METHOD AND CUTTING INSERT FOR THREADING

Abstract: The present invention relates to a method and a cutting insert for threading. The method aims to produce a thread in a rotary work piece, wherein a threading insert, including at least one cutting tip, creates the shape of the thread. The flank infeed is performed in a direction (F) obliquely towards the rotational axis of the work piece and parallel to one thread flank of the thread. The cutting tip is provided with a cutting tip which has a passive edge (26), located at least partly on one side of an imaginary line (S) parallel with a direction of infeed (F) for the cutting insert and touching the cutting tip, said side facing away from the connected thread flank (23).

Description: Method and cutting insert for threading The present invention relates to a method and a cutting insert for threading. The method aims to produce a thread in a rotary work piece, wherein a threading insert, including at least one cutting tip, creates the shape of the thread through a number of passes along the work piece. The threading insert aims to create threads including two thread flanks in a work piece, by flank infeed and comprises at least one cutting tip provided with cutting edges. Prior art In known indexable threading inserts the cutting tip is in top view identical with the profile of the finished the thread, which means that at flank infeed wear develop on the passive flank of the cutting tip due to abrasion from the work piece. Thereby these cutting inserts can not attain optimal tool life or reduce the time for processing at threading. At flank infeed a chip is obtained with rectangular cross section, which is easy to shape and handle in comparison with a chip from radial infeed, when the chip assume a rigid V-shaped cross section. This fact together with a more efficient heat deduction from the cutting tip makes it possible to work with bigger chip thickness and to complete the thread with the same number of passes as by radial infeed. When conventional threading inserts are fed inwardly, parallel with one flank of the thread, the cutting edge, however, facing said flank, will not perform any cutting work but will only drag along said flank; something which have an abrasive effect on the cutting edge and which can give bad surface finish on the thread flank. One has tried to feed the cutting tip at an angle which is smaller than the flank angle to avoid these negative effects, but then obtained chips from the side of the minor cutting edge which have been thin and entangled, which has influenced tool life and surface finish. Objects of the invention One object of the present invention is to provide a cutting insert for flank infeed, which has good tool life. Another object of the present invention is to provide a cutting insert for flank infeed, which reduces the time for processing at threading. Another object of the present invention is to provide a cutting insert for flank infeed, which requires less energy to cut. Still another object of the present invention is to provide a method for flan infeed, which gives good production economy. Description of the drawings Fig. 1 shows a threading insert according to the present invention, in a top view. Fig. 2 shows the threading insert, in a side view. Fig. 3 shows the tip of the threading insert in engagement with a dashed work piece. Fig. 4 shows a threading perio of five passes with the tip of the threading insert. Fig. 5 shows the tip of the threading insert in engagement with a work piece. Fig. 6 and 7 show alternative embodiments of cutting corners on threading inserts according to the present invention. Figs. 8 and 9 show alternative embodiments of threading inserts for trapezoidal threads, according to the present invention. Figs. 10 and 1 1 show cross sections of the cutting inserts in Figs. and 9, respectively. Fig. 12 shows the tip of the threading insert according to Fig. 9. D taile description of the invention With reference to Figs. 1 and 2 a cutting insert according to the present invention is designated by 10. The cutting insert preferably is made by coated cemented carbide. The cutting insert has a substantially triangular basic shape and comprises an upper and a lower side 11 and 12 respectively. The basic shape can also be square for example, such as is shown in Fig. 9. The sides connects substantially perpendicularly to side surfaces 13, 14 and 15. The side surfaces form a n acute angle of about 60° with each other. The cutting insert has a central hole 16 for receiving a fastening device for clamping of the cutting insert against a cutting insert pocket of a holder, not shown. The cutting insert is provided with three substantially identical cutting corners 17 in the areas for the imaginary intersection of the side surfaces. The cutting insert corner 17 comprise a cutting tip 18, a cutting edge which runs along the intersection between a chip surface 19 and a clearance surface 20, a topping surface 21 and a broken chip breaker rim 22. Th cutting insert has a center axis CL and each cutting tip 18 has a bisector B. The bisector is substantially parallel with the connected edge surface 15 and extends on the side of the center axis at a distance L. The distance is 10 to 30% of the imaginary edge length of the cutting insert. In Fig. 3 an enlarged cutting corner is shown, which engages a work piece, the thread 23 of which is dashed. The cutting edge consists of a number of segments and includes an active major cutting edge 24, a nose edge 25, an active minor cutting edge 24A, a passive edge 26 and a topping edge 27. The cutting tip 18 of the cutting corner projects a distance L,, measured from a line touching the topping surface 27 and the extreme points of the nose edge 25. The bisector is defined by the major cutting edge, the nose edge and minor cutting edge, wherein the major cutting edge is provided on one side of the bisector and the minor cutting edge on the other side of the bisector while the nose edge cutting intersects the bisector. The major cutting edge 24 forms an acute angle α, of about 25 to 30°, with the bisector B. The major cutting edge softly connects to the nose edge 25, which substantially is defined by an radius r, of about 0,05 to 1,5 mm. The nose edge further softly connects preferably to the active minor cutting edge 24A or directly to the passive cutting edge 26. The minor cutting edge connects to the passive cutting edge on the perpendicular distance L 2 from a tangent T of the nose edge in the extreme points of the nose edge. The distance L 2 is bigger than or the same as the maximum depth of infeed per pass, but less than the half of the distance L, and preferably less than 2.5 mm and is preferably of the size of the radius r. Also the minor cutting edge or the part of the nose edge which is closest to the passive cutting edge forms the angle α with the bisector. The passive cutting edge 26 forms an angle β with the bisector, which is 4 to 8°, preferably about 5°, less than the angle α. The passive cutting edge connects to the topping edge 27 via a concave substantially passive, curved edge 28, defined by a radius R, the size of which depends of the actual thread profile but the radius is bigger than the radius of the nose edge. The cutting tip thus has a passive edge 26, which at least partly is provided on one side of an imaginary line S parallel with the direction of infeed F for the cutting insert and touching the cutting tip 18, said side facing away from the connected thread flank 23. The line S touches the nose edge 25 as well as intersects the curved cutting edge 28. The function of the cutting insert shall be explained closer hereinafter in connection with Figs. 4 and 5, which show flank infeed without modification by additional tilting. In the first pass I, substantially the entire nose edge 25 of the cutting tip is brought, radially into the work piece a predetermined depth (the depth of the infeed), which separates from radial infeed only through the axial placement. The depth of the infeed is smaller than or the same as said distance L 2 to avoid poor surface qualiiy on the passive thread flank. Before pass II is commenced, the cutting insert is removed in direction of the arrow F obliquely inwardly toward the rotational axis of the work piece, parallel to the thread flank 23 A. The passive cutting edge 26 thereby becomes cleared from the thread flank in the direction of infeed such that abrasion is avoided. Same will apply for the passes III to V. At the last pass V the thread also will be topped. The flank infeed is thus performed in the direction F, obliquely relative to the rotational axis of the work piece and parallel with one thread flank of the thread, and the cutting tip is provided means 26 which clears or lifts parts of the cutting tip from the thread flank in the direction F of the flank infeed. This cutting insert allows considerably larger depth of infeed per pass since unnecessary friction is avoided. This means in turn that the number of passes can be essentially reduced; for example from the conventional 8 passes to 5 passes at thread Ml 2. Thereby reduced time for processing is attained and more details can consequently be made per shift. With reference to Figs. 6 and 7 cutting inserts are shown, the passive edge 26' respective 26" of which is provided with a clearance by a recess 30' and a skew chamfer 30", respectively. The recess preferably extends from the minor cutting edge 24' A at the distance L 2 to the radiussed bridge at the connected topping edge. The recess preferably extends from the passive cutting edge to the lower side 12 of the cutting insert. The passive cutting edge may be parallel with the generated thread flank or may form an angle with said flank, such as in Fig. 5. The chamfer 30" preferably extends from the minor cutting edge 24"A at the distance L 2 to the radiussed bridge at connected topping edge. The chamfer form an obtuse inner angle with the connected clearance surface 20, said angle preferably being larger than 160°. The chamfer provides clearance for the passive cutting edge when the cutting insert is mounted leaning in the cutting insert pocket. Both passive cutting edges 26' and 26" form an angle with the bisector B, which is smaller than the above mentioned angle α, which is defined by the relation between the bisector and the major cutting edge and the minor cutting edge, respectively. Figs. 8 to 12 show threading insert for trapezoidal threads, wherein the cutting tip comprises a cutting edge. The cutting edge consists of a number of segments and includes an active major cutting edge 124, a depth of the infeed 125, a minor cutting edge 124A, a passive edge 126 and a topping edge 127. The major cutting edge and the minor cutting edge each form an angle of about 15° with the bisector B. The nose edge is preferably perpendicular to the bisector. The passive cutting edge may be parallel with the bisector or be angled relative to the bisector, such as in Fig. 3, or recessed such as in Fig. 6; the most important in this connection is that the passive cutting edge is provided inside the line S such that the cutting edge does not engage with the connected thread flank. The passive cutting edge 126 thus can be provided with clearance by means of a recess, said recess extending from the minor cutting edge 124A to a radiussed bridge at the connected topping edge and the recess then extends preferably from the passive cutting edge to the lower side of the cutting insert. Alternatively the passive cutting edge can be provided with clearance by a chamfer, said chamfer extending from the minor cutting edge 124A to a radiussed bridge at the connected topping edge, wherein the chamfer forms an obtuse inner angle with the connected clearance surface. For all above-mentioned cutting inserts the major cutting edge is substantially uniform with one, connected, generated thread flank and the passive cutting edge is substantially non-uniform with the other, connected, generated thread flank as well as the distance L 2 is bigger than or the same as the maximum depth of the infeed for the cutting tip per pass. The present invention consequently relates to a threading insert wherein for example a clearance angle of about 5° is provided in the tool's minor cutting edge side, why full profile is needed only on the major cutting edge side and substantially on outermost point of the tip. Advantages following such a configuration are that lower cutting forces (about 40 % lower) arise in comparison with a conventional cutting insert with a symmetrical cutting tip and that the number of passes can be reduced from for example 8 down to 5 passes for an ISO-profile 2.0 mm. That gives shorter threading periods and more details per cutting edge. The chip surfaces of the cutting inserts may b provided with recesses and/or projections in order to improve chip forming and in certai cases improve heat deduction.

Claims: Ql ms. 1. Method for producing a thread in a rotary work piece, wherein a threading insert, including at least one cutting tip with a bisector (B), creates the shape of the thread through a number of passes along the work piece, characterized in that flank infeed is performed in a direction (F) obliquely towards the rotational axis of the work piece and parallel to one thread flank of the thread, said cutting tip being provided with means (26;26';26";126), at a side of the bisector (B), which clears parts of the cutting tip from the thread flank in the direction (F) for the flank infeed. 2. Method according to claim 1, characterized in that one thread flank is touched, at a side of the bisector (B), by only a portion (24A;24'A;24"A;124A) of the connected part of the cutting tip (18) and that the depth of the infeed for the cutting tip is smaller than or the same as the length (L 2 ) for the first mentioned portion and that the length (L 2 ) is smaller than the half of the protrusion (L j ) of the cutting tip (18) but larger or the same as the depth of infeed of the cutting tip and that the thread (23) is completed after five passes, said/wherein the thread is peaked at the last the pass. 3. Threading insert for to creating threads including two thread flanks in a work piece, by flank infeed, including at least one cutting tip (18) with a bisector (B), said cutting tip being provided with cutting edges (24,25,24A;25',24'A;25",24"A; 124,125, 124A), characterized in that a major cutting edge (24;24';24";124) is substantially uniform with one connected, generated thread flank and a passive edge (26;26';26";126), at a side of the bisector (B), is substantially non-uniform with the connected, generated thread flank. 4. Threading insert according to claim 3, characterized in that the cutting tip has a passive edge (26;26';26";126), which at least partly is located on one side of an imaginary line (S) parallel with a direction of infeed (F) for the cutting insert and touching the cutting tip (18), said side facing away from the connected thread flank (23). 5. Threading insert according to claims 3 or 4, characterized in that an active cutting edge (24; 124) and a minor cutting edge (24A;24'A;24"A;124A) form a first angle (α) with a bisector (B) of the cutting tip on each side of the bisector and that the passive cutting edge (26;26';26";126) forms a second angle (β) with the bisector, said second angle being smaller than the first angle. 6. Threading insert according to anyone of the claims 3-5, characterized in that the periphery of the cutting tip (18) consists of a number of segments and includes a major cutting edge (24;124), a nose edge (25;25';25";125), a passive edge (26;26';26";126) and a topping edge (27:127), wherein said major cutting edge softly connects to the nose edge, which is substantially defined by an radius (r), wherein the nose edge further softly connects to the passive cutting edge on a perpendicular distance (L 2) from a tangent (T) to the nose edge in an extreme point of the nose edge and that the passive cutting edge connects to the topping edge (27; 127) via a concave, substantially passive, curved edge (28). 7. Threading insert according to claim 6, characterized in that the major cutting edge (24) forms an acute angle (α), of about 25 to 30°, with the bisector (B) and that the radius (r) is about 0,05 to 1 ,5 mm and that the distance (L 2 ) is bigger than or the same as the maximum depth of the infeed for the cutting tip per pass and less than 2,5 mm and preferably is of the size of the radius (r). 8. Threading insert according to anyone of the claims 6 or 7, characterized in that the part of the nose edge (25;25';25";224) which is closest to the passive cutting edge (26;26';26") forms a first angle (α) with the bisector (B) and that the passive cutting edge forms a second angle (β) with the bisector, which is 4 to 8°, preferably about 5°, less than the first angle (α) and that the curved cutting edge (28) is defined by an radius (R), which is bigger than the radius (r) of the nose edge. 9. Threading insert according to anyone of the claims 3 to 8, characterized in that the passive cutting edge (26'; 126) is provided with a clearance by means of a recess (30'), said recess extending from the nose edge (25') or a minor cutting edge (224) to a radiussed bridge at the connected topping edge and that the recess preferably extends from the passive cutting edge to the lower side (12) of (he cutting insert. 10. Threading insert according to anyone of the claims 3 to 8, characterized in that the passive cutting edge (26"; 126) is provided with a clearance by means of a chamfer (30"), said chamfer extending from the nose edge (25") or a minor cutting edge (224) to a radiussed bridge at the connected topping edge, said chamfer forming an obtuse inner angle with the connected clearance surface (20).

Inventors: LARSEN STAFFAN, LARSEN, STAFFAN
Applicants: LARSEN STAFFAN, SECO TOOLS AB, LARSEN, STAFFAN
Application year: 1996
Main classification: B23G5
IPC codes: B23B27, B23G5, H01L21, H01L23