After the Napkin Sketch the Engineering Design Drawings take over. Being a CAD Designer in the Silicon Valley for about 25 years has given me a unique way of looking at things. I imagine drawings morphically developing. I see machine drawings, sheet metal drawings, injection molded drawings, assembly drawings, cable harness drawings, schematic diagrams, interconnect diagrams, floor plans, PI&D, Piping & Instrumentation Diagrams, and just about anything were someone had to draw a picture to explain to someone else how to make that thing. CAD, Computer Aided Design, is the engineering science of graphic communications. If you do it long enough it becomes a hi-tech art-form.
You never know when a good idea pops in someones head. It could be at any given time of the day or night. In my many years working in the Silicon Valley I’ve seen my share of ideas sketched on napkins after lunch and the next morning after a happy hour with the crew. That napkin sketch usually turns into a design review and the transformation from napkin idea to real working drawings is about to begin.
A good CAD designer will be able to create a design layout that conveys ideas effectively from attending an engineering design review. From the design layout the designer should be able to extract fab drawings, parts lists, interconnect diagrams, and assembly drawings for engineering prototype development and prepare a full documentation release of engineering drawings to production through an ECO, Engineering Change Order.
3 Main Design Phases
The 1st phase
From my point of view there are 3 phases of engineering design. The 1st phase is the Conceptual Layout phase which begins after attending a design review and have the basic information to start creating a layout. The drawing layout is at the discretion of the designer and is not an engineering released document. Geometry created will be extracted as fabricated peice parts.
The 2nd phase
The 2nd phase is the creation of Fabrication Drawings. These drawings are created for the fabricator, the purchasing agent, and for anyone involved in the engineering design review. These drawings consist of machined peice parts, sheet-metal parts, injection molded parts, cable harnesses, PCB printed circuit boards, and anything that requires fabrication development. Together after all parts have been created they are put together in an assembly and tested to see if the unit works. Modifications may be required at this point and revisions to the parts may be necessary. This will be in the form of an engineering RN revision notice that stays within the engineering department and not released to production. This creates quick change turn around and only needs approval by the engineering manager involved. This avoids changes having to be reveiwed in a CCB (Change Control Board) meeting by company wide representatives of different departments. CCB meetings are for any changes made to the product after the full design package has been released to production. An ECOs Engineering Change Orders is used to describe the changes and managers and representatives from different departments in the company affected by the changes attend to review the ECO request and either approve or request more corrections.
The 3rd phase
The 3rd phase is the Assembly drawing phase. Assembly drawings basically consist of geometry of the overall assembly, sub-assemblies if any, and a PL parts lists or BOM bill of materials. The assembly drawing basically identifies peice parts where they are located on the assembly. Multiple views may be necessary to identify parts on different sides. The parts list will identify parts, any sub-assemblies, cables, and identifying labels and markers. There maybe reference dimensions to disply overall size of the assembly but never detailed dimensions, leave those dimensions to be viewed on the fabrication drawings. There also will be general assembly notes and shipping requirement notes.
The “Revision Notice”
is used exclusively at the prototype development stage between the originator and the engineering manager. This Change Notice is a quick way of documenting a change to a part or assembly during the fabrication stage. To streamline the change only the engineering manager reviews, approves, and signs the Revision Notice. All revisions are numeric and the very 1st initial revision is always “Engineering Release.” When all changes have been made to all fabricated parts and are correct and complete, the part is ready for Production Release.
The “Engineering Change Order”
is used exclusively at and after the Production Release stage in the event when the finished product is released to the public or to the customer. Any changes made at this point will need to be reviewed by every department manager whose department is affected by the change. The revision levels are in letter form at this point and beyond. The review of the Engineering Change Order is conducted at a CCB meeting. CCB stands for Change Control Board and members of the board are the department managers or their assigned representatives and the originator of the ECO. The Document Control Manager calls the meeting to order then has the attendees review the ECOs, then gathers signatures for approval, or rejects ECO if denied. The Document Control Manager will take the approved ECOs with related drawings and documents and integrate them into the MRP system. MRP = Material Requirements Planning system. The rejected ECOs will be returned to the originator.