Common problems in mold manufacturing and processing

1. What is the most important and decisive factor when choosing die steel?

A: Forming method - can be chosen from two basic material types.

A) Hot working tool steels, which can withstand relatively high temperatures during die casting, forging and extrusion.

B) Cold working tool steels, which are used for blanking and shearing, cold forming, cold extrusion, cold forging and powder pressure forming.

Plastics - Some plastics, such as PVC plastics, produce corrosive by-products. Corrosion can also be caused by condensation, corrosive gases, acids, cooling/heating, water, or storage conditions due to extended downtime. In these cases, steel made of stainless steel is recommended.

Dimensions - Prehardened steel is often used for larger sizes. Monolithic hardened steels are often used in small sizes.

Use times - for long term use (> 1 000 000 times), use high hardness steel with a hardness of 48-65 HRC. For medium and prolonged use (100 000 to 1 000 000 times), pre-hardened steel of 30-45 HRC shall be used. For short time use (<100 000 times), mild steel with a hardness of 160-250 HB shall be used.

Surface roughness - Many plastic manufacturers are interested in good surface roughness. When sulfur is added to improve metal cutting performance, surface quality is reduced. Steels with high sulfur content also become more brittle.

2. What is the primary factor affecting the machinability of materials?

A: The chemical composition of steel is important. The higher the alloying content of steel, the more difficult it is to work. As the carbon content increases, the machinability of the metal decreases.

The structure of steel is also very important to the cutting properties of the metal. The different constructions include forged, cast, extruded, rolled and machined. Forgings and castings have very difficult machining surfaces.

Hardness is an important factor affecting the cutting performance of metal. The general rule is that the harder the steel, the more difficult it is to work. High speed steel (HSS) can be used to process materials with hardness up to 330-400 HB; High speed steel + TiN coating can process materials with hardness up to 45 HRC; For materials with a hardness of 65-70 HRC, cemented carbide, ceramics, cermet and cubic boron nitride (CBN) must be used.

Non-metallic impurity generally has adverse effects on tool life. For example, Al2O3 (alumina), which is pure ceramic, has a strong abrasive property.

The last is residual stress, which can cause problems with metal machinability. Stress relief is often recommended after rough machining.

3. What are the parts of the production cost of mold manufacturing?

A: Roughly speaking, the cost distribution is as follows:

Cutting 65%

Work piece material 20%

Heat treatment is 5%

Assemble/adjust 10%

This is also a very clear indication of the importance of good metal cutting performance and excellent overall cutting solutions to economic production.

4. What are the cutting characteristics of cast iron?

A: Generally speaking, it is:

The higher the hardness and strength of cast iron, the lower the metal cutting performance, and the lower the life that can be expected from the blade and cutter. Cast iron used in metal-cutting production generally has good machability for most types of metal. The machinability of metal is related to the structure, and it is difficult to process the hard pearlitic cast iron. Flake graphite cast iron and malleable cast iron have excellent cutting properties, while ductile cast iron is rather poor.

The main wear types encountered in machining cast iron are abrasion, bonding and diffusion wear. Abrasion is mainly caused by carbide, sand particles, debris and hard casting skin. Bonding wear with accumulated chip nodules occurs at low cutting temperatures and cutting speeds. The ferrite portion of cast iron is most easily welded to the blade, but this can be overcome by increasing cutting speed and temperature.

Diffusion wear, on the other hand, is temperature-dependent and occurs at high cutting speeds, especially when high strength cast iron grades are used. These brands have high resistance to the variant, which causes the high temperature. This wear is related to the interaction between cast iron and the tool, which causes some cast iron to require ceramic or cubic boron nitride (CBN) tools to be machined at high speeds to achieve good tool life and surface quality.

Generally, the typical tool properties required for machining cast iron are: high thermal hardness and chemical stability, but also related to working procedure, workpiece and cutting conditions; The cutting edge is required to have toughness, heat resistance fatigue wear and cutting edge strength. The degree of satisfaction in cutting cast iron depends on how wear on the cutting edge develops: rapid dulling means thermal cracks and gaps that lead to premature cutting edge fracture, work piece damage, poor surface quality, excessive waviness, etc. Normal afterface wear, balance and a sharp cutting edge are what is generally required.

5. What are the main and common processing procedures in mold manufacturing?

A: All manufacturing processes go through the cutting process, which should be divided into at least three types:

Rough, semi-finish and finish, and sometimes even super-finish (mostly for high speed cutting applications). Residual milling is, of course, prepared for finishing after a semi-finishing process. It is important in each process to strive to leave a evenly distributed margin for the next process. If there is little rapid change in the direction of the tool path and in the workload, the life of the tool is likely to be extended and more predictable. If possible, the finishing process should be carried out on a special machine. This results in improved geometric accuracy and quality in less commissioning and assembly time.

6. What kind of tools should be mainly used in these different processes?

A: Rough machining process: round blade milling cutter, ball end milling cutter and end milling cutter with large tip arc radius.

Semi-finishing process: circular blade milling cutter (diameter range 10-25 mm), ball end milling cutter.

Finishing process: round blade milling cutter, ball end milling cutter.

Residual milling process: circular blade milling cutter, ball end milling cutter, vertical milling cutter.

It is important to optimize the cutting process by selecting a specific combination of tool sizes, grooves and grades, as well as cutting parameters and appropriate milling strategies.