WO2020174065A1

WO2020174065A1 - Method for additive manufacturing of a friction lining

Info

Publication number: WO2020174065A1
Application number: PCT/EP2020/055193
Authority: WO
Inventors: Isabelle Alix; Gérard Crosland
Original assignee: Valeo Materiaux De Friction
Priority date: 2019-02-27
Filing date: 2020-02-27
Publication date: 2020-09-03
Also published as: FR3093153A1; DE112020000961T5; CN113518870A; FR3093153B1

Abstract

The invention concerns a method for additive manufacturing of a friction lining, in particular for a clutch, comprising the following steps: a) supplying starting products comprising a reactive organic material, fillers and/or continuous fibres, b) forming a friction lining preform from said starting products and using an additive manufacturing device, then c) hot pressing of the preform obtained at the end of step b).

Description

Title of the invention: ADDITIVE MANUFACTURING PROCESS

A FRICTION PAD

[1] [The present invention relates to an additive manufacturing process of a friction lining as a composite material, in particular for the clutch of motor vehicles, such as passenger vehicles or industrial vehicles. The invention also relates to a friction lining obtained by such a process.

[2] For example, a motor vehicle clutch comprises, in general, a friction or friction disc bearing on each of its faces friction linings fixed to a possibly common support, the support being fixed to a hub splined meshed with an input shaft of a gearbox. The transmission can also take place using a wet clutch (single or double for example).

[3] Usually, friction linings are made from a compression mold. A friction lining comprises a friction material with a fixing face facing the support, and a planar friction face opposite the fixing face and able to contact a counter material, such as a reaction plate or a plate. clutch pressure, to transmit engine torque.

[4] Each friction lining conventionally in the form of a flat ring-type preform is produced by compressing a mixture of threads impregnated with a thermosetting resin and fillers. A friction lining is an element which comes into friction with another body and which has physical and mechanical properties which allow it to withstand high mechanical and thermal stresses. The composition, shape, and dimensions of the friction pads are important.

[5] Such a compression manufacturing process generally comprises operations comprising in particular the preparation of the mixture, the annular shaping, the compression molding, the curing in order to obtain the polymerization of some of these components possibly followed by a post-baking operation, grinding and possibly drilling for fixing the friction lining by riveting.

[6] One of the drawbacks associated with this type of manufacturing process lies in the high cost of the necessary tools, in particular that of the production molds. Another drawback lies in the difficulty of being able to produce parts according to a geometry particular and thin without adding additional material which will then be machined to rectify the surfaces and shapes, in line with the size of the fibers used. In the case of wet friction linings, there are also many paper cutting operations which result in a lot of waste.

[7] The present invention therefore aims to provide a method of manufacturing friction lining having a lower cost than those of the prior art by using only the material sufficient and necessary for the production of the part, its shaping and its structure.

[8] To this end, the present invention relates to an additive manufacturing process for a friction lining, in particular for a clutch, comprising the following steps: a) supply of starting products comprising an organic reactive material, fillers and / or continuous fibers,

b) forming a friction lining preform from said starting materials and using an additive manufacturing device, then

c) hot pressing at a temperature of 500 ° C or less of the preform obtained at the end of step b).

[9] The process according to the present invention thus makes it possible to produce friction linings by using only the quantity necessary and sufficient for their manufacture. Due to the optimization of the number of manufacturing operations, the process improves material yield and gains in industrial area. Such a process also makes it possible by 3D printing to obtain a friction lining in which the porosity has been controlled. Indeed, the porosity of the friction lining is closely linked with the method of assembly of the starting products, which are the fillers and the organic reactive material, as well as with the temperature pressing conditions. Additive manufacturing, that is to say, layer by layer, allows for example to have layers of friction material different in thickness without interpenetration of materials.

[10] Being able to control the porosity is important because it then becomes possible to modify the dynamic coefficient of friction, but it has been shown in the prior art that the fluid permeability has the most significant effect on the dynamic friction of materials. of wet friction.

[1 1] The present invention also relates to a friction lining obtained using the method according to the present invention. [12] Finally, the present invention relates to a speed synchronization component for a vehicle powertrain, comprising a friction lining obtained using the method according to the present invention, the component being chosen from a clutch, a brake , a torque limiter, a torque converter and a gearbox synchronizer, in particular double-clutch gearboxes.

[13] Other characteristics and advantages of the invention will become apparent on reading the detailed description accompanied by the following figures:

[14] [Fig. 1 a] illustrates a top view of a half flat annular friction lining obtained according to a first embodiment of the method of the present invention.

[15] [Fig. 1 b] illustrates in axial section the friction lining 1 a on a support.

[16] [Fig. 2a] illustrates a top view of a half flat annular friction lining obtained according to a second embodiment of the method of the present invention.

[17] [Fig. 2b] illustrates in axial section the friction lining 2a on a support.

[18] [Fig. 3a] illustrates a top view of a flat annular friction lining being manufactured according to a third embodiment of the method of the present invention.

[19] [Fig. 3b] illustrates in axial section the friction lining 3a on a support.

[20] The additive manufacturing processes also called 3D printing allow the manufacture of all types of materials in complex shapes and with a much lower cost because there is no need to manufacture a mold and the amount of waste is very low. The design of the object using a computer aided design (CAD) tool is first achieved. The 3D file obtained is then processed by specific software which organizes the slicing of the different layers necessary for the production of the part. The cutting is then sent to the 3D printer which deposits, for example by extrusion or solidifies the material layer by layer depending on the type of additive manufacturing until the final part is obtained, as opposed to the machining which removes material. By freeing designers from the constraints of material removal, allowing them to design an object by placing material only where it is needed and giving them quick access to making shapes optimized for an application, such as than specific groove profiles, 3D printing offers many advantages.

[21] Conventionally, the material used is a thermoplastic resin composed of acrylonitrile-butadiene-styrene (ABS) or polylactides (PLA) copolymers because it can be deposited as a molten layer to form the final part. This type of resin However, there is a problem linked to the presence of micropore and significant anisotropy which limit the functionality of the part. Indeed, it becomes very difficult during the rest of the printing process to correct these defects. In addition, thermoplastics do not meet the requirements related to the rigidity of the system and resistance to high temperature, the thermoplastics are not suitable for the thermal stresses of materials for clutch, at least up to 350 ° C . The pressing step therefore requires starting materials suitable for the manufacture of friction linings.

[22] The process according to the present invention thus makes it possible, from starting products comprising an organic reactive material and fillers supplied during step a) to form, during step b), a preform with a friction lining. using an additive manufacturing device.

[23] Advantageously, at least two of the starting products are separated or mixed.

[24] When two or more starting materials are separated, each starting material can then form an independent layer from the other layers of the preform, the whole then being subsequently consolidated under pressure and thermosetting. This is the case, for example, when the fillers are on one side and the resin as an organic reactive material on the other.

[25] Two starting materials can also be mixed. For example, the organic reactive material and the fillers can also be in the form of a liquid mixture or a pre-melted mixture of small granules of resins and fillers (granules mixed by pre-melting with the organic filler) which will be extruded by the printhead. It is also possible to have the organic reactive material mixed with one or more charges on one side and a second mixture of charges on the other.

[26] Advantageously, the organic reactive material is chosen from thermosetting resins, elastomeric resins and their mixtures. Preferably, the resin is chosen from phenolic, epoxy, melamine, formaldehyde resins and their mixtures. Even more preferably, the resin is a phenolic resin.

[27] Advantageously, the fillers are chosen from organic, inorganic, staple fiber, powdered fibers and their mixtures.

[28] For the purposes of the present invention, the term “filler” is understood to mean a solid substance, immiscible and dispersed by mechanical means in a matrix.

[29] Preferably, the organic and inorganic fillers are chosen from metals, plastics, ceramics, glass and their mixtures. [30] Preferably, the organic fillers are chosen from graphite, carbon black, NBR rubber, nitrile-butadiene rubber, cashew nut, activated carbon, diatomaceous earth and their mixtures. Preferably, the inorganic fillers are chosen from metal sulphides, barium sulphate and their mixtures.

[31] Preferably, the fibers (continuous or not) are synthetic or natural fibers.

Preferably, the fibers are chosen from fibers of glass, acrylonitrile, carbon, aramid, copper, brass, cotton cellulose and their mixtures. The fibers used as filler i.e. the chopped and powdered fibers are of short sizes, i.e. less than 10 mm in length in opposition to the continuous fibers which do not fit into the load definition.

[32] Advantageously, the starting products can also comprise plasticizers. Plasticizers are molecules incorporated by mechanical means (for example pultrusion) between macromolecules, to reduce the binding forces which associate them; thus the mixture, in particular of pre-melted thermosetting resins, becomes flexible, the more so as the level of plasticizer is high. This can have an advantage in additive printing. The level of plasticizer typically ranges between 1 and 10% by weight of the resin mixture.

[33] In the context of the present invention, the geometry of the preform obtained by the additive manufacturing device is defined on its perimeter, its shape and its thickness. In the context of dry friction lining, the preform typically has a conventional annular shape. In the context of wet friction lining, it is then possible to print an annular-shaped packing with pads of complex shape other than the classic circular, elliptical, trapezian or triangular shapes. Typically, the final thickness of the printed friction pad is between 0.5 and 7mm and depends on the chosen application (dry or wet).

[34] Advantageously, the additive manufacturing device implements printing by deposition of molten material (better known under the English name FDM for Fused Deposition Modeling), by binder jet (better known under the English name of BJ for Binder Jetting) or by material jet (better known under the non-English of MJ for Material Jetting).

[35] Advantageously, the formation of the preform during step b) is carried out on at least one face of a base structure. The basic structure makes it possible to maintain the level of mechanical resistance and geometric stability of the shapes of the friction surfaces in the field of friction discs.

[36] Advantageously, the basic structure is one of a metal support, for example of the steel type, of a woven structure based on organic fibers on a flat support and of a paper based on organic fibers. The organic fibers are chosen from cellulose fibers (cotton, flax, hemp, wood fibers, etc.), aramid, and carbon.

[37] When the basic structure is a paper based on organic fibers, the formation of the preform by additive manufacturing is preferably carried out on both sides of the paper.

[38] Advantageously, an adhesive such as glue is applied to the base structure before the additive printing of the preform on the structure. This has the advantage of replacing the usual fixing mechanism by rivets and of allowing adhesion between the support and the printed preform, after heat treatment by crosslinking the adhesive. Micro-material interpenetration of the preform with the backing, especially when the backing is a woven structure or paper, can also supplement or replace the use of adhesive.

[39] After the formation of the preform of a friction lining using the additive manufacturing device during step b), the method advantageously comprises a step b ') carried out after step b) and before step c) consisting of preheating the preform obtained at the end of step b). The preheating is carried out at a temperature less than or equal to 120 ° C, preferably at a temperature between 60 and 120 ° C. This step is typically performed without the application of pressure.

[40] This step b ′) makes it possible to prepolymerize the preform and to arrive at a gel phase in which the organic reactive material such as the resin is at least 60% crosslinked. Depending on the type of friction lining that is to be obtained, this preheating step makes it possible to obtain a part meeting the durability criterion which is defined by resistance to crushing.

[41] The last step c) of the process according to the invention makes it possible to make the lining suitable for use as a friction lining. This step consists of a hot pressing of the preform obtained at the end of step b). Indeed, the pressing step is necessary in order to shape the filling before its application and makes it possible in particular to obtain the desired density and porosity.

[42] The pressing step is carried out at a temperature advantageously less than or equal to 500 ° C, preferably between 100 and 500 ° C, preferably between 150 and 270 ° C, even more advantageously between 180 and 220 ° C. Such temperatures make it possible not to destroy organic materials. For wet friction linings, the pressure is typically between 5 and 30 bars, preferably between 10 and 20 bars, while for dry friction linings the pressure is typically between 250 and 320 bars. Those skilled in the art will therefore know adapt and choose the pressure values according to the type of friction lining he seeks to manufacture.

[43] In the context of the present invention, the method may further comprise a step d) consisting of machining or laser edge cleaning of the part obtained at the end of step c). This step eliminates the slight excess obtained after step c) of hot pressing.

[44] The friction lining obtained typically has an outside diameter less than or equal to 360 mm and an inside diameter greater than or equal to 80 mm.

[45] Examples of friction linings obtained according to different embodiments of the process according to the invention (the percentages expressed being percentages by weight) are presented below.

[46] Example 1: Wet friction lining obtained by binder jet (figure 1 a and 1 b)

[47] A wet friction pad A as shown in Figure 1a was prepared according to the additive process of the present invention and comprises the following steps:

[48] a) Supply of starting materials described in Table 1 below, the charges and the reactive material being separated (the charges for their part being mixed together).

[49] [Table 1]

[50] b) Formation of a friction lining preform from said starting materials and using an additive manufacturing device by jet of binder on a steel support 1 on which a layer has been previously applied of glue 2. The printer projects the resin 4, layer after layer, onto a bed of charges spread out beforehand 3, in order to agglomerate the particles which will ultimately constitute the part. The projection is done by print heads, also called nozzles which will sweep the entire bed of charges and selectively project the resin in the areas where parts are to be manufactured. The alternation of resin layers and fillers makes it possible to generate a controlled porosity (60% by volume at this stage).

[51] b ’) Preheating the preform obtained at the end of step b) to a temperature below 120 ° C. This step consolidates the binder and gives the parts sufficient strength to be handled. Therefore, the parts are extracted from the bed of charges by blowing and suction means.

[52] c) Thermocompression between 10 and 20 bars and 180 and 220 ° C to give the part its porosity (50% by volume in this embodiment) and its final mechanical properties.

[53] Alternatively, a pre-loaded phenolic resin (eg with diatomaceous earth) can be used as the organic reactive material.

[54] Example 2: Dry friction lining obtained by depositing molten material (FIGS. 2a and 2b)

[55] A dry friction lining B as shown in Figure 2a was prepared according to the additive process of the present invention and comprises the following steps:

[56] a) Provision of starting materials described in Table 2 below, the fillers and the reactive material being mixed in the form of a pre-melted mixture into small granules of resins and fillers.

[57] [Table 2]

[58] b) Formation of a friction lining preform from said starting materials and using an additive manufacturing device by depositing molten material on a steel support 1 on which has been previously applied a glue layer 2. The printer projects the mixture of resin and fillers layer by layer according to the pattern recorded in the printer. The spraying is done by heated nozzles so as to melt the pre-melted mixture into small granules of resins and fillers (depending on the starting products, the temperature is suitable and typically chosen between 70 and 120 ° C). Each layer sticking to the previous one by re-fusion. It is then possible to obtain pads 6 and grooves 7 alternately as shown in Figure 2b. The porosity measured at this stage is 20% by volume.

[59] c) Thermocompression between 250 and 320 bars and 150 and 200 ° C to give the part its porosity (less than 10% by volume in this embodiment) and its final mechanical properties.

[60] Example 3: Dry friction lining obtained by depositing molten material (FIGS. 3a and 3b)

[61] a) Provision of starting materials described in Table 3 below, the reactive material and the continuous fibers being separated (the continuous fibers being mixed together). [62] [Table 3]

[63] b) Formation of a friction lining preform from said starting materials and using an additive manufacturing device with two nozzles by deposition of molten material (in this case, only the resin will be melted, but the whole fibers + resin will be flexible and sticky) on a steel support 1 on which a layer of glue 2 has been applied beforehand. The printer projects layer after layer and circumferentially the mixture 8 of continuous fibers surrounded by filled resin 9 (a layer consisting of an assembly of continuous fibers 8 surrounded by loaded resin 9 by pultrusion in the printer head). The dotted lines in Figure 3a represent the concentric impression of the extruded wire. Each layer sticking to the previous one by re-fusion. The porosity measured at this stage is 20% by volume.

[64] c) Thermocompression between 250 and 320 bars and 150 and 200 ° C to give the part its porosity (less than 10% by volume in this embodiment) and its final mechanical properties. ]

Claims

[Claim 1] Method for the additive manufacturing of a friction lining, in particular for a clutch comprising the following steps: a) supply of starting products comprising an organic reactive material, fillers and / or continuous fibers,

[Claim 2] The manufacturing method according to the preceding claim, characterized in that it further comprises a step b ') carried out after step b) and before step c) consisting of preheating the preform obtained at l 'outcome in step b).

[Claim 3] The manufacturing method according to any one of the preceding claims, characterized in that at least two of the starting materials are separated or mixed.

[Claim 4] The manufacturing method according to any one of the preceding claims, characterized in that the organic reactive material is chosen from thermosetting resins, elastomeric resins and mixtures thereof.

[Claim 5] The manufacturing method according to any one of the preceding claims, characterized in that the fillers are chosen from organic, inorganic fillers, staple fibers, powdered fibers and their mixtures.

[Claim 6] The manufacturing method according to the preceding claim, characterized in that the organic and inorganic fillers are chosen from metals, plastics, ceramics, glass and their mixtures.

[Claim 7] The manufacturing method according to any one of the preceding claims, characterized in that the formation of the preform during step b) is carried out on at least one face of a base structure.

[Claim 8] The manufacturing method according to the preceding claim, characterized in that said basic structure is one of a metallic support, of a woven structure based on organic fibers on a flat support, and of a paper. based on organic fibers.

[Claim 9] The manufacturing method according to any one of the preceding claims, characterized in that the additive manufacturing device implements printing by deposition of molten material, by binder jet or by material jet.

[Claim 10] The manufacturing method according to any one of the preceding claims, characterized in that step c) is carried out at a temperature between 150 and 270 ° C.

[Claim 1 1] A friction lining obtained using the method according to any one of the preceding claims.

[Claim 12] A lining according to the preceding claim, being a dry friction or a wet friction lining.

[Claim 13] A speed synchronization component for a vehicle powertrain comprising a friction lining according to claim 1 1 or 12, the component being one of a clutch, a brake, a torque limiter , a torque converter and a gearbox synchronizer, in particular double-clutch gearboxes. ]