US20070251289A1

US20070251289A1 - System and method for producing component for medical device

Info

Publication number: US20070251289A1
Application number: US11/413,471
Authority: US
Inventors: Bernard Li
Original assignee: Medtronic Inc
Current assignee: Medtronic Inc
Priority date: 2006-04-28
Filing date: 2006-04-28
Publication date: 2007-11-01
Also published as: WO2007127073A2; WO2007127073A3

Abstract

A method includes applying a constant force to at least a portion of a component configured for use in a medical device and while the constant force is applied, subjecting the component to a temperature above ambient temperature for an amount of time sufficient to-improve the flatness of the component.

Description

BACKGROUND

The present invention relates generally to the field of medical devices. More particularly, the present invention relates to systems and methods for producing components of medical devices having improved shape characteristics.
Medical devices such as implantable drug pumps and neurological stimulation devices may utilize a number of relatively small metal parts or components. For example, a drug pump may include an inner shield for providing enhanced resistance to punctures or other damage to the drug pump. The inner shield may be formed, for example, from titanium or a titanium alloy.
One difficulty associated with such metal parts is that when they are formed in a conventional cold forming process, it may be difficult to obtain a required degree of flatness (e.g., the part may not be sufficiently planar to meet design specifications). One reason for this phenomenon is that certain metals when subjected to a cold forming process exhibit a certain degree of “springback” due to internal forces within the material. Such springback may be undesirable in certain circumstances (e.g., when the component must be welded to another component).
Accordingly, it would be desirable to provide a system and/or method for forming components for implantable medical devices that have improved flatness characteristics.

SUMMARY

An exemplary embodiment of the invention relates to a method that includes applying a constant force to at least a portion of a component configured for use in a medical device and while the constant force is applied, subjecting the component to a temperature above ambient temperature for an amount of time sufficient to improve the flatness of the component.
Another exemplary embodiment of the invention relates to a method for modifying the shape of a component for use in a medical device that includes providing a fixture, providing a component for use in a medical device in the fixture, and compressing the component within the fixture. The method also includes heating the component and fixture for a predetermined amount of time while the component is compressed to modify the shape of the component.
Another exemplary embodiment of the invention relates to a method for producing a component for use in a medical device that includes providing at least a portion of a component for a medical device in a fixture configured to apply pressure to the component. The method also includes compressing the component within the fixture and providing the fixture and component in a furnace for a predetermined amount of time with the furnace provided at an elevated temperature. The component under elevated temperature and pressure conditions experiences creep behavior that results in the component having improved flatness characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an implantable drug pump according to an exemplary embodiment.
FIG. 2 is a schematic plan view of a component for use in an implantable medical device according to an exemplary embodiment.
FIG. 3 is a schematic side plan view of the component shown in FIG. 1.
FIG. 4 is a schematic perspective view of a fixture for use in producing a component for use in an implantable medical device according to an exemplary embodiment.
FIG. 5 is a schematic plan view of the fixture shown in FIG. 3 having a component provided therein.
FIG. 6 is a flow chart showing steps in a method of producing a component for use in a medical device according to an exemplary embodiment.
FIG. 7 is a box-whisker diagram illustrating flatness profiles for six samples before and after a hot sizing operation according to an exemplary embodiment.
FIG. 8 is a box-whisker diagram illustrating flatness profiles for various samples before and after different hot sizing operations according to several exemplary embodiments.
FIG. 9 is a box-whisker diagram illustrating flatness profiles for 36 samples before and after a hot sizing operation according to an exemplary embodiment.
FIG. 10 is a histogram showing the flatness distribution for the 36 samples from FIG. 9 after the hot sizing operation.
FIG. 11 is a normal probability plot showing the flatness distribution for the 36 samples from FIG. 9 before and after the hot sizing operation.
FIG. 12 is a schematic view of a die according to an exemplary embodiment.

DETAILED DESCRIPTION

According to an exemplary embodiment, an improved system and method is provided for producing parts or components for use in medical devices (e.g., implantable medical devices). The process provides for the modification or alteration of the shape of at least a portion of the component (e.g., to provide components that exhibit improved flatness as compared to parts or components produced using traditional cold forming methods).
FIG. 1 is a perspective view of a medical device 10 shown in the form of an implantable programmable drug pump. According to an exemplary embodiment, the device 10 is a SynchroMed® drug pump commercially available from Medtronic, Inc. of Minneapolis, Minn.
FIGS. 2-3 illustrate a component 12 (e.g., an inner shield or plate) of the device 10 according to an exemplary embodiment. The component 12 is provided within the drug pump to provide enhanced resistance to punctures or other damage to the drug pump, and is welded to a bulkhead (not shown) or another component of the drug pump during assembly. According to other exemplary embodiments, other components of the drug pump may be produced using the methods described herein.
It should be noted that while the exemplary embodiments shown and described in the present disclosure relate to implantable drug pumps and components thereof, the systems and methods described herein may also be used in the production of components for other medical devices as well, including but not limited to implantable neurological stimulation devices, pacemakers, cardioverters, cardiac contractility modulators, drug administering devices, diagnostic recorders, cochlear implants, or any other type of medical device (implantable or otherwise).
According to an exemplary embodiment, the component 12 is made from a metal or metal alloy and in particular from titanium or a titanium alloy. For example, the component may preferably be made of commercial pure titanium grade 1 or from any of a variety of titanium alloys suitable for use in medical devices (e.g., alloys having formulae Ti-6Al-4V, Ti-4.5Al-3V-2Fe-2Mo-0.15O, Ti-4Al-2.5V-1.5Fe-0.25O, Ti-6Al-2Sn-4Zr-2Mo, and alpha and near alpha titanium alloys such as Ti-3Al-2.5V, Ti-4Al-2.5V-0.5O, Ti-8Al-Mo-V, Ti6242, and titanium matrix composites (alpha and near alpha matrix with SiC, TiC, TiO particles distributed therein)). The component 12 may also be made from any of a variety of other metals or metal alloys.
Because at least a portion of the component 12 will typically be welded during the process of assembling the medical device 10, it is desirable that the portion to be welded be as flat or planar as possible to avoid defective or otherwise unsuitable weld formation. Such flatness or planarity may be measured using any of a variety of methods, including using flatness measuring equipment commercially available, for example, from Mycrona of North America, Inc. of Elgin, Ill. According to an exemplary embodiment, the flatness is measured as the difference between the highest and lowest point on the portion of the component being measured. According to other exemplary embodiments, the flatness may be measured in other ways (e.g., the average “height” of the component above or below a reference point, the deviation of the height over a defined distance or area, etc.).
According to an exemplary embodiment in which the inner shield is intended for use in a SynchroMed® drug pump commercially available from Medtronic, Inc. of Minneapolis, Minn., it is desirable for the flatness of the inner shield (measured as the difference between the highest and lowest points on the portion of the component being analyzed) to be less than 0.25 mm (0.0098 inches).
In order to obtain the desired degree of flatness for the component 12, a hot sizing or creep forming process is utilized. Such a process is a thermal-mechanical process that is used to slightly modify the shape of the component 12 under relatively high temperature and low stress conditions. By subjecting the component 12 to such conditions for a predetermined amount of time, the material (e.g., titanium or a titanium alloy) used to form the component will exhibit creep behavior, thus deforming the component in a manner that results in improved flatness for the part.
One advantageous feature of using a hot sizing or creep forming process is that the component 12 exhibits lower residual stress than would otherwise be present for a component formed in a cold forming operation. Such a process also allows for relatively fine adjustments to the shape of the component, even when the component is relatively small (e.g., as in the case of an inner shield for an implantable drug pump).
FIGS. 4-5 are schematic views of a fixture or die 20 used in a creep forming process according to an exemplary embodiment, and FIG. 6 is a flow diagram illustrating steps in a method or process 100 for producing the component 12 according to an exemplary embodiment.
In a step 110, the fixture 20 is provided as having a lower portion or member 22 (e.g., a lower plate or platen) and an upper portion or member 24 (e.g., an upper plate or platen). It should be noted that the terms “upper”, “lower”, “top”, “bottom”, and the like are intended for reference only, and are not intended as limiting to the subject matter disclosed herein. For example, the lower portion 22 and the upper portion 24 shown in FIG. 4 may be reversed or provided in different orientations according to other exemplary embodiments.
According to an exemplary embodiment, each of the upper portion 24 and lower portion 22 have a thickness of approximately 0.8 inches and an area of 6 inches by six inches. According to other exemplary embodiments, the dimensions of the fixture may differ, for example, based on the application for which the fixture is intended (e.g., the size and shape of the component to be compressed, etc.).
In a step 120, the component 12 to be flattened or compressed (illustrated in FIG. 5 as having portions which are bent or curved) is provided in a cavity or depression. The cavity or depression may be provided in the upper portion 24 of the fixture 20, the lower portion 22 of the fixture 20, or both. As shown in FIGS. 3 and 4, the lower portion 24 includes a cavity or depression 26 into which the component 12 is provided. The size, shape, and configuration of the cavity 26 may be selected to accommodate features of a component 12 (see FIG. 4) to be provided therein according to an exemplary embodiment.
The fixture 20 is configured such that the upper portion 24 and lower portion 22 may be forced together to apply pressure to at least a portion of the component 12. Such compression of the component 12 within the fixture 20 is maintained during the creep forming process such that the flatness or planarity of the component 12 is improved due to its creep behavior.
In a step 130, the fixture 20 is tightened to compress the component 12 so as to flatten portions of the component 12. According to an exemplary embodiment, the upper portion 24 is configured to be coupled or secured to the lower portion 22 by fasteners 27, 29 (e.g., screws, bolts, etc.) that may be tightened or torqued to a predetermined level to apply a desired amount of pressure or force on the component secured within the fixture. The lower portion 22 includes a number of apertures or holes 23 and the upper portion 24 includes a number of apertures or holes 25 for receiving the fasteners 27, 29. Apertures 23, 25 may be threaded such that the fasteners 27, 29 are screwed in to secure the upper portion 24 to the lower portion or may have relatively smooth sides (e.g., where the bolt will have a nut and/or washer secured to a distal end thereof to secure the upper portion 24 to the lower portion). According to other exemplary embodiments, no apertures (e.g., apertures 23, 25) or fasteners (e.g., fasteners 27, 29) are provided, and the upper portion 24 may be secured to the lower portion 26 by other means (e.g., by inserting the fixture 20 into a mechanical press that compresses the portions of the fixture, by providing a weight on top of the fixture to compress the fixture, etc.).
In a step 140, the fixture 20 and component 12 are heated to an elevated temperature (e.g., a temperature above ambient temperature) while the component 12 is compressed between the upper portion 24 and the lower portion 22 of the fixture. According to an exemplary embodiment, the fixture 20 may be heated by placing the entire fixture in a furnace (e.g., a vacuum furnace) along with the component 12 secured therein. One advantageous feature of utilizing a vacuum furnace is that oxidation of the component is reduced or eliminated. According to another exemplary embodiment, the fixture 20 may include one or more thermocouples (provided in one or both of the upper portion 24 and lower portion 22) that are intended to heat the die without the need for a separate furnace.
The pressure applied to the component by the fixture, the temperature of the furnace, and the duration of heating are selected according to a number of factors, including the type of material used for the component, the size and shape of the component (e.g., the thickness of the component), the degree of flattening desired, the size, shape, and configuration of the fixture, the number of bolts used for tightening or compressing the fixture, and the like. According to an exemplary embodiment in which the component is formed from commercial pure titanium grade 1 and has a thickness of between approximately 0.002 and 0.030 inches, each of the four bolts are tightened with a torque of between approximately 35 and 50 inch-pounds. The components are then heated to a temperature of between approximately 900 and 1300 degrees Fahrenheit (° F.) for between approximately six and ten minutes (e.g., according to an exemplary embodiment, the component is subjected to a temperature above 960° F. for a period of at least six minutes to cause the material used to form the component to creep).
According to a particular exemplary embodiment, the component is provided in the fixture and each of the bolts of the fixture are torqued to approximately 45 inch-pounds. The component is then placed in a vacuum furnace at 1080° F. for approximately 13 minutes or longer (e.g., to allow the temperature of the component to reach a desired level (e.g., approximately 960° F. or greater) for at least six minutes). As described above, the particular conditions for a component may vary depending on a variety of factors, and the pressure, temperature, and duration of heating should be selected such that the component undergoes creep for a desired amount of time to attain the desired flatness for the component.
FIG. 7 is a graph 200 (e.g., a box-whisker diagram) illustrating the flatness profile of six inner shields before and after a hot sizing operation. According to an exemplary embodiment, the flatness specification 210 is 0.010 inches. Before hot sizing, the six samples had an average flatness of approximately 0.018 inches (as illustrated by the data labeled with reference numeral 220). The six samples were then placed in a fixture at a temperature of between 800° F. and 827° F. for approximately six minutes and then allowed to cool to room temperature. In this embodiment, no pressure was applied to the components other than the weight of the top portion of the fixture (e.g., no weight was added on top of the fixture, and no fasteners were tightened to compress the fixture). As shown by the data labeled with reference numeral 230, the flatness of the part improved such that it was on average slightly better than the target value for the flatness specification 210.
FIG. 8 is a graph 300 (e.g., a box-whisker diagram) illustrating the before and after flatness profiles for various sets of inner shields that were subjected to various hot sizing operations. As will be apparent from a review of the data shown in graph 300, the addition of pressure or stress to the components when such components are held at an elevated temperature for a defined period of time provides improved flatness for the components as compared to components held at the same temperature with no added pressure.
For a first set of inner shields (data labeled with reference numerals 320 and 330), the average flatness before hot sizing was approximately 0.022 inches, and after subjecting the samples to a temperature of approximately 900° F. for a period of approximately ten minutes (with no added pressure), the average flatness for the samples was approximately 0.014 inches, which is above the 0.010 inch flatness specification 310.
For a second set of inner shields (data labeled with reference numerals 340 and 350), the average flatness before hot sizing was approximately 0.016 inches, and after subjecting the samples to a temperature of approximately 1000° F. for a period of approximately ten minutes (with no added pressure), the average flatness for the samples was slightly below the 0.010 inch flatness specification 310.
For a third set (data labeled with reference numerals 360 and 370) and a fourth set (data labeled with reference numerals 380 and 390) of inner shields, a weight of approximately ten pounds was placed on top of the fixture to apply pressure to the component within the fixture. For the third set of inner shields, the average flatness before hot sizing was approximately 0.016 inches, and after subjecting the samples to a temperature of approximately 900° F. for a period of approximately ten minutes with the ten pound weight added to the top of the fixture, the average flatness for the samples was approximately 0.008, which is below the 0.010 inch flatness specification 310. Similar results were obtained for the fourth set of inner shields, in which the average flatness before hot sizing was approximately 0.016 inches, and after subjecting the samples to a temperature of approximately 1000° F. for a period of approximately ten minutes with the ten pound weight added to the top of the fixture, the average flatness for the samples was approximately 0.006, which is below the 0.010 inch flatness specification 310.
FIG. 9 is a graph 400 (e.g., a box-whisker diagram) illustrating results from an experiment in which 36 inner shields were provided in a furnace at approximately 1080° F. for a period of approximately thirteen minutes (the length of time being chosen to allow the samples to reach a temperature of at least 960° F. for a period of at least six minutes). Each of the bolts in the fixture were tightened with a torque of approximately 50 inch-pounds before placing the fixture in the furnace. As shown in FIG. 9, before the hot sizing process (represented by the data labeled with reference numeral 420), the samples had an average flatness of approximately 0.019 inches, and after the hot sizing process (represented by the data labeled with reference numeral 430), the samples had an average flatness of approximately 0.006 inches, which is below the 0.010 inch flatness specification 310. FIG. 10 is a histogram showing the average flatness distribution for the 36 samples, and indicates that the samples had a Cpk of 1.96. FIG. 11 is a normal probability plot showing the flatness specification 610 of 0.010 inches along with the flatness of the components before hot sizing (represented by data labeled with reference numeral 620) and after hot sizing (represented by data labeled with reference numeral 630). As evident from FIGS. 9-11, the hot sizing operation provided a significant improvement in the flatness of the components.
According to another exemplary embodiment, the fixture used for the hot sizing operation may also be used in the formation of the component. FIG. 12 illustrates a fixture 720 having an upper portion 724 and a lower portion 722. A cavity 726 is provided in the lower portion, and a projection 728 extends from the upper portion 724. In operation, a piece of sheet material 712 (e.g., titanium or a titanium alloy) is provided within the fixture and the upper and lower portions 724, 722 are brought together such that the projection 728 and cavity 726 form the component. During the formation of the component, the component may also be subjected to an elevated temperature (e.g., by placing the fixture 720 in a furnace at a temperature sufficient to induce creep in the component during the formation process). In this manner, the component may be formed in a manner that provides improved flatness as compared to components formed using conventional cold forming operations that may induce a springback effect in the material used to form the component. One advantage of such a process is that the formation and flatness improvement may be accomplished in the same step, thus eliminating the need for a secondary operation to improve the flatness of the component.
It is important to note that the system and method as shown and described with respect to the various exemplary embodiments is illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. For example, elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. Accordingly, all such modifications are intended to be included within the scope of the present invention as defined in the appended claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the various exemplary embodiments without departing from the scope of the present invention as expressed in the appended claims.

Claims

1. A method comprising:

applying a force to at least a portion of a component configured for use in a medical device; and

while the force is applied, subjecting the component to a temperature above ambient temperature for an amount of time sufficient to improve the flatness of the component.

2. The method of claim 1, wherein the step of applying a force to at least a portion of a component comprises providing the component in a fixture having a first plate and a second plate such that the component is between the first plate and the second plate and compressing the component between the first plate and the second plate.

3. The method of claim 2, wherein the first plate is coupled to the second plate by a plurality of bolts and the step of compressing the component comprises tightening the plurality of bolts.

4. The method of claim 2, wherein the step of compressing the component comprises providing a weight on at least one of the first plate and the second plate.

5. The method of claim 2, wherein the step of compressing the component comprises applying a force to at least one of the plates to compress the plates toward each other.

6. The method of claim 2, wherein the fixture is also configured for forming the component.

7. The method of claim 6, further comprising providing a piece of sheet metal in the fixture and the step of compressing the component acts to form the shape of the component.

8. The method of claim 1, wherein the component is formed of a material comprising titanium.

9. The method of claim 1, wherein the step of subjecting the component to a temperature above ambient temperature comprises providing the component in a furnace, wherein the furnace is at a temperature of between approximately 900 and 1300 degrees Fahrenheit.

10. The method of claim 9, wherein the step of applying subjecting the component to a temperature above ambient temperature comprises heating the component to a temperature of at least 960 degrees Fahrenheit for a period of at least six minutes.

11. The method of claim 1, wherein the step of subjecting the component to a temperature above ambient temperature comprises utilizing a vacuum furnace.

12. The method of claim 1, wherein the medical device is an implantable drug pump.

13. The method of claim 12, wherein the component is an inner shield for the drug pump.

14. A method for modifying the shape of a component for use in a medical device comprising:

providing a fixture;

providing a component for use in a medical device in the fixture;

compressing the component within the fixture; and

heating the component and fixture for a predetermined amount of time while, the component is compressed to modify the shape of the component.

15. The method of claim 14, wherein the shape of the component is modified such that the flatness of the component is improved.

16. The method of claim 14, wherein the fixture comprises a first plate, a second plate, and a cavity provided in at least one of the first plate and the second plate.

17. The method of claim 16, wherein the step of providing the component in the fixture comprises providing at least a portion of the component in the cavity.

18. The method of claim 17, wherein the step of compressing the component within the fixture comprises compressing the component between at least a portion of the first plate and the second plate.

19. The method of claim 14, wherein the component is formed of a material comprising titanium.

20. The method of claim 14, wherein the step of heating the component comprises heating the component in a furnace, wherein the temperature of the furnace is between approximately 900 and 1300 degrees Fahrenheit.

21. The method of claim 16, wherein the fixture includes at least one fastener coupling the plates together and the step of compressing the component comprises tightening the at least one fastener.

22. The method of claim 16, wherein the step of compressing the component comprises applying a force to at least one of the plates in a direction towards the other of the plates.

23. The method of claim 14, wherein the predetermined amount of time is greater than approximately five minutes.

24. The method of claim 14, wherein the step of heating the component utilizes at least one of a vacuum furnace and a thermocouple.

25. The method of claim 14, wherein the component is an inner shield for an implantable drug pump.

26. A method for producing a component for use in a medical device comprising:

providing at least a portion of a component for a medical device in a fixture configured to apply pressure to the component;

compressing the component within the fixture; and

providing the fixture and component in a furnace for a predetermined amount of time with the furnace provided at an elevated temperature;

wherein the component under elevated temperature and pressure conditions experiences creep behavior that results in the component having improved flatness characteristics.

27. The method of claim 26, wherein the component is formed of a material comprising titanium.

28. The method of claim 26, wherein the elevated temperature of the furnace is between approximately 900 and 1300 degrees Fahrenheit.

29. The method of claim 26, wherein the furnace is a vacuum furnace.

30. The method of claim 26, wherein the medical device is selected from the group consisting of an implantable drug pump, an implantable neurological stimulation device, a pacemakers, a cardioverter, a cardiac contractility modulator, a drug administering device, a diagnostic recorder, and a cochlear implant.

31. The method of claim 26, wherein the component is an inner shield for a drug pump.