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.
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
|
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 | - |
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 |
| ||
Tongue and groove connection
|
| ||
Pinch seam |
|
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.
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 | |
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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?) |
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
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.
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:
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
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
What promotes stress cracks?
Possible countermeasures:
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/wall thickness using the example of polycarbonate
boundary conditions
3mm ———
2mm – — – -
1 mm -•-•-•-
Source: Sabic
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
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
Disadvantages
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 |
|
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 |
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All statements without guarantee