LUREN Precision Co.LTD. www.luren.com.tw Head Office: Via Marconi, - PowerPoint PPT Presentation

Head Office: Li Hsing Factory Location: Hsin Chu Science Park - Taiwan LUREN Precision Co.LTD. www.luren.com.tw Head Office: Via Marconi, 8 Viganò Brianza (LC)- Italy www.fubri.it Distributor for European market

LUREN Luren Hob Resharpening Machines CNC Hob Resharpening Machines producing by Luren LHG-3040 ---- LHS-3040 ---- LHG-2540 ---- LHG 1520 Distributor for European market

LUREN With this presentation we want to inform about:  Basic of hob resharpening operation  Working condition  Description of Luren hob resharpening machines The most important characteristic of Luren resharpening machines are:  High performances  High tech design and components  High flexibility  Easy to use  Low cost Distributor for European market

LUREN Basic technical information about of hob resharpening operation The accuracy of the hobbing process to a large extent on good hob resharpening and the performance of hob is very much affected by the type of resharpening carried out. If a hob is resharpened under incorrect working condition, it may at times result in tooth breakage. We examine now some aspects of this important operation. The maintenance of the hob is a very delicate operation that must be carried out by a efficient machinery and modern equipment. First examine the definition of the errors that may be generated when resharpening according to the DIN 3968 normative. Distributor for European market

LUREN The error of profile and position of the tooth face u = the movement of the resharpening face in relation to the radial plan when sharpening with a positive rake angle. In radial sharpening the u value is zero. h = useful tooth depth e = profile error found Module Class 0,6-1 1-1,6 1,6-2,5 2,5-4 4-6,3 6,3-10 10,1-16 Gash radial AA 10 10 12 16 20 25 alignment A 12 16 20 25 32 40 50 (microns) B 25 32 40 50 63 80 100 Distributor for European market

LUREN Error of profile generated on the workpiece Negative rack angle Positive rack angle Distributor for European market

LUREN The indexing error between two consecutive flutes Must be measured half way up the tooth Module Class Indexing between 0,6-1 1-1,6 1,6-2,5 2,5-4 4-6,3 6,3-10 10,1-16 AA 10 10 12 16 20 25 gashes (two adjacent teeth) A 12 16 20 25 32 40 50 (microns) B 25 32 40 50 63 80 100 Distributor for European market

LUREN Spacing between two non adjacent flutes This is the cumulated indexing error of the flutes Module Class Maximum indexing 0,6-1 1-1,6 1,6-2,5 2,5-4 4-6,3 6,3-10 10,1-16 AA 20 20 25 32 40 50 error between any two teeth A 25 32 40 50 63 80 100 (microns) B 50 63 80 100 125 160 200 Distributor for European market

LUREN Error of profile generated on the workpiece Indexing error of the flutes produces irregular profile Distributor for European market

LUREN The direction error of the flutes This error is measured in a length of 100 mm Module Class 0,6-1 1-1,6 1,6-2,5 2,5-4 4-6,3 6,3-10 10,1-16 Accuracy of gashes AA 50 over 100 mm A 70 (microns) B 100 Distributor for European market

LUREN Interference between grinding wheel and hob Sharpening a hob with helical gashes using a grinding wheel that has a rectilinear cutting Hob Gear line, the face that is generated will be slightly crowned because of the interference of the grinding wheel with the helical gash. The larger the helix angle of the gash and the larger of the diameter of the grinding wheel, the greater this convexity of the resharpening face will be. This is why resharpening machines which works helical hobs must be equipped with a special dressing unit to profile the grinding wheel, so as to generate the same convexity and compensate for the interference phenomenon. A hob with a convex cutting face will produce a gear tooth with more material on the tip and at the root. Distributor for European market

LUREN Working condition in resharpening The u movement of the grinding wheel in relation of the hob depends both on the rack angle and on the hob diameter where the following applies: a)- Movement below centre which generates a positive cutting angle b)- Movement above centre which generates a negative cutting angle Distributor for European market

LUREN Working condition in resharpening The sharpened surface roughness must be as low as possible so that the cutting edge is not irregular. R a = 0,15 If this were the case, wear and Rz = 1,12 chipping would form with more ease. The tolerable roughness is a maximum of R a = 0,20 microns If the roughness is higher the wear of the cutting face proceeds faster R a = 0,35 In order to obtain a lower Rz = 2,18 roughness the working conditions must be chosen properly Distributor for European market

LUREN Working condition in resharpening The roughness is strongly influenced by grain size of the grinding wheel abrasive The grain size is identified by a number, but this number has a different meaning for Aluminium Oxide and CBN (or Diamond) abrasive The two following slides show the standard size Distributor for European market

LUREN Grit specification of Aluminium Oxide abrasive Approximate diameter of the grain Indicative FEPA Diameter in Diameter in Indicative FEPA Diameter in Diameter in Number mm inch Number mm inch 36 0,500 0,0200 150 0,080 0,0030 46 0,350 0,0140 180 0,070 0,0028 54 0,300 0,0120 220 0,060 0,0024 60 0,250 0,0100 240 0,050 0,0021 70 0,210 0,0080 280 0,040 0,0017 80 0,180 0,0070 320 0,030 0,0012 90 0,150 0,0060 400 0,020 0,0008 100 0,130 0,0050 500 0,014 0,0006 120 0,100 0,0040 600 0,010 0,0004 Distributor for European market

LUREN Grit specification of Diamond and CBN abrasive Nominal width of USA - ASTM E11- Japan Russia CBN – FEPA Diamond FEPA Gost 3647 – 71 the mesh ( µm) 70 (Mesh) JIS 6002-63 DIN 848 DIN 848 Mesh per 1” ISO 565 dimension µm dimension µm 212 – 250 60 – 70 250 – 210 250 – 200 D251 B251 180 – 212 70 – 80 210 – 177 250 – 200 D213 B213 150 – 180 80 – 100 200 – 160 D181 B181 -- 125 – 150 100 – 120 149 – 125 160 – 125 D151 B151 120 – 140 125 – 105 125 – 100 D126 B126 106 125 90 – 106 140 – 170 100 – 80 D107 B107 -- 75 – 90 105 – 75 D91 B91 179 -200 -- 200 – 230 88 – 63 80 – 63 D76 B76 63 75 53 – 63 230 – 270 63 – 50 D64 B64 -- 45 – 53 270 – 325 53 – 44 60 – 40 D54 B54 38 – 45 325 – 400 44 – 37 50 – 40 D46 B48 40 – 25 40 – 28 --- B30 -- -- D25 -- 52 - 32 -- -- -- Distributor for European market

LUREN Working condition in resharpening Resharpening with CBN grinding wheel of High Speed Steel Hobs Some manufacturers prefer to remove all of the stock (from 0,20 to 0,40 mm) in just one pass using a reduced feed speed Cutting speed = 30 m/sec Size of grit = 90 – 100 Feed speed = 200 mm/min Concentration = 100 – 125 Cutting depth = 0,20 mm Resin alloying element Due to the low feed it’s produced a large amount of heat because the wheel works in the same area for a long time Distributor for European market

LUREN Working condition in resharpening Resharpening with CBN grinding wheel of High Speed Steel Hobs The following working condition are suggested with CBN wheels This type of grinding wheel generally has a diameter of around 150 mm. Fast passes with limited stock removal and change of gashes Stock removal Feed so as to prevent the grinding Phase per stroke mm/min wheel from heating up the hob Roughing 0,03 mm 2500 teeth. Pre-finishing 0,01 mm 2500 Finishing 0,005 mm 2500 Distributor for European market

LUREN Working condition in resharpening Resharpening with Diamond grinding wheel of Carbide Hobs The following working condition are suggested with Diamond wheels for carbide hobs This type of grinding wheel generally has a diameter of around 150 mm. Cutting speed = 30 m/sec Stock removal Feed Phase per stroke mm/min Size of grit = 64 Roughing 0,03 mm 2000 Concentration = 100 Pre-finishing 0,01 mm 900 Finishing 0,005 mm 600 Distributor for European market

LUREN Working condition in resharpening Resharpening with Ceramic grinding wheel (HSS Hobs) The following working condition are suggested with ceramic wheels Grinding wheels have a standard diameter in a range from 125 – 230 mm. The size of the grit may range from 60 to 80  Cutting speed = 30 m/sec  Feed speed = 2.500  Cutting depth = 0,03 – 0,05 mm (for modules up to 3 mm)  For modules over 3 mm cutting depth reduced to 0,01 – 0,02 mm.  The same characteristics are applied during the return stroke  Coolant must be abundant Distributor for European market