MATERIALS USED IN MOULD MANUFACTURING

1) Mild Steel (C-45)

This steel is relatively cheap. The steel is soft and cannot be fully hardened. It is extensively used to manufacture plates like top plate, bottom plate, ejector plate, core and cavity housings, spacers etc. It has high tensile strength. This steel has good shock resisting and machining properties.

2) Case hardening Steel (17MnCr95)

Initially these steels do not have sufficient carbon content essential for heat treatment process. Carbon is induced into the outer layer of the steel to convert into high carbon steels with carbon content ranging from 0.9 to 1.2%. When heat-treated achieve a hardness up to 50 – 55 HRC on the surface and retains a soft tough core. This is used for finger cam, guide pillars, guide bushes, ejector guide pillars and bushes and push back pins, as they require adequate strength as well as wear and resistance properties.

Composition:
Carbon-0.17%, Silicon-0.25%, Manganese- 1.25%, Chromium-1.15%, Sulphur-0.035%


3) Hot Die Steel (T35Cr5MoV1)

This steel has alloying element like carbon, which increases strength, elasticity and hardness. Chromium improves corrosion resistance, toughness and hardenability. Molybdenum improves creep strength and vanadium, which oxidizes and promotes fine-grained structures which is very helpful in manufacturing core and cavity of the mould. This material is hardened up to 48 – 50 HRC. This type of steel is used for core and cavity inserts, core and cavity sub inserts and side core pins.

Composition:
Carbon-0.37%, Silicon-0.25%, Molybdenum-1.2%, Vanadium- 1.0%, Chromium-5.0%

4. Oil Hardened Non Shrinkable Steel (T110W2CR5)

These steels tend to have good hardening properties and have less dimensional changes during heat treatment. They are relatively inexpensive, readily available, have good machinability, good resistance to decarburization and have a high carbon content to provide good wear resistance. The depth of hardness is homogeneous. This material is hardened up to 48 – 50 HRC. This steel is used for guide rails, wear plates, wedges, side core holder, sprue and sprue puller bushes.

Composition:
Carbon-0.95%, Silicon-0.35%, Tungsten-0.5%, Manganese- 1.20%, Chromium-0.5%

SELECTION OF TOOL STEEL

The selection of tool steel is very important for any tool upon which the development and economical operation of the process depends. Care should be taken especially while injection moulding plastics, which may affect the factors like mould life, quality, cost of mould and machine etc.

The steel used in the manufacture of mould varies depending on the applications. Proper material selection and proper combination of alloys in varying percentages are required for finished moulds.

Following properties are desired from the steels used in mold making

• Characteristics permitting economical machining
• Capacity for heat treatment without problems
• Ease of polishing
• High Wear resistance
• High Thermal conductivity
• Good Corrosion resistance
• Good Toughness
  

Commonly used Tool Steels in Press Tool

1. Water hardening tool steel.
2. Oil hardening tool steel.
3. Air hardening tool steel.
4. High carbon high chromium tool steel.
5. High speed steel.
6. Shock resisting tool steel.
7. Hot work die steel.

1. Water hardening tool steel

As its name indicates water hardening tool steel is hardened by quenching it in water after it has first been heated to proper hardening temperature. it is employed for parts which can be ground after hardening. water hardening tool steel is subject to distortion in hardening process and it should not be specified for parts with internal contours that must remain accurate and which cannot be ground after hardening.

2. Oil hardening tool steel.

oil hardening tool steel contains chromium and it is quenched in oil in the hardening process.warpage or distortion is much less than for corresponding grades of water hardening steels. when accurate surfaces cannot be ground after hardening, and anticipated production rates are average, oil hardening tool steel should be specified. the abbreviation is O.H.T.S.

3. Air hardening tool steel.

air hardening tool steel need not be quenched in either oil or water for hardening to occur. after heating beyond the critical range, it is simply exposed in air until cool. air hardening tool steels have minimum warpage and this is combined with greater toughness and wear resistance than corresponding grades of oil or water hardening tool steels.

4. High carbon high chromium tool steel.

high carbon high chromium tool steel, have about the same properties as air hardening steels except that they posses a greater degree of resistance to wear. high carbon high chromium tool steel should be specified for die parts when long production runs are anticipated.

5. High speed steel.

The outstanding quality of high speed steel is its toughness, combined with a high degree of wear resistance. it should be specified for weak die parts such as frail inserts, small diameter punches, and the like another excellent application is in dies for cold working, coining and upsetting of metal.

6. Shock resisting tool steel.

shock resisting tool steel contain a smaller amount of carbon and therefore it is tougher than other types. it is employed for heavy cutting and forming operations where steels with higher carbon content would be subject to breakage.

7. Hot work die steel.

These steels are employed in dies designed for forming hot materials because they posses high resistance to softening under heat.