CA2606982A1

CA2606982A1 - Method and apparatus for manufacturing a cast component

Info

Publication number: CA2606982A1
Application number: CA002606982A
Authority: CA
Inventors: Stephen James White; Scott Holloway
Original assignee: Individual
Current assignee: Chassis Brakes International Technologies Pty Ltd
Priority date: 2005-05-06
Filing date: 2006-05-08
Publication date: 2006-11-16
Also published as: JP2008540127A; WO2006119554A1; EP1922167A1; KR20080011429A; CN101189085A

Abstract

A method of forming a cast component (10) to have particular NVH
characteristics. The method includes selecting an insert (14, 15) for integral casting with the cast component (10), the insert (14, 15) being one which is of a material capable of altering the NVH characteristics of the cast component (10), which can be infiltrated by molten metal during casting and which has characteristics that can be altered by alteration of the composition of the insert material. The method includes determining the material composition required to achieve the desired NVH characteristics and further includes determining the appropriate position (14, 15) for the insert to be inserted into the cast component (10) and casting the insert (14, 15) into the component (10) in that position.

Description

METHOD AND APPARATUS FOR MANUFACTURING A CAST COMPONENT
The present invention relates to a method of designing and manufacturing cast components, such as brake calipers for vehicles, and principally relates to design and manufacture for achieving particular natural frequency and damping properties of cast components. The invention has been developed in relation to aluminium disc brake calipers and it will be convenient to describe the invention as it applies to that type of brake caliper. However, it should be appreciated that the invention has wider application and could for example extend to a wide variety of cast products not only of aluminium construction, but also of other cast metals, such as brass or magnesium.

The present invention employs inserts, which are cast into a brake caliper, to favourably modify the natural frequency and damping properties of the caliper.
The use of inserts in cast calipers is disclosed for modifying the structural properties of a caliper and each of U.S. Patent Nos. 5,433,300, U.S. 4,705,093 and WO 02/27048 disclose brake calipers in which integrally cast inserts have been employed. In these prior art documents however, the teaching relates to the use of inserts to enhance the structural properties of the caliper, namely tensile strength and stiffness. In these documents an insert is incorporated into a metal casting to create a metal matrix composite and the resultant cast caliper retains substantially the same mass properties of a casting which does not include the insert, but the mechanical or structural properties are significantly enhanced.
While the above documents disclose the use of inserts for structurally modifying a cast caliper, they are silent in respect of the properties to which the present invention relates. Moreover, in relation to brake calipers, the parent metal, usually aluminium, can generally exhibit strength properties sufficient for use without the structural reinforcement provided by the disclosed inserts of the above documents. However, while the structural properties of the parent metal may meet the requirements of the particular caliper application, design engineers are still required to design the caliper for frequency and damping properties, in particular to attend to brake squeal and vibration. This exercise increases in difficulty as the mass and the Young's modulus of the chosen casting material is reduced, as the frequency at which problematic squeal and vibration occurs is lower and it is therefore necessary by design to shift those frequencies.

The design exercise is further complicated by the necessity to consider the component parts with which the caliper interacts upon assembly within a vehicle. Therefore design of the caliper in isolation rarely will achieve an acceptable outcome, while geometrical changes to the shape of the caliper are often difficult to achieve, due to space limitations in the environment in which the caliper is positioned and because the general shape of the caliper has certain essential requirements.

The characteristics with which the present invention is concerned are known in the automotive industry as noise, vibration and harshness, in which "harshness"
relates to the "feel" of the vehicle under braking load. These characteristics are collectively referred to as "NVH" characteristics and hereinafter that reference will be used to describe those characteristics.
The design process presently employed to design aluminium disc brake calipers in respect of NVH involves a plurality of stages. The first stage is to establish the predicted NVH characteristics of the brake caliper assembly when included as part of a dynamic system of components in the vehicle assembly. This stage principally involves consideration of the interaction between the primary components of the braking system, including the rotor, the caliper, the anchor bracket which attaches a caliper to the vehicle suspension, and the friction lined brake pads which the caliper causes to engage the rotor during a brake application.
In the above predictive stage, the caliper assembly is designed to achieve the required physical, geometric and performance outcomes required. The brake designer employs three-dimensional computer aided design and finite element modelling to predict the NVH performance of a caliper assembly in "virtual" or simulated conditions. The NVH performance is then compared to the NVH
requirements set by the vehicle or brake manufacturer. It is generally the case, that a first attempt to match the virtual NVH performance with the actual NVH
requirements, does not result in a comparison that is acceptable. Accordingly, the designer then modifies the shape of an assembly component, and repeats the above described process, until such time as a satisfactory correlation is obtained. As stated above, the designer is limited in the degree to which geometric changes to assembly components can be made and in practice, it is the case that many small iterations to several of the assembly components is necessary before a satisfactory result is obtained.

The process of achieving satisfactory NVH results is complicated by the fact that friction lining material properties and methods for predicting the damping behaviour of friction material are not well understood so that computer simulation is difficult. The frustrating outcome of this, is that brake caliper assemblies often exhibit actual NVH characteristics that are different to the characteristics achieved through computer simulation, primarily due to unexpected friction lining or brake pad performance.
Despite the above difficulty, when a designer achieves a successful simulated NVH result, the next stage in the design process normally is to manufacture a prototype assembly for actual vehicle trials or tests. This prototype manufacture and testing is complicated and costly and extremely time consuming.
Moreover, given that an actual prototype may exhibit substantially different actual results under trial than what is expected through computer simulation, the complete design process may need to be repeated on several occasions, increasing the cost and time period before an actual acceptable assembly is derived.
It is an object of the present invention to overcome or alleviate at least one of the above disadvantages. It is a more particular object of the invention to provide a method which facilitates alteration of the NVH characteristics of a brake caliper, which method is not reliant, at least to a substantial extent, on alteration of the shape of the caliper.

According to the present invention, there is provided a method of forming a cast component, such as a brake caliper, which has certain desired NVH
characteristics by selecting an insert for integral casting with the cast component, which insert is of a material capable of altering the NVH
characteristics of the cast component and which can be infiltrated by molten metal during casting and which has characteristics that can be altered by alteration of the composition of the insert material. The method includes determining the material composition required to achieve the desired NVH
characteristics and further including determining the appropriate position for the insert to be inserted into the cast component and casting the insert into the component in that position.
In the method of the present invention the insert material having a composition which can be modified for achieving desired NVH characteristics in the cast component. Accordingly, design of a cast component for particular NVH
characteristics can be simplified, by alteration of the insert, rather than alteration of the geometric form or shape of the component. That is, by the method of the invention, the shape of the component is determined by reference to factors primarily other than NVH. NVH properties can be considered when the shape of the component is being determined, although by the method of the invention, that is not absolutely necessary. Instead, NVH can be considered when the shape of the component has been decided. Moreover, where a component which has been provided with an insert that is expected through previous virtual design, or other knowledge relating to the insert such as empirical data, to perform in a certain manner and the insert does not perform in that manner to achieve the desired NVH characteristics, the composition of the insert can be altered to achieve those characteristics. Thus, it is not necessary that the shape of the component also be changed. This has the clear advantages over the prior art, by reducing or eliminating the need for complete redesign of the shape of the component on more than one occasion. The method may require the component to be cast several times before an acceptable result is achieved, but this is very different to redesign, which requires not only the expense and time associated with redesign, but also involves the expense of retooling.

5 The method of the invention is envisaged to eliminate a major portion of the design timeframe of a component that also requires design for NVH. This is because in the method of the invention, once the desired component shape is settled, then tailoring in respect of NVH can take place by consideration of the insert composition and its placement.
The porosity of the insert material is preferably greater than 90% open porosity, although the preferred material structure has 100% open porosity. The porous structure incorporates pores of size 0.5 microns to 100 microns, although preferably the pores are in the range of 1 to 30 microns, most preferably 3 to microns.

The insert material can have a fibrous structure, a particulate structure, be of a ceramic foam or be a combination of the above.

The volume fractions of ceramic materials used for the material structure preferably is between 5 - 80%, more preferably 10 - 60% and most preferably 15-40%.

Appropriate ceramics include, but are not limited to oxides, borides, carbides and nitrides.

An appropriate insert material is a porous ceramic oxide material. A suitable example of such a material comprises a preform of alumina fibre which contains approximately 96-97% alumina (aluminium oxide) of various crystal structures with the remaining balance being primarily silica. The preform is porous and the fibres can be bound together by an inorganic binder such as silica, alumina or boehmite, to form a rigid body. The porosity of the preform is governed by the amount of fibre and can be designated by a preform volume fraction (Vf). A

suitable preform product can be obtained from the Saffil company. Other preform compositions can be employed and these include singie and mixed grade alumina fibres, combinations of such fibres with other fibres, or ceramic or metal particles, for example alumina, silicon carbide, or silicon.
Suitable preforms so far envisaged to be appropriate have volume fractions of or 30%, although other volume fractions are possible. Such suitable preforms have included 15% Vf alumina fibre and alumina particulate in about a 30:70 ratio. Other suitable preforms have the following compositions:
30% Vf alumina fibre and alumina particulate (30:70 ratio) 15% Vf alumina fibre and silicon carbide particulate (30:70 ratio) 30% Vf alumina fibre and silicon carbide particulate (30:70 ratio) In each of the above preforms, during casting, preferably squeeze casting, the preform is infiltrated with molten metal, forming a metal matrix, so that the preform becomes incorporated into the cast component.

Other materials could be employed as the insert material although the type of porous material discussed above is highly advantageous, as the porosity of the material which facilitates complete infiltration by the molten metal means that it is not necessary to have a macroscopic interface between the insert material and the surrounding cast component. This is necessary with non-porous inserts that have been employed before, for strengthening purposes rather than for NVH, and difficulties arise in ensuring complete integrity of the interface between the insert and the surrounding cast metal. In the event that the interface fails, even over a small portion of the bond surface area, the characteristics of the cast component change, in some cases dramatically, so that the insert no longer performs the function designed for.
The geometry and placement of the insert into the cast component is also important in achieving the required NVH performance. Appropriate geometry and positioning forms part of the virtual design process with the insert composition then being modified as required during actual testing to arrive at the desired NVH performance. Again, the method of the invention accelerates the design process by the external component design being completed in a virtual environment, along with the internal design including the shape and positioning of the insert. Further modification following actual testing can be made in respect of the material composition.

Virtual simulation and testing in relation to brake calipers can proceed through the early stage in the same manner as the prior art. That is, the specification for the caliper is determined by the vehicle specification to which the caliper is to be attached. The shape of the caliper is then determined using known three dimensional computer aided design and finite element modelling. Following this, the NVH performance of the caliper is simulated and compared to the required brake specification. At this point, in accordance with the invention, an insert is introduced into the caliper simulation in any suitable position. The caliper with insert is then simulated using finite element modelling and the composition and shape of the insert varied and if desired, the position, in order to achieve the desired NVH specification in the virtual environment. When the required characteristics of the caliper have been achieved virtually, the position of the insert is considered to be the optimum position. In this position, in accordance with the invention, actual testing then takes place, with insert composition modification being the only further change to the caliper, until such time as the required NVH characteristics are achieved.

The advantages of caliper design according to the invention principally relate to the accelerated design times and cost reduction due to more complete virtual design. A major advantage is that the external shape and functional elements of the caliper can be finalised much earlier in the design process through virtual means, with the design following this sometimes comprising insert shape modifications but largely or solely comprising modification of the composition of the insert. A further advantage resides in a level of flexibility that the invention provides in the use of brake calipers developed for one vehicle specification, which can be employed for different brake specifications of other vehicles, with modification only to the shape and/or composition of the insert.

An insert for a brake caliper typically will be introduced into the bridge section of the caliper housing which bridges the rotor. In a preferred arrangement, the insert extends from one side of the bridge section to the other and can extend into the finger section of the caliper at one end thereof if necessary. The insert can have any suitable shape, although preferably it is rectangular. A
rectangular insert can be elongated so that the width across the bridge section is much less than its length, or it can be broad, so that the width approaches the length. The insert may deviate from rectangular to accommodate shape restrictions of the caliper. For example, one face of the insert that faces the rotor may be scalloped for example, for accommodating a section of the periphery of a boot seal.
A pair of inserts may be provided and this is preferred if the caliper includes a central elongated opening that extends across the bridge section. In such a caliper, an insert may be provided on each side of the central opening.

A plurality of inserts may be provided if necessary. For example, two or more inserts may be provided through the bridge section, spaced across the section, either parallel to or transverse to the axis of rotor rotation. In a caliper with a central opening, two inserts may be provided on the leading side (in the direction of rotor rotation) of the opening and one on the other side. These examples illustrate that any number of inserts, having any shape and orientation, may be cast into the caliper to achieve the desired NVH
performance.

The invention further extends to a method of casting an insert into a component and the preferred method involves squeeze casting, with the preference being for a vertical squeeze casting machine. This type of casting machine facilitates preheating and rapid positioning of the insert within the casting cavity. The insert would require location within the cavity prior to introduction of the molten casting metal and therefore in a preferred arrangement the insert is formed with a location member or members which extend from the insert for engagement with the casting tooling. Upon formation of the casting, the location member or members can be trimmed as necessary.
The attached drawings show an example embodiment of the invention of the foregoing kind. The particularity of those drawings and the associated description does not supersede the generality of the preceding broad description of the invention.
Figures 1 and 2 respectively show a caliper housing 10 from outside and inside views respectively. The caliper housing 10 is formed as an aluminium housing, defining two pots 11 for enclosing pistons, a housing bridge 12 and fingers 13.
The operation of such a caliper housing 10, and its interaction with an anchor bracket and a vehicle, would be well known to a person skilled in the art, and therefore it will not be necessary to discuss that operation in any detail.

The caliper housing 10 is shown in Figure 1 as having a pair of inserts 14 and 15, while the housing 10 of Figure 2, shows similar but slightly different inserts 16 and 17. Referring to Figures 1 and 1a, each of the inserts 14 and 15 is of elongate rectangular extent, of a length that extends across the bridge 12, from one side adjacent the inside opening of the pots 11, through to the other side of the bridge 12 to exit through the junction of the bridge 12 with the fingers 13.
The portion of the inserts 14 and 15 which extends to the position outside of the bridge 12, includes a locating member 18, which in use is received within an opening formed in the casting tooling to locate each insert 14 and 15 within the cavity of that tooling prior to introduction of the molten aluminium.

Referring to Figures 2 and 2a, the inserts 16 and 17 have a different construction to the inserts 14 and 15 of Figures 1 and 1 a, but again include an elongate body 19, which extends for the full extent of the bridge 12 between the opening of the pots 11 and fingers 13. The inserts 16 and 17 also include a depending section 20 which extends from the plane of the body 19, downwardly in the same direction as the fingers 13 extend from the bridge 12. This arrangement is clearly shown in Figure 2. The inserts 16 and 17 also include a tab 21, from which extends a locating member 22 which has the same function as the locating member 18 of Figure 1.

It will be appreciated, that the inserts 14 to 17 each have a portion which extends to a position outside of the finished cast housing 10, and in the method of the invention, that extending section is trimmed from the housing 10 at any suitable time in the manufacturing process. Trimming may form part of the 10 further machining to which the housing 10 is subjected, and may involve the section being ground back to the housing surface, or severed by a suitable sawing mechanism or punch.

Figure 3 also shows the same caliper housing 10, but with a different form again of insert. In Figure 3, the inserts 23 and 24 have a broader rectangular configuration than the inserts 14 to 17, although the inserts are still positioned to extend across the bridge 12, and in the embodiment shown, each insert 23 and 24 includes a depending section 25. The insert of Figure 3 is shown in isolation in Figure 3a and in this figure, each of the inserts 23 and 24 is connected by a bridging section 26. Extending separately from each of the inserts 23 and 24, are tabs 27 and each tab 27 includes a locating member 28. The bridging section 26 is such to fix the inserts 23 and 24 relative to each other, for accurate positioning within the casting tooling, although the bridge 26 is removed, like the tab portions 28 which extend outwardly of the finished housing 10, when the casting has been formed.

The invention described herein is susceptible to variations, modifications and/or additions other than those specifically described and it is to be understood that the invention includes all such variations, modifications and/or additions which fall within the spirit and scope of the above description.

Claims

1. A method of forming a cast component to have particular NVH
characteristics, the method including, selecting an insert for integral casting with the cast component, the insert being one which is of a material capable of altering the NVH characteristics of the cast component and which can be infiltrated by molten metal during casting and which has characteristics that can be altered by alteration of the composition of the insert material, the method includes determining the material composition required to achieve the desired NVH characteristics and further includes determining the appropriate position for the insert to be inserted into the cast component and casting the insert into the component in that position.

2. The method according to claim 1, wherein the porosity of the insert material is greater than about 90% open porosity.

3. The method according to claim 2, wherein the porosity of the insert material is about 100% open porosity.

4. The method according to any one of claims 1 to 3, wherein the porous structure of the insert material incorporates pores of size 0.5 microns to 100 microns.

5. The method according to claim 4, wherein the porous structure incorporates pores of size 1 micron to 30 microns.

6. The method according to claim 5, wherein the porous structure incorporates pores of size 3 microns to 10 microns.

7. A method according to any one of claims 1 to 6, wherein the insert material comprises one or more of a fibrous structure, a particulate structure, and a ceramic foam.

8. A method according to any one of claims 1 to 7, wherein the volume fractions of materials used for the insert material structure, is between 5 to 80%.

9. A method according to claim 8, wherein the volume fractions of materials used for the insert material structure, is between 10 to 60%.

10. A method according to claim 9, wherein the volume fractions of materials used for the insert material structure, is between 15 to 40%.

11. A method according to any one of claims 1 to 10, wherein the insert material is a ceramic and the ceramic material is selected from one or more of the following: oxides, borides, carbides and nitrides.

12. A method according to any one of claims 1 to 11, wherein the insert material is a porous ceramic oxide material.

13. A method according to claim 12, wherein the porous ceramic oxide material comprises alumina fibre containing about 96 to 97% alumina and with the remaining balance being primarily silica.

14. A method according to claim 13, wherein the fibres are bound together by an inorganic binder.

15. A method according to claim 14, wherein the inorganic binder is selected from silica, alumina or boehmite.

16. A method according to any one of claims 1 to 10, wherein the insert material can include one or more of single and mixed grade alumina fibres, ceramic or metal particles, including alumina, silica carbide or silicon particles.

17. A method according to any one of claims 1 to 16, wherein the insert material has a volume fraction of about 15 or 30%.

18. A method according to claim 17, wherein the insert material has a volume fraction of 15% comprising alumina fibre and alumina particulate in about a 30:70 ratio.

19. A method according to claim 17, wherein the insert material has a volume fraction of 30% comprising alumina fibre and alumina particulate in about a 70:30 ratio.

20. A method according to claim 17, wherein the insert material has a volume fraction of 15% comprising alumina fibre and silicon carbide particulate in about a 30:70 ratio.

21. A method according to claim 17, wherein the insert material has a volume fraction of 30% comprising alumina fibre and silicon carbide particulate in about a 30:70 ratio.

22. A method according to any one of claims 1 to 21, including designing the shape of the cast component and thereafter selecting the insert in respect of material composition and position within the cast component, and thereafter casting the component about the insert.

23. A method according to any one of claims 1 to 22, wherein the cast component is cast by squeeze casting.

24. A method according to any one of claims 1 to 23, wherein the cast component is a brake caliper housing.

25. A method according to claim 24, wherein the insert is positioned in the bridge section of the caliper housing, which in use bridges a caliper rotor.

26. A method according to claim 25, wherein the insert extends from one side of the bridge section to an opposite side.

27. A method according to claim 26, wherein the brake caliper housing includes finger section extending from one side of the bridge section and the insert extends from the bridge section into the finger section.

28. A method according to any one of claims 25 to 27, wherein the insert is rectangular in shape.

29. A method according to any one of claims 25 to 28, wherein a pair of inserts are cast into the bridge section of the caliper housing on either side of a central opening in the housing.

30. A method according to any one of claims 1 to 29, wherein the insert is formed with a location member or members, which extend for engagement with casting tooling, to locate the insert within a cavity of the casting tooling into which molten metal is cast.

31. A method according to any one of claims 1 to 30, wherein the insert is positioned so that it extends outside of the cast component when the molten metal has set, and the method includes trimming the extension portion of the insert from the cast component.

32. A cast component formed according to the method of any one of claims 1 to 31.

33. A disc brake caliper housing formed according to the method of any one of claims 1 to 31.