QMT Features: March 2009
A better way to inspect
Digital engineering technologies helps mass production manufacturers, such as 3M, reduce variation and speed inspection processes.

What do you do when you have a number of mould tool-sets being used continuously in the mass production of one particular product and you’re getting variation in the final products coming out of the manufacturing process?

One answer, if you happen to be located in the north east of England, is to contact the Digital Factory team at the Institute for Automotive and Manufacturing Advanced Practice (AMAP) at the University of Sunderland. That’s precisely what Fraser Shearer, senior manufacturing technologist at 3M’s factory in Newton Aycliffe did recently – and found the solution to his quality problem.

Digital Factory is a training and technology transfer project focused around digital engineering technologies. It is designed to help organizations in North East England, from local SMEs to multinational manufacturers who are involved in product design, production, plant engineering or procurement, to effectively apply today’s digital technologies in order to improve their competitiveness.

The project is delivered by AMAP - a department of the Faculty of Applied Sciences at the University of Sunderland in the north east of England - and is funded by One NorthEast, the area’s Regional Development Agency. Digital Factory project manager, Alan Stafford, explains, “The Digital Factory project acts as a focal point for digital engineering solutions, where firms can access standard industry and software/hardware vendor CAD/CAM/CAE training, supporting e-learning material and short courses through to university-accredited courses and work-based training..”

Among the technologies in use in the Resource Centre is Geomagic digital shape sampling and processing (DSSP) software in the form of Geomagic Studio digital reconstruction and surface modelling software and Geomagic Qualify computer-aided inspection software. It was the use of Geomagic Qualify by the Digital Factory team that enabled 3M to overcome its problems.

Trouble-shooting quality problems
The project undertaken by AMAP Digital Factory for 3M provides a good example of the benefits that today’s DSSP technology – and in particular in this case – the benefits that 3D optical scanning and computer-aided inspection can bring to metal or plastics products manufacturing in general.

DSSP is a category name that encompasses the convergence of multiple technology advances.  It describes the ability to use scanning hardware and processing software to digitally capture physical objects and automatically create accurate 3D digital models with associated structural properties for downstream design, engineering, rapid prototyping, inspection and custom manufacturing.

The AMAP Digital Factory team uses DSSP in the form of Geomagic Studio in the front-end of the digital engineering and manufacturing process, when usable design data is created where none existed beforehand and in the form of Geomagic Qualify for first-article and in-process quality inspection during the manufacturing process.

However, as Sajid Abdullah, lead consultant with Digital Factory, explains, “We don’t undertake commercial work. Each individual project, like the one we undertook for 3M (see 3M case study below), is intended to provide a ‘proof-of-concept’ to a client and to indicate ways in which that client could use digital engineering technology to overcome similar problems in future. However,” he adds, “by doing this we do provide the client with a solution to the original problem he came to us with.”                                                                                                                                                                                                                                                   
Case study - 3M
At its production facility in Newton Aycliffe, County Durham, 3M, the global diversified technology company with well-known brands such as Scotch, Post-it, Scotchgard, Thinsulate and Scotch-Brite, manufactures face masks and respirators used in industry for worker health and safety.

3M was experiencing quality problems in the production of a particular model of face mask, with unacceptable variations occurring in the masks coming off the two injection moulding production lines that they were running continuously. They had tried swapping over the different mould tool-sets being used from one machine to the other but the problem still occurred. However, it wasn’t at all clear if there was a problem with the process or with the mould tool-sets themselves, which had been manufactured by two different suppliers.

Fraser Shearer, senior manufacturing technologist at 3M, therefore decided that the tool-sets should be inspected to see if the problem lay with them. However, using traditional inspection methods it would have taken as long as three weeks, at considerable cost in terms of lost production, to inspect the multiple mould tool-sets involved. So he contacted the Digital Factory team to see if there was a quicker and better way of inspecting them.

“Traditional inspection methods, using a coordinate measuring machine (CMM), require that dimensioned 2D drawings of a part are produced from the 3D CAD model”, says Shearer. “Using individual point measurements collected by the CMM at specific points on the part, these drawings enable the part to be inspected for any deviation from the nominal as defined on the drawings. It can be a long and laborious process and even then, only a selection of points on the part can be inspected,” he explains.

The Digital Factory team used Geomagic Qualify computer-aided inspection software, together with a 3D optical scanner, on the 3M project instead.

Faster results with DSSP
Geomagic Qualify takes advantage of DSSP technology to enable fast, easy-to-understand graphical comparisons between 3D CAD models and as-built parts, or between parts from different production runs.  It saves time and increases accuracy for first-article and in-process inspection and enables trend analysis, 2D and 3D dimensioning, geometric dimensioning and tolerancing (GD&T) and automated reporting in a variety of formats, including Microsoft Word, Microsoft Excel, PDF and VRML/HTML.

“The problem that 3M had was compounded by the fact that, not only were there multiple sets of mould tools, one of which seemed to be performing to specification, but there were also multiple versions of the CAD model,” explains Abdullah. “We therefore decided that, rather than using a 3D CAD model as our reference for the inspection process, as would normally be the case, we should use the mould tool-set that appeared to perform to specification to create a ‘master’ digital model and use that data as a reference for inspecting the others.”

The tool-set, with its doubly-curved surfaces, was scanned with the Digital Factory’s Z-Corp optical 3D scanner and the resulting point cloud data, accurate up to 0.05mm, was exported directly into Geomagic Qualify where, after registering and processing the scans, it could be displayed as a faithful 3D scan data model of the original physical mould tool.

With that digital model of the tool-set established as the master, the other tools were then scanned and with the data imported into Geomagic Qualify, the resulting scan data models could be compared and measured against the master model, using the ‘best-fit’ process. The results showed up – graphically, through colour maps of the parts that showed variations from the nominal in the plus and minus directions, together with numerical values – the defects in the tools that had been causing 3M its production problems.

“Using this process enabled us to complete the 3D measurement and inspection of the tool-sets in two days and without any factory down-time,” states Shearer.  
However, that wasn’t all. In addition to the visual comparison, the Digital Factory team also used Geomagic Qualify to take sections through the doubly-curved surfaces of the digital models of the mould tools and generated a series of 2D profiles. These were saved as DXF files and passed to 3M to enable them to compare the profiles of the master tools-set with the different versions of their CAD model to determine the correct version.

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