When Yorkstone company Johnsons Wellfield Quarries wanted to invest in machining robots they turned to experts from other fields to provide them with the answers they needed.
The Health & Safety Executive has said the stone industry has to think the unthinkable in the way it processes stone in order to combat the dangers of silicosis and hand arm vibration syndrome (HAVS), with its threat of white finger. A few companies have taken that idea on board as well as seeking productivity improvements by incorporating the latest, state of the art robotic processing technology, which holds out a promise of transforming the stone industry. Among them are Johnsons Wellfield Quarries (JWQ) in Huddersfield, where investment in new facilities to engineer stone solutions in a sustainable way has significantly extended the capabilities of this 150-year-old quarry.
JWQ, well known for their Crosland Hill sandstone, are part of the family owned and managed Myers Group, formed in the 1950s and focused on supplying building materials to the construction sector. They bought the Johnsons Wellfield Quarry operation in 1978 and it has been the subject of significant and ongoing investment that continues up to the present.
Their most recent investment is a robotic machining facility using Stäubli six-axes robots and the latest Robotmaster CAD / CAM software, all integrated into JWQ’s production system by the Rochdale based company CR Solutions, formed in 1995 to provide specialist solutions in machinery such as robotics.
Over the years JWQ have supplied the top quality sandstone used in many high profile projects such as paving and seating in Paternoster Square, London, and the highly praised St George’s Square restoration in Huddersfield.
An opportunity to provide artistically sculptured sandstone planters and seating for Sheffield City Council’s redevelopment of Tudor Square in association with the Crucible Theatre renovation in Sheffield city centre was what convinced John Myers that a radical approach to machining natural stone was needed.
To identify the processing equipment that would meet their needs, JWQ conducted research into alternative production techniques and concluded that, if possible, a bespoke six-axes robotic solution would be the answer. Consultation with CR Solutions provided additional expertise and guidance.
Through CR Solutions, JWQ saw a demonstration of Stäubli Robotics’ products at the firm’s premises in Telford. They were impressed with the abilities of the robots to machine stone to the shapes and precision required.
The demonstration in Telford was followed up by a visit to Stäubli Robotics’ state-of-the-art factory in Haut Savoie, France, which convinced JWQ that Stäubli had a keen interest not only in providing a machine of suitable size but also of being part of a project team who were determined to achieve a successful outcome to such a challenging project.
The contractual obligations of the Tudor Square / Crucible Theatre project demanded extraordinary levels of commitment from all the parties involved and JWQ needed considerable confidence in the robotics they chose and the team behind the technology to achieve the required outcome.
Converting CAD drawings into instructions that can be used to operate a robot arm is a specialised field. It is not easy to create software that can work in 3D so that the working head always performs the right tasks without damaging the workpiece. Robotmaster are experts in this field and provided the solutions for Johnsons.
The individual stones for the planters were works of art in themselves. There were no regular geometric shapes and the files necessary for the machining process were big enough to stress the software to new boundaries.
Machining robots are the latest introduction to the broad Stäubli robot range. They are capable of high speed machining with a spindle directly integrated into the robot arm. The drive to the spindle and all associated services – such as cooling and lubrication – can be placed inside the robot arm and connected to the various supplies through the robot foot.
This design provides a protection class of IP65 for the complete arm and IP67 for the ‘wrist’. Pressurisation can be specified where required.
Stäubli’s VAL HSM software controls the robot arm and manages all required functions. Robotmaster / Mastercam software is used to import and translate CAD / CAM data and apply and optimise six-axes robotic tool paths into Stäubli’s VAL3 language that can then be used to control the robot.
The Robotmaster software means the robot arm can be programmed as simply as a CNC machine tool and automatically generates the toolpaths, optimising them for the specific robot model and detecting and avoiding any potential collisions. There is full visual simulation of the robot machining process.
Tests on various materials, from alloy and stainless steels to Inconel 600 and aluminium, have proved the accuracy and repeatability of Stäubli’s machining robots. Machining stone is no different to machining any other material and, as with any material, the choice of tooling is critical to the accuracy achieved.
The stone machining demonstration at Stäubli convinced JWQ that robots were capable of machining and sculpting stone. Three RX270 robots were ordered with Robotmaster software. The design and construction of the production facility, machining stations, spindle design and tooling, were all carried out by the Myers Group’s own in-house teams with electronic integration provided by CR Solutions.
Robotic machining has also introduced new possibilities for surface texturing the stone with finishes that would be difficult to achieve by any other process.
Shaun Berry, Unit Manager of JWQ, mentions another benefit that the robots have brought to his company. “One of my main objectives is to improve the workplace for our employees. Traditionally stone masons have worked in dusty, hazardous conditions and when using pneumatic chisels can suffer from vibration injuries. The new robotic system removes these dangers completely.”
Machining robots are potentially more adaptable than traditional CNC machine tools which can mean that they work out less expensive. Stäubli’s range of robots is continually being developed, with high speed, high precision robot applications in the pharmaceutical, electronics and plastics sectors being extended into markets new to robotics. The range now comprises both four and six axes robots with handling capability from 1kg up to 250kg with a maximum reach of 3,210mm.
Stäubli are an international family owned group founded more than 100 years ago in Switzerland employing 3,500 people world-wide. Robotic production is centred south of Geneva in the French Alps, with facilities across Europe, North and South America and the Far East.