Neutral pen injection mold

In general, the difficulty of making pen molds mainly lies in design, manufacturing and assembly, and requires high-precision processing equipment and technology, as well as rich manufacturing experience and skills.

The pen mold shaft core is the core component in the refill mold, which is mainly used to form the hollow structure inside the refill (such as ink storage tubes, pen tip channels, etc.). Its accuracy, wear resistance and surface quality directly affect the function and life of the refill. The following is a technical analysis of the pen mold shaft core, covering design, processing, materials and common problems:

1. Functional and structural characteristics of pen mold shaft core

Core role:

The inner cavity of the molded refill core (such as the diameter of the ink storage tube 0.5~3mm) and the fine flow channel (such as the ink outlet hole 0.1~0.5mm). 

Ensure uniform wall thickness of the refill core (tolerance ±0.02mm) and smooth mold release.

Typical structure: 

Elongated shaft body: The length to diameter ratio can reach 20:1 (such as diameter 1mm, length 20mm), and is easy to bend and deform. 

Special shape features: step shaft, spiral groove (for pen tip ball assembly) or micro-hole array (control ink flow). 

Surface treatment: mirror polishing (Ra≤0.05μm) or wear-resistant coating (such as DLC, CrN).

2. Design Points and Challenges

(1) Accuracy control

Dimensional tolerance: The tolerance for key parts (such as the pen tip mating section) must be ≤±0.005mm. 

Coaxiality requirements: The coaxiality error of the multi-stage shaft core must be<0.01mm to="" prevent="" ink="" leakage="" due="" eccentricity="" of="" the="" refill.="">

Solution: 

Use split design (precise assembly after segmented processing). 

Use highly rigid materials such as cemented carbide to reduce deformation.

(2) Optimization of mold release structure

Demolding slope: Usually designed to be 0.5°~1.5°, and the deep cavity structure needs to be increased to above 2°.

 Matching the ejection mechanism: The ejection pin hole or pneumatic ejection interface must be reserved at the end of the shaft core.

Case: The shaft core of a neutral pen ink storage tube adopts a segmented slope (inlet 1.2° → end 0.8°), and the mold release efficiency is increased by 30%.

(3) Cooling and heat balance

Cooling water paths in a 3D printed special-shaped water paths close to the surface of the shaft core to shorten the cooling time (such as 15%~20%).

Thermal deformation compensation: Predict the shrinkage through CAE simulation and correct the core size in reverse.

3. Processing difficulties and process plans

(1) Microstructure processing

Micropore/microtto processing:

Micropores with diameter<0.2mm need="" to="" be="" fine="" electric="" spark="">

The processing of spiral grooves requires ultra-precision turning (nano-level resolution CNC system).

Tool selection:

Diamond tool (processed carbide shaft core, life is increased by 3 times). Coated carbide drill bit (TiAlN coating, suitable for high-speed drilling).

(2) Rigid control of slender shaft

Process optimization: 

Phase-based processing: rough processing retains margin → heat treatment → finishing (reduces residual stress). 

Use a tool holder or a center holder (supports the shaft body when turning and reduces deflection).

Case: 

The tungsten steel shaft core with a diameter of 0.8mm and a length of 18mm is processed by Swiss heart-moving machine, and the straightness is controlled within 0.005mm.

(3) Surface treatment technology

Mirror polishing:

Diamond abrasive paste (grain size 0.1~1μm) combined with fiber polishing wheel, Ra can reach 0.02μm.

Wear-resistant coating: 

Physical vapor deposition (PVD) plating CrN, hardness HV2200, friction coefficient reduced by 40%.

4. Material selection and heat treatment

(1) Common materials

Carbide (tungsten steel):

Brands such as YG15 (Co 15%), hardness HRA 89~91, optimal wear resistance, suitable for high-precision shaft core.

Powder high-speed steel: 

ASP-30 (HRC 64~66), which takes into account both toughness and wear resistance, and is suitable for special-shaped shaft cores with acute angles.

Stainless steel: 

SUS420J2 (HRC 50~55), good corrosion resistance, used in medical or high humidity environment refills.

(2) Heat treatment process

Vacuum quenching: The cemented carbide shaft core is sintered in a 1350℃ vacuum furnace to reduce the oxide layer (thickness<2μm).<>

Deep cold treatment: 

196℃ liquid nitrogen treatment eliminates residual austenite and improves dimensional stability (deformation amount<0.003%).<>

5. Common failure modes and countermeasures

(1) Wear and strain

Causes:

Friction of glass fiber/filler in plastic melt (such as PA66+30%GF). 

Frequent release of mold causes the surface coating to peel off.

Countermeasures: 

Upgrade the coating (such as diamond-like DLC, hardness HV4000). Optimize the demolding slope and reduce the ejection force.

(2) Fracture and deformation

Cause: 

The elongated shaft core is impacted by injection molding pressure (instantaneous pressure >150MPa). 

Improper heat treatment leads to internal stress concentration.

Countermeasures: 

Structural strengthening: Add transitional fillets at the root of the shaft core (R≥0.3mm). Isothermal quenching process (reducing tissue stress).

(3) Dimension drift

Cause: The temperature rise of the mold causes thermal expansion (ΔL=α·L·ΔT, such as the expansion of the steel shaft core when the temperature rises by 10°C is about 1.2μm/100mm). 

Material aging deformation (such as aluminum alloy cores that are not fully aged).

Countermeasures: Constant temperature workshop (23±1℃) and mold temperature machine (control temperature difference ±0.5℃). 

Use low-thermal expansion materials (such as Inva alloy, α=1.2×10⁻⁶/℃).

6. Innovative technologies and trends

Micro-nano composite processing: femtosecond laser + electrolytic polishing to achieve a super smooth surface with Ra<0.01μm.>

Intelligent sensing shaft core: embedded in micro pressure sensor (MEMS technology) to monitor injection molding pressure distribution in real time. 

Gradient material application: 

3D printing to prepare composite shaft cores of outer carbide + inner tough steel, taking into account both wear and impact resistance.

Our Services

1. Specialized in precision mold part ,inquiries will get highly attention and be prompt response.(within 24 hours).

2. Advanced facilities and experienced engineers, rich experience in mold parts.

3. Guaranteed quality, superior material quality compared to all other.

4. Customer oriented, efficient solution to control the cost for our client.

5. One-stop service, any questions can be solved at the first time by us.

6. Each part has been got 100% inspection before shipment.

Our adavanges

1. Clean and tidy workshop.

2.Strick and serious manangement, skilled and expericenced technicians.

3. Various raw material(imported and Chinese) to meet different needs of customers.

4.Equipment of high pricision.( Surface grinding,Sodick Wire-cutting.drilling machine).

5.The QC go along with all the production processes in our factory.

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Payment Terms

T/T,Paypal,Western Union,50% deposit, balance before shipment is available

Package:PE bag with anticorrosive oil,foaming film with carton,or wooden box according to customer's requirement.

Delivery:Delivery time is usually 7-15 working days for type of ejector pin,specific time is according to quantity.