DE1177970B - Method for grinding profile cutters - Google Patents

Description

Method for grinding form milling cutters The patent application relates focuses on a method for grinding the flank on homogeneous form milling cutters. Under homogeneous form milling cutters should be understood here, their cutting edges and In contrast to hard metal milling cutters, for example, bodies are made of one piece, in which hard metal cutting tips are attached to a body of other material are.

The known relief-ground form milling cutters have rake face planes in each rake face A generally sufficient over part of the tooth length in the circumferential direction precise profile that is generated once during manufacture. Sharpening takes place simply by regrinding the rake face, the cutter tooth being re-sharpened with each re-sharpening becomes shorter in the circumferential direction by approximately the width of the flank wear mark. The smaller the number of teeth on a relief-ground milling cutter of a certain diameter is, the greater the tooth pitch and thus the usable tooth length and number the possible re-sharpening. The greater the number of sharpenings, the more the tool costs are lower. On the other hand, however, is the possible feed rate the smaller the smaller the number of teeth on the milling cutter. With decreasing feed speed the milling times increase and with it all costs that are proportional to the working time. By increasing the number of teeth on a relief-ground milling cutter, you can achieve although a higher feed rate and lower time-proportional costs, one reduces but the number of possible resharpenings and thereby increases the tool costs. The total machining costs for milling per workpiece increase with the number of cutter teeth So initially, they reach a minimum cost and then increase again. So is the greatest possible advance that is driven from an economic point of view can be limited upwards. The design of today's milling machines, however, leaves significantly higher feed rates, so that the performance of the milling process by the cutter is limited, its performance itself again by the relief grinding process is narrowed.

There is also a relief grinding process that does not as known, generated with two compound feed movements, but by that a cylindrical free surface eccentric to the milling cutter axis is generated. the Milling cutters ground by this method have the same disadvantages as the usual relief-ground milling cutters.

Experience has shown that the most serious wear and tear is that of the open space on form milling cutters, because it leads to the rake face in order to maintain the profile shape must be re-ground until the wear mark on the open area is complete away. It has therefore always been desirable to have the free surface with form milling cutters regrind.

In the case of the known form-ground milling cutters, the open area is after sanded by copying, either with a large grinding wheel, their profile on the circumference mostly deducted in a semicircle according to the copying pen or with a cylindrical mounted point. In both cases, the executable is Cutting edge shape limited. Pressing the sanding template and sanding pen against each other as well as the copy feed are mostly done by hand. This results in a proportionate poor surface quality of the cutting edge and form defects. The profile inaccuracy the known form-sharpened milling cutter is generally larger than that of the relief-ground milling cutter Milling cutter.

Milling cutters ground in the copy process can be relatively have a lot of teeth, and yet there can be a relatively high number of possible sharpnesses be made. Because with each sharpening, however, the open area and thus the Cutting edge shape must be generated again and because with copy grinding always only one Point of the cutting edge profile and the flank is generated, the sharpening costs compared to the cost of regrinding the rake face high and the accuracy the sharpening process is relatively low.

The purpose of the invention is to improve the grinding of the form milling cutters in such a way that that larger feed rates can be achieved with a higher number of teeth and that The tool costs are low due to a very large number of possible re-sharpening remain so that the above-described increase in the total Processing costs per workpiece, with the increase in tool costs as a result of the increasing Number of teeth is justified, no longer occurs. Furthermore, a complicated relative movement should between milling cutter and grinding wheel can be avoided to reduce the jig costs reduce. So that the tool costs are low, the open space must be in a short time can be ground, with the rake face profile without trial and error with the required Accuracy must fail. That requires simple arithmetical relationships between Workpiece profile and template or roll-in disc for profiling the grinding disc.

According to the invention, this object is achieved by grooving the form grinding wheel loosened in the form cutter that is not moved during the grinding process or vice versa, making the regrinding of homogeneous milling cutters with a high number of teeth easy and economical way is possible.

For the purposes of the invention, plunge-cut grinding is a process understood, in which a part of the flank starting at the rake face the illustration of the grinding wheel circumference.

A grinding wheel is used for the method according to the invention, which is profiled with a template or roll-in disc. The procedure ensures A perfect rake face profile even with high accuracy requirements if only the free surface is sanded.

The possible grinding wheel diameters are several times this of those that can be used in relief grinding. The one in the circumferential direction Short teeth of a milling cutter result in a shorter one despite a considerably higher number of teeth Total grinding length per milling cutter, so that each removal of the grinding wheel compared to the known relief grinding process a multiple of milling cutters can be ground.

The same profiled grinding wheel is used to make a hardened one To pre-grind a tubular cutter in the profile or around a cutter that has a similar one Has a cutting edge profile that is no longer required to be pre-ground before resharpening. Since relatively large grinding wheels are useful for the method according to the invention and also possible, this procedure is very powerful.

Very important for even loading of all cutter teeth when milling and a small waviness on the workpiece is the cutter runout. One supports when grinding the rake face of the tooth to be ground with an adjusting finger, pitch errors of the rake faces do not result in any concentricity errors. Act against it In the case of the relief-ground milling cutter, there are both pitch errors in the rake face and the pitch errors of the independently generated free areas as runout errors the end.

Milling cutters that are ground and sharpened by the method according to the invention have very characteristically shaped open spaces that are clearly different from distinguish between the free areas of the known form milling cutters. So have for example the relief-ground milling cutter has an open area that is both close to the cutter tooth head as well as in the vicinity of the cutter tooth root, in relation to the cutter axis, convexly curved is. In contrast, the free surfaces of the milling cutters according to the invention form other shapes. A shape recommended from the standpoint of economy is, for example a concave open space. The open surface can be made of concave, convex and straight Surfaces to be combined. The concave flank of the ground according to the invention Milling cutter has a significantly better cutting edge performance in terms of service life and Surfaces-. good than a milling cutter ground by a known method convex open space.

In the F i g. 1 to 8 the invention is explained and are some Embodiments given.

F i g. 1 shows schematically the interaction of grinding wheel and Form cutter with straight feed of the grinding wheel; F i g. 2 shows schematically the interaction of grinding wheel and milling cutter with an arcuate tool feed (The grinding wheel is mounted on a rocker arm); F i g. 3 to 6 show the geometric Relationships between workpiece and tool when applying the method according to the invention; F i g. 7 illustrates the course of the chip removal in the case of the invention Sharpening a cutter tooth; F i g. 8 shows a section along the line VIII-VIII in Fig. 7th

An overview of the possibilities of movement in the method according to the invention with a straight grinding wheel feed is shown in FIG. 1. Circle 21 is a schematic representation of the milling cutter, namely the cutting edge points, which serve as a criterion for the largest possible grinding wheel diameter. The schematically drawn grinding wheel is designated by 22. 23 is a radial plane placed at the tip A of the cutter tooth whose flank is to be ground. The corresponding radial plane of the following tooth, which must not be touched by the grinding wheel, is designated by 24. This places an upper limit on the diameter of the grinding wheel. The directions for the grinding wheel feed are also prescribed by the neighboring teeth, and in principle all directions of movement above the semicircle with the base 25M., 25 'are permissible. The in F i g. 1 drawn position of the grinding wheel 22 corresponds to the end position of all possible movements.

It means A = tip of the cutter tooth (outer cutting end point), Ml = axis of the cutter to be ground, M2 = axis of the grinding wheel, '.A = nominal clearance angle; it applies to the outermost cutting end point A and to the cutting end line, which is parallel to the cutter axis, = tooth pitch angle, y = rake angle.

Further designations are explained in the text, The F i g. 3 to 6 show a particular advantage of the method according to the invention. Between the workpiece profile 37 (FIG. 4) respectively. the rake face profile 39 (FIG. 6) of the grinding wheel 22 has relationships that can be calculated easily and precisely. From the profile height #M (Fig. 4) on the workpiece, for example, according to the rake angle;, the profile height ÄC of the rake face AD can be deduced and from here, according to the nominal angle a A, the profile height DV on the grinding wheel. Accordingly, the grinding wheel profile B "'C"' (FIG. 5) can be developed from the workpiece profile AD ' (FIG. 4) via the rake face profile A "C" (FIG. 6). It should be noted that the penetration curves that the grinding wheel circumference with the cutter tooth results in are pure arcs of a circle (cf. levels 42-42 or 43-43 in FIGS. 3 and 5). In contrast to this, with the known relief-ground milling cutters, the corresponding penetration curves are envelope curves for the Archimedean spiral which the grinding wheel axis passes through during relief-grinding and which can only be calculated approximately or can only be determined by trial and error.

With any rectilinear movement of the grinding wheel between 25 and 28 (FIG. 1), a tooth shape with an at least partially concave free surface is created.

The machining in the directions 26 and 27 (FIG. 1) is particularly noteworthy, because here one works with values s (FIG. 3) that are easy to determine for setting the grinding wheel relative to the milling cutter. The amount s by which the milling cutter must be set "above center" for sharpening in the case of direction 26 is s = 77-M-, = ÄVz sin aA (Fig. 3), in the case of direction 27 s = Äml sin aA.

The grinding wheel can also be stored on a swing arm, ye Center then executes an arc-shaped movement.

An overview of the possibility of moving the grinding wheel in a circular arc is shown in FIG. 2. Circle 21 again represents the milling cutter, circle 22 the grinding wheel. The pivot points of the rocker are on circle 29. All positions between 30 and 32 and 33 and 35 are suitable as pivot points Mn for the rocker. There are blind spots between 32 and 33 and 35 and 30. Pivot point 30 is characterized in that it lies on a straight line which is inclined by a relative to the radial plane at the tooth tip and in front of the rake face.

The geometrical relationships are the same as with linear Move.

The flank wear mark is made by grinding on the flank removed.

In Fig. 7, AG and CH are the circular arc-shaped; Penetration curves that are formed by the free surface and by the planes 44, 45 parallel to the end face of the milling cutter. The area AIK in FIG. 7, which has an approximately triangular shape, is intended to represent the flank wear as it is caused by; the section with the plane 44 in FIG. 8 results.

To remove the flank wear mark, the entire flank must be set radially lower by the amount ÄK. The flank penetration curve of the rake face profile point A 'for the new, sharp flank is the dotted line below AG.

According to FIG. 7 is the height loss ÄK of the tooth in the radial direction with a width of the flank wear K1, which is measured in the circumferential direction e, ÄK tg aA. @1. For example, then This means that per millimeter of tooth length (in the radial or circumferential direction) with the milling cutter according to the invention, around six times as many sharpenings are possible as with relief-ground milling cutters.

w- The surface wear is well known in high-speed steel milling cutters very low. The rake face is only regrinded until it is again is clean; You can also clean it after every second or third use take place.

As a result of the simple removal of the flank wear mark from the flank, which is now possible, the tooth pitch of a milling cutter can be made almost as small as the tooth pitch of corresponding relief-ground milling cutters minus the usable tooth length. Since the gaps between the teeth become narrower downwards, when the tooth is moved radially, about the amount of tooth length in the circumferential direction that you want to grind on the rake face if you roughly maintain the original tooth length Ä U at the tooth tip (Fig. 7) ( LM -AG). With a smaller rake angle or rake angle 0 °, as shown in FIG. 8 shows, the inevitable occurrence of the grinding amounts on the rake face is more favorable than with larger rake angles.

So only very small amounts are required for grinding in the circumferential direction to be provided on the rake face, if one is concerned with the inevitable Amounts not enough. The teeth therefore only need a little longer in the circumferential direction to be made than from the point of breakage resistance and more sufficient Rigidity is required.

Compared to the length in the circumferential direction, the teeth of the milling cutters machined with the method according to the invention are high. The greater the tooth height that can be abraded in the radial direction, the greater the number of possible inserts e: Therein means according to FIG. 7; N is the height of the tooth that can be abraded in the radial direction, AK is the cut per sharpening.

For example, with milling cutters for 3 mm cutting depth and 75 mm diameter with the usual relief-ground milling cutters with twenty teeth and a flank wear mark width of 0.3 mm, a usable tooth length in Circumferential direction of 4.8 mm, which corresponds to sixteen sharpening and seventeen inserts. With a corresponding milling cutter according to the invention, thirty teeth are possible, and the milling cutter can be reground radially by 3 mm; that's sixty Sharpenings and sixty-one missions. These are because of the extremely low Amounts that have to be ground on the flank and rake face, and because of the simple and fast process for flank grinding reduces the sharpening costs very much low. The high number of inserts per milling cutter results in very low tool costs.

With the F i g. 1 and 2 are straight and circular arcs by way of example Describes the feed rates of the grinding wheel. Any other form of feed path is also possible possible, which lies within the scope of the concept of the invention.

Claims (1)

Claim: Method for grinding the free surface on homogeneous form milling cutters by means of a form grinding wheel, characterized by plunging the form grinding wheel into the form milling cutter which is not moved during the grinding process. Documents considered: German Patent No. 34,790; British Patent Nos. 678 817, 468 404; Magazine "Machinery" (London) of 17 July 1952, p 101, 102nd