Foolproof Automated Inspection Transforms Manufacturer's Quality Control

The two CNC coordinate measuring machines (CMMs) Alltrista Plastics had been using 24/7 for more than 10 years at its UK factory had become inefficient. The accuracy and repeatability of touch-trigger probing were becoming compromised due to the age of the machines. The software would sometimes crash, risking a physical collision, damage to the probe, and sometimes even to the component being checked.

As the plastic medical parts and assemblies produced had become more complex over time, an angled stylus was often required in an inspection cycle, so an operator had to choose from half a dozen pre-set probe configurations, mount one manually, and calibrate it. Additionally, the person would have to sort through different programs on a computer screen to identify and load the correct one.

To streamline this entire process and automate it, Alltrista installed two new Altera S 10.7.6 CMMs manufactured by LK Metrology. LK's CAMIO 3-axis scanning and reporting software was also provided along with a Renishaw SP25M scanning probe and PH10M motorized indexing head. It's two sensors in one, enabling continuous path tactile scanning as well as touch-trigger probing of discrete points.

Together with a Renishaw matrix plate to allow accurate placement of parts for inspection, the set-up has resulted in a vast improvement in metrology productivity by facilitating the fixturing of samples, speeding measuring cycles, and virtually eliminating human intervention and the attendant risk of errors. It would not have been feasible to retrofit scanning capability to the older CMMs, as the cost would have been prohibitive and in any case the machines were becoming obsolete.

Alltrista's quality manager Peter Makosa said, "I operated LK CMMs for several years when working for an aerospace manufacturer, which had standardized on their use. When Alltrista decided to upgrade its quality room, we approached four potential machine providers including the incumbent supplier. LK's response was by far the most comprehensive.

"It carried out an online demo on one of our parts and another trial when we visited Castle Donington. It was the only company to initiate a comprehensive on-site survey at our factory to check the feasibility of machine installation.

"On the basis of the measurements taken, bearing in mind that LK machines are taller than our previous CMMs, the manufacturer offered to reduce the height of the Altera S models during their build so they would fit comfortably through our doorways and in our refurbished inspection room.

"What finally clinched our decision to opt for LK Metrology was the favorable price of the equipment, the knowledgeable engineers that dealt with us throughout the entire sales process, and the company's reputation for good after-sales service."

Alltrista is an ISO13485-accredited firm that specializes in plastic injection molding of devices such as drug delivery systems and packaging such as contact lens blisters for the medical, pharmaceutical, and nutraceutical industries. The injection molding machines are mainly housed in one Class 7 and two Class 8 clean rooms.

Medical devices are increasing as a proportion of turnover as well as in variety and production volume, climbing over the past decade from 30 to 50% of throughput and still rising. Another trend is towards ever tighter drawing tolerances on newly designed products and more stringent GD&T (geometric dimensioning and tolerancing) requirements.

A rigorous validation process underpins the manufacture of all products at the facility. Typically, at the outset of a new production run, 30 shots containing, say, 15 components each will be run off and checked, with customers requesting a process capability of at least Cpk 1.33 and often 1.67 or 2 (six sigma). Tolerances are generally fairly open on plastic items, normally in the range of 50 to 100 microns, but any inaccuracy of measurement is undesirable, as it would consume part of the tolerance band. Even more important for validation is a high level of repeatability.

Alltrista also needed more data to better understand certain features of moldings, such as the flatness of sealing faces, freeform profiles, and chamfers. The use of a Renishaw scanning probe has resulted in more information to feed back to the production department for fine-tuning toolmaking and manufacturing. It also makes for a more detailed report for customers to understand more the manufacture that is being carried out on their behalf. Furthermore, the layout of the reports is much better now, as the previous open Excel spreadsheets have been replaced by locked PDFs generated in CAMIO. They include a color-coded part-to-CAD comparison showing product conformance, with all the accompanying data, Alltrista logo, date, and time.

When the CMMs were installed, LK wrote core programs for inspecting components for four major Alltrista customers and also devised a PC screen dashboard so the whole process is menu-driven. The first screen displays an icon for each customer, which when clicked reveals every part that is injection molded for that company. Clicking on the appropriate icon automatically sends the program to the CMM, whereupon the operator keys in their name, whether it is a standard or first article inspection report that is needed and clicks start. 

Before the program can be run, however, an array of components has to be placed in a known position on the granite table. To facilitate and speed up the procedure, LK supplied a Renishaw matrix plate with each Altera S 10.7.6. At no extra cost, anchor bolt holes were drilled into the granite at non-standard centers so the plates could be secured from underneath, avoiding retaining clamps projecting from the table surface. Included on-screen in the dashboard, alongside the relevant inspection program, is an SOP (standard operating procedure) showing the operator the exact location across the numbered grid of holes on the matrix plate that the batch of fixtured samples should occupy.