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UNIVERSITI PUTRA MALAYSIA
REDUCING PRODUCTION LEAD TIME THROUGH VALUE STREAM
MAPPING APPROACH
YAP AI KIN
FK 2008 90
REDUCING PRODUCTION LEAD TIME THROUGH VALUE STREAM MAPPING
APPROACH
YAP AI KIN
MASTER OF SCIENCE UNIVERSITI PUTRA MALAYSIA
OCTOBER 2008
Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfillment of the requirement for the degree of Master of Science
REDUCING PRODUCTION LEAD TIME THROUGH VALUE STREAM MAPPING APPROACH
By
YAP AI KIN
October 2008
Chairman : Tang Sai Hong, PhD Faculty : Engineering
The plastic injection molding has been widely used in the manufacturing industry
due to its advance improvement in producing complex net shaped parts. However, there is
still lack of efforts in the concept of early cost estimation on mold and most of the
injection molders do not have adequate mechanisms to rapidly estimating the mold cost.
This paper addresses the development of a method in estimating the cost of a plastic
injection mold at the early stages of design. In this research, an early cost estimation
formula for plastic injection mold had been developed from the ten sets of historical data
of existing injection molds. This estimation formula had been tested with another four
sets of molding part to check for its feasibility study. These all sample sets of injection
molds were from a variety of part sizes and complexity designs from a local injection
moldmaker. All tested molding parts were selected from the mold type of two-plate with
cold runner system. The mold cost formula was derived from the part’s envelope volume,
number of part dimensions, number of part actuators and part’s dimension tolerance as
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the mold cost independent variables. The strength of the relationships between the mold
cost and its independent variables were investigated by using the statistical linear
regression analysis. The results of analysis indicated that the number of part dimensions
has the highest significant correlation with the mold cost, followed by the part’s envelope
volume and then the number of part actuators, while the variable of dimension tolerance
did not show a significant correlation to the mold cost.
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Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai memenuhi keperluan untuk Ijazah Master Sains
PENGURANGAN JANGKA MASA PENGHASILAN MELALUI KAEDAH PEMETAAN ALIRAN NILAI
Oleh
YAP AI KIN
October 2008
Pengerusi : Tang Sai Hong, PhD Fakulti : Kejuruteraan
Acuan suntikan plastik telah semakin luas digunakan dalam industri pembuatan.
Ini disebabkan perkembangannya yang pesat dalam penghasilan produk yang kompleks
dan bentuk bersih. Walau bagaimanapun, konsep anggaran awalan kos pada acuan masih
kurang dalam usaha dan kebanyakan pembuat acuan tidak mempunyai mekanism yang
sesuai untuk menganggar kos acuan dengan cepat. Kertas ini akan membentangkan satu
pembangunan kaedah untuk anggaran kos acuan suntikan plastik pada awalan langkah
rekabentuk. Dalam penyelidikan ini, satu formula anggaran awalan kos untuk acuan
suntikan plastik telah dibentukkan dari sepuluh set data sejarah kos acuan suntikan yang
sedia ada dan formula anggaran ini telah diuji kebolehlaksanaannya dengan empat set
produk pengacuan yang lain yang diperolehi daripada pembuat acuan tempatan. Set-set
data sampel ini adalah terdiri dari pelbagai jenis saiz produk dan kekompleksan
rekabentuk. Produk pengacuan yang telah diuji adalah dipilih dari jenis acuan 2-plat
dengan sistem pelari sejuk. Formula kos acuan ini diterbit dari liputan isipadu produk,
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bilangan dimensi produk, bilangan penggerak produk dan had-terima dimensi sebagai kos
acuan pembolehubah tak bersandar. Kekuatan hubungan antara kos acuan dengan
pembolehubah tak bersandarnya dikaji dengan menggunakan analisis regresi lelurus
statistik. Keputusan analisa ini menunjukkan bilangan dimensi untuk produk mempunyai
korelasi bererti yang paling tinggi dengan kos acuan, diikuti dengan liputan isipadu dan
bilangan penggerak, sementara pembolehubah had-terima dimensi tidak menunjukkan
korelasi bererti dengan kos acuan.
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ACKNOWLEDGEMENTS
Firstly, I would like to express my gratitude to the chairman of the supervisory
committee, Dr. Tang Sai Hong for his invaluable supervision, guidance and comments
throughout the duration of my research project. I would also like to thank the member of
the supervisory committee, Associate Professor Dr. Datin Napsiah Ismail for her guidance
and patience.
Not forgetting to thank Mr. Khoo from STS Mould-Tech Sdn. Bhd. who has permitted
their products to be used as specimens in this research. I am thankful to his assistant, Mr.
Jeffrey, who has extended his assistance and precious time in preparing the information
data for me in this research as well as for the second mold maker, Sun Tech Sdn. Bhd. for
their evaluation samples. Without their collaborations, I would not be able to complete
my research.
In addition, I also would like to express my appreciation to my college, especially my
superior, Tuan Haji Mesran and all the staffs at KUALA LUMPUR INFRASTRUCTURE
UNIVERSITY COLLEGE (KLIUC) for their understanding and encouragement all this
while in completing my degree in Master of Science.
I am most grateful to Yayasan Kedah for their support in the form of study loan that has
greatly reduced my financial burden so that I can concentrate fully on my studies. Last
but not least, I am also indebted to my beloved family and husband, Yong Chin Keong for
their patience and concern during the years of my study.
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I certify that a Thesis Examination Committee has met on 30th October 2008 to conduct the final examination of Yap Ai Kin on her Master of Science thesis entitled “Reducing Production Lead Time Through Value Stream Mapping Approach” in accordance with the Universities and University Colleges Act 1971 and the Constitution of the Universiti Putra Malaysia [P.U.(A) 106] 15 March 1998. The committee recommends that the student be awarded the Master of Science.
Members of the Thesis Examination Committee were as follows:
Shamsuddin Sulaiman, PhD Professor Faculty of Graduate Studies Universiti Putra Malaysia (Chairman) Megat Mohamad Hamdan Megat Ahmad, PhD Associate Professor Faculty of Engineering Universiti Putra Malaysia (Internal Examiner) Mohd Khairol Anuar Mohd Ariffin, PhD Lecturer Faculty of Engineering Universiti Putra Malaysia (Internal Examiner) Norhamidi Muhamad, PhD Associate Professor Faculty of Engineering Universiti Kebangsaan Malaysia (External Examiner)
________________________________
HASANAH MOHD GHAZALI, PhD Professor and Dean School of Graduate Studies Universiti Putra Malaysia Date: 29 January 2009
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This thesis was submitted to the Senate of Universiti Putra Malaysia and has been accepted as fulfillment of the requirements for the degree of Master of Science. The members of the Supervisory Committee were as follows:
Tang Sai Hong, PhD Associate Professor Faculty of Engineering Universiti Putra Malaysia (Chairman) Napsiah Binti Ismail, PhD Associate Professor Faculty of Engineering Universiti Putra Malaysia (Member)
_________________________________
HASANAH MOHD GHAZALI, PhD Professor and Dean School of Graduate Studies Universiti Putra Malaysia
Date: 12 February 2009
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DECLARATION
I declare that the thesis is my original work except for quotations and citations which have been duly acknowledged. I also declare that it has not been previously and is not concurrently submitted for any other degree at UPM or at any other institution.
_____________________
( YAP AI KIN ) Date:
TABLE OF CONTENTS
ABSTRACT ABSTRAK ACKNOWLEDGEMENTS APPROVAL APPROVAL DECLARATION LIST OF TABLES LIST OF FIGURES LIST OF ABBREVIATIONS/SYMBOLS
CHAPTER 1 INTRODUCTION
1.0 Background of the Study 1.1 Problem Statements 1.2 Objectives 1.3 Scope of Study 1.4 Overview of the Thesis
2 LITERATURE REVIEW
2.0 Introduction 2.1 Principal Types of Injection Mold
2.1.1 Cold Runner Molds 2.1.2 Hot Runner Molds
2.2 Injection Mold Design and Construction 2.2.1 Mold Base 2.2.2 Cavity and Core 2.2.3 Mold Surface Finish
2.3 Mold Material 2.3.1 Mold Base Steel 2.3.2 Cavity Steel
2.4 Mold Cost Drivers Characteristics 2.4.1 Geometry 2.4.2 Material 2.4.3 Manufacturing Processes
2.5 Cost Function Approximation Using Regression Analysis 2.5.1 Hypothesis Testing in Linear Regression 2.5.2 Statistical Terminology
2.6 Definition of Cost Estimation 2.7 Methods of Developing Cost Estimation 2.8 Recent Researches in Cost Estimation 2.9 Review on Researches in Injection Mold Cost Estimation Models
Page
ii iv vi vii viii ix xii xiii xv
1 3 4 5 5 7 7 8 10 11 11 17 21 23 24 24 26 27 31 32 33 35 37 38 38 40 42
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2.9.1 Dixon and Poli’s Research 2.9.2 Boothroyd, Dewhurst and Knight’s Research 2.9.3 Fagade and Kazmer’s Research 2.9.4 Conclusions
3 METHODOLOGY
3.0 Introduction 3.1 Research Design & Planning 3.2 Data Preparatory
3.2.1 Selection of Research Samples 3.2.2 Data Collection 3.2.3 Data Recording
3.3 Data Analysis Using SPSS 3.3.1 Development of Cost Estimation Model 3.3.2 Examining the Linearity of Variables 3.3.3 Bivariate Correlation Hypothesis Testing 3.3.4 Examining the Model Fit from Residuals Analysis
3.4 Model Verification
4 RESULTS AND DISCUSSIONS
4.0 Introduction 4.1 Output of Collection data 4.2 Output of Scatterplot 4.3 Output of Multiple Linear Regression 4.4 Output of Hypotheses Testing 4.5 Output of Examining the Model Fit 4.6 Output of Alternative Cost Estimation Model 4.7 Output of Model Verification 4.8 Overall Discussions on Cost Estimation Models
5 CONCLUSIONS AND RECOMMENDATIONS
5.0 Introduction 5.1 Conclusions 5.2 Recommendations
REFERENCES APPENDICES BIODATA OF THE STUDENT
42 45 48 54 55 57 58 58 59 66 68 68 69 70 71 72
74 74 74 78 81 84 89 92 95
98 98 100 102 106 207
LIST OF TABLES
Table Page 2.1: Price Index for Various Surface Finish Categories (DSM Design) … ............... 28
2.2: Two Ranges of Dimensions Tolerance and Price Index for ABS Molded Part
(Extracted from Figure 2.17) ........................................................................... 29
2.3: Data for Multiple Linear Regression ................................................................... 35
2.4: Attributes For Size And Basic Complexity, Cb .................................................. 43
2.5: Quotes and Attributes of Observed Parts ........................................................... 50
2.6: Counting Dimensions of Gasket Disk ……… .................................................... 51
3.1: Guide Line to Differentiate the Level of Dimensions Tolerance ........................ 65
3.2: Collection of Data Based on 10 Sets of Sample Parts ......................................... 67
3.3: Independent Variables of Mold Cost ................................................................... 69
3.4: Data Entry Used in SPSS Analysis ..................................................................... 70
3.5: Data Collection and Data Variables for Evaluation Samples .............................. 72
4.1: Collection of Data Based on 10 Sets of Sample Parts ......................................... 75
4.2: Descriptive Statistics for All Variables ............................................................... 78
4.3: Variables Entry Method ...................................................................................... 79
4.4: Model Summary Statistics ................................................................................... 79
4.5: Regression Coefficients ....................................................................................... 80
4.6: ANOVA Table .................................................................................................... 81
4.7: Correlation Matrix ............................................................................................... 83
4.8: Descriptive Statistics for Standardized Residuals ............................................... 87
4.9: Case Summaries for the Model Observed, Predicted and Residuals Value ........ 89
4.10: Variables Entry Method .................................................................................... 90
4.11: ANOVA Table ................................................................................................. 90
4.12: Model Summary Statistics ................................................................................. 91
4.13: Regression Coefficients for Alternative Model ................................................. 91
4.14: Output of Evaluation Samples from First Cost Estimation Model ................... 93
4.15: Output of Evaluation Samples from Alternative Cost Estimation Model ......... 94
4.16: Summary of the Independent Variables for First Regression Model ................ 95
4.17: Summary of Independent Variables for Alternative Regression Model ........... 96
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LIST OF FIGURES
Figure Page 2.1: A Two Plate Cold Runner Mold (KenPlas Industry Ltd.) .................................. 9
2.2: A Three Plate Cold Runner Mold (KenPlas Industry Ltd.) ................................ 9
2.3: A Hot Runner Mold with External Heated Manifold and Drops (KenPlas
Industry Ltd.) ................................................................................................... 10
2.4: A Two-Plate Standard Mold Base and Some of Its Standard Components
(Bryce, D.M., 2005) ......................................................................................... 12
2.5: The New DME Comprehensive Line of Euro-Standard Metric Mold
Components (D-M-E Company) ...................................................................... 13
2.6: A Complex Mold for Part with Undercut Sliding Cam Action (DSM Design
Guide, 2005) ..................................................................................................... 14
2.7: Example of Calculation on Estimation of Four-Cavity Mold Base ................. 14
2.8: Different Type of Ejectors Used in Ejection System (D-M-E Metric
Components Catalog) ....................................................................................... 16
2.9: Type of Ejector Used in Related with Different Shape of Part in Mold (D-M-E
Metric Components Catalog) ........................................................................... 16
2.10: Two Methods of Cavity Mounting .................................................................. 18
2.11: Undercut Features (Fu et al. 1999) .................................................................. 19
2.12: Components Set in Slider Assembly (OMNI Mold Systems Catalog) ........... 19
2.13: Components Set in Lifter Assembly (OMNI Mold Systems Catalog) ............ 20
2.14: A Slider and Lifter Assembly (Fuh et al., 2004) ............................................. 20
2.15: Steps of the Mechanical Surface Treatment (Menges and Mohren, 1993) 22
2.16: Mold Base and Cavity Inserts in Mold Assembly (Colton, J.S., 2005) .......... 23
2.17: Practical tolerances on dimensions of molded part made of ABS plastic
material, which was developed by the Society of the Plastics Industry, Inc.
(Menges and Mohren, 1993) ............................................................................ 30
2.18: Basic Envelope and Undercuts ....................................................................... 43
2.19: Principal Mold Base Cost Driver .................................................................... 47
2.20: Placement of Four Cavities in A Mold Base ................................................... 47
2.21: Sketch of A Low Complexity Part, Gasket Disk ............................................. 51
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3.1: A Schematic Representation of a Sequence of Research Processes................. 56
3.2: Steps Involved in the Data Collection Stage .................................................... 61
3.3: Single Cavity Layout in A Mold ...................................................................... 64
3.4: Two Cavities Layout in A Mold ....................................................................... 64
3.5: Basic Steps Involved in Data Analysis SPSS ................................................... 68
4.1: Scatterplot Matrix ............................................................................................. 77
4.2: Scatterplot Matrix with Add On Best-fit Lines ................................................ 77
4.3: Standardized Predicted Values versus Observed Values ................................. 85
4.4: Standardized Residuals versus Predicted Values ............................................. 86
4.5: Histogram of Standardized Residual for Regression Model ............................ 87
4.6: Normal P-P Plot of Standardized Residual for Regression Model .................. 88
LIST OF ABBREVIATIONS/SYMBOLS
d Number of dimensions for a single cavity part
a Number of actuators for a single cavity part
v Envelope volume for a single cavity part in mm3
n Number of cavities
CMold Estimated mold cost in RM k
TEV Total envelope volume for n cavities parts in cm3
TPD Total number of dimensions for n cavities parts
TPA Total number of actuators for n cavities parts
HT High dimension tolerance
HF High surface finishing
β Regression coefficients
ρ Observed significance level
R Multiple correlation coefficient
R2 Multiple determination coefficient
R2adj Adjusted R2
Bhn Brinell hardness number
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CHAPTER 1
INTRODUCTION
1.0 Background of the Study
Nowadays the market trends and demands have changed towards a higher quality,
shorter delivery time and lower product cost. An understanding about the elements to
make up of a product cost has become more vital due to the competitive nature between
global companies. Generally, for most products and designs, cost becomes an important
concern in the early stage of development.
To be competitive, it is necessary to keep the initial cost as low as possible, as well as to
minimize the time-to-market in order to reach the maximization of profits. Studies have
shown that the greatest potential for cost reduction is at the early design stages, where
as much as 80% of the cost of a product is decided (Rehman, 1998; Geiger, 1998;
Weustink et al., 2000). Consequently, after the design process has been completed, most
opportunities of cost reduction have passed. Therefore, it is necessary to understand the
cost consequences of decisions during the planning phases of the product development
cycle. In these planning phases, many decisions have to be taken into consideration. The
engineers often need to consider a design alternative for design-to-cost in order to make
cost effective decisions in the product design process as well as to speed up the design
process planning and cost estimating activities. In the quotation preparation, cost
estimation is a critical activity that directly affects quotation acceptability and
profitability (Ni et al., 2007). Generally, this research is intended to develop an
approach to estimate cost in the early design stage by defining the economical method
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in manufacturing a product.
Plastic injection molding has been recognized as an important industrial manufacturing
process in conjunction with the extensive usage of a wide range of complex net shaped
plastic products, principally from domestic electronics and electrical products to
machineries, cars and airplanes. Due to an intense competitive market, the engineers
always need to be able to estimate the cost of a mold based on the customer’s given
part’s blueprint or sample with some basic tooling information, for example, number of
cavities and mold production cycle life to generate a quotation in a short period of time.
Injection molding is a process in which a polymer is heated to a highly molten state and
forced to flow under high pressure into a set of completed tools namely injection mold,
where it shapes and then cools the melted plastic that is injected into it. The molded
part, called a molding, is then removed from the mold cavity. Injection mold is
generally constructed by two main parts that are made of tool steels, that is mold
cavities and mold base. The mold cavities are machined out from small blocks of tool
steels, hardened and inserted into a standard mold base. For moldmaker companies
wishing to maintain the competitive edge in the global markets, it becomes necessary to
compromise the priority tooling requirements as minimum cost, shorter lead-time and
better quality with customers (Nagahanumaiah et al., 2008; Rahmati and Dickens,
2007).
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1.1 Problem Statements
Even though the concepts of early cost estimation in the product design phase have been
recognized in the last two decades of the 20th century, there are still lack of efficiency
due to the traditional cost estimation system do not have adequate mechanism to
provide engineers with a rapid cost feedback on a proposed new product. The traditional
cost estimation approaches are primarily based on cost similarity have limited
capabilities for accurate estimation of mold cost (Nagahanumaiah et al., 2008). Most
customers will have the behavior to seek for alternative designs in estimating the cost of
project until their satisfactions are achieved. This can cause lots of inconveniency to the
engineers because the redesigning process is very costly and time consuming.
Normally, engineers will base on their experiences to estimate the cost of project in
order to meet the customer requirements.
Many researches had been studied on the cost of injection mold in the past. However,
the researches made are insufficient for practical use and needs improvement. The
research from Dixon and Poli (1995), which estimates the relative tooling cost of an
injection molded part by referring relatively to a tooling cost for a simple reference part,
has encountered many difficulties particularly the lack of information and the rough
design descriptions found in the look-up table for the attributes of part’s complexity.
Whereas Boothroyd et al. (1994) used the total estimated manufacturing times for a
finished mold multiplying with an average mold shop hourly rate to get the estimated
tooling cost. The manufacturing time is difficult to be defined accurately in the early
design stage due to the different types and advance levels of machine used. Even though
Fagade and Kazmer’s (2000) have come out with a better empirical approach to
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estimate a tooling cost, however, their empirical formulas derived from multiple
regression analysis in late 20th century may not suitable to apply in today’s local market
due to the increasing global price of steel and different resource regions.
The accuracy of the cost estimation is crucial to a company. Any of underestimation
and overestimation may bring loss to the company if awarded or lost in the bidding for
the job. Presently, the cost estimation is carried out mainly based on experience or
historical cost data, which compares the part to one made in the past, making due
allowance for the differences that could lead to inaccurate and inconsistent estimation
(Fuh et al., 2004). Obviously, a quick and systematic early cost estimation tool is
needed for both mold quotation and design engineers so that they can easily make faster
and more accurate cost estimation relatively to their design-decisions. An updated mold
data is needed to be re-collected to suit the present local market as well.
1.2 Objectives
The objectives of this research are:
i) To develop a mathematical model at the early stages of plastic injection
mold tooling design based on the analysis of historical mold designs and
cost data from a local injection moldmaker company.
ii) To identify the main cost factors for a plastic injection mold and their
relative importance relationships in the mold cost by using regression
analysis.
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1.3 Scope of Study
The scope of this thesis is confined to the establishment of a linear cost estimation
function for a two-plate mold with cold runner systems of local plastic injection mold
with a maximum of two cavities. The way to carry out this study is to build an empirical
model relative to the dependent (criterion) and independent (predictor) variables based
on 10 sets of existing finish mold costs and designs. These 10 sets of data are collected
from a wide range of plastic part sizes and complexity from a designated local
moldmaker. Multiple linear regression analysis is the best statistical technique to be
used in manipulating the empirical model. A well known computer software program,
known as SPSS is used in fitting the multiple regression model as well as defining the
parameter quantities that reflects the importance of information about the regression
models.
1.4 Overview of the Thesis
The layout of this thesis is divided into five chapters. The first chapter is the
introductory section of the research with its descriptions on the problem statements and
the research objective. In addition, the scope of thesis also is well explained. The
second chapter cites the relevant literature reviews from previous researchers as well as
the theories and the hypotheses tested in the research.
Chapter three is to describe the methodology used for this research. This includes the
initial stage of the research design and planning, the data preparatory stage and data
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analysis with using SPSS. The data preparatory stage consists of the selection of
research sample, data collection from hardcopy of drawings and lastly the data
recording into a proper table. After all data has been keyed into the SPSS program, the
statistical regression analysis is performed with undertaking a few hypothesis tests to
examine the feasibility of the research results.
All outputs generated from the SPSS analysis will be clearly defined in an orderly
fashion in chapter 4 with appropriate plots and tables. The finding of the outcomes are
interpreted and discussed to validate the objective stated in this study. Chapter 5 is
about the conclusions reviewed and the important observations gained from this
research study. Recommendations to improve the research’s gaps are also proposed for
future researches.
CHAPTER 2
LITERATURE REVIEW
2.0 Introduction
The acknowledgement of the importance of early cost estimation for a product is slowly
being recognized in most fields to compete in the basis of cost leadership marketplace
for producing high-functioning and low-cost designs.
However, all too often, the industrial past practice in product cost estimation is to wait
for a complete cost analysis in a detail phase derived from the various cost components
such as material cost, machining cost, labor cost, administration and engineering cost. If
the product cost was proven to be excessive, they will try to wring the excess cost out of
the manufacturing process or to substitute a less expensive material, which is usually at
the expense of quality. Therefore, a fairly accurate estimation cost in the early design
stage is essential not only for saving product cost but also to improve productivity and
product quality if changes to the product were made in the early stage.
2.1 Principal Types of Injection Mold
There are two main types of injection mold, that is, a cold runner injection mold which
can be divided to two plate and three plate designs, and a hot runner injection mold
which is also known as the runnerless mold. A runner is the channel in the mold that
conveys the melted plastic from the barrel of the injection molding machine to the part.
The significant difference between these two types of mold is the presence of a runner
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system (sprue and runner) with molded part in the cold runner mold. A cold runner
mold type is very simple and much cheaper than a hot runner system. This is because of
the cold runner mold requires less maintenance and less skill to set up and operate.
2.1.1 Cold Runner Molds
The two plate is the simplest type of mold. It is called a two plate mold because there is
one parting plane and the mold splits into two halves, one half reams on the injection
side containing the plastic part, runner system, cavity cooling system while the moving
half containing core cooling system and ejector pins, mounted with the machine clamp
as shown in Figure 2.1. A simple part with large gate is usually molded in a two plate
mold. Sometimes it is also needed for a low activity and less expensive mold that is less
than 10,000 per year. A disadvantage of the two plate mold is that the molded parts
remain attached to the runner systems. Thus, a post molding operation is needed to exert
in order to trim off the runner system.
A three plate mold differs from a two plate in that it has two parting planes, and the
mold splits into three sections every time the part is ejected. Since the mold has two
parting planes, the runner system can be located on one, and the part on the other.
Generally, the three plate mold separates the molded part from its runner system
automatically when the mold opens as shown in Figure 2.2. Three plate molds are used
because of their flexibility in gating location. It is normally used for multi-cavity
molding parts.
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