Controlling speed--a team effort.
The use of lower horsepower machines at higher speeds can lead to improvements in productivity. Yesterday's 50-hp machine with a spindle speed of 6000 rpm moves the same cubic inches of metal as today's 10-hp machine with a 30,000-rpm spindle speed because of the impact of speed phenomena on the cutting forces. High speed machining (HSM) means running high revolutions per minute, light depth of cut, and more aggressive inches-per-minute cutting using smaller diameter tools.
Real productivity, of course, depends on inclusion. The workholding components must perform optimally with the toolholding components. Truly, the whole is greater than the sum of the parts when it comes to high speed machining.
For instance, the shorter the projection length, the better the rigidity and total indicator reading (tir). Iscar's ETM tooling systems feature a toolholder with an ER32 pocket machined up in the spindle behind the flange called ShortIN. That means less than 1 1/4" projection ([less than]0.0002 tir at the nose). This Short IN holder is pre-balanced to G 2.5 at 20,000 rpm. This is the first choice for a toolholder with an ER32 pocket.
Iscar/ETM tooling systems has developed a modular milling system called Click-Fit. Allowing for 180-deg contact between the bore and the shank. When the tool is tightened with the clamping mechanism, it is pushed onto the centerline within 0.000 04. This makes full contact along the length of the bore and simultaneously makes 360-deg full-face contact. The high degree of contact, accuracy, and rigidity yields 50%+ increases in metal removal rates.
The "balance-able" toolholder advantage begins at around 12,000 rpm. These toolholders are available with ER32 pockets to use the ShrinkIN collet extensions, enhancing tool performance. For instance, in testing, two balance-able toolholders were set up to cut 4140 material--one at 0.5 g/mm and the second at 6 g/mm (a variance of 5.5 g)--each with a 8-mm, three-flute, 45-deg solid carbide endmill. Each toolholder ran at 13,922 rpm, 0.020 radial, 0.400 axial, 0.0035 fpt, 146 ipm for 60 minutes. The tool in the holder at 6 g/mm had 0.0025 (Vb) flankwear and the tool in the holder at 0.5 g/mm had 0.0015 (Vb) flankwear--or a 38% flank-wear reduction over the same cutting time.
Three factors--speed, horsepower, and the chatter/vibration problem--limit increased productivity. Speed and horsepower are fixed but the vibration factor is adjustable. If the natural frequency of the machine is matched to the tool frequency, vibration stops. Adjusting the tool overhang--rather than adjusting the speed, feed, or depth of cut--can achieve this.
A new toolholder system that is gaining acceptance in the HSM arena is the thermal shrink phenomenon. This approach doesn't use setscrews but allows the shank of the tool to be gripped 360 deg and held on the centerline of the axis of the toolholder within 0.000 04. This makes for easier balancing and allows for higher spindle speeds. The approach Iscar Metals/ETM tooling systems uses is an ER32 upgrade called ShrinkIN, a thermal Shrink ER32 collet chucking system. The ShrinkIN collets utilize the thermal shrink phenomenon for rigid clamping of solid carbide endmills 1/8" to 3/4". This new system provides higher torque, better precision runout ([less than]0.0004, 3D from the nose of the extension not from gage line) and better repeatability than ER32 spring collets. The ShrinkIN collet extensions have a slim design (4-deg taper per side) and different projection lengths (1.500", 2.500", and 3.500") allowing the user to reach into deeper shaped cavities and perform narrow milling applications.
The benefits of ShrinkIN System include high torque transfer, rigid clamping of carbide tools, and the ability to fit into standard ER chucks.
High speed machining is here. It is time to re-evaluate the impact toolholding and workholding systems have on the bottom line!
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|Publication:||Tooling & Production|
|Article Type:||Brief Article|
|Date:||Aug 1, 2000|
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