Plastic hot air staking ideal for pneumatic valves

KV Limited is using plastic hot air staking from Phasa Developments as the fastening method of choice for its new generation of all-plastic pneumatic valves

Reliability, performance and longevity are three themes that run throughout everything produced by Milton-Keynes based KV Limited - from automatic milking systems and sliding door modules for railway trains, to pneumatically-operated vehicle suspension systems and equipment for anaesthetic trolleys or patient ventilators and resuscitators.

The company is at the forefront of control systems' research and development and sets rigorous performance standards for all its equipment.

No surprise then that it should adopt plastic hot air staking from Phasa Developments as the fastening method of choice for its new generation of all-plastic pneumatic valves.

Established as a result of a merger between Kay Pneumatics and Vento Solenoids in 1988, KV Ltd specialises in the design, development and manufacture of pneumatic and fluid control solutions.

Its products range from individual valves, cylinders, filters and fittings to complete custom-engineered systems to meet the needs of users in industries as diverse as the aerospace, medical, transport and defence sectors.

With customers and company facilities world-wide, the 300-strong organisation prides itself on applying latest technology and methods - including cell manufacturing and Kanban production - in order to maximise equipment performance, efficiency and reliability, as well as drive down manufacturing costs.

Development of its all new plastic construction valve represents a 'first' for the company; in that it eliminates the need for expensive cast or machined metal parts.

KV's Frank Mills explains: "The new unit is designed as part of a seat height adjuster for use in commercial vehicles.

It's an application calling for all of KV's core strengths, because the finished product must perform reliably over many years - while withstanding the rigours of vehicle vibration; not to mention the less than delicate touch of some truckers." Among key criteria in the development of the new valve was the need to find an assembly method that would provide consistent results and high throughput, independent of operator skill levels.

Manufactured in Acetal, the new valve has been developed with a view to assembly using either ultrasonic welding or hot air staking.

However, through pre-production trials, it soon became apparent that noise and harmonic vibration were disadvantages associated with the ultrasonic approach.

By contrast, plastic hot air staking from Phasa Developments showed itself to be quieter and cleaner - and above all, more consistent - than the alternative method, regardless of operator.

As a result, a solution based on a Phasa type 10/30 machine was selected by KV.

This has been equipped with tooling to suit two variants of finished product - one of which operates in conjunction with the vehicle's own air supply, and a second that incorporates an additional microswitch for use with external supplies.

The design of both types incorporates six rectangular pins - which provide accurate location for both halves of the body prior to final assembly.

In addition, two 3mm diameter pins are used to locate, and subsequently secure, the external microswitch on the combination valve model.

Valve bodies and internal components are first loaded into the appropriate set of purpose-designed tools in the Phasa machine.

On initiation of the automatic assembly cycle, hot air at 350oC is directed accurately on to the pre-moulded pegs to bring them to their plastic state.

Cold forming tools then re-shape them into the required profile - while also clamping the components together - providing a permanent, vibration and tamper resistant fixing as the material solidifies and cools.

"During our development trials, we received extremely good support from Phasa's engineers," reports manufacturing engineer, Bob Pack.

"Their assistance not only helped us to prove the principle of the all-plastic valve, but has also paid off in terms of the consistency of finished assemblies - by enabling the product design and assembly tooling to be fine tuned prior to production release." "Each valve undergoes stringent functional testing as part of the manufacturing process," he continues.

"At their operating pressure of 8.3 bar, the maximum allowable leakage is just 0.13 ml/min - which is the equivalent of less than 8 cc/hour." The consistency of performance achieved by KV bears out the findings of process studies conducted by Phasa in conjunction with the Faculty of Engineering at the University of Hertfordshire, which demonstrate that hot air staking will regularly produce Cpk values in excess of 2.0 - the equivalent of fewer than one reject per million operations.

In KV's case, the result is a highly reliable, cost effective, sealed valve unit with a design life of 100,000 operational cycles.

Summing up, Mr Pack concludes: "The success of this first installation has established the Phasa system as an ideal method of assembling these products.

I am sure it will remain our first choice for any further additions we make to the new generation of all-plastic valves.".

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