Peace of mind machining

Niles-Simmons ‘closed-door-machining’ concept offers the complete manufacturing of complex components without operator intervention. Aerospace Manufacturing hears how the company’s novel approach has successfully established itself in the market.

Niles-Simmons has developed the machining concept ‘closed-door-machining’ to meet the ever-increasing requirements concerning the manufacturing of complex, high-precision parts and components for the aerospace industry.

This concept allows the complete machining of parts in one continuous process within one machine and without any operator interventions. It is applicable for various part types which historically, were manufactured in several process steps on various different machines.

When using the ‘closed-door-machining’ concept, a raw part is clamped into the machine and after several fully-automatic re-clamping and re-chucking procedures, it can be removed as a completely finished part. The machining runs entirely uninterrupted and depending on the part complexity shifts can be overlapped a number of times throughout the cycle.

Since the process runs fully-automated, the time associated with labour-intensive part-handling procedures moving parts between several machines is removed and lay down spaces can be reduced. Similarly, the tasks for operators are also reduced since less machines are required and less operator interventions are necessary. By integrating all the necessary technology into one machine, there is no need to use ‘process specific’ single machines, which in the long-term considerably contributes to more cost-efficient production.

Open to new ideas

For the implementation of the concept, the company introduced several new machining and measuring technologies. In doing so, it is now possible to achieve high accuracies of <5µm in a process-reliable way by the use of scanned part measuring through Renishaw Sprint measuring sensor and automatic tool compensation after the measurement cut. At the same time, the measurement of all necessary tools also takes place, again fully-automated within the machine using a touch measuring system for fixed tools and an optic measuring system (laser) for rotationally symmetric tools.

In order to accommodate the large number of tools required to be used, it is possible to configure two tool magazines - headstock and tailstock side - with a capacity of up to 144 tools each to service the multi-axes turning-milling unit. The tools can be exchanged automatically into the working area from either side.

Alternatively, for specific machining tasks an additional magazine can be applied for the counter spindle or tailstock sided boring bar slide. This long tool magazine has a maximum of 16 positions for long tool cartridges. These long tools are also exchanged automatically into the second slide.

Up to 2m in length, these long tools can be operated with a high coolant pressure of up to 300bar and with a high flow rate of up to 150l/min. Consequently, any deep-hole drilling requirement can be achieved as part of an extremely stable and reliable process. The temperature-controlled coolant can be programmed both pressure- and volume-controlled and monitored via sensors.

For surface optimisation of the parts, it is also possible to integrate grinding operations in the machine. The grinding wheel can be exchanged, measured and dressed fully-automated. There are also sensors available for spark erosion. The coolant, which needs to be positioned close to the process, is controlled and positioned by a separate, programmable NC-axis.

A high specification CNC machine with a turning-milling unit, boring bar slide, turret (bottom), main- and counter-spindle, as well as steady rests and tool change units can be configured with up to 32 NC-axes. Due to this complexity, a CAD/CAM system with integrated post-processor is essential.

Furthermore, a liquid-cooled special concrete machine bed is used to achieve higher temperature stability and to ensure the requested accuracies despite variation of temperature. The machining centres are also equipped with damping and vibration reducing components such as finite element method (FEM) optimised slide-geometry, hydraulic clamped components of the part-axes, damping surfaces in machining direction and roller guides of the machining axes in size 45/55.

“Our aerospace customers were the first to adopt the ‘closed-door-machining’ process, but it can easily be transferred to other industries as well,” begins Rico Löffler, area sales manager of Niles-Simmons Chemnitz. “Niles is probably the first company worldwide that accomplished the goal of building a highly-automated cell with a sophisticated CNC machine like our N30MC to produce aero engine components comprising tough materials and tight tolerances within a ‘closed-door’ operation.”

“Usually the cost per part can be many thousands of Euros and there’s the risk of damaging the part during transportation from one machine to another, so ‘closed-door’ makes perfect sense. Long cycle times from 6 to 40 hours leave a lot of room for the operators to make mistakes. We’ve been successful in our goal of removing the operator as a potential error source from the entire process of manufacturing highly accurate parts made from the toughest materials.”

Behind closed doors

But isn’t ‘closed-door-machining’ just another term for ‘done-in-one’ machining? If not, how does it differ?

“It is probably the same, but reaches a total new level due to the accuracies we achieve on our machines for these types of parts and special materials required by aerospace and other sectors. Our customers like the flexibility of the entire organisation dealing with their challenges, but it requires trust - especially in this business - to get what has been asked for on-time and make it all happen within budget. We consider ourselves as a technology provider and so do our customers, which is very unique in this industry.”

Years ago, the NSH Group acquired and qualified a subsidiary company offering automation solutions like gantries and robots together with a cell controller in-situ with its Niles machines.

“Customers can now obtain everything from a single source,” says Löffler. “Automation provides a secure and safe logistical process to handle the parts going in and out of the machine and outside the machine. This alone, is enough to justify automation - even for a variety of different parts with long cycle times.”

The process security within the ‘closed-door-machining’ concept is significantly enhanced through Niles-Simmons comprehensive software modules driven by Industry 4.0, such as volumetric compensation software, spindle modulation, axis compensation, tool breakage and drive monitoring. The smooth interaction of these software components with the sophisticated machining and measuring technologies - and the resilient and well-conceived machine design - builds the foundation for successful ‘closed-door-machining’ without operator intervention.

“Industry 4.0 plays a very important role, especially within the extremely high level of automation of our Niles systems,” Löffler concludes. “It completes the entire value chain and would make no sense without it. Our customers cannot afford scrap parts created by worn out tools, ‘not-in-order’ incoming parts, bad processes or machine behaviour. Therefore, condition- and process-monitoring will always be part of the machine scope of supply in such a process, besides all other technologies. Our challenge is to stay on top of everything and provide the most efficient solution for our customers.”

www.niles-simmons.com