📈 Mid-volume keyword

Maßabweichung
Ursachen, Lösungen und Prävention beim Spritzgießen

Dimensionsinstabilität entsteht durch ungleichmäßige Schwindung, Prozessinstabilität oder falsche Werkzeugkompensation.

🔍Symptome und visuelle Erkennung

Part dimensions vary batch to batch or within a batch. Part does not fit assembly. Dimensions shift over time.

Wichtige Prozessparameter

Schussgewicht (g)KühlzeitWerkzeugtemperaturSchwindungskompensationNachdruck

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⚙️ Prozess

Shot weight variation inconsistent pack dimensional scatter
Nachdruck variation
Cooling water temperature fluctuation
Werkzeugtemperatur drift

🔲 Werkzeug

Shrinkage calculated incorrectly averaged min max should test with flat plate mold
Cavity imbalance in multi-cavity mold
Cooling system imbalance differential shrinkage

🧪 Material

MFI drift between lots shrinkage drift
Additive change talc in PP changes shrinkage
Mahlgutanteil zu hoch lower MW more shrinkage
Moisture hydrolysis lower MW more shrinkage

🗂 Werkzeugkonstruktion

Shrinkage calculation in mold is incorrect
Runner and cold slug well problems in mold
Gate location / flow length ratio is incorrect
Sprue and runner cross-section area and shape are incorrect.
Cooling system faulty
Dimensional differences between cavities in multi-cavity mold

🔧 Werkzeugzustand

Mold parting line shift

📐 Teiledesign

Tolerancing is incorrect
Corner designs at 90° (no radius)
Mold-dependent and independent dimensional tolerances not specified in drawing

📋 Allgemein

Wrong tolerance system DIN 7168 metal used instead of DIN 16742 plastic
Sharp corners in part shear stress dimensional change
Screw position repeatability shot weight variation

✅Lösungen und Korrekturmaßnahmen

⚙️ Prozess

Stabilize shot weight fix check valve barrel heaters thermocouple contacts
Monitor holding pressure and cooling water temperature
Use SPC on shot weight and key dimensions

🔲 Werkzeug

Test shrinkage on flat plate mold for exact value not average
Balance multi-cavity runner system
Fix cooling circuit imbalance
Polish parting line by procedure only 11-step protocol

🧪 Material

Materials with high MFI have greater shrinkage. Lower MFI grades can be tried.
If additive use is decided after mold construction, part dimensions tend to come out larger. For example, adding talc to PP makes it behave like PS — shrinkage decreases and parts come out longer.

🗂 Werkzeugkonstruktion

In a flat plate mold, first measure the mold dimension. Then inject the material and measure the part. The difference precisely determines the shrinkage rate.
Incorrect runner diameter and cross-section design can cause dimensional variation. Runner cross-section must be full round. Missing cold slug wells can also reduce polymer flow into the cavity. Runner cross-section and cold slug well design must be done correctly.
The maximum flow length at minimum wall thickness must be known and design should be made accordingly
Runner cross-section size must be calculated correctly based on part weight and must be full round. In hot runner systems, correct sizing must be selected based on material type and part weight.
As a principle, mold surface temperature must be uniform at every point. If not achieved, differential shrinkage will cause dimensional errors.
If cavity balance is incorrect, part dimensions vary depending on injection speed.

🔧 Werkzeugzustand

Incorrect pressure during mold polishing causes mold dimensions to grow after certain use. Polishing should be done on a bench in the mold shop, not on the machine, to apply correct pressure.

📐 Teiledesign

DIN 16742 tolerance system is used for plastics. If tolerances are not given according to mold-dependent and independent shrinkage values per material type, different dimensions result. Designers sometimes use DIN 7168 which is a metalworking tolerance.
Sharp-cornered plastic part designs create shear stress and internal stress. Minimum 0.2 mm radius should be given in plastic part design.
If the part designer does not account for these tolerances in the drawing, the mold maker machines directly on CNC. These dimensions are given in DIN 16901.

📋 Allgemein

Apply DIN 16742 tolerances not DIN 7168
Get MFI certificate for each incoming lot
Mahlgutanteil reduzieren

🛠Schritt-für-Schritt Fehlersuche

Prozessparameter prüfen

Stabilize shot weight fix check valve barrel heaters thermocouple contacts

Werkzeug prüfen

Test shrinkage on flat plate mold for exact value not average

Materialzustand prüfen

Materials with high MFI have greater shrinkage. Lower MFI grades can be tried.

❓Häufig gestellte Fragen

Was verursacht Maßabweichung beim Spritzgießen?

Maßabweichung wird durch mehrere Faktoren verursacht: Shot weight variation inconsistent pack dimensional scatter; Nachdruck variation; Shrinkage calculated incorrectly averaged min max should test with flat plate mold; Cavity imbalance in multi-cavity mold; MFI drift between lots shrinkage drift; Additive change talc in PP changes shrinkage.

Wie behebt man Maßabweichung beim Spritzgießen?

Zunächst die wichtigsten Parameter prüfen: Schussgewicht (g), Kühlzeit, Werkzeugtemperatur, Schwindungskompensation. Stabilize shot weight fix check valve barrel heaters thermocouple contacts

Welche Kunststoffe sind am stärksten von Maßabweichung betroffen?

Gängige Materialien: PA6, PA66, POM, PP, PBT. Besondere Beachtung von Trocknung, Schwindung und Werkzeugtemperatur für jeden Typ.

Wie verhindert man Maßabweichung in zukünftigen Produktionen?

Prävention basiert auf drei Säulen: (1) Prozessoptimierung — prüfen: Schussgewicht (g), Kühlzeit; (2) Werkzeugwartung — Anschnitte, Entlüftungen und Kühlkanäle prüfen; (3) Materialkontrolle — korrekte Trocknung und Neuware/Mahlgut-Verhältnis sicherstellen.

Was ist der Unterschied zwischen Maßabweichung und ähnlichen Fehlern?

Part dimensions vary batch to batch or within a batch. Part does not fit assembly. Dimensions shift over time. Dies unterscheidet es bei der visuellen Inspektion von ähnlichen Oberflächenfehlern.