TechArchive

Original article date: November 1998

Are you faced with the problem of implementing CADCAM technology for the first time? Or upgrading to a new generation of system? One of the headaches is interfacing with other systems.

The single most difficult area in defining system requirements is interfacing data both within the organisation and with external partners or design teams. It needs to be addressed first at a strategic level as regards possible choice of an industry or project standard (see panel). At a technical level you need to ensure maximum compatibility of transfer. The responsibilities for converting and adapting data input and output need to be well defined within the system supply contract.

Setting a strategic standard for design model storage and exchange such as IGES or STEP might be a requisite for major collaborative projects. This could involve an additional overhead of knowledge and understanding and may add cost or restrict choice. A pragmatic decision based on the most interchangeable format within and between your supplier and customer community could point to the use of IGES DXF or even a vendor-specific CAD file format. However in this case you should be aware of possible inconsistencies in file conversion to and from intermediate formats. Version-specific variations of native CAD formats can also cause problems.

If you have specific in-house interface requirements between for example CAD CAM and MRP systems then you should stipulate the level of interfaces that you expect as part of the RFQ (Request for Quotation) document. Most vendors will publish specified input and output formats but these may need adaptation for successful interworking between systems. Usually it is sufficient to modify only one of then systems to ensure a match but be sure to stipulate who is responsible for doing so. “The output from System A will be adapted by Vendor A to meet the published input specification of System B.”

Assuming you are not a first-time CAD user your legacy data will be in two forms: electronic and paper. Re-use of drawings from a previous CAD system will depend on possible exchange formats and also on a strategy choice as to the revision and conversion philosophy. This may be dictated by the “switch-off plan” for the legacy plan. Bear in mind the cost of ongoing software support ageing hardware and the availability of trained staff. The “convert or redraw” decision for the component drawing libraries will affect the time taken to get up to speed with the new system. Take advice from your system supplier as to the likely limitations of re-using existing elements in a 3D system and the possible short-cuts from bought-in libraries.

Paper drawings will find their way into every design organisation. Scanned paper drawings can form a vapid part of an electronically issued and managed design documentation set in their own right. Suitable viewing and red-lining tools can provide a useful communication channel for approvals distribution and archiving.

Revision or change management will be part of the NPI process as previously defined and many of the basic productivity benefits from a CAD implementation arise from the ease with which drawings can be revised. These benefits will only begin to accrue or course when a significant number of CAD-generated drawings complete the cycle and are due for revision. Consider therefore scanning and converting existing project drawings prior to revision. The CAD tools can then be used to update them.

Full design change automation requires significant process analysis and implementation usually involving an EDM or PDM system to move the change requests and associated drawings through the organisation. If you are not ready to make this sort of commitment it is advisable to start by using your existing paper-based procedures for the change notes and descriptions and to make the final changes to design files using CAD. Electronic red-lining can then be used selectively – for example to transmit change requests from the shop floor – the electronic red-lines being treated as electronic paper forms.

A free executive guide is available from the Computing Suppliers Federation (CSF) offering advice and guidance for managing system implementation effectively. Intended for directors and managers of engineering and manufacturing businesses in the widest sense it covers advice from the early stages of setting the business objectives through supplier selection to achieving the expected benefits once the system is commissioned.

STEP

For the extended enterprise and for larger companies using many different applications (eg two or more CAD systems) file exchange standards such as DXF and IGES do not provide a satisfactory solution. Data translation results in three versions of the same data – a version for each of the target and source applications and a version for the neutral format. Such a circumstance can quickly result in problems of version management and access control.

STEP is defined in an international standard – ISO 10303 Its primary function is to provide a system-neutral product model. This satisfied the need to share data between applications within an organisation and externally with team members in other organisations. STEP is independent of any system and enables the description of product data throughout its life cycle. Its nature makes it suitable not only for file exchange but also as a basis for implementing and sharing product databases and archiving.

It is important to emphasise that STEP is much more than a data exchange standard. The existence of a neutral data model which permits data to be stored on any database platform and accessed from any application via a standard API (application program interface) is a powerful concept.

• Computing Suppliers Federation
• Roger Crumpton
• 01905 727610

November 1998