igus has developed a cable carrier system that innovately combines rotary and linear movements for the DMG MORI MULTISPRINT multispindle lathe series. The solution provided represents a turning point in automatic turning: a unique energy supply system that follows the drum rotation while allowing the linear movements of the spindle holders. It also fully meets the manufacturer’s requirements in terms of maintenance and assistance.
by Alma Castiglioni
After a two-year research and development phase, DMG MORI has opened a new era for multispindle lathes. The MULTISPRINT series represents a real technological revolution in automatic turning. The state-of-the-art lathe, the high-performance, fast, precise and versatile production processes make the MULTISPRINT a machine with almost unlimited possibilities. High performance and top quality developed and manufactured in Italy with support and assistance from Germany: igus offers a special feeding system that innovatively combines rotary and linear movements.
Project development, from beginning to end
When the pre-assembled “readychain” igus system was installed on the spindle drum for the first time in April 2017, the procedures and dynamics of the system as a whole were a great innovation and the operators had to pay the utmost attention. Will it be possible to install the readychain igus cable chain system with a weight of up to 750 kg and a width of almost two metres in the horizontal machine housing? The combination in the “horizontal” position is an absolute novelty in the production technology of GILDEMEISTER Italiana, a subsidiary of DMG MORI. First the motor is positioned by two cranes in the housing inside the igus system. Then the readychain is assembled with its 8 cable chains, 64 electric cables and 73 pipes complete with motor in the machine base. The system has a core of 1.8 meters for the rotation, from which six linear cable chains are developed as arms to drive the spindles. For handling, chainflex cables wired with industrial connectors are laid in the chains, which are then connected to the lathe using electromechanical components. The process takes about two hours. The connection of the readychain to the spindle drum is completed – a perfect example of cooperation between machine manufacturer and component supplier.
The engineers and technicians worked hard until the summer of 2017 to complete the assembly of the machine on time, test it and ship it to the EMO trade fair in Hanover, the global benchmark event for the machine tool industry. Here the MULTISPRINT was presented as a revolution in mechanical engineering: the first machine to combine a multispindle lathe with SWISSTYPE technology. And this with a Y-axis on all spindle positions.
The new technology ensures the highest flexibility
Customer requirements for modern turning machines have changed due to market dynamics and globalization. Machine tool makers now demand shortened processing and tooling times, reduced effort for process development and integration, and an ability to handle the increasing degree of complexity.
The new MULTISPRINT includes, for example, nozzles for fluid power equipment, implants for dentistry and shafts for motor vehicle manufacturing, which are just three of the complex components that can be made on high-tech machines. The result is a manufacturing solution for scalable requirements from initial series production to the high-volume production of complex workpieces.
The combination of three types of machine technology enables the customer to engage in completely new forms of production, setting new standards in productivity and efficiency. The customer enjoys maximum flexibility for the mass production of components with a diameter of up to 50 mm.
Heavy drum turns with extreme precision and maximum speed
The heart of the machine is the spindle drum with six spindles for simultaneous machining of several workpieces. The main spindles in the drum can travel up to 180 mm.
The drum moves the workpieces to the tools quickly and precisely. It only takes 0.65 seconds for one of the six spindles to travel to the next position. For spindles to return to the starting position after machining has been completed in the six stations, the drum must turn 300 degrees in reverse.
Despite weighing more than three metric tons, the drum completes the rotation in just one second. The rods are pushed out of the loader through the drum to get into position for machining.
The project is fruit of a strong collaborative spirit
In summer of 2016, DMG MORI invited bids for the project, and ultimately chose to collaborate with igus.
“We have a lot of confidence in the many years of experience that igus has in the development of custom-made energy supply systems,” Passerini said. “As well as in the company’s extensive, high-quality testing facilities.”
The first meetings took place in January 2017, and two igus engineers visited Italy for a week. DMG MORI and igus engineers shared ideas and solutions regarding the design and suitable cables and hoses for supplying the drum with energy, data and fluid were chosen. “igus readychain solution has represented a real turning point for us – Passerini said.”
High precision requirements and speed
The exchange between experts has resulted in a unique energy supply system, which follows the rotation of the drum while allowing the linear movements of the spindle holders. The metal frame housing chains, cables and tubes is hung from the drum which rotates constantly and quickly in the central part of the machine. “The stability of the metal construction was one of the main challenges,” says Volker Beißel, one of the heads of the machine tool division at igus, “which accompanied the development of the readychain right from the start. “We calculated the stability of the structure after each stage of development to make sure that it could withstand all the stresses to which it was subjected. One of the main goals of igus has always been to create cable chain systems with a long service life and in this case, we were talking about at least five years.
To follow the rotation of the drum, igus selected a rotating cable chain system. These are customised systems for rotary movements with cable carrier chains, which are used not only in machine tools but also in many other types of machines. The standard rotation modules consist of two circular elements. One part of the guide channel is fixed to the static part of the system and the other to the rotating part. The reversible bending radius allows the movement of the cable-carrying chains in two directions, allowing, with the use of a single level of chains, rotation angles of up to 540°.
Space, maintenance and assistance specifications have been fully satisfied
The drum in the MULTISPRINT rotates in a range of 300 degrees and consists of two rotation systems. The outer system includes hoses with a bend radius of 160 mm. Twelve encoder cables and 12 servo cables from igus are guided on the inner circle. For each of the six linear chains in the drum, there are two encoder cables and two servo cables. One of the servo cables supplies the energy for the linear movements of the main spindles in the drum and one drives the spindle motor. They can move at a speed of 0.66 m/s and with a maximum acceleration of 10 m/s2. The six energy chain systems can be plugged in individually due to distribution boards and are easy to maintain or modify. That feature was also of the main requirements of the mechanical engineers designed the product. In addition, the chains and cables of the readychain needed a relatively small installation space. It is important to ensure that the working space for the mechanic components behind the drum be as large as possible. The system developed by igus fully met all of these requirements.
More than 800,000 test cycles without any problems
Engineers at igus had three months to develop the system. During development, a lot of value was placed on the modularity of the individual components. The linear chain systems can be plugged in and the sheet-metal parts designed by igus, for attachment to the machine, are made of several parts. This facilitates handling of the readychain on the customer’s premises and makes harnessing in the igus factory easier.
The igus specialists needed a little more than two days to complete final assembly of the chains with the harnessed cables and hoses. For fast production, it proved helpful that 95 percent of the readychain consists of parts directly made or procured by igus.
Assembly is also supported by the readychain rack, which is a metal frame with four different functions. It is an assembly tool for the connection of components at igus and makes the entire construction stable. The rack fits onto the load bed of a small truck. On the customer’s premises, the rack enables easy plug-and-play connection of the fully harnessed energy chain to the machine. “Before delivery, the entire system was intensively tested for weeks on end”, says Lukas Czaja, Head of Industry Management Machine tools at igus. A specially developed test stand simulates the movements of the multi-spindle automatic turning machine. In testing in a realistic environment used, the readychain has already completed more than 800,000 cycles without any problems.
The new machine design has definitely hit the target
The MULTISPRINT currently combines the productivity of a production lathe with the precision of an automatic lathe and the complexity of a universal lathe. It can produce turning and milling parts by machining bars and bar turned parts from bars, without system conversion costs. In June 2018, the Italian plant delivered the first MULTISPRINT to a Polish customer. To date, there are already dozens of MULTISPRINTS in operation in Germany, Italy, the USA and Spain. “Our customers are enthusiastic; the machine concept was immediately clear to users – concluded Passerini – especially the ease of maintenance made possible thanks to the pre-assembled igus cable chain system”.