The ranking of MBD and PMI is based on the general product lifecycle in figure 2-1 on page 3. MBD and PMI, its generation in any CAD software and downstream consump-tion are relevant in selected phases at the beginning of a product lifecycle and shown in detail in figure 2-7. Main processes in the phases are highlighted in figure 2-7 and ex-plained in separate subsections.
FIGURE 2-7: Ranking of MBD / PMI in product development-manufacturing-inspection chain
2.6.1 Product development and construction
Basis for the beginning of the product development and construction phase could be an innovation, modification of an existing product or a customer request for the construc-tion of a device. A list of requirements for the final product, which a contractor has agreed on with a client has usually to be done before.
The product development and construction phase can be split into product development phase and product release phase (Quintana et al. 2010, 500). Within the product devel-opment phase, the conceptual design based on a sketch is developed and more details are added. Besides, the requirement list is considered and listed functional needs should be realized within the construction. The final design is the result of this phase and the initial point for the production release phase. It is a continuous increase of the product definition level and finally all relevant information are included in the construction, so that downstream engineering processes can begin.
Figure 2-8 shows the role of MBD in this phase of the product lifecycle. It also illus-trates the difference between MBD and a model centric workflow, which describes the coexistence of a solid CAD model and a drawing derived from that model.
In this context, there is still a need for a paper-based sketch when MBD is the used method and the initial point remains unchanged for defining a product. A sketch is a mean of technical communication in order to illustrate concepts based on the general product arrangement. Further elaboration of the design within product development phase is based on a solid 3D-CAD model without 2D drawings when using MBD.
The level of changes of the constructive design is high at the beginning of the product development phase and decreases when the final design is reached. More and more de-tails and parts are added to the construction, to confirm the product intent. Before the final design is reached, stress and strength calculations based on solid MBD model are done to analyse the product performance. The obtained analysing results might lead to further changes within the construction. All changes are directly visible on the 3D-CAD model, which is the basis for technical communication and the number of annotations and PMI added to the model increase continuously within this phase.
Changes in design when using a solid model and a drawing (model centric workflow) must usually be done on the 3D-CAD model at first. After that, the 2D drawing must be updated in order to display the actual product and guarantee accurate technical commu-nication.
FIGURE 2-8: Comparison of MBD (a) and model centric (b) concept in product devel-opment and construction phase (Quintana et al. 2010, 500 Fig. 2.)
In the product development and construction phase, the final MBD model is a 3D digital prototype and ready for manufacturing (Zhu et al. 2016, 487). Its primary purpose is the creation of digital product datasets of the final design including PMI, which can be used in subsequent product manufacturing and quality inspection phases. The responsibility and workload of a product designer in an MBD workflow increases compared to a mod-el centric workflow. Reuse of PMI data in subsequent PLC phases must already be con-sidered and ensured in product development and construction phase.
In order to enable interoperability and use of PMI data generated in this phase in follow-ing software applications for manufacturfollow-ing and inspection, a suitable data format is required. As involved stakeholders might use different CAD software, the conversion is an important procedure to make an exchange of PMI data and the reuse within down-stream applications possible. Neutral file formats (e.g. STEP), which are based on inter-national standards or CAD software related data formats (e.g. part file) and supported in downstream applications, must equally represent PMI data, as generated during product development and construction phase.
2.6.2 Product manufacturing
Dedicated content of the MBD dataset including PMI, which was generated in the pre-vious product development and construction phase, can be reused in the subsequent product manufacturing phase.
For the manufacturing of workpieces using manual machining methods, MBD including all necessary PMI serves as an alternative to 2D drawings. Machine operators or me-chanics working on the shop floor level can get all necessary dimensional and tolerance information for manufacturing from an annotated 3D model including PMI. Such tasks like manual milling, lathing or drilling can be performed using GD&T information from graphical PMI, which are displayed on a screen or tablet. Graphical PMI distribute the product definition as part of technical communication between the product development and construction department and machine operators. They can retrieve graphical PMI to control manual manufacturing and are the source for proper machine setting adjustment.
PMI data can be used for the automation of CNC programming tasks, which are usually done prior to the real manufacturing process. CAM software uses the 3D-CAD model with PMI provided in a dedicated file format to define and validate machine-readable instructions for manufacturing (Lipman et al. 2015, 15). Semantic PMI can facilitate CNC programming tasks by generating optimized toolpaths as features and forms of an imported CAD model and information about tolerance and surface quality are readable for CAM software. CAM software often adopt the nominal dimension from the 3D-CAD model to create the toolpath. In order to consider tolerances for toolpath pro-gramming, manual adjustment is necessary by extracting tolerance data from 2D draw-ings.
GD&T in semantic PMI are interpretable by proper CAM software and machine opera-tors do not manually have to adjust the tolerances to the middle tolerance value any-more, which reduces the risk of errors significantly.
Tools can be selected automatically and the parameter adjustment (e.g. speed, feed) is done based on a 3D model including semantic PMI. In this context, the term Model-Based Manufacturing (MBM) is used and PMI in this phase increase the level of auto-mation3 and technical stuff on the shop floor is increasingly responsible for correct ex-amination and supervision of the program functionality.
3 The level of automation is the relation between automated functions to the overall (manual + automated) functions of a production system in terms of costs or stages of production: 𝐴𝐿 = 𝑎𝑢𝑡𝑜𝑚𝑎𝑡𝑒𝑑
𝑚𝑎𝑛𝑢𝑎𝑙+𝑎𝑢𝑡𝑜𝑚𝑎𝑡𝑒𝑑 (1).
2.6.3 Quality inspection
The utilization of manual gauging and CMM for the final control of a products quality is important during quality inspection phase and relevant in the context of MBD. Manu-al gauging as a measuring method for a products quManu-ality evManu-aluation can use graphicManu-al PMI to display a products GD&T set values. Requirements expressed in GD&T and other properties of the final product design, engineered in the product development and construction phase and their compliance after product manufacturing must usually be checked, before delivering the product to the customer.
Graphical PMI connected to a 3D-CAD model are the source to receive information about the ideal geometric shape of a product and can be used instead of 2D drawings.
Measuring points can be shown by graphical PMI and a set-actual comparison between the manufactured product dimensions and the ideal 3D model including PMI can be performed.
Software packages from different metrological companies can read GD&T included in semantic PMI, which have been attached to a 3D-CAD model and were provided in a dedicated file format during product development and construction phase. CMM soft-ware can use machine-readable PMI and the associated CAD model geometry to gener-ate a measuring program for the check of GD&T and constraints such as perpendiculari-ty or circulariperpendiculari-ty of manufactured parts. Semantic PMI act as the central distributor for products ideal GD&T properties, which are the source for measuring program genera-tion and comparison with the real parts geometry. Based on predefined tolerances in-cluded in semantic PMI, a manufactured part is evaluated, if it meets the tolerances or not (Mitutoyo Corporation 2018, 10).
In this phase, semantic PMI enable an automatic creation of measuring programs for CMMs and this increases the level of automation. Less time is spent on manual pro-gramming by CMM technicians and extraction of GD&T from 2D drawings as a manu-al input for CMM software is replaced by directly reading PMI from an imported file.
The software identifies features from the CAD geometry and PMI and prepares an ap-propriate tool for inspection and previews the CMM probe inspection path in a simula-tion environment. After CMM program execusimula-tion and quality inspecsimula-tion of a product, the delivered measurements are documented in a report.
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