Injection Molding Plastics Design Validation
There are many ways to validate your injection molding design. Are you doing it the right way? Find out from a top injection-molding house.
Injection-molded plastics enable design
engineers to overcome an array of design challenges, including
producing complex, aesthetically interesting shapes, creating
custom-tailored part properties for specific applications and
developing cost-effective solutions for high-volume part production.
Manufacturing plastic parts requires that both the part and mold
designs be optimized, which can be difficult. Additionally, the final
production of a part involves balancing a complex mix of time,
temperature, and pressure variables at the injection-molding machine,
which if incorrectly specified will result in a multitude of
manufacturing defects.
By John Pflueger
Each of these domains-part design, mold design, and process
development-is an extensive discipline requiring substantial
domain-specific knowledge. Individuals in each of these domains may not
realize the impact of their decisions on the other domains and
associated requirements. For example, consider material selection and
use. There are thousands of grades of commercial plastic materials,
each with widely varying processing characteristics. Part designers
select a material for its physical properties, but may not know how it
behaves during processing. Mold designers may understand the material's
manufacturing properties, but not be aware of how this material
addresses the part designer's needs. Machine operators may have the
best natural understanding of material processing characteristics, but
not understand how the choice of process parameters affects the
physical properties of a molded part.The Allure and Challenge of Plastics
Because of the complexity of these domains, there is a natural tendency
for individuals to pass their work on to the next person in the chain
without considering downstream impact. This is even more likely when
individuals are separated geographically and are under the pressure of
compressed project timelines. They dismiss potential future issues as
Someone Else's Problem.
In this two-part series specifically focused on the plastics injection
molding design-to-manufacturing process, we examine Someone Else's
Problem Syndrome (SEPS) and how to mitigate or avoid its effect. In
Part One, we characterize the impact of SEPS, explain how to identify
it within your organization and provide example tools currently
available to address your situation. In Part Two, we will describe how
these tools can be used to avoid SEPS and ensure that molded parts
satisfy the original design intent and meet end-user application
requirements.Someone Else's Problem Syndrome
Symptoms of SEPS include projects that are over budget or behind
schedule, products that are late to market, and substandard parts that
do not meet performance requirements or are prone to fail in end-use
applications. In this environment, upstream members of a
design-to-manufacture team have not ensured that part and mold designs
are optimized for form, fit, function, and manufacturability.
Every design decision made by a plastics part designer will affect
manufacturability, final part properties, and overall costs. Because of
the complexity of the process, it is unreasonable to expect the part
designer to anticipate all of the manufacturing consequences of a
design decision. However, the part designer cannot completely dismiss
manufacturing constraints. When a part designer assumes that a
moldmaker can address all manufacturing issues arising from part design
decisions, he may be guaranteeing project delays, higher costs, and
lower part quality.
The decisions of the mold designer have effects both downstream and
upstream. He may design a nonoptimized mold, expecting manufacturing to
resolve the problem of producing good parts at an efficient cost. The
mold designer may place gate locations in areas that are visually
significant to the part designer. Historically, these types of
production issues have been uncovered as sample parts are produced.
Part or mold design changes at this stage can be costly and
time-consuming to implement.
Firms like Original Concepts Design (Mt. Laurel, NJ) are frequently
brought into situations to mitigate the consequences of problematic
design decisions as well as provide Moldflow analysis-consulting
services prior to tool design and manufacturing. Greg Janice, president
of Original Concepts Design explains, "There are times when we are
forced to make the best of a nonoptimized part design. I've also seen
entire tools scrapped because of parts that were not analyzed at the
time they were created. These problems could have been resolved easily
and quickly with optimization tools such as those available in Moldflow
Plastics Advisers products."
Consider recent projects in which you were involved. Did a mold need
costly and time-consuming rework? Did molded parts have unacceptable
defects? Did you lose time to market because it was difficult to find
an acceptable processing window for a hard-to-run mold? If so, your
company may be infected with SEPS. Read on to learn how to begin
rehabilitation.Tools for Analysis and Simulation of Plastics Part Manufacturability
Today's plastics part and mold designers are under tremendous pressure.
Project timelines are being compressed; scaling to high-volume
production may occur overnight; design and performance requirements
push for thinner-walled, higher-pressure molding; mold design, mold
production, and part production often occur halfway across the globe;
and material choices are greater than ever. Fortunately, relatively
recent advances in technology have resulted in 3D solids-based,
easy-to-learn, and easy-to-use plastics design optimization tools for
all members of the design-to-manufacturing team. Part and mold
designers do not have to be particularly skilled in traditional
computer-aided-engineering or finite-element analysis. With the proper
tools, these engineers can identify the unintended consequences of
their design decisions early, at a time when corrections can be made
quickly and most cost-effectively. Part and mold designers no longer
have to pass their problems to someone else downstream.
By using plastics design optimization tools, engineers can investigate
the effects of their design decisions on the filling patterns and
pressure and temperature distributions in the mold cavities. Part
designers can perform simple analyses that enable them to optimize wall
thicknesses, validate material selection, and determine whether
particular design features affect part manufacturability. Part
designers can investigate the effect of different gate locations and
the presence and severity of cosmetic defects such as weld lines, air
traps, and sink marks.
Advanced tools extend these capabilities, enabling the design, analysis
and optimization of single-cavity, multicavity, and family mold
layouts. Mold designers can reuse the part designers' work and
investigate a number of advanced issues, including the effects of
changing the part orientation in the mold, variations in runner system
geometry, and hot versus cold runners. Mold designers can determine
optimal sizes for runners and gates to balance flow to all cavities,
minimize cycle time, and ensure minimum material usage and uniform part
properties.
Moldflow's design analysis solutions in this area are four tools in its
Moldflow Plastics Advisers product line: Part Adviser, for the engineer
responsible for part design; Mold Adviser, for the engineer responsible
for mold design; and Cooling Circuit Adviser and Performance Adviser,
for those needing more detailed analyses of cooling, shrinkage, and
warpage issues. Given that injection molds can cost anywhere from
thousands to hundreds of thousands of dollars (and up!), optimizing a
layout before cutting steel is an absolute requirement to avoid
unnecessary rework and lost time to market.How to Avoid SEPS
In Part Two, we will discuss how proper use of these tools and
interpretation of analysis results help engineers understand the
consequences of their design decisions-eliminating the possibility that
engineers will send poorly understood designs downstream and make them
Someone Else's Problem.
Part two of this article will run in the next issue of Time- Compression Technologies magazine.
For more information, contact John Pflueger, Ph.D., Moldflow Corporation (Wayland, MA) visit www.moldflow.com
