308 Каталог INGERSOLL 2011 Режущий инструмент и инструментальная оснастка Стр.310

Каталог INGERSOLL 2011 Инструмент и оснастка Стр. 310 0308 Lab2u

RIGIDITY ANALYSIS MAXIMIZING RIGIDITY WILL IMPROVE END MILL PERFORMANCE Rigidity Among the many variables in milling rigidity is one of the most important. Quite often it is the primary factor determining end mill performance. Due to their length-to-diameter ratio end mills are the least rigid of all cutting tools. Understanding rigidity and maximizing it can dramatically increase end milling productivity. Some of the primary factors that affect rigidity are basic machine design drive mechanism bearing placement spindle size tool diameter and length overhang workpiece and fixturing. This discussion will focus on how end mill selection affects rigidity. Rigidity: is affected by cutting force. Cutting force produces deflection. Force: is produced by a combination of cutting speed in Surface Feet per Minute (SFM) and power. Power is a function of the width and depth of cut feed rate and the material being cut. Soft materials require less power and hard materials require more. Deflection: is produced by the cutting force on the tool. The tool's length-to-diameter ratio determines the degree of effect cutting force has on the tool. Deflection is directly proportional to L3 (length to the third power) and inversely proportional to D4 (diameter to the fourth power). In other words deflection is radically reduced as diameter is increased and or length is reduced. Ingersoll has designed computer software to perform the many calculations required to determine the amount of deflection on the tool. Using Ingersoll's "Rigidity Analysis software deflection for the following example can easily be determined: Cutter: 2.000 diameter 4.00 flute length No. 50 V-Flange adaption Material: Low carbon steel Speed: 400 SFM Radial DOC: 1.00 Axial DOC: 2.00 Feed 12 IPM (.008 IPT) The calculated theoretical deflection is .007. Deflection of .001 or less is recommended for end milling operations. This example exceeds the desired maximum deflection of .001. A cutter running under these conditions is likely to chatter produce a poor surface finish and exhibit reduced tool life. The same example was recalculated after reducing the flute length from 4.00 to 3.00. Without making any other changes the rigidity of the end mill improved dramatically. The theoretical deflection was reduced to .0009. By reducing the overall length-to-diameter ratio by 25 percent deflection was reduced to less than half of the original example. Many operational variables require additional rigidity. Among these are brittle cutting edge materials and any factor causing an increase in cutting forces such as negative cutting angles or tougher workpiece materials . Tool Adaption Rotary Toolholder: Most end mills are run in rotary toolholders which connect the tool to the spindle. Ironically due to the added length and extra joint this is the least rigid of all end mill adaptions. To maximize rigidity with this adaption an end mill with the largest diameter shank and the shortest adaptor possible should be used. Poor: Straight shank end mill and rotary toolholder Better: Integral Shank 310