Patent Description:
Advances into metal injection molding (MIM) or powder injection molding (PIM) have resulted in forming small intricate parts generally less than <NUM>. The MIM process utilizes a powdered metal mixed with a polymeric binder to create a feedstock that is used in standard injection molding machines to generate a "green" part that is roughly <NUM>% oversized from final part dimensions. This part then goes through a debinding process to remove the polymeric binder that leaves the part with a porous powder structure that yields a very brittle "brown" part. This part is then sintered at extremely high temperature that solidifies the metal structure, shrinking the part, and resulting in mechanical properties very similar to their wrought counterparts.

<CIT> relates to a chestpiece for a stethoscope. The chestpiece has a mix of desirable properties through being fabricated from the group of materials known as "high gravity compounds". These compounds are prepared by loading various plastic resins with high density metal powders. In spite of the metallic content, appropriate compounds can be injection molded, providing economic and aesthetic advantages.

<CIT> relates to a detection head of a stethoscope that comprises a detection head body and a sound guiding conduit in the detection head body. The sound guiding conduit comprises a sound collecting surface, a sound guiding pore, and a lateral sound guiding aperture. The sound collecting surface, the sound guiding pore, and the lateral sound guiding aperture are disposed on the detection head body, and in combination with each other. At least a part of the detection head body is made of a second density material. The density of the material of a sound guiding layer on the sound collecting surface is greater than that of the second density material.

The invention, which relates to a method of making a metal stethoscope, is defined by the features of the independent claim.

In the case of injection molding, on the other hand, virtually any desired shape can be produced. However, metal powder injection molding has the disadvantages that anisotropies sometimes occur in the casting mould in the case of relatively large workpieces (e.g., greater than <NUM>) and that a separate step for removing the binder has to be carried out. When applied to larger workpieces (<NUM>), MIM techniques can cause cracking or discoloration. This is particularly true with stethoscopes because a stethoscope chestpiece has thick and thin sections, which present issues during debinding as the difference in heating and cooling rates can generate stresses in the material causing cracks. This makes MIM ill-suited to applications where aesthetics (such as smooth mirrored surfaces) are desirable.

The present disclosure relates to a stethoscope comprising a stethoscope chestpiece comprising a body member having a bottom surface. The stethoscope chestpiece comprises an ejector mark disposed on the bottom surface. The stethoscope chestpiece has a weight of at least <NUM>, a surface roughness (Ra) no greater than <NUM> microns in an unpolished state, and reflectivity (%R) of at least <NUM>% in an unpolished state. The stethoscope chestpiece can be produced by injection molding, extruding, or pressing a metallic thermoplastic composition into a mould forming a green molded body. The stethoscope chestpiece can also be produced by debinding a portion of binder material from green molded body at a temperature in the range of <NUM> to <NUM> over a period from <NUM> to <NUM> hours in a nitrogen-comprising atmosphere forming a brown molded body without reducing the temperature significantly. The stethoscope chestpiece can also be produced by sintering the brown molded body a a temperature in the range from <NUM> to <NUM> over a period of from <NUM> to <NUM> hours in a hydrogen or argon atmosphere to form the stethoscope chestpiece.

The present disclosure also relates to a method of manufacturing.

The present disclosure relates to a method of using metal injection molding to manufacture a stethoscope chestpiece. The stethoscope chestpiece has shown improve crack resistance by using process control conditions, feedstock selection, and ejector marks on the stethoscope chestpiece. The stethoscope chestpiece can exhibit properties that distinguish the stethoscope from traditional investment casting techniques as described herein.

As used in the instant specification and claims, "acoustical stiffness" of the diaphragm designates the mechanical stiffness of the diaphragm as influenced by the mechanical stiffness of the diaphragm material itself, the thickness of the diaphragm, the shape of the diaphragm, the diameter of the diaphragm, and the manner in which the diaphragm is attached to the stethoscope chestpiece. The phrase "plane of the diaphragm" refers to the generally planar surface of the diaphragm.

While various stethoscope chestpieces can be manufactured using metal injection molding/powder injection molding, non-symmetrical shapes are preferred. A symmetrical shape can be symmetric on a plurality of axes rotated about top-bottom axis. A non-symmetrical shape can be symmetric about only one axis (e.g., the axis intersecting a stem fitting, axis formed along the line <NUM>-<NUM> in <FIG> but not symmetrical along line <NUM>-<NUM>. Non-symmetrical shapes generally cannot be lathed. Examples of non-symmetric shares of stethoscope chestpiece include the Master Cardiology, Master Classic, and the Classic SE by <NUM> (Saint Paul, MN). The stethoscope chestpiece may be a single-sided meaning that only one diaphragm can be positioned on the stethoscope chestpiece.

A stethoscope from <CIT> can be used. For example, in <FIG>, stethoscope chestpiece <NUM> comprises body member <NUM> formed of metallic thermoplastic compositions. Stethoscope chestpiece <NUM> is attached to a conventional headset such as those commercially available under the trade designation Littman by <NUM> (St. Paul, MN) which comprises elongated flexible tubing <NUM> which contains dual air passages <NUM> which run side-by-side for a major portion of the distance between stethoscope chestpiece <NUM> and ear tubes <NUM>. In the lower end of flexible tubing <NUM> which attaches to stethoscope chestpiece <NUM>, passages <NUM> merge into a single passage 13a adapted to be coupled to stem fitting <NUM> of stethoscope chestpiece <NUM>. The upper end of flexible tubing <NUM> bifurcates into coupling arms <NUM>, each of which attaches to one of the ear tubes <NUM> and each of which contains one of the ear tips <NUM>. Ear tubes <NUM> are secured together by tubing <NUM>.

The body member <NUM> comprises a substantially disk-like portion <NUM> and column <NUM> emanating therefrom as shown in <FIG>. Top <NUM> of column <NUM> is substantially flat. Front section <NUM> of column <NUM> is sloped away from top <NUM>, is concave in configuration and is curved to meet the top surface of disk-like portion <NUM>. Side sections <NUM> and <NUM> and back section <NUM> are arcuate in configuration. The shape of body member <NUM> permits a clinician to grasp it in one of two particularly convenient ways. The clinician may grasp column <NUM> from the top with the index finger being placed on front section <NUM> and each of the thumb and the middle finger being placed on opposite sides of column <NUM> adjacent top <NUM>. Alternatively, the clinician may place the index finger and middle finger adjacent disk <NUM> on opposite sides of column <NUM> (with fitting <NUM> passing between those fingers).

In <FIG>, it is seen that body member <NUM> has a first generally bell-shaped recess <NUM>, the recess <NUM> being defined by side wall <NUM>, outer rim portion <NUM>, and inner central portion or plate-like member <NUM> (which can be the immobilizing means). Second conical-shaped recess <NUM> is defined by inner central portion or plate-like member <NUM> which is integral with body member <NUM> and has a centrally sloping depression in its surface and optional O-ring <NUM> which is situated circumjacent plate-like member <NUM> and retained thereon. The circumjacent plate-like member <NUM> itself can be raised further from a plane formed by the major surface of the portion adjacent to the outer rim portion <NUM> (the major surface contacting the compliant ring <NUM>), thus negating the need of the O-ring <NUM>. Body member <NUM> also comprises bore <NUM> extending from fitting <NUM> through body member <NUM> to aperture <NUM> within bell-shaped first recess <NUM> and conical-shaped second recess <NUM>.

The body member <NUM> can have an outside surface or top surface <NUM> at least partially defined as a region that a clinician can touch. The outside surface <NUM> includes the column <NUM>. The outside surface <NUM> is generally polished since this surface is seen by the clinician. The body member <NUM> may have an inner surface or bottom surface <NUM>. The bottom surface <NUM> includes a major surface of both the recess <NUM> and the conical-shaped second recess <NUM>. Generally, the bottom surface <NUM> is overlaid by the diaphragm <NUM> and is not polished or seen by the clinician. The bottom surface <NUM> can be planar and forms a plane defined by at least one circumference.

Diaphragm <NUM> may overlay the entirety of second conical-shaped recess <NUM> (and inner central portion or plate-like member <NUM>) and at least a portion of first bell-shaped recess <NUM> to permit contact of diaphragm <NUM> with O-ring <NUM>. Diaphragm <NUM> may comprise any material which is known in the art as being suitable for use as a diaphragm. Examples of suitable materials include plastics such as polyester, fiberglass-reinforced plastics, and polystyrene and metals such as stainless steel. A suitable thickness for diaphragm <NUM> is about <NUM> to <NUM> mils (<NUM> to <NUM> centimeters). The preferred thickness for diaphragm <NUM> is about <NUM> to <NUM> mils (<NUM> to <NUM> centimeters). A preferred diaphragm comprises a <NUM> mil-thick (<NUM> centimeter-thick) epoxy resin-fiberglass laminate.

Optionally surrounding diaphragm <NUM> is suspension member or compliant ring <NUM> which suspends diaphragm <NUM> across the first bell-shaped recess <NUM> and allows diaphragm <NUM> to move in a direction generally perpendicular to the plane of the diaphragm. Compliant ring <NUM> is generally horseshoe-shaped in cross-section having an inner edge <NUM> and an outer edge <NUM> on either side of curved portion <NUM>. Compliant ring <NUM> is attached to peripheral edge portion <NUM> of diaphragm <NUM> at inner edge <NUM>. Outer edge <NUM> is attached to first bell-shaped recess <NUM> by means of a retaining ring or plastic fitting <NUM> which engages notch <NUM> of body member <NUM>. The notch <NUM> can have an edge having a square-like profile with non-rounded corners as a result of the finer resolution of MIM.

Preferably, the diaphragm <NUM> is constructed as a single piece, meaning that the diaphragm <NUM> is connected to the compliant ring <NUM> as described in U.

The response of stethoscope chestpiece <NUM> to low frequency and high frequency sounds is affected by several parameters. The thickness of diaphragm <NUM> affects the response and suitable thicknesses for diaphragm <NUM> have been discussed hereinabove. Also, the relative dimensions of first bell-shaped recess <NUM> and second conical-shaped recess <NUM> affect the response. The following have been found to be suitable dimensions for first bell-shaped recess <NUM> and second conical-shaped recess <NUM>. First bell-shaped recess <NUM> has a diameter (as defined by side wall <NUM>) of <NUM> inches (<NUM> centimeters) and has a volume (as defined by diaphragm <NUM> and compliant ring <NUM> when no pressure is exerted on the exterior surface of diaphragm <NUM>) of approximately <NUM> in<NUM> (<NUM><NUM>). Second conical-shaped recess <NUM> has a diameter (as defined by O-ring <NUM>) of <NUM> inches (<NUM> centimeters) and a volume (as defined by diaphragm <NUM> when it is in contact with O-ring <NUM>) of approximately <NUM> in<NUM> (<NUM><NUM>). The distance that diaphragm <NUM> travels from its equilibrium position to its position in which it is in contact with O-ring <NUM> is approximately <NUM> inches (<NUM> centimeters). As indicated above, diaphragm <NUM> may be of a diameter which is greater than the diameter of second conical-shaped recess <NUM>. A diaphragm having a <NUM> inch (<NUM>-centimeter) diameter has been found to be suitable in a stethoscope chestpiece comprising first bell-shaped recess <NUM> and second conical-shaped recess <NUM> of the above indicated dimensions. A compliant ring <NUM> which includes curved portion <NUM> having a radius of curvature of <NUM> inches (<NUM> centimeters) has been found to provide the desired freedom of movement of diaphragm <NUM>.

<FIG> illustrates a flowchart of a method <NUM> of making a stethoscope. The method <NUM> includes making a chestpiece, e.g., blocks <NUM> through <NUM>, and assembling the stethoscope, e.g., block <NUM>.

The method <NUM> can begin at block <NUM> where a green molded body is formed. The green molded body is a metallic thermoplastic and can be obtained by injection molding, extruding, or pressing of metallic thermoplastic compositions or thermoplastic molding compositions comprising metal powders. Examples of metal powders are powders of Fe, Al, Cu, Nb, Ti, Mn, V, Ni, Cr, Co, Mo, W and Si, and combinations thereof. Stethoscope chestpieces which are preferred are those which can be obtained from powder injection molding compositions, particularly preferably from powder injection molding compositions of Fe and Cr.

For the purposes of the present disclosure, the terms "injection molding" (also referred to as powder injection molding), "extrusion" and "pressing" are used in the sense of processes from powder technology, in particular powder metallurgy, in which, for example, a shaped body from which the binder is subsequently removed and which is then sintered to produce the finished workpiece is produced by injection molding of a thermoplastic injection molding composition comprising metal or ceramic powder and a proportion of usually at least <NUM>% by volume of a thermoplastic binder. Thus, the mould for metal injection molding is generally larger than the finished stethoscope chestpiece.

The injection molding of the metallic thermoplastic composition can occur at an elevated temperature sufficient to bind portions of the metallic thermoplastic compositions inside of the mould. The mould is a hollow container used to give shape a molten metallic thermoplastic material, when the material cools and hardens. The mould is a negative impression of the intended stethoscope chestpiece. The mould as defined herein can be a negative of the stethoscope chestpiece described herein.

The metallic thermoplastic composition can include both a binder. The polyoxymethalene homopolymers and copolymers mentioned as binders and their preparation are known to those skilled in the art and are described in the literature. The homopolymers are usually prepared by polymerization (mostly catalyzed polymerization) of formaldehyde or trioxane. To prepare polyoxymethylene copolymers, a cyclic ether or a plurality of cyclic ethers is/are usually used as comonomer together with formaldehyde and/or trioxane in the polymerization, so that the polyoxymethylene chain with its sequence of (-OCH<NUM>)-units is interrupted by units in which more than one carbon atom is present between two oxygen atoms. Examples of cyclic ethers which are suitable as comonomers are ethylene oxide, <NUM>,<NUM>-propylene oxide, <NUM>,<NUM>-butylene oxide, <NUM>,<NUM>-dioxane, <NUM>,<NUM>-dioxolane, dioxepane, linear oligoformals and polyformals such as polydioxolane or polydioxepane and also oxymethylene terpolymers.

In general, the binder comprises at least <NUM>% by weight of polyoxymethylene (POM) and can additionally comprise further polymers, for example polystyrene, polypropylene, polyethlene and ethylene-vinyl acetate copolymers and also further auxiliaries which may be necessary, e.g. dispersants, plasticizers and mold release agents. In particular, the further polymers mentioned, e.g. polystyrene, polypropylene, polyethylene and ethylene-vinyl acetate copolymers, and also any further auxiliaries which may be necessary, e.g. dispersants, plasticizers and mold release agents, are removed from the shaped part.

The metallic thermoplastic composition may be commercially available under the trade designation Catamold, model: LG plus from BASF (Florham Park, NJ).

Once molded, then the green molded body can be optionally removed, e.g., demolded, in block <NUM>. The green molded body can be removed in order to allow shrinkage and avoid problems during the debinding and sintering process. The removal can include applying one or more ejectors (comprising ejector pins) to the green molded body to remove the green molded body from the mould. It may be beneficial for the ejectors to contact the part over the largest possible area and without tilting. The ejector pins can be any shape and be positioned roughly evenly along the stethoscope chestpiece. Preferably, the ejectors pins can contact an unseen or unpolished area of the stethoscope chestpiece such as the bottom. Once the ejector pins contact the green molded body, ejector marks can be formed in the green molded body as described herein.

The green molded body can be removed via a vacuum method which may leave a positive protruding area within the green molded body.

In block <NUM>, a portion of binder material from the green molded body is debound to form the brown molded body. For example, thermal debinding, or pyrolysis, can be used. The green molded body is heated in a closely controlled oven up to a temperature just below the softening point of the binder.

A binder can undergo gaseous decomposition. For example, if the binder is polyacetal, debinding can occur at or around <NUM> deg. C, which is below the melting range of polyacetal, <NUM> - <NUM>. Thus, the polymer can be directly converted from a solid into a gas. After the polyacetal is removed, a residual amount (usually around <NUM> weight % of the original binder content) of an acid-resistant binder component may remain. The temperature of a debinding oven is from 100C to <NUM> C, <NUM> C to <NUM> C, preferably <NUM> - <NUM> C. Block <NUM> occurs in a nitrogen comprising atmosphere, wherein nitric acid and formaldehyde are vented.

Solvent debinding is an alternative process that improves the debinding rate verses pyrolysis. The parts are immersed in liquid or vapor of an extracting solvent. The solvent accelerates the removal of binder from the parts and helps open-up porosity in the part. Solvent debinding still requires that the residual binder and solvent must be removed from the part thermally. Possible solvents may include nitric acid.

If the binder undergoes thermal debinding, a binder removal oven or debinding oven can be used. The binder removal oven is an oven through which the shaped bodies travel in a transport direction while being brought to the above-defined temperatures for the above-defined periods of time. Various designs of debinding ovens are commercially available from manufacturers such as CMFunaces, Inc (Bloomfield, NJ) or Elnik Systems, LLC (Cedar Grove, NJ).

While some debinding methods involve the transport from a first debinding oven to a second debinding oven, this may introduce partial cooling which was found to be detrimental. The method according to claim <NUM> of the present invention involves continuous debinding (e.g., debinding without transferring ovens or otherwise without significant drops in temperature). The debinding temperature is maintained within ± <NUM> during the debinding period.

The total debinding can occur between <NUM> to <NUM> hours, <NUM> to <NUM> hours, <NUM> to <NUM> hours, <NUM> to <NUM> hours, <NUM> to <NUM> hours, or <NUM> to <NUM> hours in a nitrogen-comprising atmosphere.

In block <NUM>, the brown molded body is sintered at a temperature in the range from <NUM> to <NUM> over a period of from <NUM> to <NUM> hours to produce a stethoscope chestpiece (unpolished). The sintering occurs in a pure hydrogen or argon atmosphere to form the stethoscope chestpiece.

The sintering time, i.e. the hold time at the sintering temperature, is generally set so that the sintered shaped parts are sintered to sufficient density. Sintering is preferably carried out so that the sintering process is shorter relative to debinding. In general, the sintering process (including the heating ramp up phase but without the cooling phase) will be able to be concluded after <NUM> to <NUM> hours, <NUM> to <NUM> hours, <NUM> to <NUM> hours, <NUM> to <NUM> hours, or <NUM> to <NUM> hours for a stethoscope chestpiece. The total time in both the sintering process and debinding process can be between <NUM> to <NUM> hours, or <NUM> to <NUM> hours.

Various sintering apparati may be used and are commercially available from manufacturers such as CMFunaces, Inc (Bloomfield, NJ) or Elnik Systems, LLC (Cedar Grove, NJ). After sintering, any desired after-treatment, for example sinter hardening, austenite formation, annealing, hardening, upgrading, carburization, case hardening, carbonitriding, nitriding, steam treatment, solution heat treatment, quenching in water or oil and/or hot isostatic pressing of the sintered shaped parts or a combination of these treatment steps, can be carried out. Some of these treatment steps, for instance sinter hardening, nitriding or carbonitriding can also be carried out in a known way during sintering. Once produced, the stethoscope chestpiece can be removed from the line and optionally shipped for polishing.

The unpolished stethoscope chestpiece produced by injection molding can have properties that are unexpectedly better than those produced using investment casting techniques. For example, the surface roughness of an injection molded stethoscope chestpiece is as follows:.

Rz can be no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns.

Ra can be no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns.

Rm can be no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns. The surface roughness can be measured according to ASME B46. <NUM>-<NUM>.

Further, the unpolished injection molded stethoscope chestpiece can have better manufacturing yields, improved finish, and corrosion resistance compared to an investment cast unpolished stethoscope chestpiece. The resulting stethoscope chestpiece can have a weight of at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM>, or at least <NUM> which is significantly heavier than smaller metal injection molded parts.

The reflectance can be measured according to ASTM E1331-<NUM>. The unpolished injection molded stethoscope chestpiece can have a percent reflectance (%R) of at least <NUM>%, at least <NUM>%, at least <NUM>%, at least <NUM>%, at least <NUM>%, at least <NUM>%, at least <NUM>%, at least <NUM>%, at least <NUM>%, at least <NUM>%, at least <NUM>%, or at least <NUM>% at a wavelength of <NUM> to <NUM>.

For example, <FIG> illustrates an investment cast stethoscope chestpiece <NUM> side-by-side with a metal injection molded stethoscope chestpiece <NUM>. The MIM stethoscope chestpiece <NUM> has a silver diffusely reflective finish versus the dull gray of the investment cast stethoscope chestpiece <NUM>.

In block <NUM>, the stethoscope chestpiece <NUM> can optionally be polished to further enhance the visual appearance of the stethoscope chestpiece. Polishing may produce a mirrored finish and allows any pits or surface roughness to be smoothed out. Finish on the mirror polished parts must be nearly perfect, e.g., no pits, bumps, scratches, blemishes, or stains.

In block <NUM>, a film can also optionally be deposited onto the stethoscope chestpiece. Various thin metallic films can be applied using physical vapor deposition, or chroming. With physical vapor deposition, a brass-colored or black-colored finish can be applied to the stethoscope chestpiece.

In block <NUM>, the stethoscope can be assembled. The stethoscope can be assembled by attaching a stem into the stem fitting or a portion of the stethoscope chestpiece, attaching tubing to the stem. The tubing wherein the tubing is also connected to a yoke (e.g., the coupling arms <NUM> in <FIG>), ear tubes, and eartips. The assembly can also include attaching a diaphragm to the stethoscope chestpiece. Once assembled, the stethoscope can be packaged in an appropriate packaging.

<FIG> illustrates a unpolished injection molded stethoscope chestpiece <NUM>, according to the present description. The stethoscope chestpiece <NUM> comprises a plurality of ejector marks <NUM>, <NUM>, <NUM>, <NUM>. The components of stethoscope chestpiece <NUM> can be similar to that of stethoscope chestpiece <NUM> in <FIG> with similar numbering. For example, recess <NUM> refers to a region between the outer edge <NUM> The recess <NUM> can be recessed relative to the plate-like member <NUM> and the outer edge <NUM>. The recess <NUM> can be defined by at least two side walls, side wall <NUM> and outer rim portion <NUM> which is shown tapering into a nadir <NUM>. The nadir <NUM> may be a planar bottom surface.

The ejector marks <NUM>-<NUM> can be marks from ejector pins or vacuums used in the demolding process. The ejector marks <NUM>-<NUM> may be equally spaced along the perimeter. The ejector marks <NUM>-<NUM> can also be spaced to allow even removal from a mould. Although <NUM> ejector marks are pictured, any number of ejector marks can be present. For example, a stethoscope chestpiece can include at least one ejector mark, at least two ejector marks (i.e., a plurality of ejector marks), at least <NUM> ejector marks, etc. The total number of ejector marks may be an even number (e.g., <NUM>, <NUM>, <NUM>).

As shown in stethoscope chestpiece <NUM>, the ejector marks <NUM>, <NUM> are positioned toward the front whereas ejector marks <NUM>, <NUM> are positioned toward the back of the stethoscope chestpiece <NUM> (proximate to the stem cavity). Since the top of the stethoscope chestpiece forms a complex portion overhanging the stem, the ejector marks <NUM>, <NUM> are closer together around the circumference of the recess <NUM> near the areas where force can be applied evenly to remove the top from a mould. Ejector marks <NUM> and <NUM> have a greater distance (at least <NUM> times) than the distance between <NUM> and <NUM> following the circumference of the recess <NUM>.

The ejector marks <NUM>-<NUM> may be positioned proximate to an edge <NUM>, e.g., in recess <NUM> (e.g., <FIG>, on plate-like member <NUM>, or even positioned in the conical shaped second recess <NUM> as shown in <FIG>. The ejector marks can be any shape, however circular shapes can be useful in reducing corners and sharp edges. Although shown as relatively planar to the surface established by <NUM>, the ejector marks <NUM>-<NUM> can be tapered depending on the mould shape.

<FIG> illustrates the actual cross section corresponding to <FIG>, <FIG> illustrate potential cross-sections along a similar view. The ejector marks <NUM>-<NUM> can be recessed relative to a plane of a surface or protruded. <FIG> illustrates recessed ejector mark <NUM> can be recessed relative to the nadir <NUM>. The ejector mark <NUM> can have a bottom surface <NUM> and one or more side walls <NUM>. The ejector mark <NUM> can have a depth of less than <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>. The ejector mark <NUM> may be such that it does not extend to a depth beyond notch <NUM>.

The ejector marks <NUM>-<NUM> may have an area (measured by the bottom surface <NUM>) of no greater than <NUM><NUM>, no greater than <NUM><NUM>, no greater than <NUM><NUM>, no greater than <NUM><NUM>, no greater than <NUM><NUM>, no greater than <NUM><NUM>. The ejector marks <NUM>-<NUM> can have a volume no greater than no greater than <NUM><NUM>, no greater than <NUM><NUM>, no greater than <NUM><NUM>, no greater than <NUM><NUM>, no greater than <NUM><NUM>, no greater than <NUM><NUM>.

<FIG> illustrates a protruding ejector mark <NUM>. The protruding ejector mark <NUM> can be formed by a vacuum assist of removing the green molded body from the mould. The ejector mark <NUM> can have a top surface <NUM> and one or more side walls <NUM>. The protruding ejector mark <NUM> can have a side wall <NUM> height of no greater than the plate-like member <NUM>.

<FIG> illustrates a recessed ejector mark <NUM> (having bottom surface <NUM> and side wall <NUM>) that is positioned within the conical-shaped recess <NUM>.

It is to be understood that other variations and modifications can be made without departing from the scope of the invention.

The test method used for corrosion was modified from ASTM D <NUM>, Standard Test Method for Evaluation of Painted or Coated Specimens Subjected to Corrosive Environments. The samples were then visually inspected for rust or corrosion and the results recorded in Table <NUM>.

Stethoscope chestpieces were inspected visually and any imperfections were noted in Table <NUM>.

EX1 was prepared using a metal injection molding technique using <NUM>-4PH F as a feedstock and molded into the same specifications as a Master Cardiology Stethoscope Chestpiece from <NUM>. The green molded body was sintered, continuously, for at least <NUM> hours at a temperature of at least 100C in a nitrogen atmosphere. The temperature of the sintering oven did not drop more than <NUM> deg. C while sintering. A mirror finish was achieved by polishing the chestpiece.

EX2 was prepared using a metal injection molding technique using 316LA as a feedstock and molded into the same specifications as a Master Cardiology Stethoscope Chestpiece from <NUM>. The process conditions were the same as in EX1.

EX3 was prepared lusing a metal injection molding technique using 316LG+ as a feedstock and molded into the same specifications as a Master Cardiology Stethoscope Chestpiece from <NUM>. The process conditions were the same as in EX1.

CE1 was prepared using <NUM>-4PH as a feedstock in an investment casting method used in production of existing Master Cardiology Stethoscope Chestpieces. A mirror finish was achieved by polishing the chestpiece.

EX4 was prepared as in EX1 except that a smoke-colored coating was applied using physical vapor deposition (PVD).

EX5 was prepared as in EX2 except that a smoke-colored was applied using physical vapor deposition (PVD).

CE2 was prepared as in CE1 except that a smoke-colored was applied using physical vapor deposition (PVD).

For EX1, it passed initial review of small lot quantities, but issues were noticed when larger production runs were inspected. During the inspection of the larger production lots, blemishes were noticed on about <NUM>% of the parts reviewed and was considered an unacceptable yield for this process. The blemishes were seen on a variety of surfaces on the polished area of the chestpiece with varying severity. The blemishes were attributed to the material and had pitting which rules out the EX1 for the mirror polished application.

For EX2, issues were noticed right away once the initial samples were run through the mirror polishing process. Small pits and bumps were consistently seen across the entire surface of the parts. This surface imperfection caused EX2 to be unsuitable for mirror polish applications.

For EX3, these parts showed a near perfect mirror finish that satisfies the visual specification.

Claim 1:
A method of making a metal stethoscope comprising:
injection molding, extruding, or pressing a metallic thermoplastic composition into a mould forming (<NUM>) a green molded body,
continuously debinding (<NUM>) a portion of binder material from green molded body at a temperature in a range of <NUM> to <NUM> over a period from <NUM> to <NUM> hours in a nitrogen-comprising atmosphere forming a brown molded body, wherein the temperature is maintained within ± <NUM> during the period;
sintering (<NUM>) the brown molded body at a temperature in a range from <NUM> to <NUM> over a period of from <NUM> to <NUM> hours in a hydrogen or argon atmosphere to form the stethoscope chestpiece (<NUM>).