Hard turning on EMAG turning centre: as hard as it gets – and still the costs are reducing
25/02/2013 - Oliver Hagenlocher
These days, our cars are full of high-tech materials that ensure a long life for the individual components and make the car safe to drive. These materials are also less weighty, which reduces consumption levels. To ensure that they are machined in an economical way – using high-precision processes – requires the right machinery and the correct process. When it comes to the machining of hardened surfaces, hard turning is a particularly efficient solution that – compared to grinding – offers a radical reduction in both machining times and investment costs. With its VL 5 EMAG has a machine in its product range that is tailor-made for hard turning. Its design brings a number of advantages to the machine’s particular, highly demanding field of application.
The conditions faced by sub-suppliers and manufacturing companies alike have been the same for decades: optimal component quality, flexible batch sizes and low workpiece costs. These are the kind of demands made by customers in all branches of industry and all fields of application. However, it is particularly difficult to achieve in the machining of already hardened surfaces. Grinding, the method used most often for the purpose, is very time-consuming and known for its relatively high tooling costs and energy consumption. One alternative process that is being used more often, both in the small batch and the mass production of hardened workpieces, is hard turning. With good reason, as the process offers identical surface finishes and allows for the process chain to be shortened by a complete stage. Last, but by no means least, turning machines are noticeably cheaper than grinders and their energy consumption is lower. Unlike the grinding process, hard-turning can often be carried out dry – a much more environmentally friendly method.
The design scores heavily when it comes to hard turning
In the VL 5 the turning experts from EMAG have created a tailor-made solution for the application of this innovative process. Its design features make a particularly positive impression in handling the heavy stresses exerted on tools and machine during hard turning. For instance, its machine base is in Mineralit, a polymer concrete with a vibration resistance eight times that of cast iron. “A vibration resistant machine leads to an improved surface finish on all components it machines, with tool life being much improved too”, says Peter Loetzner, CEO EMAG L.L.C. The vertical design is another feature that ensures an economical process, with the work spindle and the workpiece located above the tool. This offers ideal chip flow conditions, with the material removed being taken out of the machine by a chip conveyor. All guideways are located above and away from the machining are, keeping them safe from any possible ingress of chips or dirt. This increases the constantly maintained component accuracy and reduces the maintenance effort.
Another important quality feature of the vertical turning centres from EMAG is their integral automation. They all use a recirculating conveyor chain into which are inserted carrier prisms holding the raw-parts. The chain conveys the workpieces directly into the pick-up station, where they are picked up by the work spindle and then machined. Workpiece changeovers are very fast, as the distance travelled between loading and machining position is only 550 mm. This leads to a massive shortening of the time span between machining processes.
Convinced by low investment costs
The possibilities offered by hard turning on the fully automated, vertical turning machines from EMAG is best shown by the example of a gear production for a sub-supplier to the automotive industry. The VL 5s run by the customer produce a total of eight different gears for a dual-clutch transmission system. Following the hardening process, the workpieces are pre-turned on the machine, to remove the hardened top layer. This is followed by a synchronous ring being welded onto the workpiece away from the VL 5. The component is then returned to the EMAG machine and finish-turned. Before the customer used VLs for the job, he carried out the comparable operations on grinders. “Some time ago, this company started to invest in VL 5 machines for their hard turning process, as the investment costs were so much lower”, adds Peter Loetzner. And it has to be noted that the surface finish on the component is as excellent as ever. “Hard turning on the VL 5 is in no way inferior to the previously employed grinding process; and the machining times are noticeably shorter”, explains Peter Loetzner further.
From bearing ring to gear
When can hard turning successfully replace the grinding process in the machining of a component surface? “That depends on a number of factors. For instance, the desired surface texture is of great importance. We advise our customers on this point and show them the best way to proceed”, explains Peter Loetzner, “and where hard turning is possible, it often becomes first choice.” Apart from lower investment costs, many users are also impressed by the elimination of the grinding operations. On the VL, the turned part can be finish-machined in a single setup. It is no longer necessary to take it to another machine for finishing. The result: the output level of the whole production increases quite considerably.
The turning specialists from EMAG can look back on having already delivered a total of 3,500 VL machines. The know-how this has provided is something the new user also profits from. “Our design team orients themselves on customer demands. This ensures that the strengths of our machines are targeted on what is required.” The types and numbers of components produced on these vertical turning machines are of great diversity. Toothed components, such as gears and crown wheels can be produced with the same efficiency as bearing rings. “The system can be adapted to suit any batch size and impresses with its short cycle times and its high component quality. These advantages captivate the customer again and again. If, in addition, you can also save on a whole process stage, the user of a VL 5 will, of course, be able to enjoy an unbeatable cost advantage”, emphasises Peter Loetzner in conclusion.