Hexagon software used to build precise ship models at the Bulgarian Ship Hydrodynamics Centre (BSHC)

VISI CAD/CAM software helps BSHC achieve tight tolerances and generate accurate NC code

An upside down hull of a wooden ship being milled

The Bulgarian Ship Hydrodynamics Centre uses VISI CAD/CAM software, by Hexagon’s Manufacturing Intelligence division, to design and manufacture ship models and propellers for a variety of applications. The software’s robust programming tools help the centre produce precision workpieces, including complete hulls for marine vessels, and to fully utilise its sophisticated 5-axis machinery. VISI’s simulation capabilities likewise ensure that collisions will not occur during machining, which enables the centre to use its complex machinery with confidence.

The Bulgarian Ship Hydrodynamics Centre (BSHC), part of the Bulgarian Academy of Sciences (IMSTCHA-BAS), is a national fundamental and applied-science research centre that uses physical and numerical modelling to solve scientific and practical problems. The centre’s work focuses on fields such as shipbuilding, hydrodynamics, aerodynamics, water transport, ocean and coastal engineering, ecology, and national security and defence.

Located in the city of Varna, the BSHC serves as a hub for a wide range of scientific and experimental activities, and houses deep and shallow water-towing tanks, a seakeeping and manoeuvring basin, and cavitation and aerodynamic tunnels. Scientific and applied research services offered by BSHC are highly recognized and frequently demanded by maritime stakeholders all over the world. The centre operates in an ideal environment of broad national and international cooperation and represents the Republic of Bulgaria in a number of international organizations and projects relevant to its scope of activities.

The diverse research facility also conducts studies related to sea and river crises and disasters, marine ecology and coastal protection, facilities for fisheries and aquacultures, marine renewable energy sources, technology transfer, and national security and defence. In cooperation with national high schools and universities, the centre trains cadets and students, including post-graduates, doctoral candidates, and trainees, in its fields of study.

The production of ship models for hydrodynamic tests is a key aspect of the overall operation of hydrodynamics research facilities. As practical research requires the development of accurate digital models, the centre needed software that could provide a strong foundation for modelling and manufacturing water and air propellers, as well as struts, brackets, rudders, wings, and other components.

Within the last 10 years, more than 120 applied research contracts have been successfully implemented for a large number of customers, including Becker Marine Systems (Germany), Keppel FELS (Singapore), Hyundai Mipo, SUNGDONG Shipbuilding & Marine Engineering, Hanjin Heavy Industry, DSEC (Korea), DELTA MARINE, Sedef Shipyard, DESAN Shipyard, Ulstein, RMK Marine (Turkey), CNR – (Lyon, France), Israel Shipyard Ltd. (Israel), Spliethoff’s (Netherlands), EXMAR Offshore, Maybank Industries, Glosten Associates (United States), Flanders Hydraulics Research (Belgium), SINTEF (Norway), Rolls-Royce AB (Sweden), Stone Marine Propulsion (United Kingdom), DCNS Lorient (France), and VICUS (Spain).

Modernisation and innovation in propeller models manufacturing

VISI computer-aided design (CAD) and computer-aided manufacturing (CAM) software became the centre’s go-to modelling and manufacturing solution in 2001, when the BSHC began using the software to create 3D models for ship propellers and to generate the toolpath needed to program in 3+2 axes for a machining centre equipped with a Fanuc 6M controller.

While researching its options, the centre received product proposals from three different companies, including VISI, which is sold in the region by Hexagon reseller VISI International Technology (VIT) Ltd.

Following product demonstrations by the three companies, VIT Ltd. came out ahead by offering excellent technologies ideal for the accurate, detailed modelling and subsequent machining of ship propellers. The BSHC ultimately equipped its team with both VISI Modelling for advanced design-for-manufacturing work, and VISI Machining to program the machining of complex surfaces.

Using VISI, the company created 3 + 2-axis programs for its machining centres and achieved optimal results without requiring that the propeller be removed from the machine tool, turned over, and repositioned for additional operations. It was also important that the finished part achieve the required tolerance of +/- 0.05 mm in thickness; VIT Ltd.’s competitors were unable to provide solutions that met this tolerance requirement.

The BSHC also found that VISI represented the best priceto-quality ratio, as the software satisfies all of the centre’s requirements for a CAD/CAM system. Since its integration, the BSHC has made full use VISI’s technologies for modelling ship propellers and has taken advantage of several of the software’s other sophisticated modelling and programming capabilities.

Today, all ship propellers at the centre are manufactured on MC 302 and Haas VF3 machining centres programmed by VISI in 3+2 axes.

Models of ship propellers are characterized by complex geometry, and are often designed with overlap between fins and, or, with areas shaded for cutting tools.

Requirements for precise geometric [computer] modelling are strict, as they provide conditions for experiments and, as such, have a direct impact on the accuracy of the results of propeller studies. They are subject to mandatory inspection checks before being used for test measurements in the cavitation tunnel and towing tanks.

“Purchasing the CAD/CAM system at BSHC completed our technological chain for computer modelling and the production of models of ship propellers, addressing the needs of our hydrodynamic research and allowing it to develop and improve,” said Eng. Valeri Dimitrov, head of sector for ship propellers and cavitation at BSHC. “This was boosted by the introduction of a Haas 5-axis machining centre. This allowed the creation of products that are competitive on the world market and attracted the interest of established foreign research centres.”

During this period, BSHC performed a number of services for foreign contractors, and dozens of propeller models intended for model tests were made for export. Renowned research centres, universities and design companies, such as Germany’s SVA Potsdam and HSVA Hamburg, Croatia’s Brodarski Institute, Flanders Hydraulics Research of Belgium, Turkey’s Istanbul Technical University, and Becker Marine System of Germany and Norway took advantage of the centre’s capabilities.

“For us, the cooperation and support we can count on from our VISI International Technology is very important,” Dimitrov said.

“Creating a sustainable methodology for modelling ship propellers in a VISI modelling environment was a challenge,” said Eng. Nedyalko Grozdev, manager of VIT Ltd. “We succeeded by combining our knowledge of the possibilities of VISI with the experience of colleagues from BSHC under the direct supervision of Eng. Valeri Dimitrov.”

In addition to modelling and manufacturing model propellers, BHSC also uses VISI CAD/CAM software for the design; modelling and generation of numerical control (NC) programs for the production of fins for air screws, brackets, rudders, and wings; non-standard experimental equipment, and other products with complex geometry.

“The methodology made it possible to model precise models of ship propellers in VISI, with repetitive characteristics for accuracy and smoothness of faces,” Grozdev said. “This is a prerequisite for using VISI Machining for the production of high-quality screws that meet strict international standards. Achieving this result required creativity and hard work from everyone. We also succeeded thanks to the constant support and trust of the leaders at BSHC.”

Professor Dr. Eng. R. Kishev, head of the BSHC, said, “The centre for hydro and aerodynamics has always applied the latest technologies, not only those that concern its direct activity, but for the study of the characteristics of ships and offshore structures.

“The software was selected for the production of physical models at our facilities. Part modelling and the creation of  NC programs for 3- and 5-axis machining centres at BSHC became fast and convenient after the purchase of the VISI CAD/CAM licenses and full technological assimilation by our specialists. We benefit from continuous support from VIT that, combined with our experience, has created opportunities to expand our circle of partners.”

A history of innovation in scale shipmodel production

In 2005, VIT was asked to modernize the facility’s operations by installing computer-numercial control (CNC) machining capability on a “Kempf and Remmers” B12 CNC mill used by the institute. The mill can process models with dimensions up to 12 x 2x 1.5 meters, and machines simultaneously with two spindles.

The original machine control was used to “copy” water lines with manual guidance, and then print a drawing. But BHSC asked VIT Ltd. to create an application with VISI that could generate measuring points and paths for the movement of the contact sensor on the hull of the ship model after milling.

Developed by Bulgarian company BEL Ltd., a BEL machine control — which can handle up to 36 axes and process lengthy NC programs — was installed on the institute’s mill. Likewise, BSHC chose BEL metrology software for its flexibility and ability to be installed on all types of metal cutting and welding machines. As This software would be used to program built-in metrology software installed on the milling machine tool.

An engineering team, including specialists from VIT, BEL and BSHC, was formed to complete the upgrades. Modernization work on the mill included the replacement of electric motors along the axes and installation of four linear feedback scales, one of which is 12 meters long. To ensure that the required accuracy is produced, the CNC software simultaneously monitors and compares readings from the linear sensors and sensors installed  in the motor’s axis. A feedback sensor, which detects the number of engine revolutions, is integrated in the motor axis for each axis of the machining center. The CNC system calculates the position of the table/spindle from the number of rotations of the shaft, taking into account the pitch of the screw.

VIT has developed a special software application for VISI, called “Ship Inspect,” to generate measurement points on ship models in VISI by algorithm in accordance with international standards. It also creates a path for the contact sensor to measure points located on curved surfaces. In cases where points are located on these complex surfaces, the contact sensor must move along a trajectory perpendicular to the surface at the point of expected contact. Otherwise, the center of the sensor couldn’t be accurately calculated.

Taking this into account, Ship Inspect creates a path for the contact sensor that provides an “attack” by vector perpendicular to the contact point on the surface of the model. The results are collected by the CNC system and compared with the set points. The data of the comparison are tabulated and imported back into VISI to compare pregenerated ship-model checkpoints with the milling points collected by the sensor. This makes the identification of areas for further processing easy, fast, and accurate.

The requirements named by the BSHC were met on time, and the quality needed to ensure research integrity has been delivered. BSHC ultimately purchased additional VISI Modelling and VISI Machining 2/3-axis licences.

The K&R mill ran without issue for more than 14 years, during which time accuracy increased and productivity tripled — and sometimes quadrupled. Quality control also increased and the reduction in time spent producing models enabled the centre to attract new partners from around the world.

In 2019, BSHC invested in a new MULTIAX simultaneous 5-axis gantry machine with head-to-head kinematics that can process models with dimensions of up to 10 x 2.6 x 1.6meters at high speeds; the spindle rotates at 28,000 rpm.  

A third personal computer was purchased and equipped with VISI Modelling and VISI Machining 3/5-axis licences, and VIT has developed a new 5-axis postprocessor for the machine. BSHC specialists quickly mastered the 5-axis production of ship models with VISI Machining.

After the purchase of the CAD/ CAM system at BSHC, a complete technological chain for computer modelling and the production of models of ship propellers for the
needs of hydrodynamic research was developed and improved.”

Eng. Svetlozar Boyadzhiev, who prepares CNC programs and controls machine-tool operations, explained the role of VISI: “The design of the ship model, appendages for it (rudders, skegs, struts, etc.), the technical documentation for the workshops and the preparation of the NC files for the B12 and MULTIAX machines is done using VISI CAD/CAM. The combination of CAD and CAM gives advantages against using a CAM-only program. It is easy to make corrections of the working surfaces and to generate the NC output files. The VISI interface is user-friendly, which is true for the 5-axis machining, as well.

“Our new MULTIAX machine is being programmed quickly and easily thanks to the custom design by Nedyalko Grozdev’s postprocessor. Even at the simulation stage it ispossible to observe the tool movements and to avoid any collisions between the machine`s moving parts and the workpiece.”

Eng. Grozdev said, “Working with the BSHC`s experts and engineers from BEL Ltd., we were able to achieve our goals. We developed highly custom applications for the first time using VISI Modeling and VISI Machining, and we met all of our challenges because collective work formed the base of our success. Working as a team, the experts from BSHC, BEL Ltd., and our programmers found suitable solutions for all situations. The BSHC`s leading management believed in this project and was supportive of us throughout the project. I’m grateful to the team at BSHC for their long-term cooperation and trust.” 

BSHC has not interrupted the SMA licenses for VISI since the integration of the software.

“The Bulgarian Ship Hydrodynamics Centre has always applied the most contemporary technologies in the field of hydrodynamic experiments of ships and other ocean structures,” said Prof. Eng. Rumen Kishev, the CEO of BSHC. “Also, the technologies used for the production of the test models have always been up to date. The programming products of VIT were chosen according to those standards.”

Namely, Prof. Kishev said that VISI was chosen due to its ability to generate NC files for 3- and 5- axis milling machines at BSHC, and notes that programming has been quick and easy since the software’s integration. The Italian MULTIAX machine, purchased in January of 2019, is run with programs written with VISI for 5-axis milling. 

The creation of complex ship-hull forms, ship propellers and appendages could be completed faster after VISI was introduced to the design department at BSHC. Much less time is now needed for the creation of technical drawings for ship-models and mechanical production. 

“The cooperation between BSHC and VIT has been very successful for many years,” Prof. Kishev said. “The results are clearly visible, and we shall continue this cooperation to meet challenges that the new times shall put in front of us.”

About the company

Company name: Bulgarian Ship Hydrodynamics Centre
(BSHC)
Business: Basic and applied-science research
Website: www.bshc.bg
Key benefits achieved:

  • Ability to achieve desired tolerances
  • Generation of accurate NC code
  • Ease in developing sophisticated models

Case Study: Bulgarian Ship Hydrodynamics Centre

Case Study: Bulgarian Ship Hydrodynamics Centre

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