Download Low-Volume Injection Molding PDF

TitleLow-Volume Injection Molding
TagsIndustries Casting (Metalworking) New Product Development Machine Tool Numerical Control
File Size2.3 MB
Total Pages17
Document Text Contents
Page 1

TOP STRATEGIES TO
HELP YOU TAKE FULL
ADVANTAGE OF THE
LVIM PROCESS

AN ENGINEER’S
GUIDE TO
LOW VOLUME
INJECTION MOLDING BY RONALD HOLLIS, Ph.D., P.E.

This eBook contains expert analysis

on Low Volume Injection Molding,

including all of the basics you need

to get yourself up to speed on fully

understanding the process. As well as

insider benefits and tips for getting the

most out of LVIM, this books contains

the 6 step process that will get your

products to market fastest and the

issues and limitations of LVIM.

Page 2

LOW-VOLUME INJECTION MOLDING
TO BRIDGE OR NOT TO BRIDGE

As with most things in life, folks tend to focus on the end

game, the score, the finale, but choose to ignore the many

critical steps and decisions that are made during the journey.

DEFINITION

Low-Volume Injection Molding

(LVIM) is a manufacturing method

that creates injection molds or tools

to produce functional parts from

thermoplastic in short runs of up to

typically 50,000 parts. Significantly

faster and cheaper, LVIM offers the

same quality, accuracy, and tol-

erance as production tooling, but

without 2D drawings.

WHY YOU NEED IT IDEAL USES

02 | MFG.com | An Engineer’s Guide to Low Volume Injection Molding

Page 8

INDUSTRY OVERVIEW — A NERD’S EYE VIEW OF LVIM

With current technologies and the growing acceptance of LVIM, applications of this process continue to expand,
making LVIM a standard element of the product development process. Decades before LVIM, a production tool was
predominantly focused on proving that a part could be molded successfully. In other words, product developers
had to use full-on production tooling to validate a part; there was no intermediary refinement process to see how
the part would “behave” in reality. But the LVIM process has evolved significantly with the use of CAD and CAM
technologies. It is now considered a very useful technology in the iterative development process.

There are many ways of using this process to get your products to market faster. Product developers often
use a “bridge tooling” strategy that includes both LVIM and production tooling, either in parallel or in sequence, to
support their goals.

Applications for LVIM are found in every industry sector: industrial, automotive, medical, lawn and garden,
and consumer electronics. Close tolerances and high-end appearance are ideal for today’s short run projects.

THE PROCESS OF MOLD MAKING

Making an LVIM is a fascinating process in which you create something to create something else. One of the
major challenges in the process is that you must create a mold or tool that can be used as a receptacle for molten
thermoplastic that holds the inverse or negative shape of the part you desire. While this sounds simple enough,
some special knowledge is required.

Making the physical tool is just a piece of the battle. The part geometry you design must be conducive to
the molding process, and the end-use material must be conducive to the part, as well as the mold. The many variables
of the process — design, materials, actions, and expectations — make the process of getting from tooling to parts a
challenge.

The more efficient LVIM process is similar to the tool making process in that it has existed for more than a
hundred years. As with sculpting, the tool maker eliminates what is not required and keeps only what is essential.

08 | MFG.com | An Engineer’s Guide to Low Volume Injection Molding

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Page 9

STEP BY STEP: MAKING A MOLD

Mold making is a complex science that requires a high level of expertise in design, materials, and physics, along with

artistic and intuitive insight, all part of the mold maker’s trade. A highly valued and specialized craftsman “begins

at the beginning.” He starts with a great plan for a well-designed part and follows through with flawless execution,

resulting in a very smooth, high-quality injection mold.

If those of you who are engineers are scratching your heads, you are not alone. For some reason, this valuable mold-

making module is not taught in engineering school, so here’s an important addition to every designer’s knowledge

base. Step by step, this is how you make a mold.

When designing a mold, make sure it is conducive

to injection molding. The design process for

plastic parts is critical, taking into account the

“moldability” of a shape. With today’s easy-to-

use CAD software in the hands of very “green”

designers, it is common for parts to be designed

that can be prototyped successfully with SL,

SLS, and FDM, and accepted by the customer.

However, these parts may yet still be unable to be

injection molded. This can often cost your company

thousands of dollars in errors, issues, and lost

opportunities.

Early in the process, the expert tool maker closely

considers all that could go wrong with a design.

Defects that result from poor design arise due to lack

of draft, parting line problems, poorly fitting ejector

pins, and poor materials selection, among other things.

Consequently, the next steps happen electronically in

CAD during your design process.

A) Assess the part for the injection-molding process or Design for Manufacturability (DFM)

PLAN HOW TO MAKE THE MOLD1

09 | MFG.com | An Engineer’s Guide to Low Volume Injection Molding

Page 16

SAVING MONEY, SAVING TIME

Informed engineers always verify their design in LVIM to save money. For example, a medical equipment company spends

$300,000 per year in SLM and then moves into LVIM to verify the part design, while an automotive company uses LVIM

to verify the part design for its customer. Integrating production suppliers into the LVIM process helps everyone with the

learning curve of manufacturing a part. Purchasing LVIMs after the release of the production order gets the customer to

sign off early on the parts before submitting designs to production. And of course, always provide the final file versions at

time of order, knowing that the clock cannot start on your job until all data is received.

IN MANUFACTURING, ALMOST EVERYTHING YOU DO CAN SAVE MONEY

Build a mold that is able to support the quantity

of parts required.

Forecast accurately to avoid exceeding market

allowance in per-piece price.

Learn the limitations of the process — radii,

tolerances, feature size, and wall thickness.

Design with cutouts or windows for snap features,

making manual tool access easier.

Always verify your part is capable of being injection

molded using DFM2 rules and regulations.

With large parts, use methods of design that allow

for fully CNC-machineable parts to reduce EDM3.

Troubleshoot the design with RP prior to making

a part to avoid rework in mating or function.

Working with a single cavity versues multiple

cavities aids in preventing molding issues.

Produce marketing samples to receive solid

feedback from your target market.

Clearly define and communicate all part and

project specifications at the beginning.

Request sample LVIM parts and use functional

samples in assembly setup.

Keep parts as simple as possible to eliminate

hand loads and additional tooling costs.

Understand the proper and best use of LVIM over

CU1 for certain designs — LVIM can be more cost

xxxeffective after running about 50 parts.

Consider producing parts in large batches over

longer periods and running total parts for one

xxxyear to offset price per part.

When exceeding 10,000 parts at a time, add

automatic slides to reduce cycle times.

Use LVIM when a low quantity of parts is needed

and a production tool is unnecessary.

1 CU: Cast Urethanes
2 DFM: Design for Manufacturing
3 EDM: Electrical Discharge Machining

16 | MFG.com | An Engineer’s Guide to Low Volume Injection Molding

Page 17

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THE CLOCK ON YOUR JOB CAN’T START UNTIL ALL DATA IS RECEIVED

From sending the wrong revision to hoping that non-conducive geometries might somehow work, many tools are built

in error, wasting money. Parts with particularly thick sections undergo significant shrinkage defects to the entire diameter

of the part, causing failure. Expensive tooling changes and engineering change orders (ECOs) are often required to

compensate for part design issues.

Design decisions can also waste capital. Avoid designing parts that

have side actions, and watch out for designs that need multiple

threaded inserts — Additional costs hide in parts designed with

many side actions. With these parts, customers often expect a

much lower price than what they actually get.

Wrong expectations are the biggest waster of time and money.

Don’t expect that a tool with multiple actions or inserts can be

made on a short LVIM timeline when its manufacture truly requires

a 12-week schedule.

Remember: It’s very expensive to change a mold requiring the addition

of material in order to create a new feature. But if you follow the steps

and advice found in this book, you will no doubt save time, money,

and get your products to market faster.

“One automotive company tried to switch
from PC to acrylic after

tool completion and
was unable to produce
acceptable parts. With

orders for both materials
already sold, they were

faced with providing
product made of only

one material.

17 | MFG.com | An Engineer’s Guide to Low Volume Injection Molding

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