The Gehring Group is regarded as a specialist in high-precision transfer lines that are used to machine engine blocks. The company has developed a modular system of linear robots with which crank cases, for example, are moved quickly from one machining station to the next. For energy supply, Gehring relies on especially "fast" and quiet energy chains and ready-to-install harnessed cables from igus®.
Honing precision bore holes is one of the main competencies of the Gehring Group headquartered in Ostfildern. Special horizontal machines for holes of up to 15 metres and transfer lines for the production of motor blocks are part of the plants that are manufactured at the production site Naumburg/Thuringia. In this challenging area of precision machining, Gehring is an international market leader.
The car manufacturers typically order a set of machines from Gehring to process the crank cases, which weigh up to 120 kilograms: larger ones for the honing of the crank case bore and significantly smaller ones for the (usually three to six) cylinder bores. The machines not only take over the honing, but also further work steps such as emptying residual cooling lubricants and cleaning. They work with high throughput – the cycle times are almost always under a minute, in extreme cases even under 30 seconds – and have to fulfil high requirements regarding availability, as production takes place 24/7.
The layout of these transfer lines has changed fundamentally in the past years. Dipl.-Ing. Gerhard Hohmann, Head of Construction: "Initially we built classic transfer lines, with which transport took place from one station to the next simultaneously via roller conveyors. Today, users want higher flexibility. The motors are smaller, the product life cycles shorter. Therefore we now build individual machine modules that are connected via gantry loaders. "That gives us the advantage, that individual modules can be exchanged, e.g. in the case of model changes – or that the car manufacturer can process different crank cases on the same line.
To increase vertical integration and provide complete plants from one source, Gehring started setting up the business area "Automation" in 2014. Gerhard Hohmann: "First we developed and produced roller conveyors and slat-band chain conveyors, then in 2014 a first small gantry system. “
A modular system for linear robots has now been created that enables the combination of different carriages, vertical axes, loading systems and grippers. The cycle time and the number of modules that are loaded are also variable.
No moving cable guide without an energy chain
When choosing the energy supply for the gantries the Gehring design engineers could resort to a proven solution. Gerhard Hohmann: "We use energy chains by igus® in our honing machines. We do not have moving energy supplies without a chain. "The chains are supplied pre-assembled as a readychain®: "We pass the necessary design data on to igus®, where the chain is planned, manufactured, fitted with the relevant components, harnessed and then delivered ready to install."
Challenge: energy supplies for a 33 metre long gantry
This principle also applies even larger gantries. A modular machine for honing the crank case bore can be up to 8 metres long (including measuring device and marking). The cylinder modules require 2.60 metres and you need 3 metres space in between for access. That means that the gantries – and hence the travels of the energy chain – are 20 to 33 metres long. The application is also impressive: with a current project, the gantry moves at 3 m/s and an acceleration of 7 m/s2. However, gantries have been built for 10 m/s, which are used in a crash test station.
In principle, energy chains are used in the modular honing machines by Gehring – in all movable axes.
This combination of travel, speed and service life (ten years are required) cannot be reached with a gliding chain – and a typical roller energy chain would produce high noise and vibration levels at that speed. Therefore, igus® recommended using the profile roller chain of the series P4. Here, the rollers of upper and lower runs do not move over each other, but offset on a continuous, wide rolling surface. This allows quiet and smooth operation, even in the case of long travels (up to 800 m). The identical pitch of all e-chain® links (with or without roller) contributes to the smooth running. The autoglide crossbars ensure a safe guidance, while significantly reducing the necessary drive power. And the service life is the longest of all energy chains in the igus® product range.
View of the Z-axis of the gantry with P4 roller energy chain.
Easily visible: the autoglide crossbars of the profile rol e-chain®.
Gehring purchases the complete system from igus®, including the guide trough that was specially developed for the P4 system – and the chains are also fitted and pre-assembled ready to install in the gantries as readychain®. The reverse arrangement of the chains only requires one trough, in which both energy chains run opposing. With the energy supply from the gantry, i.e. the X-axis, to the loaders (Z-Axis), a chain from the E4.1 product range is used, as has proven successful with such applications. Here, the undercut design ensures significant lateral stability compared to conventional systems.
The chainflex® cables that are used in the energy chains, have been developed from scratch for mobile applications. For the more critical and fast X-axes Gehring uses the servo cable series CF27, which is characterised by an additional pressure-extruded TPE inner jacket, among other things. For these cables igus® provides a guarantee of 10 million cycles or 36 months. To transmit data, cables of the series CF113 are used, the expected service life of which even is 20 million cycles in the specific case.
igus® energy chains are also used at the X-axis of the gantry loader.
When choosing plugs the igus® experts made recommendations, but the car industry generally prefers chains that have connections in between. A further advantage that working with igus® brings from Gehring's point of view: the worldwide purchase of parts holds no problems. With the first large project – a gantry for a ChineseGeneral Motors engine factory – the igus® subsidiary in China was also involved. The chain is fitted reversely here.
Good start with new product line From Gehring's point of view, the own business area automation technology proved to be a good start. Gerhard Hohmann: "We have a modular solution that fulfils all requirements and also manages to be very reliable. "The first gantries have already proved that. The 33 m gantry is also proving itself with the user. Gehring feels well-supported by igus® in the entire engineering process. The energy supply by igus® contributes to the high availability of the gantry – in a three-shift operation at 160 strokes per hour.