CAD modeling

Look up in the sky, it’s CAD software

May 14, 2020 By Leslie Langnau Leave a Comment

A major CAD vendor is betting the modeling software’s future is in the cloud

By Jean Thilmany, Senior Editor

Onshape set off ripples across the computer-aided design community five years ago when it announced its computer-aided design software would exist completely in the cloud. Last fall, PTC acquired Onshape.

The purchase signals PTC’s conviction that engineering companies are ready to embrace CAD in the cloud. The SaaS model, while nascent in the CAD and PLM market, is rapidly becoming the industry’s best practice across most other software domains, said Jim Heppelman, PTC president and chief executive officer.

By bringing Onshape in-house, the software maker has placed itself ahead of the pack in what the engineering software maker sees as the inevitable industry transition to SaaS, Heppelmann said.

“Today, we see small and medium-sized CAD customers in the high-growth part of the CAD market shifting their interest toward SaaS delivery models, and we expect interest from larger customers to grow over time,” he said.

In the future, CAD sellers may reach unique arrangements with resellers to bring CAD in the cloud to a wider user base, according to one potential reseller.

But PTC isn’t going all-in with the cloud. It will continue to offer its on-premise CAD software, Creo.

With CAD in the cloud, designs reside on the software provider’s secure server —rather than on individual workstations. Because the software is accessed and managed online, engineers and designers can work on their models from any location and on any device. The SaaS refers to a provider’s capability to deliver everything needed to run CAD in the cloud—including the cloud infrastructure and the CAD software itself.

Though other CAD makers do offer some type of cloud capability, it’s generally the capability to check files into and out of an application on a cloud-based server; engineers don’t design directly with cloud-based software on other applications, said Jon Hirschtick, president of SaaS, PTC. Onshape differs in that its software exists fully in the cloud and can be used by multiple users in real-time, he added. (Hirschtick founded SolidWorks in 1993 and then went on to co-found Onshape with another former SolidWorks chief executive officer, John McEleny.)

The everyday cloud
You’re already using cloud technology. That’s almost certain. If you have an email account ending in gmail.com or yahoo.com, if you’ve checked a social media account from your desktop or mobile device, if you’ve streamed a movie via Netflix or Amazon or any other provider, you’re a cloud user. The email, social media, and streaming software exist on the software owner’s server (let’s say Google), as does your little piece of it—like your Gmail email address.

Though it’s been possible to run CAD as a SaaS for the past few years, CAD has always been slower than other large, graphic-intense and complex applications to pivot to new platforms, says Len Williams, content manager at designairspace, which gives engineering companies the capability to run any CAD system in the cloud.

“Last year’s acquisition is a very clear statement that vendors like PTC see cloud as a platform of the future for CAD and for all their other software,” Williams added, calling the acquisition a “Windows-level” move.

“CAD systems were originally based on UNIX running on silicon graphics workstations. Then Windows came along and people were laughing at the thought of using CAD on Windows,” he says. “Now most of the major CAD systems run only on Windows.”

Likewise, the way companies buy their CAD software has evolved, he said.

“We went from the old perpetual model, where you buy the software for a workstation, to today’s subscription-based model, where you rent the software,” Williams said. “The next step is when a CAD vendor is running it for you so don’t have to buy hardware or worry about upgrades.”

Large companies already run CAD in the cloud because of the benefits the delivery method offers, Williams added. The difference is, those companies—the French automotive manufacturer PSA Peugeot Citroen is one example—have the funds to build their own, private clouds. Designers, engineers, and suppliers at those companies can access CAD on the private cloud whatever their location: Tulle, France; Brussels, Detroit, or elsewhere.

Working remotely and sharing with suppliers
For the smaller guys, the cloud can bring the same benefits their larger counterparts already enjoy; mainly real-time working together and version management, Hirschtick said.

“Versioning” is built-in, which means file changes are tracked in a central database in real-time. Because any engineer with permission can access the software from any device with internet connection, engineers in different places can work together on a design, such as a power supply, for example. There’s only one power supply file; Onshape doesn’t copy it. But with cloud, everyone in the world accesses real-time single source of truth database. We’re not passing around copies all over the place, he added.

“If multiple engineers happen to be working on that file at the same time, it’s not a problem. If one engineer rounded a corner and another one drilled a hole, both changes get captured,” Hirschtick said. “If we’re both rounding a corner at the same time, you would see my hand there in real-time—at the same table—and a box around the corner would indicate that another engineer is editing that right now.”

The bigger the team is, the quicker the product development process, as everyone—even suppliers—has visibility into the real-time database rather than a copy of something emailed a week ago.

When the workflows are quicker, engineers have more design time and are more willing to innovate to try new things, he added.

Most cloud service providers automatically update their programs. Thus, IT staff can focus on other tasks and engineers know they are working with the latest version of the applications.

Also, engineers aren’t bound to their workstations. The software exists at one central server while engineers work from many. They can be globally dispersed and can work from home or other locations outside the office.

Smaller companies that scale their workforce and supplier base up and down as projects change also stand to benefit from SaaS CAD software. When suppliers move away from a project, the company can easily suspend their CAD license and use of the CAD system, Williams said.

When the coronavirus began making headlines in early 2020, engineering companies running one Onshape customer with offices in three major Chinese cities particularly welcomed the remote-work capability, Hirschtick said.

“Using Onshape analytics, they showed us where people were working before the virus situation in China,” Hirschtick said. As expected, employees worked at the offices in the three major cities.

“Then they showed a map of activity of first two weeks of virus quarantines and lockdowns in China,” he added. “This time there were 20 little circles in regions all over in China. They could see where their employees logged in remotely.

“It doesn’t matter if employees are caught at home with only an Android tablet, they can still do their work,” Hirschtick said. “Even with the phone they can even do some of their work.

There are cases where running CAD in the cloud just doesn’t make sense. Some companies may use CAD only a small amount of time and will do better essentially renting a CAD program, perhaps through the cloud, Williams said.

With cloud-based systems, issues of total cost of ownership and return on investment are generally murky because companies want to see how cloud applications compare to traditional on-site infrastructure.

“But there are so many intangibles wrapped up in the cloud that it makes it hard to put calculations on it,” said Andrew Sroka, CEO at Fischer International Systems, which helps companies manage identities for on-premise and cloud-based applications. “It’s important to factor in expenses like utility costs and power requirements.”

If you can’t buy, rent
With CAD in the cloud being not if, but when, designairspace has new ways to bring benefit to users and CAD makers; reselling vendor software in the cloud. The company would offer customers workstations with major CAD vendor’s programs already installed. Designairspace can track use, which allows the vendors to charge based on time spent using the programs.

“It would be just like mobile phone plans back in the day, where you buy a plan based on minutes. We can do this with CAD in the cloud,” Williams says. “Let’s say you buy a plan with 500 minutes. If you need it for only one or two days a week, you can buy it in a small, affordable plan that’s a small portion of what it would cost you to buy the software.

“Why limit CAD-in-the-cloud to large companies? In the olden days, only big companies could afford 3-D CAD systems. We want small companies to have cloud benefits,” he added. “They would still need to buy their own licenses, but at least they can run it in the cloud, like the big guys.”

The pricing model would benefit companies with project managers or suppliers who don’t design in CAD but log onto the program intermittently.

“These people use the software only a little bit at a time, so we can price it so it’s not so expensive for them,” Williams said. “This is a whole new market for major vendors.”

Becoming a CAD-in-the-cloud reseller and offering online training in those CAD programs is the “next step” for designairspace, he added. With the business model, potential customers can also receive on-the-spot, specialized training if needed and can test the software to see if it’s right for their needs before buying a priced plan, he said.

Or, engineering companies might choose to run hybrid CAD, in which they host some CAD systems at workstations on-premise and buy CAD in the cloud subscriptions for intermittent users, Williams said.

“That way you can gradually move more and more users to the cloud. You can move one or two and see if it works and if it does move more to the cloud,” Williams said. “The heavy users will never move to the cloud.”

That brings up another point. Workstations that run CAD will always be with us, he added.
Companies that do work for the defense department or for the military must do their engineering work on company workstations. They cannot work remotely, Williams said.
For his part, Hirschtick is dreaming big. He expects widespread cloud adoption for CAD as users begin to see the advantages.

“People think cloud tools don’t have the power or speed but that’s an old fable. Cloud tools have more advantage and speed, it’s not a fair fight,” he said. “With desktop tools, you have one CPU sitting on the desktop. With the cloud, we’re able to use unlimited amounts of CPUs. I gave a demo and opened up ten models with thousands of thousands of parts on Macbook in Chrome on a web browser. There’s no CAD workstation that could open them that fast, even the best desktop configuration.

“In a few years, people will be saying ‘how did you ever do CAD on a desktop. How was it fast enough?’” Hirschtick says.

While the future remains cloudy, PTC is backing clearing skies for CAD in the cloud. With a large CAD maker backing SaaS, expect to see a flurry of news and updates. In other words, don’t delete your desktop program.

PTC
www.ptc.com

Designairspace
www.designairspace.com

Implicit modelling for complex geometry

February 3, 2020 By Leslie Langnau Leave a Comment

Implicit modelling is enormously powerful and offers huge potential for engineering design. It is currently ready to apply in specific modelling tasks involving complex geometry. It is not yet clear whether it will be possible to fully implement it within the familiar parametric design environment, with constraint-based sketches used to define geometry. If not, it may remain a specialized tool.

Dr. Jody Muelaner, PhD CEng, MIMechE, Muelaner Engineering Ltd

Additive manufacturing enables the production of highly complex geometries such as repeating lattice-like structures and organic shapes. This design freedom can improve performance in terms of weight, stress, fluid flow and heat transfer. However, modelling, editing and processing complex geometry files is challenging for the established CAD software. Let’s look at how implicit modelling can solve these problems as well as the challenges still remaining to integrate it into the design workflow.

The problem with current CAD software
If you’ve ever tried modelling complex lattices in a typical CAD program, such as SolidWorks, you’ll know this is extremely challenging. When models have large numbers of features, the file sizes and rebuild times increase exponentially. Conventional CAD programs can also have difficulty with apparently quite simple models if they have features such as two fillets that overlap. When high feature counts are combined with these types of challenging geometry, model rebuilds become painfully slow at best and all too often they simply fail.

The problem is the fundamental way that geometry is represented. All the major CAD programs use boundary representations (b-reps) to define solid geometry. B-reps use topology, such as vertices, edges and faces, which are defined by geometry such as points, curves and surfaces. For example, an edge is a bounded region of a curve and a face is a bounded region of a surface.

B-reps work fine for relatively simple geometry. Older CAD programs sometimes used Boolean operations to combine primitive objects such as cubes and spheres. B-reps are much more versatile, allowing profiles to be swept and lofted, solids to be shelled and so forth. However, when features are combined with fillets and blends, or large numbers of features are included, calculating the topology becomes exponentially more demanding on the computer. Many modelling operations involve combining simpler shapes with Boolean and blending operations. B-rep modelling has to calculate all of the new edges that are formed where faces intersect. For objects with planar faces the individual calculations are relatively simple, but the number of intersections increases by approximately the square of the number of faces. For intersections between curved surfaces the edges are complex splines, making the calculations considerably more complex. When faces are close to tangent, things get really difficult.

Another issue with B-reps can be determining which points in the model are inside the boundary – the solid material. The method is to shoot a ray from the point in an arbitrary direction. If the ray passes the boundary an odd number of times then the point is inside the boundary. If the ray passes the boundary an even number of times then the point is outside the boundary. Since floating point arithmetic is used, rounding errors may mistakenly count boundary crossings when the ray is close to the boundary. There are also ambiguities such as when a ray is tangent to a surface or passes through a vertex – it is not clear whether this counts as a boundary crossing, or as two crossings. Because of these issues, additional checks are required to ensure that b-rep modellers are robust. This makes them mathematically inefficient.

The mathematical simplicity of Implicit Modelling
Implicit modelling is a far more efficient way to model geometry. It doesn’t explicitly calculate any edges or vertices. Instead, a single mathematical function of x, y and z is used to describe a 3D solid. Consider the simple example of a cuboid centered on the origin.

A cuboid can be defined by the implicit function. Any point on the boundary gives a function value of zero, negative values are inside, and positive values are outside, which makes the determination of whether a point is inside or outside simple.

This cuboid can be defined by the implicit function:

F_A(x, y, z) = max(|x| – 4, |y| – 1, |z| – 1)

Any point on the boundary gives a function value of zero, negative values are inside, and positive values are outside. Determining whether a point is inside or outside is therefore very simple. There is no need to try to count how many times a ray crosses the boundary. Small floating-point errors will give the wrong answer only if the point is infinitesimally close to the boundary.

Performing Boolean operations to combine implicit geometry is also very mathematically simple. Consider two solids being added together in a Boolean union. For a point P to be within the combined solid, at least one of the two implicit functions must evaluate to less than zero. The combined implicit function is, therefore, simply the minimum of the two functions.

Imagine that a sphere, centered on the origin and with a radius of 2, is added to the cuboid.

Performing Boolean operations to combine implicit geometry is also mathematically simple. Consider two solids added together in a Boolean union. For a point P to be within the combined solid, at least one of the two implicit functions must evaluate to less than zero. The combined implicit function is, therefore, simply the minimum of the two functions.

The implicit function for the sphere is:
F(subsetB) (x,y,z) = √(x^2 + y^2+ z^2 ) – 2
The implicit function for the combined solid is simply the minimum of the implicit functions for the two shapes:

F_C(x, y, z) = min(F_A, F_B)

This simplicity of calculating geometry means that complex fillets and blends can be created reliably, and highly complex models rebuilt almost instantly. The below image shows fillets where a lattice joins a ring. The fillets overlap in a way that would probably fail in most CAD systems, but they have been easily created using nTopology implicit modelling software.

Implicit functions can also give a feature’s distance from the boundary.

Distance fields – a powerful feature
Another really useful property of implicit functions is that they actually give the distance from the boundary. A good way to understand this is to simply try some values in the function for a cuboid, used in the example above:

FA(x, y, z) = max(|x| – 4, |y| – 1, |z| – 1)

The smallest value that this function can take is -1. This occurs for points down the centre of the volume. There is no upper limit to the value it can take, since you can travel infinitely far once outside it.

Implicit functions make it easy to calculate a distance field either inside or outside the boundary of any solid geometry. This makes it very easy to perform shell operations and you can even create shells with varying wall thickness.

Implicit functions make it really easy to calculate a distance field either inside or outside the boundary of any solid geometry. This makes it very easy to perform shell operations. It is even possible to create shells with varying wall thickness.

Because implicit geometry is defined as a field, it can be modified by other fields. This enables highly efficient merging between different geometries, to create features similar to fillets. It is even possible to modify a geometry field using some other property, such as a stress field generated from an FEA study. In the below example, nTopology has been used to modify the diameters of beams in a simple diamond lattice, with the diameter increasing as the stress increases. It is also possible to do this with shelled solids, so that the wall thickness depends on stress. This can be a powerful method of optimizing structures that, unlike generative design, works well with cast or injection moulded components, as well as additive manufacturing.

In this example of implicit geometry, the software program nTopology was used to modify the diameters of beams in a simple diamond lattice, with the diameter increasing as the stress increases. It is also possible to do this with shelled solids, so that the wall thickness depends on stress. This can be a powerful method of optimizing structures that, unlike generative design, works well with cast or injection moulded components, as well as additive manufacturing.

Implementation of Implicit Modelling

A number of commercial software companies are offering implicit modelling packages. The field is currently dominated by smaller specialized providers such as nTopology, which has a suit of capabilities for working with complex geometry. Another notable start-up, Gen3D is currently focused on modelling flow paths for applications such as manifolds and heat exchangers such as the one shown below. The big players in the CAD world, such as Autodesk and PTC have started acquiring start-ups in order to gain access to this technology. Autodesk recently announced their Volumetric Kernel for Fusion360 which, it is claimed, will enable implicit modelling to be fully integrated within a parametric design workflow.

A number of commercial software companies are offering implicit modelling packages. One notable start-up, Gen3D, is currently focused on modelling flow paths for applications such as manifolds and heat exchangers.

At the moment, however, it is not possible to work directly with implicit models within any mainstream CAD system. Specialized implicit modelling software is instead focused on creating the complex geometry that conventional CAD struggles with. For example, you might import an initial design from your standard CAD package and then perform operations such as creating complex lattices, shelling complex components or creating intersecting fillets.

The most obvious application is for light weighting structures using lattices for additive manufacturing. However, there are many other potential applications for complex geometry creation such as cast components with complex fillets and variable thickness shells. Many industrial designers are taking advantage of the capabilities to produce decorative grills. Implicit modelling software such as nTopology makes it extremely easy to create these types of geometry.

Stress analysis using Finite Element Analysis (FEA) can also benefit hugely from implicit modelling. One of the most time-consuming parts of analysis can often be cleaning up the geometry created by CAD software. Because b-rep modelling creates edges where any surfaces meet, there can often be thin sliver geometry at intersections and fillets. This can make even relatively simple parts difficult to mesh with high quality elements. Implicit models don’t have any of these issues giving the potential for painless creation of high quality meshes. This can, however, create its own issues as discrete surfaces may be needed to define boundary conditions. B-rep surfaces are therefore sometimes imported from CAD to enable boundaries to be defined.

Gyroids and Triply Periodic Minimal Surfaces
Triply periodic surfaces are an interesting type of geometry that is relatively new to the world of manufacturing, although they have been known to mathematics since the 19th century. These surfaces repeat in each of three dimensions, similar to conventional arrays. However, the arrays of intersections between each element are often problematic, with fillets at each interface quickly making models unmanageable. With triply periodic surfaces, there are smooth transitions between each repeating element, with the entire surface defined by a single implicit function.

Triply periodic surfaces are a type of geometry that is relatively new to manufacturing, although they have been known to mathematics since the 19th century. These surfaces repeat in each of three dimensions, similar to conventional arrays. However, the arrays of intersections between each element are often problematic, with fillets at each interface quickly making models unmanageable. With triply periodic surfaces, there are smooth transitions between each repeating element, with the entire surface defined by a single implicit function.

Within mathematics and the natural sciences, there is particular interest in triply periodic minimal surfaces (TPMS) which are minimal surfaces as well as being triply periodic. This means having zero mean curvature. Although structures used within additive manufacturing may be TPMS’, it is generally not important whether or not they are minimal surfaces.
Because triply periodic surfaces can be defined by a single implicit function, they can easily be combined and blended with other implicitly defined geometry. They can also be modified by other fields so, for example, they adapt to stress, fluid flow or heat transfer requirements. These properties can make them enormously powerful from a modelling perspective. They also have many interesting mechanical properties although understanding these properties is still very much an area of active research.

Robust modelling enables greater reuse
One of the benefits that nTopology is stressing is something they call their notebook. This is a way of recording the process used to create geometry, very much like the feature tree in parametric CAD. Variables can be changed and references to external files updated, before replaying the process. This can enable workflows and best practices for capture, reuse and refinement.

While nTopology’s notebook is conceptually similar to a parametric feature tree, the increased robustness of implicit models should make it more useful. While parametric model templates work well for simple standard parts, they are often unreliable for more complex products. This is often because topology such as vertices and edges are automatically created and assigned ID’s while the geometry is being constructed. When changes are made that affect the way features intersect, especially where fillets are involved, the number of vertices and edges may also change, resulting in different ID’s being assigned. Features that reference this topology therefore lose their references and the model fails. The designer is often faced with a choice between a lengthy debugging process and recreating the model from scratch. Implicit modelling doesn’t depend on these topology references and is therefore unlikely to fail when variables are changed. However, if b-rep geometry is referenced underlying topology may cause workflows to fail because of this dependence.

Thus, implicit modelling is enormously powerful and offers huge potential for engineering design. It is currently ready to apply in specific modelling tasks involving complex geometry with the potential to be fully implemented in the familiar parametric design environment.

Muelaner Engineering Ltd
www.muelaner.com