Understanding the Basics: Mechanical Engineering Principles Every Designer Should Know Part 1
Mechanical engineering serves as the backbone of numerous industries, including the design, analysis, and manufacturing of mechanical systems and components. For product designers and those getting their feet wet in the design of machines or physical products, grasping fundamental mechanical engineering principles, even at a high level, is essential for creating new and functional products. This post serves as a high-level introduction, highlighting some of the key principles that anyone designing products or machines should be aware of. It is highly advised that anyone developing a product or machinery involves the services of an experienced mechanical engineer to ensure that their design is not only feasible but safe for the public and cost-effective.
At a high level, those developing new products or machinery should be familiar with each within mechanical engineering as applicable. In the early stages of any project, before any of the math or expensive software even gets involved, the priority is to develop a rigorous plan and understand the design cycle. The rest of this post will go into a high-level description of some of the important processes and tools used in product and machine development.
Mechanical Design Principles
Design principles such as form follows function, simplicity, and optimization guide the development of efficient and aesthetically pleasing products. Designers must also consider factors like requirements, manufacturability, reliability, and cost-effectiveness when creating mechanical designs. Each has a role to play in the design cycle.
High Level Design Cycle
The design process itself is a cycle that loops as often as required to optimize all critical aspects of a machine or product.
You might notice a few points regarding the simplified process flow. How many times do you need to loop through the design process? And, once deployed, is the product or machine outside of the cycle?
The number of cycles is dependent on the type of project and the results of the verification process. This high-level process will be cycled through until all requirements are met and verified. Not all projects, primarily standalone machinery, require cycling through past initial testing and evaluation. However, it is a good idea to update your requirements with your verification and test results and, if applicable, compare to your analysis and design.
Once outside the loop, is the project forever deployed? Not necessarily, continuous improvement is a cornerstone of product development. For a mass-produced product, continually evaluate costs, manufacturability, quality and safety. For standalone projects, continual monitoring of maintenance requirements provides insights on how to improve both the existing piece of equipment, as well as future equipment, whether they be repeat builds or even different machines in a similar application or environment. It is the policy at Norris Engineering to routinely touch base with customers to ensure continued support and equipment/project success.
Requirements Analysis
The most important part of the process planning portion of the cycle is in determining and writing of the requirements. Requirements will become the backbone of how the project is designed, analyzed, and verified. Requirements should be comprehensive and fully describe how a project will perform and work. Any portion of the project that is not distinctly controlled by a requirement becomes up to the designer and may fall short of customer expectations.
A poorly written requirement is formed like some of the following:
· I would like to have…
· Project could have…
· If possible…
In addition, a poorly written requirement is vague and does not include a subject and predicate.
On the other hand, a strong requirement description could include some of the following:
· The system shall…
· The project must…
· The subsystem may…
A strongly worded requirement has a success criterion and is measurable and testable. A good requirement is always feasible and clear, and should be worded for the system or project, not the user or customer.
The engineer will use these requirements and convert them into numeric requirements, so being detail-oriented is crucial here. For example, a requirement may say, “The equipment shall withstand 10,000 hours of operation at the capacity load and operating speed.” The engineer will use this information to analyze conditions that will specify the reliability, the material cyclic loading strength, geometry and static loading stress, and even down to bearing sizes and lubricant and relubrication intervals.
It is important that a requirement does not force a design nor allows for an “out”. Forcing the system would be a requirement that describes how a system will work. Building in an out, uses phrases containing words like “except”, “unless”, “but”. Outs like these make testing and verification more difficult and can lead to misinterpretations.
Requirements writing is never the fun part of the design process. It is tedious and can be boring, but its importance cannot be overstated!
Failure Mode Effects Analysis (FMEA)
More than just busy work (although it can feel like it at times), the completion of the FMEA is a rigorous and thorough examination of all possible points of failure in a system, and how they correspond back to the requirements.
Within the FMEA, each failure mode is rated by the severity if it occurs, then by its likelihood that it should occur. These factors together rate and rank the failure mode and initiate recommended controls and actions to prevent failure. This ranking is often called the RPN (risk priority number).
Often, it’s not only just a good idea and a sign of a mature and developed design process to have an FMEA, but also a requirement with many customers. Additionally, it may become crucial if there is ever any legal concern or field failure.
Key Design Principles
By no means an exhaustive list, and in no order of significance. These are good things to keep in mind during the design process.
Design for Safety
Paramount in all that engineers do is ensuring the safety of the public and the users of that which is designed and made. When working with an engineer, one that is licensed and holds their Professional Engineering (P.E.) license further ensures that the engineer is putting that focus at the forefront. Safety includes not only those that will use the design, but also those that work on it, install it, and even the environment that it’s used in.
Design for Function
A product or machine must serve a purpose and must be capable of achieving that function through physics and engineering principles. Widgets and thingamajigs even have a purpose. Ensuring that a design can function for its primary intended use.
Design for Manufacturability
Considering how something will be made before beginning the detailed work of the design ensures that it can be made in the most cost-effective way possible and can be made in a way to meet the requirements. For example, a plastic component has undercuts that cannot be formed in the injection mold, even with the addition of expensive slides but it can be formed by additive manufacturing methods (i.e. 3D printing). Additive manufacturing is too costly at high volume and may not allow meeting of other aesthetic or usability requirements. In this situation, that design fails it’s manufacturability assessment.
Design for Reliability
Reliability analysis is a highly complex task that has many approaches. Whichever approach is taken, ensuring it is considered is highly important. Ensuring that a project will work for the required life is as important as designing for function. Accounting for loads, and material cycles to failure, as well as the effect of individual component reliability affects the overall system reliability can not only ensure the project will meet it’s life requirements, but often reduce the overall cost by preventing over-engineering.
Bottom Line Up Front
While in no way an exhaustive look into how engineers take a project on, I hope this introductory look into some of the processes and steps that ensure a successful project launch. Each step should be considered as early in the project as possible, then reviewed frequently. Developing a machine or a product is, unfortunately, not all formulas and interesting graphics. Next in this two-part series, I will dive into an introduction of the types of analysis and subfields of mechanical engineering that should be considered. If you or your organization need assistance with your next piece of equipment or product design, please contact us and Norris Engineering can handle the details.
