Design Review in Mechanical Engineering

From the Model to Manufacturing

A 3D model can be geometrically correct and still contain issues that only become apparent during manufacturing, assembly, or operation. The model represents the conditions that have been defined and formalized during the design process, while physical implementation introduces manufacturing processes, tooling, operational sequences, and constraints that may not be fully represented within the CAD environment.

A design review extends the verification process to include these conditions. Geometric validation is complemented by an assessment of how the design will actually be manufactured, assembled, operated, and maintained. This requires considering the project from the perspective of the stages that follow engineering design and verifying whether the decisions made during development remain valid when confronted with actual implementation conditions.

Geometry and Manufacturing Process

Consider a practical example. During the development of a welded structure, the model made it possible to verify geometry, lengths, angles, interfaces, and interferences. In these respects, the solution was correct. Comparing the design with the actual manufacturing process, however, introduced additional factors that needed to be considered.

The fabricator used specific fixtures and manufacturing methods that created conditions slightly different from the ideal geometry represented in the model. As a result, some joints would have produced larger gaps than initially expected, requiring more filler material during welding and additional manufacturing time, while also introducing an unwanted variable in a structurally significant area.

A review was therefore necessary. The geometry had to be assessed together with the process used to manufacture it. Compatibility between components is one of the conditions required for manufacturability, but the operations needed to achieve the intended result must also be considered. Working closely with the workshop made it possible to include these conditions in the assessment while the design could still be modified.

The Operational Perspective

The same principle applies to assembly, accessibility, and maintenance. During a design review, it is useful to temporarily examine the design from the perspective of the people who will physically work on the machine. A joint must provide enough space for a welder to reach it with the torch; a component must be installable through a practical assembly sequence; screws and adjustment points must remain accessible with the required tools; and components subject to maintenance must be removable while taking the surrounding space into account.

These checks depend both on geometry and on the operations that will be performed around it. Knowledge of manufacturing processes and workshop activities therefore allows surfaces, clearances, and interfaces to be evaluated in relation to people, tools, and operational sequences. Observing how components are actually manufactured, welded, assembled, and modified helps engineers formulate more precise design questions and identify conditions that may be less apparent in the model itself.

Design Review Stages

A design review can be carried out at different stages of development, with specific objectives. An initial review can take place at the concept stage, when the main architectural decisions are still open and can be changed without having to rework an already detailed design. At this stage, the overall feasibility of the solution, the complexity introduced, the materials required, the necessary manufacturing processes, and the implications of different choices for production can be assessed. A configuration that is relatively straightforward to develop in CAD may require complex manufacturing processes, while a more elaborate design choice may ultimately simplify fabrication and assembly. A concept review makes it possible to evaluate these aspects before proceeding with detailed development.

A second review can be performed once the model has reached a higher level of definition. Attention can then shift towards actual implementation conditions: accessibility, assembly sequences, joints, tolerances, maintenance, and interfaces with other subsystems. The first review therefore examines the overall design approach, while the second assesses the consequences of the decisions that have progressively defined the assembly.

Technical Challenge

A review should also consider another factor: the person developing a design knows the reasoning behind each decision, the alternatives previously considered, the constraints encountered, and the compromises that have been accepted. As development progresses, many decisions become familiar and tend to be viewed within the same line of reasoning that originally produced them.

On more complex projects, it can therefore be useful to involve someone who has not directly participated in developing the solution. Their distance from the design process allows certain choices to be reconsidered from a different starting point and raises new questions about materials, joints, dimensions, or previously rejected alternatives.

The discussion may address the reasoning behind a particular material selection, the configuration of a joint, a dimensioning decision, or the consequences of changing one of the assumptions made during development. In this way, the review also becomes a form of technical challenge in which design decisions are subjected to renewed scrutiny.

The observations generated by this process can lead to different outcomes. Some may reveal an issue and result in a design change; others may simply require the original reasoning to be reconstructed and confirm that the decision is adequately supported. In both cases, the discussion makes the technical rationale behind the design more explicit and reduces the risk that familiarity with a solution will make its weaknesses less visible.

Available Information

A second example concerns a different situation, in which some of the information required for the design was not yet available. During the development of a tubing system, some of the final components had not yet been defined. The project therefore had to proceed using the dimensions and technical information available at that stage. The assumptions used were necessarily provisional and could only be verified once the final components became available.

When those components arrived, some of their actual dimensions differed from those used during modelling. Where sufficient clearance had been allowed, the variation was accommodated without significant consequences. In other areas, however, the remaining vertical space was no longer sufficient to maintain the planned routing. Some lines could be adapted, while others required new bending operations.

This second example differs from the welded structure case. In the first example, comparison with the manufacturing process made it possible to identify an existing issue before fabrication. In the tubing system, some of the information required for verification would only become available at a later stage. A design review can identify areas where the project depends on provisional data and assess their sensitivity to possible variations, while the quality of the verification necessarily remains linked to the information actually available at the time of the review.

Predictability and Uncertainty

The two examples illustrate different types of design issues. Some can be anticipated through closer consideration of manufacturing, assembly, maintenance, and production processes. Accessibility, operational sequences, manufacturing methods, and compatibility between geometry and the way a component will actually be produced largely fall into this category.

Other variables remain uncertain when a design decision has to be made. Under these conditions, it becomes important to identify the assumptions on which the design is based and, where possible, assess how sensitive the solution is to plausible variations. Providing adequate margins can allow subsequent differences to be accommodated without requiring substantial modifications.

Design robustness therefore also includes the ability of a solution to manage a certain degree of variation between the conditions considered during development and those eventually encountered in practice. This difference cannot always be eliminated, but it can be made explicit and considered in design decisions to the extent allowed by the information available.

From Design to Machine

CAD makes it possible to control geometry, clearances, interferences, and relationships between components, providing the foundation required to develop and document a mechanical design. The machine will subsequently move through procurement, manufacturing, welding, assembly, commissioning, operation, and maintenance, with each stage introducing its own conditions and constraints.

A design review allows some of these conditions to be considered while changes to the design are still possible, connecting the model with the way the machine will actually be manufactured and used. It also helps distinguish issues that can reasonably be anticipated from conditions that depend on information that is still incomplete, while making the assumptions behind specific design decisions more explicit.

Design validation therefore requires reasonable confidence that what has been defined can be manufactured, assembled, and made to operate under the intended conditions. Design review contributes to building that confidence through technical discussion, knowledge of real manufacturing processes, and the ability to examine the project from the perspective of those who will ultimately turn the design into a physical machine.