CAD/CAM Improves Lead Times for Valve Body Patterns

Modern CAD/CAM patternmaking technology has been applied to the manufacture of Flowserve Valtek valve bodies, used in the construction of oil platforms. The casting producer, Norton Cast Products, made use of the facilities available at Castings Technology International, and with all parties working together manufacturing costs were reduced by 20% and the production time was shortened by over 2 weeks.

Oil platforms are some of the largest man-made constructions in the world and cast valve components form an integral and critical part of these units. The high levels of safety, coupled with the demand for uninterrupted performance, have led to the development of some of the most rigorous specifications in the industrial world. Meeting such demands places arduous conditions upon suppliers, especially small and medium sized producers. In the castings supply chain, continued efforts have been made to evaluate and improve performance in this sector.

When SME producer, Norton Cast Products, needed to supply a small number of 24″ 600lb and 900lb Flowserve Valtek-designed valve bodies, it was an ideal scenario for the application of modern CAD/CAM patternmaking technology and the use of computer simulation to optimise the casting process. Just two of each of these valves needed to be manufactured in a short lead time from UNS J92205 duplex stainless steel for use in a major North Sea project. Norton used the facilities and expertise available at Castings Technology International to ensure that the patterns were made to specification in the shortest possible time and at minimum cost.

Pattern Manufacture

In the manufacture of a cast component, the initial requirement to produce a pattern from which the mould and/or core(s) can be made, is often one of the most costly and time consuming elements of the whole process.

A traditional patternmaker works from drawings which provide limited information on the outline and a number of cross sections through the component. Any undefined areas are left to the patternmaker to ‘blend in’, leading to inconsistencies between products and between the internal and external profiles.

The application of the CAD/CAM patternmaking approach ensures that all surfaces are defined and precise dimensions are established at the modelling stage, prior to any pattern manufacture being undertaken.

Castings Technology International applied CAD/CAM techniques to the manufacture of the patterns and coreboxes for the 600 and 900lb Flowserve Valtek-designed valve bodies. For each valve body the manufacturing process involved the production of two half core boxes and a split loose pattern. Butt weld end patterns were made with add-on sections to allow flanged valve bodies to also be produced. The steps in the process are summarised below:

  • A fully defined surface model of a ‘half’ core was produced using Delcam’s DUCT software.
  • Core print extensions were applied to the model and the size of the core box was defined.
  • The information was transferred into Delcam’s Powermill software, and the machining parameters and Cutter Location (CL) data generated. The CL data was processed for the Fidia CNC controller.
  • The core box half was machined.
  • The mirroring function on the machine tool allowed the remaining half core to be machined from the same data.
  • The wall thickness of the valve body was applied to the existing surface model of the core. This provided the basis for the pattern model to which the additional features, such as flanges and webs, could be added.
  • The pattern information was transferred into the Powermill software and the pattern machined using the same process as the core.

Throughout manufacture, the times were detailed for each of the three stages of production, namely CAM, pattern labour and machine time. The absolute production time was 195 hrs. When the working day was taken to be an 8 hour operation this translates into a production time of 241/2 days.

The production of a 3-D surface model is a significant part of the overall process and typically it takes up to 75% of the CAM time. The availability of a fully defined surface model could have reduced the time and cost of pattern manufacture by up to 25%. Even so, the patterns were manufactured for 20% less cost than by traditional methods and in a time frame which was reduced by 2-3 weeks.

Casting Simulation

The benefit of having a 3-D surface model is its potential to generate an STL file for use in a computerised casting simulation software package. This allows the method, gating, filling and solidification of castings to be evaluated prior to manufacture in order to prevent casting defects. A simulation was carried out for both the 3 tonne and the 6.5 tonne valve body. The predicted results confirmed that they would meet the required quality standards.

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