Dave O’Leary, quality director, Accumold
It is well-understood that a micromoulding project is far more likely to be successful if the customer seeks out a vertically integrated micromoulding company; that is to say one, such as Accumold, that is able to undertake all aspects of a project in house, from the design for micromoulding (DfMM) assessment, to steel mould tool design and build, automation design and build, automated visual inspection design and programming, micromoulding, steel mould tool and part measurement, and micromoulding process validation. A vertically integrated micromoulding company is able to react quickly and in an agile way to product development changes because there is no need to rely on a third party or series of third parties.
Measurement should be a central consideration in every quote issued by a micromoulding company. If they can make the steel mould tool and subsequently mould the part, sure as night follows day, it needs to be measured. As such, process development and qualification (and this includes measurement development and qualification) must be included in any customer quote. Measurement development time and gauge repeatability and reproducibility (R&R) are vital and extremely valuable to micromoulding customers.
A micromoulding company should work closely with the customer on model and print interpretation and DfMM during the product development process. The measurement processes must be assessed and validated as the micromoulding process is qualified. The metrology department at Accumold helps the customer improve their part design, re-dimension prints, and better use geometric dimensioning and tolerancing (GD&T) so that the part design is easier to mould, easier to measure and performs better for the end user.
The key challenges
Very often in a micromoulding scenario, metrology- and validation-related issues can be challenging. The key challenges include part size, part fixturing and surface roughness.
Part size
Micromoulded parts can have micron dimensions and features that only become visible at 10x or greater magnification. In the case of such small part sizes, metrology methods need to be non-contact, namely vision (camera), laser or white light interferometry.
Part fixturing
The micromoulded part being measured must be fixtured so that repeatable and reproducible measurements can be achieved from program or manual measurement processes.
Accumold designs and manufactures plastic or steel 3D custom fixtures to hold parts in various orientations and ensure all the features on a part.
Surface roughness
The small size and critical finish requirements of a micromoulded part make surface roughness another significant metrology challenge. Again, non-contact metrology tools are vital, as tactile tools have the potential to compromise surface integrity.
Accumold uses several non-contact metrology methods, including vision (camera), laser and white light interferometry. Sometimes, these methods are used on a single part based on the part size, feature size, surface finish requirements and tolerance limits. The company also uses: Optical Gauging Products (OGP) multi-sensor machines that have vision, laser and touch trigger capabilities to measure dimensions of the steel mould tool and parts using X, Y and Z coordinates; MeasureMind 3D metrology software for GD&T and ZONE3 metrology software for comparison to the 3D model of the part; and ZYGO coherence scanning interferometers to measure fine details (including Z coordinates), 3D surface finishes and lens dimensions.
In-lab or in-process
Typically, the conversation when looking at the optimum use of metrology in advanced manufacturing settings today is between its use in-lab or in-process. Ultimately, a key driver for the shift from in-lab to in-process is a desire for faster time-to-data and, more importantly, the ability to make decisions as a result of that data faster.
Accumold prefers to perform measurements as close to production (in-process) as practical using a metrology system that is repeatable and reproducible. The metrology requirements are continually assessed during a specific product development process in terms of the number of critical dimensions and features, tolerance requirements, part geometry, measurement systems available (in-lab and in-process), estimated part volume/run rate, cost of parts, and potential for scrap if measurements are delayed.
For some projects, it is important to: work with a customer to identify critical dimensions and features; develop a measurement process on an OGP machine; prove the measurement method as repeatable and reproducible utilising a fixture and programs; buy duplicate OGP machines; deploy the machines, fixtures and programs; and have trained production personnel operate the machines and collect data in the production room.
Sometimes project details require measurements to be performed in a lab environment. If this is the case, it is important to establish processes for part handling and delivery, prioritisation of part measurements (first in, first out (FIFO), customer promise date, etc.), measurement method (machine, fixture, program, manual), data collection, and reporting of results to production.
All metrology requirements, including equipment (machine, fixture), methods (program, manual), data collection (automatic, manual) and reporting (automatic, email, data load) are included in part specific control plans.
1 of 2
Image 2
Images 2 and 3: A micromoulded fibre array for a microoptics application requiring extreme accuracy and the moulding of tiny holes with precise dimensions.
2 of 2
Image 3
Images 2 and 3: A micromoulded fibre array for a microoptics application requiring extreme accuracy and the moulding of tiny holes with precise dimensions.
An enabling technology
Here and now, metrology is a truly enabling technology. The metrology equipment available in 2021 is far superior to that available a decade ago. It provides invaluable insight concerning the demanding micro-sized steel mould tool and parts required to meet customer needs. Current metrology equipment and techniques can be used to measure details in the steel mould tool, measure the dimensions and features of parts to confirm they meet the print tolerance, and ensure the process is capable. Intense design of experiments (DOEs), stress runs, and operational qualification and production qualification runs can be undertaken to assess dimensional capability to internal or customer process capability (Cp and Cpk) and process performance (Pp and Ppk) requirements to values of 1.0, 1.33 and 1.67. Accumold uses its metrology equipment and expertise to provide data and immediate feedback that helps in determining if the steel mould tool is acceptable or if adjustments are required.
Metrology is constantly evolving and it is important to actively assess new technology by means of online/onsite or remote demonstrations.
Optical metrology and collaboration
There is no doubt that industry’s perceptions of optical metrology have changed in recent years, and its uptake is growing substantially year-on-year. An obvious reason for this is the ability to measure without damaging surfaces or features on often delicate parts. However, optical metrology also stimulates the move to greater automation in manufacturing due to it being inherently faster than contact metrology, specifically it can quickly undertake full-field measurement rather than having to focus on specific part features one at a time.
At Accumold, two ZYGO optical profilers, namely a NewView 7300 and a NewView 8300, are used to measure 3D surface roughness, lens characteristics to an aspheric lens equation and critical Z dimensions. The data obtained using the profilers’ Mx software is critical in proving moulding and measurement capability to customers. Furthermore, it is possible to send this data to customers so that they can use it to undertake their own analyses in other software such as MATLAB or MountainsMap.
Accumold selected ZYGO optical profilers on account of their ability to accurately measure parts made from clear and other high-temperature resins used to mould lenses. The company looked at competing devices, but these struggled if used on clear resin parts and some did not generate the data necessary for analysis. One device required the surfaces of clear resin parts to be sprayed in an opaque coating, and this changed the dimensions of the parts.
Accumold is currently assisting ZYGO in the development of a lens-specific application for Mx software that gathers and analyses the data from the company’s coherence scanning interferometers. Accumold has shared part design details, mould details and current metrology methods, as well as participated in a couple of online meetings to discuss the current difficulties surrounding lens aspheric measurements.
Accumold has previously worked with ZYGO to develop several specific measurement routines for the NewView 7300. This was when the profiler was new and Accumold was unfamiliar with its capabilities. The routines are still used today for internal training and new routine development.
Working collaboratively is the way forward and will ensure that the technology evolves to meet customer requirements.
Summary
Metrology is central to overall product development success, particularly in a vertically integrated micromoulding company such as Accumold. As highlighted above, it is a powerful enabling technology and has a key role to play in the timely and cost-effective production of exacting end-use parts.
Accumold