Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D31/00—Cutting-off surplus material, e.g. gates; Cleaning and working on castings
  • B22D31/002—Cleaning, working on castings

Definitions

• the present invention relates to a working process for die-cast articles, comprising the steps set out in the preamble of claim 1.
• belt retractors for safety belts of the type commonly used on motor-vehicles usually comprise a fork-shaped article essentially made up of two arms connected with each other by an interlocking bar. On at least one of these arms one or more teeth are formed that cooperate with a toothing carried by a roller on which the safety belt is wound, to cause locking of the latter when, upon intervention of an accelerometric drive device, the fork-shaped article is brought to an operating condition in which the toothings mutually match.
• the fork-shaped article Since the fork-shaped article is a component on which people safety relies in case of accident, it must comply with rigid parameters in terms of geometrical and dimensional tolerance, as well as in terms of resistance to mechanical wear and to weathering, so as to provide appropriate guarantees of reliability in time.
• die-casting is carried out through admission of a molten aluminium alloy to the inside of a mould in which a plurality of moulding cavities or so-called “patterns" are defined, each of them corresponding to one of the fork-shaped articles to be obtained and being mutually connected through channels opening into at least one admission opening for the molten metal.
• a auxiliary channel is also usually provided which extends between the two regions designed to define the opposite arms of the fork-shaped article thus obtained.
• a plurality of fork-shaped articles is obtained from the die-casting process, following solidification of the metal alloy within the mould, which articles are linked, through the respective interlocking bars, to the respective branches of a moulding sprue defined by the solidified material within the connecting channels.
• Each fork-shaped article further has the respective arms mutually interlocked by a connecting element formed following solidification of the material in the auxiliary channel, the purpose of which is, among other things, to receive the metal flowed into the mould which has metallurgically unsatisfactory features.
• the casting extracted from the die-casting mould is submitted to a blanking step to remove the moulding sprue and the connecting element from each of the fork- shaped articles.
• the fork-shaped articles, now disengaged from each other, are then submitted to finishing operations that may involve a sandblasting step designed, inter alia, to give a predetermined surface roughness to said articles and followed by application of a protective and antifriction surface coating, usually consisting of a suspension of small particles of solid lubricant, based on molybdenum disulfide, graphite and/or polytetrafluoroethylene in organic or inorganic chemical binders, for example.
• a protective and antifriction surface coating usually consisting of a suspension of small particles of solid lubricant, based on molybdenum disulfide, graphite and/or polytetrafluoroethylene in organic or inorganic chemical binders, for example.
• the articles being worked are submitted to non-negligible mechanical stresses in relation to the piece consistency, which stresses may easily cause permanent sets such as in particular bending of the arms of the fork-shaped article.
• the individual finished pieces are required to be submitted to careful geometrical and dimensional controls, for which particular equipment is required which will bring about an increase in the costs of the production plants, of the overall working cycle and, lastly, of the individual finished product.
• the Applicant has perceived that the problems of the known art can be brilliantly overcome by executing removal of the bridge elements subsequently to the working operations for carrying out surface finishing of the pieces, thereby proposing a process enabling the articles to be protected against stresses due to sandblasting and/or application of surface coatings, or any other handling operation subsequent to moulding by die-casting, so that, as a result, working rejections are eliminated and there is also the possibility of eliminating or at least greatly simplifying the geometric and dimensional control operations at the end of the production cycle.
• Fig. 1 shows a flow chart of the process in accordance with the invention
• Fig. 2 shows a plurality of 'fork-shaped articles connected with a moulding sprue
• - Fig. 4 shows a fork-shaped article provided with an auxiliary connecting element
• - Fig. 5 shows the fork-shaped article seen in Fig. 4, from which the auxiliary connecting element has been removed;
• FIG.6 shows, by way of example, a further article obtainable by the process in accordance with the present invention.
• a die-cast article obtainable by a process in accordance with the present invention has been generally identified by reference numeral 1.
• the die-cast article 1 consists of a fork-shaped article for locking winding rollers in rolling devices for safety belts.
• the fork- shaped article 1 conventionally comprises a pair of end portions defined by arms 2 mutually spaced apart, each of which has one end 2a connected with the first end of the other arm 2 by an interlocking portion 3, made in the form of a bar.
• One or more teeth 4 are formed in a second end 2b of at least one of the arms 2 and they lend themselves to interact with corresponding toothings arranged on the winding roller to restrain the latter from rotation-.
• a shaped notch 5 to be engaged by a drive member being part of the above mentioned rolling device, to move the fork-shaped article 1 around a hinging axis defined by pivot pins 6 disposed at the ends of the interlocking bar 3, between a disengaged condition and an engaged condition of the toothings arranged in the winding roller.
• the process in accordance with the invention contemplates execution of a step of die-casting an aluminium alloy or other suitable metal alloy into a mould (not shown as it can be made in any known manner) provided with one or more cavities having a shape conforming to that of corresponding fork-shaped articles 1 to be formed following the die-casting step.
• the mould cavities are in communication with each other through connecting channels opening into at least one inlet for admission of the molten metal alloy.
• the molten metal alloy reaches the individual forming cavities through the connecting channels at which, following cooling, a sprue 7 is formed which comprises branches 7a to which the fork-shaped articles 1 are linked at the respective interlocking bars 3.
• auxiliary channel connecting together those parts that are adapted to define arms 2 so as to form, upon solidification of the metal alloy, a connecting element 8, in the form of a bar as well, having the opposite ends rigidly fastened to mutually-facing inner side surfaces 2d of the arms themselves.
• the roughing-out step is advantageously carried out without causing separation of the connecting bars 8 of the individual fork-shaped articles 1 and can be therefore carried out by means of a mere punch movable towards a die to cause separation of the sprue 7, so that particular attention and accuracy is not required in making the die and the punch and in positioning the sprue 7.
• separation of the sprue 7 takes place at an intermediate point of the interlocking bar 3 of each fork-shaped article 1, where a particular accuracy in the geometric and dimensional tolerance of the bar itself is not required.
• the fork-shaped articles 1 are submitted to a surface-finishing step, denoted at block C in Fig. 1, that may contemplate application of a protective coating having a low friction coefficient.
• a surface-finishing step denoted at block C in Fig. 1
• the fork-shaped articles 1 can be submitted to a surface treatment as described in the European Patent Application EP 0976496 in the name of the same Applicant.
• the presence of the connecting bars 8 between the arms 2 of the individual fork-shaped articles 1 ensures the geometric steadiness of said articles, preventing arising of undesirable deformations that would cause mutual approaching or moving away of arms 2.
• the surface-finishing works can in fact submit the fork-shaped articles 1 to important localised stresses.
• application of the surface coating is usually carried out in a convenient manner through a step in which a great amount of fork- shaped articles 1 is dipped into a surface-treatment solution containing protective and anti-friction agents, to be then submitted to a centrifugation step which is necessary for eliminating the excess solution, before final drying of the treatment solution laid on the surfaces of the fork-shaped articles 1.
• each fork-shaped article 1 is submitted to at least one blanking step denoted at block D in Fig. 1, in which removal of the connecting element 8 extending between arms 3 is carried out after removal of possible burrs formed, in the previous die-casting step, in the same plane as one or both of the side surfaces 2c, 2d around the edges of arms 2.
• the fork-shaped articles 1 can be individually fed, in a predetermined orientation, to a blanking station comprising at least one die matching the shape of the fork-shaped article 1 to conveniently support it at the interlocking bar 3 and/or the arms 2, and a pair of punches movable in parallel with respect to the interlocking bar 3 towards the arms themselves, to cause removal of burrs.
• the connecting bar 8 conveniently bears the stresses transmitted to the individual arms 2, so that the risk of undesirable deformations being formed on the arms 2 of the fork-shaped article 1 is eliminated.
• a further punch movable between arms 2 in a direction perpendicular to the interlocking bar 3 cuts the connecting bar 8 at the bar ends integral with the inner side surfaces 2d of arms 2.
• means for geometric or dimensional detection may also operate, which means is based on image acquisition for example by a television camera or other known devices for carrying out the geometric or dimensional control of the individual finished pieces.
• the individual articles 1 can be submitted to a packaging step for final forwarding to the use places, identified by block E in Fig. 1.
• the present invention achieves different unexpected advantages with respect to the traditional methods in which blanking of the connecting element 8 is carried out concurrently with the roughing-out step aiming at removing the sprue 7.
• the possibility of eliminating the burrs by a blanking operation also eliminates the necessity to carry out sandblasting operations before application of the surface coating. Obviously, a sandblasting operation in place of the blanking operation for elimination of the burrs can be at all events carried out .
• FIG. 6 shows a further example of an article 100 to be made by the process in reference, essentially consisting of a semi-cylindrical wall 101 of reduced thickness, having end portions 102 defined along rectilinear edges 102a and an interlocking portion 103 represented by the centre of the semi-cylindrical extension of the wall itself.
• a semi-cylindrical wall 101 when submitted to sandblasting operations or other surface treatments, could be easily deformed above all if it has one or more regions of reduced thickness, for achievement of a weight reduction for example.
• a connecting element 108 is produced, at one or both ends of the semi-cylindrical wall 101, that is preferably bridge-shaped, said element extending parallel to the semi-cylindrical wall itself and having the respective opposite ends rigidly connected to the end portions 102 of said wall.
• the connecting elements 108 lend themselves to efficiently bear the stresses transmitted through the end portions 102 so as to prevent deformation of the semi-cylindrical wall 101 during the surface-finishing operations and are then easily removed by a blanking operation carried out at the end of the production cycle .

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Moulds For Moulding Plastics Or The Like (AREA)
• Molds, Cores, And Manufacturing Methods Thereof (AREA)
• Mechanical Operated Clutches (AREA)
• Injection Moulding Of Plastics Or The Like (AREA)
• Bending Of Plates, Rods, And Pipes (AREA)

Applications Claiming Priority (3)

Publications (2)

Family

ID=11449716

Family Applications (1)

Country Status (6)

Families Citing this family (2)

Family Cites Families (2)

• 2002
  • 2002-04-17 IT IT2002MI000806A patent/ITMI20020806A1/it unknown
• 2003
  • 2003-04-10 AU AU2003230202A patent/AU2003230202A1/en not_active Abandoned
  • 2003-04-10 AT AT03723057T patent/ATE301520T1/de not_active IP Right Cessation
  • 2003-04-10 EP EP03723057A patent/EP1497057B1/de not_active Expired - Lifetime
  • 2003-04-10 DE DE60301276T patent/DE60301276T2/de not_active Expired - Fee Related
  • 2003-04-10 WO PCT/IT2003/000224 patent/WO2003086685A2/en not_active Ceased

Non-Patent Citations (1)

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