Knowledge base

With us you benefit from decades of experi­ence, which we are happy to share with you. We provide you with an excerpt from our wealth of experi­ence in our knowledge database, which can help you design compon­ents in a plastic-friendly manner.

If you have any more in-depth questions or would like to discuss your design, please feel free to contact us.

  • Material matrix
  • demoul­ding
  • welding
  • Gate position
  • Wall design
  • Snap connec­tions
  • screws
  • Venting
  • Stress cracks
  • Default
  • Flow path length
  • Tool steel
  • Tier forms
Material matrix

Plastic material matrix

The material matrices below contain relevant parame­ters for common injec­tion moldable plastics.

Materials (I/III)
HDPE
PP
P.S
POM
SECTION
PA6
PA 6.6 amor.
PA12
Costs approx. [€/kg], as of 10/19

1,50 — 2,00

1,50 — 2,00

1,50 — 2,00

1,50 — 2,00

2,50 — 3,50

3,00 — 4,00

4,50 — 6,00

13,00 — 15,00

Density [g/ccm³]

0,95

0,91

1,05

1,41

1,05

1,13

1,14

1,02

Tensile strength approx., accor­ding to DIN 53455 [N/mm²]

26

29

45

60

60

55

70

60

maximum usage tempe­ra­ture [°C]

90

100

65

100

80

135

145

100

Flow path length, approx. with 2mm wall thick­ness [mm]

600

600

700

400

280

500

600

200

Proces­sing shrin­kage, injec­tion molding, approx. [%]

1,7

1,7

0,6

2,0

0,6

1,8

1,8

0,6

Required demol­ding taper at erosion level 30/3.5 µm rough­ness depth [°]

2,0

2,0

2,5

1,5

2,0

1,5

1,5

2,5

Average cavity pressure with 3mm wall thick­ness, approx. (1:150 flow path) [bar]

260

260

260

350

350

340

340

400

Material data (accor­ding to school grades)
Impact resis­tance

2

4

6

3

3

2

2

3

Chemical resis­tance

1

2

6

2

4

2

2

3

trans­pa­rency

5

5

1

5

6

5

5

2

low manufac­tu­ring tolerance

5

5

2

6

2

5

5

2

Adhesion

5

5

2

5

2

3

3

3

special proper­ties

soft, high tendency to creep

Film hinge effect, drinking water approval possible, sensi­tive to cold shock

trans­pa­rent, sensi­tive to impact

good spring proper­ties, sliding material, drinking water approval

galva­nizable, high gloss surface

Water absorp­tion changes the proper­ties of the sliding material

Water absorp­tion changes the proper­ties of the sliding material

trans­pa­rent, high chemical resis­tance

Common brand names

Hostalen, Lopolen

Vestolen, Moplen, Novolen, Vestolen, Hostalen PP

Polysty­rene

Hosta­form, Ultra­form, Delrin

Polylac, Novodur, Terluran, Cycolac

Ultramid B, Durethan, Akromid, Badamid

Zytel, Ultramid A

Grilamid, Trogamid

use

Packa­ging, contai­ners, bottles

Fittings, pipelines, packa­ging

packa­ging, housing,

Gears, sliding and guiding elements, housing parts

Shower, bathtub and kitchen fittings in galva­nized design, door handles, armrests

Plain bearings, bushings, gears, rollers, electrical compon­ents

Plain bearings, rollers, gears, guides, sliding plates, valve seats and bodies

Tubes and cathe­ters, plain bearings, valves

Materials (II/III)
PC
PPO
PEEK
ASA
PBT
PPS GF40
PPA GF30
PC/ABS
Costs approx. [€/kg], as of 10/19

4,50 — 5,50

5,00 — 5,50

from 80.00

3,00 — 4,00

3,50 — 4,50

9,50 — 10,50

6,00 — 7,00

4,00 — 5,00

Density [g/ccm³]

1,20

1,06

1,32

1,06

1,30

1,65

1,46

1,13

Tensile strength approx., accor­ding to DIN 53455 [N/mm²]

60

50

110

60

57

150

200

65

maximum usage tempe­ra­ture [°C]

135

130

260

90

135

240

180

115

Flow path length, approx. with 2mm wall thick­ness [mm]

200

250

350

280

400

150

200

240

Proces­sing shrin­kage, injec­tion molding, approx. [%]

0,6

0,6

1,0 — 1,3

0,6

1,8

0,3

0,3

0,5

Required demol­ding taper at erosion level 30/3.5 µm rough­ness depth [°]

2,5

2,0

2,5

2

2,0

1,5

1,5

2,5

Average cavity pressure with 3mm wall thick­ness, approx. (1:150 flow path) [bar]

500

400

500

350

550

400

400

400

Material data (accor­ding to school grades)
Impact resis­tance

1

3

2

3

2

5

4

2

Chemical resis­tance

6

4

1

4

3

2

2

2

trans­pa­rency

1

6

6

6

6

6

6

6

low manufac­tu­ring tolerance

2

2

2

2

5

3

3

2

Adhesion

3

2

4

2

2

3

2

3

special proper­ties

high impact strength

resistant to acidic substances, drinking water approval possible

good sliding and friction proper­ties, excel­lent wear resis­tance, highest heat resis­tance, high creep resis­tance, chemical resistant

Highly shiny surface, good aging and weather resis­tance compared to ABS

good chemical resis­tance, no water absorp­tion

Small part tolerances possible, high strength and conti­nuity, very good insula­ting proper­ties

high heat resis­tance combined with high mecha­nical stabi­lity, chemical resistant

galva­nizable

Common brand names

Lexan, Makrolon, Alyacarb

Noryl, Luranyl

Victrex PEEK

Vestolen, Moplen, Novolen, Hostalen PP

Crastin, Ultradur

Tedur, Fortron, Ryton

Grivory HT, Zytel HTN

Bayblend

use

Optical or electrical compon­ents, glass repla­ce­ment for panes

Pump parts

Automo­tive parts, insula­tors, connec­tors, switches

Plain bearings, gears, fittings, piston rings, bearing cages for engines, gears, valves

Housings for telephones, compu­ters, printers etc., car panels e.g. fittings, battery housings, hubcaps etc., window frames

Plain bearings, roller bearings, valve parts, screws, connector strips, pump housings and wheels, parts for house­hold appli­ances such as coffee machines, egg cookers, toasters, etc.

Highly stressed parts in the electrical and automo­tive indus­tries

Automo­tive, electrical industry or in

Mecha­nical enginee­ring with special strength requi­re­ments, even with

elevated tempe­ra­tures or humid environ­ments.

Housing, electrical compon­ents e.g. keyboard, cell phone, charger, trim strips, switches, center consoles, roof consoles,

Materials (III/III)
TPU
TPE
COC
PP with wood
PLA
Lignin based
glass fiber
mineral filling.
Costs approx. [€/kg], as of 10/19

4,50 — 5,50

3,00 — 3,50

8,00 — 12,00

2,00 — 3,00

5,00 — 6,00

5,00 — 6,00

rises

falls

Density [g/ccm³]

1,20

1,10

1,01

1,03

1,34

1,29

rises

rises

Tensile strength approx., accor­ding to DIN 53455 [N/mm²]

30 — 65

30 — 45

60

33

54

33

rises

falls

maximum usage tempe­ra­ture [°C]

80

70

120

110

60

70

rises

unchanged.

Flow path length, approx. with 2mm wall thick­ness [mm]

230

300

300 — 800

200 — 300

300 — 400

100 — 200

sinks slightly

sinks

Proces­sing shrin­kage, injec­tion molding, approx. [%]

1,0

1,5

0,6

0,7

0,7

0,2

drops sharply

sinks a little

Required demol­ding taper at erosion level 30/3.5 µm rough­ness depth [°]

1,5

1,5

2,0

1,5

1,5

2,5

more slant

more slant

Average cavity pressure with 3mm wall thick­ness, approx. (1:150 flow path) [bar]

340

260

500

600

500

800

increases

unchanged.

Material data (accor­ding to school grades)
Impact resis­tance

1

1

5

4

2

6

sinks

sinks

Chemical resis­tance

2

2

3

3

2

4

unchanged.

unchanged.

trans­pa­rency

6

6

1

5

1

6

sinks

sinks

low manufac­tu­ring tolerance

2

3

2

2

2

1

more diffi­cult

low tolerance possible

Adhesion

4

4

3

5

2

2

sinks

sinks

special proper­ties

good scratch resis­tance

soft feel

Glass-like trans­pa­rency, FDA and medical approval

short flow path length depen­ding on filler content, low shrin­kage

high scratch resis­tance

Compres­sive strength increases, tensile strength decreases, shrin­kage decreases

Proper­ties diffe­rent along and across the fiber­glass

Compres­sive strength increases, tensile strength decreases, shrin­kage decreases

Common brand names

Desmopan, Texin, Elastollan

Santo­prene

TOPAZ COC

ARBOfill

ARBOblend

ARBOform

GF, GK

MR, CMF, MF

use

Timing belts, shoe soles, seals, switches

Fittings, covers, automo­bile interior

Functional films in flat screens as well as lenses and sensors, medical techno­logy syringes,

Micro­titer plates, cuvettes and vials

House­hold goods, office supplies, packa­ging, clothes hangers, technical profiles, chairs

Packa­ging, office supplies, house­hold goods, films, flexible cards, toys, sports equip­ment, plant pots, labora­tory supplies, semi-finished products / profiles, filaments

Loudspea­kers, musical instru­ments, urns, toys, design objects

Aerospace, circuit boards, boats, bobsleds, etc.

Semicon­ductor industry, electro­nics, mecha­nical enginee­ring, vacuum techno­logy

demoul­ding

Draft taper

For eroded surfaces (electric erosion), the required demol­ding taper increases compared to polished surfaces. The follo­wing demol­ding tapers should be selected in relation to the rough­ness, depen­ding on the respec­tive material.

Material/draft angle
0.5°
1.0°
1.5°
2.0°
2.5°
3.0°
4.0°
5.0°
ABS, PE (hard), PP

21

24

27

30

33

36

39

42

PS, MMA, PC 

-

21

24

27

30

33

36

39

POM, Cab, PA

24

27

30

33

36

39

42

-

welding

Joining technical plastic parts: Overview of welding processes

Ultra­sonic welding

Ultra­sonic welding is a quick and econo­mical process for joining plastic parts and is ideal for assembling high-quality plastic items manufac­tured in large quanti­ties. During ultra­sonic welding, high-frequency vibra­tions are trans­mitted to the parts to be welded using a vibra­ting welding tool, the so-called “sonotrode”.


This “hamme­ring” movement melts and bonds the plastic at the contact surfaces. The strength of the weld is appro­xi­m­ately 80% of the part material. The size of the parts to be welded is limited. The welding geome­tries listed below have proven successful in practice.

Ultra­sonic welding
Charac­te­ristics
Unwelded
Welded
Butt weld with energy conductor
  • Welding geometry without barriers
  • not ideal for sealing welds
  • only amorphous plastics
Tongue and groove connec­tion
  • Welding geometry with barrier
  • possibly 0.1 — 0.2 mm
  • Cross ribs offset 90° in the bottom of the groove (roughen)
Pinch seam
  • semi-crystal­line plastics
  • no problem with tight­ness
  • high strength
  • Problem: Dimen­sions and tolerances for large parts

Vibra­tion welding (friction welding)

Due to long process times and expen­sive machine techno­logy, this welding process is signi­fi­cantly more expen­sive than ultra­sonic welding. However, slightly warped parts can also be welded, as this robust process uses high forces. During the vibra­tion welding process, two parts are moved linearly against each other under pressure, which creates the required heat through friction. After a presel­ected time, the vibra­tion slows down while the pressure on the welding surface is maintained until the melt has solidi­fied.


The strength of the weld seam is only approx. 30% of the base material. The weld seams are relatively wide, which still results in high strength.

Vibra­tion welding
Charac­te­ristics
before welding
after welding
Tongue and groove connec­tion with collec­tion zone for the melted material
  • more expen­sive than ultra­sonic welding
  • Robust process even with large tolerances
  • Weld requires more space in at least one axis
Gate position

sprue position

The sprue position should be chosen so that a free jet is avoided as much as possible. Further­more, complete filling must be guaran­teed, especi­ally with regard to inter­fe­ring contours around which the melt must flow. Weld lines form in these areas.

When using multiple molds, make sure that all mold cavities can be filled evenly. If positio­ning at the same distance from the nozzle is not possible, the sprue distri­butor should be balanced.

Free jet forma­tion due to incor­rect sprue position

Balanced sprue distri­butor

Under­floor casting

The under­floor casting is a shear casting that is automa­ti­cally separated from the part during demoul­ding. This has the advan­tage that it does not have to be separated manually later and a clean cutting edge can be achieved. An under­floor sprue gives the designer great flexi­bi­lity to optimally choose the sprue position, for example to avoid a free jet.

Dimen­sio­ning a curved tunnel gate (source GEP):

The transi­tion from d1 to d2 forms a cone of 3–5°.

Part ejection and begin­ning tunnel ejection (source GEP):

Sprue check

With this check­list you can check whether you have considered the essen­tial questions when desig­ning the sprue.

Yes
Is any rework to remove the sprue compa­tible with the price of the part?
Is the sprue marking accepted at this point?
Does the flow path/wall thick­ness ratio allow complete mold filling?
Can weld lines be accepted?
Can the air escape or do additional venti­la­tion options have to be installed for the speci­fied sprue position?
Can weld seams, for example on screw-on domes, lead to strength problems?
Can you do without an expen­sive sprue system with cascade switching to avoid weld seams?
Has any precau­tion been taken to ensure that no free steel is formed, i.e. is the injec­tion carried out against a tool wall and not in the free cavity?
Are tempe­ra­ture control channels provided near the gate?
Does the sprue position, especi­ally the shear during injec­tion, not result in extre­mely hot mold sections?
Does the gate geometry (e.g. tunnel gate) allow the material to be processed or is exces­sive shear stress to be expected?
Is the gating system naturally balanced for multiple molds or parts with multiple gates or — if not — has at least a mold filling study been carried out to deter­mine graduated distri­butor cross sections?
Is the mold filling from the thick to the thin wall and are there no thin areas near the gate (e.g. film hinge), so that the flow front freezes due to the delay effect (hesita­tion effect)?
Is it possible to provide suffi­cient additional pressure to avoid voids, sink marks, etc.?
Is the sprue position optimally chosen to avoid distor­tion (e.g. injec­tion of a ruler on the narrow side?)
Wall design

Design of walls

Uniform wall thick­nesses are important to achieve econo­mical cycle times and to prevent defects on the compo­nent. Warping can be counter­acted through the targeted positio­ning of ribs. Targeted relief of corners can help prevent tension.

1: Favorable shape

2: Unfavorable shape

3: Favorable shape

4: Unfavorable shape

Snap connec­tions

The snap connec­tion

The snap connec­tion is a simple, econo­mical and quick assembly method through which plastic parts can be connected to metals or plastics by engaging a corre­spon­ding projec­tion on the holding part in a molded undercut. The greatest possible elonga­tion (E) must be selected for the respec­tive appli­ca­tion, depen­ding on the material, based on the maximum permis­sible short-term defor­ma­tion.

The limits are 6% for unrein­forced plastics and 2% for glass fiber reinforced plastics during bending stress. If repeated assembly/disassembly is to be expected, the elonga­tion value must be reduced by 1%. The “fatigue” and the pre-tension of the hook can be improved by a gusset-like stiffener. If possible, the base of the snap hook — connec­tion to the part — should be rounded in order to reduce the notch effect.

screws

Self-tapping screws

Self-tapping screws are parti­cu­larly suitable for amorphous — but also for parti­ally crystal­line plastics. Thread-forming screws — even with flat flanks — generate high tensions, which can lead to stress cracks, especi­ally when exposed to chemical substances (oil, grease, acids, bases, brake fluid, etc.).

The follo­wing general design princi­ples apply when using self-tapping screws:

  1. The tenon hole should corre­spond to the core diameter of the screw.
  2. The external diameter of the pin should be large enough to accom­mo­date the circum­fe­ren­tial tension caused by screwing in the screw.
  3. A cam outside diameter that is twice the outside diameter of the screw is usually suffi­cient.
  4. The thread length must be at least twice the outside diameter of the screw.
  5. Repeated disas­sembly is not recom­mended.
  6. The torque must be kept as small as possible so that the tension created during assembly remains within the limits of the material.

Typical behaviors of self-tapping screws:

Knipping® Type 1 screw no.
Thread length (mm)
Spigot outside diameter (mm)
Stud inner diameter (mm)
Tightening torque (mm)
Overtorque (mm)
Resili­ence (N)

4

6,50

6,00

2,50

0 — 0,15

1,00

1200

6

6,50

7,00

3,10

0,25

2,20

1600

8

6,50

8,50

3,80

0,50

2,80

2400

10

9,50

10,00

4,40

1,00

7,50

3000

Source: GEP company publi­ca­tion


Venting

Venting

In order for the plastic to comple­tely fill the mold, the tool needs optimal venti­la­tion. Burn spots and blowholes are avoided.

Venting the cavity

Venting the cavity

Work images: EUROplast

Stress cracks

Stress cracks

What promotes stress cracks?

  • Load too high
  • Incor­rect material selec­tion in relation to the surroun­ding media
  • In general, all media that can swell or loosen the plastic are suspected of causing stress cracks
  • Use of assembly aids such as oils, sharp corners, edges, notches, etc.
  • Displa­ce­ment screw instead of self-tapping screws
  • Thermal expan­sion
  • Weak binding seam

Possible counter­me­a­sures:

  • Choosing a more durable plastic
  • Choosing a higher molecular weight variant of the same plastic
  • Selec­tion of a contact medium (e.g. adhesive / oil / varnish etc.) that does not contain the medium that triggers stress cracks
  • Resol­ving internal tensions, e.g. through tempe­ring
  • Reducing voltage through redesign, e.g. B. Fillets
Default

Problem due to delay

Warpage is parti­cu­larly common in semi-crystal­line plastic parts with high shrin­kage.

Remedy through warp-optimized design

Coring at the corners without the need for sliders

Thin ribs prevent sink marks, but lead to distor­tion — inter­rupted ribs reduce distor­tion

Flow path length

Flow path/wall thick­ness using the example of polycar­bo­nate

boundary condi­tions

  • Channel width: 8 mm
  • Mass tempe­ra­ture: 300°C
  • Tool tempe­ra­ture: 100°C
  • Spray speed: fast
  • Wall thick­ness:

3mm ———

2mm – — – -

1 mm -•-•-•-



Source: Sabic

Tool steel

Tool steel

Here you can see an overview of the main materials used in the produc­tion of injec­tion molding tools as well as their proper­ties and intended uses.

Material number.
Short name
Instal­la­tion condi­tion
Special treat­ment
Charac­te­ristic
use

1.1730

C45W

640 N/mm²

Unalloyed tool steel,

easy to machine,

good tough­ness

Struc­ture parts such as clamping plates, mold frames, etc.

1.2083

X42Cr13

52–54HRC

Corro­sion-resistant through-hardening steel, low distor­tion,

easy to machine,

high compres­sive strength,

good polisha­bi­lity

Tool for proces­sing corro­sive spray compounds, mostly for shaping parts such as inserts, sliders, etc.

1.2162

21MnCr5

58–60HRC

Standard case-hardened steel, easy to machine, high core strength, very good polisha­bi­lity

Mold plates and inserts for small to medium molds. Parts with functional wear, such as guide pins, etc.

1.2311

40CrMnMo7

tempered approx. 1000 N/mmm²

nitrided

Tempered mold steel, easy to machine, good tough­ness, good polisha­bi­lity

Medium and large tools, mold frames and struc­ture

1.2312

40CrMnMoS86

tempered approx. 1000 N/mmm²

nitrided

Tempered mold steel, easy to machine, good tough­ness, good polisha­bi­lity

Medium and large tools, mold frames and struc­ture

1.2343

X38CrMoV5‑1

50–52 HRC

Hot-work steel, easy to machine, good tough­ness, high thermal shock resis­tance and high-tempe­ra­ture strength

Medium to large tools, mold plates, mold inserts, sliders, etc.

1.2764

4X19NiCrMo4

56–58HRC

Very tough case-hardened steel, little dimen­sional change after air hardening, very high core strength, very good polisha­bi­lity

Mold plates, inserts, etc. for diffi­cult tools that should not warp or for which high core strength is required

1.2767

X45NiCrMo4

52–54HRC

Through-hardening molded steel, high tough­ness, low distor­tion, very good polisha­bi­lity

Small to medium-sized molds, shaping parts such as mold plates, inserts, etc.

1.2842

90MnCrV8

52–54HRC

Oil hardener with simple heat treat­ment, easy to machine, good dimen­sional stabi­lity

Small inserts, punches, guide bars, locking bars, cente­ring bars, sprue bushings

Ampco 18

approx. 660 N/mm²

Multi-material aluminum, bronze, good tensile strength and yield strength, good sliding behavior, high resis­tance to mecha­nical wear, approx. 2.5x higher thermal conduc­ti­vity than steel, corro­sion resistant

Forming parts such as inserts, punches, bearings, guides, spindle nuts

Ampcoloy

approx. 660 N/mm²

Highly conduc­tive copper alloy, beryl­lium-free,

good tensile strength and yield strength, approx. 7x higher thermal conduc­ti­vity than steel, corro­sion resistant

Forming parts such as inserts, stamps, etc.

Tier forms

Tier forms

The plastic molded parts are arranged in two levels one behind the other in the tool, in contrast to conven­tional tools where the parts are next to each other. The closing force compon­ents that act on the middle block from each level cancel each other out. The clamping force required for the mold is there­fore halved. Of course, the condi­tion is that the molded parts are made from the same raw material and that the geometry of the parts is suitable for this produc­tion process.

Advan­tages

  • Appro­xi­m­ately halving the proces­sing portion of the molded part costs. This is the main advan­tage of using tiered molds
  • Handling: Parts of a shot have the same spraying condi­tions and can be further processed on the machine (e.g. mirror welding or assembly processes)
  • Less space required for produc­tion. If produc­tion on two machines is neces­sary for capacity reasons, the stack form can save the second machine

Disad­van­tages

  • Due to higher tool costs, complex hot runner techno­logy, as well as actua­ting elements for the levels and additional hydraulic ejectors, the mold costs are higher than conven­tional tools
  • Higher setup and mainten­ance requi­re­ments due to double the number of cavities
  • Machine with extended bars may be neces­sary. If you don’t just want to produce flat parts with stack molds, you can consider purcha­sing a machine with extended bars for a lower additional cost

econo­mics

The follo­wing example calcu­la­tions show where the use of tiered molds is profi­table

Example 1: Compa­rison of a 1‑cavity tool and a tiered mold with one mold cavity per tier:

example 1
Usual 1‑fold tool
2‑fold stacking tool
Tool costs

50.000 €

105.000 €

Material costs/part

1 €/part

1 €/part

Machine hourly rate (inclu­ding machine opera­tion, mainten­ance, energy costs, etc.)

75 €/h

80 €/h

Partial emission

80 pieces/h

2x 75 pieces/h

Part price/piece (variable costs)

(1+75)/ 80 = €1.94/part

(1+80) / (2+75) = €1.53/part

amortiza­tion number

(€105,000 — €50,000) / (1.94 — 1.53) €/part = 134,146 parts

The additional costs of the tiered mold were paid for after around 134,000 parts, without taking capital costs into account

Example 2: Compa­rison of two 1‑fold molds and a 1+1‑fold tier mold for diffe­rent molded parts:

Example 2
Two 1‑fold tools
1+1‑fold stacking tool
Tool costs

100.000 €

115.000 €

Material costs/part

1 €/part

1 €/part

Machine hourly rate (inclu­ding machine opera­tion, mainten­ance, energy costs, etc.)

75 €/h

80 €/h

Partial emission

80 pieces/h

2x 75 pieces/h

Part price/piece (variable costs)

(1+75)/ 80 = €1.94/part

(1+80) / (2+75) = €1.53/part

amortiza­tion number

(115,000 € — 100,000 €) / (1.94 — 1.53) €/ part = 134,146 parts

Since the tooling costs of a stack mold for two diffe­rent molded parts are only slightly higher than two simple molds for these parts, the additional costs have already been paid off after around 37,000 parts.

All state­ments without guarantee

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