Concept ideation, as the term implies, is about forming ideas. Ideation is generally a cognitive task - it's something you do with your brain. Some people ideate best alone, others work better in teams.
Within the scope of design engineering, concept ideation is about looking at the requirements of a problem and coming up with a short description of the general class of product that can satisfy the requirements.
Here's an example. The design problem is: design a highly innovative urban vehicle that could be brought into production within the five years.
Some possible ideas include:
a motorised scooter with a shell to cover it
a motorised rickshaw
a front-to-back symmetric two-seat, fuel-cell powered car
a ATV for city-driving
Notice that none of the ideas address all the design issues.
In no case is a sketch suitable - or more precisely, each "idea" can be captured by an infinite number of different sketches. To sketch a solution at this point defeats the purpose of ideation because a sketch is limited to the features put on the sketch. The ideas presented here are so abstract that there is no real way to capture its essence visually without making too many other commitments about form.
What an "idea" does capture is the underlying philosophy of the proposed design concept. One can look through the ideas given above for the urban vehicle problem and immediately imagine all kinds of possible differences (and similarities!)
Concept ideation sets the stage for concept generation, wherein sketches are used to represent ideas visually.
The ideas listed above may have been developed as follows:
Idea #1 arose by thinking of conventional very small transportation devices.
Idea #2 started with idea #1 then proceeded to other non-standard two-wheeled modes of transportation.
Idea #3 came from considering that idea #2 was a "low-tech" solution, then considering the opposite possibility (i.e. a "high-tech" solution).
Idea #4 came from transposing the environment of Idea #3 (urban setting) into an alternative environment (all-terrain, non-urban setting).
In fact, here's a way to generate ideas derived from this observation:
Choose a few of the design issues from the PDS of a design problem.
Think of one idea that addresses only those issues you chose.
Change one or two of the issues for new ones from the PDS.
Think of how your first idea could change to address the new set of issues and create one or two new ideas.
For example, say you were designing a robot, and were considering the issues of lifting power and cost. One idea would be a hydraulically driven robot; hydraulics is both powerful and relatively inexpensive. Now let's change one issue; say we want to think about lifting power and maintenance (instead of cost). In this case, we might think of an electrically driven robot, because electric power systems tends to require less maintenance than hydraulic power systems.
Product ideas need to address the requirements of the design problem, although at this stage, it is not important that you address every requirement directly. So to carry out ideation, you should spend some time looking carefully through the PDS for your design problem.
The result of the concept ideation phase should be at least one, but preferably two or three ideas that are substantively different (refer again to the urban vehicle example above). Write out your ideas in your journal, using short descriptive phrases. Make sure you bring all your ideas to the table when you meet your team.
You may find that sketching is a good way to think about your ideas and to filter out the bad ones. You should feel free to sketch possible concepts for your ideas in your journal. Those sketches will be very useful later in the process, but you should not commit to any one particular sketch at this time.