Validating micro molds

Measurement should be a central consideration in every quote issued by a micro molder. If a micro molder can make the steel micro tool and mold a part, it will eventually need to measure the resulting workpiece. Process development and qualification must include measurement development and qualification in any customer quote. Considering the adage, “If you can’t measure it, you can’t make it,” metrology’s fundamental role in a successful, cost- effective, on-time product development process is obvious.

Measurement development time, and gage repeatability and reproducibility (gage R&R), are vital and extremely valuable for micro molding customers, and a micro molder should work closely with the customer on model and print interpretation and design for manufacturing (DFM) – more precisely design for micro molding (DfMM) – during product development. The measurement processes must be assessed and validated as the molding process is qualified. The metrology department can improve customers’ designs, re-dimension prints, and better use geometric dimensioning & tolerancing (GD&T) data to make part designs easier to mold and measure, and perform better for the user.

Key challenges

Metrology and validation issues can be challenging in micro molding. Complex areas include part size, part fixturing, print tolerances, and surface roughness with part size being the key challenge. Micro-molded parts can be dimensioned in microns with features that only become visible under 10x (or greater) magnification. Such small part sizes demand non-contact metrology methods such as vision (camera), laser, and white light interferometry.

Part fixturing of the component to achieve repeatable, reproducible measurements of tiny items using programmed or manual measurement processes is also challenging. Accumold designs and manufactures steel or 3D plastic custom fixtures to hold parts in various orientations and ensure all features can be measured.

Surface roughness is also difficult because of the small size and critical finish requirements. Non-contact metrology tools are vital for such applications because tactile tools could compromise surface integrity.

In-lab or in-process

Optimum use of metrology in advanced manufacturing is either its use in the lab or in-process. A key driver for the shift from in-lab to in-process is a desire for faster data acquisition, and more importantly, the ability to make decisions more quickly.

Accumold prefers to perform measurements as close to production (in-process) as practical. The company continually assesses metrology requirements during a specific product development process, including the number of critical features/dimensions, tolerance requirements, part geometry, measurement systems available (lab and in-process), estimated part volume/run rate, cost of parts, and potential for scrap if measurements are delayed.

Sometimes, it’s important to work with a customer to identify critical features/dimensions, develop a measurement process, and prove the measurement method using a fixture and programs that are repeatable and reproducible. Other projects may require buying duplicate measurement machines and deploying machines, fixtures, programs, and trained machine operators to collect data in the production room.

However, some projects may require lab measurements. Therefore, it’s important to establish processes for part handling and delivery, prioritization of part measurements (first-in-first-out, customer promise date, etc.), measurement method (fixture, machine, programs, manual), data collection, and reporting results to production.

All metrology requirements including equipment (fixtures, machines), methods (program, manual), data collection (automatic, manual), and reporting (automatic, email, data load) are included in part-specific control plans.

Enabling technology

Current metrology tools are far superior to those available 10 years ago. Today’s technology provides invaluable insight concerning demanding micro-size tooling and parts required to meet customer needs. Metrology equipment and skills can measure steel details in the mold, part features/dimensions to ensure parts meet print tolerance, and ensure the process is capable. Intense design of experiments, stress runs, operational qualification, and production qualification runs assess dimensional capability to process capability and performance indicators, whether they come from the technology partner or the customer. Metrology equipment and expertise can provide data and immediate feedback to determine if steel in the mold is acceptable or if adjustments are needed.

Metrology technology is constantly evolving, and it’s important to actively assess new technology with online/onsite or remote demonstrations. Automated vision inspection (AVI) is used on the press, on robots, and in metrology equipment. Non-contact vision and laser measurement capability and white light interferometer equipment can measure micro features and surface roughness. The expertise and experience in design, mold and automation build, production/process, and quality assurance personnel are critical to success.

Summary

The central role of metrology in a vertically integrated micro molding company is central to overall product development success. Metrology is now a powerful enabling technology and plays a key role in timely and cost-effective production of exacting specification parts and components.

Accumold

About the author: Dave O’Leary is the quality director at Accumold. He can be reached at doleary@accu-mold.com or 515.964.5741.