If the workpiece becomes more expensive, because finishing takes too long, this eats into the profit (which is vital for being able to make the necessary investments at the right time) - and again there is a risk that the customer will look for a cheaper supplier.
It would, therefore, appear that every workshop runs one or two risks: quality of the workpieces is not good (workpieces rejected, so lost profit), workpieces not ready on time (lost profit and/or customer), or workpieces too expensive (lost profit and/or customer). Perhaps, there are insufficient skilled (or poorly informed or trained) employees, which means that the company cannot undertake difficult work, (loss of competitive position) and workpieces are of poor quality; they are too slow or expensive to finish.
In the context of risk management, every workshop manager must take into account the above elements and must take the necessary steps to minimise the risks. This includes a coordinated objective of correctly finishing workpieces - quickly, cheaply, and safely. In addition, there are a number of possible risk-limiting measures that can be taken.
During the test phase for the QuattroMill, Seco examined the exact impact of a number of possible interventions in the production apparatus. This was achieved by means of a practical simulation under actual operating conditions, which threw up a number of interesting facts.
· The simplest method of limiting costs is to buy in the inserts more cheaply. The simulation indicates that buying inserts at 20 per cent lower cost has no effect on production time (productivity) of the workpieces and will reduce the total production costs by about 2 per cent
· Another possibility is to use better inserts. The better insert quality can then be used to increase tool life (under constant cutting conditions). During the same simulation we learn that a 20 per cent longer tool life of the inserts reduces the production time by about 3 per cent and the production costs by around 4 per cent
· Another way of using better inserts is to increase the cutting conditions (speeds) by 20 per cent (constant tool life). This intervention reduces he production time by 21 per cent and production cost drops by 18 percent
· Both the above factors can be combined (20 per cent higher cutting speeds and 20 per cent longer tool life, eg, by using F40M). This reduces the production time by 24 per cent and the production cost by 21 per cent
· The most complex intervention is one, which influences the entire process. A lot of time is wasted with a machine tool because problems arise (problems of any kind, but in most cases technical or organizational), and because tools have failed. Indexing inserts easily when they are worn out (see QuattroMill), whilst at the same time ensuring that if there are problems they can be dealt with quickly and efficiently (see training of personnel) results in a 60 per cent shorter finishing time and a 63 per cent cheaper finishing cost-Efficient production control (total cost and productivity management) can be achieved in different ways. Some methods are fast, but the impact on the overall picture is not all that great. Other methods demand more structural interventions, but the reward is also much greater. Every production manager or workshop manager will himself have to decide what the best method is for him. The purpose of this chapter is to draw attention to the various possibilities, and determine their impact on cost price and finishing speed.
(*) Many problems in the workplace are related to workpiece materials. Poor qualities, characteristics that are not known or not understood, or variable composition, are some of the reasons.
Major savings can be achieved (fewer problems) by using better workpiece material. However, as QuattroMill has a milling cutter that is less sensitive to workpiece material irregularities, it makes for a more rigid milling tool. This also results in fewer problems, shorter non-productive times, and consequently higher productivity and lower costs.
Patented milling cutter pocket
During the development of QuattroMill, great attention was paid to clamping the milling cutter on the machine. For example, the tool can be dimensioned very accurately and is also of superior quality in other respects. Moreover, the machine tool itself is able to meet the most stringent requirements regarding vibration damping, cutting capacity, etc, where the milling cutter clamping represents the weakest link in the machining process, if it is not perfect. Not perfect in this context means excessive runout. Where conventional tool clamping is used, the runout may be as much as 40 µm. To keep this to a minimum, the clamped milling cutter should assume a concentric position relative to the spigot. With the patented Accu-Fit tool clamping system, Seco has chosen to achieve this by means of a hydraulically expandable spigot that positions the milling cutter accurately and centrally. This eliminates the play and greatly improves runout. The axial clamping screw further ensures the contact between the tool holder and the milling cutter. The Accu-Fit reduces runout to a maximum of 5 µm and therefore increases the machining accuracy to a level that meets the requirements of modern cutting on high quality machines. The Accu-Fit guarantees maximum contact between the milling cutter and machine tool. The tool life of the cutting edges is consequently increased and noise production during milling reduced. Manufactured from hardened steel and balanced to 3 g.mm/kg, the Accu-Fit comes into its own in applications involving high speeds, and in difficult workpiece materials. The principle of self-centering ensures that the balance of the clamping unit - milling cutter combination is maintained at all times, even in highly demanding high speed machining operations. The Accu-Fit is available with an HSK, BT or V flange (DIN/ISO) back end; the diameter of the central cylinder varies from 22 to 40 mm. Through coolant is standard for arbors of 27 mm and over.
Extensive experiments
The QuattroMill-Accu-Fit combination was tested with a number of loyal customers. The tool was not only compared to existing products from well- known competitors, but also to existing tool concepts from Seco Tools themselves, such as OctoMill.
These tests revealed higher cutting conditions that are applicable to the cutting process - such as cutting speed (vc), the feed rate per tooth (fz), the table feed (vf), and the axial and radial cutting depth (ap and ae) - and the much longer tool life. In one of these tests - which related to the cutting of stainless steel AISI 316L-it was possible to apply a much higher table feed than the equivalent tool from the competitor (875 and 600 mm/min respectively), under otherwise almost identical cutting conditions. The tool itself differed significantly on one point: QuattroMill had one additional tooth - six instead of five. It is also possible to give the QuattroMill one, two or even three more teeth with the same diameter because here the characteristics of the cutter body material create the conditions for this. Besides, higher number does not detract from the strength of the milling cutter. The result of the test thus revealed a 30 per cent reduction in cycle time (due to the high table feed), and also a 30 per cent longer tool life. The high surface quality and soft cutting were explicitly mentioned as qualitative aspects when the results were evaluated.
In another test, a QuattroMill face mill was used (diameter 63 mm, 5 teeth) in preference to a larger competitive milling cutter (diameter 80 mm, 6 teeth) for machining grey cast iron GG25. With a lower cutting speed (330 as against 483 m/min), a higher feed rate per tooth (0.36 as against 0.227 mm/tooth) and otherwise identical conditions, a 40 per cent higher tool life was observed with the QuattroMill milling cutter. The low noise levels, and flexible cutting, were observed as explicit characteristics.
In tests where the QuattroMill was used for machining steel, the results were even more telling: in a case 50 to 100 per cent improvement in cycle time was noted, with a doubling of productivity (by doubling the table rate). When the milling cutter was used for cutting superalloys the productivity difference is smaller, but still impressive, with production time reductions of 28 to 50 per cent. The cycle time is the same as in the case of the competitive tool.
Blending with other milling concepts
Finally, the pressing question is what is now the specific application relative to other milling concepts from Seco Tools? The QuattroMill stands for simplicity and productivity, and can also be easily combined with Seco concepts like HexaMill and OctoMill. It is due to the extra thick inserts that the former lends itself to machining processes involving very high chip flows (greater cutting depths, high feed rates), while the latter is more suitable for lighter to moderately heavy face milling processes. OctoMill is also extremely flexible as it is suitable for slot, copy, axial, and non-linear milling. The six and eight cutting edges of HexaMill and OctoMill, respectively, also offer an interesting cost price advantage per cutting edge.
The QuattroMill milling cutter is designed exclusively for face milling, particularly on small to medium-sized milling machines. Within these application limits the milling cutter, when combined with the innovative Accu-Fit arbor, performs better than earlier or competitive concepts, and is also simple in its application (for example, in terms of insert indexing compared to the OctoMill). The QuattroMill requires less expertise and skill from the operator, allows faster insert indexing, and yet produces a perfect result in terms of productivity, surface finish, and tool life. In the case of difficult materials (hardened steel grades, stainless steel, and super alloys), the QuattroMill is preferable because it is evident from detailed tests that this milling cutter performs better, thanks to the lighter cutting process, a consequence of the geometry of the insert and seat. The milling cutter will also perform well when milling parts, which have been clamped by a vacuum method, for example, in the case of non-optimum clamping systems and thin-walled workpieces. When high productivity is an overriding consideration, the QuattroMill is the natural choice, as many practical tests demonstrate. High productivity is expressed in cost savings which more than make up for the slightly higher costs of the inserts per cutting edge (four cutting edges instead of six or eight).
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