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How 3+2 machining is beneficial and is an option to broaden what a five-axis machining can do | By Indira Rao | Machining centres are equipped as per definition with minimum three (X, Y and Z axis), in general with four axis (additional B axis table) and only few of them are with an additional 5th axis (A axis trunnion) or more. Machines with less than three axes would not be a machining centre but a special purpose machine. If one is a supplier to mainly the automotive industry most of the components are cases. The machines need to change the cutting tools from drilling, tapping, milling, reaming and honing. For these processes horizontal or vertical machines are specified. Machining of free formed surfaces is not applicable to these components with the exception of tilting spindles for non-automotive engine production (ship or locomotive engines).

Currently, the specification of the typical Indian customer requires a low cost four-axis machine to enable part piece cost efficiency, which is basically a low cost investment. This is not different to the specification supplied by the European and American customers just some years ago. Concurring, Manfred Berger, executive vice president, global sales, MAG Industrial Automation Systems says, “Today, these customers focus more on life-cyclecost which includes the total cost of ownership until the equipment is scrapped. With today’s enormous dynamic of part modernisation or modification some of the OEEs have learned about the importance of part flexibility and the retool cost for rather un-flexible CNC machines. For most of the modern projects the customer will specify five-axis machines for a part or all machines of the system to be prepared for any future parts the machines will have to produce.”

This certainly testifies the increase in popularity of five-axis operations and it looks like the trend is here to stay. Vinay Deshpande, AVP engineering & solutions, Sandvik Coromant India agrees. He says, “The trend of multitasking machining is indeed increasing as it reduces the number of setups, material movement, manpower, space, tool change time and also improves the work piece quality. The new trend has seen the usage of multitasking machines for developing components and is best suited for complicated work piece shapes. The aerospace and oil and gas industries need mostly multitasking machines.”

Although five axis machining is in vogue, it is not necessary for a machine shop to use all five axes of a five-axis machine at the same time to get large benefits. 3+2 machining can help one achieve the same. Explaining, this concept, Rupesh Mehta, MD, Macpower CNC Machines avers, “3+2 machining is a concept where there is an option of adding/removing a two axis tilting table on a three axis VMC as per convenience. This is done to reduce the number of setups, progressive fixtures and the errors associated with every added setup. The cost of the tilting table is generally justified if the machining is at compound angles and the fixture cost for each setup is high.”

The main advantage of 3+2 machining is that it allows the use of shorter cutting tools, which increases quality and tool life. This can be achieved to rotate the part with a five-axis machine into a position which allows a three linear axis to execute the part machining and the shortest possible cutting tool. While the three axes are moving, the two rotational axes (A and B) are locked. The application of this technology is used mainly for the free form machining of moulds to generate in the best way the required cavities.

“Short cutting tools are for any process the best condition to provide the maximum stability of the system to the cutting edge. With modern simulation tools, e.g. Real NC or NX CAM, processes can be optimised regarding tool length, tool path and cycle times. For automotive applications there are not many processes which require 3+2 processes. Due to fuel economy some of the cylinder heads require port machining where this technology could be supportive or milling of joint faces on block and head in order to simulate heel,” opines Berger.

Biorad Medisys is an Indian company that provides the world with innovative life saving medical devices. On asking them if they use 3+2 processes, Krishna Shetty, work coordinator, Biorad Medisys said, “Replacing all the existing three axis machines by five axis machines will involve huge additional investment. As such, we also use 3+2 axis machines and are able to perform normal operations on these machines, which do not involve very complex machining.” Precision Automation and Robotics India is another Indian company that is a global automation solution provider and uses world class robotic products and technologies and they prefer using five-axis machining too. Ajay Ramgol, corporate head – vendor development and head- central manufacturing service, Precision Automation and Robotics India (PARI) asserts, “With (3 + 2) machining the cost of manufacturing goes up as the output is less and we live with risk of relative in accuracies resulting out of the same. On the other hand, if the tolerance requirement of the components is not so stringent, then one can definitely think of adopting the 3 + 2 machining and with the aid of small fixturing concept. This will give cost reduction because of the low machining hour rate (MHR).

Both the Indian companies use five-axis machines on their shopfloor. Stating its benefits, Shetty says, “Five-axis machining centres form a part of your manufacturing set –up and with it we are able to machine complex shapes in a single operation. It also helps us reduce machining time, achieve better surface finish and eliminates multiple set ups. One example is of drilling multiple holes in different angles. In three-axis machining this will involve multiple set ups and hence it is time consuming. We also save on the cost of tooling and fixtures and the inter operational cleaning up is also eliminated. We also achieve more accuracy compared to regular three axis machine due to machining of complete part with one reference/datum.”

PARI too has two five-axis machines as a part of their set-up. Ramgol asserts, “For tooling parts which requires multiface referencing with high accuracies it can be done faster by reducing the multiple set ups. This reduces the risk of transferring references from one set up to other and thereby eliminates the inaccuracies owing to it. This helps us to reduce the throughput time for such parts and achieve the desired productivity. Secondly, it aids in development of the prototype assemblies and its components in a faster way.”

These testimonies by users of machine centres definitely indicate that the trend of five-axis is here to stay in India. Berger seconds and opines, “For India, we see the trend to purchase complete new systems in comparison to reuse of old machines for roughing and new machines for finishing along with the request to have five-axis machines in the line. Both will guarantee in the long term the lowest life cycle cost and cost efficiency for the produced parts but will require higher initial investment. The strategy will be supported by the fast growing automotive market in the next years.”

Continued appreciation of energy cost pressurises industries to save energy/increase profitability. We offer ‘productivity improvement programs’ through which customers can maximize their machine productivity and hence profitability. We also offer energy saving programs to achieve this objective and have developed cutting tools which consume less energy and help the environment,” avers Deshpande.

Energy consumption is a significant cost portion of the production and is one of the key subjects for the project specifications provided to the vendors. With minor modification of a standard CNC machine as installation of energy saving components, energy recuperation and energy on demand based on production status allows one to save approximately 25% of the energy consumption in comparison to a traditional manufacturing system.

Today, there are machines that will switch off coolant, air blow, hydraulic power unit, etc. until only the operator panel is on if no part is detected on the incoming part conveyor. With the new process technologies, such as minimum quantity lubrication (MQL) further reductions in energy consumption are available. “Currently, these features like energy on demand are available as options for the customer,” avows Berger.

Since quite some years now, five-axis machines have become smaller and more affordable than they once were. Therefore, we see a lot of companies opting for it. It is also nice to see companies taking cognisance of energy efficient machines. However, along with features, machine shops should also be aware of machining benefits. Machine shops that are still considering to move to fiveaxis should be aware of 3+2 as an option to enlarge what a five-axis machine can do.

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