I worked in the consumer electronics industry for 20 years and model making was important but generally it’s not something that the designer did personally…
The company I worked for designed set top boxes. The electronics and software was designed by our company but we used an outside design house to style the enclosure (eg the front panel). The designer would produced several different design concepts and these would be refined into a “final” design or possibly a small short list of designs. Some or all of these designs would be sent electronically to a model maker who turned them into solid models using a CNC or stereolithography. The purpose of these solid models was to select the final appearance of the product. They looked like the finished item on the outside but wern’t fully representative on the inside, no fastenings etc. Typically they had unrepresentative wall thicknesses and didn’t come apart or at least not in the way the finished product would. This was done to reduce the cost and timescales required to make the model.
Once the appearance had been decided engineering drawings were produced. These included all the details required to make the finished parts. For example these drawings include the correct wall thicknesses, fastenings etc. Items made from plastic have to take into account issues specific to injection moulding - how they items will be ejected from the mold, flow mark avoidance etc Once these drawings were completed it was normal to have several sets of parts made by stereolithography. Typically we would get three to five sets produced followed by larger quantities - perhaps as many as 50-100 units - no mean feat given they all had to be hand finished and painted. These were used for a wide variety of purposes including engineering tests (EMC, safety, packaging design etc). If the product was being designed for a third party client some would normally be shipped to the client.
In parallel the engineering drawings were then sent off to the tool makers. The process of producing an injection moulding tool was quite expensive and sometimes took upto 16 weeks. Several test shots were made before the tool was given it’s final textured finish (anti scratch, matt. gloss etc). Sometimes early samples were hand finished/painted and also used for marketing or engineering test purposes.
Hope that’s of interest.