Forming and Shaping Process for Plastic and Composite

Forming and Shaping Process for Plastic and Composite 1

Composites Shaping Injection Moulding Thermoforming Rotational Moulding Polymer Manufacturing Processes Extrusion Compression Moulding Blow Moulding Transfer Moulding 2

PLASTIC POLYMERS q The word “polymer” is a combination of the Greek words: “poly" which means "many“ and “mer” which means “part” q The basic structure of a polymer molecule can be visualized as a long chain of repeating units 3

Polymers’ Classification Thermoplastics: The word “thermoplastic” is a combination of the Greek words: “therm" which means “heat“ and “plastikos ” which means “capable of being molded” Once the polymer is formed it can be heated and reformed over and over again (allows recycling) Thermosets The word “thermoset” is a combination of the Greek words: “therm" which means “heat“ and “sets” irreversibly when heated Therefore, can not be remelted. Once these polymers are formed, reheating will cause the material to degrade 4

Composites Shaping Injection Moulding Thermoforming Rotational Moulding Polymer Manufacturing Processes Extrusion Compression Moulding Blow Moulding Transfer Moulding 5

INJECTION MOLDING PROCESS What is Injection Molding Process? • A process that utilizes melted plastics injected into steel or aluminum molds. • Method of forming a plastic to the desired shape by forcing the heat softened plastic into a relatively cool cavity under pressure. 6

INJECTION MOLDING PRODUCTS 7

INJECTION MOLDING MACHINE 8

INJECTION MOLDING MACHINE • The pellets are fed into heated cylinder and the melt is forced into the mold by hydraulic plunger or rotating screw of an extruder. • The rotating screw will move backwards under pressure to a determined distance. The movement controls the volume of materials to be injected. • The screw stops rotating and is pushed forward hydraulically forcing the plastic mold into the mold cavity. 9

INJECTION MOLDING MACHINE PARAMETER • • • Injection Pressure Injection Time Injection Speed Cooling Time Mold Temperature VIDEO : FUNDAMENTAL INJECTION MOLDING 10

TYPE OF MOULDS Advantages of Two-Plate Molds q Low fabrication cost q Simple mold/tooling design q Easy to setting injection molding machine parameter during molding q Easy to maintenance the mold q Short lead time for mold fabrication q Easy to fitting and assembly the mold q Simple ejection system of mold Disadvantages of Two-Plate Molds 2 - Plates Mold q Runner and part not automatically separated (need secondary process to cut) q The gate area can be seen clearly after cut 11

TYPE OF MOULDS Advantages of Three-Plate Molds q The runner automatic separated from the part during mold opening. q The part cycle time can be reduced. (no need to cut the gate). q Reduce production cost. Disadvantages of Three-Plate Molds 3 -Plates Mold q The mold/tooling structures are complex. q High cost of tooling fabrication. q High maintenance cost of mold. q Lead time for mold fabrication is long. 12

PHASES OF MOULDING • Filling – Volumetrically fill the cavity • Pressurization – Build up pressure in the cavity • Packing – Add extra material to reduce shrinkage Filling Phase Pressurization Phase 13 Packing Phase

GATING/DELIVERY SYSTEM Sprue Polymer Entrance Point Primary Runner Part Cavity Gate Secondary Runner 14

MOULDING STAGES • Filling – Mold closes – Screw forward – Frozen polymer skin forms at mold walls • Packing Time – Cavity filled – Pressure applied to polymer – Cooling occurs – Gate freezes Hopper Barrel Screw Mold Screw is applying a specified pressure to the polymer melt in order to pack more plastic into the cavity. 15

MOULDING STAGES (Cont…) • Cooling – Part continues to cool until rigid enough to withstand ejection – Screw moves back plasticizing resin for next shot • Mold Open – Part is ejected 16

MOULDING CYCLE TIME Cycle Time: Fill Time: Pack Time: Cooling Time: Mold Open Time: 22 Sec. 1 9 10 2 17

INJECTION PRESSURE q Pressure is required to push the plastic into the mold cavity q Limited by machine capability – Hydraulic pump limitations – Usually around 140 – 180 MPa (20, 000 – 26, 000 psi) – Modern machines can go up to 300 MPa (43, 500 psi) q Major influence on final part dimensions 18

Part Design Affecting Injection Pressure • Part Thickness • Surface Area Thin Part More surface area to be cooled Higher Pressure Thick Part Less surface area to be cooled Lower Pressure 19

Mold Design Affecting Injection Pressure • Gate size • Flow length (gate location) Restrictive Gate Higher Pressure Long Flow Length Higher Pressure Generous Gate Lower Pressure Short Flow Length Lower Pressure 20

Processing Conditions Affecting Injection Pressure • Melt temperature è Higher Pressure • Mold temperature Colder Coolant Temperature Higher Pressure Lower Pressure Hotter Coolant Temperature Lower Pressure 21

Material Selection Affecting Injection Pressure q Different grades of the “same” material can have widely different pressure requirements 22

Material Selection Affecting Injection Pressure q Different grades of the “different” material can have widely different pressure requirements 23

Factors Affecting Injection Pressure Requires Higher Injection Pressure Requires Lower Injection Pressure 24

Defect and Causes in Injection Molding Defect Causes Flashing § Injection Pressure too high § Clamping force to low § Mold fitting not good Warping Non-uniform cooling rate Bubble To much moisture in material Shot Mold Air trap Injection Pressure not enough Sink Mark Injection Pressure too low Non-uniform cooling rate Ejector Pin Mark Cooling time too short Ejection force too high 25

Reinforcing Agent • Possible geometries - fibers, particles, and flakes • Possible materials - ceramics, metals, other polymers, or elements such as carbon or boron • Particles and flakes are used in many plastic molding compounds • Of most engineering interest is the use of fibers as the reinforcing phase in FRPs 26

Fibers as the Reinforcing Phase • Common fiber materials: glass, carbon, and Kevlar (a polymer) • In some fabrication processes, the filaments are continuous, while in others, they are chopped into short lengths • The most familiar form of continuous fiber is a cloth ‑ a fabric of woven yarns 27

Open Mold FRP Processes Hand Lay‑Up Method Open mold shaping method in which successive layers of resin and reinforcement are manually applied to an open mold to build the laminated FRP composite structure • Labor‑intensive • Finished molding must usually be trimmed with a power saw to size outside edges • Oldest open mold method for FRP laminates, dating to the 1940 s when it was first used for boat hulls 28

Hand Lay-Up Method Figure 15. 4 Hand lay‑up : (1) mold is treated with mold release agent; (2) thin gel coat (resin) is applied, to the outside surface of molding; (3) when gel coat has partially set, layers of resin and fiber are applied, the fiber is in the form of mat or cloth; each layer is rolled to impregnate the fiber with resin and remove air; (4) part is cured; (5) 29 fully hardened part is removed from mold.

Vacuum Bagging 30

Rapid Prototyping (RP) University Malaysia Perlis

Introduction • RP or freeform fabrication - one of the fastest growing new technologies since its introduction in 1986. • RP started as a process to fabricate polymer prototypes in minimum lead time based on a CAD model of the item. • These prototypes were fabricated “freeform” directly from CAD files without the use of molds.

Fundamentals of Rapid Prototyping • Additive (Material addition RP) ~Processes build up a part by adding material incrementally to produce final parts • Subtractive (Material removal RP) ~Material removal from a workpiece ~Using a CNC machine • Virtual ~Use computer base visualization techniques for CAD model. ~This may not be sufficient to conduct real physical tests on the part. ~Simulated test by finite element analysis

What is additive RP ? Figure : The computational steps in producing a stereolithography file. (a) Three-dimensional description of part. (b) The part is divided into slices (only one in 10 is shown). (c) Support material is planned. (d) A set of tool directions is determined to manufacture each slice. Shown is the extruder path at section A-A from (c), for a fused-deposition-modeling operation.

Additive technologies Today's additive technologies offer advantages in many applications compared to classical subtractive fabrication methods: – Objects can be formed with any geometric complexity or intricacy – Eliminate the need for elaborate machine setup or final assembly; – Rapid prototyping systems reduce the construction of complex objects to a manageable, straightforward, and relatively fast process. – To reduce time to market in manufacturing – To better understand communicate product designs – To make rapid tooling to manufacture those products

Subtractive (Material Removal RP) • Machining using a dedicated CNC machine for machining process. Ex: drilling, turning and etc. • Prepared NC programming according the CAD model. • They are fast, versatile, inexpensive, readily available and well-understood by large numbers of practitioners.

Subtractive (Material Removal RP) • The part’s solid model will be slicing into thin layers (approximately geometry of solid part) • The CNC milling machine then contour the part layer by layer from a solid block (wax material are used) • Starting material is often wax: ~Easy to machine ~Can be melted and resolidified • The term of CNC machines is desktop machining

Virtual prototyping • Software form of prototyping, which uses advanced graphics or virtual-reality environments – testing the parts • The complex software and 3 D graphics allow viewers to change the view of the parts on a computer screen • New version: headgear and gloves.

When to use rapid prototyping (a) (b) (c) Figure: (a) Titanium engine valves fabricated with laser engineered net shaping (b) A surgical planning model using fused deposition modeling (c) Model Maker inkjet-based investment casting pattern for a ring

What are the limitation ? • Accuracy: ~Stair stepping ~Finishes • Secondary operations • Support structures must be removed • Speed • System Costs • Materials

Stair stepping in 3 DP Stair stepping in IJS Stair stepping in SLA

Finishes FDM LOM SLA 3 DP

Secondary operation • Before curing, they must be drained of excess polymer, bathed in a solvent and daubed away with paper towels any remaining excess liquid photopolymer. • 3 DP parts are often infiltrated with cyanoacrylate adhesive or wax as a secondary operation to make them more durable.

Benefit to RP technologies • Visualization, verification, iteration, and optimization for design engineers • Communication tool for simultaneous engineering • Form and fit tests of components • Test samples for marketing studies of consumer design preferences • Help in production planning

Application • The main applications of rapid prototyping in engineering are: – Concept Modeling – Functional Testing – Tooling – Manufacturing Others: ~Medicine and dentistry ~Art, Architecture, Industrial Design ~Scientific

Concept Modeling FDM concept model of a pin drive mechanism • Started as a way for engineers to hold a replica of a final part or perform some limited testing. • Years later, the testing can be more complete. • All RP technologies can be used for Concept Modeling

Functional Testing p p p SLS gets closest to final plastic materials SLA is also a good choice, but materials will emulate final thermoplastics and are not the plastics themselves FDM also offers a number of durable materials, but with somewhat lower resolution. Planetary gear by FDM Paintball mask fabricated in plastic by SLS Functional testing model by FDM

Metal tooling and parts a) b) a) A sand casting pattern for a fan made by LOM b) 3 DP sand casting patterns c) d) c) Investment casting shell fabricated by Direct shell production casting (DSPC). The openings are for gates and risers d) SLS-generated polystyrene casting patterns and castings

Thank You Bye Chapter 5