How To Increase Part Weight in Injection Moulding

Introduction

Injection moulding is a widely used manufacturing process for producing plastic parts with high precision. One critical aspect of this process is controlling the part weight, which directly impacts material usage, structural integrity, and cost efficiency. Increasing part weight may be necessary to enhance mechanical properties, meet regulatory standards, or improve product performance. This article explores methods to increase part weight, their technical parameters, applications, and maintenance practices.

Methods to Increase Part Weight

1. Adjusting Injection Pressure

Increasing injection pressure ensures better material packing, reducing voids and improving density. Typical injection pressures range from 500 to 2,000 bar, depending on material viscosity. Higher pressures (e.g., 1,500-2,000 bar) are used for engineering plastics like polycarbonate (PC) or nylon (PA6). Over-packing must be avoided to prevent flash or warpage.

2. Extending Packing/Holding Time

Packing time compensates for material shrinkage during cooling. Extending this phase from 5-10 seconds to 15-20 seconds increases part weight by 3-8%. For thick-walled parts (e.g., >5mm), longer packing times ensure uniform density.

3. Raising Melt Temperature

Higher melt temperatures reduce viscosity, improving flow and filling. For example, ABS typically processes at 210-250°C, but increasing to 260-280°C can boost part weight by 5-10%. However, exceeding thermal limits degrades polymer chains.

4. Using High-Density Materials

Switching to denser polymers (e.g., from PP (0.9 g/cm³) to POM (1.4 g/cm³)) increases weight by up to 55%. Fillers like glass fibers (30-40% loading) add density while enhancing strength.

5. Modifying Mold Design

Enlarging gate dimensions (e.g., from 1mm to 2mm) reduces flow resistance, allowing More material into cavities. Venting improvements (0.02-0.05mm gaps) prevent trapped air, ensuring complete fills.

Application Scenarios

• Automotive: Heavy-duty components like gear housings require precise weight control for durability.

• Medical: Implants or surgical tools need higher density for biocompatibility and strength.

• Consumer Electronics: Structural parts (e.g., laptop bases) benefit from added weight for stability.

Maintenance Practices

1. Screw and Barrel Inspection: Check for wear every 500,000 cycles; replace if diameter tolerance exceeds ±0.1mm.

2. Mold Cleaning: Remove residue weekly using ultrasonic baths with pH-neutral solvents.

3. Hydraulic System: Monitor oil viscosity (ISO VG 46) and filter contaminants every 3 months.