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procurement. For example, when purchasing a CNC machine approach for converting a vendor-specific machine model in
tool, it is normally hard for final users to determine whether proprietary format to a standard format (STEP) and (2)
their workpiece(s) will fit on that machine, or even if they do lessons learned through the implementation of the case study.
fit, is there an accurate, efficient location for the parts?
Having machine models beforehand will allow users to The rest of the paper is organized as follows: Section 2
better understand the machines’ capability and easily discusses the existing relevant standards and related efforts
compare candidate machines through “try before they buy.” for solving the problem of non-homogenous CAx
However, it is impossible for users to gain access to all the environments. Section 3 presents the general approach of
vendor-specific tools and machine models before the how to address this problem so that a specific approach can
procurement. A neutral format, which is a non-proprietary be derived depending on the CAx tools used and interfaces
format that can be used to represent machine models and required. Section 4 introduces the context and settings for
recognized by all vendors, of the machine models will this specific case, and presents the development of the STEP
provide the final users a convenient way to evaluate the generator. Section 5 discusses the challenges encountered in
capabilities of candidate machine tools. this study and finally Section 6 concludes the paper.

Efforts for international standards, to govern the 2. RELEVANT STANDARDS AND RELATED
representation of geometrical and functional information, EFFORTS
have been made in parallel as the machine tool
manufacturers developed their proprietary techniques [7]. This section discusses relevant standards that support the
Attempts have been made to provide a standardized solution work, interfaces that enable the conversion of data from
for model and data exchange between CAx systems, but so proprietary formats to the standard formats, and related
far it is mainly the product geometric data and definition that efforts in the field.
have been widely exchanged by the support of ISO 10303,
which is also called Standard Exchange of Product Data 2.1 Standards: ISO 10303 – STEP and ASME B5.59
(STEP). Many CAx tools can export geometric models to the
STEP format and vice versa. Standard solutions for the Two standards for representing machine models are briefly
exchange of kinematics information have not been used in introduced in this subsection: ISO 10303 and ASME B5.59.
practice and industry does need a standard way to exchange The standard ISO 10303, or STEP, was developed to
complete machine model information including the product unambiguously represent and exchange computer-
geometry, kinematics, tolerances, and classification [10]. interpretable information for a product [11]. STEP consists
of a set of standards to facilitate data modeling throughout
The increasing use of software to represent a machining the entire lifecycle of a product, and has become widely
system in a virtual representation, from a manufacturing accepted and applied internationally for exchanging product
perspective, implies an increased need to be able to reuse the data in the manufacturing field. Information models and
information. Manufacturing companies are investing more to nearly all parts of STEP are defined using the EXPRESS
digitizing their enterprises and as more information is modeling language, the standard ISO 10303-11 [12] [13].
digitally available, the interest and urgency of information The EXPRESS modeling language defines entities and the
reuse will increase. Interoperability for systems and models relationships between entities. Files that are created based on
will be more crucial and will motivate manufacturers to seek this standard are also referred to as physical files or
solutions that support standard representations of their part21/p21 files. The instances of an entity can be exchanged
resource, product, and production data. The stakeholders to by the support of p21 files or shared within applications
this approach are manufacturing companies that need to through the Standard Data Access Interface (SDAI) [14].
exchange these kinds of data, both internally and externally. The information models can be categorized into application
For example, internally, the same machine model may be protocols (AP) or integrated resources (IR). APs are
developed multiple times using different software, models developed for specific application domains, such as
have issues with different version of the software, or aerospace in AP 203 and automotive in AP 214 and they are
different units used by the different component models that designed for fulfilling the industrial requirements [12]. AP
need to work together; externally, model exchanges and 242, managed model-based 3D engineering, presents a data
communications among supply chain partners, CAx model schema to integrate the kinematics, geometry, and
developers, and machine vendors may be required. assembly models [15]. However, AP 242 is still a work in
progress and has not been widely implemented in industry
This paper introduces a case study that demonstrates the [10]. Figure 1 provides an example of the EXPRESS schema
feasibility of representing a complete machining model, for AP 242, which defines a kinematic joint. [16] lists a
including both geometric and kinematics information, using complete documentation of the AP242 EXPRESS schema.
the STEP standard. This case study reports the initial effort IRs are context-independent, and an example of IR is ISO
of converting a vendor-specific (PTC Creo) machine model 10303-105 that defines an IR for kinematics data. IR for
to the STEP AP 242 representation. PTC Creo was selected kinematics for 10303-105 specifies the structure, motion,
because (1) it is a commonly used CAx tools and (2) we have
a machine model available in Creo format for this case study.
The research contributions of this paper include (1) a general

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