Expertise

Resin Transfer Molding – RTM

Principle

The reinforcement is placed in the gelcoated mold which is then closed.

The counter-mold has one or more orifices depending on the size of the part in which the resin is injected under low pressure (5 bars approx.)

It gradually impregnates the reinforcement by chasing in front of it the air included in the reinforcement. The polymerization is then carried out without adding external temperature.

Advantages

  • good appearance of parts
  • Sandwich structured parts
  • Flexibility of workshops (organization, implementation), and flexibility of production (production campaigns)
  • Highl limit VOCs (volatile organic compounds)
  • low investment in the tooling

Raw Material

Reinforcements may be short strand mats, endless thread mats or cloths mats. Reinforcements cans be mixed to manufacture a part. The reinforcement rate varies for 30 to 50%.

Tooling

  • 2 parts steel mold with clamps
  • Resin shells
  • Die injection mould

Applications

  • Large-sized parts of any industrial sector,
  • Protection covers
  • Handling boxes
  • Small series

Compression transfer

Principle

Transfer molding (BrE moulding) is a manufacturing process where casting material (composite of plastic) is forced into a mold. Transfer molding is different from compression molding the mold is enclosed rather than open to the fill plunger resulting in higher dimensional tolerances and less environmental impact. Compared to injection molding, transfer molding uses higher pressures to uniformly fill the mold cavity. The compound used are thermoplastics and of thermosetting materials (mostly).

Application

Transfer molding is mainly used for the manufacturing of pan handles, parts for electrical devices, electronic components or connectors.

Raw materials

The main plastics shaped by compression-transfer molding are thermosets such as epoxides , unsaturated polyesters , phenol-formaldehydes , silicones and fiber-reinforced composite materials made from Bulk Molding Compound (BMC).

Procedure

The raw materials are generally in the form of powders, granules, semi-solids or preforms.

The following steps constitute the molding

  • preheating the mold
  • preheating the material to soften it
  • introducing the softened material into a holding cavity
  • transferring, by pressure, the material of the holding cavity to the preheated mold with a punch through a channel
  • maintaining, in the case of thermosetting materials, the heating until the end of cooking (crosslinking)
  • mold cooling
  • opening of the mold and recovery of the part.

Applications

Connection boxes for electrical or electronical equipments,

Electrical blocks used in the aeronautics, railways or naval industry

Parts for Connecting devices, relays, power contactor, terminal box

SMC compression

Principle

Sheet moulding compound : Semi finished product composed of unsaturated polyester resin, fiberglass reinforcement and mineral fillers. It is shaped by high pressure molding according to various transformation processes. This compound makes it possible to obtain parts of small to large dimensions. It is processed through compression moulding (for large parts with high mechanical properties). This compound is made of a polyester thermosetting resin sheet impregnating long glass fibers (20 to 30% of this reinforcement), of fillers and of a hardening agent (catalyst). The compound is ready for heated compression moulding and is placed in an open, heated (at a temperature between 140 and 160°) mold cavity. The mold is closed and pressure is then applied to force the material to fill up the entire mold cavity. The heat and pressure (of the order of 50 to 100 bars) are maintained until the plastic material is cured (.

Advantages of SMC MOULDING

  • two smooth and ready for paint faces
  • allows the production of large and complex parts
  • High precision moulding and material good propertie
  • low material cost
  • low labor cost
  • high production rates

Raw material

Pre-impregnated mat or home-made compound

  • Impreganted material : polyesters, chemical shim agent, catalysts, inhibitors, mould release agents, pigments…
  • Reinforcement : fiberglass rovings (reinforcement rate : 20 to 50%)

Equipment

  • Production line of pre-impregnated mat (optional)
  • High compression press with adjustable pressing speed
  • Thermo-regulated chrome steeled moulds

Field of application

  • Automotive (tourism and commercial vehicles), car bodywork, protection covers
  • Electrical industry : meter boxes, strip lights
  • Various industrial parts

Machining and finishing

The machining of a composite material consists of cutting the fibers while avoiding generating defects inherent in this material (superficial burns, delamination, flaking).

However, the term ‘finishing’ of the composite material parts will be preferred to the ‘machining’ one because the operations that are performed will most often be done at the final stage and will be summarized to a cut-to-length, to deburring, drilling or thickness adjustement.

The manufacturing process of composite materials ends up with a final stage called ‘finishing’.

The manufacturing process of composite materials often ends with finishing operations, this is called ‘Finishing’.

Whatever the production mode of a part, the ‘finishing’ stage is the set of operations done before the implementation of the part or proceeding to the next manufacturing step.

BMC compression

Principle

Bulk Molding Compound (BMC) is a semi-finished product made from catalyzed unsaturated polyester resin blender, various fillers and additives, reinforced by chopped glass fibers (20%) which is dedicated to large series moulding processes.

The BMC is charged with chopped fibers. The percentage of fiberglass varies from 10 to 30%, their length form 6 to 12 mm.

The BMC is generally injected in a closed cavity (made of a mold and of a backing-mold) at a  regulated in temperature (130 to 150 ° C). the closing of the mold generates the creep in compression of the compound and the compound is forced through an orifice (injection nozzle) into the closed mould.

The very short cure time allows quick stripping of the part.

Advantages of BMC

  • Two smooth faces
  • Possibility of complex shapes
  • High precision molding
  • Moderate material cost
  • High molding speeds
  • Low impact of labor on the quality of parts

Application

  • Large series
  • Small and medium-siezd parts

Raw material

Bought or home-made compound

  • Mostly polyester resins, chemical shim agent, catalysts, inhibitors, mould release agents, pigments…
  • Reinforcement : 6 to 12 mm chopped fiberglass  (reinforcement rate : 20 to 50%)

Equipment

  • Preparation : weighting devices, compound mixer
  • Moulding : High compression press with adjustable pressing speed, thermo-regulated chrome steeled moulds

Applications

  • Automotive (tourism and commercial vehicles), car bodywork, protection covers.
  • Electrical devices
  • Various industrial parts

Pultrusion

« Pull » + « Extrusion » = Pultrusion
Pultrusion is a continuous process for the manufacturing of composite materials with constant cross-section. The term is a portmanteau word, combining “pull” and “extrusion“. The shape of the profiles can be simple (tube, flat bar, rod…) or more complex (customized profiles).

Pultrusion offers the following specificities:

  • almost infinite combinations of reinforcing / matrix couplings giving free rein to the imagination of the designers and conferring on the finished products extremely varied properties
  • very good resistance to chemical agents
  • very good dielectric properties
  • very good thermal insulator
  • low thermal expansion
  • stability of mechanical characteristics guaranted even on a large temperature variation
  • easy to machine, drill and assemble.

Technical principles :

Pultrusion is a continuous process for the manufacture of profiles. Depending on the required strength, a variety of reinforcing materials (roving, mats, fabrics, complexes, non-woven fabrics) packed into rovings (1) which are reeled off guide plates (2), and then impregnated in a resin bath (3). Using hydraulic clamps or other take-off units, the reinforcing materials are then pulled through a forming and curing die (4). The crossing into the heated die (5) creates the polymerization process of the thermosetting resin and give the final geometry of the desired profile. The profile is then cut to length (6).

The pultrusion process is slower than the extrusion process.

Borflex uses fiber glass reinforcements.