上海交通大学：《现代机械工程图学》教学资源_教学课件_Lec14_polymers

Polymers ME 250:Design Manufacturing I School of Mechanical Engineering Shanghai Jiao Tong University 1

Shanghai Jiao Tong University 1 Polymers ME 250: Design & Manufacturing I School of Mechanical Engineering

Outline Introduction ■Polymer(聚合体)Processing Summary Shanghai Jiao Tong University 2

Shanghai Jiao Tong University 2 Outline n Introduction n Polymer（聚合体） Processing n Summary

Introduction ■Learning Objectives Polymers as Engineering Materials Chemical Structure of Polymers a Commonly Employed Polymer Processing Techniques ■Applications Polymer Composites Shanghai Jiao Tong University 3

Shanghai Jiao Tong University 3 Introduction n Learning Objectives n Polymers as Engineering Materials n Chemical Structure of Polymers n Commonly Employed Polymer n Processing Techniques n Applications n Polymer Composites

Polymers Thermoplastics vs Thermosets Thermoplastics(热塑形塑料)-Plastics that can be repeated softened by heating and repeatedly hardened by cooling through a temperature range that is characteristic of the plastic.In the softened state,the plastic can be shaped into articles. Thermosets(热固性塑料)-Plastics which,after having been cured by heat or other means are mostly infusible or insoluble. Thermosets cannot be reprocessed. Shanghai Jiao Tong University 4

Shanghai Jiao Tong University 4 Polymers - Thermoplastics vs Thermosets Thermoplastics（热塑形塑料） – Plastics that can be repeated softened by heating and repeatedly hardened by cooling through a temperature range that is characteristic of the plastic. In the softened state, the plastic can be shaped into articles. Thermosets （热固性塑料）– Plastics which, after having been cured by heat or other means are mostly infusible or insoluble. Thermosets cannot be reprocessed

Polymers Thermoplastics vs Thermosets Thermoplastics molecules are linear or branched,and as a rule are soluble in specific organic solvents. In thermosets,the molecules are chemically cross-linked,and cannot be dissolved by organic solvents Thermosets Thermeplastics Three-dimeasional amorphous cross-linked Filament molecules molecules amorphous partially crystelline Shanghai Jiao Tong University 5

Shanghai Jiao Tong University 5 Polymers - Thermoplastics vs Thermosets Thermoplastics molecules are linear or branched, and as a rule are soluble in specific organic solvents. In thermosets, the molecules are chemically cross-linked, and cannot be dissolved by organic solvents

Polymer Processing ■Injection Molding(注射成型 ■ Compression Molding(压塑成型) ■Transfer Molding(传递模塑法) o b Blow Molding(吹塑成型) ■ Extrusion(挤压) Thermoforming(热力塑型) Casting(铸造) ■Rotational Molding(转动成型) Shanghai Jiao Tong University 6

Shanghai Jiao Tong University 6 Polymer Processing n Injection Molding(注射成型） n Compression Molding（压塑成型） n Transfer Molding（传递模塑法） n Blow Molding （吹塑成型） n Extrusion（挤压） n Thermoforming（热力塑型） n Casting（铸造） n Rotational Molding（转动成型）

Injection Molding In the injection molding process,thermoplastic polymer granules are fed via a hopper into a heated barrel.A screw or ram forces the molten polymer into a mold cavity.Pressure is maintained until the part has hardened and then the part is ejected out of the mold. Cavities Hopper to Part feed polymer pellets Screw and ram w 日 Hydraulic Heaters for cylinder for melting mold clamp and opening Stationary half of mold Movable half of mold Shanghai Jiao Tong University 7

Shanghai Jiao Tong University 7 Injection Molding In the injection molding process, thermoplastic polymer granules are fed via a hopper into a heated barrel. A screw or ram forces the molten polymer into a mold cavity. Pressure is maintained until the part has hardened and then the part is ejected out of the mold

Injection Molding Injection Molding-products 城钱听 Pulley with Aluminum insert Water pump housing Valve cover Intake Manifold Shanghai Jiao Tong University 8

Shanghai Jiao Tong University 8 Injection Molding n Injection Molding-products

Injection Molding -Analysis Thermoplastics shrink during solidification. Cavity must be larger than part size. DC=Dp+DpS+DpS2 Dc:dimension of cavity [mm] Ds:dimension of part [mm] S:shrinkage value [mm/mm] DpS accounts for shrinkage Shanghai Jiao Tong University 9

Shanghai Jiao Tong University 9 Injection Molding - Analysis Thermoplastics shrink during solidification. Cavity must be larger than part size. Dc=Dp+DpS+DpS 2 Dc: dimension of cavity [mm] Ds: dimension of part [mm] S: shrinkage value [mm/mm] DpS 2 : accounts for shrinkage

Injection Molding Shrinkage of typical thermoplastics Plastic Shrinkage,mm/mm (in./in.) ABS 0.006 Nylon-6.6 0.020 Polycarbonate 0.007 Polyethylene 0.025 Polystyrene 0.004 PVC 0.005 Shanghai Jiao Tong University 10

Shanghai Jiao Tong University 10 Injection Molding n Shrinkage of typical thermoplastics