JP2002504440A - Multi-pass grinding method - Google Patents

Abstract

(57) [Summary] This is a multi-pass grinding method for manufacturing endodontic instruments. The tapered rod (10) is continuously advanced over the rotating grinding wheel (12) and the material layer (14, 16, 18, 20) from the rod (10) until the desired groove depth is obtained. Is removed. This method is characterized by a relatively shallow cutting depth, a relatively high feed rate and low wear of the grinding wheel. This method reduces the processing time and operator control required to manufacture nickel-titanium endodontic appliances. Other steps are disclosed for automatically compensating for wear of the grinding wheel (12) so as to eliminate or reduce periodic recalibration of the grinding wheel (12).

Description

DETAILED DESCRIPTION OF THE INVENTION

FIELD OF THE INVENTION The present invention relates generally to an improved method of making endodontic files and reamers, and more particularly to forming grooves and associated cutting edges in a tapered rod made of a nickel-titanium alloy material. For improved multi-pass grinding method.

BACKGROUND OF THE INVENTION [0002] As part of conventional root canal procedures, decay is removed from the root canal and the root canal itself is reformed prior to inserting a filling material into the root canal. . The crown is removed so that the root canal can be treated. During root canal treatment,
Certain endodontic devices such as files and reamers are used to clean and shape the root canal.

[0003] These devices are typically very flexible files and reamers that are manually rotated and / or reciprocated within the root canal by a practitioner. Practitioners start with a very small file and work their way up to a larger file until the root canal is properly shaped and cleaned. After this stage of root canal treatment is completed, the teeth are typically filled with an inert filling material, such as Gutta Perca, followed by cement. The crown is then attached to the tooth.

In the past, such endodontic devices have been provided with stainless steel tapers that are grooved along the working portion to form a helical groove with one or more cutting edges formed on the sides. Was made from rods. These grooves of the device are generally formed in one or two ways. A first method involves twisting a rod of a particular cross-sectional shape, for example, a triangle or square, such that the rod edge forms a spiral along the rod length. These helical edges act as cutting edges of the instrument. Another method involves moving a tapered rod under a grinding wheel, wherein the rod is simultaneously rotated and translated to form one or more continuous grooves along the length of the rod. If desired, the rod is indexed and rotated, and the process is repeated to form additional grooves spaced apart from each other at a predetermined angle.

[0005] The present invention is directed to an improved grinding method that is particularly suitable for forming grooves in tapered rods comprising nickel-titanium (Nitinol®) and / or similar alloys. These alloys have been found to have superior flexibility and puncture resistance compared to conventional stainless steel alloys, and therefore can be preferably applied to the endodontic field, especially endodontic files and reamers. For example, "First Study on the Bending and Torsion Properties of Nitinol Root Canal Files" Journal of Endodoncia, Journal of Endodontics, Vol.
July 1988). These devices can easily follow the curved and / or curved shape of the root canal system and are less susceptible to breakage when stressed than stainless steel. These advantages allow for a faster and more efficient treatment of the root canal with less damage to the root canal wall than stainless steel instruments.

[0006] The special material properties and superelastic properties of nickel-titanium alloys make them particularly difficult to machine using conventional grinding machines. For example, U.S. Pat. No. 5,464,362 issued to Heath et al.
Some of the difficulties arising when forming a grooved endodontic device from a titanium alloy are discussed. To alleviate some of those difficulties, Heath found that 3-8 inches / minute (approximately 76.2-203.2 mm / min) to obtain instruments of acceptable quality.
Min.) And a surface speed of less than 3000 feet / min. Are disclosed.

However, Heath's method is slow and inefficient, and has a relatively short time interval for removing nickel-titanium material accumulated on the wheel and / or for reshaping or recalibrating the wheel. It is necessary to stop the machine at and fix the grinding wheel. These operations are time consuming and labor intensive and are therefore not desirable for mass production of nickel-titanium endodontic devices.

SUMMARY OF THE INVENTION The present invention is directed to a high speed multi-pass grinding method for manufacturing files and reamers and / or other tools from tapered rods made of nickel-titanium or other materials. The preferred method produces a clinically effective device of acceptable quality while reducing production time, wheel wear, and frequency of wheel re-correction. Using the multi-pass grinding method of the present invention, high quality nickel-titanium endodontic instruments can be manufactured more quickly with improved manufacturing tolerances and reduced operator control and maintenance. The present invention also provides, in one embodiment, for automatic re-adjustment of a grinding wheel when the grinding wheel is worn to maintain the desired manufacturing tolerances over long production runs and without operator intervention. Methods and apparatus are provided.

In one embodiment, the present invention provides an improved grinding method for forming grooves and associated cutting edges in a nickel-titanium alloy tapered rod by a multi-pass grinding operation. The tapered rod undergoes successive passes or passes of the grinding wheel, with the grinding wheel gradually removing material in each pass until the desired groove is formed. Since the groove depth typically varies along the length of the tapered tool, the multi-pass grinding operation allows the feed rate in each pass to be optimized according to the cut depth for each particular grinding pass. To this is,
This is a significant advantage over conventional grinding techniques using a single pass, constant feed rate grinding wheel. Because this is a one-pass system, a high feed rate can be used to remove material from the shallow part of the groove, but a feed rate of Must be slow enough. The present invention solves this limitation using multi-pass grinding and variable feed rates.

Another advantage of the multi-pass grinding method of the present invention is that the cutting depth and feed rate in each grinding pass can be optimized to minimize grinding wheel wear. In contrast, the single pass grinding method wears the grinding wheel at a relatively high speed. This is because the ablation depth is always maximum (at least in part of the instrument) in order to remove all of the material in one pass. If the edge of the grinding wheel wears out in this state, it becomes wider, or transformed, which results in a wider and shallower groove. By convention, when this occurs, the operator must reshape or "re-correct" the edge of the grinding wheel and recalibrate it to maintain manufacturing tolerances. However, the method of the present invention adjusts the cut depth of each pass to minimize wheel wear while maintaining high speed manufacturing. Therefore,
The method of the present invention significantly reduces machine downtime and the skilled work required to monitor and maintain manufacturing operations.

In another embodiment, the present invention provides a method and apparatus for automatically recalibrating a grinding wheel when it becomes worn. Conventional grinding operations require periodic recalibration and adjustment of the grinding wheel to compensate for the gradual wear of the grinding wheel and the reduction in wheel diameter. This requires temporary stoppages and interruptions in the manufacturing process, increasing monitoring and management costs of the entire manufacturing process. However, according to one method of the present invention, automatic detection and / or adjustment of the grinding wheel position relative to the workpiece (ie, tapered rod) compensates for the gradual wear of the grinding wheel. This reduces the required production time and operator control, which is particularly advantageous for long-term production operations.

According to another embodiment, the present invention provides an adjustable head for holding a grinding wheel, which allows for different angles between the axis of the grinding wheel and the axis of the rod. This allows for further correction of grinding wheel wear and the ability to individually change the rake angle, depth and width of the groove as the grinding wheel moves along the tool.

[0013] These and other features and advantages of the present invention will be readily apparent to those skilled in the art from the following detailed description of the preferred embodiments, which refers to the accompanying drawings. However, the invention is not limited to any particular preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1A, 2A and 2B illustrate a multi-pass grinding method according to the present invention. Rod 10 is moved or passed along grinding rod 12 along the rod to remove first layer 14, second layer 16, third layer 18 and fourth layer 20, as shown in FIG. The grinding wheel is shown in a second pass removing the second layer 16 to form a groove.

The rod 10 generally includes a shank 22, a tip 24, and a working portion 26. The working portion 26 extends from the proximal end 28 adjacent to the base of the shank 22 to the distal end 24.
Rod 10 can be rotated along longitudinal axis 30. Shank 22
The chuck (e.g., to allow for use with a calibrated depth marking 32, handle 34, hand-operated or motorized handpiece if desired).
Knurling or notches (not shown) can also be included.

Although the rod 10 can have any cross-sectional shape, a circular cross-section is preferred. The rod 10 may or may not be tapered,
A taper 40 along the machined portion 26 as exaggerated in A is preferred. Rod 10 may be composed of a titanium alloy or stainless steel. The titanium alloy typically has a titanium content of at least 40%. Preferred nickel-titanium alloys for endodontic work typically consist of approximately at least 40% titanium and at least 50% nickel. In one preferred embodiment, the alloy is composed of 44% titanium and 56% nickel, and contains no appreciable amounts of other materials that can adversely affect the purity required for endodontic devices. . The dimensions of the various rods formed in the endodontic device can be conventional.

The grinding wheel 12 generally includes a first surface 50, a second surface 52, and a bevel surface 54. The second surface 52 and the bevel surface 54 form a corner 56 at an included angle of about 32 ° in one preferred embodiment. A cutting edge 58 is formed at the tip of the corner 56. The second surface 52 of the grinding wheel 12 and the longitudinal axis 30 of the rod 10 form a head angle 70. The coarse grain size of the grinding wheel 12 ranges from about 200 to about 800, preferably from about 250 to about 550, and most preferably about 400. The grinding wheel surface can be comprised of Cubic Boron Nitride (CBN) supplied and manufactured by Norton Super Brushy. A grinding wheel 12 composed of diamond ore is also shown as satisfactory. The speed of the grinding wheel 12 ranges from about 2000 rpm to about 10,000 rpm, and from about 5000 rpm to about 850 rpm.
0 rpm is more preferred. Generally, the preferred speed for a 152.4 mm (6 inch) wheel is 5730 rpm. Roll matic
3.) High speed grinding was achieved with favorable results using a 600 × -6 axis machine. A roll-omatic 24F3-3-axis machine also showed satisfactory results, but the head angle change described in more detail below could not be used.

In the multi-pass grinding method according to the present invention, the grinding wheel 12 first contacts the rod 10 at a first pass entrance location 60, somewhere between the distal end 24 and the proximal end 28. The path of the cutting edge 58 of the grinding wheel 12 forms a cutting angle 72 with the longitudinal axis 30 of the rod 10. Although the method is not limited to a particular instrument geometry, the cutting angle 72 is preferably greater than about 0 ° to form a neutral or positive rake cutting edge. The depth of the first pass or "cut" 14 is preferably less than the overall maximum groove depth, including the first cut 14, the second cut 16, the third cut 18, and the fourth cut 20. Although any cut depth is not critical, to obtain the highest surface finish quality of the grooves and associated cut edges, the final cut or final grinding pass (fourth cut 20 in FIG. 1A) should be between about 5 microns and 30 microns. And a depth of about 10 microns is more preferred. Other excision depths from a few microns
A depth range of about 100 microns or more, with an ablation of about 40 microns at a time, is most satisfactory.

FIG. 1A shows a multi-pass grinding method employing four passes. The system works satisfactorily with a small number of passes, such as two passes, and a large number of passes, including ten or more rods. Most preferably, about three to five grinding passes are appropriate for most applications. Tools formed from small diameter tapered rods generally require fewer grinding passes than tools formed from large diameter rods. In movement between the tip 24 and the first pass entry position 60, the grinding wheel 12 is moved at a high feed rate, such as, for example, 1800 mm / min (about 72 inches / min). Immediately before contacting the rod 10 at the first pass entry position 60, the feed rate is preferably reduced to a rate suitable for material removal.
Range from about 12.7 mm / min (0.5 in / min) to about 889 mm / min (35 in / min), most preferably from about 254 mm / min (10 in / min) to about 381 mm
/ Min (15 in / min), most preferably about 300 mm / min (12 in / min)
The grinding speed gives satisfactory results. This grinding feed speed is controlled by the grinding wheel 12.
Can be varied while removing material along the path or moving from pass to pass, but is preferably kept constant while grinding wheel 12 removes material from rod 10.

After the first ablation 14, the grinding wheel 12 can be moved to the second ablation inlet position 62 at an even higher feed rate and begins to remove the second layer 16 at the selected grinding feed rate. This process is repeated until the desired groove depth is reached. A third layer entry location 64 and a fourth layer entry location 66 are located at tip 24. By employing this multi-pass system, considerable time and material savings are achieved. This means that the single pass system must be operated at one grinding speed from tip 24 to proximal end 28,
This is possible in a single pass system because the speed must be relatively slow to remove the maximum amount of material at the proximal end 28. Multi-pass grinding methods can use higher grinding feed rates because less material is removed in each pass. Higher feed rates can be used when no material is removed from the rod (or only minimal material is removed), such as after the first pass and before the second pass. A four pass system with a grinding feed rate of 305 mm / min (12 in / min) saves about 20% of time over a single pass system with 38 mm / min (3 in / min). Further, the final layer in a multipath system, ie, FIG. 1A
If the fourth layer 20 is kept relatively thin, an improved surface finish is obtained.

Referring to FIG. 1B, the multi-pass method of the present invention can be implemented starting from a substantially common starting position of the tip 24. In FIG. 1B, the same reference numerals in FIGS. 1A and 1B indicate the same structural parts, and the reference numerals with dashes (') indicate members that have been modified according to the alternative principle. This method is basically the same as the method described above, except that the layers 14 ', 16', 18 ', 20' can be started by the wheels 12 at positions 60 ', 62', 64, 66 respectively. . It will be appreciated that locations 60 ', 62' have been moved to the tip from the respective locations 60, 62 shown in FIG. 1A. Also in accordance with the present invention, the grinding path can vary the axial feed rate throughout its length. For example, the feed speed at the start position of the groove grinding pass is 25.4 m.
m / min (10 in / min) and the feed rate through the rest of the grinding path is gradually increased, often exceeding 305 mm / min (12 in / min), but
Preferably it does not exceed 6.2 mm / min (30 inches / min).

Referring to FIGS. 3, 3A, 3A-1, 3B and 3B-1, the multi-pass system not only saves manufacturing time and cost, but also reduces the μm of grinding wheel 12. . The unworn cutting edge 58 of the grinding wheel 12 produces a groove 100 in the rod 10 as shown in FIG. 3a. Groove 100 must be kept within specification limits to produce a device having acceptable quality and therapeutic efficiency. Among the physical characteristics, the width “a” of the groove and the depth “b” of the groove are measured to determine whether the shape and size of the groove are acceptable. FIG. 3B-1 shows a cross section of a worn cutting edge 58 'and its corresponding rod 10 and groove 100'. As shown, the worn cutting edge 58 'forms a shallow, flat groove where a' is greater than a and b 'is less than b. Eventually worn cutting edges 58 'prevent grooves 100' from meeting specifications. This manufacturing process is then interrupted and the operator reshapes the cutting edge 58 'and moves the cutting edge 58' by the distance "c" in the direction indicated by arrow 59 in FIG. Grinding wheel 12 so as to form groove 100
Must be able to be recalibrated. This multipass system reduces the need for this calibration. This is because the grinding wheel 12 wears more slowly in a multi-pass system than in a single-pass system.

As just described, the need to stop the manufacturing process for wheel recalibration increases the process time and increases the need for operator control. Therefore, extending the length of time between recalibrations increases the efficiency of the process. This holds whether a single-pass system or a multi-pass system is used. The present invention, in one embodiment, greatly extends the required recalibration interval time by automatically feeding the grinding wheel 12 and its cutting edge 58 toward the rod 10 when the cutting edge 58 wears. . By tracking the wear of the cutting edge 58, the position of the cutting edge 58 can be adjusted to offset the wear. By repeatedly repositioning the cutting edge 58 as it wears, the groove 100 is kept within specification for a very long time. After producing 50 parts, the grinding wheel 12 used in the present invention was able to produce further grooves 100 well within specification. Feeding is accomplished by programming a computer (not shown) to move grinding wheel 12 such that head angle 70 is held constant along an axis parallel to second surface 52.

In another embodiment, the present invention can adjust the head angle 70 shown in FIG. 1A, for example. The method comprises a grinding wheel 12 and a rod 10 in this case.
It is similar to the infeed method described above, except that the head angle 70 is changed to correct for wear of the cutting edge 58 rather than the inter-axis distance. As a result, the stop time is reduced. This is because head angle correction maintains a more symmetrical groove 100 over time.

Referring to FIGS. 4, 4A and 4B, adjusting the head angle 70 can also be used to improve and control other variables of the groove 100. As one skilled in the art will notice, material is removed to form one or more grooves 100. These grooves 100 are helical and form a leading edge 102 that cuts away corrosive material as the rod 10 is manipulated within the root canal. Groove 100 also forms trailing edge 104. 4A and 4
As shown in B, the leading edge 102 forms a rake angle of 0 ° or an angle that can be positive or negative as desired. As can be seen from these two figures, the cross section at the distal end 24 has a rake angle of about 0 ° and the rake angle at the proximal end 28 is on the order of about 20 °. The varying rake angle between the distal end 24 and the proximal end 28 is caused by the fixed head angle 70 used in the system of the present invention. The fixed head angle produces a different head angle depending on the cutting depth. By changing the head angle, the head angle can be kept constant if desired, or can be changed at a controlled rate. The same is true for web thickness. The head angle can be adjusted by a programmed computer or other means, as will be readily apparent to those skilled in the art.

Although the present invention has been disclosed in the description of certain preferred embodiments, those skilled in the art will appreciate that the present invention extends beyond the specific disclosed embodiments to other equivalent embodiments and obvious alternative embodiments. It will be understood that Therefore, the scope of the invention disclosed herein should not be limited by the particular disclosed embodiments herein, but should be construed as correctly enclosing the claims, including all equivalent technical scopes entitled to law. It is intended to be determined only by reading.

[Brief description of the drawings]

FIG. 1A is an elevational view of the rod and grinding wheel, schematically showing the parts of the grinding wheel moving continuously (passing) on the rod and their different starting positions; FIG.
FIG. 3 shows a grinding wheel similar to A but having a common starting position for each pass.

2A is a front view of one type of groove ground with a wheel according to the invention, and FIG. 2B is a top view of the groove and grinding wheel shown in FIG.

FIG. 3A shows an enlarged view of the uncut cutting edge of the grinding wheel, FIG. 3A schematically shows a cross section of a rod formed by the grinding wheel of A-1, and FIG. Figure 3 shows an enlarged view of the worn cutting edge of the wheel, with B schematically showing a cross section of a rod formed with the B-1 grinding wheel.

4 is an elevation view of a groove ground according to the present invention, wherein A shows a cross-sectional view of the tip of the ground rod shown in FIG. 4, and B shows the cross-section shown in FIG. FIG. 4 is a diagram showing a cross-sectional view of a base end of a ground rod.

──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, SD, SL, SZ, UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY , CA, CH, CN, CU, CZ, DE, DK, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP , KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, UA, UG, UZ, VN, YU, ZW (72) Inventor Singleton, David, Sea United States California, Los Angeles Boeing Avenue 7647 ( 72) Inventors Nightingale, John, Tee United States California, Los Angeles, Boeing Avenue 7647 F-term (reference) 3C049 AA03 AB01 AB06 BA02 CA01 CB01

Claims (10)

[Claims] 1. A multi-pass grinding method for producing an endodontic instrument used during treatment of a root canal, comprising the steps of: grinding a certain amount of metal material from an outer surface of a rod during a first pass along a movement path; Axially displacing the metal rod against a rotating grinding wheel, and displacing a further amount of metallic material to a desired depth during at least one additional pass in at least a portion of the travel path. A multi-pass grinding method, comprising: bringing the metal rod into contact with the rotary grinding wheel and moving the metal rod in an axial direction in order to grind from an outer surface of the rod. 2. The method of claim 1, wherein the metallic material comprises at least about 40% titanium. 3. The method according to claim 1, wherein the number of passes by the grinding wheel is 3 to 10 times. 4. The rod may be about 25.4-76 with respect to the grinding wheel during each pass.
. The method of claim 1 wherein the method is moved at an axial feed rate of 2 centimeters / minute (10-30 inches / minute). 5. The method of claim 1, wherein the amount of material ground during each pass is between about 10 microns and 100 microns. 6. The method of claim 1, wherein the amount of material ground during each pass is about 40 microns. 7. The speed of the grinding wheel is from about 5000 rpm to about 8500 rpm.
The method of claim 1, wherein 8. The method of claim 1, wherein a groove having a helical cutting edge at the desired depth is formed along the path of travel. 9. The method of claim 1, wherein each pass starts at approximately the same starting point along the length of the rod. 10. The method of claim 1, wherein the first pass and the additional pass start at different locations along the length of the rod.