Free-cutting steels for optimum machining economy MACHINING RECOMMENDATIONS

Transcription

1 Free-cutting steels for optimum machining economy MACHINING RECOMMENDATIONS

2 Sandvik free-cutting steels with high, consistent quality High precision machines are gaining increasing use in the precision engineering industry to enhance productivity. However, a prerequisite for the full utilisation of such equipment is that the material being processed has the correct properties; excellent and uniform machinability consistent quality of surface, straightness and tolerances Sandvik offers free-cutting steels in stainless and carbon grades for CNC machines and automatic lathes. Materials that offer the optimum combination of properties to ensure the high quality of the final product and favourable manufacturing economy. Optimised properties The properties of the different Sandvik steel grades are tailored to meet the demands for excellent and uniform machin ing properties and at the same time having optimised mechanical and other properties. This means that each Sandvik steel grade has optimal chemical composition, mechanical properties, surface finish and tolerance to meet these requirements. It also means that the addi tion of free machining additives, e.g. sulphur, is optimised for each Sandvik steel grade and thereby giving excellent and uniform machining properties without jeopardising other properties. Machining expertise A cost efficient machining of the different Sandvik steel grades is best performed by using modern types of tools. In this brochure general machining re commendations are given, and in the separate data sheets recommendations are given for each specific steel grade. The recommended tools are Sandvik Coromant cemented carbide tools or high speed steel tools from Sandvik CTT. Detailed recommendations of the tools can be obtained from your nearest Sandvik Coromant or CTT office. Sandvik Steel, part of the Sandvik Group, is a leading international supplier of tubular and bar products, strip, wire and welding products for a wide range of applications. The products are made from stainless steels and special alloys based on nickel, titanium and zirconium. The Sandvik Group is a hightechnology enterprise with some 300 subsidiary companies, 34,000 employees and representation in more than 130 countries. Sandvik is a trademark of Sandvik AB

3 Turning Indexable-insert tools When machining in CNC-lathes indexable inserts of the type T-MAX P or U should be chosen. Wherever possible, indexinsert tools should also be used in automatic lathes. Special toolholders for automatic lathes are marketed by Sandvik Coromant. Inserts with a positive rake angle and sharp cutting edge should be chosen. For further details on cutting data, see the data sheets for each specific steel grade. For details on insert types and holding tools, see the Sandvik Coromant catalogue for turning tools, C-1000:7. Brazed carbide turning tools Brazed turning tools are used in smaller automatic lathes. The most common types are knife tools, tangential tools, forming tools and boring tools. Coromant 196 and 196S are recommended as knife and boring tools. Grade H10, and the somewhat tougher H10F, are most suitable for precision parts and feeds below about 0.05 mm/rev. Grade R1P is recommended for heavier feeds and less favourable conditions. A rake angle of 0 is frequently used for knife and boring tools, especially in longitudinal turning automatics, depending on the tool's operating mode, and to facilitate regrinding; however, a positive rake angle of can provide superior results. Brazed tangential tools and forming tools are not manufactured as standard but can be made to order. For the selection of cemented carbide grades and tool grinding, the same recommendations apply in the case of knife and boring tools. For further information on boring tools, see the Sandvik Coromant catalogue C-1000:7. For cutting data, see the data sheets for each specific steel grade. High-speed steel tools High-speed turning tools are used in the same application areas as brazed carbide-tipped turning tools. The primary applications are parting-off tools for large diameters, as well as forming tools and other processes in which cemented carbide tools cannot be used. Since high-speed steel is tougher than cemented carbide, a slightly larger rake angle may be used than for cemented carbide tools. Corona C60, is a conventional high-speed grade which is suitable for use for both carbon and stainless steel. 3

4 Parting-off and grooving Sandvik Coromant tools of type CoroCut are recommended for parting-off and grooving. Grooving for O-rings or other special profiles, see the Sandvik Coromant catalogue for turning tools, C-1000:7. For parting-off of slender stock in automatic lathes, brazed carbide tools should be used. We recommend the type 197 turning tool. Where machining conditions are unfavourable, it is advantageous to use high-speed steel tools ground as shown in the figure. Parting-off shall always be done with an ample supply of cutting fluid. Parting with Q-Cut tools. A B Grinding of high-speed steel parting-off tools. A = Top rake 10-15, B = Clearance angle, For further details on cutting data, see the data sheets for each specific steel grade. CoroCut 2-edge tools. Threading Thread turning should preferably be done by using Sandvik Coromant T-MAX U-Lock threading tools and the cemented carbide grade GC1020. The appropriate number of passes for pitches of mm are Detailed information is available in the Sandvik Coromant catalogue for turning tools, C-1000:7. In applications where cemented carbide tools cannot be used for reasons of size, the external threading should be done with a threading die in a selfopening die head and internal threads with a tap. The rake angle should be Helical-fluted taps are recommended for more complex threading. The appropriate cutting speed for a particular threading operation is determined by the degree of difficulty presented by the thread, the diameter, pitch and shape. Consequently, it may be necessary to resort to values outside the recommended values. However, it is important to maintain a sufficiently high cutting speed and to ensure an ample quantity of cutting fluid. If the cutting speed is too low, a built-up edge will form on the tools, resulting in scratched threads. For cutting data, see the data sheets for each specific steel grade. 4

5 Drilling Holes > Ø 12.7 mm Short-hole drilling with Sandvik Coromant drilling tools of type Coromant U-Drill are recommended for diameters between mm. When producing holes with diameters greater than 58 mm, short-hole drilling is used up to 58 mm, followed by internal turning up to the desired final diameter. Holes about < Ø12.7 mm Twist drills made of cemented carbide are recommended as the first choice and high-speed steel as the second choice. For highspeed steel drills a helix angle of 28 and a point angle of 118 are normally used. For very small-diameter holes, twist drills of cemented carbide is the most favourable solution. In these cases, it is normally required that both the drill and the material rotate. The hole should be cleared of chips starting at about 4 x the drill diameter. In many cases, it is sufficient to stop the feed for chipbreaking. For cutting data, see the data sheets for each specific steel grade. Milling Facemilling, square-shoulder facemilling and end milling Sandvik Coromant CoroMill milling cutters are recom mended. Hobbing Gears are often hobbed by the ge nerating process, instead of the indexing method. Hobs of the cemented carbide grade Coromant H10 are normally used. For short production runs hobs of high speed steel can also be used. A positive rake of is recommended. Feeds: Generating process Indexing method mm/tooth mm/tooth Slotting and slitting For slots between 5 and 112 mm the milling tool Coromant is used. For further details on cutting data, see the data sheets for each specific steel grade. See also the Sandvik Coromant catalogue C-1100:6. For cutting data, see the data sheets for each specific steel grade. 5

6 Reaming Both straight-fluted and helical-fluted reamers are used. The latter are to be preferred, since they work a great deal more smoothly, although helical-fluted reamers are more expensive and more difficult to grind. The bevel lead of the reamer should be about 45, the rake angle 3-5 and the clearance angle 6-8. A cylindrical land with a width of mm, depending on the diameter of the reamer, is left next to the edge on the clearance side. In automatic lathes, it has been found advantageous to use reamers ground to gundrill geometry. A suitable cemented carbide grade is Coromant H10. Cutting fluids Turning in CNC and centre lathes: Cutting emulsion of EP type. Drilling, threading, reaming and milling: Cutting oil and/or emulsion of EP-type in combination with additive fatty oil. Recommendations are for guidance only, and the suitability of a material for a specific application can be confirmed only when the actual service conditions are known. Continuous development may necessitate changes in the technical data without notice. Knurling For knurling with knurls of tool steel, a peripheral steel corresponding to the cutting speed for turning with high-speed steel is recommended. Feed, radial axial about 0.01 mm/rev. about 0.02 mm/rev. Tolerances Drawn condition Diameter Diameter tolerance Ovality D1 +/- D2 +/- D3 +/- D4 +/- for D4 mm mm mm mm mm mm Ground condition Diameter Diameter tolerance h7 h8 h9 h10 h11 mm mm mm mm mm mm >1 3 +0/ / / / / >3 6 +0/ / / / / > / / / / / > / / / / / > / / / / / > / / / / / > / / / / / Ground material is delivered with ISO tolerance class h7, h8 or h9 for diameters up to 13 mm, depending on steel grade. Please refer to the data sheets, for each specific steel grade. 6

7 Conversion hardness and tensile strength VICKERS HV Steel ball HB BRINELL Steel ball HRB ROCKWELL Diamond cone HRC Annealed Cold worked 0.5% C Tensile strengths above 1750 MPa are more uncertain. TENSILE STRENGTH MPa Cold worked 1.0% C Hardened VICKERS HV Approximate conversion between hardness values and tensile strength for unalloyed and low-alloyed steels of all types. Conversion between hardness values is based on SS and ASTM E

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