Consistent machining cycles that allow extended unmanned running, while maintaining accuracy and precise levels of surface finish and repeatability, are critical to mould production at Hereford-based TRP Sealing Systems (www.trpsealing.com) — an elastomeric rubber seal, gasket and moulding specialist.

After setting up its own tool-room and installing a large bridge-type machining centre, the company has been able to maintain high levels of productivity over the last three years.

Supplied by Hinckley-based 2D CNC Machinery Ltd (www.2DCNC.co.uk), the Wele LB421 machining centre allowed TRP to bring often very complex mould production and refurbishment operations in-house.

Rubber mouldings — some weighing as much as 5kg — are produced in ‘made to order’ batches (adding up to 250,000 parts a year), using mould tools that can vary in size from 300mm square to 3,900 x 1,700mm. All sizes of mould are now machined complete in a single operation on the Wele machine.

Quality manager Jo Privett said: “Based on customer-supplied 3-D models or drawings of the gasket or seal they require, we design and develop each mould to suit the material specification, which can include cross-blended types.

The finished-component thickness can vary between 2 and 20mm; and there can be complexities due to geometry applied to the form, special radii and transitions between areas in both the bottom and top halves of a mould. Final approval of the moulded component is always the result of a ‘fit and function’ application.”

While the final moulded component can be to a tolerance of ±0.15mm, to maximise a mould’s production life, process sizes are normally maintained very near the bottom of the designed tolerance band, which can mean within 0.08mm; even more demanding is that tolerances of form in the mould can be as tight as 0.03mm.

Here, the accuracy and repeatability of the Wele LB421 have been essential and are now well proven — even when the 4,000 x 2,000mm 15 tonne-capacity machine table is fully loaded with mould plates (these are held in place using magnetic pads).

The required tolerances have to be maintained across the whole table area, and helping achieve this requirement is the three sets of ultra-heavy-duty linear-roller guideways on the table’s X axis; Wele says most machines of this type have only two.

Following almost three years of continuous production, it was recently decided to lightly re-skim the 1,225 magnetic pads fitted to the table.

These provide a datum and hold each mould in place; this arrangement gives total access to the top surface of the mould plate by eliminating the use of clamps. A subsequent inspection report confirmed that the total area of the table had been machined within 10µm.

World-wide operation

Formed in 1981, TRP Sealing Systems has grown to become a global business, although some 80% of its sales come from within Europe.

The company has also set up manufacturing operations in China and India to serve the Asian and Middle East markets; it also has a facility in Romania and now employs some 750 people world-wide (300 are based in the UK, where all design and process engineering takes place).

TRP has many customers in the automotive sector, although it it is also a regular supplier to other sectors, including electronics, biotechnology, food, medical, chemical, marine, power generation, oil and gas, aerospace and defence.

An important part of the company’s success is its advanced laboratory for developing materials and special polymers to suit specific and often demanding applications, such as those required by the chemical sector.

Its in-house tool design and prototyping capabilities include the use of various types of 3-D printing equipment, and there is a facility for producing ‘bonded metal’ components.

Managing director Simon Children said: “The Wele machine is a ‘flagship’ investment, not only because its specification provides the ideal manufacturing capabilities but also because 2D CNC Machinery fully appreciated our needs and has continued to provide high levels of on-going support as we continue to develop our tool-room operation.”

The Wele LB421 has axis travels of 4,060mm in X, 2,180mm in Y (2,800mm is optional) and 800mm in Z (up to 1,400 mm is optional), and it features Heidenhain linear scales.

The direct-drive spindle is powered by a 30kW motor providing a maximum speed of 15,000rev/min. A 32-tool magazine is standard, and included in the machine specification is a Renishaw OMP60 optical-transmission probing system for automatic workpiece measurement.

Control is via a Fanuc 31iMb with an AICC (1,000bps) data server. Previously, TRP used external mould suppliers in the UK, but 99% of production is now within the business.

Commenting on the Wele installation, machine programmer and setter-operator Dean Sletcher said: “When we have to produce moulds for high-volume component production, we set the machine table up with two mould base plates and a top plate.

“Each plate is generally 22.5mm-thick EN8 or P20 material and up to 3,900 x 1,700mm in size; and having a complete set of moulds in production on the same table helps to ensure that we maintain our high standards across the complete set.”

Once the Wele has been set, production is continuous, running unmanned at night and through weekends. Mr Sletcher’s mobile phone will receive an alert if the process stops. He can then return to the factory, rectify the problem and allow the production cycle to continue.

Milling cycles comprise most of the production processes, using standard carbide cutters from 0.4mm in diameter for fine profiling to 63mm in diameter for face milling.

Depths of cut are generally around 4mm, while U drills (14, 20 and 24mm in diameter) are used for producing mould clamping holes.

“Due to the predominance of small tools, we specified the machine with a 30kW ISO BT40 taper direct-drive spindle in place of the standard BT50 taper specification.

“This allows us to machine at high speeds when undertaking the extensive profiling and surfacing of seal features without the use of form tools. Because our moulds are compression types and run at 160°C, there is no requirement for drilling deep cooling holes.”