong or miscalculated assumption at the beginning of the process might result in failures and extra costs later.

Step 1 – Defining the Requirement

A designer defines a problem statement that will serve as a reference for further steps.

Requirements ideally include:

• Specific functions or delivered power

• Required or anticipated performance

• Operating conditions for the product

• Size and spatial limitations

• Dimensions or anticipated loads

• Material limitations

• Safety and manufacturing requirements

• Costs and other considerations

• Standards

A wrong definition, however, makes for wrong further steps – even if a designer thinks that a created CAD model fits all criteria, it will still prove impossible for manufacturing or will fail to deliver certain results.

Step 2 – Concept Development

A designer now explores and imagines the solution and potential variations. They may build some concept sketches, diagrams, basic calculations, or a CAD model, which allows them to imagine a bigger picture before moving to more demanding steps. Here, it is also worth considering options and comparing them to one another before proceeding.

Step 3 – Performing Preliminary Calculations

Next, designers estimate some parameters of the mechanism or product to get a general idea of how the product will perform and what requirements it needs to meet. A designer will calculate size, strength, and stresses – e.g., bending or torsion. They will generally make it as basic as possible, just to get a ballpark idea of how things will work.

Step 4 – Creating a CAD Model

A designer will now build and develop a chosen concept into a working product model, which is now done using computers.

A product or mechanism will generally require several models: parts, assemblies, subassemblies, and components – with every higher class generally containing lower ones. The same applies to materials and elements. ISO defines a three-dimensional (3D) technical product data structure as “the data structure representing physical objects by means of structured design data that may also contain graphical and associated non-graphical information”.

Step 5 – Analysis and Simulation

By applying analytical calculation methods and computer-aided engineering (CAE), an engineer will evaluate the performance of a mechanism.

Depending on the required results, designers can go as far as fatigue analysis, motion or stress, bending, contact or vibration analysis, and others that support a thorough insight into a mechanism.

The process helps reduce the number of physical prototypes – albeit only if the calculations and simulation assumptions and methods are correct and valid. ASME, for instance, notes the existence of a “CAD-CAE process loop”, where an engineer constantly updates a model and runs new simulations.

Step 6 – Prototype Development and Testing

A designer can now take a model and transform it into a prototype to see how it really works – e.g., to examine its strength, vibration levels, fit, temperature performance, noise, and more.

Step 7 – Documentation for Manufacturing

The final stage prepares all documents and specifications needed for the manufacturing process. This ranges from materials, parts, and elements to their dimensions and tolerances. ASME’s set of standards Y14 specifies a range of engineering drawings and other forms of documentation, such as annotations, tolerancing, digital product definitions, and others that support the process.

CAD and 3D Modeling

Among modern design tools, computer-aided design plays an especially important role.

In it, a designer creates accurate 2D drawings and 3D models and makes modifications and updates to the design model, drawings, and other documents. Its common uses include:

• Parametric design

• Part design

• Assembly design

• Sheet metal design

• Surface design

• Drawing creation

• Exploded views in assemblies

• Configurations

• Material list and other data

• Design data management

Most importantly, with parametric modeling, a designer can change certain parameters and see how the created model or a specific component in an assembly will react. As much as the computer can recognize the chosen material’s properties and behavior, however, such a beautiful model can turn out to be impossible to manufacture.

Engineering Calculations and Simulation

Notwithstanding the CAE and simulation tools, designers will always need to use engineering calculations to verify certain aspects. For a mechanical mechanism, it can range from calculations of stresses, strain, or deflections to torque, power, or bending moments. A designer can calculate certain stresses acting on a shaft, determine its required diameter, forces that will act on certain brackets, or how certain fasteners will perform, among a lot of other parameters.

After making necessary calculations, a designer can apply finite element analysis (FEA) to take a closer look. It can help with assessing how certain stresses and strains will deform parts or products under certain conditions and forces.

Simulation can generally be useful at any stage of the design process. It supports a designer who wants to check how several geometries will perform, or what certain changes to parameters and elements will bring. A good and precise simulation can save a designer the time and money spent on a physical prototype, with faulty assumptions, wrong parameters, or a generally wrong model. A simulation, however, can only be as good as its assumptions and methodology. Incorrect values, materials, elements, geometry, or forces will lead to an incorrect model and wrong results. Thus, a simulation should generally be supported by a proper calculation as well.

Materials Selection

Materials play a large role in mechanical design.

A designer can choose not only what kind of materials to use (what steel, copper, or aluminum alloy, or composite or other material) but also define their properties based on several factors.

Some of the mechanical properties of materials include:

Yield strength

Tensile strength

The elastic modulus

Density

Hardness

Fatigue strength

Corrosion resistance

Temperature

Among metals and their alloys, carbon steel, stainless steel, aluminum, copper, titanium, among others offer varying capabilities. Plastics, composites, and ceramics are other options. Designers should also define what kind of processes will be needed to manufacture a certain mechanism, part, or product.

They should consider such factors as:

• Density

• Strength

• Stiffness

• Fatigue

• Temperature capability

• Machining requirements

• Availability and cost

For instance, aluminum allows minimization of weight with moderate costs. However, for higher strength and resilience under dynamic and static loads, stainless steels are better. It should therefore be chosen based on the intended need and environment.

Design for Manufacturing and Assembly

Design for manufacturing and assembly (DFM and DFA) helps make a product easier to manufacture and assemble.

Some products may also be more cost-effective to produce in this way. A designer will choose materials best suited for a given manufacturing method and take advantage of its benefits to simplify fabrication. They will generally apply such rules as:

• Minimize complexity

• Use common materials when needed (e.g., standard size materials)

• Avoid excessive demands on manufacturing operations

• Avoid extra and non-functional features

• Use standard material sizes

• Avoid unnecessary tight tolerances

• Use readily available components and tooling

DFM also assists designers when producing a physical prototype. While it may be produced by an expert machinist, it might not be easy or cost-efficient to manufacture this part multiple times.

Tolerances and GD&T

While drawing a part, its size cannot always be exactly defined since actual manufacturing processes will require some degree of error. Tolerance defines what range of variation from a given drawing or specification is allowed. Geometric Dimensioning and Tolerancing (GD&T) is the technical drawing standard that specifies how tolerance should define dimensions in prints and what it means for the design and function.

One of the most well-known standards is ASME Y14.5, with many others, such as those defined in ASME Y14, providing guidelines for engineering and product design, including drawings and digital product definitions.

A designer should generally seek to select the best strategy for defining tolerances that will make the created part easiest to measure and manufacture. Tight tolerance, however, demands more precise measuring instruments and operations. Therefore, not only should functional needs dictate what tolerance level should be specified, but so should manufacturing demands. Only provide the precision that is needed to keep a part functional, but no more than that.

Prototyping and Testing

Physical testing plays an important role in testing and refining a product in the face of real conditions.

A prototype can be created using various technologies such as machining, additive manufacturing, sheet metal working, casting, or others. Testing can involve:

• Whether it operates properly or as intended

• Whether it can sustain expected or required force

• Whether it fits together

• Whether it will cause any unwanted vibrations or unwanted deflection

• Whether it sustains temperatures within acceptable limits

• Whether it is noisy

• Whether it allows sufficient means for service and maintenance

• Whether it can endure continuous cyclic operations

This will provide a designer with the needed insight to refine a product further. Reaching satisfactory results may, therefore, require multiple design iterations. Designing and documenting each one takes time and effort, but an engineer should not hesitate – each such attempt only adds to the overall insight.

Such a design process is a normal part of engineering rather than an exception. It highlights that a new idea may not always be a correct one, and it often takes multiple attempts to find or determine an appropriate method and solution.

Safety and Reliability

Throughout the whole process, designers should also take safety aspects into account.

Standard ISO 12100 specifies general principles and requirements for safety and risk reduction of machinery, including a detailed methodology of risk assessment. The standard was revised and confirmed in 2022, and, according to ISO’s information, it is still current.

Depending on the type of product, safety aspects can range from moving parts, pinch points, rotating machinery, energy, temperature, pressure, electricity, structural resistance, human interactions, and considerations for servicing. Risk reduction methods can include a change of design and safeguards or information and instructions for operation, use, and maintenance. Applicable standards depend on a product, industry, jurisdiction, and application.

ASME notes that standards can support safety, reliability, productivity, and efficiency, while their legal status can depend on “their adoption in regulations or by contract”.

Common Applications

The area of interest for mechanical design is broad, encompassing numerous applications and areas. It includes:

Automotive

The automotive industry includes a wide range of applications and needs, including engine parts and assemblies, mechanisms, brackets, housings, cooling mechanisms, and systems.

Industrial Machinery

Design engineers work with various types of industrial machinery, from conveyors and simple tools to complete machines and mechanisms, pumps, compressors, and machines.

Consumer Products

There are numerous products that require such engineering expertise, including various appliances, tools, and mechanisms, sporting goods, furniture mechanisms or elements, and many others, including electronic housings.

Aerospace

Components and mechanisms have special demands concerning their performance.

Robotics

Robotic mechanisms include a wide range of elements, devices, and details, ranging from bodies and joints to actuators, bearings, and gears.

Energy and Processing Equipment

Machinery and equipment such as turbo-aggregates, various pressurized mechanisms, turbines, heat exchangers, pumps, valves, and other equipment are used in a wide range of industrial and technological applications.

Essential Software and Tools

There is a variety of software that helps modern design engineers complete their work. It includes:

• 2D CAD Tools

• 3D Parametric CAD Tools

• FEA Tools

• CFD Tools

• Product Life Cycle Management Tools

• Manufacturing Tools

• CAM Tools

• Engineering Analysis Tools

• Design Data Management Tools

• 3D Scanners and Inspection Tools

Such tools can vary depending on the needs, demands, industry, scale, and specifics of the work. In any case, they support and facilitate the work at any stage.

Common Mechanical Design Challenges

Even the most experienced and qualified engineer will face challenges on a regular basis. Some of them include:

Performance Versus Cost Trade-offs

The best solution and design may sacrifice certain factors, with no solution being applicable on all occasions and meeting all criteria. A component such as a shaft may be required to be stronger, take more torsion, or have a bigger diameter. However, it may also mean that it will be heavier, more costly, or stiffer. Its value will depend not only on these parameters, but on its purpose – it means, therefore, that the right design should meet the specified requirements, rather than the desired ones.

Managing Changes

Any changes to the design or model at any of the later stages may introduce additional issues. It can range from affecting the drawing and BOM (bill of materials) to introducing changes to manufacturing, tools, and suppliers. Good revision management helps mitigate some of the consequences for the overall process.

Avoiding Overengineering

A mechanical product or mechanism may require only the minimum set of alterations, modifications, or additions.

Communicating Intent and Requirements

An effective way of conveying the designer’s demands and expectations is needed so that the manufacturing team may produce the needed part. Clear definition of specifications, including the revision, will minimize the risks of mistakes. Standards, in turn, dictate the language of communicating them. ASME highlights the importance of design engineering drawings and documents in this case, with its Y14 series being an important and common set of standards.

Skills Required for Mechanical Designers

Besides CAD proficiency, a designer needs to acquire the following skills:

• Engineering mechanics

• Strength of materials

• Machine design

• Materials science

• Manufacturing processes

• CAD modeling

• Technical drawing

• GD&T

• Engineering mathematics

• Simulation fundamentals

• Problem-solving

• Communication

• Documentation

• Design review

• Practical manufacturing knowledge

Experience with practical manufacturing processes may be a great advantage. A designer who understands machining, welding, sheet-metal fabrication, casting, molding, and additive manufacturing can make more realistic design choices.

How to Improve the Design Process

Sometimes, the most promising way to improve the design process is to revise it. This is especially true for mechanical design automation, where the designer’s input beyond the CAD software is just as important. The most apparent ways to improve the design process are as follows:

Start With Requirements

Before you model the solution, make sure that you fully understand and document the requirements.

Use Standard Components

When possible, use bearings, fasteners, seals, motors, gears, or other standardized components.

Involve Manufacturing

Bring manufacturing engineers and suppliers into the process early enough.

Validate Critical Assumptions

Do not rely on one calculation or simulation for an important design assumption. Instead, supplement the calculations with hand calculations, simulations, prototypes, testing, and third-party reviews.

Design for the Lifecycle

Make sure that you consider the entire lifecycle of the product, from installation and operation through inspection and maintenance to replacement and eventual disposal.

Frequently Asked Questions

What is mechanical design in engineering?

It is the process of developing mechanical components, machines, products, and systems to meet specified functional and engineering requirements.

What is the difference between CAD and mechanical design?

Computer-aided design (CAD) is a software tool for creating and documenting machine components and assemblies. Mechanical design is the broader process that includes requirement specification, mathematical modeling, stress and motion analysis, material selection, manufacturing, and testing.

Why is CAD important in mechanical engineering?

Using CAD software, engineers generate and document machine components and assemblies in 2D and 3D. Moreover, CAD software often serves as the central design database for downstream analysis and manufacturing. ISO recognizes computer-aided design (CAD) as a formal method of expressing product-definition data.

What is DFM in product development?

DFM stands for Design for Manufacturing. It is a process of designing products to meet manufacturing, cost, and performance requirements.

What is GD&T?

GD&T stands for Geometric Dimensioning and Tolerancing. It is a system of symbols and rules for defining and communicating engineering requirements on drawings and electronic documents. ASME Y14.5 is the standard that governs GD&T.

Is mechanical design only about making 3D models?

No, making 3D models is only a part of the mechanical design process. Depending on the industry, engineers may also perform calculations, choose materials, analyze stress and motion, specify tolerances, prepare drawings, make prototypes, conduct tests, and prepare design reviews.

Why are engineering standards important?

Engineering standards are a set of technical specifications and nomenclature that help engineers communicate and collaborate effectively. Standards also facilitate the exchange of technical information, promote uniformity and consistency of design, and contribute to the overall safety, reliability, and quality of engineering products and processes. However, the applicability and legality of standards depend on the standard type, contract, or regulatory or jurisdictional requirements.

Conclusion

Mechanical design integrates principles from engineering science, artistic aesthetics, practical manufacturing knowledge, and systematic problem-solving methods to transform abstract ideas into functional products and processes.

Modern mechanical design is no longer limited to manual drafting and model-making. Contemporary engineers use a combination of CAD software, finite element analysis, engineering calculations, rapid prototyping, and testing to develop increasingly complex products.

At the same time, good engineers know that software tools are only as useful as the person using them. If an engineer understands the fundamental principles of statics and dynamics, materials, manufacturing, tolerance analysis, reliability, and maintainability, they can use modern tools to achieve the best possible outcome.

Standards are equally important because they help engineers communicate design specifications consistently and clearly. As a result, engineers can develop higher-quality products faster while reducing long-term costs. For instance, ASME’s Y14 standards family provides guidelines for technical documentation, and ISO standards address various aspects of machinery, including safety (ISO 12100).

Key Takeaway

In summary, there is no single best approach to mechanical design, but experience shows that the best practices are rarely found in CAD software alone. To maximize the chances of success, use the following strategies:

Design products and processes using sound engineering principles combined with CAD software, simulation tools, DFM principles, and proper material selection.

 References

• McGill University — Engineering Design Terminology and Mechanical Design.

• Dassault Systèmes — What Is Mechanical Design?

• Autodesk — CAD for Machine Design and the Machine Design Process.

• ASME — Y14 Standards and Product Development Documentation.

• ASME — Y14.100 Engineering Drawing Practices.

• ISO — ISO 10209:2022, Technical Product Documentation Vocabulary.

• ISO — ISO 12100:2010, Safety of Machinery.

• Bureau of Indian Standards — Mechanical Engineering Standards.