Keywords

1 Introduction

The industrial design project must be able to be told in a universal language, also beyond the defined systems of representation, such as technical drawing and representation, that would normally be used by the different players involved. For this reason, from the earliest evolutionary phases of the design process and throughout its realisation, the need arises to have a tangible, manipulable verification tool capable of similarly synthesising as broad a set of variables [1].

This tool is the physical model, diversified in relation to the design verifications made and to be made to the design project, which first consists of a series of formal and volumetric maquettes and then moves on to functional analysis models up to a final product prototype. Investigating the contemporary, compared to increasingly widespread digital implementation, it is interesting to discuss how the physical model has evolved, from its use to its meaning, within a process of innovation to support design by the designer. In the past, the design was mainly defined by the optimisation of geometries derived from manual work on the physical model, starting from an initial draft and arriving at its final form.

Today, the use of the physical model for design, realised through rapid additive manufacturing techniques, acquires a different value than in the past. It implements it function in support of the project from the aspect of optimising production within the design development process, decreasing verification phases and reducing production costs. In addition, the constant and rapid evolution of digital technologies is facilitating in industrial design, and in the role that the designer plays today, the transition from prototyping to rapid production in which the analysis prototype takes on a finished product configuration, thanks to more efficient rapid additive manufacturing technology and the development of increasingly high-performance materials.

Supporting this digital evolution, which is enabling a new way of producing objects, is the increasing computational efficiency of parametric and generative modelling software, through which the virtual model is defined with an increasing amount of data managed by the designer, transforming the model from physical to virtual and the “capostipite” from type model to finished product.

To better understand the role and evolution of the physical model in the design development phases, one must isolate the model. An iterative process that alternates between production and analytical phases until the final prototype is achieved, with optimal characteristics depending on the materials and production technologies assumed during design development. The phases were defined through a time chart, diversified by order of succession and execution time. Developing a single cycle in a linear fashion, the process starts with the choice of the type of material and the most suitable technique or technology, then moves on to the phase of realising the model, testing and refining, and finally to the phase of evaluating and analysing the characteristics. The graph serves as an element of investigation to understand how the process of making physical models has transformed and evolved through the influence of digital technologies.

First, the research investigated what role the physical model played in the product design process. From a tangible, manipulatable and updateable verification tool, capable of synthesising an ever-increasing set of variables and characterised by its own evolutionary timeline comprising a series of different types of models such as formal and volumetric maquettes, to a typology of functional analysis models useful for creating the prototype/model type defined by Dorfles as the “capostipite” for industrial production purposes. From Piero Polato's 1991 interview with Achille Castiglioni, it is possible to understand how the physical model played a fundamental role for the designer and how it contributed to the creation of the greatest products of design. In fact, when asked about the importance of the process of making physical models Achille Castiglioni replies: «I have always considered modelling as a fundamental moment in the process of an object project. Drawings, even the most sophisticated, are not enough: the creation of the model, often of several models, is an indispensable moment of verification of the first design hypothesis, it is the moment that allows you to establish a material, physical relationship with the object, continually intervening to correct details on a living reality that is tangibly modified. […] is also the moment in which the hypotheses for the use of materials find their match or highlight processing difficulties, possible inconsistencies in the designed solutions». The same thought emerges in Giovanni Sacchi, an undisputed master among model makers, who created models of objects that made Italian design history. When asked by Polato what kind of designer he liked to work with, Sacchi replied: «I prefer those who work manually, on the model, on the reality of the object. If one imposes the model based on the design, I find that wrong. [..] The model has a sensitivity, you can see it. Almost everyone now works on the model, and less on the design: the drawing is a sketch of the idea […] With the model you have the reality of the project.» [2]. The prototype can be defined as an artefact that approximates a characteristic (or several characteristics) of a product, service or system [3], or more specifically as a first specimen, an original model of a series of successive realisations built, mostly by hand, in its normal dimensions and susceptible to testing and refinement, on which series construction is then based. There are general trends in the way prototyping is approached. Some are driven by achieving specifications, while others focus on prototyping to explore and develop a new concept [4]. Every prototype requires a strategy to solve a problem. This strategy influences the nature of the information that can be explored and learned from the prototype [5]. Therefore, the prototyping strategy must be carefully planned [6]. Designers can explicitly consider the type of tests to be performed with the prototype [3]. A first typical taxonomic division is that between prototypes concerning form and those concerning function [3, 7, 8]. Another common distinction is the variable level of fidelity of a prototype to the final model [9,10]. A distinction is also made between virtual models (simulations, visualisations or computational approximations of behaviour) and physical models [10]. Thus, in the design development of an industrial product, prototypes and models can be grouped within a generalised prototyping process into five common categories: test prototype; form study prototype; user experience prototype; visual prototype; functional prototype.

In a first phase, the designer would make a “test prototype” to render the volume of the design and understand its actual three-dimensionality. In a second phase, a “form study prototype” was made to explore the dimensions and appearance of the product without simulating the actual function, implementing key details such as parts and components.

Its main purpose was to analytically validate its ergonomics and return the visual and formal aspects of the product. Another typology useful to designers was the “user experience prototype”, where its function was to investigate the relationship between the product and the user. While intentionally not addressing possible aesthetic treatments, this type of model more accurately represents the overall dimensions, proportions, interfaces and conceptual articulation of the product.

Next, a “visual prototype” was made, intended as a means of verifying all those characteristics that we now call “soft qualities”: simulating surface finishes; colours; textures and materials that characterise the product. It is a sample or model of a product built to test a concept or process or to serve as a visual aid to be replicated, improved and learnt from. The “visual prototyping” serves to provide an aesthetic vision of the product. The prototyping process ended with the realisation of the functional prototype in which all the features necessary to validate the design before it could be put into production were incorporated. The prototype conveys to a greater extent the practical attempt to simulate the final design, aesthetics, materials and functionality of the project. The construction of a fully functional full-scale prototype is the final test of the conceptual phase and is usually the final check for any design flaws. Analysis of the functional prototype allows improvements to be made before production. This prototype is referred to by Dorfles as the “capostipite” or “type model” because its role was to verify and compare against the products to be made, which had to be faithfully repeated. From the descriptions of these categories, a prototype can be defined as a verification product created for demonstration purposes and to test products before they are put into production. In fact, many of the advantages of prototyping relate to product refinement. Prototyping is used to validate requirements, reveal critical design issues [11], reduce errors [12], identify design changes that improve performance [13], optimise design features through sequential testing [14], design refinement through simulated use through individual or multiple tests [3] and at the same time as a time to establish a material/physical relationship with the object. The work on the physical model gave the opportunity to correct details or any inconsistencies in the solutions drawn on a living reality that was tangibly changing. To support this inherent analysis of the role the physical model played within the design process, an iterative time chart (Fig. 1a) was created that shows how the design phases varied in order of time and development. The development of physical models and prototypes took up a large part of the time allocated to product development, as once the first prototypes had been developed, they moved on to an analytical and testing phase to fine-tune their design and selection, which could either go back for a further design and prototyping cycle or move on to a production phase for the model type destined for series production.

Fig. 1.
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Graphical elaboration of the evolution of the prototyping to production process

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2 The Physical Model and the Relationship with Designers

The evolution of manufacturing processes, with a focus on rapid prototyping processes, lead to substantial changes in form and result in important functional transformations and formal variations of the industrial product. The innovation process, driven by technological implementation and the evolution of prototyping processes, has been linked to incremental improvements in process and product quality achieved through an intuitive [15], very often unplanned and mostly practical path through the development of a series of physical study models. With the introduction of digital design tools, the classification of previously expressed types of prototypes and models undergoes a transformation. The “trial prototype” and “study of form”, which until then were physical models made by manual or human-assisted machining techniques, become virtual prototypes using three-dimensional modelling software. 3D modelling is a process that defines any three-dimensional shape in a virtual space generated on a computer; these objects, called 3D models, are created using special software programmes, called 3D modellers. In computer graphics, three-dimensional modelling is the process of developing a coordinate-based mathematical representation of any surface of an object in three dimensions using specialised software by manipulating edges, vertices and polygons in a simulated 3D space. Three-dimensional models represent a physical body using a set of points in 3D space, connected by various geometric entities such as triangles, lines and curved surfaces. The opportunity to create three-dimensional models in virtual environments brings the digital modeller an advantage: that of being able to implement, analyse and refine all design features by formulating a series of design variations. In addition, digital tools offer the possibility to go into the details of the project, evaluating surface finishes, fillets and chamfers, before producing the physical model through rapid prototyping.

With the development and introduction of rapid prototyping technologies, both the “user experience prototype”, the “visual prototype” and the “functional prototype” achieve greater detail in their parts and greater surface definition, significantly reducing lead times. Rapid prototyping is a set of technologies used to rapidly produce a physical model of a product in its parts and components using three-dimensional CAD (Computer Aided Design) data. The production of a part or assembly of product parts is usually performed using 3D printing technology or “additive layer production”. Through the rapid prototyping technologies of additive printing in all its technological and material variants (powder sintering printing, photopolymerization of liquid resins, etc.), the prototype acquires greater definition of details such as joints, movement of components, joints and hollow parts. In addition to significantly speeding up the prototyping process, the possibility of working in a virtual environment and the use of 3D printing as a manufacturing process leads to complex three-dimensional geometries. Furthermore, the materials that are used in rapid prototyping technologies take on a fundamental importance, namely that of prefiguring the performance characteristics of the materials chosen for industrial production. Resuming the time chart of the prototype development process, with the implementation of three-dimensional modelling and rapid prototyping ─ utilising the layer-by-layer construction potential of additive printing technologies ─ there is a shift in the phase of analysis and selection of virtual models (Fig. 1b) and a consequent reduction in the time required to produce the physical prototype. Although new technologies and prototyping techniques have made it possible to change the development processes of a prototype into the realisation of a physical, tangible model, it still plays a fundamental role as a tool for analysis and comparison, on which the designer can assess which modifications can be implemented to continue in the subsequent design phases.

3 From Prototype to Product

The evolution of digital prototyping and production technologies has changed the concept of the physical model. It went from “study model and functional analysis”, useful in the design phase, to “functional prototype” to finished product.

What changes in the contemporary world compared to the past? Today, the designer has new tools and software for generating virtual models, which, through the implementation of tools and algorithms in information management, make modelling parametric and generative. Parametric modelling is a type of three-dimensional modelling that is based on relating components and parts of the model to each other through numerical values and construction constraints that are referred to as parameters. The parametric approach to modelling constitutes an innovation in the realisation and setting up of virtual 3D models, as it allows a series of modifications to be concatenated and modelling processes to be automated by acting on a given parameter to make a change. Generative modelling is an iterative design analysis process using a series of computational calculations that, using algorithms, generates a range of design solutions that satisfy a set of constraints and parameters.

At the same time, rapid prototyping technologies are evolving into “rapid manufacturing” technologies. Also known as “direct manufacturing”, “direct fabrication”, “digital manufacturing”, it is defined as: “the use of an additive manufacturing process to build parts that are used directly as finished products or components”. Rapid manufacturing can also be expressed as a branch of “additive manufacturing”, which refers to technologies used to create physical models, prototypes, tools or finished parts. All those phases and types of prototyping are totally managed in a virtual environment and the phase of making physical models is transformed into a rapid production process that returns the finished product. The use of parametric and generative modelling makes it possible to simultaneously study a series of possibilities or formal alternatives through algorithms and numerical data, replacing the analytical and modification phase that used to be carried out on different types of physical models. This, due to the possibility of writing the parametric definition (i.e., the ‘rules’ guiding its formal genesis) which, after specifying a series of dimensional, quantitative and topological optimisation parameters, will generate a virtually infinite number of design solutions.

The designer can then assess which design solutions returned by the generative software will be useful for the development of the project. The shift from rapid prototyping towards rapid additive manufacturing, an increase in the performance of the materials used, the continuous evolution of digital technologies and a relative reduction in time, has made it possible to increase the performance level of models, as expressed in Polato's interview with Ettore Sottsass “[…] drawing cannot give an exact idea: we need models that are as perfect as possible, as close as possible to the object, to its tactile, sensorial qualities.” [2]. Advanced tools (rapid production and advanced modelling) can cancel out those differences that previously characterised the quality and technical/physical performance of prototypes compared to products. Thus, the model made by additive manufacturing has, potentially, the same performance characteristics as a product made by an established productive technique (injection moulding, rotational moulding, etc.).

Within a few years, the technological development mentioned above allowed designers, through early experimentation, to understand the potential of rapid production tools and generative parametric modelling by producing the first experimental products (Fig. 2).

Fig. 2.
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Example of a timeline synthesizing the evolution from prototype to product

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Early research into the study of form, where the prototype begins to take on the value of the finished product, can be found in Nendo’s Diamond Chair for the 2008 Milan Design Week exhibition. Product made in rapid prototyping to highlight the positive aspects of the prototyping process. A few years earlier, the Finnish designer Janne Kyttänen, with his company ‘Freedom of Creation’, developed ‘manifesto products’ of a possible and desirable future, where objects would be manufactured through rapid prototyping processes. Ammar Eloueini's CoReFab product collection also epitomises the power of technological innovation in the field of rapid prototyping. The next step was, for the designer, to design using rapid production processes. The progressive advancement of technology has led to more affordable additive manufacturing processes, an increase in buildable volume in a single process and increasingly high-performance printable materials. Joris Laarmann's design methodology and products produced in rapid production in recent years are an example of this. A design development that utilises the potential of generative modelling, as for example in the ‘Aluminium Gradient Chair’, where the designer experiments with the use of a gradient map arranged over the entire structure of the seat to distribute, according to the areas that undergo different intensities of stress, a greater or lesser density of material from a solid starting volume. Features that limit the production of the product to rapid production technologies only. Similar principles can be found when analysing the production of the Mhox research group, where through projects and research they explore new production processes and technologies for design, with a focus on generative design and 3D printing for the innovation of wearable products. Manufacturers of additive manufacturing technologies, motivated by designers through early experimentation and the subsequent consolidation of rapid prototyping processes, have in recent years developed new types of materials for 3D printing. Performance materials that can withstand end-use applications, with performance comparable to the usual materials used in industrial production. The most significant example is the recent production of the companies Adidas and New Balance with their footwear collection. Soles or parts thereof are designed with complex, elastic and resilient lattice structures with energy return to increase walking comfort. Performance characteristics predicted and verified within the design process using digital generative modelling tools.

4 Conclusions

In the time chart of Fig. 1c, which defines the product development process through the implementation of generative parametric modelling and rapid production, there is an overlapping and merging of the phase of analysis and model selection with project progress, which are exclusively managed in the virtual environment. In addition, there is a possible shift from prototyping to rapid production, which will significantly shorten product development times. After analysing the role that the physical model has played in the past, as a tool to support the designer in the design process, and how today, thanks to new technologies, it has evolved, it is essential to highlight the transition that has taken the model or prototype from physical to virtual through a digitised prototyping process and simultaneously, through more efficient rapid additive manufacturing technology and the development of increasingly high-performance materials, to a transition of the ‘master model’ from model type to finished product. Furthermore, the “computational designer”, understood as the designer who governs the new digital technologies, will still need to be able to use the evolved physical model as a tool for tangible comparison and verification.