SOLIDWORKS Design Approach · Part 02
Four processes, one product: where CAD and CAM actually sit
An idea becomes a product by passing through four processes that nest inside one another. Knowing which process you are working in — and what its output must be — prevents most of the wasted effort in product development.
Overview
Science explains; engineering makes
Science sets out to understand physical phenomena. Engineering sets out to make things that work. That difference matters practically, because engineered systems are almost never simple enough for a closed-form answer. Designers therefore proceed by successive refinement: a rough proposal, an evaluation against requirements, a change, another evaluation, until the design is good enough to commit.
Four named processes structure that refinement. The engineering design process (EDP) is the outer loop. The CAD process implements its later stages. The manufacturing process converts an approved design into physical parts, and the CAM process handles the computational half of manufacture. Each has a defined input and a defined output, and the discipline of knowing which one you are in is worth more than it sounds.
Outer loop
The engineering design process
Input: a problem or an unmet need. Output: a design capable of solving it.
- Step 1 Identify the problem or need in terms specific enough to be tested against.
- Step 2 Research the problem: prior art, standards, constraints, users, failure history.
- Step 3 Develop candidate solutions — deliberately more than one.
- Step 4 Select the best candidate against explicit criteria.
- Step 5 Construct a prototype.
- Step 6 Test and evaluate against the requirements set in Step 1.
- Step 7 Redesign in response to what the test revealed.
- Step 8 Communicate the design so others can build it.
Steps 6 and 7 form the real engine of the process. A design that never returns to Step 3 or Step 4 after testing has usually not been tested hard enough. Step 8 is not a formality either: a design that cannot be communicated unambiguously has not finished being designed.
Sub-process
The CAD process
The CAD process is a sub-process of the EDP. In practical terms it carries Steps 5 through 8.
Create models
Build the parts, then the assemblies. Modelling decisions taken here determine how easily every later step can be performed.
Test and evaluate
Mass properties, interference and collision checks, finite element and flow studies, motion analysis, sustainability assessment.
Prototype
Generate a physical article, most commonly by additive processes driven directly from the model.
Redesign
Feed test and prototype findings back into the model. In a well-built model this is an edit; in a poorly built one it is a rebuild.
Document
Produce engineering drawings: views, dimensions, tolerances, annotations and the bill of materials.
Two things are worth noticing about this loop. First, Step 4 is where the cost of poor modelling discipline is actually paid; everything in Part 06 of this series exists to make that step cheap. Second, Step 5 is not the end of design but the handover interface — and its quality determines how much interpretation the manufacturing side is forced to invent.
Downstream
The manufacturing process
Input: an approved design. Output: the physical part or product, packaged and delivered.
- Step 1 Inspect the engineering drawings for manufacturability.
- Step 2 Create the process plan.
- Step 3 Produce the parts.
- Step 4 Inspect the parts.
- Step 5 Assemble.
- Step 6 Inspect the assembled product.
- Step 7 Package.
- Step 8 Ship to the customer.
Step 1 is not a rubber stamp. A manufacturing engineer — the process planner — reads the drawings to confirm that every dimension is consistent, that nothing is contradictory, and that the specified tolerances can actually be produced by the available equipment at an acceptable cost. A competent planner will frequently return design change requests, and those requests are usually cheap to accept early and expensive to accept late.
A concrete illustration: machining a flat-bottomed blind hole requires a milling operation with a flat end mill, whereas a conical-bottomed blind hole is produced by a single drilling operation. The two look almost identical on a model. One of them costs materially more to make. That asymmetry is invisible unless someone with manufacturing knowledge reads the design.
Computational half
The CAM process
The CAM process is to manufacture what the CAD process is to design: the part carried out on the CAD/CAM system.
- Step 1 Create the process plan — the ordered set of operations, machines, fixtures and tools.
- Step 2 Create the NC programs that drive those operations.
- Step 3 Create the remaining production details: fixturing, tooling lists, setup sheets.
- Step 4 Inspect the parts against the drawing.
Not every manufacturing task is inside CAM. Scheduling, materials management and shop-floor control typically sit in separate systems. What CAM owns is the translation of geometry into machine motion, and the verification of that motion before metal is cut. Part 19 of this series takes that translation apart in detail.
Quick reference
Inputs, outputs and owners
| Process | Input | Output | Typical owner | Primary risk if rushed |
|---|---|---|---|---|
| Engineering design | Problem or need | A validated design | Design engineer | Solving the wrong problem |
| CAD | Selected concept | Models, analyses and drawings | CAD designer / detailer | Brittle models that fail on edit |
| Manufacturing | Approved drawings | Inspected, assembled product | Manufacturing engineer | Unproducible tolerances, high scrap |
| CAM | Model plus process plan | NC programs and setup detail | Process planner / programmer | Tool collisions and rework |
Best practice
Working the interfaces
Most avoidable cost in product development appears at the joints between these processes rather than inside any one of them.
Bring the planner in during Step 3, not Step 8
Concurrent review of candidate concepts by someone who will have to make them removes whole categories of downstream change. This is the practical content of concurrent engineering.
Treat the drawing as a contract
Every dimension carries a tolerance, stated or implied by the title block. Every ambiguity will be resolved by someone, and it will not necessarily be resolved the way the designer assumed.
Prototype to answer a question
Prototypes are cheapest when they are built to test a specific uncertainty — fit, reach, grip, clearance — rather than to admire the design in three dimensions.
Keep the model as the master
Where drawings and model diverge, the organisation has two definitions of the product. Associativity only helps if the drawing is generated from the model rather than maintained alongside it.
Common questions
Frequently asked
Is the CAD process just the middle of the design process?
It is the computational implementation of the design process from prototyping onwards. Concept generation and selection still happen largely outside the CAD system, on paper, in sketches and in requirements documents. Starting to model before the concept is selected is one of the more expensive habits in the discipline.
Where does design for manufacture fit?
It is not a separate process but a constraint applied across all four. In practice it appears as manufacturing knowledge injected into design decisions — draft angles, uniform wall thickness, standard hole sizes, accessible tool paths. Part 19 covers the automated rule checking that supports it.
Do these processes still apply to additive manufacture?
Yes, though the manufacturing process shortens considerably: process planning collapses to orientation, support strategy and layer thickness, and many assembly steps disappear because functional assemblies can be built in one operation. Part 18 covers the detail.
Key takeaways
- The engineering design process is the outer loop; CAD, manufacturing and CAM are nested implementations of parts of it.
- Each process has a defined input and output — confusion about which one you are in produces most schedule loss.
- Testing and redesign, not initial concept generation, are where design quality is actually made.
- The process planner is a design reviewer with veto power and should be engaged early.
- The drawing is the contractual interface between design and manufacture, and must be generated from the model rather than maintained separately.
Series
Continue the pathway
The SOLIDWORKS Design Approach series works through computer aided design as an engineering discipline, from first principles to manufacture.