TECHNICAL PRODUCT DOCUMENTATION

Audio: Technical product documentation

Developing the product can be a long, complex, and exhausting process. There is more to product development than meets the eye. In order to make sure that the mechanical design engineer (or any engineer for that matter) covers all the areas of the product design, different documents need to be created. All the relevant documents for the specification of products, equipment, and plants are called technical product documentation.

We need to create part drawing for the manufacturing of single components; we need assembly drawings to fit different components together, calculate critical components of the product, test them, and ensure that the quality is satisfactory. Doing all these things without a plan and a clear understanding of what needs to be done is bad engineering praxis. In this article, we will discuss different documents that you could encounter as a mechanical design engineer.

Technical product documentation

The product development process involves groups of different teams working together to bring the right product to the customers. At the center of any product development are customers. There are many different requirements that customers expect from the product they are buying. Still, in general, the bare minimum is that the product fulfills the intended purpose (solving the customer’s problem) and that using the device is safe for the customer (using the product will not harm the customer).

Let us say that customer wants to buy a desk lamp. The primary function of the desk lamp is to convert one type of energy to illumination. Let us assume that our customer does not want to have any flammable liquid in their house and would want to use electric energy to produce illumination. Basically, what our customer, at a bare minimum, is expecting is that when they plug the desk lamp into the electrical outlet that it will lighten up the room and that in the process of doing so, it will not electrocute them, kill them, or burn down their house (I as a customer appreciate when my desk lamp is not trying to kill me).

Now imagine that the customer wants to have a light switch so they don’t have to plug and unplug the cable whenever they need the light. On average, let’s say that customers will press the switch ten times a day. They are expecting to use the desk lamp for at least two years. So, you must make sure that your switch, on average, can be actuated seven thousand times without failure.

Moving forward, your customers could have color preferences, shape preferences, additional functions like adjustable height, etc. The list of the requirements could go in infinity. In order to develop and introduce a sellable product, all of the main requirements should be met and adequately addressed. Without proper systems and document management, this is hard to do. For mechanical design engineers, this means that the proper line of communication should be in place.

Technology has progressed to the level that was just twenty years ago unimaginable. The products have become more complex and robust; the design is more demanding and complicated, pushing the limits of manufacturing technologies; communication only with the engineering drawings is no longer enough.

Mechanical engineering covers a wide area of different fields with various diverse technologies. For engineers to communicate complex sets of information acceptably and understandably, ISO has defined all the relevant documents for the specification of products, equipment, and plants. It is called Technical Product Documentation.

The technical product documentation types are defined with ISO 29845:2011. According to ISO 29845:2011, a document is a “fixed and structured amount of information that can be managed and interchanged as a unit between users and systems”; and documentation is a “collection of the documents related to a given subject.” While ISO 29845:2011 lists the whole range of technical product documents, we will list the most interesting for mechanical design engineers.

Part (detailed) drawing

The part drawing is defined as the drawing depicting a single part that cannot be further disassembled and includes all the necessary information required for the definition of the part. In the part drawing, everything required to manufacture the single part is defined, e.g., the form, dimensions, tolerances, material, finishes, treatments, etc.

Assembly drawing

The assembly drawing is defined as a drawing representing the relative position and/or shape of a group of assembled parts. The assembly drawing is not showing the manufacturing details of a single part but merely how the individual parts are supposed to be assembled. The main assembly consists of subassemblies, parts, and materials. On the assembly drawing, we can include the part list, or it can be provided in a separate document.

More detail about the part and assembly drawings you can find here: Introduction to the engineering drawing.

Parts list

The parts list defines the list of the object’s elements. The parts list is added directly to the drawing, or it can be provided with the assembly drawing as a separate list. The parts list shows only the top-level parts used to build the assembly.

In addition, the parts list can be automatically extracted from the company’s ERP or PDM system. With the part list, only one structural level is defined.

Parts list defined on the drawing:

Parts list defined on the separated document:

Bill-of-material – BOM

The BOM is a list of the subassemblies, parts, and materials required for building the assembly. The BOM can be added directly to the drawing or provided with the assembly drawing as a separate list. The BOM show all levels of components required to build the assembly.

In addition, the BOM can be automatically extracted from the company’s ERP or PDM system. The difference between the parts list and BOM is that the parts list defines only one structural level.

Tabular drawing

The tabular drawing is defined as the drawing listing differing variations of a specific configuration using a single, common illustration. The drawing below shows an example of a tabular drawing.

The shape of the component is always the same, but the relationship between different features is changing. In the table on the drawing, you can see that we have different values of the A, B, C, D, E, and t for the different configurations of the component. We could create a different drawing for each plate, but that is unnecessary additional work.

Fabrication drawing

The fabrication drawing is defined as the part drawing of an assembly of fully specified items permanently joined together. The components could be joined together by welding, soldering, or adhesive. Every component of the fabrication drawing should be fully specified. Also, the relationship between those components should be defined.

Outline drawing

The outline drawing gives the outside peripheral envelope, overall dimensions, and mass of an object.

Supplier drawing

The supplier drawing defines a part developed and owned by an external supplier. Usually, the supplier drawings can be found on the supplier website, or you could contact the supplier to provide you with it.

Source: McMaster-CARR

Illustration drawing

The illustration drawing shows figures and sketches for any general purpose not covered by the more specific document types. These could include figures for marketing purposes, figures for the instruction manuals or work instructions, etc.

Document list

The document list is defined as a formally built-up inventory in which all relevant documents for a specific purpose are listed. This document can belong to a system, part, project, etc. The best practice is always to display the document identification number and revision of a document list and all documents listed in it. Other information depends on the company’s preferences.

Requirement specification

The requirement specification is defined as the document compiled and evaluated with the requirements from the markets (customer), authorities, and the company itself.

These requirements are usually stated in the form of “wishes,” and they are usually not measurable. For example, the product must be robust, strong, and waterproof. This type of document describes what needs to be built and not how.

Technical specification

The technical specification is defined as the document specifying the requirements for one specific part or a group of parts with similar characteristics. The technical specifications are quantitative, and they can be verified. For example:

Requirement specification: The product must be light.

Technical specification: The product’s mass should be less than 3 kg (m ＜ 3 kg).

Part definition document

The part definition is defined as the text-based document that may be supplied with a drawing of the defined part, specifying property requirements for the part described by the document. This document is very useful if you have a procurement department. Defining the required technical data of the component supplied by an external supplier can be used for the procurement team to find a less expensive supplier without involving a design engineer or procuring the wrong component.

Calculation sheet

The calculation sheet is defined as the document providing the results of calculations regarding essential product characteristics. This can include hand calculations, calculations according to the standard, FEA, CFD, etc.

Assembly instruction

The assembly instructions document is defined as a document providing information on how and in what sequence the different parts shall be assembled to receive a specific end product. Usually, for simple assemblies, the assembly drawing is used.

The assembly instructions are created when the assembly process is complex (different tools and procedures are used). In that case, the assembly drawing shows the final assembly and the part list, and it is refereeing to the assembly instructions. The assembly instructions define the assembly process in great detail, with every step clearly and unambiguously explained.

Test plan

The test plan is defined as a document describing the scope, realization, resources, and plans for the intended test activities.

Test specification

The test specification document is defined as a specification explaining how to perform the test activities according to the test plan.

Test report

The test report is defined as documentation of test results based on the tests carried out at a new part, assembly, product, or system.

Closing words

As you can see in this text, there is more to product development than meets the eye. The mechanical design engineer is not responsible only for the design, but depending on the size and the structure of the company, the mechanical design engineer could be responsible for a whole range of different activities during the development phase.

Creating CAD models and drawings in CAD software is the “easy” part. Knowing what to design and why is the hard part. Documenting everything is not because someone wants to give you more things to do. The technical product documentation ensures that all customer requests are defined, specified, understood, and translated to the physical product with satisfactory quality for the customer.

Great quality products should have the same quality independently of the produced quantity. We want our first, tenth, and millionth customers to have the same experience with our product. Everything that you do is for your customer to be happy with the product and that they did not spend their valuable time and hard-earned money on a bad product.

Now you have an excellent overview of the types of technical product documents. However, I suggest you go through the text once more and identify areas you think need more understanding and clarity. Then, once you have identified those areas, start building up your knowledge in those areas.

To make it easier for you to find related posts, check the “Further reading” chapter below. Do you have any questions or need something to be clarified better? Leave a comment below, and I will give my best to adjust the post accordingly.

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