QMT Features: October 2017
Uprated metrology for seals
CMM, height gauge and surface testing kit meet the requirements of a new product.

When CDK Seals won an order for the production of metal components from a new aerospace customer it needed to invest in new equipment and methods in its manufacturing and metrology.

Historically, the Yeovil manufacturer produced its seals from a variety of PTFE composites, however the new order required a three-part assembly using steel, aluminium bronze and PTFE.

The three component assembly consists of both a concave and convex component as well as a housing that makes the complete assembly 80mm diameter with a 60mm height.

The issue for CDK was that the 1500 assemblies with a total of 4500 parts had to be machined to a 0.03mm tolerance. Unfortunately for CDK, its micrometers and vernier callipers couldn’t measure many of the complex features, especially the curved surfaces. One particular issue was with a 4mm diameter cross-drilled hole positioned on one of the concave surfaces.

CDK engineers visited Mitutoyo and decided that a Crysta Plus M443 Co-ordinate Measuring Machine (CMM) would provide the right solution. The low-cost and user-friendly CMM has a bridge type design and a work area of 400 by 400 by 300mm and 0.0005mm resolution.

Managing Director Mr Dave Paget said: “We agreed with Mitutoyo that the Crysta Plus was the most suitable product for measuring the highly critical parts and ordered the machine on a Thursday. It was delivered and commissioned the following Wednesday. Mitutoyo were excellent. They installed the machine and did the programming for the three seal components, so we could be instantly up and running. The training was simple and straightforward and we have the CMM networked to a PC, so we can store any subsequent programs off-line. Mitutoyo also provided a series of 3, 2 and 1mm diameter ruby probes. The small probes enable us to get inside the 4mm diameter drilled hole and check the concentricity as well as the angle of the hole that has a critical angle tolerance of +/-0.1degrees.”

Whilst the CMM proved ideal for measuring the curved surfaces, internal holes and other critical features, it was agreed that a plate with a 60mm internal bore with a bellow moulded to it, should be measured with a digital height gauge. Here Mitutoyo provided a  2D linear LH600E digital height gauge capable of measuring components up to 600mm high with an achieved accuracy of 1.1+0.6L/600 microns.

The final issue for CDK regarding the project was the surface finish on the aluminium-bronze parts. Friction between the mating parts would lead to wear, which had the potential to impact the performance of the assembly. To eliminate this issue, the mating parts required a surface finish better than 0.4Ra. From a production perspective, CDK invested in a vibratory bowl finishing machine from PDJ Vibro to enhance the surface finish of the parts. However, the parts still required measuring to ensure conformity to the required specifications and here Mitutoyo supplied a Surftest SJ-210 portable surface roughness testing machine.
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