Introduction
Multi-axis milling machine typically refers to computer aided machine that helps in rotating tools used in milling away excess parts of metals in the manufacturing process. The machine supports rotation around single or multiple axes and able to support 3-5 axes translation. In the recent years, various computer softwares have been made available to help in automation of the multi-axis milling machine (Elber,1992).
The enhancement of the global technology and multinational enterprise, more reasonable research and development have made most of the producing organizations to adjust, design and configure these tools to match the supply chain system. These technologies have been very vital paradigm for the existing generation and to the future ones. This has helped to optimize the production, provide competitive market edge and networked manufacturing process planning (Hansen,1988).
Computer Aided Multi-axis milling systems have existed for several years and have also undergone several revolutions. The evolution of the machine technique dated back 20th century in the year 1950s at Massachusetts Institute of Technology in United States of America. The initial machines were only capable operating in three axes. In the year 1960s an Integrated circuits were include in these machines to elevate their microprocessor and make them more reliable. In 1980 the initial CAM systems were invented that provided more efficient and relatively reliable machining of complex metal surfaces. Initially only 3 axis systems were used, thereafter it was advanced to 3+2 axes and further increase to 5 axes. Currently the quest of automation and efficiency in productivity has resulted in better CAM systems, particularly the 5 axes system (Bohez et al, 2003).
Valid research literatures shows that these multi axes machine have been recently used to produce prompt cutter tool paths, minimizing scull off, optimizing tool orientation and further to resolve interface challenges. These machines sometimes use the dexel buffer to simulate material removal and tool representation. .The dexel refers to a basic volume element provided in a rectangular box and orientation in the positive z direction (Roth et al, 2001)
Types of the milling machine
Multi-axis milling machines are grouped into different classes depending on their specifications, constructions and the mode of their operations. The nature of the work to be executed also usually determines the choice of the machine type. On the basis of construction the following machines are always available. First is the column and knee type; this consists of a single base housing several control mechanisms. This base posse’s a worktable platform referred as a knee. Second is the fixed bed type, it poses a table that is usually restricted to reciprocated movement only, the cutter can move vertically since it is mounted on the double spindle head (Bohez et al, 2003).
Lastly is the special type multi-milling machine; they are entirely distinguished from other machines on their designs and construction. The special type machine usually posses’ different milling cutters that are mounted on several vertical spindles at different heights of operation. Loading and offloading can be possibly done while milling is in the progress. These special machines are majorly used to finish internal and external cylindrical surfaces of the work piece. Examples of such special multi-axis milling machines are the pantograph; which is used to reproduce the work operations into the desired models, profiling machine; which is used to duplicates and finally, the tracer machine which is used to produce the complex shapes and predefined irregular moulds through its synchronization process (Bohez et al, 2003)
Basic components of the machine
First are the basic physical components of the machine which are always shown by the skeleton nature, they are always unique and of different kind. The quality of the iron used in making the machine provides it with its rigid nature. The rotary and linear axes of the machine are always onto the base, then further to each other. The value of the rotary bearings and linear slides provide the machine with the potential accuracy and flexibility required. The horse power and the spindle motor further distinctively define the machine on its physical characteristics (Hansen, 1988).
The second most vital component is The CNC drive. This refers to the muscles of the machine; these components are fully responsible for the movement of the machine on its linear and rotary axes. These components includes the ball screws, drive system and servo motors, they are solemnly responsible for the movement in precise, smooth and rapid method (Elber,1992)
Lastly is the brain of the machine referred as the CNC controller Capabilities. This is majorly used in data handling through the use of the computers for automation. Usually have a broad memory size and takes synchronizations of the dynamic rotary controls. During the selection of the CNC translator, it very vital to choose the one with powerful CAD translator and has the entire Multi-axis controller. This calls for a consultant dealer who can provide necessary support on the component checking where necessary (Roth et al, 2001).
How the machine operates
This machine uses the rotary motion principle. In the operation the rotating cylindrical tool is used to feed the work peace. This rotating tool is compost of several cutting edges. This is done in away such that the cutter blade is in a position to shave the chips every time they pass. The cutter is designed with several teethes and high motion movement to make various cuts in a single motion (Elber,1992).
As much as these multi-axis machines moves intended materials through the cutting platform so do the blades carry out swaft of the materials at regular intervals. The machine can also be used to perform indexing, that is the act of equally dividing the work piece. For example during the making of the hexagonal bolt, indexing is necessary to result into identical six milled equal flat surfaces. This is majorly done using the universal dividing head, to result into compound, simple and differential indexing., though each posses it own advantages and limitations to certain levels (Hansen, 1988).
Sometimes irregularities may occur in determining cutting parameters and generating smooth tool paths, this may be due to an error in the machine or the cutter resulting into irregular ridges, correct this errors machine simulation using relevant computer software is used to validate intend parameters for the CNC machines before the work is executed and downloaded. This is possible since the simulator is in a position to show the machining process throughout the stages. This will eliminate unnecessary errors and reduce wastage that may be experienced during the process (Elber, 1992).
These machine simulation protocols have solemnly been implemented to virtually view the machine parts on the CNC machines. This is done by the use of the CAD/CAM that generates a generic language. This machine readable language works during the processing to calculate motions necessary to provide CAN vector which is the main governor of the machine motions. Furthermore, the simulation offers the preview of the general machine status and helps the operators in making reasonable decisions to eliminate them from tedious calculations. In essence they simulator acts as an adaptor. The virtual machining procedures generally help in optimizing the productivity and reducing the violating constraints controller of the process (Roth et al, 2001).
During the process the following parameters should be made into consideration. They include; first the cutting speed; this is the peripheral linear speed originating from the operations. It formula is usually derived as meters per minute. V= π d n/1000. Second is the feed rate at which the required work piece moves under the revolving cutter on the worktable, generally it is expressed in feed per unit of time, and usually feed per tooth and feed per revolution. The final parameter to be considered during the operation is the depth of the cut; this is the measure of the degree of the penetration of the cutter on the work piece. It is the ratio of thickness the cutter removes in a single revolution on the perpendicular distance of the work piece (Bohez, et al, 2003).
Advantages of the multi-axis machine
A multi-agent integration of the software’s used in executing work in these machines have offered efficiency in the manufacturing process therefore increasing the level of production. The software’s have also allowed individual manufactures to typically execute a collaborative manufacturing exercise online. This is through the use of the prototype multi-agent programme that was developed by the National Institute and Technology (NIST). Researches shows there is a possible through the provision of Unified Modeling Language (UML), this will provide robust integration and extension towards a better distributed multi-axis machine (Alber, 1995).
The software remote simulation has also been very vital in configuration and verification of the machine structure and its entire process of operation; this has helped to improve the quality of work and also increases efficiency during operation thus proving the operators with reasonable environment of work (Hansen, 1988).
Limitation on the use of the machine
Some machines posses’ unlimited C-axis motions, though majorities have limits. Providing programming cutter path that may unwind the C-axis on every cutting is tedious and may lead to inefficiencies during the operations. Therefore it is recommended to mill every part of the working tool as separate entities. Sometimes a full 5D complexity occur as most of these machines are only restricted on 2D and 3D miller movement, therefore clear orientation and positioning of the machine is necessary (Bohez, 2003).
While using minimum axis machining tools such as the 3 axis tool paths, it is not possible to work on very narrow deep cavities and to achieve better surface finishes with respect to the cuter diameter. This is observed majorly when working on hard surfaces resulting in unnecessary wastage of time and poor quality work. The tool paths may sometimes overlap resulting in imperfect blending and wastage of unnecessary time. This calls for a longer tool length and reasonable tilting in order to cover the whole part and result in reasonably desired surfaces (Elber, 1995).
Conclusion
Multi-axis milling machines usually are available in different models, sizes and all the main components always work in coordination to provide the relevant results. Meanwhile, the operation procedure of using them is usually complex that requires relevant skills and support from the experts and consultants
Pictures sowing some of the multi-axis milling machine
Picture 1&2 showing the multi-axis milling machine
Picture 3 & 4 showing the computer aided milling machines
References
Bohez E, Minh H, Kiatsrithanakorn B, Natasukon P, Ruei-Yun H, Son LTD. (2003) The stencil buffer sweep plane algorithm for 5-axis CNC tool path verification. Computer-Aided Des pp. 35(12):1129–42.
Elber G. (1995) Freeform surface region optimization for 3-axis and 5-axismilling.Comput-Aided Desighn PP.27(6):465–70.
Hansen, A.,F. Arbab, (1988) Fixed-axis tool positioning with built-in global interference checking for NC path generation, IEEE Journal of Robotics and Automation, Vol 4, No 6 (December 1988), 610–21.
. Elber, G. (1992) Free Form Surface Analysis using a Hybrid of Symbolic and Numeric Computation, Ph.D.thesis, University of Utah, Computer Science Department. Pp24-56
Wein, O. Ilushin, G. Elber, D. Halperin, (2004)Continuous Path Verification in Multi-Axis NCMachining, Proceedings of the twentieth annual symposium on Computational geometry, ACM Press, New York, pp. 86 - 95.
D. Roth, S. Bedi, F. Ismail, S. Mann. (2001). Surface swept by a toroidal cutter during 5-axis machining, Computer-Aided Design, pp. 33(1):57-63,
