PRODUCT DESIGN: June 2011

Product Design

Although component design in thermoplastics is complex, following a few fundamental principles will help you minimize problems during molding and in part performance. Of course, the guidelines given here are general.

Depending on the particular requirements of the part, it may not always be possible to follow all of our suggestions. But these guidelines, in furthering your understanding of the behavior of thermoplastics, can help you effectively resolve some of the more common design problems.

Nominal Wall Thickness

For parts made from most thermoplastics, nominal wall thickness should not exceed 4.0 mm. Walls thicker than 4.0 mm will result in increased cycle times (due to the longer time required for cooling), will increase the likelihood of voids and significantly decrease the physical properties of

the part. If a design requires wall thicknesses greater than the suggested limit of 4.0 mm, structural foam resins should be considered, even though additional processing technology would be required.

In general, a uniform wall thickness should be maintained throughout the part. If variations are necessary, avoid abrupt changes in thickness by the use of transition zones, as shown in Figure 25. Transition zones will eliminate stress concentrations that can significantly reduce the impact strength of the part. Also, transition zones reduce the occurrence of sinks, voids, and warping in the molded parts.

A wall thickness variation of ± 25% is acceptable in a part made with a thermoplastic having a shrinkage rate of less than 0.01 mm/mm. If the shrinkage rate exceeds 0.01 mm/mm, then a thickness variation of ± 15% is permissible.

Radius

It is best not to design parts with sharp corners. Sharp corners act as notches, which concentrate stress and reduce the part’s impact strength. A corner radius, as shown in Figure 26, will increase the strength of the corner and improve mold filling. The radius should be in the range of 25% to 75% of wall thickness; 50% is

suggested. Figure 27 shows stress concentration as a function of the ratio of corner radius to wall thickness, R/T.

Draft Angle

So that parts can be easily ejected from the mold, walls should be designed with a slight draft angle, as shown in Figure 28. A draft angle of 1 ⁄ 2° draft per side is the extreme minimum to provide satisfactory results.

1° draft per side is considered standard practice. The smaller draft angles cause problems in removing completed parts from the mold. However, any draft is better than no draft at all. Parts with a molded-in deep texture, such as leather-graining, as part of their design require additional draft. Generally, an additional

1° of draft should be provided for every 0.025 mm depth of texture.

PERMANENT MOLD CASTING

This type of casting, cetakannnya can be used repeatedly (made of metal and graphite).

Is devoted to casting foundries non ferrous metals and alloys.

The quality depends on the quality of the casting mold, is generally done by machining to get a good quality then it is done with the machining process with high accuracy

Advantage Permanent Mold Casting:

1. High production

2. Moulds can be used repeatedly

3. In its operation is not required expert

4. Product accuracy is better than sand casting

5. No need for advanced process

Disadvantage Permanent Mold Casting:

1. Prices expensive mold

2. Need to do a precise calculation of the mold

3. molds for a variety of products

4. small product size and simple

5. unable to casting steel

Biomechanics in Ergonomics

Biomechanics is the application of classical mechanics to biological systems such as the human body. Although this comprises many branches of mechanics, in the context of ergonomics, we will deal only with dynamics and to a limited extent the mechanics of materials.

In physical ergonomics, the human body can be seen as a mechanical system or rather a part of a mechanical system comprising also the tools, objects, and environment with which the human operator interacts. Inverse dynamics can be applied to the analysis of this mechanical system to estimate forces and moments being produced by or acting on thehuman body, whereas mechanics of materials contributes toward understanding the effects of these mechanical loads on the body. Direct measurement of forces and moments in the human is not feasible for practical and ethical reasons. Consequently the vast majority of available methods and data rely to some extent on inverse dynamical models.

Estimating Joint Moments

The principles of inverse dynamics will probably be known to any mechanical engineer and can be found in dynamics textbooks or specialty books on biomechanics (see Additional References). To summarize, application of the equations of motion based on Newton’s second law ( F ma) and Euler’s extension of this law to angular motions ( M l ) to a system of linked segments is used to yield forces and moments acting at each of the segments in each of the links. In biomechanical analyses, moments about the joints of the human body are usually of interest, since these reflect the combined effect of all muscles spanning the

joint. Note that physically these moments are thus the effect of muscle forces. In actual analysis, the moments of force of the muscles appear as a lumped moment in the moment equilibrium equation, and they do not appear in the force equilibrium equation. To perform this type of analysis, masses and moments of inertias of the segments and the accelerations of the segments need to be known. Finally, if two or more external forces act on the system, all but one of these need to be known. If all external forces are known, redundant information is available which can be used to validate the model with respect to anthropometric assumptions

or to decrease the estimation errors that would result from assuming accelerations to be zero.

A simplified example of a linked segment model that was used to estimate the moment on the knee while climbing ladders with different rung separations is given in Fig. 1. Video data were used to approximate the positions of centers of mass of the foot and lower leg as well as the joint rotation centers of the knee and ankle. Forces on a rung were measured with a force transducer. Segment masses were estimated on the basis of anthropometric data.

First, a free-body diagram of the foot was created, and the reaction force at the ankle was calculated by equating the sum of the forces on this segment to its mass times acceleration. Next, the moment at the ankle was calculated from equating the sum of the moments to inertia times angular acceleration. Subsequently, the opposites of this force and moment were used as input for a free-body diagram of the lower leg and the reaction force and moment at the knee were calculated. Segment masses and moments of inertias cannot be directly measured when dealing with the human body. Therefore estimations need to be made on the basis of anthropometric models (see the discussion of fundamentals in Section 2.2). Obviously these estimations may introduce errors, and the magnitude of such errors can be gauged by making use of redundant information when all external forces have been measured. For example, the moment about the low back in lifting can be calculated on the basis of a model of the lower body (legs and pelvis) using measured ground reaction forces on each foot as input. This same moment can also be estimated using a model of the upper body (arms and trunk) and the object lifted. It has been shown that with a careful choice of anthropometric assumptions, errors in moment estimates will generally be below 10 N m. Accelerations can be measured or calculated from position data by double differentiation.
This involves labor-intensive measurements and is only feasible when at least a mockup of the situation to be analyzed is available. Consequently, in many ergonomic applications, accelerations are assumed to be zero, in which case only the static configuration of the human body needs to be known or predicted. This simplification will lead to underestimation of mechanical loads on the human body in dynamic tasks, which in some cases can be substantial (e.g., in manual lifting, the moments around the low back may be underestimated by a factor of 2). Such errors may lead to questionable conclusions, even in a comparative analysis. For instance, earlier studies comparing stoop and squat lifting techniques appear to have been biased toward favoring the squat technique due to the application of static models.

Consequently, early studies have often reported a lower low-back load in squat lifting as compared to stoop lifting, whereas more recent studies using dynamic models have reported the opposite.5 If an analysis of a dynamic task is performed assuming acceleration to be ze zro but inputting the measured external forces on the body into the analysis—the so-called quasidynamic approach—reasonable estimates of joint moments result. A second simplification often used is to assume that all movement and force exertion takes place in a single plane, which allows application of a 2D model. In analyses of asymmetric lifting tasks, this can cause significant and substantial errors in estimated moments around the low back (roughly 20% when the load is placed 30 outside of the primary plane of movement). At 10 of asymmetry, differences between 2D and 3D analyses have been found to be insignificant.

Data collection required for the estimation of net moments is usually not prohibitive in
a comparative analysis of working methods and techniques, since this can be done in a
laboratory mock-up setting. However, for monitoring and identification of the most stressful
tasks or task elements, field measurements covering long periods are desirable. In this case,
use of an inverse dynamics approach usually is prohibitive. Methods have been developed
to estimate moments based on measurements of the electrical activity of muscles, the latter
using electrodes applied on the skin overlying the muscle group of interest (electromyography,
or EMG). However, it has been shown that additional kinematic data and extensive
calibrations are needed to obtain valid estimates. Currently miniature kinematic sensors and
efficient calibration procedures are being developed and tested to facilitate this type of measurements.
Finally estimation of mechanical loads in the design stage can be done using
inverse dynamics when external forces are known and postures (and movements) can be
predicted. Several software programs which can in some cases be integrated with computeraided
design (CAD) applications allow for such analyses. Note that these models usually are
static (assume accelerations to be zero), and the validity of the analysis will depend on the
validity of the posture predictions made by the software or the user.
An indication of how load magnitude, as expressed by the moment about a joint, relates
to the capacity of the musculoskeletal system can be obtained by comparison of the moments
during a task to maximum voluntary moments. Usually such comparisons are made with the
results of isometric strength tests (see Section 2.3). For example, lifting a 20-kg load manually
has been predicted to exceed the shoulder strength of about 30% of the general population,
whereas the same task performed with a hoist allowed over 95% to have sufficient
strength.6 Since many tasks are dynamic in nature and both joint angle and angular velocity
strongly affect the moment capacity, dynamic reference data are needed. As noted earlier,
however, such reference data are only partially available. Some commercial software packages
provide a comparison of joint moments with population strength data, though the latter
are usually static. Several studies have shown that inverse dynamics of human movement can provide
reliable and accurate estimates of joint moments. It should be noted, though, that joint
moments do not always provide a definitive answer as to the actual extent of musculoskeletal
loading, as will be discussed in the next paragraph. Further, since human motor behavior
can be quite variable, the reliability of moment estimates derived from limited numbers of
measurements, and more so when derived from model simulations, should be considered
with care. When comparative analyses are done, substantial differences in net moments (e.g.,
10%) will usually allow conclusions to be drawn with respect to musculoskeletal loading.
For normative interpretation of joint moments with data on muscle strength, it is recommended
that a margin of safety be included in view of the variability and sources of error
both in moment estimates and strength data.

BASIC PRINCIPLES OF INJECTION MOULDING

A satisfactory injection moulding can only be achieved by the correct set-up of machinery, mould and material.

The best mastic will not allow optimum economical manufacture if

- it is difficult to process

- the machine cannot be correctly set to suit the material through having inadequate control and regulating capabilities

- the machine has not been set correctly or

- the mould has not been designed to suit the material.

However, a well designed li InionILq.aLajilELiL2 with sophisticated

and versatile controls and hig installed capacity on its own Will not

provide the optimum if

- the mould is of inadequately weak design

- the mould temperature cannot be controlled exactly

- the mould is not harmonized with the machine

- the material is not suitable

- the material has not been correctly prepared (for example not preheated nor dried).

However, a good mould, as already indicated, also requires to be matched to the material, for example in respect to
- attention to shrinkage, right draft for demolding
- attention to the correct temperature control (temperature pattern, heating and cooling systems and many other aspects)
- attention to the correct gating and the runners
- matching to the machine, for example in respect to the dimensions between tie bars and the dimensions of the platens, the maximum and the minimum mould height, the mould opening stroke, etc.

Perspective projection

Perspective projection is as shown in Figure 2.2. Perspective projection is reality in that everything we see in the world is in perspective such that the objects always have vanishing points. Perspective projection is thus the true view of any object. Hence, we use expressions like 'putting something in perspective' Projectors radiate from a station point (i.e. the eye) past the object and onto the 2D picture plane. The station point is the viewing point. Although there is only one station point, there are three vanishing points. A good example of a vanishing point is railway lines that appear to meet in the distance. One knows in reality that they never really meet, it is just the perspective of one's viewing point.Although there are three vanishing points, perspective drawings can be simplified such that only two or indeed one vanishing point is used. The drawing in Figure 2.2 shows only two vanishing points. Had the block shown been very tall, there would have been a need to have three vanishing points.

Although perspective projection represents reality, it produces complications with respect to the construction of a drawing in that nothing is square and care needs to be taken when constructing such drawings to ensure they are correct. There are numerous books that give details of the methods to be employed to construct perspective drawings. However, for conventional engineering drawing, drawing in perspective is an unnecessary complication and is usually ignored. Thus, perspective projection is very rarely used to draw

engineering objects. The problem in perspective projection is due to the single station point that produces radiating projectors. Life is made much simpler when the station point is an infinite distance from the object so that the projectors are parallel. This is a situation for all the axonometric and orthographic projection methods

considered below.

Engineering Drawing for Manufacture

by Brian Griffiths

· ISBN:185718033X

· Pub. Date: February 2003

· Publisher: Elsevier Science & Technology Books

welding

Definitions of welding according to DIN (Deutsche Industrie Normen) is a metallurgical bond at the junction of metals or metal alloys are carried out in a melted or liquid state. In other words, welding is the local connection of some metal rod using heat energy. In this connection the process is sometimes accompanied by pressure and additional material (filler material)

Simple welding technique has been discovered within the period between 4000 to 3000 BC. Once the electrical energy used with ease, advanced welding technology with the rapidly that it becomes something that advanced switching techniques. Up to now been used more than 40 types of welding.

In the preliminary stages of development of welding technology, welding is usually only used on the connections of the repair is less important. But after going through a lot of experience and practice and a long time, so now the use of welding processes and the use of construction-konsturksi welding is common in all countries in the world.

The realization of the standards of welding techniques will help broaden the scope of the use of welded joints and increases the size of building construction that can be welded. With the progress made to date, welding technology plays an important role in modern industrial society.

Classification of welding

Judging from the heat source. Welding can be distinguished three:

• Mechanics

• Electricity

• Chemical

Meanwhile, according to the way of welding, can be divided into two major parts:

• Welding pressure (Pressure Welding)

• Welding Liquid

STRESSES, STRAINS, STRESS INTENSITY

Fundamental Definitions

Static Stresses

TOTAL STRESS on a section mn through a loaded body is the resultant force S exerted by one part of the body on the other part in order to maintain in equilibrium the external loads acting on the part. Thus, in Figs. 1, 2, and 3 the total stress on section mn due to the external load P is S. The units in which it is expressed are those of load, that is, pounds, tons, etc.

UNIT STRESS, more commonly called stress , is the total stress per unit of area at section mn. In general it varies from point to point over the section. Its value at any point of a section is the total stress on an elementary part of the area, including the point divided by the elementary total stress on an elementary part of the area, including the point divided by the elementary area. If in Figs. 1, 2, and 3 the loaded bodies are one unit thick and four units wide, then when the total stress S is uniformly distributed over the area, P/A P/4. Unit stresses are expressed in pounds per square inch, tons per square foot, etc.

TENSILE STRESS OR TENSION is the internal total stress S exerted by the material fibers to resist the action of an external force P (Fig. 1), tending to separate the material into two parts along the line mn. For equilibrium conditions to exist, the tensile stress at any cross section will be equal and opposite in direction to the external force P. If the internal total stress S is distributed uniformly over the area, the stress can be considered as unit tensile stress S/A.

COMPRESSIVE STRESS OR COMPRESSION is the internal total stress S exerted by the fibers to resist the action of an external force P (Fig. 2) tending to decrease the length of the material. For equilibrium conditions to exist, the compressive stress at any cross section will be equal and opposite in direction to the external force P. If the internal total stress S is distributed uniformly over the area, the unit compressive stress S/A.

SHEAR STRESS is the internal total stress S exerted by the material fibers along the plane mn (Fig. 3) to resist the action of the external forces, tending to slide the adjacent parts in opposite directions. For equilibrium conditions to exist, the shear stress at any cross section will be equal and opposite in direction to the external force P. If the internal total stress S is uniformly distributed over the area, the unit shear stress S/A.

NORMAL STRESS is the component of the resultant stress that acts normal to the area considered

(Fig. 4).

AXIAL STRESS is a special case of normal stress and may be either tensile or compressive.

It is the stress existing in a straight homogeneous bar when the resultant of the applied

loads coincides with the axis of the bar.

SIMPLE STRESS exists when tension, compression, or shear is considered to operate singly

on a body.

TOTAL STRAIN on a loaded body is the total elongation produced by the influence of an

external load. Thus, in Fig. 4, the total strain is equal to . It is expressed in units of

length, that is, inches, feet, etc.

UNIT STRAIN, or deformation per unit length, is the total amount of deformation divided by

the original length of the body before the load causing the strain was applied. Thus, if

the total elongation is in an original gage length l, the unit strain e / l. Unit strains

are expressed in inches per inch and feet per foot.

TENSILE STRAIN is the strain produced in a specimen by tensile stresses, which in turn are

caused by external forces.

COMPRESSIVE STRAIN is the strain produced in a bar by compressive stresses, which in turn

are caused by external forces.

SHEAR STRAIN is a strain produced in a bar by the external shearing forces.

POISSON’S RATIO is the ratio of lateral unit strain to longitudinal unit strain under the

conditions of uniform and uniaxial longitudinal stress within the proportional limit. It

serves as a measure of lateral stiffness. Average values of Poisson’s ratio for the usual

materials of construction are:
Material Steel Wrought iron Cast iron Brass Concrete
Poisson’s ratio 0.300 0.280 0.270 0.340 0.100
ELASTICITY is that property of a material that enables it to deform or undergo strain and
return to its original shape upon the removal of the load.
HOOKE’S LAW states that within certain limits (not to exceed the proportional limit) the
elongation of a bar produced by an external force is proportional to the tensile stress
developed. Hooke’s law gives the simplest relation between stress and strain.

Franklin E. Fisher
Professor Emeritus
Mechanical Engineering Department
Loyola Marymount University
Los Angeles, California
and
Raytheon Company
El Segundo, California

Compression Molding

Begins this process by measuring the amount of thermosetting plastic resin required to be placed in the mold cavity. Then the mold is heated and compressed so That the will of liquid resin fills the mold cavity and having a chemical hardening process so That its shape in accordance with the mold.

Generally this process is Used for phenolic resins, alkyd resins, aldehyde resins, and urea. Resins are Used to form powder, granular, flakes, rope, and rods.

Duty cycle of this process is Quite long, about 30-20 minutes. Mold temperature must be maintained Throughout the process and the temperature range of 250-400 F depending on the type of material.

Generally, molds are made of tool steel and in polishing so very good surface finishing.

Products Produced automotive electrical systems, plastic gear, plastic panels, etc.

Range of Motion and Strength ( Physical Ergonomics )

A number of measures are required to describe the capacity of an individual (or population) to achieve task performance (e.g., reach, lift, pull). Joint range-of-motion (ROM, also called mobility or flexibility) and joint (or muscle) strength begin to describe capacity and are especially relevant for tasks performed briefly or infrequently. Additional information will be required for highly demanding, prolonged, or frequent tasks, as well as additional types of measures (e.g., fatigue and environmental stress as described below).

Range of Motion

Joint ROM refers to the limits of joint motion and is represented as rotations about a given joint or of body segments (e.g., torso flexion). Two different forms of ROM are commonly measured. The first, passive (or assisted), involves external sources of force or moment to achieve joint motion. Examples include the use of gravity during a squat, to assess knee flexion, or forces /moments applied by an experimenter or device. The second, active ROM, requires muscle contraction to achieve joint motion and is associated with narrower motion limits than passive. In practice, the relevant type of ROM is determined by task requirements.

Measuring ROM from individuals is possible using a variety of equipment, from lowcost goniometers (for measuring included angles) to high-cost and sophisticated marker tracking systems. More often, population ROM data are obtained from a number of accessible sources (often in conjunction with anthropometric data). A number of factors can be expected to have an influence on ROM. Although ROM decreases with age, the changes are usually minimal in healthy individuals until the end of typical working life (i.e., 65). Women generally have higher ROM ranges, although gender differences are typically 10%. Little association has been found between anthropometry and ROM, although ROM does decrease with obesity. In simple cases, such as those involving one joint, application of ROM data is straightforward and follows similar methods described in anthropometry (e.g., using percentiles). When multiple joints are involved, it is common to use human modeling software to assess the potential limitations due to ROM.

Maury A. Nussbaum

Industrial and Systems Engineering

Virginia Polytechnic Institute and State University

Blacksburg, Virginia

Jaap H. van Diee¨n

Faculty of Human Movement Sciences

Vrije Universiteit

Amsterdam, The Netherlands

Centrifugal CASTING

Principle: Pouring molten metal into a rotating mold and molten metal due to centrifugal force will be compressed so that the workpiece is obtained without disabilities.

The casting is used extensively for casting plastics, ceramics, concrete and all metals.

Advantage Centriugal Casting:

1. Riser is not required

2. Squiggly Items can be processed with good surface quality

3. small dimensional tolerances

4. uniform thickness of workpiece

Centrifugal Casting Disadvantage:

1. Prices expensive equipment

2. Expensive maintenance costs

3. Low production rate

4. One product in one mold

5. Large centrifugal

Centrifugal casting can be divided into 2 types, namely:

A. Horizontal Centrifugal Casting

B. Vertical Centrifugal Casting

Engineering Plastics

Many thermoplastics are now accepted as engineering materials and some are distinguished by the loose description engineering plastics. The term probably originated as a classification distinguishing those that could be substituted satisfactorily for metals such as aluminium in small devices and structures from those with inadequate mechanical properties. This demarcation is clearly artificial because the properties on which it is based are very sensitive to the ambient temperature, so that a thermoplastic might be a satisfactory substitute for a metal at a particular temperature and an unsatisfactory substitute at a different one.

A useful definition of an engineering material is that it is able to support loads more or less indefinitely. By such a criterion thermoplastics are at a disadvantage compared with metals because they have low time-dependent

moduli and inferior strengths except in rather special circumstances. However, these rather important disadvantages are off-set by advantages such as low density, resistance to many of the liquids that corrode metals and above all, easy processability . Thus, where plastics compete successfully with other materials

in engineering applications it is usually because of a favourable balance of properties rather than because of an outstanding superiority in some particular respect, although the relative ease with which they can be formed into complex shapes tends to be a particularly dominant factor. In addition to conferring the

possibility of low production costs, this ease of processing permits imaginative designs that often enable plastics to be used as a superior alternative to metals rather than merely as a tolerated substitute.

Currently the materials generally regarded as making up the engineering plastics group are Nylon, acetal, polycarbonate, modified polyphenylene oxide (PPO), thermoplastic polyesters, polysulphone and polyphenylene sulphide. The newer grades of polypropylene also possess good basic engineering performance and this would add a further 0.5 m tonnes. And then there is unplasticised polyvinyl chloride (uPVC) which is widely used in industrial pipework and even polyethylene, when used as an artificial hip joint for example, can come into the reckoning. Hence it is probably unwise to exclude any plastic from consideration as an engineering material even though there is a sub-group specifically entitled for this area of application.

In recent years a whole new generation of high performance engineering plastics have become commercially available. These offer properties far superior to anything available so far, particularly in regard to high temperature performance, and they open the door to completely new types of application for plastics.

The main classes of these new materials are

(i) Polyarylethers and Polyarylthioethers

polyarylethersulphones (PES)

polyphenylene sulphide (PPS)

polyethernitrile (PEN)

polyetherketones (PEK and PEEK)

(ii) Polyimides and Polybenzimidazole

polyetherimide (PEI)

thermoplastic polyimide (PI)

polyamideimide (PAI)

(iii) Fluompolymers

fluorinated ethylene propylene (FEiP)

perfluoroalkoxy (PFA)

A number of these materials offer service temperatures in excess of 200°C and

fibre-filled grades can be used above 300°C.

PLASTICS
ENGINEERING
Third Edition
R.J. Crawford, BSc, PhD, DSc, FEng, FIMechE, FIM
Department of Mechanical, Aeronautical
and Manufacturing Engineering
The Queen’s University of Belfast
l E I N E M A N N
OXFORD AMSTERDAM BOSTON LONDON NEW YORK PARIS
SAN DlEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO

Butterworth-Heinemann
An imprint of Elsevier Science
Linacre House. Jordan Hill, Oxford OX2 8DP
225 Wildwood Avenue, Woburn, MA 01801-2041
First published 1981
Second edition 1987
Reprinted with corrections 1990. 1992
Third edition 1998
Reprinted 1999.2001, 2002
Copyright 0 1987, 1998 R.J. Crawford. All rights reserved
The right of R.J. Crawford to be identified as
the author of this work has been asserted in
accordance with the Copyright. Designs and
Patents Act 1988