Critical capability

Consistency of production cycles enabling extended unmanned running while maintaining accuracy and precise levels of surface finish and repeatability are critical to elastomeric rubber seal, gasket and moulding specialist TRP Sealing Systems’ mould production at its Hereford headquarters. As PES reports, machine tool technology from Wele is helping it meet those objectives.  

Consistency of production cycles enabling extended unmanned running while maintaining accuracy and precise levels of surface finish and repeatability are critical to elastomeric rubber seal, gasket and moulding specialist TRP Sealing Systems’ mould production at its Hereford headquarters. As PES reports, machine tool technology from Wele is helping it meet those objectives.

TRP Sealing Systems has been able to maintain high levels of overall productivity during the last three years following the setting up of its own toolroom and the installation of a Wele large bridge-type (LB series) LB421 gantry machining centre.

Supplied by 2D CNC Machinery, the investment was critical to the business to bring often very complex mould production and refurbishment operations in-house as frontline support to its seal moulding and gasket production. Here, rubber mouldings weighing up to 5kg are produced in ‘made-to-order’ batches of up to 250,000 a year from mould tools that can vary in size between 300mm square to 3,900mm by 1,700mm. These variations in mould sizes are all now machined complete in a single operation on the Wele machining centre.

Says quality manager Jo Privett: “We design and develop each mould to suit the material specification which can also include cross-blended types, direct from customer supplied 3D models or drawings of the gasket or seal they require. This can be extremely demanding and often draws on our 35 years of production expertise where finished component thickness can vary between just 2 m and 20 mm.

“However, there are added complexities due to geometry applied to the form, special radii and especially transition between areas into both bottom and top halves of each mould. To add to its specialist operational expertise, following measurement and material specification analysis, final approval of the moulded component is always the result of a ‘fit-and-function’ application.”

Tight tolerances

This is why machining accuracy and especially consistency is important to TRP. While the final moulded component can be to a tolerance of ±0.15mm, to ensure maximum production life from the mould, process sizes are normally maintained very close to bottom of the designed tolerance band which can mean within 0.08mm. However, 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 has proven critical and is now well-proven, even when the 4,000mm by 2,000mm machine table is fully loaded with mould plates. These are retained in place using magnetic pads and tolerances have to be maintained across the whole table area. This is aided by the 15-tonne capacity table design that incorporates triple sets of ultra-heavy, linear roller guideways on the X-axis – a major advantage for stable machining against most machines of this type which have only two.

Recently, following almost three years of continuous production, as part of the company’s regular quality audit, it was decided to lightly reskim the 1,225 magnetic pads which are fitted to the table. These provide a datum and hold each mould in place giving total access to the top surface of the mould plate and eliminating the use of clamps. When completed, the inspection report qualified the total area of the table had be machined within 10µm.

Flagship investment

Originally formed in 1981, TRP Sealing Systems has progressively grown to become a global business while still maintaining 80% of sales within Europe. It has set up manufacturing operations under Hereford control in China and India to serve the Asian and Middle East markets plus a facility in Romania.

As a private company it employs some 750 people worldwide with 300 based in the UK where all design and process engineering takes place. With customers in the automotive sector, it is also a regular supplier to electronics, biotechnology, food, medical, chemical, marine, power generation, oil and gas, aerospace and defence sectors.

An important part of its success is the advanced laboratory for compilation of material specifications and seal development involving the tailoring of special polymers to suit specific and often ground-breaking applications such as those required by chemical customers and to meet the latest environmental demands. This ties in with its in-house tool design and prototyping service where the latest rapid prototyping equipment including laser and 3D printing is installed. There is also a facility to produce bonded metal components.

Says managing director Simon Children: “The Wele machine is a flagship investment, not only due to the specification that creates the ideal manufacturing and economic production environment, but also because 2D CNC Machinery fully appreciated our needs and has continued to provide high levels of ongoing support as we progressively develop our toolroom 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 1,400mm is optional) and each has high accuracy positioning through Heidenhain linear scales. The direct drive spindle motor is powered by a 30kW motor providing a maximum speed of 15,000rpm. 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 by Fanuc 31iMb with an AICC (1,000bps) data server.

Continuous production

Previously TRP used external UK mould suppliers but now 99% of production is within the business. Commenting on the Wele installation, machine programmer and setter-operator Dean Sletcher explains its versatility as a production solution: “When we have to produce moulds for volume component production, we set the machine table with two mould baseplates and a top plate,” he explains.

“Each plate in our standard requirement is 22.5mm thick and is produced from EN8 or P20 material and can be up to 3,900mm by 1,700mm in size. Having a complete set of moulds in production on the same table helps to ensure we can maintain our standards across the complete set.”

Once set, production is continuous. It is unmanned at night and through weekends. Mr Sletcher has the machine’s Fanuc 31i MB control connected to his mobile phone to alert him should the process stop at which time he returns to the factory to reset and continue the production cycle.

Milling cycles form the majority of the production processes using standard carbide cutters between 0.4mm diameter for profiling and 63mm diameter for face mills. Mostly depths-of-cut tend to be around 4mm. U-drills of 14 m, 20mm and 24mm 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 normal BT50 taper specification,” Mr Sletcher concludes. “This allows us to effectively machine at speeds up to 15,000rpm as we perform extensive profiling and surfacing of seal features without the use of form tools. As moulds are compression types and run hot at 160°C, there is no requirement for drilling deep cooling holes.

2D CNC Machinery www.2DCNC.co.uk

TRP Sealing Systems www.trpsealing.com

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