Patent Application
20080194348
1. Technical Field
The present disclosure is directed to advantageous machining techniques and associated machining apparatus. The present disclosure is also directed to advantageous screw thread designs that may be efficiently and reliably fabricated using the disclosed machining techniques and/or machining apparatus. More particularly, the present disclosure is directed to machining techniques and associated machining apparatus that include multiple thread whirling heads, e.g., two thread whirling heads, associated with a single machining assembly, such that each of the thread whirling heads is able to act on a workpiece during a single, uninterrupted machining process.
2. Background Art
Screws and bolts find wide-ranging applications for attaching and/or securing elements, e.g., securing a first member with respect to a second member. Based on the diverse applications of such products, many designs have been developed. With particular focus on screw products, attention has been focused on screw thread designs and methods for fabrication thereof.
One particular area of interest for screw design and fabrication technologies is the orthopedic field. Given the clinical requirements of orthopedic screws, product performance and reliability are of tantamount importance. Titanium bone screws are used for spinal corrective surgery, trauma, and other types of bone repair and correction. Other bone screws are made of 316 stainless steel. Manufacture of bone screws generally involves strict requirements as to tolerances, surface properties, cleanliness and packaging. Titanium screws may generally range in length from 6 mm to 80 mm and have outer diameters (ODs) from 2 mm to 8.5 mm, although screws of greater length, e.g., 150 mm, shorter length, e.g., 2 mm, greater diameter, e.g., 16 mm, and lesser diameter, e.g., 1 mm, are also known. Typical bone screws require a 0.4-micron to 0.8-micron surface finish and dimensional tolerance of ±0.025 mm. In certain applications, anodized coatings may be applied for color coding different sizes and types of screws.
In manufacture of a typical bone screw, the manufacturing operations include thread whirling, broaching, gundrilling and turning/milling. To achieve these manufacturing steps, it may be necessary to employ three or four separate machines. Two or more of the manufacturing operations may be combined using Computer Numerical Control (CNC) technology, i.e., a programmable machine tool that uses computer control technologies. CNC tools permit machine tool movements to be controlled so as to efficiently and reproducibly produce manufactured parts/products. Indeed, the manufacture of orthopedic screws generally involves a series of repetitive motions and CNC technology reduces those specific motions to computer code that guides/controls tool operations. Exemplary CNC machining tools are available under the DECO tradename from Tornos SA (Moutier, Switzerland). For purposes of Tornos machines, CNC control technology is referred to as “parallel numerical control” (PNC).
The ten-axis DECO machines can use two turning tools at the same time, completing rough and finish cuts in the same operation. One of the machine's cross slides accepts up to four live tools for operations, such as cross milling and off-center drilling. A gundrilling and high-pressure coolant attachment can be mounted on the end-working unit. Polygon milling of flats or contours can be accomplished using the machine's optional C axis on the main spindle. While the bar in the main spindle is machined, operations may be performed on the previously parted piece mounted on the counter spindle. A workpiece mounted in the pickoff spindle of a DECO machine may be typically worked by three (3) cross drilling or turning tools and by as many as six (6) end working tools.
Despite efforts to date, a need remains for improved orthopedic screw designs, manufacturing equipment and methods for fabrication of orthopedic screws. In particular, a need remains for improved bone screw designs and fabrication methods therefor. These and other needs are satisfied by the present disclosure.
According to the present disclosure, advantageous machining techniques and associated machining apparatus are provided. The disclosed machining techniques and machining apparatus permit reliable and efficient fabrication of advantageous screw thread designs. According to exemplary embodiments of the present disclosure, machining techniques and machining apparatus are provided that include multiple thread whirling heads mounted with respect to a single machining assembly/apparatus. So assembled, the disclosed machining apparatus permits each of the thread whirling heads to act on a workpiece during a single, uninterrupted machining process. As used herein, the disclosed “single, uninterrupted machining process” refers to the totality of individual machining operations undertaken and performed by individual tooling elements mounted within or with respect to a machining apparatus.
The present disclosure is further directed to advantageous screw thread designs that may be efficiently and reliably manufactured using the disclosed fabrication techniques and machining apparatus. In exemplary embodiments, screw threads that include an intermediate transition, such that a single lead thread transitions to a double lead thread, may be efficiently and effectively fabricated in a single, uninterrupted process. In alternative embodiments, various screw thread transitions and/or combinations of screw thread transitions may be achieved and/or formed through programming and control of tool elements associated with the disclosed machining apparatus. For example, the disclosed methods and machining apparatus may be advantageously employed to achieve screw thread transitions (i) from a first single lead form to a second single lead form, (ii) from a first double lead form to a second double lead form, (iii) from a single lead form to a triple lead form, and combinations and/or variations thereof. The disclosed machining method and machining apparatus are thus not limited to fabrication of a specific screw thread transition, but have wide applicability in effecting many desirable thread transition designs and geometries.
The disclosed single lead to double lead thread transition may be advantageously fabricated with the disclosed machining method/technique and machining apparatus, and such screw thread transition offers several distinct advantages, including specifically (i) a substantially uniform/symmetric geometry in the transition region(s), and (ii) potentially enhanced engagement with a substrate/structure based on the design/geometry of the transition region(s). By creating the disclosed single lead to double lead thread transition in a single, uninterrupted machining operation, enhanced screw quality and integrity is achieved.
With reference to exemplary implementations of the disclosed machining technique and machining apparatus, advantageous screw thread transitions may be efficiently and reliably manufactured using such machining technique and machining apparatus by positioning metal stock (e.g., titanium) within a CNC machine, e.g., a DECO machine from Tornos SA modified for purposes of the present disclosure. As modified, the DECO machine operates as a 12 axis machine based on an added C-axis on each spindle. Indeed, a workpiece mounted in the pickoff spindle of the disclosed modified DECO machine may be typically worked by three (3) cross drilling or turning tools and by as many as six (6) end working tools. Further increases in tooling operations are contemplated according to the present disclosure.
The advantageous thread transitions of the present disclosure are achieved in an automated fashion using a single machine in a single, uninterrupted machining process. Thus, according to exemplary embodiments, the transition region and associated thread regions defined on either side of the transition region are sequentially formed using at least two (2) thread whirling heads in a single, uninterrupted machining process. Generally, each thread whirling head supports a plurality of substantially identical cutters, e.g., three (3) cutters spaced by about 120° around the circumference of the whirling head support body.
The first whirling head associated with the disclosed machining apparatus and associated machining technique includes first cutter(s) that are configured and dimensioned to generate a first thread profile. According to exemplary embodiments of the present disclosure, the “first thread profile” generated by the first whirling head is a wider thread profile as compared to a “second thread profile” (as described below), i.e., there is a greater distance from crest-to-crest (greater pitch) in the first thread profile as compared to the second thread profile. Thus, in an exemplary embodiment of the present disclosure wherein a single lead thread transitions to a double lead thread, the first whirling head and associated cutters are shifted along a length of the part/workpiece to remove material from the workpiece so as to define the single lead section with the wider first thread profile. The length of the first thread profile (as measured along the axis of the workpiece) may be varied to meet clinical requirements and/or other performance criteria. Thus, the first whirling head/first cutter(s) are generally programmed for limited travel along the length of the part/workpiece, such that—beyond forming an initial aspect of a to-be-defined transition region—the first cutter(s) typically do not contact the part/workpiece therebeyond.
After the first whirling head has formed the first thread profile, but with the workpiece still positioned within the machining apparatus, the second whirling head is automatically activated by the disclosed machining apparatus so as to engage/contact the workpiece to define a second thread profile and the remaining aspects of a transitional region between the first and second thread profiles. More particularly, the second cutter(s) associated with the second whirling head are brought into contact with the workpiece so as to define the thinner second thread profile and the remainder of the transitional region. Initially, the second cutter(s) travel within the thread region formed by the first whirling head until the unthreaded portion of the workpiece is reached. Thereafter, the second cutter(s) are effective to remove material from the workpiece so as to define a double thread region and a complete transition between the first and second thread profiles.
In an exemplary embodiment of the present disclosure, the transition region is defined as the threaded region between a first thread profile formed by the first whirling head/first cutter(s), i.e., the single/wider thread profile, and a second thread profile formed by the second whirling head/second cutter(s), i.e., the double thread region. The transition region is advantageously formed on the part/workpiece primarily with the second whirling head/second cutter(s), as described herein above. The second whirling head typically starts in the middle of the wider thread adjacent the remainder of the to-be-formed transition region and sweeps once to the right and once to the left, varying the helix angle to form the beginning of the thread for the narrower thread profile. The thread transition feeds directly into this narrower thread profile that is formed by the second whirling head/second cutter(s). Stated differently, the second whirling head/second cutter(s) is/are effective to form (i) a thread transition region that defines a transitional thread that feeds into an extended thread profile, and (ii) the extended thread profile to which the transitional thread is joined.
In use, the disclosed first and second thread whirling heads are mounted with respect to a single machining apparatus such that both thread whirling heads are adapted to sequentially engage and machine a part/workpiece in a single, uninterrupted machining process. Thus, the part/workpiece is typically fed to a machining position and positively secured in a desired machining position by a fixture. Significant reliability and accuracy in thread formation is achieved by facilitating multiple whirling head operations while the part/workpiece is positively secured and retained in the fixture, i.e., relative alignment of the first and second cutters relative to the part/workpiece may be achieved within strict tolerances.
Additional machining operations are typically undertaken to form a desirable finished product, e.g., an orthopedic bone screw. After the first and second thread whirling operations are complete, additional machining operations may be undertaken, as are known in the art, e.g., turning, milling, drilling and deburring operations. Additional processing may be performed within the machining apparatus. Additional operations may also be performed once the workpiece is removed from the machining apparatus, e.g., additional deburring operations. However, according to the present disclosure, a thread profile is formed in the machining apparatus that includes at least a first thread profile, at least a second profile, and a transition region therebetween.
According to exemplary embodiments of the present disclosure, the first and second thread whirling heads may be mounted with respect to a commercially available CNC machining unit that has been modified, as and if necessary, to accommodate operation of at least two (2) whirling heads relative to a part/workpiece that is fixtured relative thereto. First and second thread whirling heads may be positioned in a side-by-side orientation within a CNC unit. Programming associated with the CNC unit is generally provided to control operation of the first and second whirling heads so as to achieve a desired thread profile, e.g., a single/double lead thread profile with an intermediate transition therebetween.
Additional advantageous features and functions of the disclosed manufacturing technique, manufacturing apparatus and products manufactured thereby will be apparent from the description which follows.
To assist those of ordinary skill in the art in making and using the disclosed screw and screw thread design, reference is made to the appended figures, wherein:
Advantageous machining techniques and associated machining apparatus are disclosed herein, such machining techniques and machining apparatus facilitating reliable and efficient fabrication of advantageous screw thread designs. The present disclosure also provides advantageous screw thread designs having particular applicability in orthopedic applications, e.g., bone screws, that include at least one intermediate transition between first and second thread profiles. The multiple screw thread profiles are formed in a single, uninterrupted machining process according to the present disclosure. Thus, in an exemplary embodiment of the present disclosure, the screw includes a first axial portion that defines a single lead thread profile and a second axial portion that includes a double lead thread profile. An intermediate transition is provided between the first axial portion and the second axial portion, i.e., between the single lead and double lead thread profiles. Exemplary screw thread profiles that may be achieved according to the present disclosure are schematically depicted in
Alternative advantageous thread profiles may be fabricated using the disclosed machining techniques and machining apparatus, as will be readily apparent from the detailed description which follows. For example, the machining techniques and machining apparatus disclosed herein may be used to form screw thread transitions: (i) from a first single lead form to a second single lead form; (ii) from a first double lead form to a second double lead form; (iii) from a single lead form to a triple lead form, and combinations and/or variations thereof.
With initial reference to
An exemplary thread whirling head 100 for use in a machining apparatus, e.g., machining apparatus 50 of
According to the present disclosure, at least two thread whirling heads, e.g., thread whirling heads of the general type depicted in
In an exemplary embodiment of the present disclosure, two thread whirling heads are mounted in a side-by-side orientation within a DECO machine 50, e.g., at positions designated T22, T23, T24, T25 and the region below T25, as such terms are used by Tornos in connection with DECO tool positioning. This arrangement is schematically depicted in
As modified, the DECO machine 50 operates as a 12 axis machine based on an added C-axis on each spindle. Indeed, a workpiece mounted in the pickoff spindle of the disclosed modified DECO machine may be typically worked by three (3) cross drilling or turning tools and by as many as six (6) end working tools.
Exemplary thread whirling heads for use in the disclosed machining apparatus are advantageously adapted to operate at a maximum speed of 5000 rpm and to deliver a maximum torque of about 16 Nm. Each whirling head is generally adapted to deliver a drive ratio of 1:1 and accommodate angular adjustability of ±15 degrees. The foregoing operating parameters may be varied and/or modified, as will be apparent to persons skilled in the art. For example, greater angular adjustability, e.g., ±25 degrees, may be accommodated without departing from the spirit or scope of the present disclosure. Alternative thread whirling head designs and/or alternative CNC units may also be employed according to the present disclosure without departing from the spirit or scope of the present disclosure, as will be readily apparent to persons skilled in the art. However, fundamental to the present disclosure is the inclusion of at least two thread whirling heads in a single machining apparatus so as to sequentially act on a workpiece during a single, uninterrupted machining process.
The multi-whirling head assemblies of the present disclosure are effective to form advantageous thread transitions in an efficient and reliable manner. The fabrication technique generally involves positioning metal stock (e.g., titanium) within a CNC machine, e.g., a DECO machine from Tornos SA modified for purposes of the present disclosure, and effecting the desired machining activities during a single, uninterrupted machining process. The thread transition is imparted to the metal stock in an automated fashion using a single machine in a single, uninterrupted machining process.
With reference to
According to exemplary embodiments of the present disclosure, a first whirling head associated with the disclosed machining apparatus and associated machining technique includes first cutter(s) that are configured and dimensioned to generate a first thread profile, i.e., thread 14. The “first thread profile” generated by the first whirling head is a wider thread profile as compared to a “second thread profile,” i.e., thread 16. Thus, there is a greater distance from crest-to-crest (greater pitch) in the first thread profile as compared to the second thread profile. Thus, the first whirling head and associated cutters are shifted along a length of the part/workpiece to remove material from the workpiece so as to define the single lead section with the wider first thread profile, i.e., thread 14. The length of the first thread profile (as measured along the axis of the workpiece) may be varied to meet expected clinical requirements. Thus, the first whirling head/first cutter(s) are generally programmed for limited travel along the length of the part/workpiece. While the first cutter(s) is/are generally effective to define an initial aspect of the transition region, the first cutter(s) typically do not contact the part/workpiece in therebeyond.
After the first whirling head has formed the first thread profile, i.e., thread 14, but with the workpiece still positioned within the machining apparatus, the second whirling head is automatically activated by the disclosed machining apparatus so as to engage the workpiece to define a second thread profile, i.e., thread 16, and the remaining aspects of a transitional region 12 between the first and second thread profiles. More particularly, the second cutter(s) associated with the second whirling head are brought into contact with the workpiece so as to define the thinner second thread profile 16 and the remainder of the transitional region 12. Initially, the second cutter(s) travel within the thread region formed by the first whirling head, i.e., thread 14, until the unthreaded portion of the workpiece is reached. Thereafter, the second cutter(s) are effective to remove material from the workpiece so as to define a double thread region 16 and a complete transition 12 between the first and second thread profiles.
The transition region 12 is primarily formed on the part/workpiece with the second whirling head/second cutter(s). The second whirling head typically starts in the middle of the wider thread 14 adjacent the remainder of the to-be-formed transition region 12 and sweeps once to the right and once to the left, varying the helix angle to form the beginning of the thread for the narrower thread profile 16. The thread transition 12 feeds directly into this narrower thread profile 16 that is formed by the second whirling head/second cutter(s). Stated differently, the second whirling head/second cutter(s) is/are effective to form (i) a thread transition region 12 that defines a transitional thread 18 that feeds into an extended thread profile 16, and (ii) the extended thread profile 16 to which the transitional thread 18 is joined.
Additional machining operations are typically undertaken to form a desirable finished product, e.g., an orthopedic bone screw. For example, a preliminary turning operation may be undertaken to define the major geometry of the part. Conventional single point threading may then be employed to form the tip of the part. After the first and second thread whirling operations are complete, additional machining operations may be undertaken, as are known in the art, e.g., turning, milling, drilling and deburring operations. Processing may also be performed within the machining apparatus, e.g., a modified DECO machine as described herein, using a sub-spindle positioned therewithin, e.g., turning, milling, drilling, broaching and/or micro-milling. Additional operations may be performed once the workpiece is removed from the machining apparatus, e.g., additional deburring operations. Notwithstanding the potential for additional processing steps, however, a thread profile is formed in the machining apparatus of the present disclosure as part of a single, uninterrupted machining process that includes at least a first thread profile, at least a second profile, and a transition region therebetween.
The disclosed screw thread transition may be advantageously fabricated with the disclosed machining method/technique and machining apparatus, and such screw thread transition offers several distinct advantages, including specifically (i) a substantially uniform/symmetric geometry in the transition region(s), and (ii) potentially enhanced engagement with a substrate/structure based on the design/geometry of the transition region(s). By creating the desired screw thread transition(s) in a single, uninterrupted machining operation, enhanced screw quality and integrity is achieved. The disclosed thread transition has wide ranging applications, including spinal and/or orthopedic screw applications. Exemplary implementations of the disclosed thread transition include bone screws, pedicle screws and cervical screws.
Although the present disclosure includes descriptions of exemplary embodiments and implementations of the machining apparatus, machining techniques and advantageous screws and screw thread designs, the present disclosure is not limited to or by such exemplary embodiments. Rather, the subject matter of the present disclosure extends to a host of modifications, variations and enhancements that do not depart from the spirit or scope of the present disclosure.
The present application is a continuation-in-part application that claims the benefit of a co-pending, non-provisional patent application entitled “Single Lead to Double Lead Screw Transition,” which was filed on Oct. 24, 2006 and assigned Ser. No. 11/585,532. The present application also claims the benefit of a provisional patent application entitled “Screw Design and Associated Manufacturing Method,” which was filed on Oct. 28, 2005 and assigned Ser. No. 60/731,383, priority to which was claimed in the foregoing non-provisional patent application. The entire contents of the foregoing non-provisional application and provisional patent application are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60731383 | Oct 2005 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11585532 | Oct 2006 | US |
| Child | 11786084 | US |
