Copyright Joseph Greene 20011 SMC, BMC, GMT Manufacturing Professor Joe Greene CSU, CHICO

Copyright Joseph Greene 2001 1

SMC, BMC, GMT Manufacturing

Professor Joe Greene

CSU, CHICO


Objectives • Identify BMC and SMC manufacturing • Identify chemistry and properties for BMC and SMC• Identify processing steps for BMC and SMC• Identify design requirements for BMC and SMC• Discuss current research of SMC and BMC• Discuss future research


Overview • SMC

– Materials– Suppliers and cost– Processing in detail– Design

• BMC – Materials– Suppliers– Processing in detail– Design for BMC

• GMT and Twintex – Materials– Suppliers– Processing in detail– Design


FRP Advantages • Advantages

– Fiberglass reinforced plastic (FRP) has been used for various types of equipment in the chemical processing industry since the early 1950's.

• Its use has continued to grow in pulp and paper, power, waste treatment, semi-conductor, metals refining, petrochemical, pharmaceutical, and other industries.

• Process vessels of all shapes and sizes, scrubbers, hoppers, hoods, ducts, fans, stacks, pipes, pumps, pump bases, valve bodies, elevator buckets, heat-exchanger shells and tube sheets, mist-eliminator blades, grating, floor coatings, and tank lining systems.

– The chief reason for the popularity of these materials is their excellent resistance to corrosion. When choosing the best material of construction, FRP is often chosen due to its:

– Corrosion resistance to a wide range of acids, bases, chlorides, solvents, and oxidizers

– Heat resistance – Electrical and thermal insulation – High strength-to-weight ratio – Low maintenance – Requires no cathodic protection, rust-free – Ease of repair

• Ashland Specialty Chemical Company provides five different types of resins for FRP equipment.


Sheet Molding Compound (SMC)• Materials

– Resins: polyester, vinyl ester, epoxy

– Fibers: 0.5” to 1” E-glass; Filler: Calcium Carbonate

– Body panel Class ‘A’ material- Phase epsilon from Ashland Company has 30% glass fiber

– Structural material- Has more glass fibers (up to 50%)

– SMC Lite- Lower density SMC that has glass bubbles in it to lower density to 1.2 g/cc

• Companies– Ashland Chemical COMPOSITE POLYMERS DIVISION Box 2219 Columbus, OH

43216 614-790-4191

– Ashland Chemical Company's Composite Polymers Division • Develops and manufactures thermoset polyester and other resins for composites used in automotive,

transportation, electrical, marine structures, pulp and paper, tooling, pipe, storage tanks, and construction industry applications.

• The resin product line includes unsaturated polyester, vinyl ester, modified acrylics, furans and various low-profile additive resins.

• Processes used in prototyp-ing to develop new applications include filament winding, compression molding of sheet molding compound (SMC) and bulk molding compound (BMC), hand lay-up, spray-up, pultrusion, and resin transfer molding.


SMC Properties


Sheet Molding Compound (SMC)• Mechanical Properties

– Polyester SMC

http://www.matweb.com/index.html

Physical Properties Metric EnglishPolyester SMCDensity 1.55 - 2.1 g/cc 0.056 - 0.0759 lb/in³Water Absorption 0.08 - 0.75 % 0.08 - 0.75 %Linear Mold Shrinkage 0 - 0.005 cm/cm 0 - 0.005 in/in

Mechanical Properties

Hardness, Barcol 16 - 74 16 - 74Tensile Strength, Ultimate 22.8 - 324 MPa 3310 - 47000 psiTensile Strength, Yield 100 - 300 MPa 14500 - 43500 psiElongation at Break 0.4 - 1.7 % 0.4 - 1.7 %Tensile Modulus 12 - 20 GPa 1740 - 2900 ksiFlexural Modulus 3.7 - 17.2 GPa 537 - 2490 ksiFlexural Yield Strength 83 - 482 MPa 12000 - 69900 psiCompressive Yield Strength 103 - 379 MPa 14900 - 55000 psiShear Strength 52 - 124 MPa 7540 - 18000 psiIzod Impact, Notched 1.9 - 19 J/cm 3.56 - 35.6 ft-lb/in

Thermal Properties

CTE, linear 20°C 24 - 40 µm/m-°C 13.3 - 22.2 µin/in-°FThermal Conductivity 0.25 - 0.29 W/m-K 1.74 - 2.01 BTU-in/hr-ft²-°FMaximum Service Temperature, Air130 - 300 °C 266 - 572 °FDeflection Temperature at 1.8 MPa (264 psi)204 - 260 °C 399 - 500 °FUL RTI, Electrical 160 °C 320 °FUL RTI, Mechanical with Impact 150 °C 302 °FUL RTI, Mechanical without Impact150 °C 302 °FFlammability, UL94 HB - V-0 HB - V-0

Processing Properties

Processing Temperature 100 - 150 °C 212 - 302 °F


Sheet Molding Compound (SMC)• Mechanical Properties

– Vinyl ester SMC

http://www.matweb.com/index.html

Physical Properties Metric EnglishVinyl ester SMCDensity 1.6 - 1.95 g/cc 0.0578 - 0.0704 lb/in³Water Absorption 0.05 - 0.35 % 0.05 - 0.35 %Linear Mold Shrinkage 0 - 0.001 cm/cm 0 - 0.001 in/in

Mechanical Properties

Hardness, Barcol 55 - 70 55 - 70Tensile Strength, Ultimate 70 - 620 MPa 10200 - 89900 psiTensile Modulus 24 - 26.8 GPa 3480 - 3890 ksiFlexural Modulus 11 - 41.3 GPa 1600 - 5990 ksiFlexural Yield Strength 155 - 1100 MPa 22500 - 160000 psiCompressive Yield Strength 124 - 289 MPa 18000 - 41900 psiCompressive Modulus 18.6 GPa 2700 ksiIzod Impact, Notched 4.3 - 37 J/cm 8.06 - 69.3 ft-lb/in

CTE, linear 20°C 15.5 - 17.5 µm/m-°C8.61 - 9.72 µin/in-°FCTE, linear 100°C 17.5 µm/m-°C 9.72 µin/in-°FMaximum Service Temperature, Air130 - 300 °C 266 - 572 °FDeflection Temperature at 1.8 MPa (264 psi)235 - 260 °C 455 - 500 °FGlass Temperature 145 - 160 °C 293 - 320 °FFlammability, UL94 V-0 V-0

Processing Properties

Processing Temperature 105 - 140 °C 221 - 284 °F


Sheet Molding Compound (SMC)• Processing

– SMC is produced in paste form and made into a roll which is kept for 1 month to allow for viscosity and molecular weight increases.

– SMC is cut off the roll and cut into charges (2” x 8” strips typically)

– SMC strips are placed in a hot mold at strategic locations (charge pattern) and then compression molded at 400F for 1 minute.

– SMC molded parts typically have blisters and areas of defects at the edge of the parts that need to be sanded

Cut SMC into charges

Place in moldWith robots

CompressionMold to Shape

T= 375F

Cure in mold60 seconds

Open moldTrim flash

Sand partPits and porosity

Paint

Cold SMC


Compression Molding Process

• Materials•Thermosets: Polyester, Vinyl ester, or Epoxy resins with glass fiber

•Sheet Molding Compound (SMC), Bulk Molding Compound (BMC)

Thermosets:Heat Mold

during molding


SMC Design Recommendations • SMC Advantages in design

– Light weight, parts consolidation, corrosion resistance, stiff, lower tooling costs– Best for lower volume production (less than 100,000 parts per year) versus steel

• Process for design– Review design objectives with car– Select part function and corresponding SMC material

• Body panel or Class ‘A’ painted part, choose Phase epsilon• Structural or support part, choose Structural SMC• Cover panel part or Interior part, choose SMC-Lite

– Design beneath surface• Support structure is needed for doors, hoods, or other outer surface parts• Can use SMC structural or SMC lite materials• Outer and inner panel must be adhesively bonded (Ashland adhesives)

– Preliminary structural evaluation• Design parts in CAD• Perform structural analysis on part for performance and clearance checks.

– Select a molding source• Budd, Premix, or others

http://www.smc-alliance.com/


Sheet Molding Compound (SMC)• Process for design (continued)

– Replacement of current Production panel• Is the existing body envelope sufficient • Design of SMC composite door is thicker than steel door.

– Molded SMC is 4 to 6 mm mating to ribbed 10 mm inner.• Do mating and surrounding parts have to adjust their design to fit the SMC part.• Design the number and location of fasteners.

• Class ‘A’ Body panel design recommendations– Minimum contour of door or hood.– Part thickness Figure 3-5

• Outer panel: 2 to 3 mm• Inner panel: 1.75 to 2.5 mm• Important to have constant thickness throughout part.

– Radii Figure 3-6• Inside and outside radii should have constant thickness.• Minimum inside radii of 2 mm and outside corner radii of 1.5 mm



SMC Design for Manufacturing

• Process for design (continued)– Molding openings in parts can reduce material waste and trimming.

• Example, door openings for window, tail gates, sun roofs.

– Preferred charge pattern is to place SMC charges around opening rather than a big charge at the bottom of opening due to formation of knit line. Figure 3-8 and 3-9.

– Do not mold a clearance hole or faster hole in opening area.• Drill in the holes as needed.

– Mold openings or holes can be created with mash-offs. Fig 3-10• Mash offs - thinner area in part that are molded thin and then cut-out or punched out in a

secondary operation.• Advantages – Promotes more homogeneous material through hole location.

• Designing to maximize structure– 1-piece versus 2-piece construction method

• When designing composite part decide whether the part will be 1 piece or 2 pieces that are bonded together.



SMC Design for Manufacturing• Process for design (continued)

– 1-piece versus 2-piece construction method


One-piece or two-piece construction methodConstuction One-Piece Two-Piece assembly

ApplicationFenders, quarter panels, roof panels, etc.

Doors, hoods, decklids, tailgates, etc.

Mold cost Low to moderate Moderate to highCycle Tme 60-240 seconds 60-120 seconds

Assembly costs None

Moderate: may contribute up to 35% of piece cost

Assembly time None 60-120 secondsPiece cost affect Low to moderate Moderate

Class "A" surface affectExcellent with ribs below contour lines

Excellent with proper bonding

Stiffness Should be supported Excellent

Mass SavingsExcellent with minimum ribbing Very good


SMC Design for Manufacturing• Process for design (continued)

– Ribs• One advantage over steel is the ability to add ribs where needed to stiffen the structure.

– Class “A” paint-able surfaces• Place rib opposite styling lines, surface changes or highly contoured surfaces.• Minimum rub thickness is 1.5 mm.• Minimum draft of 0.5° per side is required.• Radius of rib should be sharp (0.5mm thickness) and have a radius on the tip.• Problem: ribs can cause surface problems on opposite surface, especially problematic if

the surface is painted. Figure 3-11 and 3-12– Sink marks can form if rib is too thick. (Solution: rib thickness should be 75% or

less than the thickness of part)– For non-appearance surfaces the rib thickness can equal part thickness.

• Bosses can be added (Figure 3-13) with inside and outside draft are 0.25°. Fig 3-15– Radius at base of the boss should be 0.5mm (max)

• Stiffen structure with the use of flanges rather than increasing thickness.– Figures 3-17m 3-18

– Sections should have at least one-out turned flange (two are better for hat section)– 2-pieces bonded sections need closed section for stiffness.



SMC Design Recommendations• Tooling

– Undercuts• Parts must be designed so that they can be easily removed from the mold.• If external undercuts are essential, straight draw is not possible, a side activated

slide is required or split the mold with removable sections• Internal Undercuts are difficult and should be avoided

– Mold Parting line• Two mating mold surfaces must be sealed off to mold a flash free part• Contour and step partings lines are difficult and should be avoided

– Sharp corners• All corners should have a radius or fillet at set-in sections of the mold or at the

parting line• Avoid sharp corners• Specify fillets and corner radii of 0.8mm to 1.1 mm

– Holes or openings• Steel pins or section are needed in the mold to incorporate holes or irregularly

shaped openings• Spacing between holes and next to side walls should be as large as possible


SMC Design Recommendations• Tooling

– Shear edge design. Figure 4-3• SMC requires a shear edge design in tooling to minimize flash and to maximize fiber-

resin bonding.

• Minimum 3° per side draft for return flanges.

• Minimum 1 mm nominal flat clearance.

• Surface normal to die draw should be provided at edge of part.

• Nominal angular tolerance of +/- 20° and a 0.05 to 0.15 radius.

– Any projecting mold section should not exceed 2 times the width of its base.

– Angular mold sections should not be less than 30°

– Knife-edge shear should be avoided• Creates thin mold section that can deflect and break under molding pressure

• Can be eliminated by adding a flange (5mm min) to part edge (Fig 4-4)

– Reverse shear should be avoided• All draft be oriented in the same direction around part periphery.

– Radiused and angled shear (Fig 4-6a, Fig 4-6b)• Parts must not be designed with radii or sharp angles at the shear edge.

• Shear edge thin piece of steel on male mold can not have molding pressure on it.


Tooling for SMC

• Molds are cheaper than equivalent steel stamping dies• Materials

– Kirksite: Zn (94%) and Al (6%) cast alloy; machinable and weld-able• Low cost- typically $40,000 and 6 weeks for a bumper beam mold.

• Medium production runs of 500 to 2,000 parts depending upon the quality.

– Aluminum• Moderate cost- typically $80,000 and 6 weeks for a bumper beam mold.

• Medium production runs of 5,000 to 20,000 parts depending upon the quality.

– Steel (typically P-20) with chrome plating• Moderate cost- typically $250,000 and 12 weeks for a bumper beam mold.

• Medium production runs of 1 million parts depending upon the quality.

• Comparison to Steel stamping tooling of $1.5 Million and 24 weeks for bumper beams.


BMC Materials

• BMC- Bulk Molding Compound– Materials

• BMC is a combination of chopped glass strands with resin as a bulk prepreg.

• Unlike SMC, it is not necessary to have recourse to a maturation step, and consequently, BMC prepreg formulations contain higher filler contents.

• The reinforcements are essentially chopped glass strands of 6 or 12mm.

– The reinforcement content is generally between 10 and 20%.

– The filler is usually calcium carbonate with consequent economic benefit.

• The resins are polyester, vinyl ester, epoxy, urea, melamine, phenolic, or polyurethane

– Processing • BMC is suitable for either compression or injection molding.

– Design• Injection molding of BMC can produce complex components such as electrical

equipment, car components (headlamps), housings for electrical appliances and tools in large industrial volumes.


BMC Properties

• Mechanical properties BMC versus SMCProperties Test Method Units BMC BMC BMC SMC SMC SMCCompound Type - -Water Absorption D570 % 0.11 0.1 0.29 0.18 0.15 0.25Specific Gravity D-792 - 1.86 1.95 1.77 1.75 1.8 1.7UL94 Flame Class E-27875 UL94 Class - 94V-0 - 94V-0 - -Temp Rating - ºC 180 130 130 130 130 130Tensile Strength D638 PSI 6,300 6,500 6,900 10,000 12,000 18,500Flexural Strength D790 PSI 14,000 15,000 23,000 25,000 30,000 36,000Compressive Strength D695 PSI 15,000 13,000 21,000 28,000 28,000 21,000Impact Strength, Izod, Edgewise D256 ft.lbs/ in.notch 4 4 12-Oct 18.5 18.5 24Arc Resistance D495 Seconds 188 190 187 180 140 185Track Resistance D2303 Minutes - 600 - 600 - -Dielectric Strength, Short Time D149 VPM in oil 400 400 390 425 400 500Dielectric Constant at 60 Hz. D150 - 0.085 0.055 - 0.044 0.049 -Dissipation Factor at 60 Hz. D150 - 0.067 0.029 - 0.0096 0.006 -Glass Content for Data Shown - % 15 15 20 22 30 35Mold Shrinkage in./in. - Inch 0.0022 0.0025 0.001 0.0007 0.0025

http://www.haysite.com/HTML/chartcompounds.html


GMT Compression Molding• GMT: Glass Mat Thermoplastic• Materials

– Products: General Electric Company- Azdel– AZDEL Laminate, GMT

• Resin: thermoplastic polypropylene – 60% by weight• Glass: continuous glass mat- 40% by weight• Five layer composite of glass fiber and thermoplastic resin. • Usually compression molded in a process similar to SMC, this material may also be

thermoformed using several industry standard methods of production.• Typically used in more structural applications where surface finish is not an issue.• Typical applications include vehicle bumper beams, underbody shields, etc.• Available in three types of glass fiber mat: Chopped, Random & Uni-directional.

– AZDEL SuperLite®• A low pressure, thermoformable composite of polypropylene and long chopped fiber

combined with outer layers as needed for the application (i.e.; adhesive film, barrier film, tough PP film, non-woven, reinforcing, or just the bare surface.)

• A sheet product that is primarily thermoformed into shape.• Typically used in less demanding structural applications where a high stiffness-to-weight

ratio is required.• Typical applications include vehicle interior substrates (headliners, shelves, etc.)

http://www.azdel.com/Products.htm


Azdel Propertieshttp://www.azdel.com/Products.htm


Twin-Tex Thermoplastic Prepreg

• Twin-Tex– TWINTEX® is a commingled roving made of E-glass and PP fibers.

• Competes with SMC, BMC, and GMT

• Similar to GMT in that it is PP and glass.

• PP Pregreg

– The unique commingled structure of TWINTEX® makes it easy for the polypropylene fibers to wet out the glass fibers in a variety of processes, making continuous fiber composites.

• These vary from low-pressure processes such as vacuum molding, filament winding, and pultrusion, to high-pressure processes like co-molding, extrusion compression, or injection molding.

• TWINTEX® is easily converted into composites by heating the material above the melting point (165°C) of PP from 392°F (200°C) to 428°F (220°C). The polypropylene flows under pressure to form the matrix of the composites.

Fiber BundlePP FiberGlass Fiber

http://www.twintex.com/fabrication_processes/tw_process.html

Feb 5, 1999 Copyright Joseph Greene 2001

Select Material Properties of GMT and Twin-Tex Products

Material Density Glass Vol Tensile Tensile (g/cm3) (%) Strength Modulus

(MPa) (GPa)

S-GMT 1.19 19 99 6.2 GMT+ 1.19 19 130 6.0C-GMT40+ 1.20 19 82 4.6Satin 1.47 35 310 13.0Twill 1.47 35 400* 22.0*Uni 1.64 45 650* 30.0*

* As measured in the maximum glass value direction


Twin-Tex Vacuum Molding

• Twin-Tex– Vacuum molding

• Used to make large composite parts with a one-sided tool and a vacuum bag to form the component. This process is similar to vacuum bagging for thermoset composites. Silicone reusable membranes can be used.

– Key Processing Points:• Position TWINTEX® on an open-faced mold.

• Place a vacuum bag over the TWINTEX® and seal the material to the mold.

• Remove the air from the bag, sandwiching the TWINTEX® between the bag and the mold.

• Heat mold to achieve material temperature of 392°F (200°C).

• Cool the part to below 212°F (100°C).

• Similar to vacuum bagging for epoxy prepregs.



Twin-Tex Filament Winding

• Twin-Tex– Filament winding

• Used to produce composite structures by winding TWINTEX® rovings over a rotating mandrel.

– Key Processing Points:• Rovings are pulled from a package through a tensioning device and into an

infrared or convection oven to heat the TWINTEX® from 392°F (200°C) to 428°F (220°C).

• A guide-eye positions the molten TWINTEX® rovings onto the rotating mandrel, forming the composite.

• TWINTEX® efficiently reinforces plastic liners composed of the same thermoplastic.



Twin-Tex Pultrusion

• Twin-Tex– Pultrusion

• The process of pulling continuous fibers through a die or rollers to produce constant section profiles.


infrared or convection oven to heat the material from 392°F (200°C) to 428°F (220°C).

• The molten TWINTEX® rovings are drawn through a series of dies or rollers to consolidate and form the composite.

• The thermoplastic pultrusion process can reach line speeds of 220 ft./min.



Twin-Tex Pulextrusion

• Twin-Tex– Pulextrusion

• Combines TWINTEX® pultrusion with thermoplastic extrusion.

• Thermoplastic can provide surface functions (color, texture) or inexpensive section filling. When strategically located in an extruded profile, TWINTEX® provides high stiffness and reduced thermal expansion.


infrared or convection oven to heat the material from 392°F (200°C) to 428°F (220°C).

• The molten TWINTEX® rovings are drawn over a series of heated impregnation bars before entering a cross head extrusion die.



Twin-Tex Thermoforming Stamping

• Thermoforming stamping- low-pressure process that uses consolidated sheet – Key Processing Points:

• Control tool temperature to approximately 176°F (80°C).

• Heat TWINTEX® from 392°F (200°C) to 428°F (220°C) in an oven.

• Transport the molten TWINTEX® from the oven to mold to prevent the polypropylene matrix from cooling prior to mold closing (10 seconds).

• Close mold (60mm per second) to ensure that parts are formed prior to polypropylene solidification.

• Remove part from mold after part has cooled to below 212°F (100°C).

• Thermoplastic light cores can be added in the stamping (compression) process to form three-dimensional sandwich structures.

• Surface films or textiles can be added to the part in the stamping tool to enhance surface aspect.




• Thermoforming stamping• Extrusion compression uses a plasticator to transform TWINTEX® pellets and

PP pellets into a hot bulk molding compound.

• Can be used to make bumper beams

– Key Processing Points:• Mix TWINTEX® and PP pellets into a blender mounted in the extruder hopper.

• Transport the molten charge quickly to the press and place it in the mold.

• Close the mold rapidly.

• Remove the part from the mold after sufficient cooling to 212°F (100°C).http://www.twintex.com/fabrication_processes/tw_process.html



• Co-molding – Consists of using TWINTEX® woven roving or consolidated sheets

with a flowing material like GMT, PP sheet stock or thermoplastic bulk molding compound (TPBMC).

– Co-molded parts benefit from the use of continuous glass fibers for increased toughness and durability, and from the use of the flowing material, which allows for increased design freedom and lowers cost.

– First done by Joe Greene in 1996 at CPI Company in Winona, Minnesota


GMTTwinTex



• Key Processing Points:• Control tool temperature between 68°F (20°C) and 176°F (80°C).

• Heat TWINTEX® from 392°F (200°C) to 428°F (220°C) in an infrared or convection oven.

• Transport the molten TWINTEX® from the oven to the mold rapidly to prevent the polypropylene matrix from cooling prior to mold closing.

• Position molten flowable polypropylene material into the mold corresponding to the thicker areas of the part.

• Close mold rapidly to ensure parts are formed prior to polypropylene solidification.

• Remove part from mold after part has cooled.


GMTTwinTex



• Diaphragm forming – Uses sheets of reuseable silicone as a carrier for TWINTEX® fabrics

between a hot platen section and a forming section.

– The process transforms TWINTEX® fabrics into parts with very low air pressure. The one side tooling remains cold, and is therefore extremely inexpensive.

http://www.twintex.com/



• Key Processing Points:• Insert TWINTEX® fabrics between two silicone sheets.

• Place the silicone/TWINTEX® sandwich in the hot platen equipment until it reaches a temperature of 410°F (210°C).

• Transfer the forming unit and apply positive air pressure (30 psi).

• Demold when the part and silicone are below 100°C.

• Remove silicone membranes from the part before reuse.




• Lamination converts TWINTEX® wovens (with or without core materials) into flat panels continuously.

• Core panels include PP honeycomb, foam, wood and extruded plastics

• Key Processing Points:• Feed all materials into a double-belt laminator.

• Allow machine to heat, impregnate and cool down the panel.


Documents

Copyright Joseph Greene 20011 SMC, BMC, GMT Manufacturing Professor Joe Greene CSU, CHICO