16 November 2012
Al Dean reports on a unique software tool that combines tolerance analysis with visualisation to give a good idea of the perceived quality of future products
|Company name||Icona Solutions|
Perceived Quality (or PQ) is a growing field in many industries, none more so than in the automotive field. It’s an internal battle, to offset the drive for manufacturing efficiency and cost against the need to produce the highest quality products.
In this context PQ refers to the study of the manufacturing and assembly tolerances and the way they influence the visual quality of the product. Can tolerances be fine tuned and assembly methods adapted to improve the quality of the product (according to fit metrics) across as broad a spectrum of the production run as possible?
In the automotive world, much of this perception of quality comes down to body and interior fitting — or gap and flush. To achieve the correct balance between manufacturability and final aesthetics, two things are required.
Firstly, you need to be able to evaluate exactly how parts and assemblies will appear under different tolerance conditions. Not as an idealised nominal model, but rather at all points in the variation of tolerances.
The second is that tolerance analysis tools are available to adapt the geometry of the parts to evaluate assembly schemes and tolerances assigned at attachment points.
Now, while there are a number of tolerance analysis packages and a larger number of photorealistic rendering systems out there, there aren’t any that bring the two together, apart from Icona Solution’s aesthetica, which we’ll be exploring in this review.
aesthetica has been developed to provide an environment in which the different teams engaged in PQ issues — concept design, styling, engineering design, manufacturing planning, quality, etc — can come together and discuss the multitude of issues around the subject in a single application.
While it’s been on the market for a number of years, the system has been redeveloped to bring a much more modern and easier to use set of tools, with a firm emphasis on the concept design phase of the product design to manufacture process.
Now based on the familiar Windows Ribbon style UI, the system sets out to provide a common tool for two overlapping workflows.
Setting the PQ targets
The first step in the process is the set-up of the model within aesthetica.
The system allows the importing of CAD geometry from a number of host systems (including Catia, NX, Alias, STEP and IGES). Once imported, the next step is to apply material appearances and properties to the various components.
To achieve this, the 3D viewing windows in the system use an interactive photorealistic rendering engine that allows everyone engaged in the process to view, inspect and evaluate how the product looks under different tolerance conditions. For aesthetica 4.0 this has been completely re-written.
Based on the latest Nvidia rendering techniques and shaders, the new rendering engine offers more accurate car paints (including metallic and pearlescent paints), more accurate glass (with full control over reflection and refraction) and new bump-mapped materials (with natural and technical grains).
In terms of rendering effects, the engine includes automatic depth-sorted transparency and supports ‘on idle’ rendering that progressively improves the anti-aliasing and shadow quality while users are not interacting with the 3D window.
On the subject of shadows, the system also now supports local and global shadows. The latter are also improved with the addition of support for HDR panoramic environments to represent lighting conditions - whether replicating a design/evaluation studio, interior or location shots.
These can be imported from standard .hdr files, identical to those used in Autodesk Showcase, RTT Deltagen, BunkSpeed Shot, etc.
As you might expect, the system is supplied with a wide range of materials, textures and other visual appearances in a library. These hold not only colour and light properties, but also detailed texture, bump mapping and reflection controls.
In version 3 these were linked to the physical material properties, so assigning one would automatically assign the default value for the other. In version 4 they have been separated allowing components to have the same appearance but with different mechanical properties.
For example, plastic bumpers and metal fenders that are spraypainted have the same appearance but different mechanical properties. When you consider the customisation options now available in the automotive world, it’s key that colour can be mixed.
Their influence on the aesthetic quality of the product needs to be studied. Therefore it’s key that the visual properties can be swapped in and out without changing the underlying mechanical properties.
The objective at this stage is to arrive at a 3D model that can be used to set perceived quality targets by testing out varying gap and flush conditions and visualising and measuring them against, say, the competition.
This is an aspirational process. It doesn’t involve the use of the system’s tolerance analysis tools, only its visualisation tools.
By enabling different gap and flush scenarios to be visualised it enables the concept design and styling teams to deliver realistic PQ targets into the downstream engineering design process, where tolerance analysis and stack-up will be required.
Defining the tolerance model
Once the targets have been agreed, the next step is to start to define the attachment points for all the geometry.
In the case of the automotive world, this usually relates to the points where body or interior components are attached to the vehicle structure.
This includes not only the spatial position, but also the type of attachment (drilled hole, slot etc) as well as initial tolerance conditions.
At this point, it’s worth talking about how the software handles geometry and its deformation (according to tolerance settings). aesthetica brings in the surface data and tessellates it.
Under the hood, the system can deform each of these surfaces as the user plays with the tolerances.
Each attachment point can have a range of tolerances, it’s key that the system can deform the surface according to its material definition. The system holds information for Young’s modulus and tensile strength.
With this information in place, the system can deform each part as it would in reality during the assembly process.
This gives the ability to gauge the effect of different materials, attachment schemes and tolerance settings and how they stack up at each point. While this isn’t unique, what is is the ability to gauge how the tolerances influence the form and fit of each component across its entire form, rather than purely at specific points of measure (see below).
One model - multiple points of view
As we’ve said, the goal of aesthetica is to enable both sides of the PQ fence — aesthetics and manufacturability — to evaluate not only the form of the product and how tolerance variation effects manufacturability, but also the resultant aesthetic quality of the part.
To be able to do so effectively, the system allows both sides to define their own measures and metrics — using their own standard processes and practices.
For the manufacturing engineer, this means that specific measures can be defined at the points required. The team has done a lot of work on making this process more efficient for the 4.0 release.
Whereas in previous releases it was not possible to do multiple selections, open context menus in the 3D windows or move components and navigate at the same time, this has all been resolved in the new interface.
The system now allows users to manipulate the view, select geometry, define sections, measurements and such with much more freedom.
Sections are perhaps key for the manufacturing engineer. These are now more flexible. As users select the section in the 3D view, an interactive 2D view of the section is also displayed.
Precise positioning tools allow sections to be defined normal or tangent to edges, snapped to and dragged along existing planes and edges, or moved by an exact number of units using the new 3D manipulator with snapping controls.
One of the key metrics in the automotive world is Gap and Flush. This refers to the gap between body panels and the flushness of the panels (i.e. how aligned they are).
aesthetica supports these measurements as well as point-to-point measurements, general difference measurements (for taper and side-to-side conditions) as well as closest point discovery tools.
For the stylist, concerned predominately with the visual quality of the product, aesthetica also allows the definition of different set-ups, different material sets, different lighting conditions and environments as well as specific camera views (viewing positions for digital vehicle audits) as internal processes require.
Of course, the model can be spun, rotated, zoomed on an ad-hoc basis either from a model centred or first person perspective, but support is also there for defining the specific views required such as sight-lines in the automotive world.
Once everything is set-up, it’s a process of defining tolerances, running them through a Monte Carlo analysis to generate the variation according to the tolerances and attachment points, and then visually evaluating the results.
It’s here that the system allows both teams to use their own specialist knowledge and terminology to find problem areas.
For example, at specific instances of a production run, tolerances could cause misalignment of panels, which has an adverse effect on the quality of fit.
Panels may be out of alignment or gaps might be too narrow (or indeed, too wide). aesthetica allows these areas to be found (either through visual identification or through specific points of measure), the relative damage to the aesthetic quality to be assessed and the root causes of the problem to be identified.
These results then guide subsequent adjustments to tolerances, method of attachment (for example, swapping a hole or a slot to allow adjustment) or materials and further analysis to fix the problems.
Of course, while much of this process is done in the software, reports are going to be required to document the results and to action changes. aesthetica has built-in reporting tools that can combine statistical data with sections as well as a photorealistic 3D images and animations.
The format is fully customisable and can be adapted to organisational standards.
aesthetica isn’t a tool for everyone engaged in design and it’s adoption at the moment is pretty heavily skewed towards the automotive industry.
That said, the company has been working on pilot and consultancy projects with a number of other industries, from consumer white goods through to heavy-duty industrial machinery engineering.
What is interesting is to consider what connects all these companies and their reason for using the system. Let’s think about it. You have mass production, often with incredibly complex components that
involve a fair amount of assembly work.
The same is true of dishwashers or an industrial excavator as it is of automobiles. But what is also common is a heavy amount of configuration and customisation options available to customers and/or model variation across common platforms.
Then there’s a need for quality. While suitability for purpose is one aspect of manufacturing quality, another is how the product is perceived.
Whether that’s in terms of matching customers’ expectations or in projecting a certain level of quality associated to a brand. In the automotive world, certain brands’ customers have expectations in fit and quality.
A misaligned gap around the boot lid isn’t going to fly when you’ve just shelled out 80 grand for a car. Similarly, if you’re investing in heavy duty construction vehicles, then the product needs to appear strong, reliable and worth the investment.
aesthetica is unique in today’s market as it allows all those involved in the design, engineering, manufacturing and assembly process to engage in the process in a single tool. While there are point solutions available that solve parts of the process, this is the only software that combines everything into one package.
Both manufacturing and styling teams can evaluate a potential product, find problem areas, solve issues and effect change - and of course, document it. It’s not for everyone, but for those with the issues we’ve discussed, there’s nothing else like it out there.
Visualising how tolerances affect an entire part
When one of the major automotive OEMs was experiencing unacceptably — and unexpectedly — high levels of rejection of cars at final inspection, the use of aesthetica uncovered the previously undetected reason.
The problem they were experiencing was with the trim around the wheel arch. This was buckling and bowing on as many as one in five of the cars coming off the assembly line.
Numerical analysis of the trim’s locator scheme positional tolerances hadn’t shown up any problems. According to the tolerance analysis, the positional variation of the locators was within the agreed limits.
So was the problem caused by a design fault, a manufacturing fault or a supplier fault?
At the OEM’s request, Icona Solutions performed an analysis of the problem area. Using aesthetica, the trim’s locator scheme and its tolerances were applied to the 3D model of the appropriate area of the car in aesthetica and a Monte Carlo analysis was performed.
The results showed, visually, that while the locators were within tolerance, as shown in the numerical analysis, the problem was occurring between them because of the way the slots on the trim itself had been designed.
As a result, the OEM was able to make a small design change in future vehicles to overcome the problem — and saved over $100,000 a year on fault rectification.