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Victrex Polymer Solutions has helped Stratasys, a producer of prototyping parts, develop a finishing solution for its polyphenylsulfone (PPSF/PPSU) parts.

When Stratasys wanted a faster, more cost-effective alternative to manually finishing PPSF/PPSU parts, it used Victrex Aptiv film, to develop a thermoforming solution for surface smoothing.

When compared to traditional finishing methods such as hand sanding, the new thermoforming process can reduce lead time by 75 per cent and cost by 90 per cent.

The company’s technology creates functional prototypes and manufactured goods directly from a 3D CAD program using high-performance industrial thermoplastics.

‘Because PPSF/PPSU is a tough and durable plastic, it can be more challenging to finish with traditional means,’ explained Jesse Hanssen, application engineer at Stratasys.

‘Another traditional method for achieving a smooth surface is milling.

‘However, milling would negate many of the advantages of the FDM process.

‘In addition, to prepare for machining, time is needed for CAM programming and machine set-ups.

‘Machining also requires that an operator oversee the process,’ he added.

With the company’s new thermoforming finishing process, a thin sheet of Aptiv film is drawn onto the surface of the PPSF/PPSU part.

‘The film conforms to the part’s shape leaving a smooth outer surface,’ said Hanssen.

‘We chose Aptiv film because it preserves the mechanical, thermal and chemical advantages of PPSF/PPSU and adds value to the part,’ he added.

Aptiv is a high-performance film that provides all the performance properties of Victrex Peek polymer in a flexible format.

Aptiv film offers high-temperature performance, mechanical strength, chemical resistance, electrical insulation, wear and abrasion resistance, purity, radiation resistance and low moisture absorption.

Smoothing a PPSF/PPSU part by using thermoformed Aptiv film is a relatively simple operation that requires few modifications to a standard thermoforming process.

‘Essentially the Aptiv film is formed directly onto the part which serves as the thermoforming mould,’ explained Hanssen.

‘Once the PPSF/PPSU part is built, the supports are removed in preparation for thermoforming,’ he added.

During the thermoforming process, the PPSF/PPSU part is loaded into a vacuum forming machine along with a sheet of silicone-backed Aptiv film.

The film is heated to 140-160C (284-320F) and drawn onto the PPSF/PPSU part as soon as it reaches its forming point.

As heat is applied, it will relax and become taut.

Once the Aptiv film draws tight, the vacuum is quickly applied and held until the film cools.

It conforms to the part’s shape while smoothing its surface.

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