FAQs

Q: What is the most critical factor in choosing mold steel?

A: The selection of mold steel primarily depends on several key factors:

1. Forming Method:
- Hot-Worked Tool Steel: Ideal for applications involving high temperatures, such as die casting, forging, and extrusion.
- Cold-Worked Tool Steel: Suitable for processes like blanking, shearing, cold forming, cold extrusion, and powder press forming.

2. Plastic Type:
- Some plastics, such as PVC, can produce corrosive by-products. In such cases, stainless die steel is recommended to resist corrosion.

3. Mold Size:
- Large Molds: Typically use pre-hardened steel.
- Small Molds: Often employ integral hardened steel.

4. Mold Usage:
- Long-Term Use (>1,000,000 cycles): High-hardness steel with a hardness of 48-65 HRC is recommended.
- Medium-Term Use (100,000 to 1,000,000 cycles): Pre-hardened steel with a hardness of 30-45 HRC is suitable.
- Short-Term Use: Consider surface roughness and potential brittleness due to high sulfur content in steel.

 

Q: What are the primary factors affecting the machinability of materials?

A: Several factors influence the machinability of materials:

1. Steel Structure:
- The structure of the steel, whether forged, cast, extruded, rolled, or machined, impacts machining difficulty. Forged and cast materials can be particularly challenging to machine.

2. Hardness:
- Harder steels are more difficult to process. High-speed steel (HSS) is suitable for materials up to 330-400 HB, while HSS with titanium nitride (TiN) coatings can handle materials up to 45 HRC. For steels with hardness above 65 HRC, materials such as cemented carbide, ceramics, cermets, and cubic boron nitride (CBN) are recommended.

3. Non-Metallic Inclusions:
- Inclusions such as Al₂O₃ (alumina) can adversely affect tool life due to their abrasiveness.

4. Residual Stress:
- Residual stresses can affect machining performance. Stress relief processes after roughing are often advised to mitigate these effects.

 

Q: What are the production costs associated with mold manufacturing?

A: The typical cost distribution for mold manufacturing is as follows:

- Cutting: 65%
- Workpiece Material: 20%
- Heat Treatment: 5%
- Assembly/Adjustment: 10%

This distribution underscores the importance of effective metal cutting performance and high-quality cutting solutions for cost-efficient mold production.

 

Q: What tools should be used for different milling processes?

A: The selection of tools for various milling processes is crucial for optimizing performance:

1. Roughing Process:
- Use round insert milling cutters, ball end mills, and end mills with an arc radius for effective material removal.

2. Semi-Finishing Process:
- Employ round insert milling cutters (circular insert milling cutters with a diameter range of 10-25mm) and ball end mills to achieve desired surface quality.

3. Finishing Process:
- Use round insert milling cutters and ball end mills for precision finishing.

4. Residual Milling Process:
- Opt for round insert milling cutters, ball end mills, and vertical mills to finalize the part geometry.

Choosing the right tool size, geometry, and grade, along with appropriate cutting parameters and milling strategies, is essential to optimize the cutting process.

 

Q: What measures should be taken to eliminate vibration during cutting?

A: To mitigate vibration during cutting, follow these proven recommendations:

- Tool Selection:
- Choose a sparse or unequal pitch cutter.
- Use tools with a positive rake angle and small cutting force blade geometry.
- Opt for smaller milling cutters where feasible, especially when using a damper post.
- Utilize blades with a small cutting edge passivation radius (ER), from concentrated coatings to thin coatings. Uncoated blades can be used if appropriate. High-toughness insert grades with fine-grained particles are recommended.

- Cutting Parameters:
- Use a large feed per tooth. Either reduce speed and maintain table feed or keep speed constant and increase table feed. Avoid reducing feed per tooth.
- Decrease both radial and axial depth of cut.

- Tool Holder and Setup:
- Select a stable holder, such as Coromant Capto, and use the largest possible adapter size for optimal stability. Consider a taper extension for maximum rigidity.
- For large overhangs, use a damper post in combination with a pitch-tooth cutter. Connect the milling cutter directly to the shock-absorbing handle.
- Deviate the milling cutter from the center of the workpiece.
- If using a tool with even teeth, remove one blade every other tooth to reduce vibration.

 

Q: What is the best method to start cutting a cavity?

A: There are several methods for initiating cavity cuts:

1. Pre-Drilling:
- Pre-drilling a starting hole or corners is not recommended due to the additional tool requirements and potential for tool damage and chip re-cutting. This method can also generate undesirable vibrations.

2. Boring:
- Using a ball end mill or round insert tool for boring ensures that all axial depths are cut. However, this method may encounter chip removal issues and result in long chips.

3. Linear Slope Cutting:
- Employing linear slope cutting in X/Y and Z directions allows for full axial depth cutting, which is an effective approach.

4. Circular Interpolation Milling:
- Circular interpolation milling in a spiral form is highly recommended as it produces a smooth cutting effect and requires minimal starting space.