Total quality process control for injection molding pdf

The all-encompassing guide to total quality process control for injection molding In the same simple, easy-to-understand language that marked the first edition, Total Quality Process Control for Injection Molding , Second Edition lays out a successful plan for producing superior plastic parts using high-quality controls.

This Second Edition: Details ways to improve plastic part design and quality Includes material and process control procedures to monitor quality through the entire manufacturing system Offers detailed information on machinery and equipment and the implementation of quality assurance methods—content that is lacking in similar books Provides problem-analysis techniques and troubleshooting procedures Includes updates that cover Six Sigma, ISO , and TS , which are all critical for quality control; computer-guided process control techniques; and lean manufacturing methods With proven ways to problem-solve, increase performance, and ensure customer satis-faction, this valuable guide offers the vital information today's managers need to plan and implement quality process control—and produce plastic parts that not only meet, but surpass expectations.

Preview this book ». What people are saying - Write a review. Selected pages Page Page 4. Title Page. Table of Contents. Contents Second Edition Preface. Second Edition 4 Customer Satisfaction. Second Edition 5 Organization Responsibilities. Second Edition 7 Material Selection and Handling. Second Edition 14 Part Design Influence. Second Edition 15 Assembly Techniques. Second Edition 16 Decorating Considerations. Second Edition 17 Customer and Employee Satisfaction.

Second Edition Appendix C Checklists. Second Edition 8 The Mold. Second Edition 9 Manufacturing Equipment. Second Edition 10 Auxiliary Equipment. Second Edition 11 Processing. Second Edition 12 Part Testing at the Machine. Second Edition 13 Part Handling and Packaging. This chapter provides an introduction and The figure shows the necessary components overview of the injection molding machine for the injection molder to be successful and IMM process. It provides text with pictorial profitable.

Recognize that the first to market reviews. The young tree cannot grow if it chapter are provided in the other chapters. You need to cally summarizes what should be considered be at the top of the tree looking over the to ensure that the molded product meets per- other trees. Factors such as good engineer- formance requirements and provides a good ing and process control are very important return on investment to produce all types and but only represent pieces of the pie.

Without shapes of products for all types of markets. The old adage 3, 7. In the industry an IMM commercial success and meet product design is not regarded as an extruder; however, it requirements Chap.

IMMs have a screw plas- ucts, based on factors such as quantities, ticator, also called a screw extruder, that pre- sizes, shapes, product performance, or eco- pares the melt 3. Small- and large-size IMMs both into the next component that is the mold. For example, if sev- The clamping system closes and opens the eral small machines are used rather than one mold. However, the larger ma- melting of the plastic in the plasticator, chine is usually much more profitable while it 2 injection: injecting from the plasticator is running.

Because there are fewer cavities in under pressure a controlled-volume shot of molds for the small machines, they may per- melt into a closed mold, with solidification mit closer control of the molding variables in of the plastics beginning on the mold's cavity the individual cavities. The two-stage moplastic TP molded part in the mold until IMM also has other names, such as the piggy- it is sufficiently rigid to be ejected, or heat- back IMM.

It is comparable in some ways to ing:heating the thermoset TS molded part a continuous extruder. The injection unit, also called the mold so it is ready to start the next cycle with plasticator, prepares the proper plastic melt a shot of melt. The young tree cannot grow if it is in the shadow of another tree or if it does not keep up with the competition.

You need to be at the top of the tree looking over the other trees. DVR Fig. This cycle is more complex than that other simple ones to intricate three-dimensional processes such as extrusion in that it involves 3-D ones, and from extremely small to large moving the melt into the mold and stopping ones.

When required, these products can be it, rather than having a continuous flow of molded to extremely very tight tolerances, melt. The injection molding process is, how- very thin, and in weights down to fractions ever, extremely useful, since it permits the of a gram. Molding Plastics Machine Characteristics Most of the literature on injection mold- IMMs are characterized by their shot ca- ing processing refers entirely or primarily to pacity.

A shot represents the maximum vol- TPs; very little, if any at all, refers to ther- ume of melt that is injected into the mold. During injection factor to meet different mold packing con- ditions.

Shot size capacity may be given in molding the TPs reach maximum tempera- terms of the maximum weight that can be in- ture during plastication before entering the mold.

The TS plastics reach maximum tem- jected into one or more mold cavities, usu- perature in the heated molds. Since plastics have different densities, a better way to ex- Molding Basics and Overview press shot size is in terms of the volume of melt that can be injected into a mold at a spe- The following information provides a com- cific pressure.

The rate of injecting the shot plete overview of the process of IM Figs. Continually required is better under- process control capability for cycling the melt standing and improving the relationship of into the mold cavity or cavities fast-slow- process-plastic-product and controlling the fast, slow-fast, etc. The injection pressure in the barrel can Injection molding is a repetitive process in range from 2, to at least 30, psi 14 to which melted plasticized plastic is injected MPa.

The characteristics of the plastic forced into a mold cavity or cavities, where being processed determine what pressure is it is held under pressure until it is removed in required in the mold to obtain good products. The mold may con- pressure has to be high enough to meet pres- sist of a single cavity or a number of similar sure flow restrictions going from the plastica- or dissimilar cavities, each connected to flow tor into the mold cavity or cavities.

A specified clamping force ing the plastic in the injection or plasticizing is required to retain the pressure in the mold unit so that it will flow under pressure, 2 al- cavity or cavities. It also depends on the cross- lowing the plastic melt to solidify in the mold, sectional area of any melt located on the part- and 3 opening the mold to eject the molded ing line of the mold, including any cavities product. If a TP hot-melt runner is lo- which the mechanical and thermal inputs cated within the mold half, its cross-sectional of the injection equipment must be co- area is not included in the parting-line area.

They are also the prime de- molded products. Basically, the approach is to: of a second to many minutes. To be effective, the evaluation operation is shown in Fig. This block di- of a product should proceed according to a agram basically summarizes what should be logical step-by-step process Fig. The considered to ensure a good return on in- result is to target for zero defects. People and Productivity delivery time and that falls within budget.

As has been stated updated equipment, computer automation throughout history, to live is to change, and to systems, and adequate modern facilities. But approach perfection is to have changed often the one ingredient that ties the recipe to- in the right direction. None of the ingredients have much use without the right people.

However, while the Many thousands of different plastics also software and hardware all provide impor- called polymers, resins, reinforced plastics, tant resources for automating the manufac- elastomers, etc. Variables in Chap. There are many different tests to provide Achievable processing plans begin with all kinds of information. Important tests on the recognition that smooth does not mean molded products are mechanical tests such as perfect. Perfection basically is an unrealis- those shown in Fig.

The expectation of perfection can block gen- There are basically two types of plastic ma- uine communication between workers, de- terials molded. Thermoplastics TPs , which partments, management, customers and ven- are predominantly used, can go through dors see the section on Perfection in Chap.

Ther- the mixing alloying, blending, etc. With TPs, the mold initially is kept at as low During heating they undergo a chemical a temperature as possible, below the melting cross-linking change. Certain plastics re- point of the plastic melt. After a sufficient cool- Extensive compounding of different ing time, the mold opens and the part s are amounts and combinations of additives ejected.

When processing TSs [from the in- colorants, flame retardants, heat and light jection unit plasticizer ], the hot melt enter- stabilizers, etc. TPs are formed by combining into long chains of molecules, or molecules with branches lat- eral connections to form complex molecular Ideal choiceiCompromise shapes. All these forms exist in either two or three dimensions, Because of their geome- Fig.

Morphology melt to undergo its final chemical cross- pertains to TPs but not TSs. When TSs are linking action resulting in solidification. The term semicrystalline is techni- 30 sec 5 sec cally more accurate, but seldom used. Vari- Fig.

Plastics are therefore said to be vis- coelastic. The mechanical behavior of plastics is dominated by the viscoelastic parameters such as tensile strength, elongation at break, BRITTLE and rupture energy. The viscous attributes of melt flows are very important considerations Note: With formulation changes via addltlver, flllen,reln- lorcements. Viscosity is a material's resistance to vis- cous deformation flow. Quantitatively it plastics are used, such as their molecu- is expressed by the modulus of elasticity E lar weight distribution MWD.

A narrow Chap. MWD enhances the performance of plastic Plastics undergo non-Newtonian flow: the products. MWD affects melt flow behavior curve of pressure vs. By contrast, the flow of water is nearly Newtonian. Not only are there these two classes of Melt Flow and Rheology deformation; there are also two modes in which deformation can be produced: simple Rheology is the science that deals with the shear and simple tension.

The actual beha- deformation and flow of matter under various vior during melting, as in a screw plasticator conditions. An example is plastic melt flow. In Fig. Together with the screw design, , a and b show the ram also called the deformation determines the pumping ef- plunger systems used in the original IMMs ficiency of the plasticator and controls the re- since the s, and now used mainly to pro- lationship between output rate and pressure cess plastics with very little melt flow, such drop through the melt flow to solidification as ultrahigh-molecular-weight polyethylene.

They use a piston, with or without a torpedo, for plastication. Part c shows the single- stage reciprocating screw plasticator, and d Plasticating the two-stage screw plasticator. There are different IMM operating de- Plasticating is the process that melts the signs in use: all-hydraulic, all-electrical, plastics. Different methods are used. The and hybrid combination of hydraulic and most common are the single-stage recip- electrical.

The gas forms a series of inter- reducing plastic consumption , eliminat- connecting hollow channels within the melt. There are effect the gas packs the plastic against the also IMMs that perform specialty molding cavity Chap.

An example is the gas-injection Another design is injection-compression molding machine GIMM systems. They ba- molding, also called injection stamping or sically involve the injection of an inert gas, more often coining.

After a short shot enters mum prior to entering the mold. Heat is sup- the mold which has been previously opened plied by heater bands around the barrel and and closed so that it is unpressurized , the by the mixing action that occurs when the stress-free melt is compressed to mold the plastic is moved by the screw. Both conduc- finished product. Other systems include coin- tion heating and mechanical friction heating jection, two-color injection molding, coun- of the plastic occur during screw rotation.

The terflow injection molding, multi-live injec- different controls used during injection mold- tion molding, oscillatory injection molding, ing, such as back pressure and screw rota- reaction injection molding, liquid injection tional speed, influence the melt characteris- molding, foam injection molding, fusible- and tics Chap.

The plastic injection molding, and vacuum injec- feed section, which is at the back end of the tion molding Chap. Its length essentially de- Screw Designs pends upon how much heat has to be added to the plastic that enters the hopper, where it The primary purpose for using a screw may be preheated.

It can process controls operating at their set points. A straight leased to prevent melt burning and the for- compression-type screw is one having no feed mation of voids in the product. With TPs, or metering section. For certain plastics, par-temperature-controlled water with ethylene ticularly TSs, there tends to be no compres- glycol if the water has to operate below its sion zone, since overheating and solidifica- freezing point circulates in the mold to re- tion of the melt could occur between the move heat; with TSs, electrical heaters are screw and barrel.

As high shear action runner, a cavity gate, and a cavity. In turn, melt flows whether any additional mixing is required. With a single-cavity mold, usually no run- or no metering action can be tolerated. Both the feed and meter- Different runner systems are in use to meet ing sections usually have a constant cross sec-different processing requirements.

The most tion zero compression ratio. However, the popular are cold and hot runners. With a TP depth of flight in the feed section is greater cold runner, the melt flowing from the sprue than that in the metering section. With a TP hot runner the sprue to by that in the metering section. Depending the gate is insulated from the chilled cavity on the plastic processed, ratios usually range or cavities and remains hot, so that the melt from 0 to 4.

With a TS hot runner, the melt in the Molds runner solidifies. The TS cold runner keeps the plastic melted by using a cooled insulated The mold is the most important part of the manifold; its next shot starts from the gate, IMM. It is a controllable, complex, and ex- rather than from the nozzle as in a TP hot pensive device. If not properly designed, op- runner.

During the injection into products as well as solidified runners at the the mold, air in the cavity or cavities is re- proper time.

These basic operations in turn Nominal thickness should be maintained throughout part deeper hole intersecting side walls Fig. Different ma- chine requirements and material conditions! It is important to understand and properly operate the basic IMM as well as its auxiliary equipment. Use of TP regrind may have little effect To simplify molding, whenever possible on product performance appearance, color, one should design the product with fea- strength, etc.

However, reduction in perfor- tures that simplify the mold-cavity melt filling mance can occur with certain TPs after even operation. Many such features can improve one passage through the IMM. An example is choosing the mold-cavity additives or fillers in plastics.

Figure shows a situation where on.