While digital twinning is a relatively new phenomenon, one of the early adopters of the physical ‘twin’ concept was NASA, where a full-scale mock-up of the early space capsules were used on the ground to mirror and diagnose problems in orbit. The physical eventually gave way to fully digital simulations. The digital twin provides a representation of a physical object or system. Today, the technology behind digital twins has expanded to include large complex items such as buildings, factories and even cities, and some have said people and processes can have digital twins. In the aerospace manufacturing arena, independent CNC machine tool simulation and optimisation software, VERICUT, is leading the way.
Of course, many advanced engineering businesses closely followed the National Aeronautics and Space Administration’s lead, with civil and defence aerospace OEMs and their tiered supply chains adopting the principles behind the digital twin. In essence, a digital twin is a computer program that takes real-world data about a physical object or system as inputs and produces, as outputs, predications or simulations of how that physical object or system will be affected by those inputs.
So, digital twins can be used to predict different outcomes based on variable data. The more accurately a digital twin can duplicate the physical object, the more likely that efficiencies and other benefits can be found. In manufacturing, where the more highly controlled devices are found, digital twins can accurately simulate performance over time, which could help in predicting future performance and possible failure.
While its output is a physical object, manufacturing inevitably begins with data during the CAD design phase. That data is communicated to CNC machine tools via CAM software to execute designs — the transition point between the digital and physical worlds. As a simulation and optimisation solution, VERICUT bridges the CAD-to-CAM-to-manufacturing sequence. The software ensures that the NC machine will behave as expected by the programmer and that the manufactured component will accurately reflect the target CAD model.
Twins in aerospace
Supporting the global aerospace industry, CGTech has VERICUT users that manufacture airframe, propulsion, control surfaces and interiors for both the civil and defence sectors. For most, CAM covers every step of the manufacturing process, including the engineering master model of the component, stage definitions associated to each operation, fixturing and tooling, cutting tools, the NC toolpath and set-up information. The ‘digital twins’ of each element allow the engineering teams within the companies to test and prove processes in a virtual environment before they are applied – error free – to the real world. With OTIF (On Time In Full) being a key performance indicator for many, it is not unusual for 90 per cent or more of the machine tools used to be fully simulated.
CGTech Ltd. Managing Director, Tony Shrewsbury, states: “We know from project experience with various customers that complex components will require upwards of 400 digital twin models to truly match the virtual to actual world, including the machine tool, manufacturing stage models, tooling and fixtures and so on.
“We know that combining CAD/CAM systems and VERICUT will provide significant benefits. Even though the process of creating the virtual elements required takes time, most engineering departments can save hours by having a digital twin and using the verification capabilities of VERICUT. As well as efficiency gains in the machining cycle times, which will reduce the need for overtime, it also eliminates the risk of damages from collisions.”
It’s not just the cost of the machine tool repair and the potential scrapping of the workpiece, any collision damage will also have a detrimental effect on the delivery schedule that aerospace suppliers work to with their customers. “Any damaged machine tool is a loss of production capacity and trying to find an alternative manufacturing resource within a production process that is already fully booked can be rather difficult. It could have a negative impact on the timeline between the assembly line and the customer receiving the finished product, which is protected by contract stipulations with penalties for delay,” Tony Shrewsbury points out.
He adds: “By using VERICUT all machine tools can perform virtual production tasks for testing and approval while actually producing high end components. It can help manufacturers meet the challenges from the OEMs. Using CAD/CAM and VERICUT they can improve efficiency and ensure productivity, which helps them achieve the delivery promise to the end customer.”
A further benefit of VERICUT’s application of digital twins for the aerospace industry comes its ability to face the ongoing cost down and value definition challenges that the sector has. The Pentagon’s scruntiy of the Lockheed Martin F-35 programme being typical of the pressures faced by both civil and defence aerospace suppliers.
Since the company was founded in 1988, CGTech has been developing NC code simulation with its VERICUT software. By simulating the manufacturing process, it is possible to produce a cutting toolpath that is collision-free and, therefore, more efficient and ultimately cost-effective.
Focusing on smart factories, the term ‘Industry 4.0’ was revived in 2011 with the term ‘digital twin’ being coined a year or so later. By that time, VERICUT software had been providing digital solutions, specifically the simulations of machine tools and the digital processing of components in the virtual environment, for over a quarter of a Century.
At the time the software was launched, CGTech founder Jon Prun implemented in a small way what is today the common paradigm of the manufacturing industry: the merging of the physical and virtual world. VERICUT can simulate every CNC machine regardless of the manufacturer, and the necessary interfaces to integrate VERICUT into the specific CAD/CAM software manufacturing environment are available. All necessary data such as raw part, finished part, NC programs, fixtures, tools and zero/datum points are transferred to the CNC machine ready for production.
It’s important not to be too simplistic when creating a model for a digital twin as accuracy counts, and to be selective in choosing where to begin. CGTech encourages customers to consider these steps:
Imagine. Think about which products or processes could benefit most from having a digital twin. Good candidates typically have two characteristics. First, they are valuable enough to justify the investment. And second, there are unexplained process- or product-related issues that could potentially unlock value for either the end customer or the business.
Identify. After creating a shortlist of potential application scenarios, assess them for suitability for a pilot test, taking operational, business, and organisational factors into account. Good examples include products or components that have high variability in the manufacturing process, require tight tolerances to meet design criteria, and/or are produced from challenging materials. It can be a good idea to focus on families of parts with the potential to scale up the benefits.
Pilot. Consider moving quickly into a pilot programme using iterative and agile cycles to accelerate learning, manage risk proactively, and maximise return on initial investments. As soon as that initial value has been delivered, it is crucial to communicate it to the whole business operation.
Scale. Once successful, identify opportunities to use the digital twin. Target adjacent or interconnected processes. Use lessons learned and tools, techniques, and experience developed during the pilot to scale up. It is also important to continue to communicate the value realised to the business.
Measure. Identify the tangible benefits in cycle time, yield throughput, quality, utilisation, incidents, and cost per item, for example. Make changes to digital twin processes iteratively and optimise the configuration.
Success on a digital twin journey will depend on the ability to demonstrate increasing value for the business over time. Ultimately, it may lead to integrating the digital twin into the complete organisational structure — from R&D to sales — as well as continually leveraging the resulting insights to change how the company conducts business, makes decisions, and creates new revenue streams.
As stated, accuracy is vital and the recently launched Force Optimisation module within VERICUT strengthens further the links between the virtual and real world. “Force software uses a physics-based optimisation method to determine the maximum reliable feed rate for a given cutting condition based on four factors: force on the cutter, spindle power, maximum chip thickness, and maximum allowable feed rate,” explains Tony Shrewsbury. “It calculates ideal feed rates by analysing tool geometry and parameters, material properties of the stock and cutting tool, detailed cutting tool edge geometry, and VERICUT cut-by-cut contact conditions.
“Force excels in difficult to machine materials, and especially complex multi-axis cuts such as 5-axis flank milling. Founded on the basics, it is easy to set up and really easy to use. After materials have been characterised they can also be applied to a broad range of cutters and machines in other NC machining operation.”
Initial users of this technology are already seeing productivity improvements of up to 50 per cent. Tony Shrewsbury concludes: “We can demonstrate exactly what Force can do and the benefits of using it, including reduced development time, shorter cycle times, less process variation, longer machine life and improved part quality. It can also prevent tool breakage due to deflection. Force software provides another link between the digital and actual workshop.”