MIM Design Guide

8/12/2019 MIM Design Guide

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MIM offers greater design freedom than many other production processes. Thecombination of plastic injection molding criteria and powdered metal means de-

signers are free from traditional constraints associated with trying to shape stain-

less steel, nickel iron, copper, titanium and other metals. Metal Injection molding

(MIM) is ideal for manufacturing components small in size, typically weighing be-

tween .02 grams and 400 grams.

Staging examp

Wherever possible, parts being

designed for MIM should have

the lowest volume (minimum

cross-section) to meet these

criteria:

Sufficient structural

strength to support loads

and keep deflection within

acceptable limits.

Adequate wall thickness

for proper flow - .05-.10

is optimal.

Uniform cross-sections, or

thick-to-thin material flow.

These guidelines ensure that

cross-sections are kept to a

minimum, reducing bothprocessing time and material

usage resulting in reduced

costs and improved perfor-

mance.

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2

3

Metal injection molding often

makes it possible to integrate

and consolidate several compo-

nents into a single molded

piece. This advantage reduces

the need to work with several

manufacturers, decreasing

processing and assembly costs,

while increasing the structural

integrity of the finished compo-

nent. Since the MIM process

produces components with

excellent mechanical properties

and supports ease of manufac-

ture, it is ideally suited to com-

plex, multi-functional part

design.

Additional features that would

normally add cost using other

manufacturing processes can

be included using MIM without

adding cost to the part.

Texture, knurling, threads,

lettering and company logos

can be incorporated into the

die, which translates to mini-

mal tooling costs, if any, and

does not add any cost to the

component being produced.


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Processing considerations:

Practical cross-sections of MIM

components generally range in

size from 0.50 to 13.00 mm (.02

- .50 in), but components have

been successfully molded withsections as thin as 0.25 mm (.01

in) for short flow lengths, and as

thick as 19 mm in special appli-

cations. Strive to achieve

uniform cross-sections for the

best processing results.

Functionality, appearance and

processing parameters should all

be carefully considered when

deciding the location of the gate.

As a rule, gates should be posi-tioned to facilitate thick-to-thin

flow direction and to provide

relatively equal flow lengths

throughout the component. It is

also helpful if the feed stock flow

impinges on some coring in the

mold, causing a 90 change in

flow direction as it enters the

cavity (see Figure 1).

Wherever possible, strive for

uniform wall thickness (see figure

2). The transition from thick to

thin wall sections should be

gradual. Abrupt transitions may

cause turbulent flow, resulting inpoor appearance of the finished

part. Structurally, a sharp transi-

tion can cause stress concentra-

tion, which may degrade part

performance under loading or

impact. Figure 3 shows recom-

mended MIM transition design.

Proper gating intoheavy section of part

Thick Thin

Figure 1

Variable Wall Section

Strive for uniformwall thickness

Transitions fromthick to thin shouldbe gradual

Poor

Good

Figure 2

Wall Transition Design

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Sharp transition - not recommended

Tapered transition - better

Gradual transition - preferred designApproximately 3:1 ratio

MaterialFlow

Figure 3

a a

a-a

b b

Dynacast International Headquarters

14045 Ballantyne Corporate Place

Suite 300

Charlotte, NC 28277 USA

+1 (704) 927-2790

Other Locatons:

Austria

Canada

China - Dongguan

China - Shanghai

France

Germany

India

Indonesia

Italy

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Malaysia

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Slovenia

Spain

United Kingdom

USA - California

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Sharp inside corners can result

in stress concentrations, which

could lead to failure under

fatigue or impact. To reduce

stress levels and aid flow during

molding, use fillets on internal

corners. This will also facilitate

part ejection.

A radius equal to half the

adjacent section wall thickness

will maintain stress levels within

acceptable limits. Minimum

fillet radius should be no less

than 0.4mm (.015 in) if possible.

To ensure easy part removal,

allow a draft angle of to 2

for both inside and outside

walls. Use more draft when

the shape of the part is com-

plex or the draw is relatively

deep. Designs using cores also

require additional draft

because the feedstock tends to

shrink tightly onto cores. Draft

as low as 0 to 1/4 have been

successfully used on MIM

components, but draft angles

this small require individual

analysis.

When properly designed and

located, ribs increase functional

strength, making it possible to

reduce wall thickness. Overall,

the use of ribs can save material,

reduce processing time and

eliminate the need for

hard-to-process heavy sections.

Thickness, length and location

are the major variables for rib

design. Thick ribs may cause

voids and sinks at the intersec-

tions of mating surfaces, result-

ing in possible dimensional,structural and cosmetic issues.

Figure 4 shows recommended rib

size relationships.

T

1/2 to 1-1/2

r .. 0.010to0.015"

t., .5to.7T

Figure 4

1. Part has potential to sag

2. Pressure points

1. Ribs help in staging

2. Increased stiffness to part


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Wall sections, as already

noted, should be kept uniform

throughout the component.

One or two heavy sections in

an otherwise well-designed

part can extend processingtime, cause sinks and voids,

and increase molded-in stress-

es. Unnecessary heavy

sections also increase material

usage. Figure 5 shows exam-

ples and guidelines for coring

heavy sections. Wherever

possible, coring should be in

the direction of draw; i.e.

perpendicular to the partingline of the mold. Cores that

are parallel to the direction of

parting line require cams or

hydraulic core pulls, which can

increase tool costs.

Figure 5

Before coring

Redesign

Before coring

Redesign.5 to .7T

Before coring

Sink

Sink

Extend boss core until t=.5 to .7 Redesign

MIM components should be

designed to tolerances of +/-

.3%. In practice, tighter toler-

ances can be held, but keeping

to this guideline results in

greater-production economiesto meet the true capabilities of

the process. If tighter toleranc-

es are required, our engineers

will work with you to design

the best process.

We know you have a lot of ques-

tions regarding your design and

how MIM can apply. Send us

your idea or drawing and well

supply you with a rough order of

magnitude (ROM) quotationquickly to help determine if MIM

is right for your application. We

help you with your new or exist-

ing design to make it optimal fo

the MIM process.

Dynacast International Headquarters

14045 Ballantyne Corporate Place

Suite 300

Charlotte, NC 28277 USA

+1 (704) 927-2790

Other Locatons:

Austria

Canada

China - Dongguan

China - Shanghai

France

Germany

India

Indonesia

Italy

Korea

Malaysia

Mexico

Singapore

Slovenia

Spain

United Kingdom

USA - California

USA - Illinois

USA - Wisconsin

Documents

MIM Design Guide